Loading...
HomeMy WebLinkAboutStorm Water Report Gessner Engineering • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • Storm Water Drainage Study • The Hillel at Texas A &M University • College Station, Texas • • • • jd•a� • q. J5 .10 • iotov • 0 Gessner Engineering • • • 2 • • • • September 13, 2010 • • Mr. Josh Norton • City of College Station Planning Services 1101 Texas Avenue • College Station, TX 77842 • • Re: Storm Water Drainage Study • The Hillel at Texas A &M University College Station, Texas • Gessner Engineering Job No.: 10 -0407 • • Dear Mr. Norton: • This report conveys the results of the storm water drainage study conducted by Gessner • Engineering for the proposed Hillel at Texas A &M University 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 • • "rye • ,, .... _s ir • Melissa P. Thomas, P.E. # 1 ..* 2 • MELISSA P. THOMAS • `, /2'v` p • 98388 • Morgan S. Lund, P.E. 1 ��88 A • L • •• O ' • % Gessner �e • 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 • N: \Gessner Eng Data 10 \10 -0407 Hillel Foundation \Civil\DOC \10 -0407 Drainage Report- NRCS.doc 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 September 15, 2010 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 Hillel at Texas A &M University, at 800 George Bush Drive, • College Station, Texas 77840. • The proposed project consists of the re- development of an approximately 0.928 acre site. • The site currently includes the existing Hillel student center with accompanying gravel • parking. Proposed improvements include an approximately 11,075 square foot building to • be used as a student center and passenger car parking. • The site is located at the southeast corner of the intersection of George Bush Drive and • Dexter at 800 George Bush Drive in College Station, Texas. It is located in the upper third • of the Bee Creek watershed. The site is not located in the FEMA 100 year flood plain, • according to FIRM number48041C0144C. • The proposed site development provides for storm runoff to sheet flow off of the proposed • parking and building areas south onto Aberdeen and west onto Dexter. Runoff to • Aberdeen flows west to Dexter, then flows south to inlets that are connected to the City of College Station storm system. • • 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. • This drainage report includes discussion of hydraulic analysis with appendices including • drainage area maps and calculations, StormNET reports, and Technical Design Summary. • • Introduction • This storm water drainage report is intended to show the change in runoff from the existing • conditions to the proposed conditions for the Hillel at Texas A &M University. The general • flow of the site is depicted by directional flow areas on sheet C -05 of the Hillel at Texas • A &M University engineering plans which are attached as Appendix A. • 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 11,075 square foot building with parking for passenger cars. Curve numbers from TR -55 were used based on post- • developed uses as described above. Pre - developed flows were calculated based on the • existing improvements on the subject tract. The calculated pre - developed and post- • developed flows include the one - hundred (100) year storms in accordance with the Bryan • College Station Unified Stormwater Design Guidelines. • • N: \Gessner Eng Data 10 \10 -0407 Hillel Foundation \Civil\DOC \10 -0407 Drainage Report- NRCS.doc • 0 Gessner Engineering • • • • • 4 • • • Calculations • • Calculations were performed according to the USDA TR -55 and with the aid of StormNET • 4.18.2 by Boss International, Inc. of Madison, Wisconsin. The output data from StormNET • has been provided as Appendix C and D. • 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: • _ 0.007 x 8 (nL) ° ' • t f 50.4 Vp • 2 • Where: • tt = travel time (hours) • n = manning's roughness coefficient • L = flow length (feet) S = slope (ft/ft) • P2 = 2 -year, 24 hour rainfall (inches) • 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. • • The computed times of concentration for each drainage area are included on sheet C -05. • 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. • • 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 pulled from Table C -6 in the Unified Stormwater • • N: \Gessner Eng Data 10 \10 -0407 Hillel Foundation \Civil\DOC \10 -0407 Drainage Report- NRCS.doc • 0 Gessner Engineering • • • • • 5 • • Design Guidelines. Curve Number values (CN) were determined from Table C -7, Appendix • C of the Unified Stormwater Design Guidelines. Peak pre - developed flow for the subject • site are also included in Table One. These values are based on a combined hydrograph • for the flow from each drainage area. Drainage areas and calculations are included on • sheet C -05, attached as Appendix A. • Rainfall Depth (in), Pre - Developed Peak • Frequency 24 -hr duration Flow (cfs) 100 years 11.00 7.54 • Table One: Rainfall Depths and Resulting Flows • The post - developed flows were analyzed based on the drainage areas shown on the • attached sheet C -05. The resulting flow based on the increased curve numbers at the site • is shown in Table Two below. The increase from the pre - developed flow is also included. • • Storm Event Pre - Developed Post - Developed Flow Flow Increase (cfs) Peak Flow (cfs) (cfs) • 100 year 7.54 7.79 0.25 • Table Two: Pre - Developed and Post - Developed Site Outflows • Conclusion • • Based on visual evidence, engineering drainage calculations and sound engineering • judgment, Gessner Engineering believes that the increase from the pre - developed flow to the post - development flows is minimal for the one hundred (100) year design storms for • this site. • • Based on Section II.3.b(3) of the BCS unified stormwater design guide, detention is not required for this "small lot ", defined as "equal or less than one (1) acre for commercial use." • Additionally, the minimal increase in flow of 0.25 cfs will not have an impact on down • stream conditions. • "I have conducted a topographic review and field investigation of the existing and proposed • flow patterns for stormwater runoff from The Hillel at Texas A &M site to the main stem of • Bee Creek. At build -out conditions allowable by zoning, restrictive covenant, or plat note, • the stormwater flows from the subject subdivision or site project will not cause any increase • in flooding conditions to the interior of existing building structures, including basement areas, for storms of magnitude up through the 100 -year event." • • • • • • • • N: \Lessner Eng Data 10\ 10-0407 Hillel Foundation \Civil\DOC \10 -0407 Drainage Report- NRCS.doc • 0 Gessner Engineering • • • • • 6 • • • • • • • • • • • • APPENDIX A: • • Drainage Area Maps and Calculations • (Sheet C -05) • • • • • • • • • • • • • • • • • • • • • • • N: \Lessner Eng Data 10\10 -0407 Hillel Foundation \Civil\DOC \10 -0407 Drainage Report - NRCS.doc • 0 Gessner Engineering • • z z Sv'X31 `NOILVIS 3031100 0 . - ' ^ a3 �h� A:, O CL v 3 AIN0 NSf 9 301030 008 Lu A Ld 0 W ;.v s , O a w Q " E; W o � 31N3 a 1N3al1S 1311IH V V SVX31 w `{' d o �l 1ISa3AINf1 W'8d S`dX311`d B11IH 3H1 s € - D c. 1 § � .. E9 g<E Q U o u)< a oa r2.= 8 1.. 