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Home My WebLink AboutStormwater Drainage ReportStormwater Drainage Report for Tower Point Site Development for Lot 15 College Station, Texas Prepared for: Weiner Development Corporation Prepared by: Walter P. Moore & Associates, Inc. 1301 McKinney, Suite 1100 Houston, TX 77010 TBPE Firm Registration No. 1856 January 25, 2011 Revised February 21, 2011 OF A 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............................................................................................5 COMPLIANCE WITH PROPOSED DEVELOPMENT ASSUMPTIONS...................................6 DRAINAGE SYSTEM DESIGN..............................................................................................7 CONCLUSION APPENDIX................................................................................. ...... 7 we Stormwater Drainage Report Tower Point Site Development - Lot 15 Page 1 PROFESSIONAL CERTIFICATION This report and plans for the drainage design of Tower Point Site Development — Lot 15 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. • � * C .. ��sik11 ... / KEVIN P. SULLIVAN Lic ed Pr f ssional Engineer �•••••••••••••••••••• ••.••.•......... -0 102419 • - . State of Texas No. (72 1too \\ ANAL ENQ`?I tr�i Walter P. Moore and Associates, Inc. Tbi F Firm Reglstra8on No.1866 Stormwater Drainage Report Tower Point Site Development — Lot 15 Page 2 EXECUTIVE SUMMARY V V Site development improvements are being proposed for Lot 15 within the Tower Point-Vubdivision located at the west corner of the intersection of Highway 6 and Highway 40 in the City of College Station, Texas. Storm sewer inlets will capture stormwater runoff from the site and portions of undeveloped off site areas. An underground storm sewer system will convey runoff into the existing public storm sewer system located in Private Drive G that ultimately discharges into Spring Creek located to the west of the development. The existing bridge serving Highway 6 over Spring Creek contains stormwater detention control structures to minimize peak runoff rates generated from this development. As such, no additional stormwater detention is anticipated for this project. Previous design information indicates that the control structures at the bridge minimize runoff rates and allow stormwater 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. The Rational Method was utilized to determine peak runoff rates, pipe capacities, hydraulic grade lines, 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 Site Development - Lot 15 Page 3 GENERAL LOCATION AND DESCRIPTION OF PROJECT AREA The Tower Point Infrastructure Development - Lot 15 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, Lot 15, is approximately 0.97 acres. It is bounded by an existing Chase Bank property to the northeast, existing Drive G to the northwest, an undeveloped property to the southwest, and Highway 40 to the and southeast. The extent of the Drainage Study Area includes the project area and small portions of off -site to the southwest of the project area which contribute runoff into the site storm sewer system. 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. An existing storm sewer system is located along the recently constructed Private Drive G. No storm sewer systems currently exist within the project limits of Lot 15. Site improvements associated with this new commercial development include new parking, private driveways, storm sewer systems, domestic water service systems, and sanitary sewer service systems. The project area is a majority of undeveloped property with existing land cover consisting primarily of rocky soil with minimal vegetation. There is also a portion of Private Drive G on this lot. Stormwater Drainage Report Tower Point Site Development - Lot 15 Page 4 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 southeast to northwest across the project site area. A small portion of undeveloped land to the southwest of the project area flows onto the project site and this runoff was accounted for in the drainage calculations. Stormwater runoff from the project area will be conveyed into existing storm sewer systems located along Private Drive G and ultimately to Arrington Road. 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 the existing storm sewer systems 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. 