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HomeMy WebLinkAboutDrainage Report• Greens Prairie Elementary School Drainage Report 4300 Greens Prairie Trail College Station, Texas June 2010 Prepared for: College Station Independent School District 1812 Welsh Ave. College Station, Texas 77840 Prepared by: Kimley -Horn and Associates, Inc. 111 University Drive East Suite 105 College Station, Texas 77840 • • Kimley -Horn and Associates, Inc. Executive Summary Report Contact Information Developer College Station Independent School District 1812 Welsh College Station, Texas 77840 (979) 694-5610 Contact: John Hall Engineer Kimley -Horn and Associates, Inc. 111 University Drive East, Suite 105 College Station, Texas 77840 (979) 846 -8401 Contact: Mike Moore, P.E. Identification The Greens Prairie Elementary School site is located on the east side of a 46.027 acre tract at 4300 Greens Prairie Trail, southwest of the intersection of Greens Prairie Trail and Royder Road. The subject site is the first phase of a two part development for the College Station Independent School District. The property is an unplatted parcel of land. Location The subject tract for this development straddles a drainage divide, with the east side, the subject site for Phase I, draining in a southeasterly direction, with slopes ranging from 2.0% near the drainage divide to 0.6% across the remainder of the site, and discharging as shallow concentrated flow onto the adjacent property. The runoff from the Phase I subject site feeds a livestock pond located on the adjacent property. The west side of the tract, Phase II, drains in a westerly direction with slopes averaging 4.0 %, and discharges into the Peach Creek Unnamed Tributary bordering the southwest property line of the tract. The entire tract is currently undeveloped with portions being short- grassland and wooded. The tract is located outside of the City of College Station city limits, but within the city's Extraterritorial Jurisdiction. No portion of the subject, Phase I, site is located within the Special Flood Hazard Areas (SFHAs), however, portions of the west side of the tract do lie within the SFHA based on the FIRM (Flood Insurance Rate Map) Panel Map for Brazos County, Map No. 48041CO325E included in Appendix A. Hydrologic Characteristics The subject site for CSISD's Greens Prairie Elementary School lies within the Peach Creek watershed and will require a Type 1 detention facility due to its location within the upper portion of the watershed. Although the property straddles a drainage divide within the Greater Peach Creek Watershed, only one detention facility will be used to attenuate post - development flows for the entire tract. Hydrologic information for the basin was obtained from Figure B -12 of the City of College Station Drainage Manual. The tract contains a Singleton (SnB) fine sandy loam, Boonville (BoA) fine sandy loam, and Gredge (GrD) fine sandy loam soils. These soils exhibit low infiltration rates and were classified as Hydrologic Class D soils per the Natural Resources Conservation Service's Curve Number method. Considering these criteria the existing groundcover conditions were assigned a Curve Number of 80. The existing tract currently discharges at four separate outfall points including: a portion to the Royer Road drainage ditch, a portion from the east side of the drainage divide that flows as shallow concentrated flow to the adjacent property, the west side portion that discharges into the unnamed Peach Creek tributary, and the south central portion of the property that sheet flows in a southeasterly direction onto the adjacent property. The area of the subject site that sheet flows to the Royder Road drainage ditch in existing conditions will be adjusted to account for effects of post - development impervious conditions and match existing peak flows. The Phase I subject site (east side of the property) is an undeveloped grassland and wooded tract that sheet flows in a southeasterly direction and empties as shallow concentrated flow onto the property adjoining the southeast property line. This flow feeds a livestock pond located on the adjacent property. A portion (4.99 acres) of the property north of Greens Prairie Trail drains on to the subject site through an existing 24" corrugated metal pipe. These flows will be maintained by conveying them through the proposed storm sewer that outfalls at the existing east side location. As only one detention facility will be used for the entire property, the additional runoff generated in post - development conditions will be conveyed through storm sewer, across the drainage divide, to the detention pond located on the west side of the property. This was accomplished by decreasing the area contributing to the east side outfall point and routing all excess flows to the detention pond on the west side of the property. The area was determined by matching or reducing the peak discharge experienced for the 2, 10, 25, 50, and 100 recurrence storm events. The west side of the tract, Phase II, is also undeveloped grassland and wooded that sheet flows into the unnamed tributary of Peach Creek that adjoins the subject tract's southwest property line. Portions of this tributary have been determined to fall within FEMA's SERA; however, all proposed site development work, including the detention pond, will remain outside of these limits. Excess runoff generated in post - development conditions of Phase II will be attenuated within the proposed Phase I detention pond. A south central portion of the property that sheet flows in a southeasterly direction onto the adjacent property will remain unchanged in post - development conditions. The fully developed property will incorporate two school sites with a total impervious cover of 36 %. The grades on the site will range from 0.5% to 12 %. All four outfall peak discharges will be matched or reduced for the 2, 10, 25, 50, and 100 year recurrence storm events per hydrologic model developed with HEC -HMS 3.4. The on -site detention facility was designed using HEC -HMS 3.4 software along with the NRCS curve number method with criteria consistent with the City of College Station Unified Stonnwater Design Guidelines Dated February 2009. The hydrologic analysis for the subject site, using HEC -1IMS 3.4, can be found in Appendix B. The drainage areas used in the HEC -HMS 3.4 analysis can be seen in the plan sheet entitled HEC -HMS Models Drainage Area Maps located in Appendix B of the report. Hydraulic Criteria As designed, the runoff to the Royder Road drainage ditch will maintain its current flow pattern, and the portion that discharges to the southern property on the east side will be released in the same state as experienced in pre - development flow conditions. This is accomplished by conveying the runoff over a 33 S.Y. riprap spillway of 6" to 10" diameter stones, prior to releasing it onto the downstream property. The offsite area north of Greens Prairie Trail will be captured at the north end of the site and routed through the proposed onsite storm sewer system, and subsequently be released in a 3'x3' box culvert at the site's east outfall previously mentioned. The additional excess runoff generated from post - development conditions of the east side will be piped through a 42" RCP storm sewer pipe at an average slope of 0.4 %. The western portion of the site will remain graded into the proposed detention pond. The detention pond was sized to attenuate future build out for the entire tract (assuming 8.23 acres, of the Phase I1 area converted to impervious surfaces). The drainage areas emptying into the detention pond will include developed flows from the subject site and future development on the west side of the drainage divide. Located on the west side of the tract, the detention pond is sized to hold 6.49 acre -feet of storage (5.9 ac -ft expected in the 100 year event, plus the additional 10% for sedimentation over the life of the facility) for the 100 year storm event. The top of the berm is set at 287.0' and the maximum stage reached in the 100 year storm event is 286.47' including an additional 10% storage volume per the City of College Station's Stormwater Design Guidelines. The proposed pond outfall structure, designed to match or reduce the peak discharges for the 2, 10, 25, 50, and 100 