20052134 Ver 2_More Info Received_20120820

fJOHN W. HARRIS P. E.
CONSULTING ENGINEER, Inc.
5112 Bur Oak Circle Telephone [phone]
RALEIGH, N. C. 27612 Fax [phone]
Transmittal
Date: e -.0 -1-L
To: e-ffe°
From: John Harris
Subject: 45i4466
05 -a134 u0,
P5 �o s d�►� C-u��e�
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JOHN W. HARRIS, P. E.
CONSULTING ENGINEER, Inc.
5112 Bur Oak Circle Telephone [phone]
RALEIGH, N. C. 27612 Fax [phone]
Transmittal
O S -,a 13y v 0.
Date:'
To: 1-6Liii-He we -day
From: John Harris
Subject: CZa
15E --NR - WATER QUAUTY

® John i P E W. Harris,
CONSULTING ENGINEER, INC.
5112 BUR OAK CIRCLE
RALEIGH NC 27612
17, August 2012
Mr. Danny Smith
c/o Karen Higgins
1650 Mail Service Center
Raleigh, N.C. 27699 -1650
RE: Gates at Ethan's Glenn
Upper Barton Creek [030201, 27 -15 -2, WS -IV NSW CA]
Dear Sir or Madame:
Telephone [phone]
Fax [phone]
www.harriseng.net
In response to your request for more information on the above referenced project, we have the
following revisions, additions and responses to your letter of July 30, 2012. Comments are shown in black
and responses are in dark blue.
1. For all three level spreaders:
a. The required items checklist that we provided with the supplement forms did not
include the page /plan sheet numbers where the information may be found. In the
future, please complete these cells to allow DWQ to review your submittal more
efficiently.
The page /plan sheet numbers have been added to the required items check list provided on the
supplemental form.
b. Please provide a construction sequence per the required items check list.
A construction sequence has been added.
c. Bypass channels must be trapezoidal.
The bypass channels are shown as trapezoidal although the relative low volume of flow in these
areas does not warrant a trapezoidal channel.
d. Please show depths, dimensions and elevations of the flow splitter devices on the
plans.
The depth, dimensions and elevations of the flow splitter devices are shown on the plans.
2. For Level Spreader 2:
a. The bypass channel (including proposed one -foot contour lines) must be shown in plan
view.
The bypass channel (including proposed one -foot contour lines) is shown in plan view.
3. For Level Spreader 3:
Page 1 of 2

Y`
a. The plans do not show all of the one -foot contour lines down slope of the level spreader.
This information was requested in the DWQ's previous letter for this project and failure
to provide the information in the next submittal will result in a return of application.
The one -foot contours downstream of the level spreader are shown.
b. It appears that the slope between the base of the level lip and the top of stream bank
exceeds the allowable slope of 5 %. The next submittal must include a diffuse flow plan at
this discharge point that complies with Chapter 8 of the BMP Manual or the application
will be returned. Please provide an updated LS -VFS Supplement form for Level Spreader
3 if the design is modified.
The slope is at or less than 5% from the base of the level lip to the edge of the outer 20 foot section
of the Neuse Riparian Buffer. It is our understanding that the flow must be diffuse prior to the
buffer and that no grading would be allowed inside the buffer. This design is in compliance with
Chapter 8 of the BMP Manual.
Please note that this level spreader is not, nor was it intended to have a VFS. The degree of flow at
this point and the relative flat existing slopes do not warrant a vegetated filter strip. The 100 yr
flow at this point is less than the 1" flow in the other 2 level spreaders. It is for this reason that this
level spreader does not have nor need a flow bypass mechanism. Also please see response below.
c. The bypass channel (including proposed one -foot contour lines) must be clearly shown in
the plan view.
This level spreader does not have, nor does it need a flow bypass device. The run -off for this level
spreader in the 100 year storm (0.23 acres; 0.14 cfs 1" storm and 1.38 cfs 100 year storm) is less
than the 1" run -off from either of the other two level spreaders (1" storms of 1.9 "cfs and 2.2cfs).
Therefore it is capable of handling the maximum anticipated flow through the device without
damage. Please also note, that since the flow towards this device is not concentrated, a forebay is
not appropriate. It would be counterproductive, particularly with this small a flow to concentrate
the water in a forebay so as to re- diffuse it.
The one -foot contours are shown on the plan.
We appreciate your comments and sincerely hope we have adequately answered your questions. If
it is possible that there are any additional questions or comments, we would appreciate a telephone call or
an opportunity to come in and discuss the issues with you in person so that we can thoroughly and
accurately determine the correct steps that need to be taken, thereby avoiding any additional comments or
returned plans. We trust you will understand that we want to move on with this project as quickly as
possible. We want it done correctly and in complete compliance with DWQ and hope to work with you in
resolving any and all concerns you may have.
Sincerely;
John W. Harris, P.E.
Consulting Engineer, Inc.