0E 1 = LL a). � _ n o z LL Ice- _ = i ! : :: ° N f Z j W y K N o o cgamw f2 m W 2 ° ? D rill m a o E a w p O w o Z o w 8 > n Z a z a y a a �y 8 a a - -'+' o ° Z E K W 1 p yo F 1 0 wN 3 °�= I O I j � a g Q �c� re LL < m W UU W i (O ° g 2 (7 K y f LL N Y W S a s I F LL m ¢ pi i S ` x Fa U �$1 IL ° N 84 a 4 O g4 al n PE i i LL s k IEEI 1I ISWI" GI fi s a'° INEZ; a1 18E" d� ' W c� � 3 1 O g g 0 w z° w 8 9f iS „ al ; 1 ; 1 o iS ° a S 9 w 8 w 8 1 1 9z La. 3 & u z C � Cy N m 3 w m W F 5 ffi 0 O a 2 y1 yl 2 13� Z U ' �1 a 3 8 R 1 i 1 'g E 8 5 C F n 8 a y 52 5 5 F `a laaR g - (i @ E E M i e 6 Z O 8 SS� n 1 cc�� ° ° < i Q¢ 0 0 U ° <'P Q __.__ _ ____ S __ A311V 0 11end _ -- A 3l1V mend 0058... la '£,£t.Lt s - - - ' 005F!_. ,. SI , dr S � --- -_ ._.. ��tt �.,. - \`.337 -_� / /' ' �i -z - - - - - -- "�. _...` - -. . _._. • -_- / 1 \ `AAA 335 U ..,, i / � �� ,. 3 36' �/ ,■ . 1 �� ' 1 m 8 � I Al o< g J / n ' 3 / � ____-33 __33 y I J °d l i / ',''' . _►�. - J` - - - ,00 WI - M — fIL* N - - �► - _ � . _ 00�5f! - .O£,£t.L* N / 1 / \\I- 3 34 --'/ i L . . // I\ f 00 N ° __ ° O Jo I ' y j r- 1 a w 2 �1 S cd Q II Q AI c. � ,00 O£,B.Lt N ruyP 'p' Air oo SL?L . O££t.Lt N : � ' � 2 I v 1 'I Q i r °�.� ! — ,334 I r /: 5 Z aw w� 0 w = L 2 Q fI • 0 , , r^ / o , C yy cw7� ' 4 �\ 1 I a 0 m w ¢3 w /�3 w �Q a g N.' u� Q p g J � $ Q2> X 30 ` Z _ � g a s ` J E d O I. 0 O '-- i 34'44£1 / x C1 / , 1 I w I p o \ 005£[ - O ,f>.Lt N I I I I :::::: SF � a „ , n � \ I fi // / ,I :\ r � � Q , I I ��//�} I w • I I Im n \ '" a i 8 / " a ` 1 (t - ZIT � � _ - / � I I ''- _ / 3 35 .. = �J1'a/ z - ,__ - - - - -rir - _ _ _ ___,IS if ,?...,,, \ I ti -__ / 1' if ' PPE' A 3O spell f • /__/ - -- OFF. - - - -� / /� or, , i / � i �� - _ gip 1 / I 1 ZO9'Od'SE'1OA / -, I ' ZO9'Od'9E'10A 1WAd'HdSV a- - _329 - - -/ 1WAd'HdSVdZ- , ' \ �- S318VAH1aIM MOa S31aVAH1aIM MOa - -, 7110 2131x30 ao a31x3o • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 7 • • • • • • • • • • • • APPENDIX B: • • Hydrographs • • • • • • • • • • • • • • • • • • • • • • • • N: \Gessner Eng Data 10 \10 -0407 Hillel Foundation \Civil \DOC■10 -0407 Drainage Report - NRCS.doc • 0 Gessner Engineering • • • • • 8 • • • • • • • • • • • • APPENDIX C: • StormNET Calculations • (Existing Conditions) • • • • • • • • • • • • • • • • • • • • • • • • N: \Gessner Eng Data 10 \10 -0407 Hillel Foundation \Civil\DOC \I0 -0407 Drainage Report- NRCS,doc • 0 Gessner Engineering • • • • • • • • • • • • • • • • • • • • • • PRE- DEVELOPED • • • • • • • • • • • • • • • • • • • • • • • • • • • • • BOSS International StormNET© - Version 4.11.0 (Build 13753) Analysis Options Flow Units cfs Subbasin Hydrograph Method SCS TR -55 • Time of Concentration SCS TR -55 Link Routing Method Kinematic Wave • Pond Exfiltration None Starting Date SEP -09 -2010 00:00:00 • Ending Date SEP-10-2010 00:00:00 Report Time Step 00:05:00 • • Element Count • Number of rain gages 1 Number of subbasins 2 • Number of nodes 4 Number of links 3 • • Raingage Summary • Gage Data Data Interval ID Source Type hours • 100YR -Gage TS -1 CUMULATIVE 0.10 • • Subbasin Summary • Subbasin Total Area • ID acres PRE AREA 1 0.27 • PRE AREA 2 0.66 • * * * * * * « «« + • Node Summary • Node Element Type Invert Maximum Ponded External ID Elevation Elev. Area Inflow ft ft ft' • Jun -1 JUNCTION 0.00 0.00 0.00 • Jun -2 JUNCTION 0.00 0.00 0.00 Jun -3 JUNCTION 0.00 0.00 0.00 • Out -1 OUTFALL 0.00 0.00 0.00 • *** * * * * * * * ** Link Summary Link From Node To Node Element Length Slope Manning's • ID Type ft 6 Roughness • Con -1 Con -2 Jun -2 Jun -3 CONDUIT 1.0 0.1000 0.0100 Jun -1 Jun -3 CONDUIT 1.0 0.1000 0.0320 • Con -3 Jun -3 Out -1 CONDUIT 1.0 0.1000 0.0150 Cross Section Summary Link Shape Depth/ Width No. of Cross Full Flow Design • ID Diameter Barrels Sectional Area Hydraulic Flow Capacity city ft ft ft* ft cfs • Con -1 DUMMY 0.00 0.00 1 0.00 0.00 0.00 • Con -2 DUMMY 0.00 0.00 1 0.00 0.00 0.00 • • 411 All • • • • Con -3 DUMMY 0.00 0.00 1 0.00 0.00 0.00 • • * * * * * * * * * * * * * * * * ** * * * * * * ** Volume Depth Runoff Quantity Continuity acre -ft inches • Total * P * * * * * ** recipitation 0.866 11.170 Surface Runoff 0.073 0.032 • Continuity Error ( %) 0.000 • * * * * * * * * * * * * * * * * * * * * * * * * ** Volume Volume • * *ow * Routing * Copt * * * * * * ** acre -ft Mgallons * • External Inflow 0.000 0.000 External Outflow 0.735 0.240 Initial Stored Volume 0.000 0.000 • Final Stored Volume 0.000 0.000 Continuity Error ( %) -0.002 • Composite Curve Number Computations Report • *********** * * * * * * * * * * * * * * * * * * * * * * * * * * * * * ** • Subbasin PRE AREA 1 • Area Soil Soil /Surface Description Area Group CN • - 0.27 - 89.81 • Composite Area & Weighted CN 0.27 89.81 • Subbasin PRE AREA 2 • Area Soil Soil /Surface Description Area Group CN • - 0.66 - 87.70 • Composite Area & Weighted CN 0.66 87.70 SCS TR -55 Time of Concentration Computations Report • Sheet Flow Equation Tc = (0.007 * ((n * Lf)^0.8)) / ((P "0.5) * (Sf "0.4)) • Where: • Tc = Time of Concentration (hrs) n = Manning's Roughness 411 Lf = Flow Length (ft) P = 2 yr, 24 hr Rainfall (inches) Sf = Slope (ft /ft) • Shallow Concentrated Flow Equation • • V = 16.1345 * (Sf^0.5) (unpaved surface) V = 20.3282 * (Sf ^0.5) (paved surface) • Tc = (Lf / V) / (3600 sec /hr) Where: • Tc = Time of Concentration (hrs) • Lf = Flow Length (ft) V = Velocity (ft /sec) • Sf = Slope (ft /ft) • Channel Flow Equation V = (1.49 * (R ^(2/3)) * (Sf "0.5)) / n R = Aq / Wp . Tc = (Lf / V) / (3600 sec /hr) • • • f • • • • Where: • Tc = Time of Concentration (hrs) Lf = Flow Length (ft) • R = Hydraulic Radius (ft) Aq = Flow Area (ft') . Wp = Wetted Perimeter (ft) V = Velocity (ft /sec) Sf = Slope (ft /ft) • n = Manning's Roughness • Subbasin PRE AREA 1 • • Sheet Flow Computations li Subarea A Subarea B Subarea C • Manning's Roughness: 0.30 0.00 0.00 Flow Length (ft): 50.00 0.00 0.00 • Slope ( %): 2.00 0.00 0.00 2 yr, 24 hr Rainfall (in): 4.50 4.50 4.50 . Velocity (ft /sec): 0.10 0.00 0.00 Computed Flow Time (minutes): 8.26 0.00 0.00 • Shallow Concentrated Flow Computations • Subarea A Subarea B Subarea C Flow Length (ft): 130.00 0.00 0.00 • Slope ( %): 2.00 0.00 0.00 Surface Type: Unpaved Unpaved Unpaved . Velocity (ft /sec): 2.28 0.00 0.00 Computed Flow Time (minutes): 0.95 0.00 0.00 • Total TOC (minutes): 10.00 • • Subbasin PRE AREA 2 • • Sheet Flow Computations Subarea A Subarea B Subarea C • Manning's Roughness: 0.30 0.00 0.00 Flow Length (ft): 75.00 0.00 0.00 • Slope ( %): 4.00 0.00 0.00 2 yr, 24 hr Rainfall (in): 4.50 4.50 4.50 Velocity (ft /sec): 0.14 0.00 0.00 • Computed Flow Time (minutes): 8.66 0.00 0.00 • Shallow Concentrated Flow Computations • Subarea A Subarea B Subarea C Flow Length (ft): 265.00 0.00 0.00 • Slope (%): 0.00 0.00 Surface Type: Unpaved Unpaved Unpaved Velocity (ft /sec): 2.22 0.00 0.00 • Computed Flow Time (minutes): 1.99 0.00 0.00 • Total TOC (minutes): 10.65 • Subbasin Runoff Summary • • Subbasin Total Total Peak Weighted Time of ID Precip Runoff Runoff Curve Concentration • in in cfs Number days hh:mm:ss PRE AREA 1 11.000 9.746 2.290 89.810 0 00:10:00 • PRE AREA 2 11.000 9.479 5.470 87.700 0 00:10:38 • Averages / Totals 11.000 9.557 7.60 • • • • r 411 • • * * * * * * * * * * * * * * * * ** • Node Depth Summary * * * * * * * * * * * * * * * * ** • • Node