Stormwater Drainage Design Manual-1982

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STORMWATER DRAINAGE
DESIGN MANUAL
FOR
TOWN OF NAGS HEAD
Prepared. by:
McDowell -Jones, P.A.
Engineers -Surveyors, P.A.
Elizabeth City
North Carolina
July 1982.

1
TABLE OF CONTENTS
I. Policy Statement
II. Stormwater Drainage Design Criteria
III. Stormwater Drainage Construction Requirements
IV. Easements
APPENDIX
A.. Determination of Design Flow
Table l:
Values of.Coefficient C
Table 2:
Rainfall -Intensity Duration Curves
Table 3 &
4:Time of Concentration
B. Culvert Design
Charts 1-7:
Inlet Control Nomographs
Charts 8-14:Outlet Control Nomographs
Chart A:
Alignment Chart for Manning Formula for
Pipe Flow
Chart B:
Capacity of Grate in Sump
C. Hydraulics
of Drainage Channels
Table 1:
Elements of Channel Sections
Table 2:
Manning Formula Nomograph
Chart A:
Manning Roughness Coefficients -
Chart B:
Manning N for Vegetal -lined Channels
Chart C:
Classification of Vegetal Covers
D. Discussion of Detention -Retention Systems
Table'I: Measures for Reducing and Delaying Stormwater
Runoff
Table II: Advantages and Disadvantages of Delaying
Stormwater Runoff
E. References
F

n
I. POLICY STATEMENT
1. It.is recognized that the public demand for adequate
drainage within and adjacent to existing and proposed develop-
ment -requires the attention of qualified professionals to the
problems of design, construction and maintenance of these
developments In this light,, it is desired that engineers
seek and apply the most up to date technical information
available and treat every problem separately in order to ob-
tain the best design possible. However, in.order to obtain
a degree of uniformity and -orderly development :in the Town,
it is necessary that certain phases of design and construction
be made a matter of policy.
2. Every development shall have a drainage system adequate
for the type of project proposed and so related to existing
or potential surrounding development as to form a logical Dart
of a coordinated system minimizing potential drainage problems
for the general area. No plat or development shall take such
form as to create potential or actual impoundment.of water.
on,. or discharge of water onto, adjacent.property in such a
manner as to (a) effect adversely existing -development, or (b)
increase problems of future development on such adjacent property,
except with the written and recorded consent of the adjoining
property owners affected and the approval of the Town.
3. The drainage system shall conform to Chapter 16.1 of the
Town code titled Drainage, Soil Erosion, and Sedimentation
Control.
I-1
1

II. STORMWATER DRAINAGE DESIGN CRITERIA
1. The developer shall provide a drainage system for the proper
drainage of all surface water using the.approved design criteria
as stated in the following paragraphs below. The design of
such a system shall be subject the approval of -the Town pursuant
to these guidelines and to the North Carolina Department of
Transportation when the proposed drainage system affects
drainage coming from or going into the State's' Right of Way.
2. All surface water draining -onto the site under develop-
ment or generated on said site must be provided for in accord-
ance with these guidelines. All water drainage leaving the
site under development shall be channelled to points of approved
discharge, such as a natural or manmade watercourse,. a lake,
pond, ditch or storm drainage system.
3. No surface water shall be channelled or directed into a'
sanitary sewer or septic tank system. Distances between open
ditches and septic tank 'systems must be specified and approved
by the Dare County Sanitarian. This.approval must be obtained
by the developer prior to final approval of the drainage system
designed by the Town of Nags Head.
■ 4.. The developer shall use retention, detention, and infiltra-
tion techniques to reduce the runoff from his site. See
Appendix - -D t---- for additional data.
' 5. The drainage design criteria for open and closed drainage
systems shall generally conform to these guidelines and
Handbook of Design for Highway 'Surface'Drainage Structures
prepared by the North Carolina Department -of Transportation,
the A.S.C.E. Manual of Engineering Practice No. 37, and Urban
Hydrology for Small Watersheds (T.R. No. 55) prepared by the
Soil Conversation Service.
-■ 6. Development plans shall show size, slope, invert and rim
elevations, and ditch cross sections in the vicinity of the
' development and as is necessary to properly evaluate the exist-
ing and proposed surface water drainage system.

.7. Drainage calculations, drainage area maps, .flood routing
calculations, infiltration calculations, storm sewer back water
curve calculations, etc, shall be submitted to the Town upon
request.
8. Estimated runoff calcul.tions may be computed by the
Rational Method (Q=CIA),*the SCS method in TR No. 55, or
other approved methodologies. Sizing of structures will be
based on the Manning Equation. Culverts shall be evaluated
,for inlet and outlet. control as necessary. See Appendix for additional additional data.
9. Systems shall generally be -designed. for*..a 10. year .storm fre-
quency. There may be some situations which may warrant a
different requirement due to the size of the system. The
design engineer is encouraged to contact the Town Engineer
in the preliminary design stages to determine if a change is
warranted.
10.. A modified Rational Method hydrograph procedure may be
used in sizing retention and detention systems See Appendix--D--
for additional data.
11. Data on Existing drainage facilities, areas, and topographic
features may be obtained from reference 19, Town 'of N.aS Head
Surface Water Drainage Plan.
i.i. -2

III. STORMWATER DRAINAGE CONSTRUCTION REQUIREMENTS
-� 1. All underground storm sewers open drainage ways, and
g P g Ys
`elated structures shall be constructed to the applicable pro-
visions -of Roadway Standard Drawings and Standard Specifications
for Road and Structures produced by the North Carolina of
' Transportation.
2. During the construction; preparation, arrangement and*in
stallation of improvements and facilities in developments, the
developer shall maintain each stream, creek', ditch, or channel
contiguous to or located within the subdivision in an un-
obstructed state and shall remove from such watercourses and
the banks of the watercourses all debris, logs, timber, junk
and other accumulations that would, in time of flood,clog or
dam the passage of waters in their downstream course..Install-
tion of appropriately sized conduit, culverts, bridges or other
required structures shall not be constructed in a way which
' will obstruct the flow of drainage.
!, TT
1-1
i

LI
IV. EASEMENTS
1. Easements for existing and proposed utilities and drain-
age shall be provided across lots or adjoining rear or side
lot lines, and shall be of whatever width is required to pro-
vide for installation of such utilities or drainage and for
' access for maintenance, provided however that no such easement
shall be less than 10 feet wide.
2. Where a developmemit is traversed by a water course', drain-
age way, channel or stream, there shall be provided a storm
' water easement or drainage right-of-way conforming substanti-
ally with the lines thereof, and such further width or further
construction, or both, as will be required for the purpose of
' handling '.draina.ge . Shifts from existing locations of water
courses, drainage ways, channels or streams may be permitted
by the Town only where such result in equivalent or better
drainage within and surrounding the development than will be
' existing location; provided, however, that any such changes
shall be explained in writing, including the specific reasons
therefore, and be made a part of the permanent application
record.
' r
3. Easements may be required .to protect retention - detention
systems and to assure proper maintenance is performed. See
' Appendix D.
1-1
' IV-1

APPENDIX A
DETERMINATION OF DESIGN FLOW
The Rational Method is widely used for determing design flows
in urban and small watersheds. The method assumes that the maximum
rate of runoff for a given intensity occurs when the duratinn.of the
storm is such that all parts of the watershed are contributing to
the runoff at the interception point. The formula used is an empirical
equation that relates the quantity of runoff from,a given area to
the total rainfall falling at a uniform rate on the same area and
is expres s.ed as: .
Q _ CiA
The runoff coefficd.*ent "C"_and the drainage area "A". are both
constant for a given area at a given time. Rainfall intensity "i
however, is determined by using an approprate storm frequency and
duration which are selected on the basis of economics and engineering
judgement. Storm sewers are designed on the basis that they will
flow full during storms occurring at certain intervals. Storm fre-
quency is selected through consideration of.the size of drainage
area, probable flooding, possible flood.damage and projected develop-
ment schedule for the area
RUNOFF COEFFICIENT. The runoff coefficient "C" is the ratio
of the average rate ofrainfall on an area to the maximum rate of run-
off. Normally ranging between zero and unity, the runoff coeffi-
cient can exceed unity in those areas where rainfall occurs in con-
junction with melting snow or ice.. The soil characteristics, such
as porosity, permeability and whether or not it is -frozen are im-
portant considerations. Another factor to consider is ground cover,
such as paved, grassy or wooded. Incertain areas, the coefficient
depends upon the slope of the terrain.. Duration of rainfall and shap e
of area are also important factors in special instances. Average
values for different areas are listed in Table 1.

RAINFALL INTENSITY. Rainfall intensity "i" is the amount
of rainfall measured in inches per hour that would be -expected to
. occur during a storm of a certain duration.. The storm frequency.
.is the time in years in which a certain storm would be expected
again and is detennined statistically from available rainfall.
data. See Table II for Hatteras Rainfall -Intensity -Duration Curves.
TIME OF CONCENTRATION. The time of concentration at any point
in A sewer system is the time required for runoff from the most're
mote portion of the drainage area to reach that point.; Themost
remote portion provides the longest time of .concentration but is not
necessarily the most distant point in the drainage 'area. Since a.
basic assumption of the Rational*Method is that all portions of
the area are contributing runoff, the time of concentration is used
as the storm duration in calculating the intensity. The time of
concentration consists -of the time of flow from the most remote
portion of the.drainage area to the first inlet (called the inlet
time) "and the time of flow from the inlet through*:the system to the
point under consideration (called the flow time). The inlet time
is affected by the rainfall intensity, topography and ground condi
tions .Minimum inlet time shall be 10 minutes. See Tables III
and IV to assist in computing inlet time and time of concentration.
RUNOFF AREA. The runoff area "A" is the drainage area in acres
served by'the storm sewer. This area can be accurately determined
from topographic maps or field surveys.
A-2

_ - Lawns :
�5
Sandy soil, flat, 2% . ...
0.10
Sandy soil, average, 2-7%. . . . . . . . .
0.15
�0
Sandy soil, steep, 7%. . . . . . . . . .
flat, 2%
0.20
0.17
Q B
Heavy soil, . . . . . . . .
Heavy soil, average, 2-7%. . . . . I . . .
Heavy soil. steep, 7%. . . .
0.22
0.35
. .
Paving Stone/Porous Pavement:
4
flat - 2% . . . . . . . . . . . . . .
0.20
2% - 7% . . . . . . . . . . . . . .
0.30
2
Business:
�.
Downtown areas . .
0.95
~
Neighborhood areas .
0.70Sri
Residential:
06
Single-family areas. . . . . . . . . . .
0.50
multi -units, detached. . . . . . . . . . .
0.60
10Q
Multi -units. attached. . . . . . . . . . .
0.70
.
Suburban . . . . . . .:...
0.40
welling areas . . . . . . . .
' Apartment.
0.70
.2
Industrial:
Light areas. . . . . . . . . . . . .
0.70
Q
Heavy areas.
0.80
[�
Parks, cemeteries. . . .
0.25
A?J1YV1 &�
.
HOURS.
Playgrounds. . . . . . . . . . . . .
0.35
pURRT1ON
Railroad yard areas.
0.40 .
Unimproved areas - -
0.3o
RRJNFRC 4 INTENSITY DURRTloN
: CURVES
Streets:
' Asphaltic .... ....... .....
0.95
NORTH CRROL tNR 5TRTE H16HWRY
COMM1551ON
Concrete ... ..:.. ......
0.95
0RN, 1qV
Brick .. ...
0.85
Drives and walks . . . . . ... . . . . . . . . . . . . . . .
0.95
Roofs. . . . . . . . . . . . .
0.95

t_t
I
.
.
H (FT.)
500
400
300
EXAMPLE
Te (M1N.)
200
Height a 100F1.
150
-.
�-
200
Length--3,000Ft.
W+
Time at concentration =14Min.
Io0
L,
t5o
100
L (FT.)
80
r
W
>
10,000 '
;,
60
'
50 1
a
50.
`Mi°� F
.z
40
i Z
40
` -�
5,000
F.
30
30
W
\�
a
H
'
W
~0
20
Note?
Use nomograph Tc for natural
2,000
.
z
\ ,�
20
15
w
u.
basins with well defined channels, 0
1,500
0
W
for overland flow on bare =
0
i
10
for mowed gross road- 1—
:Ids
1000
10
..
c
side channels. •w
8
0
For overland flow, grassed sur.
w
faces, multiply Tc by 2. J
6
0
5
Foroveriond flow, concrete or
500
5 _
q
asphalt surfaces, multiply Tc _
q
by 0.4, x
300
,
=
3
For concrete channels, multiply
3
Tc by 0.2.
200
2
150
2
'
100'
.
Based on sludy by P.Z. Kirpich,
Civil Engineering, Vol.101 No.6, June 1940, p. 362
f
Flour# S.—Time of concentration of small drainage basins.
TABLE 3
eoo
_
400
• W Wo
W
v.
z
200
.
o
,00
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TABLE 4

i1
'
APPENDIX B.
'
CULVERT DESIGN
The following data has been taken directly from
Hydraulic
Engineering Circular No, 5 prepared by the Bureau of'Public
Roads,
December 1965.The discussion provides an'in'depth'look
at the.
.design,of,,culverts:'as well as provides useful' charts
for'sizing cul-
r
verts for inlet and outlet 'control conditions. Some
pages of the
circular were not reproduced in`this manual. Several
additional
charts have been provided from other ' sources that may
be helpful
in culvert system design.
B-1

U. S. DEPARTKL OFCOMHk]iCE
Bureau of Public Roads
HYDRAULIC CHARTS FOR THE SELECTION OF HIGHWAY CULVERTS
Prepared by Lester A. Herr.
Chief, Hydraulics Branch, Bridge,Division
: In Collaboration With Herbert G. Bossy
A
Highway Research Engineer, Hydraulic Research Division
Introduction
HW
Designing highway culverts involves many factors including esti-
mating flood peaks, hydraulic performance, structural adequacy, and
overall construction and maintenance costs.- This circular contains a
PROJECTING END -. UNSUBMERGED
.brief discussion of the hydraulics of 'conventional culverts and charts
for selecting a culvert size for a given set of. conditions. Instruc-
tions for using the charts are provided. No attempt is made to cover
B
all phases of culvert design. Subsequent circulars will cover culverts
-
with modified inlets and outlets designed to increase performance or to
apply to a particular location. Some approximations are made in the.
HW
hydraulic design procedure for -simplicity. These approximations are
discussed at appropriate points throughout the circular.
" -- - --_ -
For this discussion, conventional culverts include those commonly
installed, such as circular, arch and oval pipes, both metal and con-
crete, and concrete box culverts. All such conventional culverts have
PROJECTING ENO - SUBMERGED
a uniform barrel cross section throughout. The. culvert inlet may con- ".
sist of the culvert barrel projected from the roadway fill or mitered
to the embankment slope.. Sometimes inlets have headwalls, wingwalls
(,
and apron slabs, or standard end sections of concrete or metal. The
-
more common types of conventional culverts are considered in.this cir-
z
cular.
KW
Culvert Hydraulics
Laboratory tests and field observations show two major types of
MITERED ENO- SUBMERGED
' culvert flow: (1) flow with inlet control and (2) flow with outlet '.
control. For each type of control, different factors and formulas are
-
CONTROL
used to compute- the hydraulic capacity of a culvert. Under inlet con-
INLET.
trol, the cross -sectional area of the culvert barrel, the inlet geom-
etry and the amount of ueadwater or ponding at the entrance are of pri-
mary importance. Outlet control involves the additional consideration
-
of the elevation of the tailwater in the outlet channel and the slope,
roughness and length of the culvert. barrel.
•
.. _
Figure I'.:
It is possible by involved hydraulic computations to determine
the probable type of flow under which a culvert will operate fora
5-1
5-2

given set of conditions. The need for making these computations may be
avoided, however, by computing headwater depths from the charts. in this'
circular for both inlet control and outlet control and then using the .
higher value to indicate the .type of control and to determine the head-
water depth. This method of determining the type of control is accurate
except for a few cases where the headwater is approximately the same for -.
both types of control.
WATER Q
SURFACE
Both inlet control and outlet control-types'of flow are discussed
— H W S
briefly in the following paragraphs and procedures for the use of the
charts are given.
HW
Culverts Flowing With Inlet Control"
IF
Inlet control means that the discharge"capacity of a culvert is
8
controlled at the culvert entrance by the depth of headwater (HW) and
the entrance geometry, including the barrel shape 'and cross -sectional
area, and the type of inlet edge.- Sketches of inlet -control flow for
H
both unsubmerged and submerged projecting entrances are shown in fig-
rt-.
Hwy
ures lA and 1B. Figure 1C shows a mitered entrance flowing under a sub-..:
'��W.S.
merged condition with inlet control.in
inlet control the roughness and length of the culvert barrel -
C
and outlet conditions (including depth of tailwater).are not factors in
determining culvert capacity. An increase in barrel slope reduces head-
water to a small degree -and any correction for slope can be neglected
for conventional or commonly used culverts flowing with inlet control.
LG.UNE A H
In all culvert design, headwater or depth. g , p pondiag at the en- -
HW -' — -- — — — _ V—
trance to a culvert is an important factor in culvert capacity. The :
��f� �..� -W'S'_
headwater depth (or headwater HW) is the vertical distance from the
culvert invert at the entrance to the energy line of the headwater pool
(depth + velocity head): Because of the low velocities in most en-
trance pools and the difficulty in determining the velocity head for
a11'flows, the water surface and the. energy line at the entrance are
assumed to be coincident, thus the headwater depths given by the inlet •:
'
control charts in this circular can be higher than will occur in some :.
installations. For the purposes of measuring headwater, .the culvert
invert at the entrance is the low point in the culvert opening at the
_ — — — — — — — — — — — — — — — ---
��
W.S.,
beginning of the full cross-section of the culvert barrel..
.HW
���.. —
— -- -
- .
Headwater-discha rge relationships for the various types of circu-
lar and pipe -arch culverts flowing with inlet control are based on
OUTLET CONTROL
laboratory research with models and.verified'in some instances by pro-
totype tests. This research is reported in National Bureau of Stand-
ards Report No. k entitled "'Hydraulic Characteristics of Commonly
F19Uf@ `L
Used Pipe Entrances", by John L. French and, :'Hydraulics of Conventional-;.;
Available on loan from Division of Hydraulic Research, Bureau of
Public Roads.: -;•
5'3
4

