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HomeMy WebLinkAboutStormwater Drainage ReportStormwater Drainage Report for Tower Point Infrastructure Development College Station, Texas Prepared by: Walter P. Moore & Associates, Inc. TBPE Firm Registration No. 1856 January 27", 2012 KEVIN P. TABLE OF CONTENTS PROFESSIONAL CERTIFICATION....................................................................................2 EXECUTIVE SUMMARY...................................................................................................3 GENERAL LOCATION AND DESCRIPTION OF PROJECT AREA.......................................4 DRAINAGE WATERSHEDS AND STUDY AREAS..............................................................5 DRAINAGE DESIGN CRITERIA.........................................................................................6 COMPLIANCE WITH PROPOSED DEVELOPMENT ASSUMPTIONS..................................6 DRAINAGE ASSUMPTION FOR FUTURE DEVELOPMENTS..............................................7 DRAINAGE SYSTEM DESIGN..........................................................................................8 OUTFALL VELOCITIES.........................................................................I..........................9 CONCLUSION...............................................................................................................10 APPENDIX............................................................ ...... . ......................... . ........................11 Stormwater Drainage Report Tower Point Infrastructure Development Page 1 PROFESSIONAL CERTIFICATION This report and plans for the drainage design of Tower Point Infrastructure Development project 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 will be issued prior to construction. Licensed Professional Engineer State of Texas No. Stormwater Drainage Report Tower Point Infrastructure Development Page 2 EXECUTIVE SUMMARY Infrastructure improvements are being proposed for future development of the Tower Point Subdivision located at the west corner of the intersection of Highway 6 and Highway 40 in the City of College Station, Texas. These improvements include a storm sewer system to capture stormwater runoff generated from adjacent future development and minimize runoff within the proposed streets. Strom sewer inlets will capture storm water runoff and an underground storm sewer system will convey runoff into Spring Creek located to the west of the development. The existing bridge serving Highway 6 over Spring Creek contains storm water detention control structures to minimize peak runoff rates for this development. As such, no additional storm water detention is anticipated for this project. Previous design information indicates that the control structures at the bridge minimize runoff rates and allow storm water runoff to back up within the Spring Creek tributary during storm events. Storm sewer system components have been designed according to the Unified Stormwater Design Guidelines of the City of College Station based on anticipated future development. StormCADO by Bentley Systems was utilized to determine peak runoff rates, pipe capacities, hydraulic grade lines throughout the system, and other necessary hydraulic information. The storm sewer system components have been designed to mitigate impacts to the existing downstream storm sewer system and watercourses. No adverse impacts are expected with these improvements. Stormwater Drainage Report Tower Point Infrastructure Development Page 3 GENERAL LOCATION AND DESCRIPTION OF PROJECT AREA The Tower Point Infrastructure Development project is located within the Tower Point Subdivision. This subdivision is approximately 128 acres and is located at the west corner of the intersection of Highway 6 and Highway 40, The project area is approximately 5.5 acres and for the purposes of this report is the extent of the Drainage Study Area. It is bounded by Highway 6 to the north, Arrington Road to the southwest, and an existing stormwater detention facility to the south. Surrounding the project area is generally undeveloped property. The land developer for this project is the Weiner Development Corporation and the owner is College Station Marketplace, L.P The project area is located within the Spring Creek named regulatory