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Home My WebLink AboutDrainage ReportGALINDO ENGINEERS AND PLANNERS, INC. 3833 South Texas Ave., Suite 213 Bryan, Texas 77802 (979) 846-8868 Mr. Alan Gibbs, P .E. City Engineer City of College Station College Station, TX February 29, 2008 Subject: Abbreviated Drainage Report Allen Honda Show Cars Sales College Station, TX Dear Alan: 4-08 Pleased find enclosed the referenced report for your review. Although we are proceeding to prepare the site plan for this project using the Small Lot Exception for drainage considerations we have made an effort to slow down and detain the increased storm water run off up to the 10-yr event. Sincerely, GALINDO ENGINEERS AND PLANNERS, [NC. Christian A. Galindo, P .E., R.P .L.S. President cc: John Allen Allen Honda 1. TRACT DESCRIPTION ALLEN HONDA SHOW CARS LOT ABBREVIATED DRAINAGE REPORT 4-08 This project lies within the Bee Creek Drainage Basin and covers all of Lot 9, Block "B", Resubdivision Final Plat of Block "B", Eastmark Subdivision Phase II. The total area of this lot is 0. 9152 acre. The project is located in the northeast corner of the intersection of Southwest Parkway East and Eastmark Dr. The tract is currently vacant. The proposed development will consist of a parking lot for show cars owned by Allen Honda. The attached 24"x36" sheet, Site and Drainage Plan, is part of this report and will be ref erred here as Exhibit 1. The adopted Flood Insurance Study does not identify the existence of a 100-yr flood plain affecting this tract (FEMA FIRM# 48041 C 0144 C, July 2, 1992). 2. STORMWATER RUNOFF Exhibit 1 shows the tract, its location and topography and the proposed construction project. The existing topographic data shown was developed under the supervision and control of the undersigned. This Exhibit also depicts the proposed grading. Only one drainage area has been defined for this tract. No offsite runoff comes onto this property and all runoff flows in a southeast direction towards adjoining Lot 8 and towards Southwest Parkway. A runoff detention area has been located within the parking lot and has been designed to detain the 10-yr event. Rains exceeding this intensity will overflow into the adjoining Lot 8 and the lower end of Southwest Parkway. All parking lot curbing is 6" high with the exception of the outflow weir where the flow line is 7" lower than the top of the curb. Exhibit 2 is a report, in nine pages, prepared using Hydraflow Hydrographs software by lnellisolve. The existing and ultimate conditions hydrographs for the 2-, 5-and Page 2 10-year events using the NRCS Unit Hydrograph Method are included in this report. The ultimate conditions hydrographs for the 2-, 5-and 10-year events using the same methodology. The data resulting from these Exhibits is summarized as follows: 2-y_r 5-y_r 10-y_r Q pre-development, cfs 1.57 2.65 3.44 Q post-development, cfs 1.79 2.47 3.01 Water elevation 285.72 285.83 285.90 Required Storage, cuft 3,638 5,765 7,308 This same report calculates the storage capacity of the area designated as pond to be 7,319 cuft, sufficient to cover the required capacity. A weir, designed as a 1.95' (approx1mately 2.0') curb cut controls the flows as given above reaching a maximum elevation of 285.9' at the 10-yr event. Exhibit 3 shows the calculations for the flume and opening under the sidewalk that will be necessary to convey the 10-yr event from the pond to the gutter of Southwest Parkway. This flume will have a rectangular concrete section with an average width of 3. 75' and a depth of 4". This flow will discharge the 3.01 cfs at a velocity of 5.25 fps (flume slope of 2.86%). 