A ��`'A
NC®ENR
North Carolina Department of Environment and Natural Resources
Division of Water Quality
Beverly Eaves Perdue Charles Wakild, PE Dee Freeman
Governor Director Secretary
July 30, 2012
DWQ Project # 05 -2134 v.2
WakeCounty
CERTIFIED MAIL 7012 0470 00013843 3359
RETURN RECEIPT REQUESTED
Contentnea Creek Development Company
Attn: Daniel Sullivan
8502 Six Forks Road, Suite 202
Raleigh, NC 27615
Subject Property: Gates of Ethan's Glen
Upper Barton Creek [030201, 27 -15 -2, WS -IV NSW CA]
REQUEST FOR MORE INFORMATION
Dear Sir or Madame:
On April 11, 2012, the Division of Water Quality (DWQ) received your application dated April 11, 2012 to fill or
otherwise impact 1,508 square feet of Zone 1 Neuse River protected riparian buffer and 929 square feet of Zone 2
Neuse River protected riparian buffer for a residential subdivision. On June 28, 2012, DWQ received additional
information. The DWQ has determined that your application and additional information was incomplete and/or
provided inaccurate information as discussed below. The DWQ will require additional information in order to
process your application to impact streams and wetlands on the subject property. This project is on hold and
incomplete until we receive the additional information requested below. If we do not receive the requested
information, your project will be formally returned as incomplete. Please provide the following information so that
we may continue to review your project.
Additional Information Requested:
For all three level spreaders:
a. The required items checklists that were provided with the Supplement Forms did not include the
page /plan sheet numbers where the information may be found. In the future, please complete these
cells to allow DWQ to review your submittal more efficiently.
b. Please provide a construction sequence per the required items checklist.
c. Bypass channels must be trapezoidal.
d. Please show depths, dimensions and elevations of the flow splitter devices on the plans.
Nose Carolina
�vatura!!rff
North Carolina Division of Water Quality Raleigh Regional Office Surface Water Protection Phone [phone] Customer Service
Internet, www ncwaterquality org 1628 Mail Service Center Raleigh, NC 27699 -1628 FAX [phone]
An Equal Opportunity /Affirmative Action Employer — 50% Recycled /10% Post Consumer Paper

liar,
Page 2
2. For Level Spreader 2:
a. The bypass channel (including proposed one -foot contour lines) must be shown in plan view.
For Level Spreader 3:
a. The plans do not show all of the one -foot contour lines downslope of the level spreader. This
information was requested in the DWQ's previous letter for this project and failure to provide the
information in the next submittal will result in a return of application.
b. It appears that the slope between the base of the level lip and the top of streambank exceeds the
allowable slope of 5 %. The next submittal must include a diffuse flow plan as this discharge point
that complies with Chapter 8 of the BMP Manual or the application will be returned. Please provide
an updated LS -VFS Supplement Form for Level Spreader 3 if the design is modified.
c. The bypass channel (including proposed one -foot contour lines) must be clearly shown in plan view.
Please submit three copies of this information within 30 calendar days of the date of this letter. Please send
additional information to DWQ Central Office, Attn: Karen Higgins, 1650 Mail Service Center, Raleigh,
NC- 17.699- 1650._If we do-not-receive this requested information within 30 calendar days of the date of this
letter, your project will be withdrawn and you will need to reapply with a new application and anew fee:-- --
This letter only addresses the application review and does not authorize any impacts to wetlands, waters or
protected buffers. Please be aware that any impacts requested within your application are not authorized (at this
time) by the DWQ. Please call Lauren Witherspoon at 919 - 791 -4258 if you have any questions regarding this
letter or would like to set up a meeting to discuss this matter.
Si erely,
U r
Yth Danny S
Raleigh Regional Office Supervisor
Surface Water Protection Section
cc: DWQ Raleigh Regional Office File Copy
WeBSCaPe — 1650 Mail Service Center
Jennifer Burdette — Burdette Land Consulting, 10212 Creedmoor Road, Raleigh, NC 27615
Filename, 05 -2134 v 2—Gates of Ethan's Glen SD_BA_On- Hold(2)

