20051117 Ver 2_More Info Received_20090107

off- 111-1 V4
LISSARA PARTNERS. LLC
1210 Forest Wood Drive
Lewisville, NC 27023
January 5, 2009
North Carolina Department of Environment and Natural Resources
Division of Water Quality
1650 Mail Service Center
Raleigh, NC 27699-1650 p
Cyndi Karoly, Supervisor SAN 7 2009
401 Oversight/Express Review Permitting Unit
DENR - WATER QUALITY
Subject: Lissara Development WETLANDS ANDSTORMWATERBRMCN
Ut to Yadkin River [030702, 12-(86.7), WSIV, C]
401 Water Quality Certification No. 3742 with Additional Conditions
Reference: DWQ Project #05-1117, Ver.2, Forsyth County
DWQ certified letter dated November 4, 2008
Lissara Partners letter dated November 15, 2008
Dear Ms. Karoly,
Thank you for your phone call of December 9 discussing the status of Conditions
12 and 14 of our 401 Water Quality Certification. It appears we now have clear
direction on the target 7Q10 stream-flow number and our low-flow release
criteria.
As discussed, we are designing a full-pool level drain that will ultimately meet
your requirements. We understand the 7Q10 number is 0.02 cfs, consistent with
the information provided us by USGS and NCDENR-DWR. Our understanding is
that we will be required to release an amount equal to the amount of water
flowing into the lake from existing streams, springs and rain events when the full-
pool elevation of the lake is at 800' msl, or above. We can accept this scenario.
We contended that several conditions relative to our site, as it pre-existed and at
post-construction, would contribute to an increased and more consistent stream
flow than previously experienced. Our lake site has a relatively small drainage
basin and the stream reach we are impounding is located near the upper end of
the basin. The existing stream within our lake site presently receives irregular
flows of water. The lake site was originally covered with 21 acres of mature
deciduous forest. During dry periods the water uptake demand of this vegetation
completely utilizes all available flow to the point where there are no visible live
stream flows. In the lake's completed form we will have eliminated the 21 acres
of uptake demand from the forest and replaced it with the surface area of the
lake. The residential development surrounding the lake will create an estimated
impervious surface area of roads, homes, driveways and sidewalks of
approximately eleven (11) percent. The completed development will direct a
larger volume and more consistent flow of water into the surrounding tributary
areas serving the stream than previously experienced. Therefore a drain set at
our normal pool elevation will provide stream flows in excess of pre-development
quantities.
As requested I am attaching a report which outlines the design criteria and
details of the overflow drainage structure we are incorporating into our dam as
prepared by Engineering Tectonics, P. A., our dam engineer. As described to you
in our phone call this 12" ductile iron pipe will be placed in residual soil on the
West end of the dam. The invert pipe elevation will be set at our normal pool
elevation of 800' MSL. The pipe will slope downward at a 2% grade for a
distance of approximately 70' before turning down the slope of the existing
hillside (on the downslope outside of the dam) to the base of the dam. At the
base of the dam the pipe will terminate with a 90 degree elbow to reduce water
velocity and discharge it into an off-channel rip-rap apron. The water will then re-
enter the existing stream channel.
I hope you will find that the above information, attached design plan and details
will satisfy you of our ability to meet your requirements.
Very truly yours,
Lan ilcox
Lissara Partners, LLC
cc: Brant Godfrey, Esquire
C.J. Ramey
Beau Dancy
James W. Armentrout, Esquire
Steve Tedder, NCDENR-DWQ - Winston-Salem, NC
MINIMUM WATER RELEASE PLAN
LISSARA DAM
FORSYTH COUNTY, NORTH CAROLINA
PREPARED FOR:
Lissara Partners LLC
5121 North Causeway Road
Winston-Salem, NC 27106
Contact: Lang Wilcox
[336 - 399 0445]
BY:
ENGINEERING TECTONICS, P.A.