3. CERTIFICATION I hereby certify that I am familiar with the adopted ordinances, regulations, standards and policies of the City of College Station governing development, that this plan has been prepared under my supervision and that, to the best of my knowledge, it complies with said ordinances and regulations. Furthermore, as stated above, this site does not lie within a special flood hazard area as established by FEMA and shown on the FIRM# 48041 C 0144 C for the City of Bryan , effective on July 2, 1992 . .................... :\\\ ,,~ ~--~t o F r £ '•e1 =~'to ................. ,,..-1 i~ : C::> .... •• ••• ~ ,,,,, - * .. . J,, ,., "' .. •• 11' 'i. $*:' ~.*,,, if/!-•••••·································~ icHRISTIAN A. GALINDOi ~··••eeeMeee•••• .. eeeee•eaeee ... ••••o•e•e90eee•-i/!_ ~-o~. 53425 lQ:! "'~ •·• • .P~ <v~··',4.1""' 11. 0~ ···.~~GJsTt.~ .... ·· .~ # 1,, ~Ss ..... ..... (>' .: tea IONAL t. $' ,,,, ~ ..... \ '!t.."ti. ... °""' .... CHRISTIAN A. GALINDO, P.E. # 53425, R.P.L.S. # 4473 February 29 , 2008 Page 3 ; . ,..iO 1 2 \/ 4 "' Legend Hyd. Origin Description 1 SCS Runoff PRE DEVELOPMENT 2 SCS Runoff POST DEVELOPMENT 3 Combine COMBINE 4 Reservoir ROUTING Hydraflow Hydrographs Model Project: 4-08 POND.gpw Monday, Feb 25 2008, 5:13 PM 1 Hydrograph Return Period Recap Hyd. Hydrograph Inflow Peak Outflow (cfs) Hydrograph No. type Hyd(s) description (origin) 1-Yr 2-Yr 3-Yr 5-Yr 10-Yr 25-Yr 50-Yr 100-Yr 1 SCS Runoff --------------1.57 __ .. ____ 2.65 3.44 ---------------------PRE DEVELOPMENT 2 SCS Runoff -------------2.72 -------3.84 4.62 ------------------POST DEVELOPMENT 3 Combine 1, 2 -------4.29 ------6.49 8.06 ------------·----COMBINE 4 Reservoir 3 -----1.79 ------2.47 3.01 --------------·-ROUTING Proj . file: 4-08 PON D.gpw Monday, Feb 25 2008, 4:54 PM 1 Hydrograph Summary Report Hyd. Hydrograph Peak Time Time to Volume Inflow Maximum Maximum Hydrograph No. type flow interval peak hyd(s) elevation storage description (origin) (cfs) (min) (min) (cuft) (ft) (cuft) 1 SCS Runoff 1.57 3 726 5,233 -------... -· -----PRE DEVELOPMENT 2 SCS Runoff 2.72 3 726 9,738 --------------POST DEVELOPMENT 3 Combine 4.29 3 726 14,971 1, 2 ------------COMBINE 4 Reservoir 1.79 3 741 14,966 3 285.72 3,638 ROUTING 4-08 POND.gpw Return Period: 2 Year Monday, Feb 25 2008, 4:56 PM 2 Hydrograph Summary Report Hyd. Hydrograph Peak Time Time to Volume Inflow Maximum Maximum Hydrograph No. type flow interval peak hyd(s) elevation storage description (origin) (cfs) (min) (min) (cuft) (ft) (cuft) 1 SCS Ru noff 2.65 3 726 8,814 ---------------PRE DEVELOPMENT 2 SCS Runoff 3.84 3 726 14,025 ----------------POST DEVELOPMENT 3 Combine 6.49 3 726 22,838 1, 2 ----------COMBINE 4 Reservoir 2.47 3 741 22,833 3 285.83 5,765 ROUTING 4-08 POND.gpw Return Period : 5 Year Monday, Feb 25 2008, 4:56 PM 3 Hydrograph Summary Report Hyd. Hydrograph Peak Time Time to Volume Inflow Maximum Maximum Hydrograph No. type flow interval peak hyd(s) elevation storage description (origin) (cfs) (min) (min) (cuft) (ft) (cuft) 1 SCS Runoff 3.44 3 726 11,495 --------------PRE DEVELOPMENT 2 SCS Runoff 4.62 3 726 17,064 ----------POST DEVELOPMENT 3 Combine 8.06 3 726 28,559 1, 2 --------COMBINE 4 Reservoir 3.01 3 741 28,554 3 285.90 7,308 ROUTING 4-08 POND .gpw Return Period: 10 Year Monday, Feb 25 2008, 4:56 PM Pond Report Hydraflow Hydrographs by lntelisolve Pond No. 1 -POND Pond Data Monday, Feb 25 2008, 5:22 PM Pond storage is based on known contour areas. Conic method used. Stage I Storage Table Stage (ft) 0.00 0.35 0.60 Elevation (ft) Contour area (sqft) 285.30 285.65 285.90 00 18,000 23,900 Culvert I Orifice Structures [AJ [BJ [CJ Rise(in) = 0.00 0.00 0.00 Span (in) = 0.00 0.00 0.00 No. Barrels = 0 0 0 Invert El. (ft) = 0.00 0.00 0.00 Length (ft) = 0.00 0.00 0.00 Slope(%) = 0.00 0.00 0.00 N-Value = .013 .013 .013 Orif. Coeff. = 0.60 0.60 0.60 Multi-Stage = nla No No Stage I Storage I Discharge Table Stage Storage Elevation Clv A ft cuft ft cfs 0.00 0 285.30 0.35 2,100 285.65 0.60 7,319 285.90 [DJ 0.00 