watercourse. Spring Creek proceeds into Lick Creek, followed by the Navasota River and then the Brazos River. Beyond the west limits of the project and within the Tower Point Subdivision is a stormwater detention facility located within Spring Creek constructed previously to serve this development. No storm sewer currently exists within the project limits. The limits of the infrastructure development portion of this project is bounded by Arrington Road and the existing storm water detention facility All infrastructure improvements included in this report serve the Tower Point Subdivision plat. All infrastructure improvements are also located within this subdivision. This extent of this project includes infrastructure improvements for future site development within the Tower Point Subdivision. Infrastructure improvements include a new streets and driveway, storm sewer systems, water supply systems, and sanitary sewer systems. These improvements are Stormwater Drainage Report Tower Point Infrastructure Development Page 4 designed and constructed to allow future development to occur. Future land development in this project area is expected to be commercial development, particularly retail shops and restaurants. The project area is currently undeveloped and existing land cover consists primarily of rocky soil with minimal vegetation. DRAINAGE WATERSHEDS AND STUDY AREAS The entire project area is within the Spring Creek named regulatory watershed and drains into Spring Creek. A FEMA flood panel map of the project area is located in the Appendix. From aerial photography, it appears the Spring Creek watershed is generally undeveloped at this time. Relatively small portions of the watershed along the northern and southern sides are currently developed as primarily single family residential homes. The land cover of the remaining portions of the watershed is predominately forested with small amounts of agricultural land. Stormwater runoff in the existing undeveloped condition generally flows from northwest to southeast across the project site area. The limits of the project area to the west and north generally represent the limits of the watershed boundary of storm water runoff that flows onto the project site. A small portion of Arrington Road at the intersection of the Private Drive will flow into the project site and this runoff was accounted for in the drainage calculations. Proposed site improvements maintain existing drainage patterns to the extent possible. All stormwater runoff generated from the project area proceeds overland into the proposed storm sewer systems. The proposed storm sewer systems convey the captured runoff into Spring Creek as mentioned previously. A proposed drainage area map is located in the Appendix that delineates the overall watershed boundaries and the individual drainage boundaries for each proposed storm sewer inlet in the proposed condition. Stormwater Drainage Report Tower Point Infrastructure Development Page 6 DRAINAGE DESIGN CRITERIA Storm sewer systems have been designed according to the Unified Stormwater Design Guidelines contained within the Site Design Standards manual of the City of Bryan and the City of College Station. All storm sewer inlets and pipes have been designed according to these standards to convey storm water runoff from the anticipated future development within the project area for a 10 year storm event. Inlets have been placed along the roadways to limit gutter flow rates and spreads and allow for future storm sewer connections for individual properties as they become developed within the project area. Runoff rates have been calculated based on future development using conservative runoff coefficients of 0,90 for all areas with minimum times of concentrations of 10 minutes. According to the above referenced Design Guideline, rainfall intensities for the 10 year storm event were calculated using the following equation: i=80/(Tc+8.6)"" The 100 year storm event was also calculated to determine the impacts on the storm sewer systems and surrounding development. The rainfall intensity equation used for this storm event was: i = 96 / (Tc + 8.0)0.130 COMPLIANCE WITH PROPOSED DEVELOPMENT ASSUMPTIONS As indicated previously, all storm water runoff from the proposed site development is conveyed into Spring Creek. The existing