Average Maximum Maximum Time of Max Maximum Total. Retention ID Depth Depth HGL Occurrence Ponded Time Time • Attained Attained Attained Volume Flooded ft ft ft days hh:mm acre -in minutes hh:mm:ss 411 Jun -1 0.00 0.00 0.00 0 00:00 0 0 0:00:00 Jun -2 0.00 0.00 0.00 0 00:00 0 0 0:00:00 411 Jun -3 0.00 0.00 0.00 0 00:00 0 0 0:00:00 Out -1 0.00 0.00 0.00 0 00:00 0 0 0:00:00 • * * * * * * * * * * * * * * * ** • Node Flow Summary * * * * * * * * * * * * * * * ** • • Node Element Maximum Maximum Time of Maximum Time of Peak ID Type Lateral Total Peak Inflow Flooding Flooding • Inflow Inflow Occurrence Overflow Occurrence cfs cfs days hh:mm cfs days hh:mm • Jun -1 JUNCTION 2.22 2.21 0 12:05 0.00 Jun -2 JUNCTION 5.47 5.40 0 12:09 0.00 • Jun -3 JUNCTION 0.00 7.54 0 12:09 0.00 Out -1 DUTFALL 0.00 7.54 0 12:09 0.00 • Outfall Loading Summary * * * * * * * * * * * * * * * * * * * * * ** • • Outfall Node ID Flow Average Maximum Frequency Flow Flow 411 (6) cfs cfs • Out -1 89.62 0.41 7.54 System 89.62 0.41 7.54 • Link Flow Summary • * * * * * * * * * * * * * * * ** Link ID Element Time of Maximum Length Peak Flow Design Ratio of Ratio of • Total Type Peak Flow Velocity Factor during Flow Maximum Maximum • Time Occurrence Attained Analysis Capacity /Design Flow • Surcharged days hh:mm ft /sec cfs cfs Flow Depth 1 • Minutes • Con -1 DIRECT 0 12:09 5.40 Con -2 DIRECT 0 12:05 2.21 • Con -3 DIRECT 0 12:09 7.54 • * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * ** Highest Flow Instability Indexes All links are stable. • • Analysis begun on: Thu Sep 09 10:48:59 2010 Analysis ended on: Thu Sep 09 10:49:00 2010 • Total elapsed time: 00:00:01 • • • • • • i • • • 9 • • • • • • • • • • • • APPENDIX D: • StormNET Calculations • (Developed Conditions) • • • • • • • • • • • • • • • • • • • • • • • • N: \Gessner Eng Data 10 \10 -0407 Hillel Foundation \Civil\DOC \10 -0407 Drainage Report- NRCS.doe • 0 Gessner Engineering • • • • • • • • • • • • I • • • • • • • • POST - DEVELOPED • • • • • • • • • • • • • • • • • • • • • • • • $ BOSS International StormNET® - Version 4.11.0 (Build 13753) * * * * * * * * * * * * * * ** Analysis Options Flow Units cfs 1 Subbasin Hydrograph Method SCS TR -55 Time of Concentration SCS TR -55 Link Routing Method Kinematic Wave • Pond Exfiltration None Starting Date SEP -09 -2010 00:00:00 . Ending Date SEP -10 -2010 00:00:00 Report Time Step 00:05:00 • • E *emen * * *o *n* • Number of rain gages 1 Number of subbasins 2 • Number of nodes 4 Number of links 3 • Raingage Summary * * * * * * * * * * * * * * ** • Gage Data Data Interval ID Source Type hours i 100 YR Gage TS -1 CUMULATIVE 0.10 • * * * * * * * * * * * * * * ** Subbasin Summary * * * * * * * * * * * ** • Subbasin Total Area ID acres Al - POST 0.28 • A2 - POST 0.65 • * * * * * * * * * * ** Node Summary * * * * * * * * * * ** Node Element Invert Maximum Ponded External • ID Type Elevation Elev. Area Inflow ft ft ft' • Jun -1 JUNCTION 0.00 0.00 0.00 • Jun -2 JUNCTION 0.00 0.00 0.00 Jun -3 JUNCTION 0.00 0.00 0.00 • Out -1 OUTFALL 0.00 0.00 0.00 • * * * * * * * * * * ** Link Summary • Link From Node To Node Element Length Slope Manning's ID Type ft 8 Roughness Con -1 Jun -2 Jun -3 CONDUIT 8151.0 0.0000 0.0150 • Con -2 Jun -1 Jun -3 CONDUIT 3561.5 0.0000 0.0150 Con -3 Jun -3 Out -1 CONDUIT 466.2 0.0002 0.0150 • • * * Cross Section Summary Link Shape Depth/ Width No. of Cross Full Flow Design ID Diameter Barrels Sectional Hydraulic Flow Area Radius Capacity ft ft ft* It cfs • Con -1 DUMMY 0.00 0.00 1 0.00 0.00 0.00 • Con -2 DUMMY 0.00 0.00 1 0.00 0.00 0.00 411 • • 1 111 Con - 3 DUMMY 0.00 0.00 1 0.00 0.00 0.00 • • * * * * * * * * * * * * * * * * * * * * * * * * ** Volume Depth Runoff Quantity Continuity acre -ft inches Total Precipitation 0.866 11.170 • Surface Runoff 0.081 0.035 Continuity Error (8) 0.000 • * * * * * * * * * * * * * * * * * * * * * * * *** Volume Volume • Flow Routing Continuity acre ft Mgallons * * * * * * * * * * * * * * * * * * * ** • External Inflow 0.000 0.000 External Outflow 0.809 0.264 Initial Stored Volume 0.000 0.000 • Final Stored Volume 0.000 0.000 Continuity Error (8) - 0.001 • Composite Curve Number Computations Report • *********** * * * * * * * * * * * * * * * * * * * * * * * * * * * * * ** • Subbasin Al - POST • Area Soil Soil /Surface Description (acres) Group CN • - 0.28 - 93.42 • Composite Area & Weighted CN 0.28 93.42 • Subbasin A2 - POST • Area Soil Soil /Surface Description (acres) Group CN • - 0.65 - 95.45 • Composite Area & Weighted CN 0.65 95.45 SCS TR -55 Time of Concentration Computations Report • ******************** * * * * * * * * * * * * * * * * * * * * * * * * * * * * * ** • Sheet Flow Equation • Tc = (0.007 * ((n * Lf) ^0.8)) / ((P 1 0.5) * (Sf ^0.4)) • Where: • Tc = Time of Concentration (hrs) n - Manning's Roughness • Lf - Flow Length (ft) P = 2 yr, 24 hr Rainfall (inches) • Sf = Slope (ft /ft) Shallow Concentrated Flow Equation • • V = 16.1345 * (Sf ^0.5) (unpaved surface) V = 20.3282 * (Sf ^0.5) (paved surface) • Tc = (Lf / V) / (3600 sec /hr) Where: • Tc = Time of Concentration (hrs) • Lf = Flow Length (ft) V = Velocity (ft /sec) • Sf = Slope (ft /ft) • Channel Flow Equation • V - (1.49 * (R ^(2/3)) * (Sf ^0.5)) / n R = Aq / Wp • Tc = (Lf / V) / (3600 sec /hr) • • • All • Where: • Tc = Time of Concentration (hrs) Lf = Flow Length (ft) • R = Hydraulic Radius (ft) Ag = Flow Area (ft *) 411 Wp = Wetted Perimeter (ft) V = Velocity (ft /sec) Sf = Slope (ft /ft) • n = Manning's Roughness • Subbasin Al - POST • • Sheet Flow Computations Subarea A Subarea B Subarea C • Manning's Roughness: 0.40 0.00 0.00 Flow Length (ft): 50.00 0.00 0.00 • Slope (8): 3.50 0.00 0.00 2 yr, 24 hr Rainfall (in): 4.50 4.50 4.50 • Velocity (ft /sec): 0.10 0.00 0.00 Computed Flow Time (minutes): 8.31 0.00 0.00 • Shallow Concentrated Flow Computations • Subarea A Subarea B Subarea C Flow Length (ft): 250.00 0.00 0.00 • Slope (8): 2.30 0.00 0.00 Surface Type: Paved Unpaved Unpaved • Velocity (ft /sec): 3.08 0.00 0.00 Computed Flow Time (minutes): 1.35 0.00 0.00 • Total TOC (minutes): 10.00 • • Subbasin A2 - POST • Shallow Concentrated Flow Computations • Subarea A Subarea B Subarea C • Flow Length (ft): 368.00 0.00 0.00 Slope (8): 2.00 0.00 0.00 • Surface Type: Paved Unpaved Unpaved Velocity (ft /sec): 2.87 0.00 0.00 • Computed Flow Time (minutes): 2.13 0.00 0.00 Total TOC (minutes): 10.00 • • * * * * * * * * * * * * * * * * * * * * * ** • S *bbas *n * R * *f * S *mma *y • Subbasin Total Total Peak Weighted Time of • ID Precip Runoff Runoff Curve Concentration in in cfs Number days hh:mm:ss • Al - POST 11.000 10.197 2.440 93.420 0 00:10:00 411 A2 - POST 11.000 10.448 5.700 95.450 0 00:10:00 Averages / Totals 11.000 10.372 8.14 • Node Depth Summary is * * * * * * * * * * * * * * * * ** • Node Average Maximum Maximum Time of Max Maximum Total Retention ID Depth Depth HGL Occurrence Ponded Time Time • Attained Attained Attained Volume Flooded ft ft ft days hh:mm acre -in minutes hh:mm:ss • • • • • • • • Jun -1 0.00 0.00 0.00 0 00:00 0 0 0:00:00 • Jun -2 0.00 0.00 0.00 0 00:00 0 0 0:00:00 Jun -3 0.00 0.00 0.00 0 00:00 0 0 0:00:00 • Out -1 0.00 0.00 0.00 0 00:00 0 0 0:00:00 • .. * **.