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 Stormwater Drainage Report Tower Point Site Development — Lot 15 Page 5 convey stormwater runoff within the project area for a 10 year storm event. Runoff rates have been calculated 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/(To +8.5)0763 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 / (To + 8.0)"" The existing storm sewer inlets in the vicinity of the project area along Private Drive G were evaluated as well. COMPLIANCE WITH PROPOSED DEVELOPMENT ASSUMPTIONS As indicated previously, all stormwater runoff from the proposed site development is conveyed into the existing storm sewer systems along Private Drive G. The existing stormwater detention controls located at the bridge serving Highway 6 and the existing storm sewer systems took into account for future development. Both the Spring Creek detention control structures and the existing 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 stormwater 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 stormwater detention in anticipated for this project. The stormwater drainage report submitted for the storm sewer system improvements for Private Drive G included assumptions of the anticipated runoff rates that would be generated from adjacent Stormwater Drainage Report Tower Point Site Development — Lot 15 Page 6 lot development. These assumptions were reviewed during the storm sewer system analysis of this site development and it was determined that there will be no adverse impacts on the existing storm sewer systems within Private Drive G. DRAINAGE SYSTEM DESIGN Storm sewer system peak runoff rates and system components were designed using the Rational Method. The Rational Method determines utilizes the 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. The Rational Method calculations are included in the Appendix for both the 10 year storm event and the 100 year storm event. CONCLUSION The storm sewer system for the Tower Point Site Development — Lot 15 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 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 has been determined that during the 100 year storm event, stormwater runoff that cannot enter the storm sewer system will continue flowing off site onto Private Drive G. Runoff will continue to flow within the roadway until it has an opportunity to enter the storm sewer system or discharges into Spring Creek as it currently does. Stormwater Drainage Report Tower Point Site Development — Lot 15 Page 7 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 Site Development - Lot 15 Page 8 _ SWIM Exhibit 1.................................................................. USGS Quadrangle - Wellborn Texas Exhibit 2................................................................................................ FEMA Flood Map Exhibit 3........................................................................................... Overall Grading Plan Exhibit 4..........................................................Developed Conditions Drainage Area Map Exhibit 5............................................. Arrington Road Drainage Area Map & Calculations Exhibit 6..................................Private Drive G and Pre -Development Drainage Area Map Exhibit 7...................................................................................Storm Sewer Calculations Exhibit 8...........................................................Appendix D - Technical Design Summary Stormwater Drainage Report Tower Point Site Development - Lot 15 Page 9 EXHIBIT 1 f F •naweu.w T " �wwnv 4si• .ewnw�m n "�J M�a•• ELI • . an.. u.n r.s �..w��nTn pf42F Y�•fuXM •N wa�� µnYuia�MN'W IMF �VVV�1 wmne a.•wn.w wnMwwn • �.n..n�a ra.vin na •�•e...r EXHIBIT 2 APPROXIMATE SCALE 100E 0 1000PEET ZONE X / LIMIT OF DETAILED STUDY / o Spring Creek Zy6 HOOK Sprri ng Creek Spring s f ry�y Tributary 1� TributaryA Creek e �¢� A,) OG JQP SpF < NATIONAL FLOOD INSURANCE PAOORAM LIMIT OF ry �j/ x'+: ZONE AE 'FFVL F tJ DETAILED STUDY N N� Q � ^ '�`F, �� FIRM �� N 2s19 QPP� FLOOD INSURANCE RATE MAP Pjo Spring Creek Tributary LIMIT OF R DETAILED BRAZOS COUNTY, N� ZONEAE a� 2F STUDY o�. TEXAS AND INCORPORATED AREAS P, h 90 274 PLO �1 PANEL 205 OF 250 2Si61{t67y to _ • (SEE MAP INDEX FOR PANELS NOT PRINTED) g ZONE A CONTAINS AN n 276 Spring Creek JP a a N emNxuxm xunen vtxst sxmt � w ZONEAE Tributary i N N ^' Cva®CTItnt.Umvr 'Ixxl, I'Sen v B �4vE AE _ rvavvxnrtN exsas n+ss mas o + Q N�t� Spring Creek Tributary / � Py •� T n°N�° m"awn m:mmm"mm" M.N., ui0 City of College Station _ONE X ?sa I I1 480083 2O LIMIT OF DETAILED STUDY MAP NUMBER `°S> a 48041CO205 D ZONE•AEi I /Pp�P�Q, MAP REVISED: 2 Q DRIVE ® FEBRUARY 9, 200E _ 9g O S OAK O 302 I I / Federal EmeCgencyManagement Agency Tributary to 00) Spring Creek 1 Q \ 307 Tributary D � 2 /�y a �`_ .. a by P O � \ ^�PNOPIPE v� QGO�� 2 9 1pNE \ P 315 o NpPeO MISTY N �� Q W +_' V a• Thia is an oI.ial copy of a portion of the above referenced fiood map. It LIMIT OF (G�.