HomeMy WebLinkAboutStorm Water Draiange StudyStorm Water Drainage Study
Southside Plaza Phase 2
College Station, Texas
0 Gessner Engineering
March 24, 2011
Ms. Erika Bridges
City of College Station
1101 Texas Avenue
College Station, TX 77842
Re: Storm Water Drainage Study
Southside Plaza Phase 2
College Station, Texas
Gessner Engineering Job No.: 10 -0548
Dear Ms. Bridges:
This report conveys the results of the storm water drainage study conducted by Gessner
Engineering for the proposed Southside Plaza Phase 2 in College Station, Texas. Gessner
Engineering believes that all information contained in this report is valid. Please contact us
if you have any questions or if we can be of further assistance.
Sincerely,
GESSNER ENGINEERING, LLC F -7451
W ( { Y deitim N�
Melissa P. Thomas, P.E.
Kyle M. Zapalac, M.E., E.I.T.
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MELISSA P. THOMAS
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Gessner
Engineering
2501 Ashford Drive
Suite 102
College Station, Texas 77840
P.O. Box 10763, 77842
979.680.8840
fax 979.680.8841
2204 S. Chappell Hill Street
Brenham, Texas 77833
979.836.6855
fax 979.836.6847
3
Executive Summary
This storm water drainage report is submitted to the City of College Station, Texas for
review on March 24, 2011 by Melissa P. Thomas, P.E. of Gessner Engineering, located at
2501 Ashford Drive, Suite 102, College Station, Texas 77840. This report is submitted on
behalf of the owner, Mr. Ron Smith with Aggieland Carpet One at 4093 State Highway 6
South.
The proposed project consists of the development of an approximately 1.66 acre
undeveloped site. Proposed improvements include an approximately 12,424 square feet
commercial building with parking.
The site is located along the Highway 6 frontage road in between Aggieland Carpet One at
4093 State Highway 6 South and the Silk Stocking at 4075 State Highway 6 South in
College Station, Texas. It is located in the Lick Creek watershed. The site is not located in
the FEMA 100 year flood plain, as shown by FIRM number 48041 CO201 D.
Currently, the property is covered in moderate grass and weeds. A small portion of the Silk
Stocking property currently drains onto the subject property.
The proposed site development routes runoff from the proposed parking and landscape
islands, into one (1) proposed surface detention pond by sheet flow and shallow
concentrated flow and runoff from the building into three (3) proposed water detention tanks
behind the building. The pond and water storage tanks will outflow into the bordering
property directly northeast of the subject property following current drainage patterns.
Due to the size of development at this site, a Notice of Intent is not required for submittal to
the Texas Commission on Environmental Quality. In addition, a Storm Water Pollution
Prevention Plan has been prepared by Gessner Engineering.
This drainage report includes a report detailing the methods of calculations and results
summary, with appendices including drainage area maps and calculations, HEC -HMS
reports, and Technical Design Summary.
G Gessner Engineering
Introduction
This storm water drainage report is intended to determine the required detention to match
pre- existing storm runoff conditions for the proposed Southside Plaza Phase 2. A small
portion of the Silk Stocking property currently drains onto the subject property and is
proposed to drain along the border of the Silk Stocking property and Southside Plaza
Phase 2 property into a surface inlet on the Southside Plaza Phase 2 property.
Drainage Calculations for this site were prepared according to the National Resource
Conservation Method as detailed in Technical Release 55 (TR -55) published in June of
1986. Proposed improvements include an approximately 11,960 square foot commercial
building with associated landscape areas and parking. Curve numbers from TR -55 were
used based on developed uses as described above. Pre - developed flows were calculated
based on the undeveloped land on the subject tract. The calculated pre - developed and
developed flows include the two (2), ten (10), twenty -five (25), fifty (50) and one - hundred
(100) year storms in accordance with the Bryan College Station Unified Stormwater Design
Guidelines.
Calculations
Calculations were performed according to the USDA TR -55 and with the aid of HEC -HMS
3.5 by the U.S. Army Corps of Engineers. The output data from HEC -HMS has been
provided as Appendix B.
Time of Concentration
The time of concentration (travel time) for each drainage area was estimated by summing
the flow time for each segment of travel. For sheet flow, travel time was estimated by
Manning's Kinematic equation:
Where:
_ 0.007 x (n 8
S °4 VP 2
t = travel time (hours)
n = manning's roughness coefficient
L = flow length (feet)
S = slope (ft/ft)
P2 = 2 -year, 24 hour rainfall (inches)
4
For shallow concentrated flow, the travel time was calculated from the flow velocity based
on the slope in the direction of flow. These velocities were taken from Table C -4 of the
Bryan College Station Unified Stormwater Design Guidelines.
G Lessner Engineering
Frequency
Rainfall Depth (in),
24 -hr duration
Pre - Developed Peak
Flow (cfs)
2 years
4.50
5.3
10 years
7.40
10.1
25 years
8.40
11.7
50 years
9.80
14.0
100 years
11.00
15.9
The computed times of concentration for each drainage area are included on sheet C -06.
Computed values were increased to a minimum time of ten (10) minutes as required.
Unit Hydrograph
A generic unit hydrograph was computed by distributing the rainfall depths (Table One)
according to the distribution factors for the NCRS Type III 24 hour storm. This hydrograph
was then applied to each subarea based on the curve number and time of concentration of
that area.
Reach Routing
Hydrographs were routed from subareas to the outflow through the kinematic wave
method. This method allows for hydrographs to be translated with time but not attenuated.
The effects of backwater flow and pressure flow in channels were neglected.
Peak Runoff Flow
Peak Runoff Flow from the site was determined based on the Type III 24 hour storm
applied to each drainage area. The depth- duration - intervals for each frequency are
included in Table One below, and were obtained from Table C -6 in the Unified Stormwater
Design Guidelines. Curve Number values (CN) were determined from TR -55, Table 2 -2a.
Peak pre - developed flow for the subject site is also included in Table One. Drainage areas
and calculations are included on sheet C -06, which is attached as Appendix A.
Table One: Rainfall Depths and Resulting Flows
5
Inlets
The storm design utilizes area grate inlets and curb inlets with grates manufactured by ADS
(or approved equivalent). The inlet capacities were determined based on curves provided
by the manufacturer.
Storm Pipe Calculations
The proposed storm system was sized for the 25 year storm inflow for site runoff. Capacity
was calculated based on Manning's equation with a roughness coefficient "n" of 0.012 for
HDPE pipe.
Pond Design
The proposed pond and tanks shown on the grading and storm sheets of the Southside
Plaza Phase 2 Engineering plans were designed to detain the post - developed flows to or
below pre - developed levels. The surface detention pond is located on the east corner of
Gessner Engineering
Depth (ft)
Area (sqft)
0
0
0.1
79
0.2
295
0.3
520
0.4
736
0.5
869
0.6
1021
0.7
1195
1.2
1957
1.6
5015
the property and detains runoff from the parking and landscaped areas. The elevation -area
curve for the designed pond is shown in Table Two below, Pond Elevation -Area Data, and
in Figure 1, Pond Elevation -Area Curve. The three water storage tanks area located
directly behind the proposed building and detains runoff from the roof of the main building.
The elevation -area curve for the combined water storage tanks is shown in Table Three
below, Combined Tank Elevation -Area Data, and in Figure 2, Combined Tank Elevation -
Area Curve. The storage volumes are computed based on a trapezoidal estimate from the
areas given at each elevation.