0.00 0 0.00 0.00 0.00 .013 0.60 No Clv B cfs Iner. Storage (cuft) 0 2,100 5,220 Total storage (cuft) 0 2,100 7,319 Weir Structures [AJ [BJ Crest Len (ft) 1.95 0.00 Crest El. (ft) = 285.30 0.00 WeirCoeff. = 3.33 0.00 Weir Type Re ct Multi-Stage = No No [CJ [DJ 0.00 0.00 0.00 0.00 0.00 0.00 No No Exfiltration = 0.000 in/hr (Contour) Tailwater Elev. = 0.00 ft Note: Culvert/Orifice outflows have been analyzed under inlet and outlet control. ClvC Clv D WrA WrB WrC WrD Exfil Total cfs cfs cfs cfs cfs cfs cfs cfs 0.00 0.00 1.34 1.34 3.02 3.02 Hydrograph Plot Hydraflow Hydrographs by lntelisolve Hyd. No. 4 ROUTING Hydrograph type Storm frequency Inflow hyd. No. Reservoir name = = = = Reservoir 2 yrs 3 POND Storage Indication method used. Q (cfs) ROUTING Hyd. No. 4 --2 Yr 5.00 -I --!-TTT--1 I i I I i I I I 4.oo ---: -__ : --I ·----1 - I I 3.00 t -1· ···--1--· I I I : I 2.00 -+--t--t --;--_,_1+- I 1~- 1 I 1.00 ----L--t-----;-----+---+l'-+-1 I I I Monday, Feb 25 2008, 5:9 PM Peak discharge Time interval Max. Elevation Max. Storage = 1.79 cfs = 3 min = 285.72 ft = 3,638 cuft Hydrograph Volume= 14,966 cuft Q (cfs) ,--1 -r 5.oo I -~'----+----4.00 ~ I I I I ~ . +1 -13.00 I I -T 2.00 I I I I I 1.00 1 I I 0.00 0.00 __ __:__ ____ ~~:::::.._ L__ _L=_::=:±::::::::::=:I::::::~h~::l--1 0 3 5 8 10 13 15 18 20 23 25 28 --Hyd No. 4 --Hyd No. 3 Time (hrs) 1 Hydrograph Plot Hydraflow Hydrographs by lntelisolve Hyd. No. 4 ROUTING Hydrograph type Storm frequency Inflow hyd. No. Reservoir name = = = = Reservoir 5 yrs 3 POND Storage Indication method used. Q (cfs) ROUTING Hyd. No. 4 --5 Yr Monday, Feb 25 2008, 5:9 PM Peak discharge Time interval Max. Elevation Max. Storage = 2.47 cfs = 3 min = 285.83 ft = 5,765 cuft Hydrograph Volume = 22,833 cuft Q (cfs) 7.00 -1_ ·-1 -----1 ~---I I 17.00 ::: , --~~i ~~~~i_ -~-~~~~~1 --_ ~-~~~~~~~~~·~~-·-~-·~~~~~1 6.00 -+-----1 I 5.00 4.00 _L_ -t-~ !--+----+---·--+------+--+ 4.00 ' ' I I I I I I ! I I 3.00 . --1 ___ ..._i __ --+-----+---1 --~il ---+---+--------+---+---3.00 2.00 ' 1--~---1--+--·--+-Hi-\+----.,.--1 ----+---+----+----!-----2 .00 1.00 ~ .. ___(_ ~---t---11 --+---+t--+1 --\\--!--->--~-~--+-_J 1.00 0.00 ___ L__l ---1.1 ......... ~~~::::L/ __ L l=:::t::::::::::::!::::::~:::::::=-i::::=:L _ _J_ 0.00 0 3 5 8 10 13 15 18 20 23 25 28 --Hyd No. 4 --Hyd No. 3 Time (hrs) 2 Hydrograph Plot Hydraflow Hydrographs by lntelisolve Monday, Feb 25 2008, 5:7 PM Hyd. No. 4 ROUTING Hydrograph type Storm frequency Inflow hyd. No. Reservoir name = = = = Reservoir 10 yrs 3 POND Peak discharge Time interval Max. Elevation Max. Storage = 3.01 cfs = 3 min = 285.90 ft = 7,308 cuft Storage Indication method used. Hydrograph Volume = 28,554 cuft Q (cfs) ROUTING Hyd. No. 4 --10 Yr 10.00 -, ---r--T --i ·-r ·-r Q (cfs) 10.00 j I I ~I I I 8.00 -~--+-~· -----+--~-·-··~-+---+-----+-----+---i 8.00 I I ' I I ' I I 6.00 -, +--+-·--+-----·-·-·--4-1---+-----+----t----1-·--r 6.00 ' I I i I I 4.00 -· ---+-+--! II ~ 4.00 i I I 2.00 _' I 1 ;--1-r· I hl-,_ -· -_,_ 2.00 ! I I I o.oo · ___ _:...I _.........!.I ............ _...,,._ ~~~=.Ji ____ L ____ _l:~:::::±:! ::::::~~d~~-_J_ o.oo 0 3 5 8 10 13 15 18 20 23 25 28 --Hyd No. 4 --Hyd No. 3 Time (hrs) 1 Rect.angular Channel Analysis & Design Open Channel -Uniform flow Worksheet Name: ALLEN HONDA Comment: RECTANGULAR CONCRETE FLUME Solve For Depth Given Input Data: Bottom Width .... . Manning's n ..... . Channel Slope ... . Discharge ....... . Computed Results: Depth ........... . Velocity ........ . Flow Area ....... . Flow Top Width .. . Wetted Perimeter. Critical Depth .. . Critical Slope .. . Froude Number ... . 3.75 ft 0.013 0.0286 ft/ft 3.01 cfs 0.15 ft 5.25 fps 0.57 sf 3.75 ft 4.06 ft 0.27 ft 0.0046 ft/ft 2.36 (flow is Supercritical) Open Channel Flow Module, Version 3.21 (c) 1990 Haestad Methods, Inc. * 37 Brookside Rd * Waterbury, Ct 06708 EXHIBIT 3