� \ w a w waa ,,trOotod wing F-MIT On -Line. mie map dose not reNect changes DETAILED STUDY �� JCS 1 1 /1 . m a i (� p or amendments which may have been made subsequent to the date on the < Z p Q U title block. For the latest product information abaut National Flood Insurance Program flood maps check the FEMA Flood Map Store at v mew. mac fema.gov EXHIBIT 3 Stormwater Drainage Report for Tower Point Site Development for Lot 15 College Station, Texas Prepared for: Weiner Development Corporation Prepared by: Walter P. Moore & Associates, Inc. 1301 McKinney, Suite 1100 Houston, TX 77010 TBPE Firm Registration No. 1856 January 25, 2011 Revised February 21, 2011 Revised March 11, 2011 KEVIN P. TABLE OF CONTENTS PROFESSIONAL CERTIFICATION.......................................................................................2 EXECUTIVESUMMARY ......................... ................................ .............................................. 3 GENERAL LOCATION AND DESCRIPTION OF PROJECT AREA.........................................4 DRAINAGE WATERSHEDS AND STUDY AREAS.............................................I...................5 DRAINAGE DESIGN CRITERIA............................................................................................6 COMPLIANCE WITH PROPOSED DEVELOPMENT ASSUMPTIONS...................................6 DRAINAGESYSTEM DESIGN..............................................................................................7 CONCLUSION.................................. .............. .... ........................................... ......................8 APPENDIX...........................................................................................................................9 Stormwater Drainage Repor Tower Point Site Development - Lot 15 Page 1 PROFESSIONAL CERTIFICATION This report and plans for the drainage design of Tower Point Site Development - Lot 15 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 tngineer State of Texas No. t0ztt(q Stormwater Drainage Report Tower Point Site Development - Lot 15 Page 2 EXECUTIVE SUMMARY Site development improvements are being proposed for Lot 15 within 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. Storm sewer inlets will capture stormwater runoff from the site. An underground storm sewer system will convey runoff into an existing public storm sewer system located at the intersection of Private Drive G and Private Drive C that ultimately discharges into Spring Creek located to the west of the development. The existing bridge serving Highway 6 over Spring Creek contains stormwater detention control structures to minimize peak runoff rates generated from this development. As such, no additional stormwater detention is anticipated for this project. Previous design information indicates that the control structures at the bridge minimize runoff rates and allow stormwater 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. The Rational Method was utilized to determine peak runoff rates, pipe capacities, hydraulic grade lines, 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 Site Development - Lot 15 Page 3 GENERAL LOCATION AND DESCRIPTION OF PROJECT AREA The Tower Point Infrastructure Development — Lot 15 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, Lot 15, is approximately 0.97 acres. It is bounded by an existing Chase Bank property to the northeast, existing Drive G to the northwest, an undeveloped property to the southwest, and Highway 40 to the and southeast. The extent of the Drainage Study Area includes a third of the project area which is being captured by the site storm sewer system and the remaining portion of the site sheet flows into the public storm sewer system in Private Drive G. 