storm water detention controls located at the bridge serving Highway 6 and the existing storm sewer systems located along Arrington Road took into account for future development. Both the Spring Creek detention control structures and the Arrington Road storm sewer system used hydrologic assumptions of the anticipated land development to calculate fully developed peak runoff rates for this project site. The hydrologic assumptions made for the proposed storm sewer system are in compliance with the assumptions made for the existing storm Stormwater Drainage Report Tower Point Infrastructure Development Page 6 water control structures as well as the existing storm sewer system. These assumptions include using minimum time of concentrations and fully development runoff coefficients. As a result, no additional storm water detention in anticipated for this project and there will be no adverse impacts on the existing system within Arrington Road. DRAINAGE ASSUMPTION FOR FUTURE DEVELOPMENTS The drainage system along the private drive has been designed to accommodate future development of the adjacent lots. The following is a list of assumptions made to accommodate future development: • Runoff rates have been calculated based on conservative runoff coefficients of C=0.90 • Future flows are assumed to have a minimum time of concentration To = 10 minutes • Lot 32 A is assumed to have an area of 1.08 acres, the full runoff from this lot (F1 on exhibit 5) will connect to the drainage system through the back of inlet 1 (11). Based on the assumed values of C and To, the flow from this lot for a 10 year storm event is 0=7.43 CFS • Lot 32 B is assumed to have an area of 1.08 acres, the full runoff from this lot (F2 on exhibit 5) will connect to the drainage system through the back of inlet 2 (12). Based on the assumed values of C and To, the flow from this lot for a 10 year storm event is 0=7.43 CFS • Lot 30 is assumed to have an area of 2.03 acres, the full runoff from this lot (F3 on exhibit 5) will connect to the drainage system through the storm line stub provided on the lot. Based on the assumed values of C and To, the flow from this lot for a 10 year storm event is Q= 15.90 CFS • Lot 30 is assumed to have an area of 0.80 acres, the full runoff from this lot (F4 on exhibit 5) will connect to the drainage system through the storm line stub provided on the lot. Based Stormwater Drainage Report Tower Point Infrastructure Development Page 7 on the assumed values of C and Tc, the flow from this lot for a 10 year storm event is Q= 6.23 CFS DRAINAGE SYSTEM DESIGN Storm sewer system peak runoff rates and system components were designed using the aid of StormCAD® by Bentley Systems. Storn-CAD® utilizes the rational method to developed peak runoff rates along with Manning's equation and the Continuity equation to determine pipe sizes, flow rates, head and friction losses, gutter spreads, and hydraulic grade lines throughout the storm sewer system. StormCADO input data and output results are included in the Appendix for both the 10 year storm event and the 100 year storm event. The HGL calculations from StromCAD® are based on the assumption that the water surface elevation at the outfall is at the crown of the pipe, per the Unified Stormwater Design Guidelines As mentioned previously, the proposed storm sewer system has been designed for anticipated future development within the project area. It is expected that separate storm sewer systems will be designed and constructed for individual future lot developments which will capture a majority of the stormwater runoff and convey it into the underground pipe systems. Individual watershed boundaries and peak runoff rates have been estimated to the extent possible based on the limited knowledge of the future development of the surrounding lots. The storm sewer design is based on this limited information. It is recommended that future lot developers and owners analyze their development's impacts on the storm sewer system to ensure compliance with the Unified Stormwater Design Guidelines and limit impacts to surrounding areas and the downstream storm sewer systems and watercourses. Stormwater Drainage Report Tower Point Infrastructure Development Page 8 OUTFALL VELOCITIES Stormwater runoff for this project site enters Spring Creek at one