0
Table Two: Pond Elevation -Area Data
1 1 1 1 1 1 1
0.2 0.4 0.6 0.8 1 1.2 1.4
Elevation (FT)
Figure One: Pond Elevation - Area Curve
18
6
G Gessner Engineering
0.00530
0.00528
0.00526
0.00524
a
o
m
0.00522
0.00520-
0.00518
Table Three: Combined Tank Elevation -Area Data
Depth (ft)
0.00
11.00
Area (sqft)
208
208
0.00516 i i i i
0 2 4 6 8 10
Elevation (FT)
Figure Two: Combined Tank Elevation -Area Curve
12
7
Outlet Design
It was determined that staged outlet structures were required for the pond and tanks to
efficiently keep the post developed flows below the pre - developed flows for the 2, 10, 25,
50 and 100 year storms. Details of the outlet structures are shown on sheet C -07. Table
Four below shows post - developed peak flow rates and the maximum water surface
elevations in the pond and water storage tanks for each storm event. Using the proposed
outlet structure, it was determined that the pond will have 1.1 feet of freeboard during the
25 year design storm and 1.0 feet of freeboard for the 100 year storm, with a top of berm
elevation of 279.80. The tanks will have 4.16 feet of freeboard during the 25 year design
storm and 2.48 feet of freeboard for the 100 year storm, with a top of tank elevation of
12.42' above the tank bottom.
G Gessner Engineering
Storm Event
Pond Water Surface
Elevation (ft) Post-
Developed
Pond Water Surface
Elevation Above Outlet (ft)
Post - Developed
Tank Water Surface
Elevation Above Bottom (ft)
Post - Developed
2 Year
278.46
1.16
6.12
10 Year
278.66
1.36
7.62
25 Year
278.70
1.40
8.26
50 Year
278.76
1.46
9.17
100 Year
278.80
1.50
9.94
Storm Event
Pre- Developed Peak Flow
(cfs)
Post - Developed Peak Flow,
no Detention (cfs)
Post - Developed Peak Flow,
with Detention (cfs)
2 Year
5.3
6.5
5.0
10 Year
10.1
11.1
10.1
25 Year
11.7
12.7
11.6
50 Year
14.0
14.9
13.7
100 Year
15.9
16.8
15.4
• Pond /Tank Outflows and W.S.E.Ls
8
The peak post - developed flow out of the site equals the sum of the hydrographs from the
pond, tanks and from some landscaped areas to the north and west. These post -
developed peak flows compared to the pre - developed peak flows are shown in Table Five
below for each storm event. Post - Developed flows without onsite detention are also
included in the table for reference.
- D eveloped and Post - Develo Site Outflows
To dissipate energy at the pond outflow structure, rip rap was designed based on the
discharge velocities. The discharge velocity for the 100 year design storm is 10.05 feet per
second at the pond.
Conclusion
Based on visual evidence, engineering drainage calculations and sound engineering
judgment, Gessner Engineering believes that the post - development flows can be detained
below or at the pre - developed flows for the two (2), ten (10), twenty -five (25), fifty (50) and
one hundred (100) year design storms for this site.
Gessner Engineering
APPENDIX A:
Drainage Area Map and Calculations
(Sheet C -06)
9
0 Gessner Engineering
-,--,---= 1 /
/
i 1
1 i
/
0
A
GO
0
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CO
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w
C
w
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,
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1 1
1,1 -\
G =UI •I G
FFE= 279.40
SOUTHSIDE PLAZA PHASE 2
4081 HIGHWAY 6 SOUTH
COLLEGE STATION, TEXAS
0
0
z
-
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z
TANKS
AS
POND
A3 I
A4
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05
IV
NOLLIINDISSU
SONY
N
0.70
A3
m�i
DRAINAGE AREA
(AC)
0.12
0.27
POST -DEVELOPED FLOWS _
WA [ N/A
MAX DETANNED ROUTED FLOW
80.0 I_ _... 10
r
N/A r N/A
95.8 _._. 10
82.3 10
COMPOSITE CURVE C
NUMBER "CUT CONCENTRATION (MIN)
96.3 10
98.0 10
100 YEAR STORM
DEPTH ON)
11
11
1.7
15.4
0.0
- - -- 10.7 - --
100 YEAR STORM
MAXIMUM FLOW
(CFS)
1.1
2.5
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z-0
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SOUTHSIDE PLAZA PHASE 2
4081 HIGHWAY 6 SOUTH
COLLEGE STATION, TEXAS
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8
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POSTDEVELOPED AREA AS COMPOSITION
APPENDIX B:
HEC -HMS Output
10
0 Gessner Engineering
a
A5 M4
HEC -HMS Pre - Developed Model
▪ Al
• A2
HEC -HMS Post - Developed Model
0 Gessner Engineering
Show Elements:
Al
A2
Start of Run: 01Jan2010, 00 :00
End of Run: 03Jan2010, 00:00
Compute Time: 24Mar2011, 12:14:31
Hydrologic
Element
Start of Run:
End of Run:
Compute Time:
Show Elements: ; r
Hydrologic
Element
Project: POST DEVELOPMENT Simulation Run: PRE 2 YR
Drainage Area
(MI2)
0.0027031
.00021875
01Jan2010, 00:00
03Jan2010, 00:00
24Mar2011, 12:16:38
Pre - Development
Basin Model: SOUTHSIDE PRE DEVELOPMENT
Meteorologic Model: 2YR
Control Specifications: Control 1
Volume Units: ® IN 0 AC -FT
Peak Discharge
(CFS)
4.8
0.5
Time of Peak
01Jan2010, 12:08
01Jan2010, 12:07 4.26
2 Year Storm: Pre - Development
Project: POST DEVELOPMENT Simulation Run: PRE 10 YR
Drainage Area Peak Discharge Time of Peak
(MI2) (CFS)
0.0027031 9.2 01Jan2010, 12:07
.00021875 0.9 01Jan2010, 12:07
10 Year Storm: Pre - Development
Sorting:
Volume
(IN)
Hydrologic v1
2.82
Basin Model: SOUTHSIDE PRE DEVELOPMENT
Meteorologic Model: 10YR
Control Specfcations: Control 1
Volume Links: ® IN 0 AC -FT Sorting: Hydrologic '4
Volume
(IN)
5.52
7.16
G Gessner Engineering
Show Elements:
Hydrologic
Element
Al
A2
Show Elements:
Hydrologic
Element
Al
A2
Project: POST DEVELOPMENT Simulation Run: PRE 25 YR
Start of Run: 01Jan2010, 00:00
End of Run: 03Jan2010, 00:00
Compute Time: 24Mar2011, 12 :17:22
Drainage Area
(MI2)
0.0027031
.00021875
Peak Discharge
(CFS)
10.7
1.0
Time of Peak
01Jan2010, 12:07
OlJan2010,12:07
Volume
(IN)
6.48
8.16
Project: POST DEVELOPMENT Simulation Run: PRE 50 YR
Start of Run: 01Jan2010, 00:00
End of Run: 03Jan2010, 00:00
Compute Time: 24Mar2011, 12:18 :38
25 Year Storm: Pre - Development
Drainage Area Peak Discharge
(MI2) (CFS)
0.0027031
.00021875
Basin Model: SOUTHSIDE PRE DEVELOPMENT
Meteorologic Model: 25YR
Control Specifications: Control 1
Volume Units: 0 IN 0 AC -FT
Basin Model: SOUTHSIDE PRE DEVELOPMENT
Meteorologic Model: 50YR
Control Specfications: Control 1
Volume Units: ® IN 0 AC-FT
12.8
1.1
Time of Peak
01Jan2010,12:07