** * * * ** * * ** • Node * Flow * Summary • Node Element Maximum Maximum Time of Maximum Time of Peak • ID Type Lateral Total Peak Inflow Flooding Flooding Inflow Inflow Occurrence Overflow Occurrence • cfs cfs days hh:mm cfs days hh:mm Jun -1 JUNCTION 2.44 2.34 0 12:13 0.00 • Jun -2 JUNCTION 5.70 5.45 0 12:13 0.00 Jun -3 JUNCTION 0.00 7.79 0 12:13 0.00 • Out -1 OUTFALL 0.00 7.79 0 12:13 0.00 • Outfall Loading Summary • Outfall Node ID Flow Average Maximum • Frequency Flow Flow ( %) cfs cfs • Out -1 95.38 0.43 7.79 • System 95.38 0.43 7.79 • • L * Link Flow Summary • • Link ID Element Time of Maximum Length Peak Flow Design Ratio of Ratio of Total • Type Peak Flow Velocity Factor during Flow Maximum Maximum Time • Occurrence Attained Analysis Capacity /Design Flow Surcharged • days hh:mm ft /sec cfs cfs Flow Depth Minutes Con -1 DIRECT 0 12:13 5.45 • Con -2 DIRECT 0 12:13 2.34 Con -3 DIRECT 0 12:13 7.79 • * Highest * Instability • Indexes • All links are stable. • Analysis begun on: Thu Sep 09 11:45:19 2010 • Analysis ended on: Thu Sep 09 11:45:20 2010 Total elapsed time: 00:00:01 • • • • • • • • • • ■ • • • • 10 • • • • • • • • • • • • APPENDIX E: • Technical Design Summary • • • • • • • • • • • • • • • • • • • • • • • • • N: \Gessner Eng Data 10 \I0 -0407 Hillel Foundation \Civil \DOC \10 -0407 Drainage Report- NRCS.doc • 0 Gessner Engineering • ,• • • • • SECTION IX • APPENDIX D - TECHNICAL DESIGN SUMMARY • Part 2 — Project Administration Start (Page 2.1) ID Engineering and Design Professionals Information • Engineering Firm Name and Address: Jurisdiction • Gessner Engineering City: Bryan 2501 Ashford Drive Suite 102 X College Station • College Station, TX 77840 Date of Submittal: 9 /15/10 • Lead Engineer's Name and Contact Info.(phone, e-mail, fax): Other: • Melissa P. Thomas, P.E. • mthomas @gessnerengineering.com • Supporting Engineering / Consulting Firm(s): Other contacts: • Developer / Owner / Applicant Information • Developer / Applicant Name and Address: Phone and e-mail: The Hillel at Texas A &M University 979- 696 -7313 • 800 George Bush Drive hillel@tamuhillel.org • College Station, TX 77840 Property Owner(s) if not Developer / Applicant (& address): Phone and e-mail: • • Project Identification • • Development Name: Texas A &M Hillel Student Center 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) • Lots 1 -4, Block 20, College Park • • • 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. • N/A • • General Location of Project Area, or subject property (phase): • 800 George Bush Drive, College Station, TX 77840 • • In City Limits? Extraterritorial Jurisdiction (acreage): • Bryan: 0 acres. Bryan: 0 College Station: 0 • College Station: 0 . 928 acres. Acreage Outside ETJ: 0 • STORMWATER DESIGN GUIDELINES Page 3 of 26 APPENDIX. D: TECH. DESIGN SUMMARY • Effective February 2007 As Revised February 2009 • • • • • • SECTION IX • APPENDIX D - TECHNICAL DESIGN SUMMARY • Part 2 — Project Administration Continued (page 2.2) • Project Identification (continued) • Roadways abutting or within Project Area or Abutting tracts, platted land, or built • subject property: developments: • George Bush Drive South: Protestant Episcopal Dexter Drive East: St. Thomas Episcopal • Aberdeen Place • Named Regulatory Watercourse(s) & Watershed(s): Tributary Basin(s): • Bee Creek Watershed Lick Creek Watershed • Plat Information For Project or Subject Property (or Phase) • Preliminary Plat File #: Final Plat File #: Date: • Name: Status and Vol /Pg: Vol 38, Pg 602 • If two plats, second name: File #: • Status: Date: • Zoning Information For Project or Subject Property (or Phase) • Zoning Type: R1 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: • Preapplication Conference City of College Station • July 16, 2008 Slattery Tackett Architects • • 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 • • • • • • • STORMWATER DESIGN GUIDELINES Page 4 of 26 APPENDIX. D: TECH. DESIGN SUMMARY • Effective February 2007 As Revised February 2009 • • • • • • • SECTION IX • APPENDIX D - TECHNICAL DESIGN SUMMARY • 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 Dept. Contact: Date: Subject: • With Other N/A Departments of • Jurisdiction City (Bryan or • College Station) • Coordination With Summarize need(s) & actions taken (include contacts & dates): • Non - jurisdiction City Needed? • Yes No X • Coordination with Summarize need(s) & actions taken (include contacts & dates): • Brazos County Needed? • Yes No X • Coordination with Summarize need(s) & actions taken (include contacts & dates): • TxDOT Needed? • Yes No X • Coordination with Summarize need(s) & actions taken (include contacts & dates): • TAMUS Needed? • Yes No X • 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 • • • STORMWATER DESIGN GUIDELINES Page 5 of 26 APPENDIX. D: TECH. DESIGN SUMMARY • Effective February 2007 As Revised February 2009 • • AI • • • • SECTION IX • APPENDIX D - TECHNICAL DESIGN SUMMARY • 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? • Existing building and gravel parking; approx. 22% impervious • • Site X Redevelopment of one platted lot, or two or more adjoining platted lots. • Development Building on a single platted lot of undeveloped land. Project Building on two or more platted adjoining lots of undeveloped land. • (select all Building on a single lot, or adjoining lots, where proposed plat will not form • applicable) a new street (but may include ROW dedication to existing streets). • Other (explain): • Subdivision N/A Construction of streets and utilities to serve one or more platted lots. • Development Construction of streets and utilities to serve one or more proposed lots on • Project lands represented by pending plats. • Site projects: building use(s), approximate floor space, impervious cover ratio. Describe Subdivisions: number of lots by general type of use, linear feet of streets and • Nature and drainage easements or ROW. • Size of Approximately 11,075 sq. ft student center, Proposed 100% impervious roof • Project • • Is any work planned on land that is not platted If yes, explain: or on land for which platting is not pending? N/A • X No Yes • FEMA Floodplains • Is any part of subject property abutting a Named Regulatory Watercourse No X Yes • (Section II, Paragraph B1) or a tributary thereof? Is any part of subject property in floodplain No X Yes Rate Map48041C0144C • area of a FEMA - regulated watercourse? • Encroachment(s) into Floodplain Encroachment purpose(s): Building site(s) Road crossing(s) • areas planned? Utility crossing(s) Other (explain): • No X 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. • • • • • • STORMWATER DESIGN GUIDELINES Page 6 of 26 APPENDIX. D: TECH. DESIGN SUMMARY • Effective February 2007 As Revised February 2009 • • • • • • • SECTION IX • APPENDIX D - TECHNICAL DESIGN SUMMARY • 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 management plan for the property in substantial conformance with the • earlier study? Yes No If not, explain how it differs. N/A • • • No If subject property is not part of multi -phase project, describe stormwater management • X plan for the property 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 runoff? X No Yes • Describe them (include approximate size, volume, outfall, model, etc). • • • Any known drainage or flooding problems in areas near subject