s
RA
O�O� W ATFAOG
sq ft Forebay is adequately sized
Depth of forebay at stormwater entry point
HCDENR
in
STORMWATER MANAGEMENT PERMIT APPLICATION FORM
401 CERTIFICATION
APPLICATION FORM
LEVEL SPREADER - VEGETATED FILTER STRIP (LS -VFS) SUPPLEMENT
This form must be completely filled out, printed, initialed, and submitted.
I. PROJECT INFORMATION
Computed minimum length of the level lip needed
Project name
Gates at Ethan's Glenn
Contact name
Dan Sullivan
Phone number
919- 9613690
Date
March 20, 2012
Drainage area number
LS -1 (Areas A & B combined)
II. DESIGN INFORMATION
Elevation at the end of the VFS that is farthest from the LS
The purpose of the LS -VFS
Buffer Rule: Diffuse Flow
Stormwater enters LS -VFS from
The drainage area
Type of VFS
Engineered filter strip (graded & sodded, slope < 8 %)
Explanation of any "Other" responses above
This is a re- design of a previously approve Level Spreader
If Stormwater Enters the LS -VFS from the Drainage Area
Drainage area
143,312 fe
Impervious surface area
21,225 fe
Percent impervious
14.81 %
Rational C coefficient
0.60
Peak flow from the 1 in/hr storm
1.97 cfs
Time of concentration
5.00 min
Rainfall intensity, 10- yrstorm
1.5 in/hr
Peak flow from the 10 -yr storm
2.96 cfs
Design storm
1 inch /hour storm
Maximum amount of flow directed to the LS -VFS
1.97 cfs
Is a flow bypass system going to be used?
y (Y or N)
Explanation of any "Other" responses above
If Stormwater Enters the LS -VFS from a BMP
Do not complete this section of the form.
Type of BMP
Peak discharge from the BMP during the design storm
cfs
Peak discharge from the BMP during the 10 -year storm
cfs Do not complete this section of the form.
Maximum capacity of a 100 -foot long LS -VFS
10 cfs
Peak flow directed to the LS -VFS
cfs Do not complete this section of the form.
Is a flow bypass system going to be used?
(Y or N)
Explanation of any "Other" responses above
LS -VFS Design
Forebay surface area
44
sq ft Forebay is adequately sized
Depth of forebay at stormwater entry point
16
in
Depth of forebay at stormwater exit point
6
in Depth is appropriate.
Feet of level lip needed per cfs
10
fucfs
Computed minimum length of the level lip needed
20
ft
Length of level lip provided
20
ft
Width of VFS
30
ft
Elevation at downslope base of level lip
321.73
fmsl
Elevation at the end of the VFS that is farthest from the LS
321.20
fmsl
Form SW401 - LS -VFS - 27JU12011 - Rev 9 page 1 of 3

1 �
r-
Slope (from level lip to the end of the VFS)
Are any draws present in the VFS?
Is there a collector swale at the end of the VFS?
Bypass System Design (if applicable)
Is a bypass system provided?
Is there an engineered flow splitting device?
Dimensions of the channel (see diagram below):
M
B
W
y (flow depth for 10 -year storm)
freeboard (during the 10 -year storm)
Peak velocity in the channel during the 10 -yr storm
Channel lining material
Does the bypass discharge through a wetland?
Does the channel enter the stream at an angle?
Explanation of any "Other" responses above
1.77 %
n (Y or N) OK
n (Y or N)
y (Y or N)
y (Y or N) Please provide plan details of flow splitter i£ supporting calcs.
2.00
ft
0.50
ft _
6.00
ft
1.30
ft
1.00
ft
2.65
ftlsec
r UK vi It.
n (Y or N)
y (Y or N)
The spread sheet would not allow input for the channel linning... it is grassed.
j B +
III. REQUIRED ITEMS CHECKLIST
EDIT Please indicate the page or plan sheet numbers where the supporting documentation can be found. An incomplete submittal package will
result in a request for additional information. This will delay final review and approval of the project. Initial in the space provided to indicate the
following design requirements have been met. If the applicant has designated an agent, the agent may initial below. If a requirement has not been
met, attach justification.
Requried Item:
1. Plans (1" - 50' or larger) of the entire site showing:
- Design at ultimate build -out,
Off -site drainage (if applicable),
Delineated drainage basins (include Rational C coefficient per basin),
Forebay (if applicable),
High flow bypass system,
Maintenance access,
-Proposed drainage easement and public right of way (ROW), and
- Boundaries of drainage easement.
2. Plan details (1" = 30' or larger) for the level spreader showing:
- Forebay (if applicable),
High flow bypass system,
One foot topo lines between the level lip and top of stream bank,
Proposed drainage easement, and
Design at ultimate build -out.
R
Page or plan sheet number and any notes:
/r -1 /y
t4 5
Form SW401 - LS -VFS - 27Ju12011 - Rev 9 page 2 of 3