rar . �r , rr s �r � rr r� :' �r r �
rr �� � ■r� �r ; ��� �-:: �;
Highway Culverts", by H. G. Bossy . F,xperimcntal data for box culverts
with headwalls and wingwalls were obtained from an unpublished report of
The friction loss Hf is the energy required to overcome the rough-
•< the U. S..Geologicel Survey.: _
ness of the culvert barrel. Hf can be expressed in several ways. Since
most highway engineers are familiar with Manning's n the following ex -
These research data were analyzed and nomographs for determining
Pression is .used:
culvert capacity for inlet control were developed by the Division of Hy—
29n2 L
V2
draulic Research, Bureau of Public Roads. These nomographs, Charts 1
through 6, give beadwate r-di s charge relationships for most conventional
Hf '`[Ri.33_.]
, 2g
culverts flowing with inlet control through a range of headwater•depths
'
and discharges. Chart No. 7, discussed on P. 5-13, is included in this
where -
revised edition to stress the importance of improving the inlets of cul-
verts flowing with inlet control. :
n = Manning's friction factor -(see homographs and page 5-30
values)for
L = length ofulvert barrel (ft.)
Culverts Flowing With Outlet Control
V = mean velocity of flow. in culvert barrel (ft./sec.)
g = acceleration of gravity,.32.2 (ft./sec.2)
Culverts flowing with outlet control can flow with the culvert bar-
R =hydraulic radius or Wr ft.)
rel full or.part full for part of the barrel length or for all of it, :.
(see fig. 2). If the entire cross section of the barrel is filled with
water for the total length of the barrel, the culvert is said to be in
where
full flow or flowing full, figures 2A and 2B. Two other common types of
outlet -control flow are shown in figures 2C and 2D.-.The procedures given
A = area of flow for full cross-section (sq. ft.)
in this circular provide methods for the accurate determination of head-
WP = wetted perimeter (ft.)
water depth for the flow conditions shown in figures 2A, 2B and 2C. The
:. method given for the part full flow condition, fig. 2D, gives a solution
Substituting in equation l and simplifying, we get for full flow
for headwater depth that decreases in accuracy as the headwater decreases.
The bead H (fig. 2A) or energy required to pass a given quantity of
r 29a2 L 1 V2
water through a culvert flowing in outlet control with the barrel flowing
H =
C1 + ke + 1.
1
(2)
full throughout its length is made up of three major parts. These. three
R
parts are usually expressed in feet of water and include a velocity head
Hy, an entrance loss He, and a friction loss Hf. -This energy is obtained •,
from ponding of water at the entrance and expressed in equation form
H =Hy+He+Hf (l)
The velocity head Hv equals VP_, where V is the mean or. average. ve-
y 2
locity in the culvert barrel. (The mean velocity is the discharge Q, is
S _�_2g He
cfs, divided by the cross -sectional area A, in sq. ft., of the barrel.)
_ NERGY SIN€
loss He depends the inlet
__ _-H�
I _
HYDR�A��IC GRq_DE LINE
HW dl
H
►+ I W.S.
The entrance upon the geometry of edge.
_�,
-
This loss is expressed as a coefficient ke times the barrel velocity
„„"'
d2
2
_
i DATUM
bead or He = ke 2g . The entrance loss coefficients ke for various types
lso
of entrances when the flow is in outlet control are given in Appendix B,
Table 1, (P•:5-49)•
• Figure 3
2 Presented at the Tenth National Conference; Hydraulics Division,
A.S.C.E., August 1961. Available on loan from Division of Hydraulic
Research, Bureau of Public Roads.
;. 5-5 :.
_56

Figure 3 shows the terms of equation 2, the energy line, the hydrau-
lic grade line and the headwater depth, HW. The energy line represents
the total energy at any point along the culvert barrel. The hydraulic'
grade line, sometimes called the pressure line, is defined by the eleva-
tions to Which water would rise in small vertical pipes, attached to the
culvert wall along its length. The energy line and the pressure line are
-parallel over the length of the barrel except in'the immediate vicinity
of the inlet where the flow contracts and re-expands:The difference in
elevation between these two lines is the velocity head, 2g .
The expression for H is derived by, equating the total energy up-
stream from the culvert entrance to the energy, just inside the culvert
outlet with consideration of all the major losses in energy. By refer-
ring to figure 3 and using the culvert invert at the outlet as a datum,
we get: 2
dl+ V1+LSo=d2tHy+He+Hf
where _
dl and d2 = depths of flaw as shown in fig. 3
V 2
1 velocity head in entrance pool
2g
LSO = length of culvert times barrel slope
then
2
dl+2g +LSO _ d2 =H +He +gP
and
2
H=dl+Vl +LSo- d2=Hr+He+AP
• 28 From :L'z %Ilevelop=.ent of this energy equation and figure 3, head H
is the difference between the elevations of the hydraulic grade line at
the outlet and the energy line at the inlet. Since the velocity head
in the entrance pool is usually small under ponded conditions, the
water surface or headwater pool elevation can be assumed to equa the
elevation of the energy line. Thus headwater elevations and headwater
depths, as computed by the methods given in this circulars for outlet
control, can be higher than.might occur in some• installations. Head-
water depth is the vertical distance from the culvert invert at the en-
trance to the water surfs.ce, assuming the water surface (hydraulic grade
2
line) and the energy line to be coincident, 41 + in figure 3.
5-7
Equation 2 can be solved for H readily by the use of the full -flow
nomographs, Charts 8 through 14. Each nomograph is drawn for a partic-
ular barrel shape and material and a single value of n as noted on the
respective. charts. These nomographs can be used for other values of n
by modifying the culvert-le%th as directed in the instructions (p- 5-29)
for the use of the full -flow nomographs.
In culvert design the depth of headwater HW or the elevation of the
ponded water surface is usually desired. Finding the value of H from
the nomographs or by equation 2 is only part of the solution for this
headwater depth or elevation_ In the case of figure 2A or,figure 3,
where the outlet is totally submerged, .the headwater pool elevation (as-
sumed to be the same elevation as the energy line) is found by adding H
to the elevation of the tailvater. The headwater depth is the difference
in elevations of the pool surface and the culvert invert at the entrance.
When the tailwater is below the crown of the culvert, the submerged
condition discussed above no longer' exists and the determination of
headwater is somewhat more difficult. In discussing outlet -control
flow for this condition, tailwater will be assumed to be so low that it
has no effect on the culvert flow. (The effect of tailwater will be
discussed later.) The co mmm types of flow for the low tailwater con-
dition are shown in figures 29, 2C and 2D. Each of these flow condi-
tions are dependent on the amount of discharge and the shape of the
culvert cross section. Each condition will be discussed separately.
,Full flow at the outlet, figure 2B, will occur only, with the higher_
rates of discharge.. Charts 15 through 20 are provided to aid in deter-
mining this full flow condition. The curves shown on these charts give
the depth of flow at the outlet for a given discharge when a culvert is
flowing with outlet control- -This depth is called critical depth dc.
When the discharge is sufficient to give a critical depth equal to the
crown of the culvert barrel, full flow exists at the outlet as in fig-
ure 2B. The hydraulic grade line will pass through the crown'of the
culvert at the outlet for.all discharges greater than the discharge
causing critical depth to reach the crown of the culvert. Head H can
be measured from the crown of the culvert in computing the water sur-
face elevation of the headwater pool.
.When'critical depth falls below the crown of :the culvert at the
outlet, the water surface drops as shown in either figures 2C or 2D,
depending again on the discharge. To accurately determine headwater
for these conditions, computations for locating a backwater curve are
usually required. These backwater computations are tedious and time
consuming and they should be avoided if possible. Fortunately, head-
water for the flow condition shown in figure 2C can be solved by using
the nomographs and the instructions given in this circular.
For -the condition shown in figure 2C, the culvert must flow full
for part of its length. .The hydraulic grade line for the portion of
the length in full flow will pass through a point.where the water
breaks with the top of the culvert as represented by point A in figure
2C., Backwater computations show that the hydraulic grade line if.
5-8 ._

extended as a straight line will cut the plane of the outlet cross sec-
depth TW is the distance in feet from the culvert invert at the outlet
tion at a point above critical depth (Water surface). This point is at
to the water surface in the outlet channel. The relationship of HW to
a height approximately equal to one half the distance between critical .,
the other terms in equation 3 is illustrated in figure 4.
depth and the crown of the. culvert. The elevation of this point can be
used as an equivalent hydraulic grade line and H, as determined by equa-
tion 2 or the homographs, can be added to this elevation to find the
water surface elevation of the headwater pool.
The full flow condition for part of the barrel length,. figure 2C,
-- H
will exist when the headwater depth HW, as computed from the above bead-
HW
water pool elevation, is equal to or greater than the quantity
Dr
TW ho
i
D+ (1+ke).28
L
LSo -
where V is the mean velocity for the full cross section of the barrel;
ke, the entrance loss coefficient; and D, the inside height of the cul-
Figure 4
vert. If the headwater is less than the above value, a free water sur-
face, figure 2D, will extend through the culvert barrel.
The part full flow condition of figure 2D =st be solved by a
If the tailwater elevation is below the top of the culvert open -
backwater computation if accurate headwater depths are desired. De-
ing at the outlet, figure 2B, 2C.and 2D, ho is more difficult to deter-
c
tails for making this computation are not given in this circular. In-
must be
mine. The discharge, size and shape of culvert, and the be
stead the solution used is the same as that given for the flow condi-
• tion of figure 2C, with'the reservation that headwater depths become
considered. In these cases, ho is the greater of two values (l) TW
less accurate as the discharge for a particular culvert decreases.
depth as defined above or (2) do + D . The latter dimension is the dis-
Generally, for design purposes, this method is satisfactory for head-.
2
water depths above 0.75D, where D is the height of the culvert barrel.
tance to the equivalent hydraulic grade line discussed previously. In
Culvert capacity charts found in Hydraulic Engineering Circular No. 10
this fraction do is the critical depth, as read from Charts 15 through .
give a more accurate and easy solution for this free surface flow con-
20 and D is the culvert height. The value of do can never exceed D,
dition.
making the upper limit of this fraction equal to D. Where Tip is the
greater of these two values, critical depth is submerged sufficiently
*Headwater depth HW can be expressed by a common equation for all
to make TW effective in increasing the headwater. The sketch in.fig-
outlet-control conditions, including all depths of tailwater.' This
ure 5 shows the terms of equation 3 for this low tailwater condition.
is accomplished by designating the vertical dimension from the cul-
Figure 5 is drawn similar to figure 2C, but a change in discharge can
vert invert at the outlet to the elevation from which H is measured
change the water surface profile to that of figure 2B or 2D. ••.
as ho. The headwater depth HW equation is
HW=H+ho -LSO (3)
All the terms in this equation are in feet. H is computed by
equation 2 or found from the full -flow, nomographs. L is the length of
culvert in feet and So the barrel slope in ft. per ft. The distance
ho is discussed in the following paragraphs for the various conditions
of outlet -control flow. Headwater HW is the distance in feet from the
invert of the culvert at the inlet to the water surface of the head-
water pool.
When the elevation of the water surface in the outlet channel is
equal to or above the elevation of the top of the culvert opening'at
the outlet, figure 2A, ho is -equal to the.tailwater depth. Tailwater
5-9 .
5-10
d � —�•Tw .
do +D �
2 or TW-ho

Computing Depth of Tailwater
the need for channel protection. 'A change in size of culvert does not
change outlet velocities appreciably in most cases.
In culverts flowing with outlet control, tailwater can be an im-
portant factor in computing both the headwater depth and the hydraulic
Outlet velocities for culverts flowing with inlet control may be
capacity of a culvert. Thus, in many culvert designs, it becomes nec-
approximated bj computing the mean velocity for the culvert cross sec-
essary to determine tailwater depth in the outlet channel.
-tion using Mdnning's equation
Much engineering judgment and experience is needed to evaluate
2,/3 1/2
R. SO
possible tailwater conditions during floods. A field inspection should
• Y - n
be made to check on downstream controls and to determine water stages.
Oftentimes tailwater is controlled by a downstream obstruction or by
Since the depth of flow is not kno the use of tables or charts
water stages in another stream. Fortunately, most natural channels are
is recommended in solving this equation . 'The outlet velocity as
wide compared to the culvert and the depth of water in the natural chan-
computed by this method will usually be high because the normal depth,
nel is considerably less than critical depth, thus the tailwater is in-
assumed in using Manning's equation, is seldom reached in the rela-
effective and channel depth computations are not always warranted.
tively short length of the average culvert. Also, the shape of the
outlet channel, including aprons and wingwalls, have much to do with.
An approximation of the depth of flow in a natural stream (outlet
be by
the velocity occurring at the end of the. culvert barrel.
channel) can made using Manning's equation (see page 5-12) if the
Taichanging
is not considered in reducing outlet velocities
channel is reasonably uniform in cross section, slope and roughness. •
tions.effectire
for most inlet control conditions.
for most
Values of n for natural streams for use in Manning's equation may be
found in Table 2, appendix B. p. 5-50. If the water surface in the
In outlet control, the average outlet velocity will be the dis-
outlet channel is established by downstream controls,, other means must..
charge divided by the cross -sectional area of flow at the outlet.
be found to determine the tailwater elevation. Sometimes this neces-
This flow area can be either that corresponding to critical depth,
sitates a study of the stage -discharge relationship of another stream
tailwater depth (if below the crown of the culvert) or the full cross
into which the stream in question flows or the securing of data on res-
section of the culvert barrel.
ervoir elevations if a storage dam is involved.
Velocity of Culvert Flow
o es
Pert rmance Curves
A culvert, because of its hydraulic characteristics, increases
Although the procedure given in this circular is primarly for
use in selecting a size of culvert to pass a given discharge at a
the velocity of flow over that in the natural channel. High velocities
given headwater, a better understanding of culvert operation can be
are most damaging just downstream from the culvert outlet and the ero-
sion potential at this point is a feature to be considered in culvert
gained by plotting performance curves through some range of discharges
design.
and barrel slopes. Such curves can also be used to compare the per-
formance of different sizes and types of culverts. The construction
Energy dissipators p
for channel flow have been investigated in the
of such curves is described in Appendix A, page 5-45•
laboratory and many have -been constructed, especially in irrigation
•
channels. Designs for highway use have been developed and constructed
Inlets and Culvert Capacity,
at culvert outlets. All energy dissipators add to the cost of a cul-
vert, therefore, they should be used only to prevent or to correct a
(See
Inlet shape, edge geometry and skew of the entrance affects cul-
serious erosion problem. reference 5, p. 5-14.) .
vert capacity. Both the sbape and edge geometry have been investiga-
The judgment of engineers working in a particular area is re-
ted by recent research but the effect of skew for various -flow condi-
inlet edge
quired to determine the need for energy dissipators at culvert out -
tions as not been examined. Results show that the geometry
h
in inlet -control flow.
lets. Asian aid in evaluating this need, culvert outlet velocities
is particularly important to culvert performance
A comparison of several types of commonly used inlets can be made by
should be computed. These computed velocities can be compared with
outlet velocities of alt-rnate culvert designs, existing culverts in
referring to charts 2 and 5. The type of inlet has some effect on
the area, or the natural stream velocities. In many streams the max -
capacity in outlet control but generally the edge geometry, is'less
imam velocity in the main channel is considerably high&r than the mean
important than in inlet control.
velocity for the whole channel cross-section.' Culvert outlet veloci-
ties should be compared with maximum stream velocities in determining
3 See references page 5-1$.
5-12 . .
5-11
. i

As shown by the inlet control nomograph on Chart 5, the capacity
of a thin edge projecting metal pipe can be increased by incorporating
the thin edge in a headwall. The capacity of the same thin edged pipe REFERENCES
can be further increased if the entrance is rounded, bevelled or. tapered
by the addition of an attachment or the building of these shapes into a
headwall. Although research on improving culvert entrances is not com- 1. "Hydraulic Tables", Corps of Engineers, U. S. Army. For sale by
plete, sufficient data are available to permit the construction of Superintendent of Documents, Government Printing Office, Washington,
Chart 7, an inlet control nomograph for the performance of a bevelled D. C. Price $2.75.
inlet on a circular culvert. A sketch on the nomograph shows the di-
mensions of two possible bevels. Although nomographs have not been 2.."Hydraulic and Excavation Tables", U. S. Bureau of Reclamation.
prepared for other barrel shapes, the capacity of box culverts can be For sale by Superintendent of Documents, Government Printing Office,
increased at little cost by incorporating a bevel into the headwall. Washington, D. C. Price $1.50. „
In computing headwater depths for outlet control, when the above bevel
is used, ke equals 0.25 for corrugated metal barrels and 0.2 for con- 3. "Handbook of Hydraulics"i by H. W. King, McGraw-Hill Book Company,
crete barrels. New York City.
Figure 6 shows a photograph of a bevel constructed in the headwall 4. "Design Charts for Open -Channel Flow",-U. S. Department of Commerce,
of a corrugated metal pipe. Bureau of Public Roads. For sale by Superintendent of Documents,
Government Printing Office, Washington, D. C. Price 70 cents.
_� ��� t�j �� I�•• �� �� r. 5. "Hydraulic Design of Stilling Basins and Energy Dissipators", by
. ��, r�� ; -.�•-.,"+'�'� ,',1 ,, �, i A. J. Peterka, U. S. Department of Interior, Bureau of Reclamation,
'".zr �;,:�jz:. t• ri:' 'rt ° e =,s 1964. For sale by the Superintendent of Documents, Government
�`-~� �-''�.'.�'�` sr : c "f'>, ,• �* w�= � �' Printing Office, Washington, D, C,, 2040C Engineer,
rJ- Z 4 plt ��. S�'•L� 2 or the Chief
,--r- , �. ; �� �7 _ .. ,... i, � Bureau of Reclamation, Attention 841, Denver Federal Center, Denver,
. . VN Colorado, 80225. Price $1.75.
t' f ''. •a. t .y
71.
1:. ' °` fA�� �e 'NN
'
F.
Photo -- Courtesy of Oregon State Highway Department
ir
Figure 6
5-13
5-14

zr r
r■i '�r it „�,� ,,,,,, ,,, ,,, rr
�r
,rr ; r �.. r r _,
Procedure for Selection of Culvert Size Step 3:
Find headwater depth for trial -.size culvert.
Step 1:
List design data- • (See suggested tabulation form, figure 70
a.. Assuming INLET COXML
P• 5-18.)
(1)
-Using,the trial size from step 2, find the headwater
a. -Design discharge Q, in cfs., with.average return period.
"depth HW by use of the appropriate inlet control nomo-
(i.e- Q25 or Q50 etc.)
.graph (Charts 1-7)- Tailwater TW conditions are to be
neglected in this determination. HW in this case is
b. Approximate length L of culvert, in feet.
'
found by multiplying D obtained from the nomographs _
c. Slope of culvert. (If grade is given in percent,'convert
by the height of culvert D.
to slope in ft. per St.)
(2)
If HW is greater or.less than allowable, try another
trial size until HW is acceptable for inlet control
_
d. Allowable headwater depth, in feet, which is the vertical
before computing HW for outlet control.
distance from the culvert invert (flow line) at the en-
trance to the water surface elevation permissible in the
b. Assuming ouTLET cCnTRpL -
headwater pool or approach channel upstream from the cul-
vert.
(1)
Approximate the depth of tailwater TW, in feet, above
-
the invert at the outlet for the design flood condi- '
e. Mean and maximum flood velocities in natural stream.
tion in the outlet channel. (See general discussion'
on tailwater, P• 5-11.)
f. Type of culvert for first trial selection, including bar-
(2)
-.For tailwater TW elevation equal to or greater than
rel material, barrel cross -sectional shape and entrance
the top of the culvert at the outlet set ho equal
type,
to TW and find HW by the following equation (equation
3)•
Step 2:
Determine the first trial size culvert.
HW=H+ho-LSO .
Since the procedure given is one of trial and error, the ini-
tial trial size can be determined in several ways:
Wwhere
_
a. By arbitrary selection.
HW = vertical distance in feet from culvert
invert (flow line) at entrance to the
b. By using an approximating equation such as = A from
pool surface.
10
H e head loss in feet as determined from the
which the trial culvert dimensions are determined.
appropriate nomograph (Charts 8-14)
:..
ho = vertical distance in feet from culvert
,.,
c. By using inlet control nomographs (Charts 1-7) for the
invert at outlet to the hydraulic gradeHW ..
culvert type selected. If this method is used an
-line (In this case ho equals TW, measured
`
HW
in feet above the culvert invert.)
must be assumed, say = 1.51 and using the given Q a -
So =slope of barrel in ft:/ft.
trial size is determined. _
L. _ culvert length in ft.
If any trial size is too large in dimension because of limited
(3)
For tailwater TW elevations, less than the top of the ,
height of embankment or availability of size, multiple cul
-
culvert at the outlet, find headwater HW by equation .
i
verts may be used by dividing the discharge equally between
3 as is b(2) above except that
the number of barrels used. .Raising the embankment height or.
ho d- D
the use of pipe arch and box culverts -with width greater than
= or 2N, whichever is the greater
2
height should to considered. Final selection should be based
on an economic analysis. .
'
where •
dc = critical depth in ft. (Charts 15 through
-
' 20) .
Note: do cannot exceed D
o
D = height'of culvert opening in ft. `
5-16