location through the use of concrete headwall structures. From the storm sewer analysis contained within the Appendix the velocity of the water as it exits the system is 4.72 fps. City of College Station Unified Stormwater Design Guidelines, Section IX, Appendix C, Table C-11 states that velocities in excess of 12 fps require additional methods to reduce exit velocities. The City of College Station Typical Concrete Headwall detail is incorporated within the construction plans and is to be used at the exit location mention above. Stormwater Drainage Report Tower Point Infrastructure Development Page 9 CONCLUSION The storm sewer system for the Tower Point Infrastructure Development has been designed in compliance with the Unified Drainage Design Guidelines for the City of College Station, Texas. Storm sewer inlets and underground storm sewer pipes have been designed to capture and convey stormwater runoff generated from the anticipated future development of adjacent lots within the project area for a 10 year storm event. It should be expected that during less frequent, more intense storm events all stormwater runoff may not be able to enter the underground storm sewer system. It have been determined that during the 100 year storm event, storm water runoff that cannot enter the storm sewer system will continue flowing within the proposed roadways. Runoff will continue to flow within the proposed roadway until it has an opportunity to enter the storm sewer system or discharges into Spring Creek as it currently does. This report and the data contained within the Appendix should be reviewed during the design of the storm sewer systems for future lot development within the project area to ensure that the assumptions made in this report are valid and consistent with future land development and land use. Stormwater Drainage Report Tower Point Infrastructure Development Page 10 Exhibit 1....................................... Exhibit 2....................................... Exhibit 3....................................... Exhibit 4....................................... Exhibit5....................................... Exhibit 6....................................... Exhibit 7....................................... Exhibit S....................................... ....................... USGS Quadrangle - Wellborn Texas ...............................................Overall Grading Plan .............................. Overall Storm Sewer Utility Plan ................................................... FEMA Flood Map ...............Developed Conditions Drainage Area Map .......................................Storm Sewer Calculations ......................10 year Hydraulic Grade Line Profiles .................... 100 year Hydraulic Grade Line Profiles Stormwater Drainage Report Tower Point Infrastructure Development Page 11 EXHIBIT 1 L„ 4" wELB�II WFIMANaIF: •^ 1fAb �, McM.K�M.w H^�w Mw GakV�Kr✓rr1 Lam- •—�•• m__ __ w�.r vr. �Y1�M .. I ^�.� nsa r I.-�-1�.�'•• ror r {�n�r1 Iry wrr� T•�i(••r urm�r9rCririii �:ria,�p°im P"�� •••.:• N,11H.Yd. TEII, ,� ...... �a�:rs,�sr..� rr,.. ..r,.r ..� nw. ^,e�:.ur�. �.,�r u'"M.e"��.b.:".`,: r": Lrrwr,ror w«-.vr rw r..wW.r...,.,.r .....,.. � wrr... «... rrrr wm Irn��nvNFw��� EXHIBIT 2 �—n I 04 �J I -I----- toFUTURE f\ FUTURE F ! �1 FIIURE BLOC —K2, 0 1 to �; b NE SHEEP C5.7/2 j 1L 1 LOT 33 1 ` I s�Er a•t/t it — I— OTU i } , i 1 ' — I t I � 1 J � 1 j1 I RE FUTURE i - ! FUTURE ' I BLOCK 2� \l 3111 1r T UTUR 1 D \ +o SCALE: t•=ao' WALTER P MOORE Wp aDf MONINN'Y. II UITEE 1100 ixc. NOUSiON, iENPS ]]Of0 rnax[, Ifa.0a01900 rna. if 3.ea0.]p90 PPGFCf N0.NECO v ru e e uxv TOWER POINT INFRASTRUCTURE PLANS FOR PHASE 12, LOTS 1-3, BLOCK 2 NABS WDC WEINER DEVELOPMENT CORPORATION 520 POST OAK BOULEVARD SUITE 850 HOUSTON, TEXAS 77027 PHONE: 713-623-OIN FAX: 713-623-0178 waw IBPE 3 .................. , P. uom axe AaaeB+`x. I� Flnn PepliVetlm Nx lBR °``.. 