3. Section view of the level spreader (1" = 20' or larger) showing:
- Underdrain system (if applicable),
Level lip,
Upslope channel, and
Downslope filter fabric.
4. Plan details of the flow splitting device and supporting calculations (if applicable).
5. A construction sequence that shows how the level spreader will be protected from
sediment until the entire drainage area is stabilized.
6. If a non - engineered VFS is being used, then provide a photograph of the VFS showing
that no draws are present.
7. The supporting calculations.
8. A copy of the signed and notarized operation and maintenance (0 &M) agreement.
N1lk-
Ly 6"1
Form SW401 - LS -VFS - 27Ju12011 - Rev 9 page 3 of 3

®®
O�o� W ATF90y
r
NCDENR
Y
STORMWATER MANAGEMENT PERMIT APPLICATION FORM
401 CERTIFICATION
APPLICATION FORM
LEVEL SPREADER - VEGETATED FILTER STRIP (LS -VFS) SUPPLEMENT
This form must be completely filled out, printed, initialed, and submitted.
I. PROJECT INFORMATION
10
Project name
Gates at Ethan's Glenn
Contact name
Dan Sullivan
Phone number
919 - 961 -3690
Date
March 20, 2012
Drainage area number
LS -2 (Area C)
II. DESIGN INFORMATION
321.73
The purpose of the LS -VFS
Buffer Rule: Diffuse Flow
Stormwater enters LS -VFS from
The drainage area
Type of VFS
Engineered filter strip (graded & sodded, slope < 8 %)
Explanation of any "Other" responses above
This is a redesign of a previously approved Level Spreader
If Stormwater Enters the LS -VFS from the Drainage Area
Drainage area
161,000 fe
Impervious surface area
23,500 fe
Percent impervious
14.60 %
Rational C coefficient
0.40
Peak flow from the 1 in/hr storm
1.48 cfs
Time of concentration
5.00 min
Rainfall intensity, 1 0-yr storm
1.05 in/hr
Peak flow from the 10 -yr storm
1.55 cfs
Design storm
1 inch /hour storm
Maximum amount of flow directed to the LS -VFS
1.95 cfs
Is a flow bypass system going to be used?
y (Y or N)
Explanation of any "Other" responses above
If Stormwater Enters the LS -VFS from a BMP
Do not complete this section of the form.
Type of BMP
Peak discharge from the BMP during the design storm
cfs
Peak discharge from the BMP during the 10 -year storm
cfs Do not complete this section of the form.
Maximum capacity of a 100 -foot long LS -VFS
10 cfs
Peak flow directed to the LS -VFS
cfs Do not complete this section of the form.
Is a flow bypass system going to be used?
(Y or N)
Explanation of any "Other" responses above
LS -VFS Design
Forebay surface area
48
sq ft Forebay is adequately sized.
Depth of Forebay at stormwater entry point
16
in
Depth of forebay at stormwater exit point
6
in Depth is appropriate
Feet of level lip needed per cfs
10
fucfs
Computed minimum length of the level lip needed
20
ft
Length of level lip provided
20
ft
Width of VFS
30
ft
Elevation at downslope base of level lip
321.73
fmsl
Elevation at the end of the VFS that is farthest from the LS
321.30
fmsl
Form SW401 - LS -VFS - 27Jul2011 - Rev 9 page 1 of 3