Note: Headwater depth determined in b(3) becomes in-
creasingly less accurate as the headwater com-
puted by this method falls below the value
2
D + (1 + ke)2g. (See discussion under"Culvert
Flowing Full with Outlet Control", p• 5-9•)
c. Compare the headwaters found in Step 3a and Step 3b (In-
let Control and Outlet Control). The higher headwater
governs and indicates the flow control existing under
the given conditions for the trial size selected.
d. If outlet control governs and the HW is higher than is
acceptable, select a larger trial size and find HW as in-
structed under Step 3b. (Inlet control need not be
checked, since the smaller size was satisfactory for this
control as determined under Step 3a.)
Step 4: Try a culvert of another type or shape and determine size and
HW by the above procedure.
Step 5: Compute outlet velocities for size and types to be considered
in selection and determine need for channel protection.
a. If outlet control governs in Step 3c above, outlet veloc-
ity equals -, where Ao is the cross -sectional area of
Ao
flow in the culvert barrel at the outlet. If do or TW is
less than the height of the culvert barrel use Ao corres-
ponding to do or TN depth, whichever gives the greater
area.of flow. Ao should not exceed the total cross -
sectional area A of the culvert barrel.
b. If inlet control governs in step 3c, outlet velocity can'
be assumed to equal mean velocity in open -channel flow
in the barrel as computed by Manning's equation for the
rate of flow,.barrel size, roughness and slope of culvert.
selected.
Note: Charts and tables are helpful in . p computing outlet
velocities. (See references p. 5-14.)
Step 6: Record final selection of culvert with size, type, required
headwater, outlet velocity, and economic justification.
5-17

.n
It.
co
� '
PROJECT:
DESIGNER:
DATE:
HYDROLOGIC AND CHANNEL INFORMATION
01 = TWI =
02 = Tw2 =
01 - DESIGN DISCHARGE. SAY 025 \
02 - CHECK DISCHARGE SAY 050 OR 0100 J
SKETCH
STATION:
EL.
AHW=
--.r..� Tw
EL.—,. C° -
- EL, .
MEAN STREAM VELOMY=
MAX STREAM VELOCI Y='
CULVERT
DESCRIPTION
(ENTRANCE TYPE)
0
SIZE
HEADWATER COMPUTATION
z
¢ i
,
»
�>
COST
COMMENTS
INLET CANT.
OUTLET CONTROL HW=H + hp -LSp
o
HW
Ke
H
dp
d +D
TW
hp
LSp
HW
SUMMARY 8 RECOMMENDATIONS

mur-CONTROL MOGRAPES
CHART
Charts 1 through T
t2
Instructions for Use
11
600
(2) (3)
500
EXAMPLE
6
9 10
1. To determine headwater (RW), given Q, and size and type of culvert.
10
400
3'.2'ee. o.retr.
0/0 • 1Sefs/rt
s
T
8
a. Connect with a straightedge the given culvert diameter or
9
.
300
MW
1.t.e 0 ae/
6
6
65height
6
6
(D) and the discharge Q. or Q for box culverts; mark
(1)) 1•75 3.5
S
B
intersection of straightedge on RW scale marked (1).
9
-
200
(2) 1.90 3.6
(3) zas a1
4
4
S
4
D
b. If D scale marked (1) represents entrance type used, read D
T
3
y
on scale (1). If another of the three entrance types listed on
►-
too
3
the nomograph is used, extend the point of intersection in (a)
6
0
horizontally to scale (2) or (3) and read D
m
so
2
2
-••
c. Compute RW by multiplying HW by D.
D
S
In
60
S0
/ ►-
2
1.S
2. To determine discharge (Q) per barrel, given NW, and size and type
w
?
40
LS.
of culvert.
w U.
m
.
a. Compute HW for given conditions.
z
o
4
0
x
30
P2`�
0
D
m
�-
3
rz
U.
1.0
b. Locate D on scale for appropriate entrance type. If scale
�/
(2) or (3) is used, extend D point horizontally to scale (1).
U.
0
�'
_
9
1.0
to
F
3
f w
Aglt el
�„
c. Connect point on scale (1) as found is (b) above and the
x
w
/ 0
/ a
to
Wi.•.411
i1...
- '
d
c
e
9
9
D
size of culvert on the left scale. Read Q or Q on the dis-
x
x
m
s
w
charge scale.
U,
6
3
0
.T
-�
d. If B is read in .(c) multiply by B (span of box culvert) to
2/
0
a
4
Ho SCALE wFLARE L
x
6
T
► '
find Q.
z
(1) 30.16 rs•
3. To determine culvert size, given Q, allowable RW and type of cul-
•
3
(2) 90•..• IS•
131 0•I4a1t..teea
.S
vert.
,t
of
a. Using a trial size, compute BW
.s
.s
DU.S.
stale 121 •r pl ,re)tt1
.
b. Locate Pi scale for appropriate entrance type. If scale
eerltt.tell, le stele (1), let•
.. ..e .Uayel I.tre rrt .t tewll
.4
Don
'
(2) or (3) is used, extend f point horizontally to scale (1).
t
0 eM 0 ueln, ar none •.
IItY.lrelt�.
D
HW
c. Connect point on 7. scale (1) as found in (b) above to given
.s
.4
4
discharge and read diameter, height or size of culvert required
t
.6
.s
30
.35
t .3s
for HW vat°°'
HEADWATER DEPTH
FOR BOX
CULVERTS
d. If D is not that originally assumed, repeat procedure with a
WITH INLET
CONTROL
•
new D.
BUREAU O. PV•llt
ROADS J.N. He)
5-19
5-21

CHART
2
CHART
3
180
10,000
168
6,000
EXAMPLE
(1)
(2)
(3)
151 x 97
5000
EXAMPLE
156
6.000
0.42 Inches (3.5 feel)
6
6
-s-
30.300 of g'
- O. 3o0 $#e
(2)
144
5.000
a. 120 cte
5.
136aST
7.z000
(3)
4.000
tit • nw
6.
5.
N ' Hw
la.t)
4.0
132
3,000
o toot
(1) Ls e.e
5.
4
4.
121 x T7
Pl =.B n.e
(1)
a.0
3.0
120
(2) 2.1 7.4
113 x 72
1000
It)c.= s.e
13) x•3 SA
3.0
.
2.000
(3) 2.2 7.7
4.
3.
800
+D In fed
- -
108
AD In fed
3.
106168
600
i.
2.0 _
2.0
96
1.000
3'
98 x 63
500
j
-
91 x56
40i
'w�fr'
�.X! -
2.0
-
800
LS
84
6
__
__ -►
2.
2-
0
83 x 53
00
1.5
--
00
//
r
200.
\
3
S
LS
T2
400
2.
_
�
6 x 48
W
x
300
tet��
Ef�
S
1.5
1.5
Z
IL
_
-
To..* ... 4 (2)er(3)
d- a $#.eight li o
W
N
¢
2
eA
/
- on
o.
68 x 43
a
U.
100
sh••.sh sn..n veba.
. Z
60
0
200
1.5
J
z
80
e.: t.r.of it, ect sH.h (Ij
I.0
1.0
. 2
W
j
I- point - avoid (1)
2
1'0
O
54
C
U-60
x 38
W60
1.117 to
iM
W
•9
,9
fY
100
G
0
-
c9
SO
-%W- we- .M.
W er l!).
f
.9
143
>
48
/ W
¢
80
?
a
53 x 34
cc
=
40
Z
e
.9
lx
30
u
/2
p
60
w
1.0
L0
K
49 x32
c
d
m
U.
_
50 HW ENTRANCE
a
20
T
.7
.7
rr
40
D SCALE TYPE
1'0
D-
45 x 29
36
9
9
in
HW�D ENTRANCE
W-
►w
W
30
(1) SB••ro edge .Its
�
W
N
42 x 2T
-
SCALE TYPE
Q
ir
6
.6
us
33 .
hoed.an
c
.9
U)
a
6
a
QQ
(2) Groove end with
W
10
to) Save. edge .ith
W
C
30
Med.elt
=
.6
8
38 x 24
8
hese.etl
=
(3) Greev end
.8
-
allr.w.e end .ith
27
grePeliy
6
... he•e.e0
S
.5
.S
10
5
93) G..v. end
8
.T
T
4
Mel.cling
-
24
.7
6
30 x l9
3
To a.a scale 12) or (3) yro)ett
-
21
5
herlcontell) to acola (1).tMa
-
-
,4
.4
4
au ahelghl I.cilnod line throng►
2
.4
•
o sad o webs. or reverse as
.6
_
�
-
3
Illtntretod.
6
6
s o
2
1.5
23 x )4
1.0
15
11.0
HEADWATER
DEPTH
FOR
5
5
OVAL CONCRETE PIPE
CULVERTS
. LONG AXIS
HORIZONTAL
12
HEADWATER
DEPTH
FOR
WITH INLET CONTROL
aVaf:AU Or ►UBLtC *DADS J11 N. i%!
-
CONCRETE
PIPE
CULVERTS
HEADWATER
SCALES 293
REVISED MAY 1964 WITH
INLET
CONTROL
-
'.
5_23
-
BUREAU
Or PUBLIC
ROADS JAN. 1*93
5-22

CHART
4
CHART 5
97 a iSl
190
10.000
I' )
5000
Ise
8,000
EXAMPLE
87 ■ 136
4000 .EXAMPLE
2 )
(3)
IS6
6,000
o•ssl.ct..p.oH.q
12)
6.
3000 site: 36'. to'
6
5,000
6. cs cf•
.. (3)
0.200 too
_
6
144
4.000
Rw' Rw
5.
6.
T7 a 121
72000 • Rw
5
5
132
3,000
B j1i1j
S.
6.
72 a 113
(1) 2.6 13.0
5
-
4
120
W
2.000
(t1 2.t 6.3
S.
sea 106
It) 2.0 10.0
4
y
<
rn L.z c.6
4.
1000 . lal 2.t IO.e
3_
108
i
to 1. feet
3.
4.
63 a 98
800 0 : Het
3
a
3•
96
1,000
SB a 91
600
/
2
800
3'
500
a,
N
W
53 2 83
-
/
400 f�
=
2
84
m
600
SOO
-
2.
I.s
LS
r
400
Z.
=
48 a 78
200
m
LS
1
m
72
300
W
/ on
To too .col. (2) o,(3)
V•
O
•
43 a 6�
v
ere. It.er•ifM live -
p
?
60
U
-
200
f,/
.
I.S
1.5
i
'7.
tM.•at too- -I.•e
y
=
Z
f*'�
cclot
J
of site Me ei.ct.rfe -
100 to 1.1.....I ...1. (1).
2
W
1.0
1.0
0
34
�
w
-
de
'
38 a 60
O
..
6p fn. iei.l •..c.t.11l
F
1.0
_�
101��
U
tJ
ir.l•.t tnrit..tol1T to
=
.9
.9
1
ct:
u
a
0
p
60 a1.1i•. •. •i1Mr $col.
-
,9
w
48
cc
80
p
IN
34 a 53
a
=
50 (1)0,0
)_-
•8
•8
�N
_�
v
60
Z
1.0
1.0
N
N
40
Co.
4
42
/
p
50
F
At
32 a 49
O
30
G
T
7
C
40
0
1.0
z
HW/D ENTRANCE
' m
•T
.
w
36
30
HW ENTRANCE
o
,
H
29a45
20 SCALE TYPE
<
m
U SCALE TYPE
9 .
2T x 42
••
(1) swe .he .itR
o
.6'
.6_
a
S3
20
(q R.•e..0
c
.8
.8
tW,(
(L) Cww...e .i.R
W
i
-
30
- Mlluse to nnlsrs
Q
S
.8
24 a 38
10 A..e..0
u
..10
to.foie
6rm0 e.e
.5
.5
Cl -
27
fnl.cll.t
.5
8
8..
i
24
..
_
.T
5
a
6
4 -
..
-
5
T.... ... to It) or 131 ir.iat
19 s 30
q
21
-'
4
Bwit-1.1y to $..1. (1). the.
.6
3
.4
... weigh I.clI..e li.e Welsh
.6
I
I3
O -4 o .c.t.., •r r... no as
.6
2
O
2
1S
y
1.0
1.0
.5
14 it 23
HEADWATER
DEPTH FOR
(2
HEADWATER DEPTH FOR
OVAL CONCRETE
PIPE CULVERTS
C. M.
PIPE CULVERTS
LONG AXIS
VERTICAL
WITH
INLET CONTROL.
WITH INLET CONTROL
BUREAU Of PUBLIC ROADS Jr1R..9.a
BUREAU Of PUBLIC ROADS JAR. 1993
5-24
5-25

CHART 6 CHART 7
to.'
4.000 -
-
4
IS'-4'a 9'-3'
3,000 EXAMPLE
4
3)
- sic.: 39. It*
3
4
2.000 0• to CIS
-
r3
Nw• Nw.
3
. aw
D (f..l)
3
a j
11'-S'a
(1) L10 2.0
2
50,
1.000
tt) 135 2.1
- `
800 (31 L12 2.2 .
• u Ir
_
9'-6' x 6'-S'
600 •o to t•.r
2
2
-
S00 -
_c
8'-2' it S''9'
400
l.5
1•5
300
I.S
7'- 0' a 5'-1'
200
=
6'-I• it 4'-T
--
--
u
1.0
• a
TZ' a 44'
u
100 � 3
I.0
_
o.
Z
8O "ol _
.9
1.0
o
63'x 40'
60 +��� a
.9
I
W
O
SO
.9_
•8
.8
w
W
58' a 36'
" U.
K
40 0
0
30 ��
.8
aS
0' x 31' _N
/ m
.7
7
rn
c
20 H
N
HW ENTRANCE ?
D SCALE TYPE
_
T
43's 2T' ��
_
- �
10 lil MO•r•i q nnl.Iw 0
-
.6
• t3
/ -
/36'
B 1. dq•cc
-
It 22'
(31 haj•cliy H
e
it
6
z
a
S o
a
4 IS,
'S
S
S
29' i IB'
3 a.Acsel.11i b ud. (II. IM.
n• .IralyM LcNn/ lie. IM..9A
25' a 16'
2
-
_
.4
.4
1.0 ( I
.4
.6
35
.35
B' a 11'
LL S
L
35
'�FADOITIONAL
SIZES NOr DIMENSIONED
ARE. .: HEADWATER
DEPTH
FOR
LISTED IN
FABRICATOR'S CATALOG
C. M. PIPE -ARCH
CULVERTS
W"AU
M PUPLIC RDADa JAI. tIN3
WITH INLET
CONTROL
a
I80
168
156
132
120
108
1
O
j
C
EN7R.NCE
iV/E
0.04L
QO43
0.04%
0.053
A
0.051
sits
0.042
0.1tS
6
-3000 BEVELLED RING
MINIMUM 300'
r2000 e
'1
DIAMETER•
96
1000
800
84
600
S00
400
T2
rA
300
W
?
60
200
V
Z
_
i
o
S4
F
-100
W
48
Z
80
o
60
a`
42
u
SO
40
1-
36•
uuf
30 _ X'Mt`E�
a
0
33
_��
0
A 8
3.6 3.0
3.0
O
2.0
- 2.0 N
C
W
I.-
W 1.3
1.5 a
0
Z
O.
►
W
O
c
W
4i 1.0
I.0 c
W
.6 r .8
2T 10 .7 .T
24
6 .
S
21 4 .6 .6
3
18
2 .
.S2 .52
IS
1.0
HEADWATER DEPTH FOR
1z CIRCULAR PIPE CULVERTS
BUREAU OF PUBLIC ROADS WITH BEVELLED RING
AIARCN 1964
INLET CONTROL
5-27