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. A public storm sewer system is located along the recently constructed Private Drive G which connects to the public storm sewer system in Private Drive C. An existing junction box and an existing 18" RCP pipe is located near the north corner of the site in public utility easement along Private Drive G which connects into the storm sewer system that crosses Private Drive C. No storm sewer systems currently exist within the project limits of Lot 15. Site improvements associated with this new commercial development include new parking, private driveways, storm sewer systems, domestic water service systems, and sanitary sewer service Stormwater Drainage Report Tower Point Site Development — Lot 15 Page 4 systems. The project area is a majority of undeveloped property with existing land cover consisting primarily of rocky soil with minimal vegetation. There is also a portion of Private Drive G on this lot. 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 southeast to northwest across the project site area. A small portion of undeveloped land to the southwest of the project area sheet flows across the project site and into the public storm sewer system in Drive G. Stormwater runoff from the project area will be conveyed into the public storm sewer system by connection into an existing junction box located at the intersection of Private Drive G and Private Drive C. The existing 18" RCP storm sewer pipe does not have the capacity to handle the adjacent Chase Bank lot site and Lot 15, therefore it will be removed and replaced with a new 24" RCP (Class III) storm sewer pipe. This new 24" RCP storm sewer pipe will connect into the existing storm sewer system located at the intersection of Private Drive G and Private Drive C and ultimately to Arrington Road. 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 the existing Stormwater Drainage Report Tower Point Site Development — Lot 16 Page 5 storm sewer systems 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. 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 stormwater runoff within the project area for a 10 year storm event. Runoff rates have been calculated 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 + 8.5)0'163 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 The existing storm sewer inlets in the vicinity of the project area along Private Drive G and near Private Drive C were evaluated as well. COMPLIANCE WITH PROPOSED DEVELOPMENT ASSUMPTIONS As indicated previously, all stormwater runoff from the proposed site development is conveyed into the existing junction box and new 24" RCP pipe within the public utility easement near the north corner of the site. This new 24" storm sewer pipe will connect into the existing storm sewer system located at the intersection of Private Drive G and Private Drive C and ultimately to Arrington Road. Stormwater Drainage Report Tower Point Site Development — Lot 15 Page 6 The stormwater drainage report submitted for the storm sewer system improvements for Private Drive G included assumptions of the anticipated runoff rates that would be generated from adjacent lot development. These assumptions were reviewed during the storm sewer system analysis of this site development and it was determined that both the adjacent Chase Bank lot and Lot 15 were to be captured in the storm sewer system near the intersection of Private Drive G and Private Drive C. Based on this information, the existing 18" RCP storm sewer pipe does not have the capacity to handle the runoff from both lots and will be removed and replaced with a proposed 24" RCP storm sewer. The proposed 24" RCP storm sewer pipe will connect to the existing junction located on the east corner of Private Drive G and Private Drive C and outfall into the existing 24" storm sewer system that crosses Private Drive C. There are no additional impacts to the existing storm sewer systems downstream. The existing stormwater detention controls located at the bridge serving Highway 6 and the existing storm sewer systems took into account for future development. Both the Spring Creek detention control structures and the existing 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 stormwater 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 stormwater detention in anticipated for this project. DRAINAGE SYSTEM DESIGN Storm sewer system peak runoff rates and system components were designed using the Rational Method. The Rational Method determines utilizes the peak runoff rates along with Manning's Stormwater Drainage Report Tower Point Site Development — Lot 15 Page 7 