Slope (from level lip to the end of the VFS)
Are any draws present in the VFS?
Is there a collector Swale at the end of the VFS?
Bypass System Design (if applicable)
Is a bypass system provided?
Is there an engineered flow splitting device?
Dimensions of the channel (see diagram below):
M
B
W
y (flow depth for 10 -year storm)
freeboard (during the 10 -year storm)
Peak velocity in the channel during the 10 -yr storm
Channel lining material
Does the bypass discharge through a wetland?
Does the channel enter the stream at an angle?
Explanation of any "Other° responses above
1.43 %
n (Y or N) OK
n (Y or N)
y (Y or N)
y (Y or N) Please provide plan details of flow splitter & supporting calcs.
2.00
it
0.50
ft
6.00
ft
1.64
It
1.00
ft
2.99
ft/sec
Pick one:
n
(Y or N)
y
(Y or N)
the bypass device flows to an existing channel that enters the buffer area.
♦ B 1
III. REQUIRED ITEMS CHECKLIST
EDIT Please indicate the page or plan sheet numbers where the supporting documentation can be found. An incomplete submittal package will
result in a request for additional information. This will delay final review and approval of the project. Initial in the space provided to indicate the
following design requirements have been met. If the applicant has designated an agent, the agent may initial below. If a requirement has not been
met, attach justification.
Requried Item:
1. Plans (1" - 50' or larger) of the entire site showing:
- Design at ultimate build -out,
Off -site drainage (if applicable),
Delineated drainage basins (include Rational C coefficient per basin),
Forebay (if applicable),
High flow bypass system,
Maintenance access,
Page or plan sheet number and any notes:
Proposed drainage easement and public right of way (ROW), and 81L2JP�'J �:' � r -
Boundaries of drainage easement. y�g 511 ;k5
_ —,_„`_
2. Plan details (I"= 30' or larger) for the level spreader showing: uW�
- Forebay (if applicable).
High flow bypass system,
One foot topo lines between the level lip and top of stream bank,
Proposed drainage easement, and
Design at ultimate build -out.
Form SW401 - LS -VFS - 27Ju12011 - Rev 9 page 2 of 3

3. Section view of the level spreader (1" = 20' or larger) showing:
- Underdrain system (if applicable),
Level lip,
Upslope channel, and
Downslope filter fabric.
4. Plan details of the flow splitting device and supporting calculations (if applicable).
5. A construction sequence that shows how the level spreader will be protected from
sediment until the entire drainage area is stabilized.
6. If a non - engineered VFS is being used, then provide a photograph of the VFS showing
that no draws are present.
7. The supporting calculations.
8. A copy of the signed and notarized operation and maintenance (0 &M) agreement.
5hc�s g, 4-
NJ�
" - d,
Form SW401 - LS -VFS - 27Ju12011 - Rev 9 page 3 of 3

AD&-
>
NCDENR
STORMWATER MANAGEMENT PERMIT APPLICATION FORM
401 CERTIFICATION
APPLICATION FORM
LEVEL SPREADER - VEGETATED FILTER STRIP (LS -VFS) SUPPLEMENT
This form must be completely filled out, printed, initialed, and submitted.
I. PROJECT INFORMATION
Project name
Gates at Ethan's Glenn
Contact name
Dan Sullivan
Phone number
919 - 961 -3690
Date
March 20, 2012
Drainage area number
LS -3 (Area D)
II. DESIGN INFORMATION
The purpose of the LS -VFS
Buffer Rule: Diffuse Flow
Stormwater enters LS -VFS from
The drainage area
Type of VFS
Protected riparian buffer (slope < 5 %u)
Explanation of any "Other" responses above
If Stormwater Enters the LS -VFS from the Drainage Area
Drainage area
10,020 f?
Impervious surface area
1,500 fe
Percent impervious
14.97 %
Rational C coefficient
0.60
Peak flow from the 1 in /hr storm
0.14 cfs
Time of concentration
5.00 min
Rainfall intensity, 10- yrstorm
7.2 in /hr
Peak flow from the 10 -yr storm
0.99 cfs
Design storm
1 inch /hour storm
Maximum amount of flow directed to the LS -VFS
0.14 cfs
Is a flow bypass system going to be used?
y (Y or N)
Explanation of any "Other" responses above
If Stormwater Enters the LS -VFS from a BMP
Type of BMP
Peak discharge from the BMP during the design storm
Peak discharge from the BMP during the 10 -year storm
Maximum capacity of a 100 -foot long LS -VFS
Peak flow directed to the LS -VFS
Is a flow bypass system going to be used?
Explanation of any "Other" responses above
LS -VFS Design
Forebay surface area
Depth of forebay at stormwater entry point
Depth of forebay at stormwater exit point
Feet of level lip needed per cfs
Computed minimum length of the level lip needed
Length of level lip provided
Width of VFS
Elevation at downslope base of level lip
Elevation at the end of the VFS that is farthest from the LS
Form SW401 - LS -VFS - 27Ju12011 - Rev.9
cfs
cfs
2 cfs
cis
or
4 sq ft
0 in
6 in
50 ft/cfs
7 ft
20 ft
50 ft
321.98 fmsl
321.50 fmsl
Do not complete this section of the form.
Do not complete this section of the form
Do not complete this section of the form.
Forebay is adequately sized.
Depth is appropriate
Ten feet is the minimum level spreader length.
page 1 of 3