01Jan2010, 12:07
50 Year Storm: Pre - Development
Sorting:
Sorting:
Hydrologic
Hydrologic *r1
Volume
(IN)
7.83
9.56
Gessner Engineering
Start of Run: 01Jan2010, 00:00
End of Run: 03Jan2010, 00:00
Compute Time: 24Mar2011, 12:19:43
Show Elements:
Project: POST DEVELOPMENT Simulation Run: PRE 100 YR
Basin Model: SOUTHSIDE PRE DEVELOPMENT
Meteorologic Model: 100YR
Control Specifications: Control 1
Volume Units: 0 IN 0 AC -FT
100 Year Storm: Pre - Development
Sorting: Hydrologic ;++;;
Al
A2
Hydrologic
Element
Drainage Area
(MI2)
0.0027031
.00021875
Peak Discharge
(CFS)
14.6
1.3
Time of Peak
01Jan2010, 12:07
01Jan2010, 12:07
Volume
(IN)
9.00
10,76
Gessner Engineering
Hydrologic
Element
Drainage Area
(MI2)
Peak Discharge
(CFS)
Time of Peak
Volume
(IN)
Al
.0001875
0,4
01]an2010, 12:07
4.07
A2
.000421875
1.0
01Jan2010, 12:07
4,26
A3
0.0019062
4,4
01Jan2010, 12:07
4.02
A4
.00025
0.4
01Jan2010, 12:08
2.66
A5
.00015625
0.2
013an2010,12:08
2.46
OUTFALL
0.0027656
4,8
01Jan2010, 12:11
3.94
POND
0.0019062
3.8
01Jan2010, 12:11
4.02
TANKS
.000421875
0.3
01Jan2010, 12:28
4.26
Start of Run: 01Jan2010, 00:00
End of Run: 03Jan2010, 00:00
Compute Time: 24Mar2011, 12:20:42
Show Elements: _ " Eie erL
Project: POST DEVELOPMENT Simulation Run: POST 10 YR
Start of Run: 01Jan2010, 00:00
End of Run: 03Jan2010, 00:00
Compute Time: 24Mar2011, 12:23:26
Al
A2
A3
A4
A5
OUTFALL
POND
TANKS
Post - Development
Project: POST DEVELOPMENT Simulation Run: POST 2 YR
2 Year Storm: Post - Development
Show Elements: L' F: roF Volume Units: ® IN 0 AC-FT
Hydrologic Drainage Area Peak Discharge
Element (MI2) (CFS)
.0001875 0.7
.000421875 1.7
0.0019062 7.4
Basin Model: SOUTHSIDE POST DEVELOPMENT
Meteorologic Model: 2YR
Control Specifications: Control 1
Volume Units: Q IN 0 AC -FT Sorting:
Basin Model: SOUTHSIDE POST DEVELOPMENT
Meteorologic Model: 10YR
Control Specifications: Control 1
Time of Peak
01Jan2010, 12:07
01Jan2010, 12:07
01Jan2010, 12:07
.00025 0.8 01Jan2010, 12:07
.00015625 0.5 01Jan2010, 12:08
0.0027656 9.6 01Jan2010, 12:09
0.0019062 7.1 01Jan2010, 12:09
.000421875 1.1 01Jan2010, 12:15
10 Year Storm: Post - Development
Alphabetic sfri
Sorting: I Alphabetic v
Volume
(IN)
6.96
7.16
6.91
5.33
5.06
6.81
6.91
7.16
Gessner Engineering
Hydrologic
Element
Drainage Area
(MI2)
Peak Discharge
(CFS)
Time of Peak
Volume
(IN)
Al
.0001875
0.8
OlJan2010, 12:07
7.96
A2
.000421875
1.9
01Jan2010, 12:07
8.16
A3
0.0019062
8.4
01Jan2010, 12:07
7.91
A4
.00025
1.0
01Jan2010, 12:07
6.28
A5
.00015625
0.6
01Jan2010, 12:07
6.00
OUTFALL
0.0027656
11.0
013an2010,12:09
7.80
POND
0.0019062
8.1
01Jan2010, 12:09
7.91
TANKS
.000421875
1.3
OlJan2010,12:14
8.16
Hydrologic
Element
Drainage Area
(MI2)
Peak Discharge
(CFS)
Time of Peak
Volume
(IN)
Al
.0001875
1.0
OlJan2010,12:07
9.35
A2
.000421875
2.2
OlJan2010, 12:07
9.56
A3
0.0019062
9.9
01Jan2010, 12:07
9.30
A4
.00025
1.2
01Jan2010, 12:07
7.62
AS
OUTFALL
.00015625
0,7
01Jan2010, 12:07
7.33
0.0027656
13.0
01Jan2O10, 12:09
9.19
POND
0.0019062
9.5
01Jan2010, 12:09
9.30
TANKS
.000421875
1.5
01Jan2010, 12:14
9.56
Start of Run: OlJan2010, 00:00
End of Run: 03Jan2010, 00:00
Compute Time: 24Mar2011, 12:24:27
Show Elements: ; A!! EL ents
Show Elements: AN ile=n
Project: POST DEVELOPMENT Simulation Run: POST 25 YR
Basin Model: SOUTHSIDE POST DEVELOPMENT
Meteorologic Model: 25YR
Control Specifications: Control 1
Volume Units: C.' IN 0 AC -FT
25 Year Storm: Post - Development
Project: POST DEVELOPMENT Simulation Run: POST 50 YR
Start of Run: 01Jan2010, 00:00
End of Run: 033an2010, 00:00
Compute Time: 24Mar2011, 12:25:30
Sorting: Alphabetic •r
Basin Model: SOUTHSIDE POST DEVELOPMENT
Meteorologic Model: 50YR
Control Specifications: Control 1
Volume Unts: ® IN 0 AC -FT
50 Year Storm: Post - Development
Sorting: !Alphabetic *+ s
Gessner Engineering
Hydrologic
Element
Drainage Area
(MI2)
Peak Discharge
(CFS)
Time of Peak
Volume
(IN)
Al
.0001875
1.1
01Jan2010, 12:07
10.55
A2
.000421875
2,5
013an2010,12:07
10.76
A3
0.0019062
11.1
01Jan2010, 12:07
10.50
A4
.00025
1.3
01Jan2010, 12:07
8.78
A5
.00015625
0.8
01Jan2010, 12:07
8.48
OUTFALL
0.0027656
14.6
OlJan2010, 12:09
10.39
POND
0.0019062
10.7
01Jan2010,12:09
10.50
TANKS
.000421875
1.7
01Jan2010,12:14
10.76
Start of Run: 01Jan2010, 00:00
End of Run: 03Jan2010, 00:00
Compute Time: 24Mar2011, 12:26:34
Show Elements:
Project: POST DEVELOPMENT Simulation Run: POST 100 YR
Basin Model: SOUTHSIDE POST DEVELOPMENT
Meteorologic Model: 100YR
Control Specifications: Control 1
Volume Units: 0 IN 0 AC -FT
100 Year Storm: Post - Development
Sorting: Alphabetic &i+:;1
Gessner Engineering
0
0
2
0
0
i 1
0.2 0.4 0.6 0.8 1 1.2
Elevation (FT)
Pond Weir Outflow Curve
2 4 6
Elevation (FT)
Combined Tank Orifice Outflow Curve
8
1.4
1.6 1 8
10
12
Gessner Engineering
APPENDIX C:
Technical Design Summary
11
Gessner Engineering
Part 2 — Project Administration
Start (Page 2.1)
Engineering and Design Professionals Information
Engineering Firm Name and Address:
Gessner Engineering
2501 Ashford Drive Suite 102
College Station, TX 77840
Jurisdiction
City: Bryan
X College Station
Date of Submittal: 12/06/10
Lead Engineer's Name and Contact Info.(phone, e-mail, fax):
Melissa P. Thomas, P.E.
mthomas @gessnerengineering.com
Other:
Supporting Engineering / Consulting Firm(s):
Other contacts:
Developer / Owner / Applicant Information
Developer / Applicant Name and Address:
Mr. Ron Smith, RSCS Enterprises, LP
8706 Sandstone Drive
College Station, TX 77845
Phone and e-mail:
979- 690 -6766
rsmith @aggielandcarpetone.com
Property Owner(s) if not Developer / Applicant (& address):
Phone and e-mail:
Project Identification
Development Name: south Side Plaza Phase 11
Is subject property a site project, a single -phase subdivision, or part of a multi -phase subdivision?
Site Project If multi - phase, subject property is phase of .
Legal description of subject property (phase) or Project Area:
(see Section II, Paragraph B -3a)
The project scope consists of the proposed one -story building, with an
attached covered patio. The new retail building totals approximately
12,000 square feet and the attached covered patio measures approximately
600 square feet as indicated via phone conversation with Mr. Ron Smith on
November 8, 2010.