year storm events, is a two staged, sharp- crested weir. The first stage is 2' -6" wide with an invert elevation at the base of the pond equal to 282.50'. The second stage is designed to be 7' -0" wide with an invert elevation of 285.00'. The top of the weir is set at an elevation of 286.50', allowing the portion above the weir to the top of the berm (elevation 287.00') to act as the emergency overflow spillway for the detention pond. This also allows for 6" of freeboard in the 100 year storm event. Energy from the pond discharge will be dissipated through the use of 30 S.Y. of 12" to 18" diameter rock rip rap that is underlain with Mirafi 140N filter fabric at the end of the pond outfall structure. The drainage system is designed to convey, collect, and release runoff from the Greens Prairie Elementary School Phase 1 at flows that do not exceed existing discharges, based on each of the design storms, entering the respective outfall point. Coordination and Permitting No coordination of storinwater with entities outside the City of College Station will be required. Included by Reference The following documents are included by reference: • 26 -page drainage report dated June 14, 2010. • CSISD Green Prairie Elementary School — Phase 1, Civil Enginccring Plans by Kimley -Horn and Associates, Inc. "This report for the drai age design of LSD Greens Prairie Eleni ntaw School tiros prepared under nn' supervision in accorc nc with pro ions of the Bryan/College Station Unified Drainage Design Guidelines for the o of the pi All licenses and permits required by any and all state and federal regulc ory gen ; es for he 'opc sed drainage improvements have been issued. Licensed Pr State of Texas No. essiona Engineer Appendix A FEMA FIRM Map No. 48041CO325E OS 30 p 1 1 Azb p !LIP , 11 fi pp g2 % f pt��i �� ,] l bpi a y 7 g 4 t ! ey 1Sj° ijyi 1 :2! 2RS �rI 11 ,, j illsl. ! 1 ti iti Hi s ➢Y 3i ii d r, li_1 o 11 s F S gg i I`- d^ o iii 111111!1; P9,1 IV 1 1114111; I: s P q 7, 551/1) 1 ih s i 13 ea p 8 a iE § i L a8 j• in 1 0 g C.Fi x £i gg �aA 2s tv'+ Ili q'..-' y r 2 ,111 p I 11;:04,1 8.6iE WI i �. � � s x 2,1' ;c_° € 59L013NVd SNIOf 13 3.0 i it ug 7 Appendix 13 HEC -HI\1S 3.4 Hydrologic Analysis CKLIS ,14 Is II 1111 I i r m G) m z 0 e 0 0 m m 0 m m z 0 z H 0 c rc 0 0 0 ■ ■ ■ ■ ado8 213C1A02 — r 0 m m 0 m z 0 0 0 H 0 z HEC -HMS MODELS & DRAINAGE AREA MAPS GREENS PRAIRIE ELEMENTARY SCHOOL BRAZOS COUNTY, TX ❑ � � Kimley -Horn and Associates, Inc. III U, ..,s ty Drive. Suite 105 College Stu ion, Texas 7'840 08PE Regis ration No. 0-028 ie1. No.(079) 816 -8901 00. No.(979) 846 -8150 Drainage Area Basin Area (acres) Percent Impervious Slope (ft /ft) Curve Number Time of Conc. (min) Lag Time (min) OS -1 4.2 0 0.009 84 31.7 19.0 DA -1 11.08 0 0.003 86 10.0 6.0 DA -2 1.8 0 0.008 81 10.0 6.0 DA -3 10.96 0 0.007 86 10.0 6.0 DA -4 15.83 0 0.040 93 10.0 6.0 DA -5 3.12 0 0.010 80 10.0 6.0 Drainage Area Basin Area (acres) Percent Impervious Slope (ft /ft) Curve Number Time of Conc. (min) Lag Time (min) OS -1 4.2 0 0.009 84 31.7 19.0 OS -2 0.8 0 0.010 93 10.0 6.0 EX -1 20.12 0 0.011 80 34.4 20.6 EX -2 2.8 0 0.021 80 15.0 9.0 EX -3 18.99 0 0.040 80 27.1 16.3 Hydrologic Conditions College Station Independent School District - Greens Prairie Elementary School Prepared By: Kimley - Horn & Associates, Inc. Pre - Development Conditions !Total Acreage 46.91 I Post - Development Conditions (Total Acreage 46.99 l K: \CST Civil \66077400 -CSISD \HMS \Drainage Analysis.xls 6/12/20105:23 PM Max. Runoff (cfs) 1 E'8 1 S'L£ 1 IS 1 T'L£ 1 L'99 I S'8 1 Z'1b 9 Time to Peak (hh:mn) ZZ:Z1 LO:ZT 80 :ZT LO :Z1 LO:Z1 80:ZT 80:ZT 61:Z1 Total Infilt. (in) Z .- E Sb'1 L8'T btI1 Z9 56'T ti£'Z 81•£ Total Runoff (in) 1E' Z 1SZ 60 ZS' Z bE'E TO'Z 96 96 Total Precip. (in) 96 96 96'£ 96 96'£ 96 08 08 ND r 178 98 18 98 176 08 0 0 sno uadw! wailed 0 0 0 0 0 0 0 0 Basin Area (acres) r i7 80' 11 08 96'01 £8'S1 Z1'£ 8£'S1 S8'6Z Drainage Area 1 T -SO T vaI z -vaI E -va I v -vaI s -vaI IIe3 }nO laaa0 1Se31 'Peach Creek Outfall Max. Runoff (cfs) I Es £ E 1 6'Z£ 1 L'9 I S£ I £'Z1 0'S£ Time to Peak (hh:mn) ZZ:ZT LO :Z1 bZ :ZT 1T:ZT 61:Z1 SZ:ZT 61: Z T (u!) le1o1 Z9'1 8L'0 56'1 56'T 56'1 Total Runoff (in) ti£'Z 81•£ 10'Z 10'Z 10'Z Total Precip. (in) 96 96 96 96 96 ND 178 E6 08 08 08 Percent Impervious 0 0 0 0 0 0 0 Basin Area (acres) Z'b 8'0 Z1'OZ 8'Z 66'81 11•SZ 1 66'81 Drainage Area T -SOI Z-S ° T - X31 Z E 1East Creek Outfall 'Peach Creek Outfall TD ra er aQ 0- o � cu E o 0 ' u N C CO TO 13 ra CL CL 113 c D- 2 Year Recurrence Interval Event Post-Development Results Pre-Development Results Max. Runoff (cfs) CST S'b9 1 9'6 ! 9'E9 ! 8'001 l t'91 L'ZL Time to Peak (hh:mn) Time to Peak (hh:mn) TZ:ZT LO:ZT LO:ZT LO:ZT LO:ZT LO:Z1 80:ZT I TZ:ZT (u!) 'TI!}ul Ielol I 88'1 59 ZZ'Z £9 bE'Z zs•s LS '9 Total Runoff (in) - ZS'S SL's 81•5 L L's Total Precip. (in) 90'S _ J 017'L 017'L Total Precip. (in) b' b' L b' L b' L ti'L b'L 08 08 ND ti8 98 18 98 17 6 08 0 0 Percent Impervious 0 0 0 0 0 0 0 0 Basin Area (acres) I z 'v 80'11 08'1 96'01 E8'S1 Z1'E TT'SZ I 66'81 Drainage Area I iSOI -ea Z -da E -VO I 17 s-val !East Creek Outfall 1 'Peach Creek Outfall Max. Runoff (cfs) ! L'S1 ! 0 ' S ! Z'L9 ! 1'E1 l S'OL 8 1 78 1 Time to Peak (hh:mn) TZ:ZT LO:Z1 EZ:ZT O1:Z1 81:Z1 bZ:ZT 81:21 1 (u!) '1I!ful le }ol 1 88'1 E8'0 17 17E'Z b5'Z Total Runoff (in) zs•s LS '9 90'S 90'S 90'S Total Precip. (in) Ob' L 017'L 017'L (AIL OVL I ND I 178 I E6 08 08 08 sno!n.iadw ;uaDJad 0 0 0 0 0 0 0 Basin Area (acres) I Z17 I 80 Z1'OZ 8'Z 66'81 11•SZ 66'81 Drainage Area I t-S0 Z-S° I T -X3 Z -X3 E - X31 !East Creek Outfall 1 'Peach Creek Outfall co 0 CU uci CI- Cl o - - Y N V) c CO T v -a 0. co 10 Year Recurrence Interval Event Post-Development Results Pre-Development Results Max. Runoff (cfs) 1 S' 81 1 0'SL 1 ETC 1 6'EL 1 7'S11 1 E•61 1 6 1 8'6L Time to Peak (hh:mn) TZ:ZT I LO:ZT LO :Z1 LO :Z1 LO:Z1 LO :Z1 80:ZT 1Z :Z1 Total Infilt. (in) Z6'T I 69'1 I 8Z'Z 99'1 L9•0 00 87'9 9S•L Total Runoff (in) 87'9 I IL9 Z1'9 I 17L 9 EL.L 00'9 07' 8 07'8 Total Precip. (in) 7'8 7'8 7'8 7'8 7'8 7'8 08 08 ND 178 98 18 98 O 08 O O Percent Impervious O O O O O O O O Basin Area (acres) I Z7 80'1T 08'T 96•01 E8'S1 Z1•E 11'SZ 66'81 Drainage Area T SO1 T -da l z-val E -va 7-dal Seal !East Creek Outfall 1 'Peach Creek Outfall Max. Runoff (cfs) S'81 1 L'S 1 7•08 l S'S1 178 l E•TOT I 0'78 1 Time to Peak (hh:mn) 1Z :Z1 LO:Z1 EZ:ZT 01: Z1 81:Z1 7Z:ZT 81:Z1 Total lnfilt. (in) Z6 T 78'0 07'Z 07' Z 07'Z (u!) lounb le;ol 87'9 9S•L 00'9 00'9 00'9 Total Precip. (in) 07'8 07' 8 07'8 07'8 017'8 ND 178 E6 08 08 08 Percent Impervious O O O O O O O Basin Area (acres) Z '7 8'0 Z1'OZ 8'Z 66•81 11•SZ 66•81 Drainage Area I l T-so l Z -SO -X3 Z - X3I E !East Creek Outfall 1 'Peach Creek Outfall CL � o E a u Y VI C ▪ ▪ CO ts CU CO Ct. CL b.0 2 irs ra 25 Year Recurrence Interval Event Post-Development Results Pre-Development Results Max. Runoff (cfs) O'TZ 1 0'178 8'ZT 1 L'Z8 I T'LZT 1 O•ZZ I 9•S6 Time to Peak (hh:mn) Time to Peak (hh:mn) TZ:ZT LO :ZT LO :ZT LO:Z1 LO:ZT LO:Z1 LO :Z1 I OZ:Z1 Total Infilt. (in) L6•1 ZL'1 17 69'1 89'0 L17'Z E8'L S68 Total Runoff (in) E8'L sus 917' L T1'8 Z1•6 EE'L 08'6 08'6 Total Precip. (in) 08 08'6 08'6 08'6 08'6 08'6 08 08 ND 17 8 98 18 98 17 08 0 0 Percent Impervious 0 0 0 0 0 0 0 0 Basin Area (acres) Z'17 80'1T 08'1 96'01 E8•ST Z1•E 1T'SZ I 66'81 Drainage Area T SO1 T da I Z - d a 1 £ -d a1 ti - V0 I S - l eflnO 31aaa0 ise3I 'Peach Creek Outfall Max. Runoff (cfs) 0'TZ E•9 17'Z6 L' LT 17'96 T I Time to Peak (hh:mn) I TZ:ZT LO :Z1 EZ:ZT 01 :Z1 81 :Z1 17Z:ZT BT:ZT (u!) 11!1 Ie�o1 L6 I S8 L17' Z L17•Z L17'Z Total Runoff (in) E8'L S68 EE'L EE•L EEL Total Precip. (in) 08'6 08'6 08'6 08'6 08'6 ND 1 178 I E6 08 08 08 Percent Imperviou 0 0 0 0 0 0 0 Basin Area (acres) Z' 8'0 ZT'OZ 8•Z 66'81 11•SZ 66'81 Drainage Area 1 i 5O1 Z - SO 1 Z - X31 Z - X31 £ 1East Creek Outfall 'Peach Creek Outfall w CD CD RS cu cu a o1i 0 o ° - o u C ? v -0 CO 1 Z ) C s- CO ra cu 50 Year Recurrence Interval Event Post-Development Results Pre-Development Results Max. Runoff (cfs) 17' S•Z6 £'171 1'16 L•8£1 I S L•SOT I Time to Peak (hh:mn) Time to Peak (hh:mn) TZ:ZT LO :ZT LO:ZT LO:ZT LO:Z1 LO:ZT LO :ZT I OZ :ZT I Total Infilt. (in) 007 17L'T 6E'Z ZL'T 89'0 ZS'Z 00'6 ST•OT Total Runoff (in) 00'6 9Z•6 19•8 8Z'6 ZE'01 817'8 00 00'11 Total Precip. (in) 00'11 00 00'T1 00' 11 00'11 00'11 08 08 ND