property? X No Yes Identify: • • • Based on location of study property in a watershed, is Type 1 Detention (flood control) needed? • (see Table B -1 in Appendix B) • Detention is required. Need must be evaluated. X Detention not required. • What decision has been reached? By whom? • If the need for How was determination made? • Type 1 Detention • must be evaluated: • • • • STORMWATER DESIGN GUIDELINES Page 7 of 26 APPENDIX. D: TECH. DESIGN SUMMARY • Effective February 2007 As Revised February 2009 • • • • • • • SECTION IX • APPENDIX D - TECHNICAL DESIGN SUMMARY • 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? X No Yes If yes, • describe splits below. In Part 4 describe design concept for handling this. • Watershed or Basin Larger acreage Lesser acreage • Bee Creek Watershed 0.928 • • • Above - Project Areas(Section II, Paragraph B3 -a) • Does Project Area (project or phase) receive runoff from upland areas? X No Yes • Size(s) of area(s) in acres: 1) 2) 3) 4) • Flow Characteristics (each instance) (overland sheet, shallow concentrated, recognizable concentrated section(s), small creek (non - regulatory), regulatory Watercourse or tributary); • N/A • • • Flow determination: Outline hydrologic methods and assumptions: • N/A • • Does storm runoff drain from public easements or ROW onto or across subject property? X No Yes If yes, describe facilities in easement 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). • Runoff flows down Aberdeen and then Dexter into • City of College Station storm system. • • • • • STORMWATER DESIGN GUIDELINES Page 8 of 26 APPENDIX. D: TECH. DESIGN SUMMARY • Effective February 2007 As Revised February 2009 • • • • • • • SECTION IX • APPENDIX D - TECHNICAL DESIGN SUMMARY • Part 3 — Property Characteristics Continued (Page 3.4) • Hydrologic Attributes of Subject Property (or Phase) (continued) • Conveyance Pathways (continued) • Do drainage If yes, for what part of length? % Created by? plat, or • easements instrument. If instrument(s), describe their provisions. exist for any • part of N/A pathway(s)? • X No • Yes • Where runoff must cross lower properties, describe characteristics of abutting lower • property(ies). (Existing watercourses? Easement or Consent aquired ?) Streets • Pathway • Areas • • • Describe any built or improved drainage facilities existing near the property (culverts, • bridges, lined channels, buried conduit, swales, detention ponds, etc). none • • • • Nearby • Drainage Do any of these have hydrologic or hydraulic influence on proposed stormwater Facilities design? X No Yes If yes, explain: • • • • • • • • • • • • • • STORMWATER DESIGN GUIDELINES Page 9 of 26 APPENDIX. D: TECH. DESIGN SUMMARY • Effective February 2007 As Revised February 2009 • • • • • • • SECTION IX • APPENDIX D - TECHNICAL DESIGN SUMMARY • • 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 Establishing Easements (Scenario 1) • property(ies)? X Pre - development Release (Scenario 2) sheet flow 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 # ) • sheet flow onto Aberdeen and Dexter • • • 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)? No Yes Explain and provide • documentation. • N/A • • • STORMWATER DESIGN GUIDELINES Page 10 of 26 APPENDIX. D: TECH. DESIGN SUMMARY • Effective February 2007 As Revised February 2009 • 11110 • • • • SECTION IX • APPENDIX D - TECHNICAL DESIGN SUMMARY • Part 4 — Drainage Concept and Design Parameters Continued (Page 4.2) • • Stormwater Management Concept (continued) • Within Project Area Of Multi -Phase Project Identify gaining Basins or Watersheds and acres shifting: di Will project result N/A • in shifting runoff between Basins or • between What design and mitigation is used to compensate for increased runoff Watersheds? from gaining basin or watershed? • X No • Yes • • How will runoff from Project 1. With facility(ies) involving other development projects. Area be mitigated to pre- • development conditions? 2. Establishing features to serve overall Project Area. • Select any or all of 1, 2, 3. X On phase (or site) project basis within Project Area. and /or 3, and explain below. • 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) project: Describe planned mitigation measures for phases (or sites) in • subsequent questions of this Part. N/A Are aquatic echosystems proposed? X No Yes In which phase(s) or • project(s)? • -. N N • m Are other Best Management Practices for reducing stormwater pollutants proposed? • o- No X Yes Summarize type of BMP and extent of use: a , -Silt fencing at limits of construction • o z -Sod or landscaping in all disturbed areas • • ° I If design of any runoff- handling facilities deviate from provisions of B -CS Technical • Specifications, check type facility(ies) and explain in later questions. • m Detention elements Conduit elements Channel features Q Swales Ditches Inlets Valley gutters Outfalls • Culvert features Bridges Other • • • STORMWATER DESIGN GUIDELINES Page 11 of 26 APPENDIX. D: TECH. DESIGN SUMMARY • Effective February 2007 As Revised February 2009 • • • • • • • SECTION IX • APPENDIX D - TECHNICAL DESIGN SUMMARY • 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): • N/A • • • 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? �• a • Steepest side slopes: Usual front slopes: Usual back slopes: } • N Flow line slopes: least Typical distance from travelway: • -0 (Attached Exhibit # ) o typical greatest • N Z a • 2 x Are longitudinal culvert ends in compliance with B -CS Standard Specifications? • Yes No, then explain: Q • At intersections or otherwise, do valley gutters cross arterial or collector streets? • 3 �• ) No Yes If yes explain: U "O • N y �, Are valley gutters proposed to cross any street away from an intersection? • o No Yes Explain: (number of locations ?) • in • 2 CO X • • • STORMWATER DESIGN GUIDELINES Page 12 of 26 APPENDIX. D: TECH. DESIGN SUMMARY • Effective February 2007 As Revised February 2009 • • • • • • • SECTION IX • APPENDIX D - TECHNICAL DESIGN SUMMARY • • Part 4 — Drainage Concept and Design Parameters Continued (Page 4.4) • Stormwater Management Concept (continued) • Within Or Serving Subject Property (Phase, or Site) (continued) • 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. • a a) = 0 Will inlet size and placement prevent exceeding allowable water spread for 10 -year • 43 z design storm throughout site (or phase)? Yes No If no, explain. • m • D Saci curves: Are inlets placed at low points? Yes No Are inlets and • g .5 conduit sized to prevent 100 -year stormflow from ponding at greater than 24 inches? o Yes No Explain "no" answers. • :" s" § • w a) N • 2 Will 100 -yr stormflow be contained in combination of ROW and buried conduit on • Q 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. • • Are any 12 -inch laterals used? No Yes Identify length(s) and where • used. • m Pipe runs between system • } access points (feet): Typical Longest • m I Are junction boxes used at each bend? Yes No If not, explain where • w and why. c • ' E2Z a • E X • ti Are downstream soffits at or below upstream soffits? Least amount that hydraulic w Yes No If not, explain where and why: grade line is below gutter line • (system- wide): • • • STORMWATER DESIGN GUIDELINES Page 13 of 26 APPENDIX. D: TECH. DESIGN SUMMARY • Effective February 2007 As Revised February 2009 • • • • • • • SECTION IX • APPENDIX D - TECHNICAL DESIGN SUMMARY • • Part 4 — Drainage Concept and Design Parameters Continued (Page 4.5) • Stormwater Management Concept (continued) • Within Or Serving Subject Property (Phase, or Site) (continued) • Describe watercourse(s), or system(s) receiving system discharge(s) below (include design discharge velocity, and angle between converging flow lines). • as 1) Watercourse (or system), velocity, and angle? • • ° E 2) Watercourse (or system), velocity, and angle? • • o • o U C • Eo a� E = 42 3) Watercourse (or system), velocity, and angle? 