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Home My WebLink About53 Development Permit 621 Allen Hoda ParkingTO : COLLEGE ~STATION P. 0 . Bo x 9960 1101 Te xas Aven ue Tel: 409 764 3500 MEMORANDUM W . C. Scarrnardo, WCS Architects Co ll ege St at ion , TX 77842 FROM: DATE: September 28, 1998 RE : Al len Honda parking lot expansion. Staff reviewed the above mentioned site plan for a new parking area to be constructed at the existing Allen Honda facility at 2450 S·tate Highway 6 South. The following is a Ii-st of staff comments/concerns that must be addressed pri'Of t o further <feview: -6abel th e .existing dumpster location . I s -the exi sting dumpster being relocate? (There are two dumpster locations shown on the site plan, pl ease clarify .) _J[ A-dd a general note that the new parking area will not ·be accessible -t o -the public . (Since em ployees only a:re allowed in this area, <faised parking islands are not bei...'1.g required.) Once y-0u have addressed all of the r edlined comments, submit the following to -continue with the development of the subject property: _Completed development permit appiication; ~ ~ l/$100 application fee ; A-t.J<__ ~ ~ VErosion Control Plan ; and, tJJ.J s<1r ~ -fr ~ ~ copies o f the r evised site plan. (One copy will be returned to you stamped approved; however, if you need more than one, provide additional copies to be stamped and r eturned .) Staff is currently revi ewing t he Drainage Report submitted and will return comments once the review is 'Complete. If there are comments that you are not able to address, submit -a letter addressing those items to be r:eviewed by staff If you have any questions or need additional infonnation, please call me at 764-3570 .. Thank you . cc : C . J. Allen, Allen Honda, 2450 State Highway 6 South, College Station, TX 77845 Case file #98-440 Home of Texas A&M Un iversity ,. .- GALINDO ENGINEERS AND PLANNERS, INC. 3833 South Texas Ave., Suite 213 Bryan, Texas n802 (409) 846-8868 Mrs. Veronica Morgan, P.E. Assistant City Engineer City of College Station College Station, TX Subject: Drainage Study September 8, 1998 Allen Honda Parking Lot Lot 6R, Block "B" Eastmark Subdivision ~ Phase 11 College Station, TX Dear Veronica: Pleased find enclosed the referer:leed report for your review. This reports. covers the proposed exi;>ansion of the parking· lot of the Allen Honda facitity located at the northwest comer of the intersection of Southwest Parkway and the S.H. 6 East Bypass. Sincerely, GAUNDO ENGINEERS AND PLANNERS, INC. C ns 1an A. Galindo, P .E., R.P .L.S. President cc : W. S. Scarmardo, Architect ; GALINDO ENGINEERS AND PLANNERS, INC. 3833 South Texas Ave., Suite 213· Bryan, Texas 77802 (409) 846-8868 1. TRACT DESCRIPTION ALLEN HONDA PARKING LOT COLLEGE STATION, TX DRAINAGE REPORT The parking. lot is to be located at the southwest corner. of Lot 6R, Block "B", Eastmark Subdivision, Phase II. The total area of this lot is 2.418 acres, of which the proposed parking lot is to cover 0.255 acre. Lot 6R is. in turn part of the total acreage owned by he developeF, acreag.e that includes Lots 7R, 6R , SR, 11 and 12R, Block "B" of the referenced subdivision-. Exhibit 1 shows the general· location of· this property. The g.eneral runoff flow direction is-to the northeast side of the property 'wheFe an "area wide" detentioA facility could be located. However, since there are several lots involved in this study only the specific lot, Lot 6R, has been studied. Lot 6R has. a total are8' of 2.418 ac r.es .. The adopted Flood Insurance Study does not idenlliy the existence of a 1-00-flood plain affecting. this tract (Map# 48041 C 0144 C, July 2-, 1992). 