If subject property (phase) is second or later phase of a project, describe general status of all
earlier phases. For most recent earlier phase Include submittal and review dates.
Yes
General Location of Project Area, or subject property (phase):
4093 State Highway 6 South
College Station, TX 77845
In City Limits?
Bryan: o acres.
Extraterritorial Jurisdiction (acreage):
Bryan: o College Station: 0
College Station: 1 acres.
Acreage Outside ETJ: o
SECTION IX
STORMWATER DESIGN GUIDELINES
Effective February 2007
APPENDIX D - TECHNICAL DESIGN SUMMARY
Page 3 of 26 APPENDIX. D: TECH. DESIGN SUMMARY
As Revised February 2009
Part 2 — Project Administration
Continued (page 2.2)
Project Identification (continued)
Roadways abutting or within Project Area or
subject property:
4093 State Highway 6 South
College Station, TX 77845
Abutting tracts, platted land, or built
developments:
The Silk Stocking
Carpet One
Named Regulatory Watercourse(s) & Watershed(s):
Lick Creek Watershed
Tributary Basin(s):
Lick Creek Watershed
Plat Information For Project or Subject Property (or Phase)
Preliminary Plat File #:
Final Plat File #: Date:
Name:
Vol 3809, Pg 87 and
Status and Vol /Pg: V01 - 381 , Pg - ;4
If two plats, second name: File #:
Status: Date:
Zoning Information For Project or Subject Property (or Phase)
Zoning Type: C -E Commercial Existing or Proposed? Existing Case Code: N/A
Case Date N/A Status:
Zoning Type: Existing or Proposed? Case Code:
Case Date N/A Status:
Stormwater Management Planning For Project or Subject Property (or Phase)
Planning Conference(s) & Date(s):
Participants:
Preliminary Report Required? NO Submittal Date Review Date
Review Comments Addressed? Yes N/A No In Writing? When?
Compliance With Preliminary Drainage Report. Briefly describe (or attach documentation
explaining) any deviation(s) from provisions of Preliminary Drainage Report, if any.
N/A
SECTION IX
APPENDIX D - TECHNICAL DESIGN SUMMARY
STORMWATER DESIGN GUIDELINES Page 4 of 26 APPENDIX. D: TECH. DESIGN SUMMARY
Effective February 2007
As Revised February 2009
Part 2 — Project Administration
Continued (page 2.3)
Coordination For Project or Subject Property (or Phase)
Note: For any Coordination of stormwater matters indicated below, attach documentation
describing and substantiating any agreements, understandings, contracts, or approvals.
Coordination
With Other
Departments of
Jurisdiction
City (Bryan or
College Station)
Dept.
Contact:
Date:
Subject:
N/A
Coordination With
Non - jurisdiction
City Needed?
Yes No X
Summarize need(s) & actions taken (include contacts & dates):
Coordination with
Brazos County
Needed?
Yes No X
Summarize need(s) & actions taken (include contacts & dates):
Coordination with
TxDOT Needed?
Yes No X
Summarize need(s) & actions taken (include contacts & dates):
Coordination with
TAMUS Needed?
Yes No X
Summarize need(s) & actions taken (include contacts & dates):
Permits For Project or Subject Property (or Phase)
As to stormwater management, are permits required for the proposed work from any of the entities
listed below? If so, summarize status of efforts toward that objective in spaces below.
Entity
Permitted or
Approved ?
Status of Actions (include dates)
US Army Crops of
Engineers
No X Yes
US Environmental
Protection Agency
No X Yes
Texas Commission on
Environmental Quality
No X Yes
Brazos River
Authority
No X Yes
SECTION IX
STORMWATER DESIGN GUIDELINES
Effective February 2007
APPENDIX D - TECHNICAL DESIGN SUMMARY
Page 5 of 26 APPENDIX. D: TECH. DESIGN SUMMARY
As Revised February 2009
Part 3 — Property Characteristics
Start (Page 3.1)
Nature and Scope of Proposed Work
Existing: Land proposed for development currently used, including extent of impervious cover?
Grass and Weeds
Site
Development
Project
(select all
applicable)
Redevelopment of one platted lot, or two or more adjoining platted lots.
Building on a single platted lot of undeveloped land.
x Building on two or more platted adjoining lots of undeveloped land.
Building on a single lot, or adjoining lots, where proposed plat will not form
a new street (but may include ROW dedication to existing streets).
Other (explain):
Subdivision
Development
Project
N/A Construction of streets and utilities to serve one or more platted lots.
Construction of streets and utilities to serve one or more proposed lots on
lands represented by pending plats.
Describe
Nature and
Size of
Proposed
Site projects: building use(s), approximate floor space, impervious cover ratio.
Subdivisions: number of lots by general type of use, linear feet of streets and
drainage easements or ROW.
Approximately 11,960 sq. ft commercial building,
100% impervious roof, Parking lot and landscape
islands.
Project
Is any work planned on land that is not platted
If yes, explain:
N/A
or on land for which platting is not pending?
X No Yes
FEMA Floodplains
Is any part of subject property abutting a Named Regulatory Watercourse
(Section II, Paragraph B1) or a tributary thereof?
No X Yes
Is any part of subject property in floodplain
area of a FEMA - regulated watercourse?
No X Yes Rate Map48041CO201D
Encroachment(s)
into Floodplain
areas planned?
No X
Encroachment purpose(s): Building site(s) Road crossing(s)
Utility crossing(s) Other (explain):
N/A
Yes
If floodplain areas not shown on Rate Maps, has work been done toward amending the FEMA-
approved Flood Study to define allowable encroachments in proposed areas? Explain.
SECTION IX
APPENDIX D - TECHNICAL DESIGN SUMMARY
STORMWATER DESIGN GUIDELINES Page 6 of 26 APPENDIX. D: TECH. DESIGN SUMMARY
Effective February 2007
As Revised February 2009
Part 3 — Property Characteristics
Continued (Page 3.2)
Hydrologic Attributes of Subject Property (or Phase)
Has an earlier hydrologic analysis been done for larger area including subject property?
Yes
Reference the study (& date) here, and attach copy if not already in City files.
N/A
Is the stormwater
earlier study?
N/A
management plan for the property in substantial
Yes No If not, explain how
conformance with the
it differs.
No
X
If subject property
plan for the property
is not part of multi -phase project, describe
stormwater management
in Part 4.
If property is part of multi -phase project, provide overview of stormwater management plan
for Project Area here. In Part 4 describe how plan for subject property will comply
therewith.
N/A
Do existing topographic features on subject property store or detain
Describe them (include approximate size, volume, outfall, model, etc).
runoff? X No Yes
Any known drainage or flooding problems in areas near subject property?
Identify:
X No Yes
Based
(see Table
on location of
B -1 in Appendix
Detention is required.
study property in a watershed, is Type 1 Detention (flood control) needed?
B)
X Need must be evaluated. Detention not required.
If the need for
Type 1 Detention
must be evaluated:
What decision has been reached? By whom?
Detention is required.
How was determination made?
Type II detention is needed.
SECTION IX
STORMWATER DESIGN GUIDELINES
Effective February 2007
APPENDIX D - TECHNICAL DESIGN SUMMARY
Page 7 of 26 APPENDIX. D: TECH. DESIGN SUMMARY
As Revised February 2009
Part 3 — Property Characteristics
Continued (Page 3.3)
Hydrologic Attributes of Subject Property (or Phase) (continued)
Does subject property straddle a Watershed or Basin divide?
describe splits below. In Part 4 describe design concept
X No Yes If yes,
for handling this.
Watershed or Basin
Larger acreage
Lesser acreage
N/A
Above - Project Areas(Section II, Paragraph B3 -a)
Does Project Area (project or phase) receive runoff from upland areas?