ENGINEERS • GEOLOGISTS - HYDROLOGISTS
1720 Vargrave Street Winston-Salem, NC 27107
[phone]
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Minimum Water Release Plan
Lissara
Page 1
Page
Title 1
Content 2
Figures, Exhibits 3
Design Sheet 3
PART A. SITE PARAMETERS
1. INTRODUCTION 4
2. WATERSHED CHARACTERISTICS 4
2.1 DRAINAGE AREA DESCRIPTION 4
2.2 SOIL TYPES AND PERMEABILITY 4
2.3 DETERMINATION OF RUN-OFF CURVE NUMBER 5
2.4 TIME OF CONCENTRATION AND LAG TIME 6
3. HYDROLOGICAL ANALYSIS 6
PART B. DESIGN AND CONSTRUCTION OF SPILLWAY SYSTEM
1. INTRODUCTION 7
2. DESIGN CRITERIA 7
2.1 INFLOW AND STORAGE CONSIDERATIONS 7
2.2 SPILLWAY SYSTEM 7
2.2.1 System Discussion 7
2.2.2 Outflow Requirement Discussions 8
2.2.3 Spillway Layout 8
2.2.4 Spillway Outflow Computations 9
3. CONSTRUCTION DETAILS OF PRINCIPAL / EMERGENCY SPILLWAY SYSTEM 9
3.1 CONSTRUCTION OF THE SPILLWAY SYSTEM 9
3.1.1 Construction of the Control Section 9
3.1.2 Construction of the Discharge Section 10
Minimum Water Release Plan Page 2
Lissara
Figures
Figure 1 Site Map
Figure 2 Drainage Area
Figure 3 Soil Map
Exhibits
Exhibit 1 Parameters and Run-of Curve Number Calculations
Exhibit 2 Calculations for Time of Concentration (TJ (TR-55) and Lag Time
Exhibit 3 Spillway Outflow Rate
Exhibit 4 Bernoulli Equation: Control Section Outflow Calculation
Exhibit 5 Bernoulli Equation: Discharge Section Outflow Calculation
Exhibit 6 Critical depth of Water in Discharge Pipe
Design Sheet
Minimum Water Release Plan
Lissara
Page 3
MINIMUM WATER RELEASE PLAN
LISSARA DAM
FORSYTH COUNTY, NORTH CAROLINA
PART A - SITE PARAMETERS
1. INTRODUCTION
The Minimum Water Release Plan has been compiled to fulfill the requirement as set out in Condition
12 of the 401 Water Qualification Certification.
The dam location is designed at the northern end of a north-south valley located some 2 miles west of
Lewisville, Forsyth County. This valley comprises a minor south to north flowing first order stream which
is an unnamed tributary of the Yadkin River and is shown on the USGS Quad Map (Clemmons) as an
intermittent stream (see Figure 1). The location of the dam site is at 36° 06' 43" North and 080° 26' 57"
West.
2. WATERSHED CHARACTERISTICS
2.1 DRAINAGE AREA DESCRIPTION
The drainage area of the tributary extends to the south of the project site, roughly bordered by both ridges
on either side of the valley and Shallowford Road to the south. The watershed comprises some 152
acres or 0.24 sq miles (see Figure 2), which includes the 22 acres covered by the lake area.
While the drainage area is presently characterized by densely wooded slopes, it is the developer's
intention to maintain the wooded characteristics of the area as much as possible, except for the southern
portion of the development that will have a denser housing distribution. The western side slopes of the
valley display an angle of about 20° while eastern slopes have an angle of about 15°. While length of the
drainage area is about 4,500 ft, due to the length of the lake, some 2,600 ft, there will remain only some
1,900 ft of linear stream above the upper end of the proposed lake, descending in elevation from 900 ft at
the upper reaches of the drainage area, to 800 ft which is the intended normal pool elevation of the lake.
The topographic slope, channel slope and morphology of the basin determine the rate at which the storm
water runoff will travel towards the proposed pond site. The steeper the slope, the faster the water will
reach the pond.
2.2 SOIL TYPES AND PERMEABILITY
While the topographic slope in the drainage basin contributes to the rate at which run-off reaches the
creek, additional controlling factors such as the soil and its infiltration characteristics determine the volume
Minimum Water Release Plan Page 4
Lissara
of water that will eventually reach the creek and lake as runoff. These factors include soil types and the
amount of impervious surface in the drainage basin (see Soil Map in Figure 3).