I 178 I 98 T8 98 176 08 0 0 sno!na luaDJad 0 0 0 0 0 0 0 0 66'81 I Z 17 80'11 08'T 96•01 E8'S1 Z1'E i LZ'S1 I 8•6Z Drainage Area T-S T Z -da E I v-da I s-va I 1East Creek Outfall 'Peach Creek Outfall Max. Runoff (cfs) 1 17'EZ 1 6'9 1 9 1 L'61 1 ELOT 1 O'OET Time to Peak (hh:mn) I 1Z :Z1 LO:Z1 EZ:Z1 OT :Z1 8T:Z1 17Z :ZT 81:Z1 I (u!) '�I!ful Ie1 0 07 S8•0 ZS'Z ZS'Z ZSc Total Runoff (in) 00'6 ST•OT 817'8 817'8 817'8 Total Precip. (in) 00•11 00 00'11 00•11 00 ND I 178 E6 08 08 08 Percent Impervious 0 0 0 0 0 0 0 I Z 17 8'0 Z1'OZ 8'Z 66•81 1T•SZ I 66'81 Drainage Area I - S ° Z SOI 1 - X31 Z E 1 1East Creek Outfall 'Peach Creek Outfall co CD CL CO Oa s E u Y Y Ts - C 3 CD CL CL C.1 CU CU 100 Year Recurrence Interval Event Post-Development Results Pre-Development Results 0 v e--1 0 N T-1 0 0 e--1 0 00 (s ;p) alieq sia 0 to 0 Tr 0 N 0 0 0 0 0 0 N e-7 0 0 i0 0 0 0 0 0 CO ,-1 ; w 1 0 3 0 I TA' u 3 0 w c I O Vf CL C a O L. C o L a) 0 = O -1 4-1 • 3 • N N 0 i 0 c 9- Lr1 N o° o o o (sp) a2JeLpsia O O O 0 O io 0 O 0 0 N 0 w 0 13 0 c o 0 0 0 0 0 0 0 0 0 0 0 N 0 N N - a , 00 l0 -1 �-1 -1 ▪ (N (sp) a2JeLpsia 0 0 i0 0 0 0 0 0 0 0 0 0 00 U1 t 3 0 4- 0 O O O O O O O O O O O O N N N O � i�-I ��-4 aN-1 O 00 (.0 N (sp) a ietps a O O O O O O O 0 c Appendix C Greens Prairie Elementary School — Storm Sewer Layout (2 Sheets) Appendix C Greens Prairie Elementary School — Storm Sewer Layout (2 Sheets) qn VII O M WIN 1,1 1 STORM SEWER PLAN MATCH LINE SHEET C -08.2 GREENS PRAIRIE ELEMENTARY SCHOOL BRAZOS COUNTY. TX ❑ Kimley -Horn and Associates, Inc. 111 Univers ty Drive, safe 105 College Station. Texas 77840 0BPE Registration No. F -928 fel. No. 979) 846 -8401 Fo. Na. 979) 846 -8450 • F r G) m 2r 0 MATCH LINE SHEET C-08.1 6 I IP VII MAMI NI, N,, 1■■%1 1 STORM SEWER PLAN GREENS PRAIRIE ELEMENTARY SCHOOL BRAZOS COUNTY, TX „ Kimley-Horn NMI 1 and Associates, Inc. III Univers fly Dr1vo. Suite 105 0 0411.9, Slo Te•os 77840 0 N 73 TEIPE Regis r lion 80 0-928 SECTION IX APPENDIX D - TECHNICAL DESIGN SUMMARY The Cities of Bryan and College Station both require storm drainage design to follow these Unified Stormwater Design Guidelines. Paragraph C2 of Section III (Administration) requires submittal of a drainage report in support of the drainage plan (stormwater management plan) proposed in connection with land development projects, both site projects and subdivisions. That report may be submitted as a traditional prose report, complete with applicable maps, graphs, tables and drawings, or it may take the form of a "Technical Design Summary ". The format and content for such a summary report shall be in substantial conformance with the description in this Appendix to those Guidelines. In either format the report must answer the questions (affirmative or negative) and provide, at minimum, the information prescribed in the "Technical Design Summary" in this Appendix. The Stormwater Management Technical Design Summary Report shall include several parts as listed below. The information called for in each part must be provided as applicable. In addition to the requirements for the Executive Summary, this Appendix includes several pages detailing the requirements for a Technical Design Summary Report as forms to be completed. These are provided so that they may be copied and completed or scanned and digitized. In addition, electronic versions of the report forms may be obtained from the City. Requirements for the means (medium) of submittal are the same as for a conventional report as detailed in Section III of these Guidelines. Note: Part 1 — Executive Summary must accompany any drainage report required to be provided in connection with any land development project, regardless of the format chosen for said report. Note: Parts 2 through 6 are to be provided via the forms provided in this Appendix. Brief statements should be included in the forms as requested, but additional information should be attached as necessary. Part 1 — Executive Summary Report Part 2 — Project Administration Part 3 — Project Characteristics Part 4 — Drainage Concept and Design Parameters Part 5 — Plans and Specifications Part 6 — Conclusions and Attestation STORMWATER DESIGN GUIDELINES Page 1 of 26 APPENDIX D: TECH. DESIGN SUMMARY Effective February 2007 As Revised February 2008 SECTION IX APPENDIX D - TECHNICAL DESIGN SUMMARY STORMWATER MANAGEMENT TECHNICAL DESIGN SUMMARY REPORT Part 1 — Executive Summary This is to be a brief prose report that must address each of the seven areas listed below. Ideally it will include one or more paragraphs about each item. 1 Name, address, and contact information of the engineer submitting the report, and of the land owner and developer (or applicant if not the owner or developer). The date of submittal should also be included. 2 Identification of the size and general nature of the proposed project, including any proposed project phases. This paragraph should also include reference to applications that are in process with either City: plat(s), site plans, zoning requests, or clearing /grading permits, as well as reference to any application numbers or codes assigned by the City to such request. 3 The location of the project should be described. This should identify the Named Regulatory Watershed(s) in which it is located, how the entire project area is situated therein, whether the property straddles a watershed or basin divide, the approximate acreage in each basin, and whether its position in the Watershed dictates use of detention design. The approximate proportion of the property in the city limits and within the ETJ is to be identified, including whether the property straddles city jurisdictional lines. If any portion of the property is in floodplains as described in Flood Insurance Rate Maps published by FEMA that should be disclosed. 4 The hydrologic characteristics of the property are to be described in broad terms: existing land cover; how and where stormwater drains to and from neighboring properties; ponds or wetland areas that tend to detain or store stormwater; existing creeks, channels, and swales crossing or serving the property; all existing drainage easements (or ROW) on the property, or on neighboring properties if they service runoff to or from the property. 5 The general plan for managing stormwater in the entire project area must be outlined to include the approximate size, and extent of use, of any of the following features: storm drains coupled with streets; detention / retention facilities; buried conveyance conduit independent of streets; swales or channels; bridges or culverts; outfalls to principal watercourses or their tributaries; and treatment(s) of existing watercourses. Also, any plans for reclaiming land within floodplain areas must be outlined. 6 Coordination and permitting of stormwater matters must be addressed. This is to include any specialized coordination that has occurred or is planned with other entities (local, state, or federal). This may include agencies such as Brazos County government, the Brazos River Authority, the Texas A &M University System, the Texas Department of Transportation, the Texas Commission for Environmental Quality, the US Army Corps of Engineers, the US Environmental Protection Agency, et al. Mention must be made of any permits, agreements, or understandings that pertain to the project. 7 Reference is to be made to the full drainage report (or the Technical Design Summary Report) which the executive summary represents. The principal elements of the main report (and its length), including any maps, drawings or construction documents, should be itemized. An example statement might be: STORMWATER DESIGN GUIDELINES "One -page drainage report dated , one set of construction drawings ( sheets) dated , and a -page specifications document dated comprise the drainage report for this project." Page 2 of 26 APPENDIX D: TECH. DESIGN SUMMARY Effective February 2007 As Revised February 2008 Part 2 — Project Administration Start (Page 2.1) Engineering and Design Professionals Information Engineering Firm Name and Address: Kimley -Horn and Associates, Inc. 111 University Drive East, Suite 105 College Station, Texas 77840 Jurisdiction City: Bryan X College Station Date of Submittal: June 14, 2010 Lead Engineer's Name and Contact Info.