MR"
CHART
4
97051 151
180
10.000
(, )
5000
I68
8,000
EXAMPLE
87 a 136
4000 EXAMPLE
(Q)
(3)
156
6.000
0.36I.cAee 13.0 feel 6. (2)
3000 34.: 3a-■ 60•
. 6
5.000
0.66 •la
)
\3)
O•LDO cla
(�)
6
144
4.000
Nay ter
S.
8•
77 a 121
r 2000 Vic• Nw
6
S
5
132
3.000
0 P.01
5, rs.
M s 113 '.
-
0 P••q
.. 10 1.4 13.0
-
5
4
4
120
S
a
2,000
- III 1.5 3.4
- 1Lf L.1 6.3
5.
66 a 106
(21 2.0 10.0
4
3
i
ts) [.L ss
4.
1000 t31 2.1 10.5
3_
108
,�
3.
4.
63 a 98
000 •0 i. 1..1
J
a
00 {o feet
3
96
F
1,000
-
3•
58 a 91
600
2
600
3.
to\
500
400 �,,,
3
2
84
WP
0600
y
w
0
53 a 83
�
1.3-
LS
1
500
300 /�
2
2.
48 a T6
/ /
let400
y
1.5
}
to
72
300
/ g
2
w
/
200
To
U.
1
_
U
/� ;
2
1.5
-
d
43. 6
to
/ Y.
o• •cote (L) ar (3)
4•. s sirsight lino
p
=
U.
O
200
6�
LS
d
/ U
N1ee.SA know .oN•a
U)Z
60
Z
*6�
LS
O
100 a {n.rseaea{a0).
1
1.0>
1.0
C
54
w
•
BOFom rnw t.te
1.00
'
f•,
-,
w
100
%
-
w
Msj•at k.N..n1.11L 10
_
9
.9
1
v
Q
• f7
Co
60 s.1.Y.n .w aMo .cote
-
,9
>
48
.4
80/
c
W
34 A 53
.4
_
50 ILIsr131.
_
1-
.8
8
J
=
�•
60
Z
1.0
1.0
N
40
W
4
42
�o
SO
m
32:49
0
30
o
7
T
O
40
W
1.0
_
HW/O ENTRANCE''Yw1
7
36
30
p
HW ENTRANCE w
N
29a45
20 SCALE TYPE
a
1w
k-
SCALE
p TYPE F w
w
27 a 42
(1 36o .or. ad.ilk
0
.6
6_
Q
33
20
G
Iq M•od.al G
.8
,B
,9
N
` y
- M.d.oll
(L) rows .nd RNIr
4
w
=
�
p
50
Y{lvai eeaferm - Q
(>) to
-
24 a 38 -
10 Mod.ou -
-.
b SN • _
r
.8
6 13) cr.oc• ..d
5
.S
.5
c
27
10
(A ►r.j.Oti.S
.T
,T
8
6
i
24
.7
5
m
6
.
4
S
To Colo (L) N 131 rr.1.c1
19 a 30
�,�
4
4
4
21
4
A«Itona111 1. atd• tl), IA.A
.6
_
5
I
_
3
su olni•AI Intlln.d IU• IAr soSA
0 o.d 0 scd.o, or ...0". to
.6
.6
2
0
2
IS
11.0
3
14 a 23
1.0
.5
HEADWATER
DEPTH FOR
--
12
HEADWATER DEPTH FOR
OVAL CONCRETE
PIPE CULVERTS
C. M. PIPE CULVERTS
LONG AXIS
VERTICAL
WITH INLET -CONTROL
WITH INLET CONTROL
BUREAU Or
►OSI.IC
ROADS JAN. 1943
BUREAU 0% WSUC ROADS JAN.
1963
- -
5-24
5-25

■� ■■� r i■�
Minn M M r M M
' OUTLET -CONTROL NOMOGRAMS
2. Values of n for commonly used culvert materials.
Charts 8 through 14
Concrete
Instructions for Use: _
Pipe Boxes
Outlet control nomographs solve equation 2, P. 5-6, for head H
0.012 0.012
when the culvert barrel flows full for its entire length.. They are
also used to determine head H for some part -full flow conditions with
outlet control. These nomographs do not give a complete solution for
Corrugated Metal
finding headwater HW, since they only. give H in equation 3, HW - H+ho-LSo•
(See discussion for "Culverts Flowing with Outlet Control", P. 5-5-)
1 Medium Large
Corrugations Corrugations Corrugatic
1. To determine head H for a given culvert. and discharge Q.
2'
a. Locate appropriate nomograph for type of culvert selected.
Unpaved 0.024 0.027 Varies-'
Find ke for entrance type in Appendix B, Table 1, p• 5-49•
25% Paved 0.021 0.023 0.026
b. Begin nomograph solution by locating starting point on length
scale. To locate the proper starting point on the length
Fully paved 0.012 0.012 0.01'
scales follow instructions below:
*Variation in n with diameter shown on charts. The various n
(1) If the n value of the nomograph corresponds to that of
values have been incorporated into the nomographs and no ad -
the culvert being used, select the length curve for the
justment for culvert length is required as instructed in lb(3).
proper ke and locate the starting point at the given cul-
vert length. If a ke curve is not shown for the selected
ke, see (2) below. If the n value for the culvert se-
3. To use the box culvert nomograph, chart 8, for full -flow for other
lected differs from that of the nomograph, see (3) below.
than square boxes.
(2) For the n of the nomograph and a ke intermediate between
a. Compute cross -sectional area of the rectangular box.
the scales given, connect the given -length on adjacent
scales by a straight line and select a point on this
b. Connect proper point (see instruction 1) on length scale to bar
line spaced between the two chart scales in proportion
to the ke values.
1�
rel area) and mark .point on turning line.
(3) For a different rougbness coefficient nl than that of
C. Pivot the straightedge on_this point on the turning line and
the chart a, use the length scales shown With an adjusted
connect given discharge rate. Read head in feet on the bead
(H) scale.
length Ll, calculated by the formula
Ll = L n 1 See instruction 2 for n. values.
c. Using a straightedge, connect point on length scale to size of
culvert barrel and mark the point of crossing on the "turning
line". See instruction 3 below for size considerations for
rectangular bcx culvert.
The area scale on the nomograph is calculated for barrel cross-
d. Pivot the straightedge on this point on the turning line and
sections with span B twice the height D; its close correspondence wit:,
connect given discharge rate. Read head in feet on the head .
area of square boxes assures it may be used for all sections interme-
(H) scale. For values beyond the limit of the chart scales,
diate between.square and B - 2D or B = 1/2D. For other box proportio:.
' find H by solving equation 21 P- 5-6.
use equation 2 for more accurate results.
5-29 .
5-30

CHART 8
CHART 9
5000
2000
4000
N
3000
�iy
�. _
N
a
�)•
R.
4
s1.F. So-..
2000
.,
1000
_
_
..
` SUBMERGED OUTLET CULVERT FLOWING FULL
.5 .
SUBMERGED OUTI[T CULVERT FLOWING FULL
800
120
- iM wlNl cr..n nN .ub—t-d —V.I. MW by
/
own. III -ob, IM {..i" MK.dm
•6
_ - MIN!• N. �.-L$• -
12X12
F. -M.l s.... MI .+Mn.n.•, s«nwl. Nw by 4
RMIb.4 d.... i►N M MN A.NM p....W. -
600
108
B
1000
.S
500
96
N,'
1.0
800 tOX10
1600
100w
6
400
84
9X9
BO Uw
�
-
S00 w BXB
60 �
�
B
300
72
/
M.
400 Z 7%T
SO Q
. FACT
9
t.0
66
ti-
��
(F`yc
2
0
X
300 0 6X6
40 Vl
?
44. 4.� �( w
OJ .� �i ti
U)
200
60
Op
/ �6
W
U.
o
m
30 X
F
• .0 Op yA z
o
54
b /y
Z
_
2
200 -K 5X5
m
'� ti lI'l., V
. - by t
2
Z
.-
In
=
p.4e
48�
��•110 ry00 _
=
b
H
20 -a
b
1� W
100
z
/
�j pp �J
a
U- 4X4
Z
apa t+� =
3
42
�p0
=
4
0 33X3 S
o
j /. mop ypp
4
_
BOi//z
�
160
_
3 6
�p0 ap�
.
S
o
100
i
BO
10 ¢
`•,
,�09 MOO
S
U
a
m
33
6 C0
6
w 3X3
U.
g O
/�• p0
b
6
0
50
F
LO
30
hop
60
25X2.5
a
¢
/
/ I[Y�MFL�- _ __�- �- _'- M�7.i
8
40
2
a
O
27
y00
O
g
S0
6
_ ���� -
•
40
eD+30
Y4
30
-
20
21
20
20
IB
20
10
iS
10
B .
B
HEAD FOR
HEAD FOR
CONCRETE BOX CULVERTS
CONCRETE PIPE CULVERTS
FLOWING FULL
GURE.0
of HSS
n = 0.012
FLOWING FULL
PUBLIC ROADS JAN.
BUREAU OF "L IC RODS JAN. 1963
- n = 0.0 12 -.
5-31
5-32

CHART
10
CHART II
2000
2000
N .4
1000
r
'—}
0.4
1000
`
_i
Nw
_.-
.S
000
_
SIe O. Sys
SUBMERGEO OUTLET CULVERT. FLOWING FULL -
O•S'
-
800
►
J
•6
151 s 97
IOW. N•e.-Ls.
120
SUBMERGED OUTLET CULVERT FLOWING FULL
-
600
136 087 -
t.. MIL1 ew-w M1 evC..a.N. taw F.I. NW 111 -
nNIN.. MpieN iR IM d.a/. px..eM
0.6
600
500
108
"We N • A* —Ls*
01
- M wlM1l CIea1 wel wS.we. �. eew q MR,
- I y
.6
500
0.7
UMI1q N.cNMe IM Ir :4 MK er.
121R77
.�..
0.8
400
96
to
400
1133172
:' -
0.9 �-
300
84
106 2 68
1.0
?J
300
98163
I e •Q?
F
200
T2
y
91R58
.'p ��
• 'A
66
p� Cry W
2
200
W
831153
.p `p0
s 'y
60
; w
!�
4
O
u
z
76R48
'Oo �y w
LL
O
s 4.
y0 2
y
68R43
y0
p AN W
"41
'S l^�'
2.
2
100 W
80
48
0 ,e - V
3
�V
_
. O —
/ Ii.,
c
Z
42
Lqo/ 00 ,� c
4
LJ
100
`038
`
ry0
'/ .100 i
3
_
60cc
m%
x
a
B0
K
give___
i
cp
` li 0 Q
0
=
30 0
36
Too
5
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- - rn
=
a
49a32
O by m
\ 'E�'4R• ap x
4 -
-
o
N
40 w
3 3
//
'moo
'.
6
c
60
45s29
O
o•ss m
—F-
—
36"
/•
_Lx1tM►_Lc
`�-_'_ ____.5OO N`.s
SO
N
42s27
5
S0
8
- -
40
a
38 S 24
NOTE �`
Di.w.m:ew. ew .;Is c 1. R.. N•
6
c
20
27
- 400
10
-
- rc.•N ter 1-9 ..:e Mr:.ewlN - ��
7
24
400
30
:..wl.I-. Th.? .M� d Ye -
.1
6
.
rMr.N I. I.we w.:. Hrl:ce1.
9
21
500
301119
10
b� .
...
20
..
10
8
to'
-
23x14
6
1S .
5
10
20
4
12
3 '.
6
5
2
HEAD•FORHEAD
FOR
OVAL CONCRETE PIPE CULVERTS
STANDARD
LONG AXIS HORIZONTAL OR ,VERTICAL
C. M. PIPE CULVERTS
. FLOWING- FULL'.
FLOWING FULL.,
- BUREAU
OF PUBLIC RODS JAN.1963
:: :. - .; . '- n = 0.012 " - .•
.....
BUREAU OF PUBLIC ROAOS JM .Bes
... "�. .• = ". n = 0.024 -
5-33
-
5-34 -

CHART
12
- CHART
13
300
N91
�.
5000
-
200
__
N
'
sNr• Sew
SUBMERGED OUTLET CULVERT FLOWING FULL.
4000
M W . N. 4e—LSe
�
11•
1
.
_
I. MINI eleee MI we►ele Nw M
M lheee Me•ri►e• iR lee ee.i" McCeewe
SHF•
=
4
3000
SUBMERGED OUTLET GULULvER[RT FLAWING FULL ..
'
O�
180
NW N.M—LSe
90
- J ep -
•5
fer MIN ae.R eel wMwgq, ewewl• Nw ET
R�e1R•ee 1••wleN in IM •eNp rree.eere
.
e0
O
(
'r tl`y
6.
2000
168
70
72eX44'
i00 ^'A F-
T.
156
2
-
60
6TX40'
400 y w
40 �' _
.8
N
144
-'
SO
_
u�
51 rX3CC
y —
`Op S
.9
L0
_
Z
132
3
40—.....a
CL
\f�
--—��
�.L Q.
W
1000
120
'_
`�JbO �yG+� W
S1YX31�
--� zErAYR! Z00 =
~�
114
-
4
30
. '� —� �� Ne1.7
B00 O
I
.-
108
O y W
'J Y.
c
O
4�X27•
y00
L6
T00 F
102
90 �O C%y
5
¢
\
2.
=
600
96
60
ZO
2
-
300
\es�o 300
O
500 C
90
`�\L4f.!`00 �� W
T
O
as
36'x22•
- \-
r 4e'Q`
3
u
a
84
�� 04 /� y0F1 =
y
.. "0
_
¢
400 Z
N
. 400
4
L2
U)
=
78 /i
�- y00
0.eepCF—�wPLC 300
9
t0
10
N
2s'xIer
500
Soo
S
c
300
2
►T
s
ItSx1
-bop
6'
IS
7
7
200
_
q00
8
8
60
g
~
S CO
20
S
t0
-
100
30
3
—40
-
IV
IV
0.0311 - -
QObOz
SO
.Q HEAD FOR '
So
HEAD. FOR
STANDARD M. PIPE -ARCH CULVERTS
STRUCTURAL PLATE
CORR. METAL . PIPE. CULVERTS
R
FLOWING FULL
F NG FULL
BUREAU or rftlC ROADS JAN. 1993
•
n=0.024
n = 0. 3281 TO 0.0302
0
• _
...... ;
" ..: : .. ...
, ' .:
BUREAU OF PUBLIC ROADS J/N. t963
-
.. ..
. 5-35 . -:
5-36 .

CHART . 14 CHART 15
5
4
3000 " 3'
"w
_t M Z
CRITICAL DEPTH
SUBMERGED OUTLET CULVERT FLOWING FULL '� -
2000 "w•"••.�s. RECTA GULAR S CTION
1 1 -' - - - isr MINI stw11 MI .MwwN/r HwP•N "M �!
' - wslM/s hssrlN/ in IM /sslp PrsNhrs - - -
0 10 20 30 40 50 60
16.6 X 10.1 O2J by �yC� Q/p
1000 �, W
15.3 X 9.2 QJ p y w 2
LL
16
boom
qg Fi^ z
a
�
1600
129 X 8.3
9p
15
=
L3
TOO S
3
h
U.
cc
`p0
14
0
500 a
1 L4It 7.2
/
z
a
OZ/ 20C
4
O
400 a
. • 900
13
4
U.
0
9.5 X & 4
5
u
300
3p0 4p0
12
Uf
6.2 X 5.6-
EXAMPLE
6
- p
Z
0.260 CfS
"•6.1 iT. -
400
7
1 1
a
IL
/
i
9
LL.
E00 m
7.0: 0.1
bp0
9
Z 10
N
rA
10
-.
6.1 It4.6
S"'
..
A -.
9
- -
6.1 t 4.6
0.03ET - -
n
z�
u . 3.e
0.0321
.
i
z
11.4 ■ T.2
mil aIm1
0.0313
0.0306 -
15
8
100
7
-.
20
HEAD FOR
6
STRUCTURAL PLATE
CORRUGATED METAL
s
50
PIPE- ARCH CULVERTS
IB IN. CORNER RADIUS

Appendix B - TABLES
Table 1. - Entrance Loss Coefficients
Coefficient ke to apply to velocity head � for determination of head
loss at entrance to a structure, such as a culvert or conduit, operat-
ing full or partly full with control at the. outlet.'
Entrance head loss He = ke V2
Type of Structure and Design of Entrance
Coefficient ke.
Pipe, Concrete
Projecting from fill, socket end (groove -end)
0.2
Projecting from fill, sq. cut end . ... . . .
. . . 0.5
Headwall or headwall and wingwalls
Socket end of pipe (groove -end) . . . . . .
. . . 0.2
Square -edge . . . . . . . . . . . . . . . .
. . . . 0.5
Rounded (radius = 1/12D). . . . . . . . .
0.2
Mitered to conform to fill slope ..
0.7
*End -Section conforming to fill slope . . . . . .
. . . 0.5
Pipe, or Pipe -Arch, Corrugated Metal
Projecting from fill (no headwall) . . . . . . .
0.9
Headwall or headvall and wingwalls.... .
Square -edge . . . . . . . . . . . . . .
. . 0.5
Mitered to conform to fill slope . . . .
0.7
*End -Section conforming to fill slope . . . .
. _ 0.5
Box, Reinforced Concrete
Headwalt parallel to embankment (no vingvalls)
Square -edged on 3 edges . . . .
. . . . 0.5
Rounded on 3 edges to radius of 1/12 barrel
dimension . . . . .
. 0.2
Wingwalls at 300 to 75°•to barrel
Square -edged at crown . . . •. . . . .
0.4
Crown edge rounded to radiusof.1/12 barrel
dimension . . •. . .
Wingwalls at 100 to 25Qto barrel•
0.2
Square -edged at crown . . . ..
0.5
Wingwalls parallel (extension of sides).
Square-edged.at crown . . . . . .
0.7
*Note: "End Section conforming to fill slope", made of either metal or
concrete, are the sections commonly available
from manufacturers.
From limited hydraulic tests they are equivalent in operation to "
a headwall in both inlet and outlet control.
Some end sections,
incorporating a closed taper in their design have a.superior hy-
draulic performance. These latter sections can be designed using. .
the information given for the bevelled inlet, p..5-13.
5-49
w-i CTT
y N n
0 O
« e
.
s 9
f"
N :S1
�� Or
ill
i
11 II
m
�
a o 1"'N"
m
ON
n Z
0
h
px=
a
0
N
0
aoo
o
A
m
z
N. 0
► _
Q�
\
a
Q.
G►
4
N
o H n
o�
o�
4
�;
�
yA tiQ D
�-
p
Z
ly
N
a Z
z
z
i e yl
.�
h
M
N
h'
OI4
fr+1
N N
i i r
.
\0
A S
n
E4
4
N
V
h
g
a II II
_
_p S
0
8 �' �
n
IN
n o
_
fA
%0
w
V
=
m
-
O
^e 'o i
CL
-4
rn
M
Z
to
W
W
=
0
CIO
0
�
0
N00
n
rn
f
e^
r
fl
r
f
n
o
h
u
h
x
n
��
I\, rn
11
O
am 0 r
x
S,
P,
S
+
p
o
o
Q
e
r
zXI
0
1
as ry
o+ •' e,
1A
C
!0
W
Z
S
0
i LMop
N
1N
r r m
.
ql�N
0 Q I�pp VI � � -j
�
p
!O
CONTROLLING
:
h
N
11
N
�D
6.
N YW
52 -1 C)
M
\
\
OUTLET
11 II
2
VELOCITY
m
� S
r
�m
IV N
l..
•
klp
a
df
n..
a
m
S'-allaofd 3 IVUSWI'II - 3 xTpuaddy