2 . STORMWATER RUNOFF "fhe site currently is currently vacant. Exhibit 2 shows the tract, i+.s topography and tl'le proposed location of. the parking, lot. This Exhibit also shows the possible location of a detention pond should one be built in connection with the development of· this parking lot. This. pond may. have to be moved should the terms of the platted p Fivate parking. easement may not allow it at this locat1on. Two drainag_e sections. were defined for this project. Section 1, 2.163 acres, will remain non- developed at this time. Section 2 will contain the proposed parking lot and it covers 0.255 acre. Exhibit 3 shows the runoff calculations for 5, 10, 25, 50 and 1 oo~y,ear rainfalls . Runoff detention estimate was made for the 100-year return period. The increased in runoff for Q-100 from pre to post-development conditions represents 24% (11 .26 to 14.00 cfs). -1 - Exhibit 4 shows a preliminary estimate of the size of detention facility for these conditions . Should the pond have an averag.e depth of 0.5' the area required for it would not exceed 1 ,800 s.f. The log.ical location for this pond is shown in· Exhibit 2. The pond size estimate was obtained using Haestad Methods Pond pack V. 5. 17 software. 3. CONCLUSION Since onl~ a small area of· Lot 6R is being_ proposed for development, since the remainder of the lot is owned by the same p~. and since there are no current plans for developing. the remainder of the lot, it is. recommended that the construction of any detention facility be postponed until further development plans are prepared. It should however be made clear that current Ci~ Ordinance would require the detention pond facilit}r sized hereon if no-additional development, be contemplated. CHRISTIAN A. GALINDO, P.E. # 53425, R.P.LS. # 4473 September 8, 1998 ''''''"'\\\\ __ ......... t. 0 F I ''-s, - 2 - .: ~tr".············· ~.-t •1. -r-,•' * ·· .. A/.<'l It • .., -.; •• • v.' .. ,i :: * ... · ....... 'I. :;*/ \*~ ,. ............................... : ...... ~ ~CHF:I STIAN A. GALINDOi ~·••••••••e ••••••-•••••••••••• .. -••••••••••••aif' ~ . . -I,; .-0 ... 53425 .: ~.,, f r. ~ • L'. ,,._ .• '·: , "• .. -, ·.·ri:-x,v .· "-:V .,, rt l> ... -,, .. ,...· ... ' C ISTt~ / "'-'V .;: tf (.,·· •...•• \~-~-v ":I, ••• •••• '"' : •·... ...,..-~"AL c~ -~\.:-' \..t ff ~ ..... ~ \.{'··· ,, . ·~ '-\ \. \. \ ....... ...,,.-{." GALINDO ENGINEERS AND PLANNERS, INC. 3833 South Texas Ave., Suite 213 Bryan, Texas n802 )( 288.2 (409) 846-8868 21H .l x EXHIBIT 1 N SCALE : , .. = 150' 1 18.00 ) / 268.6 x B L O 0 x \ 1.916 acr. TOTAL 2.418 ACR. ~~ ~ ~ \ '\~ f\: s tj \~\ ;:r "ii} 0 ;~ \ /'-\ \ r' ~ ~~ ; ~ \ ,,> Y\ \/ w ~ m Cl') !~ )( i~ ~~ -; ~ ~ Yl CX> ~ m~ :::c -n m =i / ,I\) / Job: 30-98 Date: 09/08/98 RUNOFF CALCULATIONS -RATIONAL METHOD ALLEN HONDA COLLEGE STATION, TX (County: Brazos) Tc : 10.0 when calc . value < 10 .0 :::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::t: :::::::::::::::::::::::::::::::::::::::: Section Soil Type A Acres c Veloc. Length T cone. in mi fps ft Cale. Used 5 yrs I I I 10 yrs 25 yrs 50yrs I 100yrs Q 5yrs Q Q Q 10 yrs 25 yrs 50yrs Q 100yrs ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::~:::::::::::::::::::::::::::::::::::::::::: :::::::::::::::::::::::::::::::::::::::: Pre-development Conditions 1 Grass 1 ~ Grass Total Maximum Development Total Grass Parking 2. 163 0.400 1.400 0.255 0.400 1.400 2.418 2. 163 0.450 1.400 0.255 0.900 7 .000 2.418 450 150 450 200 5.4 10.0 7.693 8.635 9.861 11. 148 11 i 639 1.8 10.0 7.693 8.635 9.861 11. 148 11.639 5.4 10.0 7.693 8.635 9.861 11.148 11 .639 0.5 10.0 7.693 8.635 9.861 11. 