(phone, e -mail, fax): Mike Moore, P.E. (979) 846 -8401 Mike.Moore@kimley-horn.com Other: Supporting Engineering / Consulting Firm(s): Other contacts: Developer / Owner / Applicant Information Developer / Applicant Name and Address: College Station I.S.D. 1812 Welsh Avenue College Station, TX 77840 -4800 Phone and e -mail: Contact: Jon Hall (979) 694 -5610 Property Owner(s) if not Developer / Applicant (& address): Phone and e -mail: Project Identification Development Name: Greens Prairie Elementary School Is subject property a site project, a single -phase subdivision, or part of a multi -phase subdivision? Part of a multi -phase subdivision If multi - phase, subject property is phase 1 of 2 . Legal description of subject property (phase) or Project Area: (see Section II, Paragraph B -3a) A001300 SAMUEL DAVIDSON, TRACT 64.3, ACRES 46.027 VLB # 125065 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. General Location of Project Area, or subject property (phase): The tract is located at 4300 Greens Prairie Trail, southwest of the intersection of Greens Prairie Trail and Royder Road. In City Limits? No Extraterritorial Jurisdiction (acreage): Yes Bryan: Bryan: acres. College Station: 46.027 College Station: acres. Acreage Outside ETJ: SECTION IX STORMWATER DESIGN GUIDELINES Effective February 2007 APPENDIX D - TECHNICAL DESIGN SUMMARY Page 3 of 26 APPENDIX D: TECH. DESIGN SUMMARY As Revised February 2003 Part 2 — Project Administration Continued (page 2.2) Project Identification (continued) Roadways abutting or within Project Area or subject property: Greens Prairie Road and Royder Road Abutting tracts, platted land, or built developments: 1. Crossroad Woods, BLOCK 2, LOT 1, ACRES 5.027 2. John Duncum, 42.214 acres of A001300 Samuel Davidson, Tract 6, ACRES 43.1474 3. Travis Nelson, 35.39 aces ofA001300 Samuel Davidson, TRACT 13, ACRES 35.485 Named Regulatory Watercourse(s) & Watershed(s): Peach Creek Watershed Area Tributary Basin(s): Plat Information For Project or Subject Property (or Phase) Preliminary Plat File #: Not Applicable Final Plat File #: Not Applicable Date: Status and Vol /Pg: Name: If two plats, second name: File #: Status: Date: Zoning Information For Project or Subject Property (or Phase) Zoning Type: A -0 Existing or Proposed? Existing Case Code: Not Applicable Case Date Not Applicable Status: Not Applicable Zoning Type: A -0 Existing or Proposed? Existing Case Code: Not Applicable Case Date Not Applicable Status: Not Applicable Stormwater Management Planning For Project or Subject Property (or Phase) Planning Conference(s) & Date(s): March 10, 2010 Participants: CSISD VLK Architects Kimley -Horn and Associates, Inc. Preliminary Report Required? No Submittal Date Review Date Review Comments Addressed? Yes 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. Not Applicable. SECTION IX STORMWATER DESIGN GUIDELINES Effective February 2007 APPENDIX D - TECHNICAL DESIGN SUMMARY Page 4 of 26 APPENDIX D: TECH. DESIGN SUMMARY As Revised February 2008 Part 2 — Project Administration Continued (page 2.3) Coordination For Project or Subject Property (or Phase) Note: For any Coordination of stormwater matters indicated below, attach documentation describing and substantiating any agreements, understandings, contracts, or approvals. Coordination With Other Departments of Jurisdiction City (Bryan or College Station) Dept. Contact: Date: Subject: N/A N/A N/A N/A Coordination With Non - jurisdiction City Needed? Yes No X Summarize need(s) & actions taken (include contacts & dates): Coordination with Brazos County Needed? Yes No X Summarize need(s) & actions taken (include contacts & dates): Coordination with TxDOT Needed? Yes No X Summarize need(s) & actions taken (include contacts & dates): Coordination with TAMUS Needed? Yes No X Summarize need(s) & actions taken (include contacts & dates): Permits For Project or Subject Property (or Phase) As to stormwater management, are permits required for the proposed work from any of the entities listed below? If so, summarize status of efforts toward that objective in spaces below. Entity Permitted or Approved? (include Status of Actions include dates) US Army Corps of Engineers No X Yes Not Applicable US Environmental Protection Agency No X Yes Not Applicable Texas Commission on Environmental Quality No Yes X Not Applicable NOI included in submittal. Brazos River Authority No X Yes Not Applicable SECTION IX STORMWATER DESIGN GUIDELINES Effective February 2007 APPENDIX D - TECHNICAL DESIGN SUMMARY Page 5 of 26 APPENDIX D: TECH. DESIGN SUMMARY As Revised February 2008 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? Undeveloped grassland and wooded tract. Site Development Project (select all applicable) Redevelopment of one platted lot, or two or more adjoining platted lots. Building on a single platted lot of undeveloped land. Building on two or more platted adjoining lots of undeveloped land. X Building on a single lot, or adjoining lots, where proposed plat will not form a new street (but may include ROW dedication to existing streets). Other (explain): Subdivision Development Project Construction of streets and utilities to serve one or more platted lots. Construction of streets and utilities to serve one or more proposed lots on lands represented by pending plats. Describe Nature and Size of Proposed Project Site protects: building use(s), approximate floor space, impervious cover ratio. Subdivisions: number of lots by general type of use, linear feet of streets and drainage easements or ROW. Phase l: Elementary School; 85,254 GSF floor area; 31% total site impervious cover. Phase 11 :: Middle School; 93,989 GSF floor area; (assumed) 43% total site impervious cover. (8.2 ac assumed) Fully Developed: Both Schools; 179,243 GSF floor area; 36% total imperious cover Is any work planned on land that is not platted or on land for which platting is not pending? X No Yes If yes, explain: FEMA Floodplains Is any part of subject property abutting a Named Regulatory Watercourse (Section II, Paragraph B1) or a tributary thereof? No Yes X Is any part of subject property in floodplain area of a FEMA - regulated watercourse? No Yes X Rate Map 48041CO325E Encroachment(s) into Floodplain areas planned? No X Encroachment purpose(s): Building site(s) Road crossing(s) Utility crossing(s) Other (explain): 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. FEMA Map Modernization # 48041CO325E was used to determine this information. See Appendix A. SECTION IX STORMWATER DESIGN GUIDELINES Effective February 2007 APPENDIX D - TECHNICAL DESIGN SUMMARY Page 6 of 26 APPENDIX D: TECH. DESIGN SUMMARY As Revised February 2008 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. Is the stormwater earlier study? management plan for the property in substantial Yes No If not, explain how it conformance with the differs. No X If subject property is not part of multi -phase project, describe stormwater management 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. The analysis anticipated developed conditions for both Phase I and Phase 11 and a single detention pond was sized to serve both phases. Post - development runoff on the east area of the tract, Phase 1, was adjusted to match pre- development conditions and the excess runoff was piped across the property's central drainage divide to the detention pond on the west side of the property. The detention pond, located on the west portion of the tract, will subsequently discharge into the Peach Creek Tributary on the west boundary of the property. Do existing topographic features on subject property store or detain Describe them (include approximate size, volume, outfall, model, etc). runoff? X No Yes Any known drainage or flooding problems in areas near subject property? Identify: X No Yes Based (see Table X on location of B -1 in Appendix Detention is required. study property in a watershed, is Type 1 Detention (flood control) needed? B) Need must be evaluated. Detention not required. If the need for Type 1 Detention must be evaluated: What decision has been reached? By whom? How was determination made? SECTION IX STORMWATER DESIGN GUIDELINES Effective February 2007 APPENDIX D - TECHNICAL DESIGN SUMMARY Page 7 of 26 APPENDIX D: TECH. DESIGN SUMMARY As Revised February 2008 Part 3 — Property Characteristics Continued (Page 3.3) Hydrologic Attributes of Subject Property (or Phase) (continued) Does subject property straddle