PROJECT:
DESIGNER:
DATE: 2-/B - 64
HYDROLOGIC AND CHANNEL INFORMATION
SKETCH
STATION : 3 7-/ f /4
EL, //z
AHW= e•.S
=----L
01 = /bo c/.R Qco TWI = S. o '
4_
02= TW2=
So _/X
TW s.
� .
/o L= /vo• EL99
r 01 DESIGN DISCHARGE, SAY OZS
MEAN STREAM VELOCITY= 8 yea
OZ = CHECK DISCHARGE , SAY 050 OR 0loo >
MAX. STREAM VELOCITY= /0 7sec.
CULVERT
HEADWATER
COMPUTATION
Z
,
OESCRIPTION
0
SIZE
¢ _
�o
COST
COMMENTS
INLETCONT.
OUTLET CONTROL HW=H+hO-LSD
o
HW
KD
H
dC
dC+D
TW
h0
LSD
HW
(ENTRANCE TYPE)
Cb7P (Cl-)
A'--
N.d..i(
/60.
ILO
4B�
2.ZS
0.0
S
B.3
3.7
3.8
3
3.8
/. o
//./
//./
/.Jt
N`' Nyw
V-/-os/r -r d�
/Fio
34
ASG
7.0
,S
4.7
.3.6
4.1.
3
4./
/.o
78
7.B
c- crotc c:r)
sr.rdye-11.e-1
/60
4B-
2-35'
9.4
4.7
3.7
3.8
38
/.o
7.1"
9.Q
/4'
//., Arh
.S
3
Yr st^
••
/6o
S4"
/.6
7 Z
-S
2.9
'.6
4.1
3
4.1
/a
6.o
7.L
/4,1
Ru.
Nw oc.
V-1 -c^V
C-..craM c:r)
end
ijraoVC .N0
/�
48
/-9S
7.8
-Z
4.o
3.7
3.9
3
as
la6.8
7.8
/4.
Nw-c
V�/• Ir 1r
SUMMARY 8 RECOMMENDATIONS
THE SELECTION Of A 54'
DIP WITH HEAOMALL WILL KEEP THE HEADWATER SELOM THE AHB WITH A MINIMUM
OUTLET VELOCITY. A IBN CONCRETE PIPE WITH GROOVE EDGED ENTRANCE
GIVES EQUAL Hill AND SLIGHTLY NIGHER OUTLET VELOCITY.
PROTECTION OF ;
OUTLET CHANNEL HIGHT RE NECESSARY IN SORE LOCATIONS.
_

i.
1.500
2.400
0.004
0.6'
0.4
2.000
0.3
0.005
I
t.000
800
1,500
0.006
0.6
0.2 I
600
1'�0
0.007
0.008
0.7
500
809
0,009
_
0.1
400
600
0.01
0.8
0.08
'
300
800
0.9
0.06
0.05
400
t.0
0.04
200
300
20
�
0.02
'
0.03
1
200
15 a
0.02
Alf0.03
100
'
80
30
0.01
100
9 a
0.04
0.008
so 50
B0
96
8 0
0,10 Us
0.006
1
T 40
60
84
7y
7
d
6 or
w
9.08
D.06
0.06010
2
0.005
0.004
9 30
50 c
LM
5 '=
u
OQ
0.003
60
0.
n
40 n
Ln 54
u
0.030.09
1
"
° 20
�a`�
° 48
42
4
w
0.02
0/�
0.002 I
m
20
'5-U
3
O.OtS
3
3
o
='
_a 33
a 30
Q`
d
It/.
s a
0 00J
to
a A
0.001
0.0008
C10
`0 27
24
w
c
0.006
in
0.0006 f
0.0005
29 6
20
a 21
A
`
4 .5
I.
0.0004
5'
t
C 18
0,3
0.0003 t
1
G 4
6 p
15
5
I
'
5
0.4
_
0.0002 '•
3
4
2 1
0.5
�
2
3.
10
0.6
6
•
0.0001. �...
1
9
0.7
'
0.00008 !
2
0,9
0100006
1.0
6
1.0
8
0.00005 .:
0,00004
1
0.8
9
0.00003
0.6
1.0
4
=
10
0.5
0.6
�
v
0.00002
1
2
\
0.4
0.6
r
0.3
0.5
�
0.00001 1
0.4
0 3
0.000008 i
1
0.2
0.3
15
0.000006
4
0.000005
0.:3
f .?
5
18
0.000004
-Alignment chart for Manning formula for pipe flow.
CHART•A (REF. 2)

f0
9
� 8
Curb
W 6
----
a
-�--_�.
a
WIDTH(8)
W 4
Li
cr-
-.•� LENGTH (Lb)
2
P■ 2B+Lp
'
As AREA OF CLEAR OPENING IN GRATE
TO ALLOW FOR CLOGGING DIVIDE P OR
1.5
A 15Y 2 BEFORE OBTAINING d.
'n
WITHOUT CURB P■ 2(B+Lh)
.0
a. 08
LLJ 0 3 •a 5 6 7 a 910 15 20
' DISCHARGE PER SQUARE FOOT OF
EFFECTIVE CLEAR OPENING,
r
o.a
'
W
0.6
W
Lt.
Z
oa
t�
LD
-'
W
0.2
0
CC
W
�o
d
W
CURVE (A)
,.
i
USE CURVE (A) FOR
GRATE LESS THAN
DEPTHS
0.f3
FT.
OVER
1
0.1 015 0.2 0.3 QV 0.5 O.G QT ORO.91.0 l5 .2 3
DISCHARGE PER FOOT OF EFFECTIVE PERIMETER
' HYDPtAULIC CAPACITY OF GRATE
INLET IN SUMP
CHART B (REF. 12)

' APPENDIX C
' HYDRAULICS OF DRAINAGE CHANNELS
' THE MANNING EQUATION. Water flows in a sloping drainage .
channel because of the force of gravity. The flow is resisted
' bythe friction between the water and the wetted surface of the
channel. The quantity of water flowing (Q), the depth of floe (d),
' and the velocity of flow (V) depend upon the channel shape, roughness,
and slope (So). Various equations have. been devised to -express the
flow of water.in open channels. A useful equation for channel de-
sign is that named for Robert. Manning, an Irish engineer. The
Manning equation for velocity of flow in open channels is
V =.149 R2/3S1/2
n
Where
' V means velocity in feet per second-(f.p.s.)
n = Manning coefficient of channel roughness
R hydraulic radius,' in feet,
' a
S _..slope', in feet per foot. When the Manning qu equat
ion
applies, S = SO.
The value of the Manning coefficient n-is determined by experi
ment. Some n values for various types of channels are given in
' Table 2
R, the hydraulic radius, is a shape factor that depends only
upon the channel dimensions and the depth of the flow. It is com-
puted by the equation,
1 A
R =`TP
' Where
A = cross -sectional area of the flowing water in square feet
taken at right angles to the direction of flow.
-- WP= wetted perimeter or the length, in feet, of the wetted
contact between a stream of water and -its containing channel,
__. C-1

measured in a plane at right angles to the
flow.
direction of
Another basic equation in hydraulics is
Q=AV
'
or discharge (Q) is the product of -the cross -sectional
area (A)
and the mean. velocity (V).
By combining equations (2) and (4), the Manning
equation can
be used to compute discharge directly or
Q = 1..49 AR2/3S1/2
The.following tables and charts have been taken
from existing
technical publications to assist the design engineer
drainage channels.
in designing
1
C-2

i m m m r m m= m m m m m= m m m m m
Section
Area
Wetted Perimeter
Hydrou/ic,Fodias
Tov Width
cr
P
r
T
T`
Z
bdf�d2
bf2�d
b
bh2d Z2t/
Trooc2oid
- ---
bd
bo'
b t 2d
b
b
bf 2d
Rectangle
T
' g sAI
d2
2d �2t/
�d
2gd
v bJ
2 f/
Trion g/e
T
------
2
8d2
2dTZ
3 0
3 . dT
rf
3T'
3T2t8d2
Zd
Porob o/a
L-
L
�
A
D 2 Ile_ sine
7rDe
45.Ia 711
- sin 6
B
1� sin 2
8 /80
364
Fel8O
or 2 d�.D-d�
Circle-<%z fuj/
T
D
TT9
---- Z Zr sine
TI,D �360-6�
45D IT0
27T--tsinB
B
.D sin Z .
8 /80
360
7r(36o•B) /so
_
or 2 d�D dJ
3
Circle -> �---
(l satisfactory cooroximotion for the interval O< < 0.25
ep=dWhen d/7>025: f8 zsinh-�
L 9=4sin_� d/_DI Insert 6 in eogrees in above e9c '1ations
13 0=4cos ld—ID J.

.3 .2 CO
EQUATION: V • 1. 9 R% Soh
t ,
40
i W 30
1 _I
-' .01
10 =
09 i
0
06 S ~ 20
07
.06 .6 .
05
T,
0• •8 .0Y
.03 9
Ao 1.0 10 C
I
I 9 �
NO2 CO 6 3 Z 03
LLI
° a 1Qs uai T r.o V
•o c
u-
(f) �4) 6 U_ .04
a _ a
W
.01
009 Q 2 m S U
�•- w .006 � 05 0R` 1a to
'C :007 4 (n
W 006 J /� r W 06 Z
005000a a 3;�� _ aT
J s�%/ C 0 3
' V) o4 )- J O .08
= w
4 > .09
005
10
S 2
002
6
T
6
001, 9
0009 10 I,0 •2
0008
0007 9
' 0006 6
0005 .T
.3
0004 .8 •
0003 120 .5.
.4
MANNING FORMULA NOMOGRAPH
TABLE 2 (.REF. 2 2 )

' Table 2.-Manning Roughness Coefficlents, n'
Manning n
I. Closed conduits: range s
A. Concrete pipe .......................................... 0.011-0.013
B. Corrugated metal pipe or pipe arch:
1. 2;6- by 15•ln. corrugation (riveted pipe) s
it. Plain or fully coated .............................. 0.024
b. Paved invert (range values are for 25 and 60 per-
cent of etrcumfereace paved):.
(1) Flow full depth ............................... 0.021-0.016
(2) Flow 0.8 depth ................................ 0.021-0.016
(3) Flow 0.6 depth ................................ 0.019-0.013
2. 3. by 1-in. corrugation ............................... 0.027
3. 6• by 24n, corrugation (Geld bolted) .................. 0.032
C. Vitrified cloy pipe ...................................... 0.012-0.014
D. Cast•Iron pipe, uncoated ............................... 0.013
E. Steel pipe .............................................. 0.009-0.011
F. Brick.................................................... •-••..................•---... 0.034-0.017
G. Monoithc concrete:
1. 11'ood forms, rough... . 0.015-0.017
2. \food forms, smooth.. . 0.012-0.014
3. Steelforris.......................................... 0.012-0.013
H. Cemen led rubble masonry walls:
1. Concrete Moor and top .. 0.017-0.022
2. Natural floor........................................ 0.010-0, 02S
I. Lam►nated treated woo0. 016-0.017
1. Vitrified day Ilner plates. 0.015
II: Lined open channels:'
A. Concrete, with surfaces as Indicated:
2 Formed, no finish .................................. 0.012-0.014
2. Trowel finish ........................................ O.Ol2-0.014
3, Float finish .......................................... 0.013-0.015
4. Float finish, some gravel on bottom ................. 0.015-0.017
5. G unite, good section ................................ 0.010-0.019
6. Gunite, wavy section ................................ 0.0194.022
B. Concrete bottom float -finished, sides as Indicated:
1. Dressed stone InI mortar ........................... 0.015-0.017
20
2. Random stone In mortar _ 0.017-0, 020
3. Cement rubble masonry ............................. 0, 020-0.025
4. Cement rubble masonry, plastered ................ 0.O10-0.020
S. Dry rubble(rlprap)................................. 0.0204.030
C. Gravel bottom, sides as Indicated:
1. Formed concrete .................................... 0.017-0.020
i♦ 2. Random stone In mortar ............................. 0.020-0. 023
3. Dry rubble (riprap)..............A..........._...... 0.023-0.033
D. Brick ................................................. 0.014-0.017
CHART • A (REF. 4 )
II. Lined open ebannela-Continued
Manning n
E. Asphalt:
range t
1. Smooth ..............................................
0.013
2. hough ..............................................
0.015
F. Wood, planed clean ....................................
G. Concrete -line excavated rock:
0. 011-0.013
1. Good section ........................................
0. 017-0.020
2 Irregular section .....................................
0.022-0.027
Vnllnod open channelsl 4
A. Earth, uniform sections
1. Clean, recently completed ...........................
0. 01". cis
2. Clean, after weathering ..............................
3. With short grass, few weeds ..........................
0.018-0.010
0. 022-0. 027
4. In gravely, soil, uniform section, clean ...............
0.022-0.025
B. Earth, fairly uniform section:
1. No vegetation ........................................
0.022-0.025
•0.02S-0.030
2. (bass, some weeds ...................................
3. Dense weeds or aquatic plants In deep channels......
0.030-0.035
4, Sides, clean, gravel bottom ...........................
0.02S-0.030
5. Sides, clean, cobble bottom ..........................
0.030-0.040
C. Dragtine excavated or dredged:
1. No vegetation........................................
0.028-0.033
2. Light brush on banks ................................
0.035-0.050
D. Rnck:
1. !lased on design section ..............................
2. Based on actual mean section:
a. Smooth and uniform ..............................
0.035-0.040
b. lagged and irregular ..............................
0.040-0.045
E. Channels not maintained weeds and brush uncut:
dow
1. Dense weeds, high as depth .....................
2. Clean bottom, brush on sides ........................
0.09-0.12
0.05-0.08
3. Clesa bottom brush on sides, highest stage of flow...
0.07-0.11
4. Densu brush, high stage ..............................
0.10-0.14
IV. Highway channels and swnles with malntalnedvecetallon t'
(values shown are for velocities of 2 and 6 f.p.a.):
A. Depth of now up to 0.7 foot:
1. Bermuda grass, Kentucky bluegrass, buffalo grass:
a. Mowed to 2 Inches ................................
0.07-0.045
b. Length 4in 6inches ...............................
0.09-0.05
2. Good stand, any grass:
a. Length about 12Inches ...........................
0.1s-0.09
b. Length about 24inches ...........................
0.30-0.16
3. Fair stand, any gross:
a. Length about 12Inches ...........................
0.14-0.08
b. Length about 24Inches ..........................
0.25-0.13
B. Deppth of llow 0.7-1.5 feet:
1. Bermuda grass, Kentucky bluegrass, buffalo grass: .
A. Mowed to 2 Inches ................................
0.05-0.035
b. Length 4 to 6Inches ...............................
0.064.04
2. Oood stand, any grass: .
n. Length about 12Inches ...........................
•0.12-0.07
b. Length about 24Inches ...........................
0.204.10
3. Fair stand, any grass:
a. Length about 12Inches ............................
0.104.06
b. Length about24 inches ............................
0.17-0.09
V. Street and expressway gutters:
A. Concrete gutter, troweled finish .........................
0.012
B. Aspphalt pavement:
0.013
1. Smooth texture ......................................
2. Rough texture. ...............
0.016
C. Concrete gutter with asphalt pavement:
1. Smooth..............................................
0.013
2. Rough ...............................................
0.013
D. Concreto pavement:
1. Float Mlsh..........................................
0.014
2. Broom llWsb.........................................
0.016
E. For gutters with small slope, where sediment may ac-
.
cumulate, Increase all above values of n by............
0.002
YI. Naluml stream channels:'
A. Mlaor streams' (surfece width at flood stage less ;han
100 IQ:
1. Fairly regular section:
a. Some grass and weeds, little or no brush........... 0.030-0.035
b. Dense growth of weeds, depth of flow materially
greater titan weed lueight........................ 0.035-0.05
a. Some weeds, light brush on banks .................
0.0•t-0.05
d. Some weeds, heavy brush on banks ...............
0.054-07
e. Some weeds, dense willows on batiks ..............
0.06-0.03
f. For trees within channel, with branches submerged
at high stnge. Increase all above values by .......
0.01-0.10
2. Irregular sections with pools, slight channel ntcander.
0.01-0. 02
Increase values 16 1 a-e about .......................
7. Mountain streams, no vegetation In channel, banks
.
usually steep, trees and brush along banks submerged
at high stage:
a. Bottom of gravel, cobbles, and few boulders.......
0. 04-0.05
b. Bottom of cobbles, with large boulders............
0.05, .07