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. The Rational Method calculations are included in the Appendix for both the 10 year storm event and the 100 year storm event. CONCLUSION The storm sewer system for the Tower Point Site Development — Lot 15 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 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 has been determined that during the 100 year storm event, stormwater runoff that cannot enter the storm sewer system will continue flowing off site onto Private Drive G. Runoff will continue to flow within the 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 Site Development — Lot 15 Page 8 EXHIBIT 4 10-YEAR STORM SEWER CALCULATIONS WALTER P. MOORE & ASSOCIATES, ING 1301 MCKINNEY, SUITE 1100 HOUSTON, TX 77010 LOCATION: Tower Point Lot 15 - College Station, TX BY: HMG DATE: 3/14/2011 CHECKED BY: DATE: JOB NO: 23-05040-13 MH/ MH/ AREA AREA SUM OF C'A SUM OF INTENSITY T. At REACH DIAM. Width SLOPE MANNINGS DESIGN FALL FLOWUNE Yn ACTUAL HYDRAULIC CHANGE ELEVATION OF ELEVATION OF INLET INLET AREA C'A I Height "n" Q full V full ELEVATIONS V GRADIENT IN HEAD HYDRAULIC GRADIENT GROUND FROM TO (FT') ACRES ACRES IN/HR MIN MIN F IN IN % CFS FT/S F UPSTREAM DOWNSTREAM F FT/S % F UPSTREAM DOWNSTREAM UPSTREAM DOWNSTREAM 1-1 1-2 5055 0.12 0.12 0.10 0.10 8.63 F4.4O 10.00 0.19 56 12 0 1.00 0.009 5.146 6.55 0.56 316.10 315.54 0.28 4.93 1.000 0,560 304.090 303.53 319.10 318.85 1-2 MH-3 4019 0.09 0.21 0.08 0.19 8.57 10.19 0.22 75 12 0 1.00 0.009 5.146 6.55 0.75 315.54 314.79 0.38 5.79 1.000 0.750 303.630 302.78 318.85 319.11 MH-3 1-4 0 0.00 0.34 0.00 0.30 8.49 10.41 0.19 73 12 0 1.00 0.009 5.146 6.55 0.73 314.79 314.06 0.50 6.55 1.000 0.730 302.780 302.05 319.11 318.00 1-4 EX. JBOX 2992 0.07 0.58 0.06 0.52 8.43 10.59 0.24 105 12 0 1.00 0.009 5,146 6.55 1.05 300.05 299.00 0.71 7.36 1,000 1.050 302.050 301.00 318.00 304.00 EX, JBOX OUTFALL 0 0.00 0.58 0.00 0.52 8.35 10.83 0.03 15 24 0 0.55 0.009 24.234 7.71 0.08 294.33 294.25 0.96 7.59 0.550 0.082 297.330 297.25 304.00 304.00 1-3A MH-3 5525 0.13 0.13 0.11 0.11 8.53 0.99 10.00 0.10 31 12 0 1.00 0.009 5.146 6.55 0.31 1 315.36 315.05 0.30 5.05 1.000 0.310 303.090 302.78 319.11 318.60 I-4A 14 1 7657 1 0.18 0.18 0.16 0.16 8.63 1.37 10.00 0.18 60 12 0 1.00 0.009 5.1 66 6.55 0,601 313.23 1 312.63 0.35 5.54 1.000 0.600 302.650 1 302.05 318.00 318.60 CHASE EX. JBOX 39200 0.90 0.90 0.81 0.81 8.63 6.99 10.00 0.18 60 18 0 0.32 0.009 8.583 4.86 1 0,191 305.49 1 305.30 1.03 1 5.41 1 0.320 1 0.192 1 302.972 1 302.78 1 318.60 318.60 CAPACITY OF EXISTING INLET THAT WILL TAKE THE CHASE BANK & AT&T STORM WATER IS 12.74 C.F.S. NOTES: DESIGN BASED ON 2-YEAR RAINFALL RUNOFF COEFFICIENT EQUALS INTENSITY CALCULATIONS BASED ON CITY OF HOUSTON DESIGHN MANUAL CHAPTER 9 PAGE CH9115 OF 17 TIME OF CONCENTRATION (T c) = 10A0'17s + 15 MIN (USE =MIN) (6) STARTING HGL EQUALS THE TOP OF INSIDE OF OUTFALL PIPE ALL PIPES ARE CIRCULAR P:\23\2005\05040-13\Design & Studies\Calculations\3-14-11 05040-13 Drainage calcs 3/11/2011 EXHIBIT 7 100-YEAR STORM SEWER CALCULATIONS WALTER P. MOORE & ASSOCIATES, INC 1301 MCKINNEY, SUITE 1100 HOUSTON, TX 77010 LOCATION: Tower Point Lot 15 - College Station, TX BY: HMG DATE: 3/14/2011 CHECKED BY: DATE: JOB NO: 23-05040-13 MH/ MH/ AREA AREA SUM OF - C'A SUM OF INTENSITY FLOW Tc Al REACH CIAM. Width SLOPE MANNINGS DESIGN FALL FLOWLINE Yn ACTUAL HYDRAULIC CHANGE ELEVATION OF ELEVATION OF INLET INLET AREA C'A I Q Hei ht "n" full ELEVATIONS V GRADIENT IN HEAD HYDRAULIC GRADIENT GROUND FROM TO (FT2) ACRES ACRES IN/HR CFS MIN MIN F IN IN % /S F UPSTREAM DOWNSTREAM F FT/S % F UPSTREAM DOWNSTREAM UPSTREAM DOWNSTREAM 1-1 1-2 5055 0.12 0.12 0.10 0.10 11.64 122 10.00 0.17 56 12 0 1.00 0.009 55 0.56 316.10 315.54 0.33 5.36 1.000 0,560 304,439 303.88 319.10 318.85 1-2 MH-3 4019 0.09 0.21 0.08 0.19 11.56 2.17 10.17 0.20 75 12 0 1.00 0,009 55 0.75 315.54 314.79 0.45 6.27 1.000 0.750 303.879 303.13 318.85 319.11 MH-3 1-4 0 0.00 0.34 0.00 0.30 11.47 3.46 10.37 0.17 73 12 0 1.00 0.009 f24.2347.71 55 0.73 314.79 314.06 0.60 7.03 1.000 0.730 303,129 302.40 319.11 318.00 1-4 EX. JBOX 2992 0.07 0.58 0.06 0.52 11.39 5.94 10.55 0.23 105 12 0 1.00 0.009 55 1.05 300.05 299.00 1.00 7.56 1.332 1.399 302.399 301.00 378.00 304.00 EX, JBOX OUTFALL 0 0.00 0.58 0.00 0.52 11.29 15.31 10.78 0.03 15 24 0 0.55 0.009 71 0.08 294.33 294.25 1.15 8.16 0.550 0.082 297,330 297.25 304. 