Slope (from level lip to the end of the VFS) 0.96 %
Are any draws present in the VFS? n (Y or N) OK
Is there a collector swale at the end of the VFS? n (Y or N)
Bypass System Design (if applicable)
Is a bypass system provided?
n (Y or N)
Is there an engineered flow splitting device?
n (Y or N)
Dimensions of the channel (see diagram below):
M
ft
B
ft
W
ft
y (flow depth for 10 -year storm)
ft
freeboard (during the 10 -year storm)
ft
Peak velocity in the channel during the 10 -yr storm
fVsec
Channel lining material
Pick one:
Does the bypass discharge through a wetland?
(Y or N)
Does the channel enter the stream at an angle?
(Y or N)
Explanation of any "Other" responses above
W
1 B 1
111. REQUIRED ITEMS CHECKLIST
EDIT Please indicate the page or plan sheet numbers where the supporting documentation can be found. An incomplete submittal package will
result in a request for additional information. This will delay final review and approval of the project. Initial in the space provided to indicate the
following design requirements have been met. If the applicant has designated an agent, the agent may initial below. If a requirement has not been
met, attach justification.
Requried Item:
1. Plans (1" - 50' or larger) of the entire site showing:
- Design at ultimate build -out,
Off -site drainage (if applicable),
Delineated drainage basins (include Rational C coefficient per basin),
Forebay (If applicable),
High flow bypass system,
Maintenance access,
-Proposed drainage easement and public right of way (ROW), and .
- Boundaries of drainage easement.
2. Plan details (1" = 30' or larger) for the level spreader showing:
- Forebay (if applicable),
High flow bypass system,
One foot topo lines between the level lip and top of stream bank,
Proposed drainage easement, and
Design at ultimate build -out. _
Initials_ Page or plan sheet number and any notes:
Form SW401 - LS -VFS - 27Ju12011 - Rev 9 page 2 of 3

3. Section view of the level spreader (1" = 20' or larger) showing:
- Underdrain system (if applicable),
- Level lio.
Upslope channel, and
Downslope filter fabric.
4. Plan details of the flow splitting device and supporting calculations (if applicable).
5. A construction sequence that shows how the level spreader will be protected from
sediment until the entire drainage area is stabilized.
6. If a non - engineered VFS is being used, then provide a photograph of the VFS showing
that no draws are present.
7. The supporting calculations.
8. A copy of the signed and notarized operation and maintenance (0 &M) agreement.
54ek3
g1;L.
5e'e' VA('Br
Form SW401 - LS -VFS - 27M2011 - Rev 9 page 3 of 3

DESIGN REPORT AND CALCULATIONS
For
Modification of Level Spreader Design
Gates at Ethan's Glenn
Wake County
Date:
01 December 2011 (Revised 8-10-12)
L]
John W. Harris, PE
CONSULTING ENGINEER, Inc
Corporate # C-3017
5112 Bur Oak Circle
Raleigh, NC 27612
[phone]
www.harrisen�.net

TABLE OF CONTENTS
PROJECT NARRATIVE
DRAINAGE DELINEATION & HYDROLOGY
PT FLUSH COMPUTATION
BY -PASS FLOWS
BMP SYSTEM HYDRAULICS
DITCH BLOCKS
CONVEYANCE PIPE SIZING
LEVEL SPREADER DESIGNS
SPREADER LENGTH
FOREBAY
ATTACHMENTS:
RAINFALL DATA
RUNOFF COEFFICIENTS