VI. Natural atresun dutnnela-Continued
D._Flood Dlalna (ad)aceaR to natural ettroame); ManniaI a
1. Pasture, no brush; tango
a. Short grass•...... .... ._-.. _. 0.030-0.035
b. High grass_...... -.-so-so •-•-- ---- --• 0.03".05
2. Cultivated areas:
s. No crop ------------------------------------------- 0.03-0.04
b. Mature row crops--------------------------------- 0.035-0.045
c. Mature Acid crops --------- _---------------------- 0.04-0.D5
3. 1leavy weeds, scattered brush ....................... 0.05-0.07
4. Light brush and trees: s
a.`Ylnter............................................ 0.05-0.06
b. Summer__________________________________________ 0,06-0.08
5. Medium to dense brush: s
a. Winter ............................................. 0.07-0.11
b. Sutumt:r...................................... 0.10-U.16
6. Dense willows, summer, not bent over by current.... 0.15-0.20
7. Cleared land with tree stumps, 100-130 per acre:
a. Vo sprouts.........................sons...•....... 0.01-0.05
a Friction Losses In Corrugated Metal Plpe, by M. 7. Webster and L. R.
Metcalf Corps or Engineers, Department of the Army; published in Journal
of the hydraulics Division, Proceedings of the American Society of Clvii
En ricers, xcers, Vo). 85r No. IiY 9, Septemb,•r 1050, Paper No. 214S, pp. ws• 7.
+ For important work and where accurate determination of vter prodles
1. necessary, the designer is urged to consult the following references and to
select n by comparison of the specific conditions wlth the ebannels tested:
Flats of Water to Irrigation and Similar Canals, by F. C. Scobey, U.S.
Department of Agriculture, Technical Bulletin No. 652 February 1930.
Plots of Water fitDralrtnge Channrls, by C. 1:. Rainier, U.S. Dep:ultuent
of Agriculture, Technical Bulletin No. 139. November 1929.
s tIu'ndGook of CAumisl Design for Soil and 111aier Conservation, prepared by
rho Stillwater Outdoor hydraulic Laboratory in cooperation with the
Oklahoma Agricultural Experiment Station, published by the Soil Con-
servation Service, U.S. Department of :agriculture, Publ. No. SCS-TP-61,
March 1957.rev. lime 1054.
s Flow of Water in C.Aannels Protected by 1'egelalive Linings, by W. O. Ree
and V. J. Pulmor, Division of Drainage and Water Control, nesaarch, Soil
Conservatlon Service, U.S. Department otAgriculturs, Tech. Dull. No. 907,
b. With heavy growth or sprouts .................... U.08-0.08
8. IIeavy stand of timber, a few dawn trees, little under-
growth:
a. Flood depth below branches ....... ....... :........ 0.10-0.12
h. Flood depth reaches branches ................ .. 0.12-0.15
C. Major streams (surlacc width at flood stage more than
too it.): Roughness coefficient is usually less than for
minor streams of similar description on account of less
eilective rasistancc ollered by Irregular banks or voge.
is tlon on banks. Values of n may bo somewhat reduced.
Follow rncommendatlon of note 7 it possible. Tha valuo
of n for aweor streams f most ri gult r sections, with no
bouldtrs or brusb, meyts In She ranso offrain........... 0.028.0,033
Foolnolrs to Table 2
t Estimates are by Bureau of Public Roads unless otherwise noted and are
for straight alinement. A small increase in value of n may be mado for
cbaanel alinement other than straight.
s Ranges for secs. I through III are for good to fair construction. For
poor quality construction, use larger values of n. .
Table 8.-Maximum permissible velocities in erodible
channels, based on uniform flow in continuously wet,
aged channels t
Maximum permissible
velocities for -
Material
Water Water
Clear carrying carrying
water fine , sand and
slits gravel
F.p.s.
Fine sand noncoiloldai
1.6
Sandy loam (nontolloldel)..................
1.7
SM. loam (noncelloidat).....................
2.0
Grdinary aria lour[ .........................
• 2.5
VolcEalc ash .................................
2.6
F(nE gravel .................................
2.5
Stiff clay (very colloidal) .............
.' 3.7
Graded, loam to cobbles (boncolloidal).....
3.7
Graded slit to cobbles (colloidal)...........
4.0
2.0
Atlltvil1.illtl (noncollolda)).................
A11usial fllts (colloidal).... ............ ...
3.7
Coarse gravel (noncolloldal)................
4.0
Cobbles and shingles ........................
6.0
Sbales and bard pans ...................:...
0.0
Fc ruury 9f0.
t For calculations of state or discharge In natural stream channels. It is
recommended that the designer consult the local District Ot11ca of the
Surface Water Dranch of lho U.S. Ocological Surrey, to obialn data regarding
values of n Applicable to streams of any specific locality. Whera this pro-
eudive is not followed, the table cony Do used as a guide. The values of
n tabulated have been derlvud from data reported by C. E. Ramser (sea
footnote 4) and from other Incomplete data.
"The tentative values of n citud are principally durived from mensuromonts
made ou falrly short but slrgh ht reaches uI natural streams. Where slopes
cuicnlated (ruin flood ulavatluns along a considerable length of channel.
Invuiving uteunders and tends are to ba used it, velocit y calculations by the
Munniug lurinulu, the vuluu at n must be ittcromed to provide for the addl-
tlull1u) fuss ul anurNy euusad by bonds, Tha Ineruaw fussy be In the rnnga of
lei'1`Iws) icsoncu of folingo on trees aid bntsh resider flood t1ngo will watvrlally
In crease the vuluo of n. Thoroforo, rongllllCYY COa111Clallt. Jor YCgetat1011 la
Icuf will bu larger than for bare branches. For trees in channels or on
baukY.
and for brush on banks where submergence oI branch,. increases with depth
of flow, n will Increase with rising stag,.
Table 4.-Maximum-permissible velocities in channels
lined with uniform stands of various grass covers, well
maintained t '
Maximum permis-
sible velocity oar
Cover Slope range
Erosion. Easily
resistant eroded
soils soil.
F.p.s.
P.P.S.
2.5
1.3
Dermudagross....................'.'...
2.3
2.0
3.0
2.0
nuQniogrrtss............................
3.5
2.2
Kentucky bluegrass ....................
3..5
2.0
Smooth brome.......................
5.0
3.7
Blue grams ..............•..............
5.0
5.0
.0
5
gross misture................
5.3
5.0
Lespedoza sericea.:........::...........
3.6
2.0
Wocpin` loveanss......................
610
3.0
Yellovi 1,101tilm........................
e.Q
a.5
Kildzu.................... I..........
5.5
0.5
Alfalfa ..................................
8.0
6.0
Crtn6rass ..............................I
t As recommended by Speclei Committee on Irrigation Research, American
Society of Civil Engineers, 1926. for channels with straight alinement. For
sinuous channels multiply allowable velocity by 0.95 for slightly sinuous, by
0.9 for moderately sinuous channels, and by 0.8 for highly sinuous channels
(4J. p. 1257).
Corliluon icspcdeza t..........:.......:.
Sudangrasst...........:....::..........
0-b eretnt•..
f.p.r�
fops.
5-10... _•__._
Over 10.....
7
0
5
4
0-5..........
5-10.........
7
0
a
4
Over 10.....
5
3 ,
0-54 .....
5
4
5-31..;...... I 3.3 1 ' 2.3
t.........� 3.3 1 2.3
t From Handbook of CAarind.Design for Soft and Water Constrvo(imt. (See .
footnote 5 table 2.)
s Use velocities over S f.p.s. only where good covers and proper maintenance
can be obtained.
e Do not use on slopes steeper than IO percent.
4 Use on slolxs steeper than 5 percent is not recommended. '
+ Annuals, used on mild slopes or as temporary protection until permaneot
covers are established.

.5
.4
.3
.2
I us
FOR CLASSIFICATION OF VEGETAL
COVER AS TO DEGREE OF RETAROANCE
I
kill
hq
Zqm=�SMP
■■���Illll����iii
�:
-VR, PRODUCT OF VELOCITY AND HYDRAULIC RADIUS
—Manning n for vegetal -lined channels (from handbook of channel design for soil and water conser•
vation SCS-TP-6I revised June I964).
CHART B ( REF.. 4

CHART C (REF. 4)
•�—Ciassineation or vegetal covers as to degree of
relardance t
(NoTa: Covers classified have been tested In experimental channels. Covers
were green and generally uniform)
Retardance
Cover
Condition
'
A ...........
Weeplag buegrass........
Yellow bluc3tem Ischae-
mum.
Kudzu ....................
Bermudegra3s.............
Native grass mixture
(little bluestem, blue
arena, and other long
and short midwest
Excellent stand, tall (average 30
inches).
Excellent stand, tailleverage 36
inches).
Veryry dense growth, uncut.
Good stand, tall (average 12
inches).
Good stand, unmowed.
_.,
'
9...........
'
C...........
asses).
Moping lovegraw........
Wpedoza 3erioes.........
Alfalfa:...................
Weeping lovegrast........
Kudzu ...................
Blue grams ...............
Crabgrass .................
Bermudsgram.............
Common le3pedeza........
Gress -legume mixture—
summer (orchard grass,
redtop, Italian ryegrass,
and common lespe-
GD stand, tall (average 24
Good stand, not woody, tali
(average 19 Inches).
Good stand, uncut (average It -
inches).
Good stand, wowed (average 13
Inches).
Dense growth, uncut.
Good stand, uncut (average 13...
Inches).
Fair stand, uncut (10 to 48
Inches).
Good stand, mowed (average 6
Inches).
Good stand, uncut (average It
Inches).
Good stand, uncut (8 to 8
Inches).
deza).
Ceatlpcdcgrass............
Kentucky bluegrass.......
Bermudagrass.............
Very dense cover (average e
inches).
Good stand, headed (6 to 12
inches).
Good stand, cut to 2.6-inch
-_
D...........
Common le3pedeza........
BuQalogress...............
Grass -legume mixture—
fall, spring (orchard-
grass, redtop, Italian
height.
Excellent stand, uncut (average'
4.5 Inches).
Good stand, uncut (3 to 8
inches).
Oood stand, uncut (4 to 6
Inches).
_
ryegrass, and common
lespedeza).
iespedeza serlces.........
After cutting to 2-inch height.
Very good stand before
-
cutting.
Illermudagraw............. Good stand, cut to 1.6Inches
E........... height
Bermudagra33...........: Burned stubble.
I From Handbook of Ckannd Dufen for Solt and Willer Consrroatlon. (bee
footnote 6, table 2.)
i
1

APPENDIX D
DISCUSSION OF DETENTION -RETENTION SYST121S
' Thefollowing data has been provided to assist the design
g p g
engineer to maximize the use of detention -retention systems as
well as infiltration techniques where the soils will permit this
application. The data represents information and experiences that
other communities, researches, and engineers have found significant
in developing these techniques.
The design engineer is encouraged to develop these techniques
and to meet with Town officials early in the design of a project
' so these procedures may be implemented in an orderly manner.
It should also be noted that due to the normal problems re-
lated to maintenance of detention -retention systems that easements,
maintenance bonds, and maintenance agreements may be required to
assure the Town that the proposed system will continue to function
as designed.
1
D,l

TABLE I ( REF.
l)
TABLE II (REF.'
1)
Measures for Reducing and Delaying Stormwateir Runoff
Advantages and Disadvantages of Measures for
..
. Reducing and Delaying Stormwater Runoff
Area
Reducing Runoff
Delaying Runoff - •'
Measure
Advantages
Disadvantages
Large flat roof
1. Cistern storage
1. Ponding on roof by
2. Rooftop gardens
constricted downspouts
A. Cisterns and
1. Water may be used for:
1. Expensive to install
3. Pool storage or
2. Increasing roof roughness
covered ponds
a. Fire protection
2. Cost may be restrictive V
fountain storage
a. Rippled roof
b. Watering lawns
the cistern must accept
4. Sod roof cover
b. Gravelled roof
e. Industrial processes
water from large drainap
•
d. Cooling purposes
areas
Parking lots
1. Porous pavement
1. Grassy strips on parking
2. Reduce runoff while only
3. Require slight maintenanc
a. Gravel parking
lots
occupying small area
4. Restricted access
b. Porous or punctured .
2. Grassed waterways drainin
3. Land or space above
S. Reduced available` space
2. Concrete vaults and
parking lot
cistern may be used for
basements for other use.,
•
cisterns beneath parking
3. Ponding and detention
other purposes
lots in high -value areas
measures for impervious
3. Vegetated ponding areas
areas
B. Rooftop gardens .
1. Esthetically pleasing
1. Higher structural loading:
around parking lots
a. Rippled pavement
2. Runoff reduction
on roof and building
4. Gravel trenches
b. Depressions
3. Reduce noise levels
2. Expensive to install and
e. Basins
4. Wildlife enhancement
maintain
Residential
1. Cisterns for individual
1. Reservoir or detention •
C. Surface pond storage
1. Controls large drainage
1. Require large areas
homes or groups of homes
basin
(usually residential
areas with low release
2. Possible pollution from
2. Gravel driveways (porous)
2. Planting a high delaying
areas)
2. Esthetically pleasing
storm water and siltation
3. Contoured landscape
grass (high roughness)
3. Possible recreation
3. Possible mosquito breedin
4. Groundwater recharge
3. Gravel driveways
benefits:
areas
a. Perforated pipe
4. Grassy gutters or channels
a. Boating
4. May have adverse algal
b. Gravel (sand)
5. Increased length of travel
b. Ice skating
- blooms as a result of
c. Trench
of runoff by means of
c. Fishing
eutrophication
d. Porous pipe
gutters, diversions, etc.
d. Swimming
5. Possible drowning
e. Dry wells
4. Aquatic life habitat
6. Maintenance problems
'
5. Vegetated depressions
5. Increases land value of
adjoining property
General
1. Gravel alleys
1. Gravel alleys
2. Porous sidewalks
D. Ponding on roof by
1. Runoff delay
1. Higher structural loadzns.
3. Mulched planters
constricted down-
2. Cooling effect for building:
2. Clogging of constricted
spouts
a. Water on roof
inlet requiring maintena-.r
b. Circulation through
3. Freezing during winter
3., Roof ponding provides fire
(expansion)
protection for building (roof
4. Waves and wave loading
water may be tapped in case
5. Leakage of roof water in:
of fire)
building (water damage)

= = M = IM r
TABLE 11, Continued
Measure
Advantages
Disadvantages
• E. Increased roof
1. Runoff delay and some
1. Somewhat higher structural
roughness:
reduction (detention
loadings
a. Rippled roof
in ripples or gravel)
b. Gravel on roof
' F. Porous pavement
1. Runoff reduction (a and b)
1. Clogging of holes or .
(parking lots and
2. Potential groundwater
gravel pores (a and b)
alleys):
recharge (a and b)
2. Compaction of earth below
a. Gravel parking lot
3. Gravel pavements may be
pavement or gravel
b. Holes in impervious
cheaper than asphalt or
decreases permeability of
pavements (} in. 0
concrete (a)
soil (a and b) -
filled with sand
3. Groundwater pollution from
salt in winter (a and b)
4. Frost heaving for
impervious pavement with
holes (b)
5. Difficult to maintain
6. Grass or weeds could grow
in porous pavement (a and 1
i
G. Grassed channels and
1. Runoff delay
1. Sacrifice some land area
vegetated strips
2. Some runoff reduction
for vegetated strips
(infiltration recharge)
Z. Grassed areas must be
"
3. Esthetically pleasing:
mowed or cut periodically
a. Flowers
(maintenance costs)
b. Trees
H. Ponding and detention
1. Runoff delay
1. Somewhat restricted move- I
measures on
(a, b, and c)
ment of vehicles (a) 1
impervious pavement:
2. Runoff reduction
2. Interferes with normal
a. Rippled pavement
(a and b)
use (b and c)
b. Basins
3. Damage to ripple pavement
• e. Constricted inlets
during snow removal (a)
4. Depressions collect dirt
and debris (a, b, and c)
I. Reservoir or detention 1. Runoff delay 1
1. Considerable amount of
basin 2. Recreation benefits:
land is necessary
a. Ice Skating
2. Maintenance costs:
b. Baseball, football,etc.,
a. Mowing grass
if land is provided
b. Herbicides
3. Esthetically pleasing
e. Cleaning periodically
4. Could control large
(silt removal)
drainage areas with
3. Mosquito breeding area
low release
4. Siltation in basin
t
TABLE n, Continued
Measure Advantages Disadvantages
J. Converted septic
1. Low installation costs
1. Requires periodic
tank for storage
2. Runoff reduction
maintenance (silt remora:
and groundwater
(infiltration and
2. Possible health hazard
recharge
storage)
3. Sometimes requires a
.3. Water may be used for:
pump for emptying after
a. Fire protection
storm
b. Watering lawns and
gardens
e. Groundwater recharge
K. Groundwater recharge: 1. Runoff reduction
1. Clogging of pores or
a. Perforated pipe
(infiltration)
perforated pipe
or hose
2. Groundwater recharge
2. Initial expense of
b. French drain
with relatively clean water
installation (materials)
c. Porous pipe
3.-May supply water to
d. Dry well
garden or dry areas
4. Little evaporation loss
L. High delay grass
1. Runoff delay
1. More difficult to mow
(high roughness)
2. Increased infiltration
M. Routing flow over 1. Runoff delay 1. Possible erosion or scour
lawn 2. Increased infiltration 2. Standing water or, lawn in
depressions

Modified Rational Method Analysis (.REF .. 1
The ModifiedRational Method Analysis alters the basic Rational Method by
Once the peak hydrograph is developed it is a simple procedure to develop
hydrographs of storms having longer durations. The maximum runoff rate
assuming the design storm duration is not equal to the time of concentration of
the design basin, but equal to various time periods greater than the estimated
for each of the remaining hydrographs is calculated by using equation one
time of concentration. This basic assumption results in the approximation of
(1), where "i" the intensity, is representative of storms having different
durations. Time span associated with the rising and falling limbs of each
larger volumes of runoff at lower peak runoff rates, which is a critical factor
in the design of small stormwater impoundments.
hydrograph equals the time of concentration for the developed site. It is
shown in Figure 3. 1, the area under each hydrograph represents the volume
'The Modified Rational Method Analysis basically utilizes a family of runoff
of runoff associated with each storm. Shown in Figure 3.2 are a group of
hydrographs developed by the Modified Rational Method Analysis-
hydrographs developed by approximating runoff rates for storms having the
same recurrence interval but varying durations (refer to Figure 3.2). The
first hydrograph in the family represents the runoff rate generated by peak
storm conditions. The peak storm runoff rate is approximated using the basic
pational Method assumption of storm duration equal to the time of concentration.
In this case, the time of concentration is derived from the developed site con-
Peak runoff rate
dition. The resultant hydrograph is shown in Figure 3. 1.
--• " Uax runoff role for storms having various duration
1O
_
CIA =Peak runoff rate (T - Shc
%
�rA47
o
a
rc --I
a order curve represents volume Of
off generated by storm having a
0
)
Afiafi
equal to the lime of
l
ecenMo/inn.
O
rime
0/Z
c.
'
O
Figure 3.2 Family of Hydrographs - Modified Rational Meb'lod Analysis
Time -
Figure 3.1 ,- Rational Method Peak Runoff Hydrograph
The volume of runoff associated with each hydrograph is easily calculated by
multiplying the maximum runoff rate for each curve with its respective storm
duration. Care should be taken to balance the units since runoff rate is mess-
ured in cubic feet per second and duration is in minutes:
�r • : � err rr � r � rr • r • r
r� r r ri rr r ri r : r�

Once the hydrographs have been developed it is necessary to convert the .
maximum runoff rates for each rainfall to storm runoff volumes. These
volumes should be computed in cubic feet.
A maximum permissible release rate is then calculated as described pre-
viously in article 3. 1. That rate is then converted to a release volume
representative of each storm duration. This is accomplished by multiplying
the release rate by each respective storm duration converting the units and
arriving at a release flow volume in cubic feet.
The final step in the storage approximation is a simple subtraction of the
release flow volume from the storm runoff volume for each respective storm
duration, so as to develop a required storage volume. Upon completing this
final step throughout the chosen range of storms, it should be noticed that the j
required storage volume increases as the storm duration gets longer until a
peak volume occurs. The storm duration associated with that maximum re-
quired storage volume is known as the "critical duration". This process
should be carried out so that a true maximum storage volume can be realized.
To simplify the procedure, it is recommended that a table as shown in Fig-
ure 3. 3 be developed.
Required Storage Volume
Roin/a//
Duiahiovi,
min. f
Roinlo//
(nl nsNy,
�lu, p
Peo,k Rundl
Rile,
ClS
Porm Runoff
olums,
f" 4
Re/eose flow'
Vo/ums,
/I.+ ,r
eorrredS
Vo i ne,
/Ls 6
•
60
Re/eats
for thorns
. a ®
60 :JO
hoving
'
d✓alidu = OJ
.
Figure 3.3 Table for Approximating Required Storage Volume