The soil types identified in the drainage area belong to the Wilkes Series (WIC, WID, WIF) which can be
found mainly along the lower slopes of the valley and the higher grounds along the west side of the valley,
and southeast portion of the drainage area, comprising a total of some 45% of the soils in the watershed
area; the Pacolet Series (PaB, PaC, PaD, PaF) which are mainly present on the higher grounds to the
east of the valley, and some to the south of the valley, comprising a total of some 33%; Iredell Series (IrB)
are mainly represented in the south and comprise some 7.5%; Hiwassee Series (HIB) are also located to
the south (some 4%); Wehadkee Series (Wh) are found along the valley bottom (some 3.8%); Chewacla
Series (some 2.2%) and Cecil Series (some 1.7%) are both identified on some of the slopes to the south
of the valley; Enon Series (Enc, EnD) can be found along some of the higher grounds to the west of the
valley and some in the southern portion of the watershed area, only comprising some 2.2% of the soils in
the watershed.
With regards to Hydrology Groups, some 57% of the soils present in the watershed area belong to
Hydrology Group C (Wilkes, Iredell, Enon, and Chewacla), some 39% to Hydrology Group B (Pacolet,
Hiwassee, and Cecil), and some 4% to Hydrology Group D (Wehadkee). All these soil types are formed
as residuum weathered from schistose rocks which are prevalent in this area. Once the dam has been
constructed and the impoundment filled with water, the lake area will cover about 22 acres of the original
152-acre drainage area. Due to the fact that these 22 acres of water cover all 6 acres of Hydrology Group
D soils and 16 acres of Group C soils, it results in a shift in the percentages of soils in the drainage basin
above the normal pool. Consequently, in the remaining 130 acres of the watershed area not covered by
the lake some 45% of the soils belong to Hydrology Group B and some 54% to Group C.
The soils belonging to Soils Group C range from well-drained (Wilkes) to poorly drained (Chewacla) soils;
while the Wilkes soils are generally shallow, ranging from 13 - 48 inches, the other soil types can be 80
inches deep.
The soils belonging to Soils Group B are well-drained soils and generally have soil depths to 50 - 80
inches. The Cecil and Hiwassee soils may have clay from 6 - 50 inches deep; in the fine sandy, loams of
the Pacolet, clayey layers may extend to a depth of 40 inches.
2.3 DETERMINATION OF RUN-OFF CURVE NUMBER
In addition to the drainage area parameters discussed above, land use and the amount of impervious
area are critical factors in storm water management in the drainage basin.
Presently, large areas of the drainage area are undeveloped wooded areas. Some older and small
developments have occurred along Plemmons Road in the southeastern corner and along Pilot Ridge
Road, in the south-western corner of the watershed. Notwithstanding the fact that it is the developers'
Minimum Water Release Plan Page 5
Lissa ra
intention to preserve as much wooded area as possible, the presence of additional streets and houses will
have an impact on the percentage of impervious area. However, in this semi-rural setting, substantial
amounts of storm water are able to infiltrate into the soils to a certain degree. The future development lay-
out and land-use have been taken into account with the determination of the composite Run-off Curve
Number (CN). By using the above parameters, the CN was calculated as 71 (see Exhibit 1).
2.4 TIME OF CONCENTRATION AND LAG TIME
The Natural Resources Conservation Service (NRCS) publication Technical Release (TR-55) was used to
calculate the Time of Concentration (T,), the total travel time of water from the most distant point to the
dam area. Three types of flow occur along the longest water path in the watershed area of Lissara Lake,
which due to the 22-acres size of the lake is effectively reduced from 152 to 130 acres. The upper 100 ft
starts as sheet flow, which then becomes shallow flow for about 850 ft before becoming an intermittent
blue line on the USGS Quad map for about 900 ft before it enters the proposed lake at an elevation of 800
ft.
The 2-yr/24-hr rainfall in this portion of Forsyth County is 3.42 inches. The individual Travel Times are
shown in Table 2 which results in a Time of Concentration (Tc) of 0.455 hours = 27.3 minutes.
Consequently, the Lag Time (TO which is a function of the Time of Concentration (TL = 0.6 Tj was
calculated as 0.273 hours = 16.4 minutes (see Exhibit 2). In addition, the Time to Peak equals 18.3
minutes (0.67 x Tc) and is the time of the highest run-off quantity after the storm commences. These
numerical basin characteristics have been used in the hydrologic calculations in HEC-1.
3. HYDROLOGICAL ANALYSIS
In this part of Forsyth County, a 1/ PMP / 6-hr design storm produces some 9.67 inches of rain. HEC-1
computations have been applied to calculate the peak discharge and consequently a stage storage curve
for the planned impoundment by using the parameters discussed above. The HEC-1 computation
resulted in a peak discharge of 659 cubic feet per second (cfs).