148 11.639 County: Brazos Constants for use in for1ula: l=b/(t+d)·e 2-yr 5-yr 10-yr 25-yr ~0-yr 100-yr b 65 .000 76.000 80.000 89.000 98.000 96 .000 e 0.806 0.785 0.763 0.754 0.745 0.730 d 8.000 8.500 8.500 8.500 8.500 8.000 6.66 7.47 8.53 9.64 10 .07 0.78 0.88 1.01 1.14 1.19 7.44 8.35 9.54 10 .78 11.26 7.49 8.40 9.60 10.85 11.33 1.77 1.98 2.26 2.56 2.67 9.25 10.39 11 .86 13.41 14.00 MODIFIED RATIONAL METHOD ----Graphical SUrrrna.ry for MaxillllrTI Required Storage ---- Jl.LLEN HONDA COLLIDE STATION· After DeveloIX'f)ent EXHIBIT .4 ********************************************************************** * * * REI'URN FREQUENCY: 5 yr Allowable OUtfl ow : 7 . 44 cfs * * 'C' .Adjustment: 1.000 Required Sto~age: 589 cu.ft. * * * * STORM· DURATION = Tc for Max . Storage * *--------------------------------------------------------------------* * Peak Inflow: 8. 42 cfs Inflow .HYD stored: SIN .HYD * ********************************************************************** F L 0 w c f s I . '. 0 0 0 0 Tc:; I = Q= 10.00 7. 69-3 8.42 minutes in/hr cf s Area (ac): Weighted· C: Adjusted C: Required Storage -----------589 c~.ft. I '. 0 o o· o I I• I ' I ' I ' I I Q= 7 .4.4 cfs (All ow. OUtfl ow) NOT TO SCALE ------------------------ '-----------------------:------------------------ 11.17 minutes, 2.42 n.45 0-.45 MODIFIED RATIONAL .METHOD ----Graphical Sumrary for Ma~imum Required Storage ALLEN HONDA COLLEGE STATION After Develoµnent ********************************************************************** * * RETURN FREQUENC'i: 10 yr * 'C' Adjustment: 1.-000 * Allowable Outflow: Required Storage: * 8.35 cfs. * 662 cu.ft. * * * STORM DU'"'~TION = Tc for Max.Storage * *--------------------------------------------------------------------* * . Peak Inflow: 9.45 cfs Inflow .HYD stored: lOIN .HYD * ********************************************************************** F L 0 w c f s 0 0 I •I• 0 0 Tc= I = Q = 10.00 8.635. 9'. 45 minutes in/hr cf s Area (ac): Weighted C: Adjusted C: Required Sto~age -----------662 cu.ft. I I• I I • I I 0 0 0 0 Q= 8.35 cfs (Al 1 ow. Out fl ow) NOT TO-SC.ALE ------------------------ 11 17 minutes 2.42 0.45- 0.45 MODIFIED RATIONAL METHOD Graphical SUrrrnary for Maximum Required Storage ·_·;,,. __ ~HONDA OOLLEGE S'PATIOO After Develoi:nient ********************************************************************** * * * RETURN FREQUENCY: 25 yr * 'C' Adjustment: 1.000 Allowable Outflow: Required Storage: 9.5.4 cfs. * 753 cu.ft. * * * * STORM IXJRATION = Tc for Max. Storag.e * *--------------------------------------------------------------------* * Peak Inflow: 10. 79 cfs Inflow .HYD stored: 25IN .HYD * ********************************************************************** F L ·o w c f s 0 0 I •I• 0 o. Tc= 10. 00 minutes l = 9. S.&l in/!rr Area (ac): Q = 10. 79 cfs Weighted C: Adjusted C: Required Storage -----------7-S3 cu·. ft·.- I I• 0 000 Q= 9.. 54. cf s (A11ow.OUtflow) ------------------------ 11 16 minutes. 2.42 Cl-. 45 0.45 I • MODIFIED. RATIONAL METHOD ----Graphical SUmnary fo:r Maximum Required Storage · ..:.· __ _ ALLm HONDA COLLEGE STATION After Developme."'t ********************************************************************** * * * * RE'IUR..~· FREQCIENCY: 50 yr 'C' Adjus:t:Inest: 1.000 Allowable outflow: Required Storage: 10.78 cfs. * * 854 cu.ft. * * * STORM DURATION = Tc for Max. Storage * *--------------------------------------------------------------------* * Peak Inflow: 12.20 cfs Inflow .HYD stored: 50IN .HYD * ********************************************************************** I •I• F L I Tc= 10·. 00. minutes. I = 11.148 in/hr Q-= lZ.20" cfs Mea (ac): Weighted C: Adjusted C: Requiired Stoir(l9e 2'. 