PLAN: PAvERLOGc Tl1Ri�5foNE
su.Lc : Iks' f I'- c'
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6
INVESTIGATION OF CONCRETE GRID PAVEMENTS
CAR.Y E. DAY
Division of Architecnoc and E nviroomental Design. Virginia Po!} -technic Institute and State
University, Blacksburg, VA
Summary
The following research involves laboratory simulation and testing
of typically installed concrete grid pavements. Five pavements
exhibiting different physical characteristics were subjected to rain-
fall in order to collect runoff data. Coefficients of runoff and lag
times are derived based on the following variables: (1) subgrade soil,
(2) slope, (3) rainfall intensity, and (4) rainfall duration. The
tentative runoff coefficients can provide the basis for design and
implementation of the pavements as an alternative on -site technology
within an overall stormwater management scheme. Future directions
for investigations not directly related to hydrological characteristics
are also included.
Background
Current directions in stormwater management emphasize the"
maintenance of pre -development runoff levels through on -site controls.
Where traditional practices have utilized curbs and gutters to quickly
convey stormwater to storm sewers, new approaches use roadside drain-
age swales to slow the velocity of drainage and allow for infiltration.
New techniques emphasize the use of natural drainage systems with
their low -velocity flow characteristics, and take advantage of
opportunities for infiltration and groundwater recharge. Convention-
ally, parking lots have been designed to drain quickly. New goals also
encourage the absorption or detention of stormwater in parking lots and
on -street parking. Stormwater can be detained and allowed to either
infiltrate into the soil or be slowly released after the storm event.
Concrete grid pavements have potential as a management practice
for maintaining pre -development runoff levels by allowing for infiltra-
tion and groundwater recharge. These pavements can decrease the
quantity of peak flow and increase lag time. Furthermore, this would
minimize stream bank erosion and sedimentation due to increased runoff
loads during and after storm events, thereby improving water quality.
Concrete grid pavements have been used extensively in Europe and are
presently available from manufacturers throughout the United States.
On a properly compacted subgrade and properly designed and installed
subbase, these pavements can support extremely heavy vehicular loads.
Unfortunately, very little information is available concerning their
hydrological characteristics either from the manufacturers or in the
form of research data. Consequently. the cost effectiveness of the
pavers cannot be estimated until their performance characteristics are
delineated. lie believe this is a key factor which inhibits the use of
these pavements as an alternative technology for the reduction of
stormwater runoff.
man M
C•quipmcnt
Pavements were tested under a controlled setting at the
Environmental Systems Laboratories of the College of Architecture and
Urban Studies, Virginia Polytechnic Institute and State University,
Blacksburg, Virginia. The testing apparatus contained three major
elements: the rain simulator, the testing bins and the water collection
system.
Rain Simulator. The rain supply was provided by a rain simulator
built and designed by the University's Laboratory Support Services.
The rain simulator consisted of a single rotating irrigation nozzle
' selected because it produced a drop size and distribution similar to
that of natural rainfall. The nozzle was rotated by a 1/15 horsepower
motor geared at 2 rpm. The nozzle was situated approximately 14 feet
above the pavement surface. Water pressure was governed by a pressure
regulator and was displayed on a pressure gauge.
Testing Bins. The.pavements were installed in three bins. Each
bin was 6 feet long. 4 feet wide, and 3 feet deep. Their floors were
i constructed with 3/4 inch plywood glued to 2" by loll joists, 6" on
i center. These platforms rested on two level steel I beams. The sides
of the bins were constructed with 3/4 inch plywood glued to 2" by 4"
j studs, 9" on center. One side wall of each bin was removable to
facilitate material extraction. The bins were waterproofed with 6 mil
polyethelene film. Corrugated sheet metal was placed at the bottom of
each bin to provide protection for the underlying waterproof plastic.
film. An inch and a half of cleaned gravel was spread over the
corrugated sheet metal to facilitate subsurface drainage. Eleven to
j fourteen inches of soil were compacted manually with tampers in lifts
of three inches. Soil compaction was tested with a hand-held penetro-
meter to document the level of compaction reached and assure uniformity.
A minimum compressive strength of 3.5 tons per square foot was attained.
Six inches of cleaned gravel were installed over each "subgrade."
Aggregate size of this gravel ranged from 1" to 1/511. The depth of
this "subbase" is typical for the pavements tested. Two inches of sand
were added on top of the gravel. This sand was compacted and leveled
to provide an adequate bearing surface for the pavers. The pavers
were then installed. Voids were filled with top soil and sod.
Turfgrass selection was made in consultation with Dr. Richard E. Schmidt
of the University's Turfgrass Research Center. Mixtures of Kentucky
Blue Grass sod were selected because of its durability under traffic
-and drought. See Figures l and 2 for illustrations of the test bins.
Water Collection System. The collection system gathered water -
which flowed off the surface of the pavers and percolated through the
soil. The water flowed into covered channels and through hoses to
calibrated tanks. From these tanks periodic measurements could be
taken. Each test bin had two tanks: one to collect surface runoff
and one for subsurface drainage. Figure 2 illustrates the water
collection system for the bins. Pavement slopes were adjusted by lift-
ing the bins at one end with hoists. The pavements were tested at
three slope settings: 2%, 4%, and 7:. These slopes represent the
range found in typical parking lots. .
45 46

2X10 Jo'
Figure 1
Typical Test Bin
Cross Section
� I� i� � 11 �1 �� �► ' /I �I �I I_i � �I ��Bill
II � 7.►
Figure 2
The Test Bins
47
DAY
Soils. Soils used in this investigation were obtained from
Ilniversity land close to the laboratory. The following soils were
chosen l'or "suhgrade": Bin 11. B horizon of Greensdale Silt Loam;
Bin 12, B horizon of Groseclose; and Bin N3, C horizon of Frederick
Silt Loam. For the purpose of this discussion we have named the
3-4"
Greensdale a "loose" soil. the Groseclose a "moderate" soil, and the
Frederick Loam a "tight" soil. These three soils offered the greatest
+se
range of permeability values indigenous to this area and within close
I W.
proximity to the laboratory. See Figure 3 for a comparison of hydraulic
ase
conductivity and permeability classes of each soil derived from soil
tests.
it II-14"
Bulk Density. Soil bulk density is the ratio of mass to the bulk
I II/r••
or -volume of a soil sample. The maximum bulk densities were determined
by using the Harvard Miniature Compaction Apparatus. Pavement manufac-
turers generally specify a compacted subgrade from 85 percent to 9S
axed S•c•el
percent of the maximum dry density. Moisture content must be in a
range of plus 4 percent or minus 2 percent of the optimum moisture
content. Soils used in test bins were compacted to within the following
percentages of their maximum dry bulk densities and within the following
range of optimum moisture: Test Bin N1, Greensdale Silt, 83.2% maximum
density at -2% optimum moisture; Test Bin N2, Groseclose, 78.8% maximum
S�eel1-tern
- density at optimum moisture; and Test Bin N3, Frederick Silt Loam, 82%
maximum density at +1.5% optimum moisture.
Classification of Pavers. The five different paver types were
classified in two categories, lattice and castellated, as shown in
Figures 4 and S. Table 1 specifics the dimensions and weight of
each pavement.
Table 1
% Open Area
Weight
Thickness
Length/Width
Paver
at Bottom
(lbs)
inches
inches
GRASSTONE
34
59
3.625
23/17.25
Boi ardi Prods.
TURFBLOCK
40
63
3.125
23.5/15.5
Paver Systems,
Inc.
Wausau Tile
GRASSCRETE
30
Poured
4 E 6
24/24
Bomanite Corp.
in
Place
MONOSLAB 15 82
Grass Pavers, Ltd.
CHECKER BLOCK 25 84
Hastings Co.
i
48
i
4.S• 23.5/1S.5
3.75 24/24

:. r � . ■� r■i � �r r � �■ r■i � � r r � r r ,r � r
DAY .
very Rapid
id
10 LY W
Rapid 6'
"Grasscrete" (Poured in Place)
by Bomanite Corp.
Moderately
Rapid
Moderate
i
Moderately
Slow
Slow
Very Slow
Bin l Bin 2 Bin 3
Figure 3
Comparison of Soil Hydraulic Conditions (in/hr)
to Permeability Classes
49
E E
i "Turfblock"
Paver Systems, Inc.
Wausau Tile
i
i
"Grasstone"
Boiardi Prods.
' Figure 4
Lattice Grid Pavers
so

DAY
"Monoslab"
Grass Pavers, Ltd. .
"Checker Block"
Hastings Co.
Figure 5
Castellated Grid Pavers
51
Procedure
Testing Procedure. There were three tests performed with each
paver type under observation through one testing cycle (described in
the next section). Monoslab, a castellated type paver comprised test
one. Turfblock, a lattice type paver, comprised test two. Both of
these pavers were tested in all three bins with the three subsoil types.
Our third test consisted of placing one of the three remaining
paving systems --Grasstone, Check Block, and Grasscrete--in each of the
bins. Grasstone was in bin fl (loose soil), Grasscrete in bin 12
(moderate soil) and Checker Block in bin M3 (tight soil). Limited funds
did not allow us to test each of these pavers on all three subsoil
types. In spite of these constraints, we used the three remaining
pavers to check the difference in the performance of the pavers used in
test one and test two.
Testing Cycles. A testing cycle for each paver consisted of a two-.
hour rain followed by a two-hour drain period for three consecutive
days. The rain simulator was activated for two hours and the surface
runoff recorded. Subsurface drainage was monitored for another two
hours after the rainfall period. The bins were then allowed to drain
for 20 hours between each day of tests. During the first day the
slope was set at 7%. Prior to starting the second and third days
of tests, the slope was lowered to 4% and 2% respectively. Figure 6
charts the testing cycle for each pavement.
The day before the three test cycles the bins were saturated with
rain at identical durations and slopes. Surface runoff and subsurface
drainage were monitored to be sure that each bin was 100t saturated.
The bins were allowed to drain 20 hours before commencing the next day's
tests. This was done to insure that each subsoil had a baseline
moisture content before gathering runoff test data. Surface runoff in
gallons was recorded at 5 minute intervals during the rain periods.
Subsurface drainage was recorded every 15 minutes during both the two-
hour rain and two-hour drain periods.
Results
Results from Tests 1, 2, and 3 are displayed in Figures '„ B and
9. The performance curves at each slope setting are referenced against
the 100% runoff curve for each bin. These curves show the total volume
(gallons) of surface runoff plotted against time (duration of rainfall).
Notice that the difference in lag time for each bin varies.
Coefficients of runoff were developed from the performance curves
which are displayed in Table 2. Coefficients were developed for storm
durations of 30, 60, 90 and 120 minutes.
Conclusions
1.. Before commencing the tests we hypothesized. that under the same
rainfall, soil, and slope conditions, the paver with the highest
percent of open area at the bottom should have the least amount of
52

DAY
Here
a concrete grid paver is being placed
into a rain simulation bin to be tested.
Here
a concrete grid paver is being placed
into a rain simulation bin to be tested.
DAY I Sul. Slope At 271.
1 Hour rain
I Hour Drain
Change Slope to
7%
1 Hour Rain
Drain
Change Slope to
I Hour Rain
I
Ii
I
4%
1 Hour Drain
•
DAY 2
20 Hour Drain
(unmonitored)
Change Slope to
.. 2 Hour Rain
..........
..........
7%
!
I.
2 Hour Drain
DAY 3
20 Hour Drain
(unmonitored)
Change Slope to
.............
2 Hour Rain
4%
2 Hour Drain
DAY 4
20 Hour Drain
(unmonitored)
Change Slope to
2%
2 Hour Rain
I.
-
T.
IT
X.
-X
2 Hour Drain
Figure 6: Testing Cycles for Each Pavement
53 54

DAY
30 100% Runor f
25
BIN s1.
GRASSTONE.
20
N
-
(Lattice Type)
15
- .
Loose Soil
q 10
1.2.34In./hr.
O S
2%. 4%
K a0. 83 in.
0
.•�• �__7%
20 40 60 80 100 120
Minutes
50
1 w/. Runoff
45
40
/-_ 7i%
BIN 02
35
/ .. 4%
/ : 2%
GRASSCREfE
30
/•.�
(Lattice Type)
25
//••
X.
Moderate Soil
0 20
O 15
/.• '
1 . 4.15 tn./hr.
��•/
K • 0.85 tn./hr.
10
%�
0
20 40 50 80 100 110
Minutes
40
35
100% Runoff '
30
BIN a3
25
CHECKER BLOCK
20
-7%
(Castellated type)
u
15
�
�i •• 4%
Tight Soil
O
1 O
�� ..•'
_ I- . • ' - 2%
1.2.97 In./hr.
K a 0.30 in./hr.
5
i� •••��
��•••• .
'
O
_�r•'��'� .
20 40 60 80 100 120
Minutes
Test
3: Runoff from Pavers
(Note Lattice and Castellated Types) '
i . Rainfall Intensity
K . Hydraulic Cori vctivlty of Subsoil
Figure 9
Test 3
RUNOFF COEFFICIENTS FOR
CONCRETE GRID PAVEMENTS
ML,18•
BIN el
BIN 62
BIN 43
PAVING SYSTEM
of
Loose Soil
Moderate Soil
Tight Soil
(Percent of Open Bottom
Rain-
Slope Ott
Slope at:
Slope Ott
Area)
fall _
2%
4A
7%
2%
4X
7%
2%
4%
7%
MONOSLAB
90
O
0
O
_ O
-_09
.09
O
.09
.09
F
Grass Pavers. Ltd.
60
O
OS
OS
.64
,O6
0g
,09
,09
.12
go
•05
.08
06
.07
.10
.15
.15
.20
(
120.
.07
.09
_09
.10
_
.07
.09
.11
.17
.19
.23
N
TURP'BLOCK
30
O
O
':03
O
-.09
O
.01
.05
O
0
.10
I -
Paver
Paver Systems. Inc.
60Y
01
.21
.28
.32
.23
.26
.35
I-
Wausau Tile
90
rO8
.O8
.16
.37
„t37
,42
37
.43
'.45
(40%)
120
.09
.17
.20
.43
.48
.51
.48
.54
.56
tv
Hydraulic Conductivity In./hr.
0•83
0.65
0.30
WRainfall
lntenelty In./hr.
2.54
3.51
2.77
W
1-
Gallons/Minute
0.47
0.60
0.55
PAVING SYSTEM
Mina.
BIN 01
BIN a2
BIN s3'
of
Loose Solt
Moderate Soil
Tight Soil
(Percent of Open Bottom
Rain-
•
Slope at:
Slope at:
Slope at:
Area)
fall
2%
4%
7%
2%
4%
7%
2%
-4%
7X
CHECKER BLOCK
30
-•
.•
O
O
.09
.�--
Hastings Co.
..
_ ry
03
.07
.12
•
90
.10
.16
.22
(25%)
120
..
_
...
.78
.21
,27
_ GRASSCRETE
- 30
-
,02
0
.02
Bomanite Corp.
60
--
.13
.15
.10
90_ •.
^-
-
1-
0%
120
.29
.31
.35
.
y
FGRASSTONE
90_
O
O
O
_
r
Botadl Prods.
so -
0
O
0
(34%)
120
.01
.01
O •
-_
-
Hydraulic Corductivl In./hr.
0•83
0.65
1 0.30
F
VI
W
Rainfall Intensity In./hr.
2.34
4.15
2.97
F
I
Gallons/Minute
0.48
0.68P
0.60
Table 2
57 58

a ' �■ a a a �a as as � � a a is is is is ai as �a
DAY
30
30
100% Runoff
. 100% Riroff SIN 01 25
BIN sl 25 - Loose Soil 20
Loose Soil 20 1 2.54 in. a 15 7%
15
I.2.54 1n/hr K �0.83 In./hr. 3 �r'�_4%
K. 0. 83 Whr e 10 '' - 2
A 10 47% (9 5 � ' • %
O 20 40 60 80 100 120
20 40 60 80 ' too 120 - Minutes
Minutes -
50 7%
50
45 tOtJ% /4%
45 100% Runoff - BIN *2 40 Runoff /•• 2%
40
BIN !2 Moderate Soil 95IE
/
Moderate Soil 35 - 1 - 3.51 tn./hr. 30♦� •�
1 . 3.51 tn/hr fi 30 K .0.65 In.
K e0.65 tn/hr ° 25/..
a 25 O 20
O 20 t S/157%5
10 �^ 020 40 60 80 100 120
0
20 40 60 80 100 120 Minutes _
Minutes
2%
40 ,%
AO 35 ,00% a%
35 Runoff /
30VPC"
100% Runoff 30 / .
/i
BIN l3 25 20 j
Tight Soil BIN i3 /
20 Tight Soil O
T - 1 2.77 In./hr. 15
K . 0.30 In/hr ° 15�� -- a� K . ;
O 10 " 0.30 in./hr. 10 /
2n /
0
0� 20 40 • • 80 80 100 120
20 40 60 80 100 120 Minutes .
Minutes
Test 20 Runoff from. T'JRFBLCCK (lattice type)
Test 1 I Runoff from MONOSLAB (Castellated type)
1 Rainfall Intensity1 . HRainfall intensity
K Hydraulic Conductivity of Subsoil K,= Hydraulic Conductf.icY of Subsoil
Figure 7 Figure 8Test 2 i
Test 1
55 56

DAY
surface runoff. Turfblock, however, the paver with the highest
percent of open area on the bottom, does not have the lowest runoff
coefficients (note Table 2)r In fact, Monoslab, with the lowest
percent of bottom open area (15%), yielded lower coefficients when
tested under similar conditions to Turfblock. Therefore, our
hypothesis is challenged by this data. The ability of the paver
to absorb and detain rainwater tends to be a function of its
surface gocmetry, not the percent of bottom open area.
2. An increase in slope (up to 7%) increases the coefficient of runoff
regardless of paver type, subsoil type, or rainfall intensity. The
greater the slope, the greater the runoff. Is there a '.'critical
slope,, at which the runoff coefficients approach that of asphalt
or solid concrete paving? Is that critical slope different for
each paver type? Is it different for each subsoil type on which
the paver is placed? A potential area of investigation is in
studying the relationship of the orientation (in plan) of a paver
to a given slope. The five pavers tested were placed longitudinally
in the bins. Would there be a difference in runoff if these pavers
were placed askew at a 4S0angle to the slope? Would there be more
or less of a difference in percentage of runoff between the two
categories of pavers? The difference, -if one exists, may lead to
more sensitive and effective application.
3. Subsoil type, as expressed by hydraulic conductivity, has an
effect on the coefficient of runoff. Lower hydraulic conductivity
of the subsoil yields a higher coefficient of runoff, especially
on steeper slopes. This is consistent unless the rainfall intensity
approximates the hydraulic conductivity of the subsoil. When this
occurs, little or no surface runoff is produced. Note Grasstone
in Test 3, Table 2. The hydraulic conductivity of the subsoil
approaches the rainfall intensity on this bin;,hence, no runoff.
Future Directions
Be'end hydrological Research. In addition to the ability to
reduce runoff, the pavements should have the following potential
environmental benefits: (a) nonpoint pollution reduction, (b) glare.
reduction, (e) sound absorption, and (d) mieroclimatie temperature
reduction. These aspects are- favorable by-products of the pavement's
function of runoff reduction. It is possible to also consider redesign-
ing the configuration of the pavements to achieve better ergonomic
aspects. Improvements could produce a surface compatible with walking,
bicycling and use by -handicapped adults or, children. .Figure to indicates
that the runoff coefficients derived in this investigation are
sufficiently lower than standard asphalt and concrete pavements. In
view of this observation, these pavements could actually be less
expensive to install than conventional pavements when a corresponding
reduction of storm sewer pipe sizes and lengths' are taken into account.
In addition, the rising cost of petroleum -based asphalt is diminish-
ing the price differences between conventional pavement and concrete
grid pavements.
59
•'i
Porous grid pavers with grass cover and vegetated rooftop
detention form a attractive and well -maintained design
solution in Stuttgart, West Germany.
60
.ff46