7; 2 • c a O • El) ▪ n • E m For each ouffall above, what measures are taken to prevent erosion or scour of • i 8 2 receiving and all facilities at juncture? 1) • `f m • 2) • 3) • 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): • ui a) • m � y in } Flow line slopes (minimum and maximum): ET! 0 • • o Z Ouffall characteristics for each (velocity, convergent angle, & end treatment). • m� • 3 • . Will 100 -year design storm runoff be contained within easement(s) or platted drainage • ROW in all instances? Yes No If "no" explain: • • • • • STORMWATER DESIGN GUIDELINES Page 14 of 26 APPENDIX. D: TECH. DESIGN SUMMARY • Effective February 2007 As Revised February 2009 • • • • • • • SECTION IX • APPENDIX D - TECHNICAL DESIGN SUMMARY • III Part 4 — Drainage Concept and Design Parameters Continued (Page 4.6) • Stormwater Management Concept (continued) • Within Or Serving Subject Property (Phase, or Site) (continued) • Are roadside ditches used? X No Yes If so, provide the following: Is 25 -year flow contained with 6 inches of freeboard throughout ? Yes No • .$ Are top of banks separated from road shoulders 2 feet or more? Yes No Are all ditch sections trapezoidal and at least 1.5 feet deep? Yes No • m p P — For any "no" answers provide location(s) and explain: • a m 0 • cc • If conduit is beneath a swale, provide the following information (each instance). • Instance 1 Describe general location, approximate length: • v, N / A a) • > - Is 100 -year design flow contained in conduit/swale combination? Yes No III If "no" explain: • a� U • 0 o Space for 100 -year storm flow? ROW Easement Width z . c Swale Surface type, minimum Conduit Type and size, minimum and maximum • x I T and maximum slopes: slopes, design storm: • o c' v • (/) m Inlets Describe how conduit is loaded (from streets /storm drains, inlets by type): c T a c .c m U • . O 0 c Access Describe how maintenance access is provided (to swale, into conduit): • o `° E • = L w 0 • .G .a) Instance 2 Describe general location, approximate length: 73 • 0 • y N/A • c a Is 100 -year design flow contained in conduit/swale combination? Yes No °— o If no explain: • f n c • E c Space for 100 -year storm flow? ROW Easement Width w a Swale Surface type, minimum Conduit Type and size, minimum and maximum • 5 m and maximum slopes: slopes, design storm: • 2 Inlets Describe how conduit is loaded (from streets /storm drains, inlets by type): • a—' • c • Access Describe how maintenance access is provided (to swale, into conduit): • L • • • STORMWATER DESIGN GUIDELINES Page 15 of 26 APPENDIX. D: TECH. DESIGN SUMMARY • Effective February 2007 As Revised February 2009 • • • • • • • SECTION IX • APPENDIX D — TECHNICAL DESIGN SUMMARY • Part 4 — Drainage Concept and Design Parameters Continued (Page 4.7) • Stormwater Management Concept (continued) • Within Or Serving Subject Property (Phase, or Site) (continued) • If "yes" provide the following information for each instance: • Instance 1 Describe general location, approximate length, surfacing: • 1 • n E w • 6 Is 100 -year design flow contained in swale? Yes No Is swale wholly • } within drainage ROW? Yes No Explain "no" answers: • a) • a Access Describe how maintenance access is provide: L o • , Z o xl • " Instance 2 Describe general location, approximate length, surfacing: a • o • c • a' o E _c 0112 • m Is 100 -year design flow contained in swale? Yes No Is swale wholly • a) (I) within drainage ROW? Yes No Explain "no" answers: Tti 0 • y O • w Access Describe how maintenance access is provided: • U • c d • Instance 3, 4, etc. If swales are used in more than two instances, attach sheet • providing all above information for each instance. • "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. E Will design replicate natural channel? Yes No If "no ", for each instance • o n describe section shape & area, flow line slope (min. & max.), surfaces, and 100 -year • o w design flow, and amount of freeboard: • ( I nstance 1: v • • o Instance 2: • E o _ Z N • c H Instance 3: ca • 0 U • • • STORMWATER DESIGN GUIDELINES Page 16 of 26 APPENDIX. D: TECH. DESIGN SUMMARY • Effective February 2007 As Revised February 2009 • • • • • • • SECTION IX • APPENDIX D - TECHNICAL DESIGN SUMMARY • Part 4 — Drainage Concept and Design Parameters Continued (Page 4.8) • Stormwater Management Concept (continued) • Within Or Serving Subject Property (Phase, or Site) (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. • • a) • Watercourses (and tributaries): Aside from fringe changes, are Regulatory • Watercourses proposed to be altered? No Yes Explain below. • Submit full report describing proposed changes to Regulatory Watercourses. Address existing and proposed section size and shape, surfaces, alignment, flow line changes, • > length affected, and capacity, and provide full documentation of analysis procedures • n a nd data. Is full report submitted? Yes No If "no" explain: E • m c • U 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 maintenance space? Yes No If not, identify location(s) and explain: • • • • STORMWATER DESIGN GUIDELINES Page 17 of 26 APPENDIX. D: TECH. DESIGN SUMMARY • Effective February 2007 As Revised February 2009 • • • • • • • SECTION IX • APPENDIX D - TECHNICAL DESIGN SUMMARY • Part 4 — Drainage Concept and Design Parameters Continued (Page 4.9) • • Stormwater Management Concept (continued) • Within Or Serving Subject Property (Phase, or Site) (continued) How many facilities for subject property project? 0 For each provide info. below. • For each dry -type facilitiy: Facility 1 Facility 2 • Acres served & design volume + 10% • 100 -yr volume: free flow & plugged • Design discharge (10 yr & 25 yr) • Spillway crest at 100 -yr WSE? yes no yes no • Berms 6 inches above plugged WSE? yes no yes no Explain any "no" answers: • • a) • } • For each facility what is 25 -yr design Q, and design of outlet structure? • Facility 1: 0 Z Facility 2: • Do outlets and spillways discharge into a public facility in easement or ROW? • Facility 1: Yes No Facility 2: Yes No • aaa) If "no" explain: • N 0 CL 0 • For each, what is velocity of 25 -yr design discharge at outlet? & at spillway? • Facility 1: & Facility 2: & 7 Are energy dissipation measures used? No Yes Describe type and • location: • 0 c • a� a� • For each, is spillway surface treatment other than concrete? Yes or no, and describe: • Facility 1: • Facility 2: • For each, what measures are taken to prevent erosion or scour at receiving facility? Facility 1: • Facility 2: • If berms are used give heights, slopes and surface treatments of sides. • Facility 1: • • Facility 2: • • STORMWATER DESIGN GUIDELINES Page 18 of 26 APPENDIX. D: TECH. DESIGN SUMMARY • Effective February 2007 As Revised February 2009 • • • • • • • SECTION IX • APPENDIX D - TECHNICAL DESIGN SUMMARY • Part 4 — Drainage Concept and Design Parameters Continued (Page 4.10) • Stormwater Management Concept (continued) • Within Or Serving Subject Property (Phase, or Site) (continued) • Do structures comply with B -CS Specifications? Yes or no, and explain if "no ": • Facility 1; u) • a) • 2 c Facility 2: • c 0 0 • aa) o For additional facilities provide all same information on a separate sheet. • Are parking areas to be used for detention? No Yes What is • maximum depth due to required design storm? • 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: • • • ui rn • o Are culverts parallel to public roadway alignment? Yes No Explain: • U N a) } • f6 > • 'a Creeks at Private Drives: Do private driveways, drives, or streets cross drainage Ti ways that serve Above - Project areas or are in public easements/ ROW? • N z No Yes If "yes" provide information below. • D XI How many instances? Describe location and provide information below. • > Location 1: D U • m Location 2: • Q • 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. • • STORMWATER DESIGN GUIDELINES Page 19 of 26 APPENDIX. D: TECH. DESIGN SUMMARY • Effective February 2007 As Revised February 2009 • • • • • • • SECTION IX • APPENDIX D — TECHNICAL DESIGN SUMMARY • Part 4 — Drainage Concept and Design Parameters Continued (Page 4.11) • • Stormwater Management Concept (continued) • Within Or Serving Subject Property (Phase, or Site) (continued) Named Regulatory Watercourses (& Tributaries): Are culverts proposed on these • facilities? No Yes, then provide full report documenting assumptions, criteria, analysis, computer programs, and study findings that support proposed • design(s). Is report provided? Yes No If "no", explain: • • • - Arterial or Major Collector Streets: Will culverts serve these types of roadways? c X No Yes How many instances? For each identify the • u, location and provide the information below. • } n Instance 1: • Instance 2: c • 0 Instance 3: c 0 • z E Yes or No for the 100 -year design flow: 1 2 3 • >14- Headwater WSE 1 foot below lowest curb top? c • E Spread of headwater within ROW or easement? • u ° Is velocity limited per conditions (Table C -11)? rn .N m Explain any "no" answer(s): • o U c • o N U • -a O o -Q Minor Collector or Local Streets: Will culverts serve these types of streets? • 2 a X No Yes How many instances? for each identify the • 0 a location and provide the information below: n a) • m a Instance 1: O c Instance 2: • 0 m o Instance 3: • -t 0 , 0 For each instance enter value, or "yes" / "no" for: 1 2 3 • U 06 a) w Design yr. headwater WSE 1 ft. below curb top? • < .0 100 -yr. max. depth at street crown 2 feet or less? • E 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: • • • • • STORMWATER DESIGN GUIDELINES Page 20 of 26 APPENDIX. D: TECH. DESIGN SUMMARY • Effective February 2007 As Revised February 2009 • • • • • • • SECTION IX • APPENDIX D - TECHNICAL DESIGN SUMMARY • Part 4 — Drainage Concept and Design Parameters Continued (Page 4.12) • Stormwater Management Concept (continued) • Within Or Serving Subject Property (Phase, or Site) (continued) • All Proposed Culverts: For all proposed culvert facilities (except driveway /roadside • ditch intersects) provide information requested in next eight boxes. • 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 culvert and surfaced • approaches thereto? No Yes If "yes" identify location(s), 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 to culvert ends? • No Yes If "yes" identify location(s), describe outfall design treatment(s): • • ti • > 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 street ROW, and /or • drainage easements/ ROW? Yes No if not, why not? • • Do appreciable hydraulic effects of any culvert extend downstream or upstream to • neighboring land(s) not encompassed in subject property? No Yes If • "yes" describe location(s) and mitigation measures: • • • Are all culvert designs and materials in compliance with B -CS Tech. Specifications? • Yes No If not, explain in Special Design Section of this Part. • • STORMWATER DESIGN GUIDELINES Page 21 of 26 APPENDIX. D: TECH. DESIGN SUMMARY • Effective February 2007 As Revised February 2009 • • • • • • • SECTION IX • APPENDIX D - TECHNICAL DESIGN SUMMARY • Part 4 — Drainage Concept and Design Parameters Continued (Page 4.13) • Stormwater Management Concept (continued) • Within Or Serving Subject Property (Phase, or Site) (continued) • Is a bridge included in plans for subject property project? X No Yes • If "yes" provide the following information. Name(s) and functional classification of the roadway(s)? • N/A • • What drainage way(s) is to be crossed? • N/A • ca • • A full report supporting all aspects of the proposed bridge(s) (structural, geotechnical, • hydrologic, and hydraulic factors) must accompany this summary report. Is the report provided? Yes No If "no" explain: • N/A • • Is a Stormwater Provide a general description of planned techniques: Pollution Prevention Disturbed area is less than 1 acre • Plan (SW3P) • O established for project construction? • X No Yes • • Special Designs — Non - Traditional Methods Are any non - traditional methods (aquatic echosystems, wetland -type detention, natural stream • replication, BMPs for water quality, etc.) proposed for any aspect of subject property project? • X No Yes If "yes" list general type and location below. • • • • • Provide full report about the proposed special design(s) including rationale for use and • expected benefits. Report must substantiate that stormwater management objectives will not be compromised, and that maintenance cost will not exceed those of traditional design • solution(s). Is report provided? Yes No If "no" explain: • N/A • • • • STORMWATER DESIGN GUIDELINES Page 22 of 26 APPENDIX. D: TECH. DESIGN SUMMARY • Effective February 2007 As Revised February 2009 • • AI • • • • SECTION IX • APPENDIX D - TECHNICAL DESIGN SUMMARY • 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 from provisions of • B -CS Technical Specifications, check type facility(ies) and explain by specific detail element. Detention elements Drain system elements Channel features • Culvert features Swales Ditches Inlets Outfalls • 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) • • 2 ) • • 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) • 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 Design Drainage Area to which the Rational Formula • has been applied? 