In the case of a Class A Low Hazard Dam, NC DENR's rules limit activation of the emergency spillway to
a 25-yr storm with a 6-hr duration or greater unless the spillway is protected by a liner that prevents
erosion. HEC-1 computation of the 25-yr / 6-hr storm in this watershed resulted in a peak discharge of 225
cfs.
Minimum Water Release Plan Page 6
Lissara
PART B - DESIGN AND CONSTRUCTION OF
SPILLWAY SYSTEM
1. INTRODUCTION
The elevation of the crest of the dam has been designed at 806 ft with a normal pool elevation of 800 ft.
As discussed in Part A, the dam location was selected at the northern end of a north-south trending valley
to create a 2600 ft long 22-acre lake featuring a restricted use ski club, as the focal point of a new housing
development some 2 miles west of Lewisville, NC.
2. DESIGN CRITERIA
ETPA has performed HEC-1 computations to establish the discharge during the design storm and to
determine the dimensions of the spillway systems in order to pass the outflow without overtopping the
dam.
2.1 INFLOW AND STORAGE CONSIDERATIONS
While this dam is classified as a Low Hazard dam, due to its height, it is considered a Large Class A
dam; therefore, the design storm to be used for the hydraulic analysis is a'/ PMP / 6-hr storm, while
activation of the emergency spillway is limited to a 25-yr / 6-hr storm or greater. Consequently, the
HEC-1 computations as discussed in Section A-3 imply that the discharge during the'/ PMP storm is 659
cfs, while the discharge during the 25-yr storm is computed as 225 cfs.
The storage capacity between the normal pool elevation of 800 ft and a crest elevation of 806 ft is 150 Ac-
ft. With this large storage capacity and an inflow of 659 cfs, associated HEC-1 computations indicate that
no outflow occurs during the design storm; in fact, the entire storm can be stored in the lake such that the
water level would only rise to an elevation of 802.96 ft, some 3.0 ft below the dam's crest elevation.
2.2 SPILLWAY SYSTEM
2.2.1 System Discussion
Due to the 70-ft height of the dam, using a riser barrel as the primary spillway system would be very
costly due to the required height of the riser pipe. Instead, due to the minute outflow during the design
storm, we propose using a culvert pipe as a primary spillway as well as an emergency spillway. A
spillway system located in the residual soil to the side of the dam could consist of a grassed control
section and an approximately 310-ft long discharge channel with either a 20-ft wide bottom and lined
with a 54-in thick layer of D50 24-in riprap or constructed as a concrete chute. As the material cost of
the required tonnage of riprap or the costs for constructing such a long concrete chute would by far
Minimum Water Release Plan Page 7
Lissara
exceed the material costs of a discharge pipe, we recommend using a ductile iron pipe for the
combined spillway system, in addition to a low water release pipe.
2.2.2 Outflow Requirement Discussions
In order to evaluate the size of spillway pipe, several aspects were reviewed. Regulations require that a
dam shall have a spillway that has the capacity to pass the flow from a design storm without overtopping
the dam. In addition, the spillway system has to be capable of removing within 15 days at least 80% of the
water volume that is temporarily stored above the normal pool elevation.
The inflow computations for the 1/3 PMP / 6-hr storm discussed above in Section 2.1 indicate that even
without any outflow system in place, the water level in the lake only rises from 800 ft to 802.9 ft, i.e. to
3 ft below the crest elevation during the design storm. Therefore, a relatively small diameter outflow
pipe could suffice for the primary spillway. Outflow computations for a 6-in diameter, 8-in diameter and
12-in diameter pipe resulted in minimum variations of the resulting water levels during the design storm as
802.95 ft, 802.93 ft and 802.90 ft respectively.
Taking into account the spillway requirements cited above, calculations indicated that following the inflow
of the design storm, a 12-in diameter pipe with an invert elevation of 800 ft would be able to remove all of
the water volume above the normal pool elevation. Exhibit 6 shows that it will take approximately 13.4
days to lower the lake level from 803 ft to 800 ft, the normal pool elevation. As this complies with the
spillway requirements, one 12-in diameter pipe is able to function as the principal as well as the
emergency spillway system of this dam.
2.2.3 Spillway Layout
To avoid constructing the spillway pipe through the fill body of the dam, we recommend the pipe intake
to be situated in the residual soil at the far left (western) side of the dam and the inclined discharge
pipe section also located within the residual soil outside the footprint of the dam. To ease the
construction of the pipe, we recommend using ductile iron pipes as this would reduce the need for
concrete cradles and large concrete collars.