a Watershed or Basin divide? describe splits below. In Part 4 describe design concept X No Yes If yes, for handling this. Watershed or Basin Larger acreage Lesser acreage Above - Project Areas(Section 11, Paragraph B3 -a) Does Project Area (project or phase) receive runoff from upland areas? Size(s) of area(s) in acres: 1) 4.99 2) 1002 3) No X Yes 4) Flow Characteristics (each instance) (overland sheet, shallow concentrated, recognizable concentrated section(s), small creek (non - regulatory), regulatory Watercourse or tributary); Above- Project Area offsite runoff to the east side of the property, Phase 1, includes overland sheet and shallow concentrated flows. These flows are discharged to the east side of the subject property through an existing 24" RCP that flows south under Greens Prairie Trail. Above - Project Area offsite runoff to the west side, Phase 11, enters the site as small creek (non - regulatory) flow through two 72" corrugated metal pipes that flow south under Greens Prairie Trail. Flow determination: Outline hydrologic methods and assumptions: Above Project Areas were determined through the use of the City of College Station's 2' contours and runoff hydrographs were developed with HEC -HMS software. Does storm runoff drain from public easements or ROW No X Yes If yes, describe facilities in easement onto or across subject property? or ROW: line discharge onto the subject Portions of Greens Prairie Trail adjoining the north property site. Are changes in runoff characteristics subject to change in future? Explain The total impervious cover for the property will increase with the future completion of Phase 11 on the west side of the tract. 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). The Phase I of the project site drains directly to southern property, owned by Travis E. Nelson, in the form of shallow concentrated flow. The runoff from the west side of the project site, Phase 11, discharges directly into an upstream tributary of Peach Creek. SECTION IX STORMWATER DESIGN GUIDELINES Effective February 2007 APPENDIX D - TECHNICAL DESIGN SUMMARY Page 8 of 26 APPENDIX D: TECH. DESIGN SUMMARY As Revised February 2008 Part 3 — Property Characteristics Continued (Page 3.4) Hydrologic Attributes of Subject Property (or Phase) (continued) Conveyance Pathways (continued) Do drainage easements exist for part of pathway(s)? X No any If yes, for what part of length? % Created by? plat, or instrument. If instrument(s), describe their provisions. Yes Pathway Areas Where runoff must cross lower properties, describe characteristics of abutting lower property(ies). (Existing watercourses? Easement or Consent required ?) The existing watercourse for the east side discharge is a grass channel that conveys the water to an existing stock pond on the abutting lower property. Neither an easement nor consent is required. Nearby Drainage Facilities Describe any built or improved drainage facilities existing near the property (culverts, bridges, lined channels, buried conduit, swales, detention ponds, etc). There are no improved drainage facilities downstream of the property. However, a constant storage livestock pond is located downstream of the east side of the site. Do any of design? these have hydrologic or hydraulic influence on X No Yes If yes, explain: proposed stormwater SECTION IX STORMWATER DESIGN GUIDELINES APPENDIX D - TECHNICAL DESIGN SUMMARY Page 9 of 26 APPENDIX D: TECH. DESIGN SUMMARY Effective February 2007 As Revised February 2008 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. The Upland Area runoff onto the east side of the property, Phase 1, will be captured immediately after it is discharged onto the subject site with a 36" headwall, and subsequently piped and discharged at the southern, downstream, portion of the site. The Upland Area of the west side of the site, Phase II, enters through two 72" corrugated pipes under Greens Prairie Trail. Post - development construction will be avoided in the current small creek (non - regulatory) flow path for this area so that existing condition will remain. Discharge(s) To Lower Property(ies) (Section II, Paragraph El) Does project include drainage features (existing or future) proposed to become X No Yes Separate Instrument? X No Yes public via platting? Per Guidelines reference above, how will runoff be discharged to neighboring property(ies)? Establishing Easements (Scenario 1) Release (Scenario 2) of the two Scenarios X Pre development Combination Scenario 1: If easements are proposed, describe where needed, and provide status of actions on each. (Attached Exhibit # ) Scenario 2: Provide general description of how release(s) will be managed etc.). (Attached Phase I was adjusted exceed the 10, 25, 50, by development detention pond on the the tract, will detain excess Creek Tributary on to pre - development Exhibit # Appendix C1 & C2) conditions (detention, sheet flow, partially concentrated, Post - development runoff on the east area of the tract, development peak discharges for the 2 year and not events without detention. The excess runoff generated across the property's central drainage divide to the The detention pond, located on the west portion of site and subsequently discharge flows into the Peach property. to match pre - and 100 year recurrence of Phase I will be piped west side of the property. runoff for the entire the west boundary of the Combination: If combination is proposed, explain how discharge will differ from pre - area (or point) of release. development conditions at the property line for each If Scenario 2, or Combination are to be used, has proposed design been coordinated with owner(s) Explain and provide documentation. has been mitigated down to existing condition of receiving Discharge flow property(ies)? X No Yes point is located within subject property and rates. SECTION IX STORMWATER DESIGN GUIDELINES Effective February 2007 APPENDIX D - TECHNICAL DESIGN SUMMARY Page 10 of 26 APPENDIX D: TECH. DESIGN SUMMARY As Revised February 2008 Part 4 — Drainage Concept and Design Parameters Continued (Page 4.2) Stormwater Management Concept (continued) Within Project Area Of Multi -Phase Project Will project result in shifting runoff between Basins or between Watersheds? No X Yes Identify gaining Basins or Watersheds and acres shifting: The west side drainage basin is receiving 10.9 acres of runoff from the east side. What design and mitigation is used to compensate for increased runoff from gaining basin or watershed? The detention pond on the subject site's west side was sized and designed to attenuate all post development inflow quantities (existing and additional Phase 1 quantities) to peak discharges less than the pre - development values for the west side basin for the 2, 10, 25, 50, and 100 year recurrence events. How will runoff from Project Area be mitigated to pre- development conditions? Select any or all of 1, 2, and /or 3, and explain below. 1. With facility(ies) involving other development projects. 2. X Establishing features to serve overall Project Area. 3. On phase (or site) project basis within Project Area. 1. Shared facility (type & location of facility; design drainage area served; relationship to size of Project Area): (Attached Exhibit # ) 2. For Overall Project Area (type & location of facilities): (Attached Exhibit # ) The 3.2 acre, detention pond on the west side of the property will service the 100 year event for the entire property (Phase I & 11). 3. By phase (or site) project: Describe planned mitigation measures for phases (or sites) in subsequent questions of this Part. Are aquatic ecosystems proposed? X No Yes In which phase(s) or project(s)? Are other Best Management Practices for reducing stormwater pollutants proposed? X No Yes Summarize type of BMP and extent of use: If design of any runoff - handling facilities deviate from provisions of B -CS Technical Specifications, check type facility(ies) and explain in later questions. X Detention elements Conduit elements Channel features Swales Ditches Inlets Valley gutters Outfalls Culvert features Bridges Other SECTION IX STORMWATER DESIGN GUIDELINES Effective February 2007 APPENDIX D - TECHNICAL DESIGN SUMMARY Page 11 of 26 APPENDIX D: TECH. DESIGN SUMMARY As Revised February 2008 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): The project site (Phase 1, east side) runoff excess will transferred to the detention pond on the west side of the property. This is accomplished by capturing the western 10.9 acres of the subject site (See Appendix B, Drainage Area Map,DA -3) sheet flow in a channel and subsequently piping these excess flows across the property's central drainage divide to the detention pond on the west side of the property. The detention pond will release the runoff from the site into the Peach Creek Tributary bordering the west property line. The detention pond will be built simultaneously with Phase 1. 