[9
We would like to thank the following concrete grid pavement
manufacturers for their contribution of funds and pavers to this
research effort.
Monoslab
Grass Pavers Ltd.
3807 Crooks Road
Royal Oak, MI 48073
0
°
AM1
2
Turfblock Turfblock
Paver Systems, Inc. Wausau Tile
1800 4th Avenue, North P. 0. Box 1520
0.1
0.2 0.3 0.4 0.5
0.6 0.7 0.8 0.9 1.00
P.O. Box 1221 Wausau, WI 54401
Lake Worth, FL 33460
Grasscrete
K
Bomanite Corporation
81 Encina Avenue
o
d
- Palo Alto, CA 94301
n
S.
1-16
43
o
c
Checker Block
6
K
Z
Hastings Pavement Co., Inc.
H r
410 Lakeville Road
w
Lake Success, NY 11040
.y
^+
;
K
q
Grasstone
a
Boiardi Products Corp.
0
.► 0
K
211 East 43rd Street
"
New York, NY 10017
r
o 0 c
uQ1
0M0
o
c
BIBLIOGRAPHY
ti M
r
N<
N
C
w N
a
n
Blake, G. R., "Bulk Density," Methods of Soil Analysis, the American
a
n a
Society of Agronomy and The American Society for Testing Materials.
0
c ^+
w ti
Philadelphia, 1964.
M 0
2
Day, Gary, Site and Community oesign Guidelines for Stormwater Manage -
N 0
x
ment, Virginia Polytechnic Institute and State University,
x
Blacksburg, Va., February 1978.
y
u
Klute, A., "Laboratory Measurement of Hydraulic Conductivity of
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(No slope)
Agronomy and The American Society for Testing Materials,
Philadelphia, 1964.
Leopold, Luna B., Hydrology for Urban Land Planning -- A Guideline-
?
book on the Hydrologic Effects of Urban Land Use, Geological Survey
(No slope)
Circular 554, Washington, D. C., 1968.
i
•
Leopold, Luna B., "The Hydrologic Effects of Urban Land Use" in
Detwyler, Thomas R., Man's Impact on Environment, McGraw-Hill Book
Company, New York, 1971.
62

` 'r r r r � � r r r r r • r rr �r _ rr
DAY
Sclson, Samuel B., "Water Engineering," Standard Iandbook for Civil
Engineers, Fredrick S. Merritt, McGraw-Hill, New .York, 1976.
"Ncw Porous Paving Material Could Ease Runoff Problems," Water News,
Virginia Water Resources Research Center, Blacksburg, a�+ , May
1978, p. 9.
Obrist, Alfred, "Ponding Against the Storm," Landscape Architecture,
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Perry, Douglas, "A Rain Fall Simulator for Laboratory Studies,"
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Va., 1976.
Poertner, Herbert G., "Drainage Plans with Environmental Benefits,"
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Seelye, E. E., Design, Volume One, Wiley and Sons, Inc., New York,
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PP• 385-387.
Tourbier, J. and Westmacott, R., Water Resources Protection Measures in
Land Development -- A Handbook. Delaware Water Resources Center,
Newark, Delaware (NTIS PB-236-049),. April 1974, p. 50-51.
"Towards Zero Runoff," Landscape Architecture, October, 1974, p. 381.
.The Virginia State Water Control Board. Virginia Urban Best Management
Practices for the Control of Nonpoint Source Pollution, Virginia
State Water Control Board, Richmond, Virginia, November, 1978.
63

' Comments on Porus Pavement from a report prepared by the Franklin Institute
Research Laboratories, 1972. See also reference No;'.9.
Objectives and Benefits'
The investigation of porous pavements was undertaken•primarily because.
of the potential of porous pavements for alleviating combined sewer
overflow pollution. Over -flow pollution is currently a problem for the
' approximately 18% of the nation's population served by combined sewers.
During storms, interception sewer capabilities are too small to'handle
the volume of flow generated, and the major portion of the stormwater
is outflowed directly into receiving watercourses.. These stormwater
' outflows carry with them as much as 25 to 40 percent of the year's
production -of suspended solids, putrescible organic matter, and bacteria,
which tend to settle at the bottom.of a sewer to be swepC up and out
' untreated to surrounding watercourses by the stormwater overflow. The
delivery of these untreated pollutants contributes significantly to the
pollution of surrounding waters. Porous pavement, by allowing stormwater
' to percolate into the soil rather than overflow combined sewer systems,
could alleviate much of -this pollution.
Further, where separate storm sewer systems already exist or are to be
' installedy the use of porous pavement could produce substantial cost
savings. In the former case, the use of porous pavement could alleviate.
the need to install'.additional capacity where the present storm -sewer
systems capacity is fully utilized. In the latter case, the use of
porous pavement would allow reduction in the design parameter of the
storm drainage collection system installed..
' In addition to the primary objective of finding.a means of eliminating
combined sewer pollution, as well as reducing the cost of storm drainage.
collection systems, a number of other benefits were found to result from
' porous pavement applications.. These benefits are identified separately
below:
�. 1. Storm-Water'Retention. Evidence on the polluted character of storm -
water indicates -that it -may be necessary in the future to store such
water for subsequent treatment when system capacity is available. The,
' construction.,ofporous �pavement over an impervious membrane offers a
potential mechanism of storing pollute( stormwater and•slowly releasing
it for subsequent treatment.
• l
' 2. Enhanced Water Supply. Substantial areas of the country are now
subject to water supply deficiencies.. By allowing precipitation to
percolate back into the soil, the use of porous pavement could help to
alleviate water supply problems for the 24% of the nation's population
currently clustered in water shortage areas. This is particularly
important since existing water -transfer agreements will not be able to
' supply the demand in many of these areas past - the end of the century.
1

W
3. Elimination of Curbing. Curbs and gutter could be eliminated
on low traffic density porous pavements, effecting considerable
cost economies as well as aesthetic enhancement.
4. Safety Improvement
a. Skid Resistance. Porous pavement overlays on conventional
surfaces have been found successful in preventing wet
skidding or hydroplaning accidents. For safety application
'
a 3/4" to 1" layer over normal dense pavement is used to
provide rapid lateral surface drainage. Such applications
'
have been used successfully on road surfaces in, California,
Louisiana, Utah, and Pennsylvania and airport runways in
England and New Mexico.
b. Enhanced Visibility. Visibility of pavement markings is
expected to be improved because of rapid removal of water
and because of the marking material penetrating the voids
to present an oblique view. The enhanced visibility.of
pavement markings would be an important factor in accident
mitigation during storms.
i5.
Use of Urban Debris. The porous pavements designed will require
a base reservoir capacity. There is the possibility that this
reservoir can be created using broken -bricks, ceramic wastes,
solidified fly ash and other solid urban residue.
6. Low Maintenance Cost. As the recommended porous pavement
design consists of currently used road materials, maintenance costs
should not exceed the level of expense currently incurred.
7. Relief of flash flooding. About 300 square miles of new pave-
ment of all types is laid in the United States each year. Runoff
from such pavement may contribute to local floods downstream, which
can cause loss of life'and property. Flash flooding presents an
ecological problem where storm water from large paved areas is drained
off directly into neighboring streams or other small water courses.
This practice produces considerable flash flooding and stream beck
terosion
during periods of heavy rainfall. Porous pavement would pre-
vent this flash flooding and preserve local streams from erosion.
8. Preservation of Vegetation. Plants and vegetation along con-
ventional roads, particularly in areas of high pavement densities,
are often starved for water because the dry soil under the roads
tend to rob their supply. Porous pavement would restore natural
'
moisture to the benefit of roadside vegetation.
9. Preservation of Natural Drainage Patterns - In contrast to
impervious surfaces, porous pavement would preserve natural drain-
age patterns. it is desirable to preserve natural drainage
patterns where paving is imposed on otherwise open areas whose
natural character is worth preserving and/or areas where the
surfacing will be only temporary..
i
2

fF7
LJ
10. Temperature and storm control. In dense urban areas alight
colored pavement would provide a cooling effect. Further, the
heated air from large expanses of dark asphalt paving is suspected
-
by meteorologists of causing thunderheads to develop on summer
afternoons. This may cause moisture -laden air to dump its water on
the cities where it loads the sewers, rather than carrying it over
to the farmlands beyond. A light-colored pavement should not have
this effect.
11. Color.Infusion. A demand for colored porous surfaces was
evidenced in a wide variety of -applications. Laboratory tests
indicated that colored roofing granules applied to a porous surface
offer a promising colored pavement at economical costs of 354 to
60q per square yard, but further field evaluation of the color's
durability are required. The use of naturally colored aggregates
would provide a satisfactory colored surface, but their use would
be economically limited to areas where colored aggregates occur,
naturally. The use of light colored binders in place of an asphalt
binder was reported to be unsatisfactory because of a tendency of
dirt to adhere to the binders and because of evidence of low
durability.
12: The presence of puddles in parking lots and other areas ,
traversed by pedestrians, is not to be expected with porous pave
ments
Formulation and Test
A variety of conventional and unconventional materials were consid-
ered and the most promising ones tested to.determine their physical
.and economic feasibility as porous pavement materials. An open -
graded asphalt concrete was selected as the most suitable. material
because of its superior physical characteristics, its low cost, and
its ability to be laid by conventional paving methods.. Porous
portland cement surfaces were found unsuitable because of pavement
failure cause by the shifting and settling of the subgrade under
the load application point. Artificial turfs were found insuffic
iently permeable for porous playground pavements. A resilient
porous surface of adhesively bonded chopped rubber, intended for
playground use, exhibited suitable physical characteristics, but
was judged too expensive for more than very limited -use. Similarly,
pavements assembled at the site from factory -made components such as
bricks or honeycombs, were seen to be uneconomical..
Porous asphalt concrete can bemixed in usual hot mix planta, and
compacted and laid with the machines customarily used for asphalt.
concrete paving.
Three types of porous asphaltic concretes, corresponding to Asphalt
Institute, British, and California aggregate specifications, were
.analyzed. Because of differences in size -of -aggregate specifications,
the infiltrations rates of these types.varied from less than 5"/hr.
to more than 25"/hr. Each type was examined with asphalt binder
contents of from.4.0% to 5.5% of total weight.
3

-1
The most porous of the open -graded asphalt concretes contained
aggregate graded in accordance with a California specification:
-Sieve Opening (MM) Specification FIRL Product
1/211 12.7 100 100
3/811 9.51 90-100 97
#4 4.76 35-50 34
#8 2..38 15-32 16
# 16 1.19 0-15 13
#200 .o74 0-3 2
Five and one-half percent by weight of 85-100 penetration road .
asphalt was the binder of choice. It is customary, when designing
a pavement, to test the asphalt -aggregate mix for its resistance to
stripping.by water using ASTM D 1664. If the estimated coated area
is. -not above 95% in this test anti -stripping agents are added to the
asphalt.' ..
Marshall stability tests were performed on all specimens to deter-
mine their load -bearing suitability in road use. All specimens con-
siderably exceeded the minimum Marshall stability criterion for
medium traffic uses.
Freeze -thaw tests were conducted to determine whether porous asphal-
tic concrete could withstand normal climatic cycles. Two samples
each of the.Asphalt Institute, British and California specifications
were subjected to 265 freeze -thaw cycles. No physical dimensional
changes were noted .for any of the samples after the test cycles, nor,
was there any impairment of Marshall stability values or flow rates.
Durability tests were conducted'to determine whether the heightened
exposure to air or water would'produce excessive asphalt hardening
which would cause cracks to form in -the road surface. Only the
California mix with 4.5% asphalt concrete exhibited excess hardening,
due mostly to its highly open structure. The California specifics
tion with 5.5% asphalt content, however, proved to combine high
durability and high permeability, and was selected as the optimal
porous asphalt concrete surface.
Further tests were conducted to determine the effect of porous pave-
ment on the survival of aerobic soil bacteria. It was deemed ,
important that these aerobic bacteria flourish under porous pavement
to metabolize oils, animal and•bird excrements, and other organics
that might otherwise tend to clog the system or pollute the water.
Rather sketchy tests for aerobic activity in soil located underneath
porous asphaltic concrete revealed no inhibition of these bacterial
processes.

r�
Design of Porous Asphaltic Concrete Roadways
The design of porous asphalt concrete roadways equivalent to con-
ventionally constructed roads was found to depend primarily on the
load -bearing capacity of the subgrade, the expected traffic volume
and the reservoir capacity of surface and base.. Specifications of
the Asphalt Institute were used to design the porous pavement road-
ways illustrated in the table below:
Requirements for Surface and Base Course
Surface Base Reservoir Capacity
Thickness Thickness (inches of rainfall)
CBR DTN (IN) (IN) Surface Base Total
2 1 4 6• .60 1.80 2.40
2 10 4 12 .60 3.60 4.20
2 20 4-1/2 13 .66 3.90 4.56
2 50 5 14 .75 4.20 4.95
2 100 5 16 .75 4.80 5.55
2 1000 6 20 6.00 6.90
.90
2 5000 7 22 1.05 6.60 7.65
Because -of the low load -bearing capacity of a wet subgrade a poor
subgrade (California Bearing Ratio Q 2) was assumed in establishing
these designs. Traffic volumes are indicated by the Design Traffic
Number (DTN). Traffic volumes.are designated by the DTN reading as
follows: 1-10, light traffic; 10-100 medium traffic, 100-5,000
heavy traffic (primarily highway.) The gravel base depths are
minimums provided by Asphalt Institute specifications. These
minimum base depths would -have to be increased in designing porous
pavements for areas where the expected maximum precipitation
exceeds the indicated surface and base reservoir capacities. 'Thus
for an expected'5.4" maximum precipitation in one hour, typical of
Philadelphia, the minimum base thickness for all types of uses -would
have to be 16". Adding additional base thickness is relatively
cheap and does not greatly affect the economic feasibility of porous
pavement.
It was judged that a soil permeability of .042, sufficient to remove
a 5-inch rainfall in ten -days, would prove adequate for most uses.
low
In areas with high rainfall in:combination with soils of water
infiltration rates, less than 0.02 inches per hour, consideration
should be given to either penetrating the low permeability soil
layer by sand or other type of -drain if a higher permeability soil,
--
horizon lies beneath, or by constructing nearby storage ponds to
retain the water until infiltration can occur. With the latter
eventuality, water penetrating the pavement layer would run-off
laterally to be drained to the ponds.
5

APPENDIX E.
-' References
1. Charlotte Stormwater Det , sj Manual, Department of
Publ'i.c Works.,. Charlotte.' N. C, September 1�78 ,
2. De�sfgri and Coristructiori 'of' S•ariitary and Storm 'Sewers, ASCE
Manuals and Reports on Engineering Practice No. 37, 1974.
3. Desi n 'of Exfiltrat' on� "Treric1 'Syst'ems' 'for •Underground Disposal
of Storm Water Runoff by- Darrell E. McQueen, P.E. Briston, Childs
and Associates, Inc,, Coral Gables, �'la. May, 1979,
4. Desigri'of Roadside•Drainage Channels, Hydraulic Design
Series No. 4, U.S. Department of.Commerce,•Bureau of,
Public Roads, 1965.
5. Guidelines' 'for Control of Erosion and S*edij6ent 'During Construc-
tion, North Carolina Department of Transportation, July 1, 1980.
6. Handbook of De*s'ign 'for Highway Surface 'Drainage 'Structures,
prepared by Bridge Location & Hydrographi.c Department, C.R.
Edgerton, State Hydrog'raphic Engineer, 1973.
7. Hydraul•ics, Engineering Handbook, Section 5, Soil Conservation
Service, U.S. Department of Agriculture.
8. Hydrology, Section 4, SCS National Engineering Handbook, U.S.
Department of Agriculture, Soil Conservation Service, August
1972.
9. Porous Pavement, The Franklin Institute Research Laboratories,
Edmund Thelen and L. Fielding Howe, 1978.
E-1

10. Practices in Detention of Urban Stormwater Runoff, American
' Public Works Association Special Report No. 43., 1974.
11. Proceedings of a Workshop - North Carolina Workshop on
Management of Stormwater, Sedimentation, and Flood Control
in Urban Areas, January 5, 1978, published"by Water Resources
Research Institute of The University of.North Carolina.
12. Public Facilities Manual, Volume 1, "Policies and Guidelines",
County of Fairfax, Virginia, 1977.
13. Roadway Standard Drawings, State -of North Carolina, Department
of Transportation, Division of Highways Roadways Design Unit,
July 1, 197.8..
14. Sedimentation Control, Chapter 4,. Title 15, North Carolina
Administrative Code, January 11, 1978.
15. Standards and Specification for Roads and Structures, North
.' Carolina Department of Transportation July 1, 1978.
16. Soil Survey of the.0uter Stinks, North Carolina, Unites States
Department of Agriculture, Soil Conservation Service June 1977.
17. Stormwater Management Alternatives, J. Tourbier and R. West-
macott, Editors, Water Resources Center, University of Delaware
April 1980.
18. Subdivision Roads - Minimum -Construction Standards, North
Carolina Department of Transportation July 1, 1979.
19. Town of Nags Head Surface Water Drainage Plan, Coastal
Consultants, LTD and McDowell -Jones, P.A., June 30, 1980.
E-2

20. Underground Disposal of Storm Water Runoff, Design Guide-
lines Manual by Joseph B. Hannon, P.E., U.S. Department of
Transportation, Federal Highway Administration (FHWA - TS -
8-1 218) February 1980.
21. Urban Hydrology for Small Watersheds, Technical Release No.
55, United States Department of Agriculture, Soil Conservation
Service, January, 1975•
22. Urban Storm Drainage Criteria Manual,. -Volume 2, Denver Regional.
Council of Governments, Wright -McLaughlin Engineers, March 1969.
23. Water Quality and Urban Stormwater, A Management Plan,' Division
of Environmental Management, North Carolina Department of
Natural Resources and Community Development' -July 1979•
E-3