1 I.EVIN P, Sillry oi�tia��Yt, NO. W1E PEVISION 12-1]-M10 CITY SUBMITTAL IX21-2011 CtTYCOMMENTS © 01-2B12 CITYBEVISICNSSMMBTAL 01-27-Mi2 C"CCMMENTS BESIf Day MJS flEw MBY SNP DMWNBY BP PROJECt N11MBEP 23050d412 GATE 01-0s2012 SNEETTIBE CIVIL SITE GRADING PLAN EXHIBIT 3 WALTER P MOORE -- EXISRN6 CRY OF COLLEGE sTAwK im -- 20' WIDE EASEMENT VOL 4328, PG. 164 i i FUTURE I a yL1 TEI FUTURE WAT& UK W- (RE:SHEET C7.4) C7.1 h FUTURE HIGHWAY 6 ED 11 MBE PUi�;' EASEMENT 71l � 16 n LOT S2A ip DSED 20' WIDE POW ACCESS TENT AND PUBLIC UOUTY EASEMENT V EASEMENT ART SEWER LINE S-1 SHEET C7.1 R C7.2) r PROP ELECTROL --(BY OTHERS) __----:------=�'---— ------------- �- --- --�RRP ELECRMW. • 11 _ (BY amen) ! i ItOT 32B - - - I R FUTURE � •� � �— `-. T it � 1 ' f— BLOCK 2 j 131 r STORM SEWER UK ST-2 I I 1 (RE: SHEET C7.7)�11 SHEET C7.3) — Ii WATER UK W-z --- (RE: SHEET C7.7) (RE: SHEET C7.5) -- YMTER U(IEI1E-1 (HE SHEET C7.4) q0 24O 80 SCALE: 1'=40' WA ERoMOO FN Ax A350CIA0iBE.. S. 3HS GTON. TE AS]]0,0 axox[. ]I3. 030.]3B0 [Ax. ]13.890 ]308 A_" P.ELTNAMEnus TOWER POINT INFRASTRUCTURE PLANS FOR PHASE 12, LOTS 1-3, BLOCK 2 NA�n WD \ 1VEINER DEVELOPMENT CORPORATION 520 POST OAK BOULEVARD SUITE 850 HOUSTON, TEXAS 77027 PHONE: 713-623-0188 TAX: 713-623-0176 i / i / ] / / f / / I / •I f57F.RAL CONIRACTOR FOR TOWER POINT INFRASTRUCTURE DEVELOPMENT, CERRFY THAT THE / IMPINWfHENIS SHOWN ON THIS SHEET WERE ACTUALLY BULT, AND THAT / STUD IMPROVEMENTS ARE SHOWN SUBSTANTIALLY HEREON. I RENEW / CERIRY THAT TO THE BEST OF MY KNOWLEDGE, THAT THE MATERIALS / OF CONSTRUCRON AND SIZES OF MANUFACTURED ITEMS, F ANY ARE / STATED CORREMY HEREON.- �> WYd, P. Mme eMAvadelm. Nc. iBPE Flnn PeylattaLLn Hw 1 &6 9' NEVIH P_9LLLNAN 5 Md19 Wi% NI P��ENS � S NO WEE REVISION 12-17-2010 CRYSUBMITTAL 0 21-2011 CITYCOMMENTS Oi 2012 CITY REVISIONS SUBMITTAL Oi-V-MI2 CITY COMMENTS BsINO. MJS REInEviEo9v SRP ISM" BY BP PNOIEM NLMBER 23-050401E DATE 01-OS2012 BHEE . CIVIL SITE OVERALL UTILITY PLAN EXHIBIT 4 0 0 O O x Q \ A ` l �6 O Z a o RI Fti m a r NO c r.1 3 r o y 0 A '" \� get lit ASS a o 000 v O °°a4 ((D c mo a W (D zi N Z n m pm Nm m z72� \\\ 9FF \ °0M1 - \ Ogt N ID � n m ~O 90 PS x w 0 a N a z D c ti y m m C tu ROAD 3oN °Fmo B J a xsSps " gce5{ 33 �@ 5 ie ox A g �p y O 0 Via\ M. o S&a � c 3 }i� .. G p `C m 5 °°off$ y tiw c3 T o ~ na? EXHIBIT 5 EXHIBIT 6 Pipe Label 0I'° ? i Upstream Structure II N a O 3 oo I T m a x Downstream Structure N aAla N Tributary Area (acres) 0 0'_ ''.n _ n Runoff Coeiffalml (C) o"� o 0 nIo o a a Inlet C'A r. m "W w m r r N w r &, Intensity, (iNhr) N 8 c N Tributary Runoff (cis) -- N -a Carryover Flow (cis) O 0,0 oo 0 o N Piped Flow lcfs) m 6 � m II V o w Total Flow to Intel (cis) F A - rn m a Total Intercepted Flow (cis) N m Bypass Flow(cis) ?� - m Bypass Target N I m o Capture Efficiency(%) Z r a Gutter Spread fp D n Gutter Velocity (fps) r w n a Inlet Length Needed (it) = O Inlet Capacity (cis) (Calculated) N Pipe Diameter (inches) J G O 0. Pipe Length (it) R1 0 Total System Flow (cis) a (Calculated) (n 0 Full Capacity (cis) 0 A �Ivw• A m Ol0 0 oio o e $ Pipe Slope I%) m G N IIN m A "' Average Velocity (fps) m o o (Calculated) z Frauds # vWi A w e __NmN r" ? Upstream Invert Elevation (fi) o m 0IN w Downstream Invert Elevation (it) m c v rj or Upstream Ground Elevation (fl) Downstream Ground Elevation (it) a w N N Upstream Hydraulic Grade Line fl) w m Downstream Hydraulic Grade Line (it) Pipe Label N p N Upstream Structure T T T w Y Downstream Structure o c.HIQ 0 0 I Tributary Area (acres) 0 o q',z o 0o z3n b o Runoff Coefficient(C) o a o Inlet C'A o I v r m ' o> Intensity gnmr) a N i m N o w a l00 o m $' Tributary Runoff lots) o W Carryover Flow (cis) M A A Piped Flow (cis) (CJ) T 1 N 'rn Total Flow to Intel (cis) 0 f M En v 'n Total lntercepled Flow (cis) aN m i Bypass Flow (cis) Bypass Target M fll N N " o0 Capture Efficiency(%) Z n • W A Gutter Spread (it) r 0 Gutter Velocity (fps) C I o m Intel Length Nestled (%) O N Inlet Capacity (cis) (Calculated) z NW N m W a Pipe Diameter (inches) J p o Pipe Length (It) M 0 0 A� m M N b wo ° N Total System Flow (cis) o i gwp O W In Full Capacity (cis) I M A V N A roW E w N O olio b $ Pipe Slope I) G W Average Velocity (fps) Z (Calculated) a �..A � N o Froutla # s w ? Upstream Invert Elevation (it) 0 Downstream Invert Elevation (it) OW 9 i o Pft Upstream Ground Elevation (it) Downstream Ground Elevation N ro Upstream Hydraulic Grade Line (it) in A N Downstream Hydraulic Grade in m b Une Ifp EXHIBIT 7 Elevation (ft) DMZ + l N N rn � ut o b o 0 0 Elevation (ft) N O T N O O O O N O 0 0 i 1 V O O N NN W V N N �N� 3 N W A m = Q � N m3= N CO pN N I1G� •y m N 0 O 3 rt 0 wrt ,I V <m 3LD �N rn w N N 'gym <m3 N N �� Nm f.J N F SAO <m 3 '1 r1 N N � to o O �` I