PROJECT NARRATIVE:
The development of the Gates at Ethan's Glenn subdivision required the crossing of an existing stream
which is designated as a "Jurisdictional" Stream and at a location where Neuse Riparian Buffers (NRB) were
required. Subsequently this crossing required that stormwater run -off from the road ditches needed to be
dispersed or dissipated prior to entering the 50 foot NRB. It is required that the 1St flush or 1 " -24hr storm be
handled by dispersement so as to prevent the flow from being "concentrated" as it flows thru the NRB. To
accomplish this task Level Spreaders were designed for all four corners of the road's crossing of the stream. As
lots were sold and recorded, and the property developed it was found that insufficient easement space had been
allotted for the installation of the originally proposed level spreaders and they could not be installed.
To correct this, the site investigation found that it was possible to collect the 1St flush flows and divert
them to a single source Level Spreader to be located at one of the (south west) remaining un -sold corners. This
Report represents the design analysis of how this new design is to be accomplished. Basically, the Ist flush from
the north east and north west quadrants will be diverted to a level spread of approximately 20 if on the south
west quadrant. Flow from the south east quadrant will be handled in and at that location. The normal flows from
the south west quadrant will be handled with a 2nd Level Spreader of about 201f.
DRAINAGE DELINEATIONS and HYDROLOGY
Careful review and comparison of the existing conditions and the original design plans were conducted
to insure the actual stormwater flows are still as they were designed. The design of the Level Spreaders will be
based upon the drainage delineations as shown on the design plans which accompany this report. To design the
level spreaders we must know 2 flow volumes, the 1 st flush or 1" 24hr storm and the 10 yr storm which is
required of NCDOT ditches. The Ditches will be adapted with "Ditch Blocks" to capture the 1 st flush, but allow
the larger flows to bypass directly to the stream.
It is important to note here that the method of computation for determining these flows will be the
Rational Method. Wake County typically prefers that the SCS method be used but that method is more suited to
larger areas and does not give an accurate representation of flow for an existing development with very small
drainage basins.
Basin Area Run -off Coef. Storm Intensity 1" Vol. 10yr -Vol.
A 2.26
0.6
1"
&
7.2"
1.3 cfs
9.8 cfs
B 1.03
0.6
1"
&
7.2"
0.6 cfs
4.4 cfs
C 3.7
0.6
1"
&
7.2"
2.2 cfs
16.1 cfs
D 0.23
0.6
1"
&
7.2"
0.14cfs
1.0 cfs
Note: Level Spreader #3 has a very small drainage area, the 100 yr storm for Basin D is 1.38 cfs. This is less
than the 1" WQ flow going to each of the other 2 Level Spreaders.

SEE HYDROLOGY RUNOFF HYDROGRAPHS FOR AREAS A, B, C, and D
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BMP SYSTEM HYDRAULICS
Ditch Blocks for Flow By -Pass
In accordance with the NCDENR stormwater BMP manual, the Level Spreader must be designed for the
first flush run -off volume. That first flush volume is defined as the 1 "/hr storm intensity. In addition, we will
also analyze the 10 yr storm event to enable us to design the proper depths of the roadside ditches and ditch
blocks. The Ditch Blocks act as a Flow diversion (by- pass). They are constructed to a specific elevation that
equates to the 1" first flush storm. When the first flush storm is exceeded, the flow goes over the ditch block,
thereby allowing the excess flow to be diverted away from the Level Spreader.
Ditch Blocks are berms built in the ditch line at the height of the first flush flow. When the first flush
occurs, it is trapped by the ditch block and feed via a yard inlet and connecting outlet pipe to the proposed Level
Spreader. Any flow deeper than the first flush is allowed to flow over the ditch block and into the stream as a
concentrated storm flow.
It is important to note, that Level Spreader #3 does not need a flow by -pass mechanism. The computed
100 year flow for this device is less than the 1" storm for Level Spreaders #1 and #2. The depth of flow over
Level Spreader #3, in the 100 yr event is 1.08" deep and has a velocity of only 0.78 fps. This is not erodible and
the Level Spreader will function effectively without a by -pass channel.
Ditch Ditch Block Height for Flow By -Pass
A
0.64 feet
B
0.48 feet
C
0.78 feet
D
Not Needed

S££ CHANNEL REPORT FOR DITCHES A, B, C, and D
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DESIGN CONVEYANCE PIPES:
To convey the proposed 1st flush stormwater to the appropriate level spreader location, a yard inlet will
be placed to collect the water and transport it, by gravity flow pipe. This will be required in two locations, one
for area "A" and one for area "B ". From our design software we have determined that a 10" PVC will be needed
for area "A ", and an 8" PVC pipe is needed for area "B ". They will be bored under the existing roadway to
allow the storm water to reach the intended Level Spreader located in Phase -IV.
Pipes will need to be designed to carry storm water, from the 1 St flush volume from each of the 2 north
road areas to the south west quadrant. Area "A" will be a 10" PVC pipe and Area `B" will need an 8" PVC
pipe. The pipe hydraulics were computed and noted on the design plans and also as shown on the Culvert
Reports:

SEE CULVERT REPORT FOR PIPES A and B:
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LEVEL SPREADER DESIGNS:
The Level Spreaders noted below were sized in accordance with the NCDENR BMP manual for Level
Spreader with Engineered Vegetated Filter Strip. The Level spreader is to handle the 1 "/hr storm Intensity and
must be 10 if in length for every 1 cfs of flow volume. Please note that Level Spreader #3 has a very small
drainage area. This area produces minimal flow and therefore neither a flow diversion device nor a forebay are
needed
Device cfs Required Length
LS -1
1.9
10 /cfs
20 if
LS -2
+/ -2.2
10 /cfs
201f (max. length)*
LS -3
0.14
10 /cfs
10 if (min. length) Use 20 feet
*as this is an estimation of potential flow, we have determined that with the depth of flow being 0.12'
(<1.4 ") and the velocity of 0.91 fps the device is acceptable and meets the intent of the maximum length rule.
To verify the adequacy of the design lengths we have computed a broad crested weir analysis to
illustrate the effect of flow depth and flow velocities prevalent with these designs.
Device Flow Length V -fns Depth of Flow
LS -1
1.9
20
0.86
0.11 ft (1.3 ")
LS -2
2.2
20
0.91
0.12 ft (1.4 ")
LS -3
0.14
20
0.36
0.02 ft ( <1/4 ")
LS -3 (100yr)
1.38
20
0.78
0.09 ft (1.08 ")
Please note that both the velocity and the depth of flow are extremely low and it is not expected that
these devices will be subject to erosion or "rills" which would allow re- concentration of overland flow.

SEE WEIR REPORT FOR LEVEL SPREDERS 1, 2 and 3:
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FOREBAY:
There will be 2 locations where a forebay is needed, at Level Spreaders #1 and #2. Level Spreader #3
does not need a forebay because it is feed from primarily overland flow. The size of the fore'bays are relevant to
the impervious area of the contributing drainage basin and are generally 0.2% of the impervious drainage basin
area.
The sizes are tabulated as follows.
Drainne Area Percent 1mvervious
0.2% Required
Forebay
Size L
W
A & B: 2.6 + 1.03 ac's 15%
.002 x 43560
44 SF
6ft
x 7.5ft
C: 3.7 ac's 15%
.002 x 43560
48 SF
7ft
x 7ft.
43
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FOREBAY:
There will be 2 locations where a forebay is needed, at Level Spreaders #1 and #2. Level Spreader #3
does not need a forebay because it is feed from primarily overland flow. The size of the fore'bays are relevant to
the impervious area of the contributing drainage basin and are generally 0.2% of the impervious drainage basin
area.
The sizes are tabulated as follows.
Drainne Area Percent 1mvervious
0.2% Required
Forebay
Size L
W
A & B: 2.6 + 1.03 ac's 15%
.002 x 43560
44 SF
6ft
x 7.5ft
C: 3.7 ac's 15%
.002 x 43560
48 SF
7ft
x 7ft.

ATTACHMENTS:
• RAINFALL DATA
RUNOFF COEFICIENTS
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GRAPHIC SCALE
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DRAINAGE DELINEATION ............................2
SITEPLAN ..........................0 . .......... ........................ 3
PIPES PLAN AND PROFILE .........................4
LEVEL SPREADER SECTION .....................5
DETAILS ......................................... ............................... 6

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BLOCK
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PER INDICATED DIMINSIONS
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USE AS DITCH BLOCK
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III
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----------- — ----- .......
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LEVEL SPREADER
EXISTING
ROAD
TOP OF LEVEL
------ -
SPREADER
23-
—
-3
22-
2.31 2.95'
2.32'
— -- ----
PROPOSED GRADE
-324
23-
21-
—
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PROPOSED LEVEL SPREADER
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99
DE TA ID 99 B
CHANNEL GRADE A 1,0
/
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MAXIMUM GRADE OF 1 % FOR A N.
TRANSITION OF 15' MINIMUM
A
DIVERSION DIKE
IF NEEDED PLAN VIE
A EARTH BERM
R/W INLET: DITCH BLOCK
EARTH SHOULDER—`
DITCH BLOCK -- EOP
TOP OF LA PIPE OUTLET
DITCH EANK
EAAM`BERM
DITCH B20�\
DITCH
DITCH ATURA
INVERT GROUND
LIN 12"
MIN
NC E:
AN= H 0 R STAKES 30" LONG
AND SET MINIMUM 12 DEEP
SECTION A—A
LS -1 LS -2 LS -3
W 6 7 N/A
L 10 10 N/A
24„ 48"
`9 2� HARDENED MIX OF
NATIVE SOIL AND
MORTAR MIX
TYPICAL DdTCH BLOCK DETAIL
DETAIL "C"
VEGETATED
DIVERSION
10 vp-ts
® ♦ ♦ ®: ♦ ® —
♦♦ ® ♦ ♦,,
NOTE:
"LEVEL SPREADERS SHALL BE CONTAINED
WITHIN A 20' MAINTENANCE AND DRAINAGE
EASEEMENT AND SHALL CONFORM TO
TOPOGRAPHY TO MEET THE INTENT OF
DIFUSE FLOW."
LEVEL SPREADER
SECTION DETAIL
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