Size(s) of area(s) in acres: 1) 2) 3)
X No Yes
4)
Flow Characteristics (each instance) (overland sheet, shallow
concentrated, recognizable
Watercourse or tributary);
concentrated section(s), small creek (non - regulatory), regulatory
N/A
Flow determination: Outline hydrologic methods and assumptions:
N/A
Does storm runoff drain from public easements or ROW
X No Yes If yes, describe facilities in easement
onto or across subject property?
or ROW:
Are changes in runoff characteristics subject to change in future? Explain
No
Conveyance Pathways (Section II, Paragraph C2)
Must runoff from study property drain across lower properties before reaching a Regulatory
Watercourse or tributary? No X Yes
Describe length and characteristics of each conveyance pathway(s). Include ownership of
property(ies).
Property to northeast for approximately 300' and then
to Lick creek.
Ownership: MD Wheeler LTD.
SECTION IX
APPENDIX D - TECHNICAL DESIGN SUMMARY
STORMWATER DESIGN GUIDELINES Page 8 of 26 APPENDIX. D: TECH. DESIGN SUMMARY
Effective February 2007
As Revised February 2009
Part 3 — Property Characteristics Continued (Page 3.4)
Hydrologic Attributes of Subject Property (or Phase) (continued)
Conveyance Pathways (continued)
Do drainage
easements
exist for
part of
pathway(s)?
X No
any
If yes, for what part of length? % Created by? plat, or
instrument. If instrument(s), describe their provisions.
N/A
Yes
Pathway
Areas
Where runoff must cross lower properties, describe characteristics of abutting lower
property(ies). (Existing watercourses? Easement or Consent aquired ?)
Undeveloped Property; Grass and Trees
Nearby
Drainage
Facilities
Describe any built or improved drainage facilities existing near the property (culverts,
bridges, lined channels, buried conduit, swales, detention ponds, etc).
Culvert at Front Drive
Underground detention at Carpet One
Do any of
design?
these have hydrologic or hydraulic influence on proposed stormwater
X No Yes If yes, explain:
SECTION IX
APPENDIX D - TECHNICAL DESIGN SUMMARY
STORMWATER DESIGN GUIDELINES Page 9 of 26 APPENDIX. D: TECH. DESIGN SUMMARY
Effective February 2007
As Revised February 2009
Part 4 — Drainage Concept and Design Parameters
Start (Page 4.1)
Stormwater Management Concept
Discharge(s) From Upland Area(s)
If runoff is to be received from upland areas, what design drainage features will be used to
accommodate it and insure it is not blocked by future development? Describe for each area,
flow section, or discharge point.
N/A
Discharge(s) To Lower Property(ies) (Section II, Paragraph El)
Does project include drainage features (existing or future) proposed to become public via
platting? X No Yes Separate Instrument? X No Yes
Per Guidelines reference above, how will
runoff be discharged to neighboring
property(ies)? shallow
concentrated
Establishing Easements (Scenario 1)
X Pre - development Release (Scenario 2)
Combination of the two Scenarios
Scenario 1: If easements are proposed, describe where needed, and provide status of actions
on each. (Attached Exhibit # )
N/A
Scenario 2: Provide general description of how release(s) will be managed to pre - development
conditions (detention, sheet flow, partially concentrated, etc.). (Attached Exhibit # )
Release will be managed by a weir outlet structure from a
detention pond and multiple orifice outlet structures from
water storage tanks. Shallow concentrated flow will be
released from the property.
Combination: If combination is proposed, explain how discharge will differ from pre -
development conditions at the property line for each area (or point) of release.
N/A
If Scenario 2, or Combination are to be used, has proposed design been coordinated with
owner(s) of receiving property(ies)? X No Yes Explain and provide
documentation.
SECTION IX
STORMWATER DESIGN GUIDELINES
Effective February 2007
APPENDIX D - TECHNICAL DESIGN SUMMARY
Page 10 of 26 APPENDIX. D: TECH. DESIGN SUMMARY
As Revised February 2009
Part 4 — Drainage Concept and Design Parameters
Continued (Page 4.2)
Stormwater Management Concept (continued)
Within Protect Area Of Multi -Phase Project
Will project result
in shifting runoff
between Basins or
between
Watersheds?
X No
Identify gaining Basins or Watersheds and acres shifting:
N/A
What design and mitigation is used to compensate for increased runoff
from gaining basin or watershed?
Yes
How will runoff from Project
Area be mitigated to pre-
development conditions?
Select any or all of 1, 2,
and /or 3, and explain below.
1. With facility(ies) involving other development projects.
2 Establishing features to serve overall Project Area.
3. X On phase (or site) project basis within Project Area.
1. Shared facility (type & location of facility; design drainage area served; relationship to size of
Project Area): (Attached Exhibit # )
N/A
2. For Overall Project Area (type & location of facilities): (Attached Exhibit # )
N/A
3. By phase (or site) proiect: Describe planned mitigation measures for phases (or sites) in
subsequent questions of this Part. Detention Pond /Tanks
Are aquatic echosystems proposed? X No Yes In which phase(s) or
project(s)?
Are other Best Management Practices for reducing stormwater pollutants proposed?
No X Yes Summarize type of BMP and extent of use:
-Silt fencing at limits of construction
-Sod or landscaping in all disturbed areas
If design of any runoff - handling facilities deviate from provisions of B -CS Technical
Specifications, check type facility(ies) and explain in later questions.
X Detention elements Conduit elements Channel features
Swales Ditches Inlets Valley gutters Outfalls
Culvert features Bridges Other
SECTION IX
STORMWATER DESIGN GUIDELINES
Effective February 2007
APPENDIX D - TECHNICAL DESIGN SUMMARY
Page 11 of 26 APPENDIX. D: TECH. DESIGN SUMMARY
As Revised February 2009
Part 4 — Drainage Concept and Design Parameters
Continued (Page 4.3)
Stormwater Management Concept (continued)
Within Project Area Of Multi -Phase Project (continued)
Will Project Area include bridge(s) or culvert(s)? X No Yes Identify type and
general size and In which phase(s).
If detention /retention serves (will serve) overall Project Area, describe how it relates to subject
phase or site project (physical location, conveyance pathway(s), construction sequence):
Surface detention northeast side of property
Tank detention at back of commercial building
Within Or Serving Subject Property (Phase, or Site)
If property part of larger Project Area, is design in substantial conformance with earlier analysis
and report for larger area? Yes No, then summarize the difference(s):
N/A
Identify whether each of the types of drainage features listed below are included, extent of use,
and general characteristics.
Typical shape?
Surfaces?
ditches use
Yes
Steepest side slopes:
Usual front s opes:
Usual back slopes:
Flow line slopes: least
Typica distance from travelway:
(Attached Exhibit # )
typical greatest
Are longitudinal culvert ends in compliance with B -CS Standard Specifications?
Yes No, then explain:
At intersections or otherwise, do valley gutters cross arterial or collector streets?
No Yes If yes explain:
eets with cl
Cutter used'
Jo
Are valley gutters proposed to cross any street away from an intersection?
No Yes Explain: (number of locations ?)
SECTION IX
STORMWATER DESIGN GUIDELINES
Effective February 2007
APPENDIX D - TECHNICAL DESIGN SUMMARY
Page 12 of 26 APPENDIX. D: TECH. DESIGN SUMMARY
As Revised February 2009
Part 4 — Drainage Concept and Design Parameters
Continued (Page 4.4)
Stormwater Management Concept (continued)
Within Or Serving Subject Property (Phase, or Site) (continued)
Are streets with curb and gutter used?
(continued) No
Gutter line slopes: Least Usual Greatest
Are inlets recessed on arterial and collector streets? Yes No If "no ",
identify where and why.
Will inlets capture 10 -year design stormflow to prevent flooding of intersections (arterial
with arterial or collector)? Yes No If no, explain where and why not.
Will inlet size and placement prevent exceeding allowable water spread for 10 -year
design storm throughout site (or phase)? Yes No If no, explain.