The invert of the spillway pipe will be set at 800 ft and the end of the 70-ft long control section of this
pipe will be set at an elevation of 798.6 ft, at which point the pipe connects to the discharge pipe
section through a 45-degree elbow. At the base of the hill (at 736 ft), the approximately 337-ft long
discharge pipe will connect to a 60-ft long horizontal pipe, incorporating a 90-degree turn up at the end
to dissipate the water energy and which will be surrounded by a riprap apron.
Minimum Water Release Plan Page 8
Lissara
2.2.4 Spillway Outflow Computations
The outflow calculations used in the HEC-1 design storm computations for the spillway pipe configuration
discussed above show that a maximum water elevation of 2.90 ft above the invert of the spillway pipe will
be reached. At this elevation, the maximum outflow through the pipe will be 6 cfs. The Bernoulli equation
supports the capacity requirement showing that the capacity of a 12-in pipe under these conditions is
about 7 cfs (see Exhibit 7).
With regards to the inclined discharge pipe section, the Bernoulli equation indicates that the 12-in pipe is
able to pass 15.2 cfs during the design storm (see Exhibit 8), which is more than the minimum
requirement. Calculations were further performed to determine whether the discharge pipe would
actually be flowing full or partly full. To achieve this, hydraulic calculations as discussed in "Design of
Small Dams" (pp. 576 - 579) were used to establish the critical depth of the water through the pipe.
Using Table B-3, calculations imply that during a design storm with 6.5 cfs flowing through the pipe,
the critical depth of the water through the 12-in discharge pipe is 0.41 ft, demonstrating that the pipe is
not flowing full (see Exhibit 9).
3. CONSTRUCTION DETAILS OF PRINCIPAL / EMERGENCY SPILLWAY SYSTEM
3.1 CONSTRUCTION OF THE SPILLWAY SYSTEM
As discussed above (Section B-2.1), even without any outflow system, the lake level would only rise to
802.96 ft during the 1/3 PMP design storm. While the most economical design for the spillway system
consists of a 6-in diameter ductile iron pipe, spillway outflow requirements indicated the need for a 12-
in diameter DIP as primary and emergency spillway system (see Section B-2.2.2) (in addition to the
24-in diameter DIP low water release pipe). In order to facilitate the construction and produce an
esthetically pleasing configuration, it is recommended to place the spillway pipe through the residual
soil underneath the far western end of the crest which would then allow the downstream pipe also to
be buried within residual soils along the western abutment, rather than having the pipe exposed along
the surface of the downstream slope of the dam. Once the construction of the dam has reached an
elevation of 800 ft, the spillway system will be installed.
3.1.1 Construction of the Control Section
The horizontal section of the pipe will be located in the residual soil underneath the far left (western)
abutment of the dam prior to completing the fill at the abutment. In order to provide an inlet for the pipe, a
section of the original side slope at the lakeside of the dam will be excavated which allows for the
installation of a straight pipe from the lake to the downstream side of the dam, thus avoiding the need for
incorporating an elbow or the construction of a manhole. The inlet of the pipe will incorporate a concrete
headwall as shown on the attached Design Sheet allowing an invert elevation of 800 ft. The downstream
Minimum Water Release Plan Page 9
Lissara
end of the 70-ft long control section of the pipe will be at an elevation of 798.6 ft, at which point an elbow
with thrust block will be installed to connect the pipe to the discharge pipe.
In order to provide a solid base for the pipe, a concrete cradle will be constructed underneath this section
of the pipe. The cradle will consist of non-reinforced concrete with a 2,000 PSI or better. The minimum
thickness of the cradle measured perpendicular to the pipe will be 3 inches (= 1/4 ID diameter of the pipe),
while the cradle will extend upwards to the spring line of the pipe equal to about 5 inches (=1/4 OD
diameter of the pipe) providing a total thickness of about 8 inches. Laterally, the cradle will extend to
about 8 inches outside the external width of the pipe (see attached Design Sheet).