00 304.00 1-3A MH-3 5525 0.13 0.13 0.11 0.11 11.64 1.33 10.00 0.09 31 12 0 1.00 0.009 55 0.31 315.36 315.05 0.35 5.50 1.000 0.310 303.439 303A3 319.11 318.60 I-4A 1-4 1 7657 0.18 1 0.18 0.16 0.16 11.64 1.84 10.00 0.17 60 12 0 100 1 0.009 5.146 6.55 0.60 313.23 312.63 0.41 6.01 1.000 0.600 302,999 302A0 318.00 318.60 CHASE EX. JBOX 39200 0.90 0.90 0.81 0.81 1 11.64 1 9.43 1 10.001 0.19 1 60 1 18 0 0.32 1 0.009 8.583 4.86 0.19 305.49 305.30 1.50 6.33 0.386 0.232 303.361 303.13 318.60 318.60 CAPACITY OF EXISTING INLET THAT WILL TAKE THE CHASE BANK & AT&T STORM WATER IS 12.74 C.F.S. NOTES: DESIGN BASED ON 2-YEAR RAINFALL RUNOFF COEFFICIENT EQUALS 0.9 (5) INTENSITY CALCULATIONS BASED ON CITY OF HOUSTON DESIGHN MANUAL CHAPTER 9 PAGE CH9/15 OF 17 TIME OF CONCENTRATION (Tc)=10A0"6+15 MIN (USE =MIN) (6) STARTING HGL EQUALS THE TOP OF INSIDE OF OUTFALL PIPE ALL PIPES ARE CIRCULAR P:\23\2005\05040-13\Design & Studies\Calculations\3-14-11 05040-13 Drainage calcs 3/11/2011 Stormwater Drainage Report for Tower Point Site Development for Lot 15 College Station, Texas Prepared for: Weiner Development Corporation Prepared by: Walter P. Moore & Associates, Inc. 1301 McKinney, Suite 1100 Houston, TX 77010 TBPE Firm Registration No. 1856 January 25, 2011 Revised February 21, 2011 Revised March 11, 2011 Revised November 21. 2011 21 1W V 13 :W �� 3 �g' TABLE OF CONTENTS PROFESSIONAL CERTIFICATION 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 ................................... 7 DRAINAGE SYSTEM DESIGN............................................................................................. 8 CONCLUSION..................................................................................................................... 8 APPENDIX......................................................................................................................... 10 Stormwater Drainage Report Tower Point Site Development — Lot 15 Page 1 PROFESSIONAL CERTIFICATION This report and plans for the drainage design of Tower Point Site Development - Lot 15 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 Site Development - Lot 15 Page 2 EXECUTIVE SUMMARY Site development improvements are being proposed for Lot 15 within 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. Storm sewer inlets will capture stormwater runoff from the site. An underground storm sewer system will convey runoff into an existing public storm sewer system located along Private Drive G, near the intersection at Private Drive C that ul imately discharges into Spring Creek located to the west of the development. The existing bridge serving Highway 6 over Spring Creek contains stormwater detention control structures to minimize peak runoff rates generated from this development. As such, no additional stormwater detention is anticipated for this project. Previous design information indicates that the control structures at the bridge minimize runoff rates and allow stormwater 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. The Rational Method was utilized to determine peak runoff rates, pipe capacities, hydraulic grade lines, 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 Site Development — Lot 15 Page 3 GENERAL LOCATION AND DESCRIPTION OF PROJECT AREA The Tower Point Infrastructure Development — Lot 15 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, Lot 15, is approximately 0.97 acres. It is bounded by an existing Chase Bank property to the northeast, existing Drive G to the northwest, an undeveloped property to the southwest, and Highway 40 to the and southeast. The extent of the Drainage Study Area includes a third of the project area which is being captured by the site storm sewer system and the remaining portion of the site sheet flows into the public storm sewer system in Private Drive G. 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. A public storm sewer system is located along the recently constructed Private Drive G which connects to the public storm sewer system in Private Drive C. An existing junction box and an existing 18" RCP pipe is located near the north corner of the site in public utility easement along Private Drive G which connects into the storm sewer system that crosses Private Drive C. No storm sewer systems currently exist within the project limits of Lot 15. Site improvements associated with this new commercial development include new parking, private driveways, storm sewer systems, domestic water service systems, and sanitary sewer service Stormwater Drainage Report Tower Point Site Development — Lot 15 Page 4 systems. The project area is a majority of undeveloped property with existing land cover consisting primarily of rocky soil with minimal vegetation. There is also a portion of Private Drive G on this lot. 