Saq curves: Are inlets placed at low points? Yes No Are inlets and
conduit sized to prevent 100 -year stormflow from ponding at greater than 24 inches?
Yes No Explain "no" answers.
Will 100 -yr stormflow be contained in combination of ROW and buried conduit on
whole length of all streets? Yes No If no, describe where and why.
Do designs for curb, gutter, and inlets comply with B -CS Technical Specifications?
Yes No If not, describe difference(s) and attach justification.
Is storm drain system used?
No X Yes
Are any 12 -inch laterals used? No X Yes Identify length(s) and where
used. Approximately 330'; North side of property.
Pipe runs between system
access points (feet):
Typical 10 0 ' Longest 10 0 '
Are junction boxes used at each bend? X Yes No If not, explain where
and why.
Are downstream soffits at or below upstream soffits?
Yes X No If not, explain where and why:
Least amount that hydraulic
grade line is below gutter line
(system- wide):
SECTION IX
STORMWATER DESIGN GUIDELINES
Effective February 2007
APPENDIX D - TECHNICAL DESIGN SUMMARY
Page 13 of 26 APPENDIX. D: TECH. DESIGN SUMMARY
As Revised February 2009
Part 4 — Drainage Concept and Design Parameters
Continued (Page 4.5)
Stormwater Management Concept (continued)
Within Or Serving Subject Property (Phase, or Site) (continued)
Storm drain system (continued)
(on separate sheet provide same info. for more instances)
(s)Ilelln0
Describe watercourse(s), or system(s) receiving system discharge(s) below
(include design discharge velocity, and angle between converging flow lines).
1) Watercourse (or system), velocity, and angle?
Riprap outfall; 4.8 f/s
2) Watercourse (or system), velocity, and angle?
3) Watercourse (or system), velocity, and angle?
For each outfall above, what measures are taken to prevent erosion or scour of
receiving and all facilities at juncture?
1) Riprap concrete
2)
3)
Are swales used to drain streets?
X No Yes
Are swale(s) situated along property lines between properties? No Yes
Number of instances: For each instance answer the following questions.
Surface treatments (including low -flow flumes if any):
Flow line slopes (minimum and maximum):
Outfall characteristics for each (velocity, convergent angle, & end treatment).
Will 100 -year design storm runoff be contained within easement(s) or platted drainage
ROW in all instances? Yes No If "no" explain:
SECTION IX
STORMWATER DESIGN GUIDELINES
Effective February 2007
APPENDIX D - TECHNICAL DESIGN SUMMARY
Page 14 of 26 APPENDIX. D: TECH. DESIGN SUMMARY
As Revised February 2009
Part 4 — Drainage Concept and Design Parameters
Continued (Page 4.6)
Stormwater Management Concept (continued)
Within Or Serving Subject Property (Phase, or Site) (continued)
Roadside Ditches
Are roadside ditches used? X No Yes If so, provide
the following:
? Yes No
Is 25 -year flow contained with 6 inches of freeboard throughout
Are top of banks separated from road shoulders 2 feet or more?
Are all ditch sections trapezoidal and at least 1.5 feet deep?
Yes No
Yes No
For any "no" answers provide location(s) and explain:
(on separate sheet provide same information for any additional instances)
If conduit is beneath a swale, provide the following information (each instance).
Instance 1 Describe general location,
approximate length:
N/A
Is 100 -year design flow contained in conduit/swale combination?
If "no" explain:
Yes No
Space for 100 -year storm flow? ROW Easement Width
Swale Surface type, minimum
Conduit Type and size, minimum
and maximum
and maximum slopes:
slopes, design storm:
Inlets Describe how conduit is loaded
(from streets /storm drains, inlets by type):
Access Describe how maintenance
access is provided (to swale, into conduit):
Instance 2 Describe general location,
approximate length:
N/A
Is 100 -year design flow contained in conduit/swale combination?
If "no" explain:
Yes No
Space for 100 -year storm flow? ROW Easement Width
Swale Surface type, minimum
Conduit Type and size, minimum
and maximum
and maximum slopes:
slopes, design storm:
Inlets Describe how conduit is loaded
(from streets /storm drains, inlets by type):
Access Describe how maintenance
access is provided (to swale, into conduit):
SECTION IX
STORMWATER DESIGN GUIDELINES
Effective February 2007
APPENDIX D - TECHNICAL DESIGN SUMMARY
Page 15 of 26 APPENDIX. D: TECH. DESIGN SUMMARY
As Revised February 2009
Part 4 — Drainage Concept and Design Parameters
Continued (Page 4.7)
Stormwater Management Concept (continued)
Within Or Serving Subject Property (Phase, or Site) (continued)
Will swales without buried conduit receive runoff from
public ROW or easements? X No Yes. Explain
If "yes" provide the following information for each instance:
Instance 1 Describe general location, approximate length, surfacing:
Is 100 -year design flow contained in swale? Yes No Is swale wholly
within drainage ROW? Yes No Explain "no" answers:
Access Describe how maintenance access is provide:
Instance 2 Describe general location, approximate length, surfacing:
Is 100 -year design flow contained in swale? Yes No Is swale wholly
within drainage ROW? Yes No Explain "no" answers:
Access Describe how maintenance access is provided:
Instance 3, 4, etc. If swales are used in more than two instances, attach sheet
providing all above information for each instance.
Channel improvements proposed?
X No Yes Explain
"New" channels: Will any area(s) of concentrated flow be channelized (deepened,
widened, or straightened) or otherwise altered? No Yes If only slightly
shaped, see "Swales" in this Part. If creating side banks, provide information below.
Will design replicate natural channel? Yes No If "no ", for each instance
describe section shape & area, flow line slope (min. & max.), surfaces, and 100 -year
design flow, and amount of freeboard:
Instance 1:
Instance 2:
Instance 3:
SECTION IX
STORMWATER DESIGN GUIDELINES
Effective February 2007
APPENDIX D - TECHNICAL DESIGN SUMMARY
Page 16 of 26 APPENDIX. D: TECH. DESIGN SUMMARY
As Revised February 2009
Part 4 — Drainage Concept and Design Parameters
Continued (Page 4.8)
Stormwater Management Concept (continued)
Within Or Serving Subject Property (Phase, or Site) (continued)
Channel Improvements (continued)
Existing channels (small creeks): Are these used? No Yes
If "yes" provide the information below.
Will small creeks and their floodplains remain undisturbed? Yes No How
many disturbance instances? Identify each planned
location:
For each location, describe length and general type of proposed improvement
(including floodplain changes):
For each location, describe section shape & area, flow line slope (min. & max.),
surfaces, and 100 -year design flow.
Watercourses (and tributaries): Aside from fringe changes,
are Regulatory
Explain below.
Watercourses proposed to be altered? No Yes
Submit full report describing proposed changes to Regulatory
existing and proposed section size and shape, surfaces, alignment,
length affected, and capacity, and provide full documentation
and data. Is full report submitted? Yes No
Watercourses. Address
flow line changes,
of analysis procedures
If "no" explain:
All Proposed Channel Work: For all proposed channel work,
provide information
requested in next three boxes.
If design is to replicate natural channel, identify location and length here, and describe
design in Special Design section of this Part of Report.
Will 100 -year flow be contained with one foot of freeboard? Yes No If
not, identify location and explain:
Are ROW / easements sized to contain channel and required
Yes No If not, identify location(s) and explain:
maintenance space?
SECTION IX
STORMWATER DESIGN GUIDELINES
Effective February 2007
APPENDIX D - TECHNICAL DESIGN SUMMARY
Page 17 of 26 APPENDIX. D: TECH. DESIGN SUMMARY
As Revised February 2009
Part 4 — Drainage Concept and Design Parameters
Continued (Page 4.9)
Stormwater Management Concept (continued)
Within Or Serving Subject Property (Phase, or Site) (continued)
I
How many facilities for subject property project? 2 For each provide info. below.