3.1.2 Construction of the Discharge Section
The control section of the primary / emergency spillway pipe will be connected to the discharge pipe with
an elbow. The 12-in diameter DIP discharge pipe will be buried in the existing soil down the slope outside
the footprint of the dam as shown on the Design Sheet. The estimated length of the pipe is 337 ft along a
slope with a grade of 0.19 ft/ft. The invert of the discharge pipe at the elbow will be at 798.6 ft and the
invert elevation at the bottom of the hill will be at approximately 733 ft where another elbow will be
installed in the pipe from where the pipe continues horizontally for another 70 ft. In order to dissipate the
energy of the discharging water, an upturned 90° - elbow will be added to the end of the horizontal section
at which point the water will discharge vertically. The area around this elbow outlet (outlet elevation 737
ft) will be protected by a riprap apron of which the top elevation will be 736 ft (see Design Sheet). Thrust
blocks will be placed at the upper elbow, halfway down the slope, the bottom elbow, and at the discharge
elbow at the end.
Minimum Water Release Plan Page 10
Lissara
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EXHIBIT 1
PARAMETERS AND RUN-OFF CURVE NUMBER CALCULATIONS
Project: Lissara
Dam No. Forsyth
Dam Location: 36° 06'42.6" N 080° 26'57.5" W
Watershed Parameters
Drainage Area (as measured) = 6,604,000 ft2 = 151.6 ac = 0.24 sq mi
Hydraulic Length (as measured to top of lake) = 1,900 ft
Avg. Hydraulic Slope (as measured) = 4% 80 ft drop
Dam and Lake Parameters
Length of Dam 560 ft
Height of Dam 70 ft
Nomal pool elevation 800 ft
Crest Elevation 806 ft Storage Volume
Normal pool area 962,015 ft2 22.08 Ac 455.00 Ac-ft
Pool area at crest elevation 1,211,813 ft2 27.82 Ac 605.00 Ac-ft
Calculate Runoff Curve Number (CN)
Hydrology Soil Group before lake: 39% Group B; 57% Group C; 4% Grou p D.
Lake underlain by Group C and Group D soils. outsid e lake area:45% Group B; 54% Group C
Land Use Soil Area % CN"
Wooded ood : B 2,135,000 ft2 = 49.01 ac = 32.3 x 55 = 1778.09
Wooded (good): C 2,400,000 ft = 55.10 ac = 36.3 x 70 = 2543.91
grasslands B 280,000 ft= 6.43 ac = 4.2 x 69 = 292.55
grasslands C 480,000 ft2 = 11.02 ac = 7.3 x 79 = 574.20
Impervious areas (roofs, roads, driveways) B&C 340,000 ft2 = 7.81 ac = 5.1 x 98 = 504.54
Water Areas 960,000 ft2 = 22.04 ac = 14.5 x 98 = 1424.59

,Average Runoff Curve Number (CN) 151.40 ac 99.9 7117.88
71
" Table 8.03b - Runoff Curve Numbers (CN)
updated 061708
EXHIBIT 1
EXHIBIT 2
CALCULATIONS FOR TIME OF CONCENTRATION Tc (TR-55) AND LAG TIME TL
FORSYTH COUNTY
Initial Flow in upper reach of watershed:
Sheet Flow (max 100 ft)
use: _ 0.007 (nL)o.a
Tt1 (P,)o.s S 0.4
Flow Length (L) 100 ft
Manning's n 0.41 grass
P2 (2-yr/24-hr storm) 3.42 in
Height 3 ft
S (slope) 0.03 ft/ft
Ttt = 0.300 hr
Shallow Flow next stages of watershed
use _ L
Tt2 3600 V
Flow Length (L) 850 ft
Height (H) 45 ft
Slope (S) 0.05 ft/ft

Velocity (V) 3.6 fps
(use Fig. 3-1, TR-55)
Tt2 = 0.066 hr
Channel Flow Section
use V = 1.49 r 21SI-I
n
Length 900 ft
Height elev 35 ft
Slope s 0.039 ft/ft
width of channel 40 ft
flow depth 1 , ft
hydraulic radius 0.93
Manning n 0.1
V = 2.80 fps
use in: L
Tta _ 3600 V
F Tt3 = 0.089 hr
Time TL
Tc= Tt1+ Tt2.... + Tts
Tc= 0.455 hr
27.3 min.
TL= 0.6 Tc
TL= 0.273 hr
16.4 min.