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): Identify whether each of the types of drainage features listed below are included, extent of use, and general characteristics. Typical shape? Triangular Surfaces? Grass Steepest side slopes: 5H:1 V Usual front slopes: Usual back slopes: Flow line slopes: least 0.005 ft/ft Typica distance from travelway: (Attached Exhibit # ) ec typical 0.01 ft/ft greatest 0.025 ft/ft Are longitudinal culvert ends in compliance with B -CS Standard Specifications? X Yes No, then explain: At intersections or otherwise, do valley gutters cross arterial or collector streets? No Yes If yes explain: eets with c gutter usec vo Are valley gutters proposed to cross any street away from an intersection? No Yes Explain: (number of locations ?) SECTION IX STORMWATER DESIGN GUIDELINES Effective February 2007 APPENDIX D - TECHNICAL DESIGN SUMMARY Page 12 of 26 APPENDIX D: TECH. DESIGN SUMMARY As Revised February 2008 'art 4 — Drainage Concept and Design Parameters Continued (Page 4.4) Stormwater Management Concept (continued) Within Or Serving Subject Property (Phase, or Site) (continued) With curb and gutter used? X No Yes Gutter line slopes: Least Usual Greatest Are inlets recessed on arterial and collector identify where and why. Not Applicable. streets? Yes No If "no ", Will inlets capture 10 -year design stormflow to prevent flooding (arterial with arterial or collector)? Yes No of intersections If no, explain where and why not. Not Applicable. Will inlet size and placement prevent design storm throughout site (or phase)? Not Applicable. exceeding allowable water spread for 10 -year Yes No If no, explain. Sag curves: Are inlets placed at low points? conduit sized to prevent 100 -year stormflow inches? Yes No Explain Yes No Are inlets and from ponding "no" answers. at greater than 24 Not Applicable. Will 100 -yr stormflow be contained in combination of ROW whole length of all streets? Yes No If no, and buried conduit on describe where and why. Not Applicable Do designs for curb, gutter, and inlets Yes No If not, describe comply with B -CS Technical Specifications? difference(s) and attach justification. Not Applicable Is storm drain system used? No X Yes Are any 12 -inch laterals used? No X Yes Identify length(s) and where used. Roof Drain connections only Pipe runs between system access points (feet): Typical 200 ft Longest 1090 ft Are junction boxes used at each bend? where and why. X Yes No If not, explain Are downstream soffits at or below upstream Yes X No If not, explain soffits? where and why: Least amount that hydraulic grade line is below gutter line (system- wide): 0.5' SECTION IX STORMWATER DESIGN GUIDELINES Effective February 2007 APPENDIX D - TECHNICAL DESIGN SUMMARY Page 13 of 26 APPENDIX D: TECH. DESIGN SUMMARY As Revised February 2008 Part 4 — Drainage Concept and Design Parameters Continued (Page 4.5) Stormwater Management Concept (continued) Within Or Serving Subject Property (Phase, or Site) (continued) On separate sheet provide same info for Describe watercourse(s), or system(s) receiving system discharge(s) below (include design discharge velocity, and angle between converging flow lines). 1) Watercourse (or system), velocity, and angle? One 3'x3' Concrete box culvert under discharges from Phase I development to southern, downstream, property. 4.89 fps in 25 year design storm, parallel with flow. (s)Ile }in0 2) Watercourse (or system), velocity, and angle? Detention pond outfall structure to the Peach Creek Tributary on the west side of the property, 5.61 fps in 100 year design storm, parallel with flow. 3) Watercourse (or system), velocity, and angle? For each outfall above, what measures are taken to prevent erosion or scour of receiving and all facilities at juncture? 1) 33 S. Y. riprap spillway of 6" to 10" diameter stones (See Appendix C1) 2) 30 S. Y. riprap spillway 12" to 18" diameter stones. (See Appendix C2) 3) Are swales used to drain streets? X No Yes Are swale(s) situated along property lines between properties? X No Yes Number of instances: For each instance answer the following questions. Surface treatments (including low -flow flumes if any): Flow line slopes (minimum and maximum): Outfall characteristics for each (velocity, convergent angle, & end treatment). Will 100 -year design storm runoff be contained within easement(s) or platted drainage ROW in all instances? Yes No If "no" explain: SECTION IX STORMWATER DESIGN GUIDELINES Effective February 2007 APPENDIX D - TECHNICAL DESIGN SUMMARY Page 14 of 26 APPENDIX D: TECH. DESIGN SUMMARY As Revised February 2008 Part 4 — Drainage Concept and Design Parameters Continued (Page 4.6) Stormwater Management Concept (continued) Within Or Serving Subject Property (Phase, or Site) (continued) Roadside Ditches Are roadside ditches used? No X Yes If so, provide the following: ? X Yes No Is 25 -year flow contained with 6 inches of freeboard throughout Are top of banks separated from road shoulders 2 feet or more? Are all ditch sections trapezoidal and at least 1.5 feet deep? X Yes No X Yes No For any "no" answers provide location(s) and explain: o m co a� Q -- ` L cu cp , o (on separate sheet provide same information for any additional instances) If conduit is beneath a swale, provide the following information (each instance). Instance 1 Describe general location, approximate length: A 475' conduit, swale combination is used to convey the excess runoff from the west side of Phase 1. Is 100 -year design flow contained in conduit/swale combination? If "no" explain: X Yes No Space for 100 -year storm flow? ROW Easement Width 45' Swale Surface type, minimum and maximum slopes: Grass Lined, © 1.0% Longitudinal 1:6.5 Side Slopes Conduit Type and size, minimum and maximum slopes, design storm: 42" RCP @ 0.40% Inlets Describe how conduit is loaded (from streets /storm drains, inlets by type): The developed west side of Phase I is captured with 2 - 15' curb inlets and a number of landscape and roof drains throughout the proposed system and conveyed in the conduit beneath the swale. The undeveloped portion of the Phase I that is routed to the pond is captured by the swale above the 42" RCP. Both flows combine at the end of the swale where they are routed to the pond in a 42" RCP @ 0.40% slope. Access Describe how maintenance access is provided (to swale, into conduit): The swale and conduit will be accessible for future maintenance. Instance 2 Describe general location, approximate length: Is 100 -year design flow contained in conduit /swale combination? "no" explain: Yes No If Space for 100 -year storm flow? ROW Easement Width Swale Surface type, minimum and maximum slopes: Conduit Type and size, minimum and maximum slopes, design storm: Inlets Describe how conduit is loaded (from streets /storm drains, inlets by type): Access Describe how maintenance access is provided (to swale, into conduit): SECTION IX STORMWATER DESIGN GUIDELINES Effective February 2007 APPENDIX D - TECHNICAL DESIGN SUMMARY Page 15 of 26 APPENDIX D: TECH. DESIGN SUMMARY As Revised February 2008 Part 4 — Drainage Concept and Design Parameters Continued (Page 4.7) Stormwater Management Concept (continued) Within Or Serving Subject Property (Phase, or Site) (continued) Will swales without buried conduit X No Yes If "yes" provide the following information for each instance: Instance 1 Describe general location, approximate length, surfacing: Is 100 -year design flow contained in swale? Yes No Is swale wholly within drainage ROW? Yes No Explain "no" answers: Access Describe how maintenance access is provide: Instance 2 Describe general location, approximate length, surfacing: Is 100 -year design flow contained in swale? Yes No Is swale wholly within drainage ROW? Yes No Explain "no" answers: Access Describe