For each dry -type facilitiy:
Faci
ity 1
Faci
ity 2
Acres served & design volume + 10%
1.22
2395ft
0.27
2472ft
100 -yr volume: free flow & plugged
2124ft
2124ft 3
2038ft
2673ft
Design discharge (10 yr & 25 yr)
7.09 cfs
8.10 cfs
0.78 cfs
1.04 cfs
Spillway crest at 100 -yr WSE?
Berms 6 inches above plugged WSE?
Explain any "no" answers:
Tanks do not have a berm but
head if the 2" and 3" orifices
X yes no
X yes no
X yes no
yes X no
will have at least
are plugged.
2' of extra
For each facility what is 25 - yr design Q, and design of outlet structure?
Facility 1: 8.10cfs, concrete weir
Facility 2: 1. 04cfs, 2" and 3" oriface
Do outlets and spillways discharge into a public facility in easement or ROW?
Facility 1: Yes X No Facility 2: Yes X No
If "no" explain:
The outlets discharge into the property which currently receives
flow from the site.
For each, what is velocity of 25 - yr design discharge at outlet? & at spillway?
Facility 1 : 2 . 6 f/s & 2 . 6 f/s Facility 2: 4 . 8 f/s & 4 . 8 f/s
Are energy dissipation measures used? No X Yes Describe type and
location: Riprap from spillways to property line.
For each, is spillway surface treatment other than concrete? Yes or no, and describe:
Facility 1: Yes, Riprap is also used
Facility 2: Yes, Riprap is also used
For each, what measures are taken to prevent erosion or scour at receiving facility?
Facility 1: Energy dissipation by riprap.
Facility 2: Energy dissipation by riprap.
If berms are used give heights, slopes and surface treatments of sides.
Facility 1: Sides of detention pond are created by retaining walls,
max heights approximately 2.5
Facility 2: N/A
SECTION IX
STORMWATER DESIGN GUIDELINES
Effective February 2007
APPENDIX D - TECHNICAL DESIGN SUMMARY
Page 18 of 26 APPENDIX. D: TECH. DESIGN SUMMARY
As Revised February 2009
Part 4 — Drainage Concept and Design Parameters
Continued (Page 4.10)
Stormwater Management Concept (continued)
Within Or Serving Subject Property (Phase, or Site) (continued)
Detention Facilities
(continued)
Do structures comply with B -CS Specifications? Yes or no, and explain if "no ":
Facility 1; No, retaining walls are utilized for the edge of the pond
Facility 2: No, Tanks for detention are not discussed.
For additional facilities provide all same information on a separate sheet.
Are parking areas to be used for detention? No X Yes What is
maximum depth due to required design storm? 3 " in parking area
Are culverts used at private crossings?
X No Yes
Roadside Ditches: Will culverts serve access driveways at roadside ditches?
No Yes If "yes ", provide information in next two boxes.
Will 25 -yr. flow pass without flowing over driveway in all cases? Yes No
Without causing flowing or standing water on public roadway? Yes No
Designs & materials comply with B -CS Technical Specifications? Yes No
Explain any "no" answers:
Are culverts parallel to public roadway alignment? Yes No Explain:
Creeks at Private Drives: Do private driveways, drives, or streets cross drainage
ways that serve Above - Project areas or are in public easements/ ROW?
No Yes If "yes" provide information below.
How many instances? Describe location and provide information below.
Location 1:
Location 2:
Location 3:
For each location enter value for:
1
2
3
Design year passing without toping travelway?
Water depth on travelway at 25 -year flow?
Water depth on travelway at 100 -year flow?
For more instances describe location and same information on separate sheet.
SECTION IX
STORMWATER DESIGN GUIDELINES
Effective February 2007
APPENDIX D - TECHNICAL DESIGN SUMMARY
Page 19 of 26 APPENDIX. D: TECH. DESIGN SUMMARY
As Revised February 2009
Part 4 — Drainage Concept and Design Parameters
Continued (Page 4.11)
Stormwater Management Concept (continued)
Within Or Serving Subject Property (Phase, or Site) (continued)
(for more instances of any type describe location and same information on separate sheet)
Named Regulatory Watercourses (& Tributaries): Are culverts
proposed on these
assumptions,
support proposed
", explain:
facilities? No Yes, then provide full
report documenting
that
If "no
criteria, analysis, computer programs, and study findings
design(s). Is report provided? Yes No
Arterial or Major Collector Streets: Will culverts
serve these
types of roadways?
For each identify the
X No Yes How many instances?
location and provide the information below.
Instance 1:
Instance 2:
Instance 3:
Yes or No for the 100 -year design flow:
1
2
3
Headwater WSE 1 foot below lowest curb top?
Spread of headwater within ROW or easement?
Is velocity limited per conditions (Table C -11)?
Explain any "no" answer(s):
Minor Collector or Local Streets: Will culverts serve
these types
for
of streets?
each identify the
X No Yes How many instances?
location and provide the information below:
Instance 1:
Instance 2:
Instance 3:
For each instance enter value, or "yes" / "no" for:
1
2
3
Design yr. headwater WSE 1 ft. below curb top?
100 -yr. max. depth at street crown 2 feet or less?
Product of velocity (fps) & depth at crown (ft) _ ?
Is velocity limited per conditions (Table C -11)?
Limit of down stream analysis (feet)?
Explain any "no" answers:
SECTION IX
APPENDIX D - TECHNICAL DESIGN SUMMARY
STORMWATER DESIGN GUIDELINES Page 20 of 26 APPENDIX. D: TECH. DESIGN SUMMARY
Effective February 2007
As Revised February 2009
Part 4 — Drainage Concept and Design Parameters
Continued (Page 4.12)
Stormwater Management Concept (continued)
Within Or Serving Subject Property (Phase, or Site) (continued)
Culverts (continued)
All Proposed Culverts: For all proposed culvert facilities (except
driveway /roadside
boxes.
ditch intersects) provide information requested in next eight
Do culverts and travelways intersect at 90 degrees? Yes No If not,
identify location(s) and intersect angle(s), and justify the design(s):
Does drainage way alignment change within or near limits of
approaches thereto? No Yes If "yes" identify location(s),
culvert and surfaced
describe
change(s), and justification:
Are flumes or conduit to discharge into culvert barrel(s)? No Yes If yes,
identify location(s) and provide justification:
Are flumes or conduit to discharge into or near surfaced approaches
No Yes If "yes" identify location(s), describe
to culvert ends?
outfall design treatment(s):
Is scour /erosion protection provided to ensure long term stability of culvert structural
components, and surfacing at culvert ends? Yes No if "no" Identify
locations and provide justification(s):
Will 100 -yr flow and spread of backwater be fully contained in
drainage easements/ ROW? Yes No if not, why
street ROW, and /or
not?
Do appreciable hydraulic effects of any culvert extend downstream
neighboring land(s) not encompassed in subject property?
"yes" describe location(s) and mitigation measures:
or upstream to
No Yes If
Are all culvert designs and materials in compliance with B -CS
Yes No If not, explain in Special Design Section
Tech. Specifications?
of this Part.
SECTION IX
STORMWATER DESIGN GUIDELINES
Effective February 2007
APPENDIX D - TECHNICAL DESIGN SUMMARY
Page 21 of 26 APPENDIX. D: TECH. DESIGN SUMMARY
As Revised February 2009
Part 4 — Drainage Concept and Design Parameters
Continued (Page 4.13)
Stormwater Management Concept (continued)
Within Or Serving Subject Property (Phase, or Site) (continued)
Bridge(s)
Is a bridge included in
If "yes" provide the following
plans for subject property project? X No Yes
information.
Name(s) and functional classification of the roadway(s)?
N/A
What drainage way(s) is to be crossed?
N/A
A full report supporting all aspects of the proposed bridge(s)
hydrologic, and hydraulic factors) must accompany this summary
provided? Yes No If "no" explain:
(structural, geotechnical,
report. Is the report
N/A
Water Quality
Is a Stormwater
Pollution Prevention
Plan (SW3P)
established for
project construction?