0 acres Location (or identifier): • • STORMWATER DESIGN GUIDELINES Page 23 of 26 APPENDIX. D: TECH. DESIGN SUMMARY • Effective February 2007 As Revised February 2009 • • • • • • • SECTION IX • APPENDIX D - TECHNICAL DESIGN SUMMARY • 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 % • 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 N/A N/A • Detention facilities: outlet and conveyance structure(s) N/A N/A • Detention facilities: volume when outlet plugged N/A N/A • 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: • • • • STORMWATER DESIGN GUIDELINES Page 24 of 26 APPENDIX. D: TECH. DESIGN SUMMARY • Effective February 2007 As Revised February 2009 • • • • • • • SECTION IX • APPENDIX D - TECHNICAL DESIGN SUMMARY • 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? N/A Yes No Are elevation drops provided at inlets, manholes, and junction boxes? N/A Yes No • Explain any "no" answers: • • 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? Identify • each location and explain: • N/A • • • Open Channels If a HEC analysis is utilized, does it follow Sec VI.F.5.a? kl Yes No Outside of straight sections, is flow regime within limits of sub - critical flow? Yes No • If "no" list locations and explain: • N/A • 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 • • • STORMWATER DESIGN GUIDELINES Page 25 of 26 APPENDIX. D: TECH. DESIGN SUMMARY • Effective February 2007 As Revised February 2009 • • • • • • • SECTION IX • APPENDIX D - TECHNICAL DESIGN SUMMARY • 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 • StormNet Version 4.18.2.17854 • Apr082009 Gigasoft, Inc. • • • • 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, the increase from the peak • pre- developed levels will be minimal 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 Part B was prepared by me (or under my supervision) in accordance with provisions of the Bryan /College Station • Unified Drainage Design Guidelines for the owners of the property. All licenses and permits required by any and all state and federal regulatory agencies for the proposed drainage • improvements have been issued or fall under applicable gene` =,a i it ." • (A c F � .T E X X 1 1 • . ° ulhil % � .� �• • • • Licensed Professional Engineer %** . 1 %•MELIS P TH .... .. % • State of Texas PE No. 98398 � � f •• ' • "98 ' S • .� • `iF'� c�li . O S P • STORMWATER DESIGN GUIDELINES Page 26 of 26 APPENDIX. D: TECH. DESIGN SUMMARY • Effective February 2007 As Revised February 2009 • • • • • • • SECTION II POLICIES • discharge point at a main channel of the primary system. The • designated "conveyance pathway" must follow or provide clearly • identifiable watercourses. Needs for easements or ROW for • conveyance pathways are to be assessed per the provisions of Paragraphs E and F of this Section. The purpose of providing for the • 100 -year storm level is to prevent the creation of situations hazardous • to life, or harmful to public and private property. Accordingly, a major emphasis is on deliberately confining storm flow to designated • conveyance pathways. • Watershed Diversion Generally stormwater emitting from land drained by one named regulatory watercourse of the primary system shall not be diverted to • drain into a different named regulatory watercourse of the primary • system. • 3. Detention / Mitigation • Detention Purposes Detention is an important mitigation measure. It can be used • effectively for either or both of two fundamental purposes. As a tool for watershed management, it can be deployed with other features to • minimize potential flooding along major watercourse(s). It can also be • used to manage how stormflow is discharged from a property to adjacent properties. Thus, it can be an integral part of stormflow conveyance in route to the primary system or to a tributary thereof. Both are legitimate reasons for using detention facilities, and any one detention facility might work toward both purposes, depending on its • location in a watershed. The functional purposes for detention are • further defined in foregoing Paragraph B3 -b of this Section. • a. Detention Requirements • Right Uses For optimum results detention facilities must be deployed for the right • reasons at the right locations. It is the intent of these Guidelines to stipulate the conditions under which detention must be used and why. • These Guidelines are not intended to preclude the use of detention at • locations where qualified engineers may deem it to be beneficial. Nevertheless, where detention is required by these Guidelines • designed facilities must meet the criteria stipulated herein. Peak Flow Regulated Where detention facilities are required, peak stormflow rates from a • project area resulting from the two (2), ten (10), twenty -five (25), and one hundred (100) year storm frequency events shall not be increased • at any point of discharge. Regulation of peak flows to allowable levels, • as determined by the provisions of these Guidelines, shall be achieved by storage facilities on, or away from, a project area, or by participation • in an approved Regional Stormwater Management Program. • • • • STORMWATER DESIGN GUIDELINES Page 10 of 18 SECTION II: POLICIES ID Effective February 2007 As Revised February 2009 • • • • • • SECTION II • POLICIES • • b. Detention Facilities May Be Optional • Detention Limited At the discretion of the City Engineer, land development activity is not subject to the stormwater detention requirements of these Guidelines if • one or more of the four conditions listed in Sub - paragraphs 3 -b(1) • through 3 -b(4) before are satisfied, and an engineer registered in the State of Texas submits a signed, sealed, and dated letter addressed to • the City Engineer, stating the following without qualification: • "1 have conducted a topographic review and field investigation of the existing and proposed flow patterns for stormwater runoff from (name • of subdivision or site project) to the main stem of (name of creek). At • build -out conditions allowable by zoning, restrictive covenant, or plat note, the stormwater flows from the subject subdivision or site project • will not cause any increase in flooding conditions to the interior of existing building structures, including basement areas, for storms of • magnitude up through the 100 -year event": • (1). Adjacent to Primary System • • Any development adjacent to the Primary System may demonstrate that detention is not beneficial to the system with an engineering timing • analysis. The analysis should include all upstream development • broken into basins of size similar to the development being studied and carried downstream until the development represents Tess than • 2% of the total drainage basin. • (2). One Existing Lot • The proposed development project involves one single existing legal lot that is limited to single - family land use by zoning, restrictive • covenant, or plat note. • Small Lot The size of a platted lot is equal to or Tess than one (1) acre for • commercial use, or two (2) acres for detached single family use. • (4). Draining to Designated Streams • At locations included in the drainage watersheds of certain streams stipulated as not requiring detention in Table B -2 in Appendix B, • provided Type 2 Detention is not needed for managing property -to- • property stormflow. • 4. Water Quality • • Concurrent Objectives The intent of these Guidelines is to cause development of stormwater • management facilities that effectively collect and convey stormflow without causing water damage impacts on life and property. A • concurrent objective is to achieve facilities that minimize any adverse affect(s) on the quality of water conveyed into natural waterways that • traverse and /or drain the Cities. • • • STORMWATER DESIGN GUIDELINES Page 11 of 18 SECTION II: POLICIES • Effective February 2007 As Revised February 2009 • •