how maintenance access is provided: Instance 3, 4, etc. If swales are used in more than two instances, attach sheet providing all above information for each instance. Channel improvements proposed? X No Yes Explain "New" channels: Will any area(s) of concentrated flow be channelized (deepened, widened, or straightened) or otherwise altered? X No Yes If only slightly shaped, see "Swales" in this Part. If creating side banks, provide information below. Will design replicate natural channel? Yes No If "no ", for each instance describe section shape & area, flow line slope (min. & max.), surfaces, and 100 -year design flow, and amount of freeboard: Instance 1: Instance 2: Instance 3: SECTION IX STORMWATER DESIGN GUIDELINES Effective February 2007 APPENDIX D - TECHNICAL DESIGN SUMMARY Page 16 of 26 APPENDIX D: TECH. DESIGN SUMMARY As Revised February 2008 Part 4 — Drainage Concept and Design Parameters Continued (Page 4.8) Stormwater Management Concept (continued) Within Or Serving Subject Property (Phase, or Site) (continued) Channel Improvements (continued) Existing channels (small creeks): Are these used? No X Yes If "yes" provide the information below. Will small creeks and their floodplains remain undisturbed? How many disturbance instances? Identify each X Yes No planned location: For each location, describe length and general type of proposed improvement (including floodplain changes): For each location, describe section shape & area, flow line slope (min. & max.), surfaces, and 100 -year design flow. Watercourses (and tributaries): Aside from fringe changes, Watercourses proposed to be altered? X No Yes are Regulatory 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 and data. Is full report submitted? Yes No If "no" explain: All Proposed Channel Work: For all proposed channel work, provide information requested in next three boxes. If design is to replicate natural channel, identify location and length here, and describe design in Special Design section of this Part of Report. Will 100 -year flow be contained with one foot of freeboard? not, identify location and explain: Yes No If SECTION IX STORMWATER DESIGN GUIDELINES Effective February 2007 APPENDIX D - TECHNICAL DESIGN SUMMARY Page 17 of 26 APPENDIX D: TECH. DESIGN SUMMARY As Revised February 2008 Part 4 — Drainage Concept and Design Parameters Continued (Page 4.9) Stormwater Management Concept (continued) Within Or Serving Subject Property (Phase, or Site) (continued) Are Detention Facilities Proposed? X Yes No How many facilities for subject property project? below. 1 For each provide info. For each dry -type facility: Faci ity 1 Facility 2 Acres served & design volume + 10% 26.8 ac 6.49 ac -ft 100 -yr volume: free flow & plugged 5.9 ac -ft 5.9 ac -ft Design discharge (10 yr & 25 yr) 57.9 cfs 71.5 cfs Spillway crest at 100 -yr WSE? X yes no yes no Berms 6 inches above plugged WSE? X yes no yes no Explain any "no" answers: For each facility what is 25 -yr design Q, and design of outlet structure? Facility 1: The 25 -yr design flow is 71.5 cfs. The outlet structure is a two part, staged, sharp- crested weir. The first stage is 2' -6" wide with an invert elevation at the base of the pond equal to 282.50 ft above msl. The second stage is 7' -0" wide with an invert elevation of 285.0 ft above msl. Facility 2: Do outlets and spillways discharge into Facility 1: Yes X No a public Facility facility in easement 2: Yes or ROW? No If "no" explain: The detention pond outfalls into a tributary of Peach Creek. For each, what is velocity of 25 -yr design discharge at outlet? Facility 1: 5.26fps (outlet) & 3.41 fps (spillway) & at spillway? Facility 2: Yes Describe type and comprised of 12" to fabric. & No X Are energy dissipation measures used? location: Rock Rip Rap pad 15' long (30 S.Y.) 18" diameter rock rip rap that is underlain downstream of spillway with Mirafi 140N filter For each, is spillway surface treatment other than concrete? Yes 0 and describe: Facility 1: No, a concrete weir and splash -pad are propose.. Facility 2: For each, what measures are taken to prevent erosion or scour at receiving facility? Facility 1: A 30 S. Y. (15 L.F.) concrete splash - pad /spillway downstream of weir and of 12 " -18" rock rip rap is proposed to dissipate energy and prevent erosion. Facility 2: If berms are used give heights, slopes and surface treatments of sides. Facility 1: 4.5 feet — max height near outlet, 1:4 grass covered side slopes Facility 2: SECTION IX STORMWATER DESIGN GUIDELINES Effective February 2007 APPENDIX D - TECHNICAL DESIGN SUMMARY Page 18 of 26 APPENDIX D: TECH. DESIGN SUMMARY As Revised February 2008 Part 4 — Drainage Concept and Design Parameters Continued (Page 4.10) Stormwater Management Concept (continued) Within Or Serving Subject Property (Phase, or Site) (continued) Detention Facilities(continued) Do structures comply with B -CS Specifications? Yes or X no, and explain if "no ". Facility 1: The bottom slopes in the pond are at a minimum of 1.0% to the concrete flumes. Facility 2: For additional facilities provide all same information on a separate sheet. Are parking areas to be used for detention? X No Yes What is maximum depth due to required design storm? Are culverts used at private crossings? No X Yes Roadside Ditches: Will culverts serve access driveways at roadside ditches? No X Yes If "yes ", provide information in next two boxes. Will 25 -yr. flow pass without flowing over driveway in all cases? X Yes No Without causing flowing or standing water on public roadway? X Yes No Designs & materials comply with B -CS Technical Specifications? X Yes No Explain any "no" answers: Are culverts parallel to public roadway alignment? X Yes No Explain: Creeks at Private Drives: Do private driveways, drives, or streets cross drainage ways that serve Above - Project areas or are in public easements/ ROW? X No Yes If "yes" provide information below. How many instances? Describe location and provide information below. Location 1: Location 2: Location 3: For each location enter value for: 1 2 3 Design year passing without toping travelway? Water depth on travelway at 25 -year flow? Water depth on travelway at 100 -year flow? For more instances describe location and same information on separate sheet. SECTION IX STORMWATER DESIGN GUIDELINES Effective February 2007 APPENDIX D - TECHNICAL DESIGN SUMMARY Page 19 of 26 APPENDIX D: TECH. DESIGN SUMMARY As Revised February 2008 Part 4 — Drainage Concept and Design Parameters Continued (Page 4.11) Stormwater Management Concept (continued) Within Or Serving Subject Property (Phase, or Site) (continued) Are culverts used at public roadway Named Regulatory Watercourses (& Tributaries): Are facilities? X No Yes, then provide full report culverts proposed on these documenting assumptions, that support proposed "no ", explain: criteria, analysis, computer programs, and study findings design(s). Is report provided? Yes No If Arterial or Major Collector Streets: Will culverts serve X No Yes How many instances? these types of roadways? For each identify the location and provide the information below. Instance 1: Instance 2: Instance 3: Yes or No for the 100 -year design flow: 1 2 3 Headwater WSE 1 foot below lowest curb top? Spread of headwater within ROW or easement? Is velocity limited per conditions (Table C -11)? Explain any "no" answer(s): Minor Collector or Local Streets: Will culverts serve these X No Yes How many instances? types of streets? for each identify the location and provide the information below: Instance 1: Instance 2: Instance 3: For each instance enter value, or "yes" / "no" for: 1 2 3 Design yr. headwater WSE 1 ft. below curb top? 100 -yr. max. depth at street crown 2 feet or less? Product of velocity (fps) & depth at crown (ft) = ? Is velocity limited per conditions (Table C -11)? Limit of downstream analysis (feet)? Explain any "no" answers: SECTION IX STORMWATER DESIGN GUIDELINES Effective February 2007 APPENDIX D - TECHNICAL DESIGN SUMMARY Page 20 of 26 APPENDIX D: TECH. DESIGN SUMMARY As Revised February 2008 Part 4 — Drainage Concept and Design Parameters Continued (Page 4.12) Stormwater Management Concept (continued) Within Or Serving Subject Property (Phase, or Site) (continued) Culverts (continued) All Proposed Culverts: For all proposed culvert facilities (except driveway /roadside 