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 southeast to northwest across the project site area. A small portion of undeveloped land to the southwest of the project area sheet flows across the project site and into the public storm sewer system in Drive G. Stormwater runoff from the new shared driveway between Lot 15 and Lot 16 will be collected by a new BB -inlet located on the north side of the shared driveway, near Private Drive G. The new BB - inlet will connect to the existing junction box located near the west corner of the property where the new shared driveway connects to Private Drive G. This existing junction box is designed to collect drainage from Lot 16 per the Drainage Area Map - Exhibit 6, therefore a new 18" stub -out has been extended into Lot 16 for future development. Stormwater runoff from the rest of the project area will be conveyed into the public storm sewer system by a new BB -inlet located on the north corner of the property and a new 12" connection into an existing junction box north located northwest of the property, near the intersection of Private Drive G and Private Drive C. The existing junction box also captures the drainage from the adjacent Chase Bank lot site and is connected by an existing 18" Stormwater Drainage Report Tower Point Site Development - Lot 15 Page 5 RCP storm sewer pipe to the existing storm sewer system located at the intersection of Private Drive G and Private Drive C and ultimately to Arrington Road. 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 the existing storm sewer systems 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. 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 stonnwater runoff within the project area for a 10 year storm event. Runoff rates have been calculated 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 / (To + 8.5)"" 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)0 730 The existing storm sewer inlets in the vicinity of the project area along Private Drive G and near Private Drive C were evaluated as well. Stormwater Drainage Report Tower Point Site Development — Lot 15 Page 6 COMPLIANCE WITH PROPOSED DEVELOPMENT ASSUMPTIONS As indicated previously, stormwater runoff from the proposed site development is conveyed into existing junction boxes located on the west and north corners of the property and outfall into the existing storm sewer system located at the intersection of Private Drive G and Private Drive C and ultimately to Arrington Road. The stormwater drainage report submitted for the storm sewer system improvements for Private Drive G included assumptions of the anticipated runoff rates that would be generated from adjacent lot development. The storm sewer system analysis of this site development included review of the design runoff from the adjacent Chase Bank lot and Lot 15 to be captured in the storm sewer system near the intersection of Private Drive G and Private Drive C. Based on this information and review of the new hydraulic grade line, the existing 18" RCP storm sewer pipe and the existing junction box near the north property corner can handle the runoff from both the Chase Bank lot and Lot 15 and can remain in place with the new 12" storm sewer installed per the elevations on the plans. Assumptions of the anticipated runoff rates from Lot 16, along with the additional runoff from a portion of Lot 15 were also reviewed and it was determined the new BB - inlet can capture the runoff from the shared driveway and not cause an adverse impact to the existing storm sewer systems downstream. The existing stormwater detention controls located at the bridge serving Highway 6 and the existing storm sewer systems took into account for future development. Both the Spring Creek detention control structures and the existing 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 stormwater control structures as well as the existing storm sewer Stormwater Drainage Report Tower Point Site Development — Lot 15 Page 7 system. These assumptions include using minimum time of concentrations and fully development runoff coefficients. As a result, no additional stormwater detention in anticipated for this project. DRAINAGE SYSTEM DESIGN