060408
EXHIBIT 2
EXHIBIT 3
LISSARA
RATE OF OUTFLOW THROUGH 12-IN DIAMETER SPILLWAY PIPE
FOLLOWING 113 PMP DISCHARGE INFLOW
HEC-1 calculations indicate a maximum lake level of 802.9 ft following the 113 PMP Design Storm
The following calculations indicate the number of days it would take the 12-in diameter pipe
to lower the lake level back to the normal pool elevation of 800 ft.
(Spillway Design requires 80% of volume above normal pool
to be removed within 15 days following the passage of the design storm)

Lake Level
(ft) estimated
lake volume
cu ft volume
decrease
cu ft height wate
above 800
(ft) flow water
through 12"
pipe (cfs) outflow
per hour
3600 sec hours
to next
level
803 23,000,000 3 6.5 23,400 21
802.5 22,500,000 500,000 2.5 5.8 20,880 24
802 22,000,000 500,000 2 5 18,000 28
801.5 21,500,000 500,000 1.5 4.1 14,760 34
801 21,000,000 500,000 1 2.9 10,440 57
800.5 20,400,000, 600,000 0.5 1 3,600, 158
800 19,830,000 570,000 0 0 0
3,170,000 (pipe invert @ 800 ft) Total 323 hrs
13.4 days
EXHIBIT 3
EXHIBIT 4
LISSARA DAM
FLOW CALCULATIONS 12-IN DIP
control pipe section
Parameters
Pipe diam.D 12 in 1 ft
Pipe area 0.785 sq ft
Length of pipe 80 ft including 10-ft elbow loss equivalent
Invert pipe 800 ft Crest at 806 ft
Outlet elev. 798.6 ft at elbow with Discharge section
Height H 4.4 ft max water height during storm
Inflow 6.5 cfs required capacity
Manning's 0.011 for DIP

Using Bernoulli's Equation H = v2 + Ho + H, + Hb
2g
whereby Ho = entrance loss = 0.78 uz (inlet inward projected)
2g
H, = friction loss = KP L v2
2g
KP = 5087 n2
D 413
thus KP = 0.0226
Hb = bend losses 45° elbow = 20 x D = 20 ft equivalent
applying data: H = 1 + 0.78 + Kp L
9
H = v2 + 0.78 x v2 +
2g 2g
H = v2 x 3.587
2g
4.4 = v2 x 3.587
64.4
v2 = 79 v =
Q = A v = 6.9804 cfs
0.0226 x 80 x V
2g
8.89 fps
EXHIBIT 4
EXHIBIT 5
LISSARA DAM
FLOW CALCULATIONS 12-IN DIP
discharge pipe section
Parameters
Pipe diam.D 12 in 1 ft
Pipe area 0.785 sq ft
Length of pipe 432 ft including additional feet for elbow loss e quivalent
Invert pipe 798.6 ft at elbow with "control" pipe
Outlet elev. 736 ft at upturned elbow
Height H 67 ft max water level at 803' with 1/3 PMP
Inflow 6.5 cfs required capacity
Manning's 0.011 for DIP

Using Bernoulli's Equation H = v2 + H. + H,
2g
whereby Ho = entrance loss = 0.78 x v2
2g
H, = friction loss = KP L v2
2g
KP = 5087 n2
D 4/3
thus KP = 0.0226
Hb = bend losses 90° elbow = 30 x D = 30 ft equivalent
bend losses 45° elbow = 20 x D = 20 ft equivalent
number of 45° elbows 1 25 ft equivalent
number of 90° elbows 1
applying data: H = v2 + 0.78 x V + 0.0226 x 432 x v2
2g 2g 2g
H = v2 x 11.539
2g
67 = v2 x 11.539
64.4
v2 = 374 v = 19.34 fps
Q = A v = 15.187 cfs
EXHIBIT 5
EXHIBIT 6
LISSARA DAM
DETERMINATION CRITICAL DEPTH FOR PARTLY FLOWING FULL DISCHARGE PIPE
Using Table B-3 in Design of Small Dams (page 579) (Attached)
Value calculations for pipe diameter and slope relationship (column 4)
then apply d/D value in column 1 to calculate critical depth (d) in pipe
pipe calcs
12-in DIP required flow (per pipe) critical depth d
D = 1 ft Q 6.5 cfs d = 0.41 d= 0.41 ft
Qxn D8/3 x S1/2 = 0.1659 D 0.011ft D length 337 ft
s 0.19 ft/ft invert 798.6 ft
outlet 736 ft
EXHIBIT 6
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