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 approaches thereto? No Yes If "yes" identify location(s), culvert and surfaced describe change(s), and justification: Are flumes or conduit to discharge into culvert barrel(s)? No Yes If yes, identify location(s) and provide justification: Are flumes or conduit to discharge into or near surfaced approaches No Yes If "yes" identify location(s), describe outfall to culvert ends? design treatment(s): Is scour /erosion protection provided to ensure long term stability of culvert structural components, and surfacing at culvert ends? Yes No If "no" Identify locations and provide justification(s): Will 100 -yr flow and spread of backwater be fully contained drainage easements/ ROW? Yes No if not, why in street ROW, and /or not? Do appreciable hydraulic effects of any culvert extend downstream neighboring land(s) not encompassed in subject property? "yes" describe location(s) and mitigation measures: or upstream to No Yes If Are all culvert designs and materials in compliance with B -CS Yes No If not, explain in Special Design Section Tech. Specifications? of this Part. SECTION IX STORMWATER DESIGN GUIDELINES Effective February 2007 APPENDIX D - TECHNICAL DESIGN SUMMARY Page 21 of 26 APPENDIX D: TECH. DESIGN SUMMARY As Revised February 2008 Part 4 — Drainage Concept and Design Parameters Continued (Page 4.13) Stormwater Management Concept (continued) Within Or Serving Subject Property (Phase, or Site) (continued) Bridge(s) Is a bridge included in plans provide the following information. for subject property project? X No Yes If "yes" Name(s) and functional classification of the roadway(s)? What drainage way(s) is to be crossed? A full report supporting all aspects of the proposed bridge(s) hydrologic, and hydraulic factors) must accompany this summary provided? Yes No If "no" explain: (structural, geotechnical, report. Is the report Water Quality Is a Stormwater Pollution Prevention Plan (SW3P) established for project construction? No X Yes Provide a general description of planned techniques: Storm water pollution control measures during construction will include silt fence, rock check dams, construction entrances, and other best management practices as required. Special Designs — Non - Traditional Methods Are any non - traditional methods replication, BMPs for water quality, X No Yes If "yes" list (aquatic ecosystems, wetland -type detention, natural stream etc.) proposed for any aspect of subject property project? general type and location below. Provide full report about the proposed expected benefits. Report must be compromised, and that maintenance solution(s). Is report provided? Not Applica special design(s) including rationale substantiate that stormwater management cost will not exceed those of Yes No If "no" explain: for use and objectives will not traditional design SECTION IX STORMWATER DESIGN GUIDELINES Effective February 2007 APPENDIX D - TECHNICAL DESIGN SUMMARY Page 22 of 26 APPENDIX D: TECH. DESIGN SUMMARY As Revised February 2008 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. X 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) 1.0% used for minimum bed slopes in the detention pond Existing ground topography is less than the 5.0% listed in the guidelines. A shallower slope is necessary to achieve the required detention. 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) Yes, 3/24/2010, Alan Gibbs 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: The Rational Method was utilized strictly in the design and sizing of on -site storm lines. Intensities and "C" factors were assigned per Bryan /College Station design guidelines with a minimum time of concentration of 10 minutes. What is the size and location of largest has been applied? 3.63 acres Design Drainage Area to which the Rational Formula Location (or identifier): Sheet C0.7.0, DA -1 SECTION IX STORMWATER DESIGN GUIDEUNES Effective February 2007 APPENDIX D - TECHNICAL DESIGN SUMMARY Page 23 of 26 APPENDIX D: TECH. DESIGN SUMMARY As Revised February 2008 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? In approximately what percent of Design Drainage Areas? °/o X No _Yes As to intensity- duration - frequency and rain depth criteria for criteria other than those provided in these Guidelines used? identify type of data, source(s), and where applied: determining X No runoff flows, Yes were any If "yes" 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 Storm drain system for local streets Open channels Swale /buried conduit combination in lieu of channel 100 100 Swales Roadside ditches and culverts serving them Detention facilities: spillway crest and its outfall 2, 10, 25, 50, 100 100 Detention facilities: outlet and conveyance structure(s) 2,10, 25, 50, 100 2,10, 25, 50, 100 Detention facilities: volume when outlet plugged 2, 10, 25, 50, 100 100 Culverts serving private drives or streets 2, 10, 25 25 Culverts serving public roadways Bridges: provide in bridge report. Hydraulics What is the range of design flow velocities as outlined below? Design flow velocities; Gutters Conduit Culverts Swales Channels Highest (feet per second) 6.63 fps 2.79 fps Lowest (feet per second) 1.06 fps 2.54 fps Streets and Storm Drain Systems Provide the summary information outlined below: Roughness coefficients used: For street gutters: For conduit type(s) RCP Coefficients: 0.013 SECTION IX STORMWATER DESIGN GUIDELINES Effective February 2007 APPENDIX D - TECHNICAL DESIGN SUMMARY Page 24 of 26 APPENDIX D: TECH. DESIGN SUMMARY As Revised February 2008 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? X No Yes Head and friction losses X No Yes Inlet coefficients? Explain any "yes" answer: In conduit is velocity generally increased in the downstream direction? Are elevation drops provided at inlets, manholes, and junction boxes? Explain any "no" answers: X Yes No X Yes No Are hydraulic grade lines calculated and shown for design storm? X Yes No For 100 -year flow conditions? X 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: At the outfall structure of the detention pond the tailwater elevation was assumed to be 282.5 per the extent of the Zone X shown on the FEMA Modernization Map 48041 CO325E in that area. See Appendix A. The top of pipe was used for the 3'x3' box outfall on the east side system. Open Channels If a HEC analysis is utilized, does it follow Sec VI.F.5.a? Yes No Outside of straight sections, is flow regime within limits of sub - critical If "no" list locations and explain: flow? Yes No Culverts If plan sheets do not provide the following for each culvert, describe it here. For each design discharge, will operation be outlet (barrel) control or inlet control? Entrance, friction and exit losses: Bridges Provide all in bridge report SECTION IX STORMWATER DESIGN GUIDELINES Effective February 2007 APPENDIX D - TECHNICAL DESIGN SUMMARY Page 25 of 26 APPENDIX D: TECH. DESIGN SUMMARY As Revised February 2008 Part 4 — Drainage Concept and Design Parameters Continued (Page 4.17) Design Parameters (continued) Computer Software What computer software has been used in the analysis and assessment of stormwater management needs and /or the development of facility designs proposed for subject property project? List them below, being sure to identify the software name and version, the date of the version, any applicable patches and the publisher HEC -HMS; Version 3.4; August 19. 2009; U.S. Army Corps of Engineers Office Excel® 2007; (12.0.6214.1000) SP1 MSO (12.0.6213.1000); ©2006 Microsoft Corporation 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: 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 me (or under my sup: rvision) in ac rdance with provisions of the Bryan Drainage Design G /del'nes for t - •wners of the property. All licenses any and all state .,d f: deral re • story agencies for the proposed draina been issue: or f er appliv. • general permits." di a r I Part B was prepared by /College Station Unified and permits required by ments have ZE F r k - .4 1 1 41 . i J. MOORE j i 68815 45: GISTEA `� s+,: .....E. �. ONAL _gam Licensed 'ro • :nal Engineer MICHAEL 14 QQQQ X • • /� OIM�� + ,f � • c e. State of Texas PE No. (� I SECTION IX STORMWATER DESIGN GUIDELINES Effective February 2007 APPENDIX D - TECHNICAL DESIGN SUMMARY Page 26 of 26 APPENDIX D: TECH. DESIGN SUMMARY As Revised February 2008