No X Yes
Provide a general description of planned techniques:
Silt fence, construction entrance and
inlet protection.
Special Designs — Non - Traditional Methods
Are any non - traditional methods
replication, BMPs for water quality,
No X Yes If "yes" list
(aquatic echosystems, wetland -type detention, natural stream
etc.) proposed for any aspect of subject property project?
general type and location below.
detention tanks
and catch runoff from roof and release
- Above ground water
- Behind building
at a lower rate.
Provide full report about the proposed
expected benefits. Report must
be compromised, and that maintenance
solution(s). Is report provided?
The above - ground tanks
They take advantage of
detention area on site.
lower than traditional
special design(s) including rationale
substantiate that stormwater management
cost will not exceed those of
Yes X No If "no" explain:
for use and
objectives will not
traditional design
detention ponds.
to minimize
be the same or
funtion the same as the surface
the height of the building
The maintenance cost should
detention designs.
SECTION IX
STORMWATER DESIGN GUIDELINES
Effective February 2007
APPENDIX D - TECHNICAL DESIGN SUMMARY
Page 22 of 26 APPENDIX. D: TECH. DESIGN SUMMARY
As Revised February 2009
Part 4 — Drainage Concept and Design Parameters
Continued (Page 4.14)
Stormwater Management Concept (continued)
Within Or Serving Subject Property (Phase, or Site) (continued)
Special Designs — Deviation From B -CS Technical Specifications
If any design(s) or material(s) of traditional runoff - handling facilities deviate
B -CS Technical Specifications, check type facility(ies) and explain by
X Detention elements Drain system elements
from provisions of
specific detail element.
Channel features
Inlets Outfalls
Culvert features Swales Ditches
Valley gutters Bridges (explain in bridge report)
In table below briefly identify specific element, justification for deviation(s).
Specific Detail Element
Justification for Deviation (attach additional sheets if needed)
1) Detention
Tanks
Limited space for detention
2) Retaining walls for
edge of surface
detention
Limited space for detention.
3)
4)
5)
Have elements been coordinated with the City Engineer or her /his designee? For each item
above provide "yes" or "no ", action date, and staff name:
1) No
2)
3)
4)
5)
Design Parameters
Hydrology
Is a map(s) showing all Design Drainage Areas provided? X Yes No
Briefly summarize the range of applications made of the Rational Formula:
Rational Formula not used.
Calculations in accordance with USDA TR -55
What is the size and location of largest
has been applied? N/A acres
Design Drainage Area to which the Rational Formula
Location (or identifier):
SECTION IX
STORMWATER DESIGN GUIDELINES
Effective February 2007
APPENDIX D - TECHNICAL DESIGN SUMMARY
Page 23 of 26 APPENDIX. D: TECH. DESIGN SUMMARY
As Revised February 2009
Part 4 — Drainage Concept and Design Parameters
Continued (Page 4.15)
Design Parameters (continued)
Hydrology (continued)
In making determinations for time of concentration, was segment analysis used?
No X Yes In approximately what percent of Design Drainage Areas? 100 cio
As to intensity- duration- frequency and rain depth criteria for determining runoff flows, were any
criteria other than those provided in these Guidelines used? X No Yes If "yes"
identify type of data, source(s), and where applied:
For each of the stormwater management features listed below identify the storm return
frequencies (year) analyzed (or checked), and that used as the basis for design.
Feature
Analysis Year(s)
Design Year
Storm drain system for arterial and collector streets
N/A
N/A
Storm drain system for local streets
N/A
N/A
Open channels
N/A
N/A
Swale /buried conduit combination in lieu of channel
N/A
N/A
Swales
N/A
N/A
Roadside ditches and culverts serving them
N/A
N/A
Detention facilities: spillway crest and its outfall
2, 10 , 2 5 , 5 0 , 10 0
100
Detention facilities: outlet and conveyance structure(s)
2, 10 , 2 5 , 5 0 , 10 0
100
Detention facilities: volume when outlet plugged
2, 12 4 f t
2, 6 7 3 f t
Culverts serving private drives or streets
N/A
N/A
Culverts serving public roadways
N/A
N/A
Bridges: provide in bridge report.
N/A
N/A
Hydraulics
What is the range of design flow velocities as outlined below?
Design flow velocities;
Gutters
Conduit
Culverts
Swales
Channels
Highest (feet per second)
N/A
N/A
N/A
N/A
N/A
Lowest (feet per second)
N/A
N/A
N/A
N/A
N/A
Streets and Storm Drain Systems Provide the summary information outlined below:
Roughness coefficients used: For street gutters: N/A
For conduit type(s) N / A Coefficients:
SECTION IX
APPENDIX D - TECHNICAL DESIGN SUMMARY
STORMWATER DESIGN GUIDELINES Page 24 of 26 APPENDIX. D: TECH. DESIGN SUMMARY
Effective February 2007
As Revised February 2009
Part 4 — Drainage Concept and Design Parameters
Continued (Page 4.16)
Design Parameters (continued)
Hydraulics (continued)
Street and Storm Drain Systems (continued)
For the following, are assumptions other than allowable per Guidelines?
Inlet coefficients? X No Yes Head and friction losses X No Yes
Explain any "yes" answer:
In conduit is velocity generally increased in the downstream direction?
Are elevation drops provided at inlets, manholes, and junction boxes?
Explain any "no" answers:
N/A Yes
No
N/A Yes
No
Are hydraulic grade lines calculated and shown for design storm? N/A Yes No
For 100 -year flow conditions? N/A Yes No Explain any "no"
answers:
What tailwater conditions were assumed at outfall point(s) of the storm drain system?
each location and explain:
N/A
Identify
Open Channels If a HEC analysis is utilized, does it follow Sec VI.F.5.a?
N/A Yes
No
Outside of straight sections, is flow regime within limits of sub - critical
If "no" list locations and explain:
N/A
flow? Yes
No
Culverts If plan sheets do not provide the following for each culvert, describe it here.
For each design discharge, will operation be outlet (barrel) control or inlet control?
N/A
Entrance, friction and exit losses:
N/A
Bridges Provide all in bridge report
SECTION IX
STORMWATER DESIGN GUIDELINES
Effective February 2007
APPENDIX D - TECHNICAL DESIGN SUMMARY
Page 25 of 26 APPENDIX. D: TECH. DESIGN SUMMARY
As Revised February 2009
Part 4 — Drainage Concept and Design Parameters
Continued (Page 4.17)
Design Parameters (continued)
Computer Software
What computer software has been used in the analysis and assessment of stormwater
management needs and /or the development of facility designs proposed for subject property
project? List them below, being sure to identify the software name and version, the date of the
version, any applicable patches and the publisher
HEC -HMS 3.5
U.S. Army Corps of Engineers
Part 5 — Plans and Specifications
Requirements for submittal of construction drawings and specifications do not differ due to use of a
Technical Design Summary Report. See Section III, Paragraph C3.
Part 6 — Conclusions and Attestation
Conclusions
Add any concluding information here:
Based on engineering analysis, there will be no increase in
flow from the peak pre- developed levels for the 2,10,25,50
and 100 year storms.
Attestation
Provide attestation to the accuracy and completeness of the foregoing 6 Parts of this Technical
Design Summary Drainage Report by signing and sealing below.
"This report (plan) for the drainage design of the development named in
by me (or under my supervision) in accordance with provisions of the
Unified Drainage Design Guidelines for the owners of the property. All
required by any and all state and federal regulatory agencies ``
improvements have been issued or fall under applicable ge
Part B was prepared
Bryan /College Station
licenses and permits
he proposed drainage
1 4%
THOMAS
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Licensed Professional Engineer % MELISSA P.
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State of Texas PE No.
SECTION IX
APPENDIX D - TECHNICAL DESIGN SUMMARY
STORMWATER DESIGN GUIDELINES
Effective February 2007
Page 26 of 26 APPENDIX. D: TECH. DESIGN SUMMARY
As Revised February 2009