Storm sewer system peak runoff rates and system components were designed using the Rational Method. The Rational Method determines utilizes the 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. The Rational Method calculations are included in the Appendix for both the 10 year storm event and the 100 year storm event. CONCLUSION The storm sewer system for the Tower Point Site Development - Lot 15 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 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 has been determined that during the 100 year storm event, stormwater runoff that cannot enter the storm sewer system will continue flowing off site onto Private Drive G. Runoff will continue to flow within the roadway until it has an opportunity to enter the storm sewer system or discharges into Spring Creek as it currently does. Stormwater Drainage Report Tower Point Site Development - Lot 15 Page 8 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 Site Development - Lot 15 Page 9 10-YEAR STORM SEWER CALCULATIONS WALTER P. MOORE & ASSOCIATES, INC 1301 MCKINNEY, SUITE 1100 HOUSTON, TX 77010 LOCATION: Tower Point Lot 15 - College Station, TX BY: HMG DATE: 11/15/2011 CHECKED BY: DATE: JOB NO: 23-05040-13 MH/ MH/ AREA AREA SUM OF C*A SUM OF INTENSITY FLOW Tc At REACH DIAM. Width SLOPE MANNINGS DESIGN FALLI FLOWLINE Yn ACTUAL HYDRAULIC CHANGE ELEVATION OF ELEVATION OF INLET INLET AREA C*A I Q Height W.I Q full V full ELEVATIONS V GRADIENT IN HEAD HYDRAULIC GRADIENT GROUND FROM TO FT ACRES ACRES IN/HR) (CFS) (MIN MIN F IN IN % CFS FT/S F UPSTREAM DOWNSTREAM F FT/S % F UPSTREAM DOWNSTREAM UPSTREAM DOWNSTREAM 1-1 EX. JBOX 0 0.52 0.52 0.47 0.47 8.63 4.04 10.00 0.21 90 12 0 1.00 0.009 5.146 6.55 0.90 301.90 301.00 0.67 7.25 1.000 0.900 302,142 301.24 318.00 304.00 EX, JBOX OUTFALL 0 0.00 1.42 0.00 1.28 8.56 17.93 10.21 0.02 15 18 0 0.32 0.009 8,583 4.86 0.05 298.08 298.03 1.50 10.15 1.397 0.210 301.242 301.03 304.00 302.35 CHASE EX. JBOX 39200 0.90 0.90 0.81 0.81 8.63 6.99 10.00 0.18 60 18 0 0.32 0,009 8,583 4.86 0.19 305.49 305.30 1.03 5.41 0.320 0.192 301.434 301,24 304.00 318.60 1-2 EXJBOX2 0A0 0,40 0.36 0.36 8.63 3.11 moo 0.06 23 12 0 1.00 0.009 5.146 6.55 0.23 299A7 299.24 0.56 6.86 1.000 0.230 302.470 302.24 30900 308.75 CAPACITY OF EXISTING INLET THAT WILL TAKE THE CHASE BANK & AT&T STORM WATER IS 12.74 C.F.S. NOTES: 1. DESIGN BASED ON 2-YEAR RAINFALL 2. RUNOFF COEFFICIENT EQUALS 0.9 (5) 3. INTENSITY CALCULATIONS BASED ON CITY OF HOUSTON DESIGHN MANUAL CHAPTER 9 PAGE CH9/15 OF 17 4. TIME OF CONCENTRATION (Tc) = 10A°"c+ 15 MIN (USE =MIN) (6) 5. STARTING HGL EQUALS THE TOP OF INSIDE OF OUTFALL PIPE 6. ALL PIPES ARE CIRCULAR P:\23\2005105040-13\Design & Studies\Calculations\11-15-11 05040-13 Drainage caics 11/21/2011 100-YEAR STORM SEWER CALCULATIONS WALTER P. MOORE & ASSOCIATES, INC 1301 MCKINNEY, SUITE 1100 HOUSTON, TX 77010 LOCATION: Tower Point Lot 15 - College Station, TX BY: HMG DATE: 11/15/2011 CHECKED BY: DATE: JOB NO: 23-05040-13 MH/ MH/ AREA AREA SUM OF C-A SUM OF INTENSITY FLOW Tc et REACH MANNINGS DESIGN FALL FLOWUNE Yn ACTUAL HYDRAULIC CHANGE ELEVATION OF ELEVATION OF INLET INLET AREA C`A 1 Q "n., O full V full ELEVATIONS V GRADIENT IN HEAD HYDRAULIC GRADIENT GROUND FROM TO FT ACRES ACRES IN/HR CFS MIN MIN CFS FT/S UPSTREAM DOWNSTREAM FT/S % F UPSTREAMDOWNSTREA UPSTREAM DOWNSTREAM 1-1 EX. JBOX 0 0.52 0.52 0.47 0.47 11.64 5.45 10.00 0.20 90 0.009 5.146 6.55 0.90 301.90 301.00 0.89 7.40 1,000 0.900 302.313 301.41 318.00 304.00 EX. JBOX OUTFALL 0 0.00 1.42 0.00 1.28 11.54 24.18 10.20 0.02 15 0.009 8.583 4.86 0.05 298.08 298.03 1,50 13.68 2.540 0,381 301.413 301.03 304.00 302.35 CHASE EX. JBOX 3 2200 0.90 0.90 0.81 0.81 11.64 9.43 10.00 0.19 60 0.009 8S83 4S6 0.19 305.49 305.30 1.50 5.33 0.386 0,232 301.645 301.41 304.00 318.60 1-2 EX JBOX2 0.40 0.40 0.36 0.36 11.64 4.19 10.00 0.05 23 001.00 0.009 5.146 6.55 0,23 299.47 299.24 6.69 7.30 1.000 0.230 302.470 302.24 309.00 308.75 CAPACITY OF EXISTING INLET THAT WILL TAKE THE CHASE BANK & AT&T STORM WATER IS 12.74 C.F.S. NOTES: 1. DESIGN BASED ON 2-YEAR RAINFALL 2. RUNOFF COEFFICIENT EQUALS 0.9 (5) 3. INTENSITY CALCULATIONS BASED ON CITY OF HOUSTON DESIGHN MANUAL CHAPTER 9 PAGE CH9/15 OF 17 4. TIME OF CONCENTRATION (Tc) = 10A°''76 + 15 MIN (USE =MIN) (6) 5. STARTING HGL EQUALS THE TOP OF INSIDE OF OUTFALL PIPE 6. ALL PIPES ARE CIRCULAR P:\23\2005\05040-13\Design & Studies\Calculations\11-15-11 05040A3 Drainage talcs 11/21/2011