42 0-.45 0-.45 -------------0---'-·--· . ----·;-------~ -------------------g5_4, cu-. ft. w c f s 0 0 0 0 I I• I l • I I 0 0 0 0 Q= 10. 7-8 cfs. (A1 low. OUtf 1 ow) NO'X TO SCALE ------------------------ 11 17-minutes ~-...:..~------ > ... MODIFIED RATIOOAL METHOD ----Grap~ca~ SUmnar~ for Maxirrun Required Storage ·~~-- ALLEN HONDA- CQLI.fm: STATION After Developme."1t ****************************************************************~***** * * RETURN FREQUENCT: 100 yr Allowable outflow: * 11.26 cfs * * 'c' Adjustment: . 1. 000 Required Storage: BS.9 cu. ft. * * * * STORM DURATION·= Tc for Max.Sto~age * *--------------------------------------------------------------------* * Peak Inflow: 12. 74 cfs Inflow .lfiD stored: lOOIN .HYD * *************************************************************~******** F L 0 w c f I • 1 • 0 0 0 Tc= I = Q = 10>. 00 minutes 11. 639-in/hr 12. 74 cfs Area (ac}: Weiighted C: Adjusted c: Req,\:lired S~o~age -----------88~ cu.ft. I I • I I • I I o· Q . 0 0 I I• Q.= ll . 2'6 cf s (Al low·. Outflow) ------------------------ '-----------------------:------------------------ 11.16 minutes 2.42 0.45- C>.45 GALINDO ENGINEERS AND PLANNERS, INC. 3833 South Texas Ave., Suite 213 Bryan, Texas 77802 (409) 846-8868 Mrs. Veronica Morgan, P.E. Assistant City Engineer City of College Station College Station, TX Subject: Drainage Study September 8, 1998 Allen Honda Parking Lot Lot 6R, Block "B" Eastmark Subdivision ,..., Phase II CoHege Station, TX Dear Veronica: Pleased find enctosed the referenced report for your review . This reports covers the proposed expansion of the parking lot of the Allen Honda facility located at the northwest comer of the intersection of Southwest Parkway and the S.H. 6 East Bypass. Sincerely,, GAUNDO ENGINEERS AND PLANNERS, INC. cc: W. S. Scarmardo, Architect GALINDO ENGINEERS AND PLANNERS, INC 3833 South Texas Ave., Suite 213 Bryan, Texas 77802 (409) 846-8868 1. TRACT DESCRIPTION ALLEN HONDA PARKING LOT COLLEGE STATION, TX DRAINAGE REPORT The parking lot is to be located at the southwest corner of Lot 6R, Block "B", Eastmark Subdivision, Phase II. The total area of this lot is 2.418 acres , of which the proposed parking lot is to cover 0.255 acre. Lot 6R is in turn part of the total acreag.e owned by he developer, acreage that includes Lots 7R, 6R, SR , 11 and 12R, Block "B" of the referenced subdivision. Exhibit 1 shows the general location of this property. The genera~ runoff flow direction is to the northeast side of the property where an "area wide" detention facility could be located. However, since there are several lots involved in this study onlY-the specific lot, Lot 6R, has been studied. Lot 6R has-a total area of 2.418 acres .. l'l'"le ad·opted Flood Insurance Study does· not identify the existence of a 1 00-flood pialn affecting. this tract (Map # 48041 C 0144 C, July 2, 1992) .. 2·. STORMWATER RUNOFF The site currently is currently vacant. Exhibit 2 shows the tract, its topography and the proposed location of· the parking lot. This. Exhibit also shows the possible location-of a detention pond should one be built in connection with the development of this parking lot. This pond may, have to be moved should the terms of the platted pFivate parking easement may not allow it at this location. Two drainage sections were defined for this prolect. Section 1 , 2.1 e3· acres, will remain non - developed at this time. Section 2 will contain the proposed parking-lot and it covers-0.25S. ac re. Exhibit 3 shows the runoff calculations for 5, 10, 25, 50 and 1 OO•y.ear rainfalls. Runoff detention estimate was made for the 100-year return period . The increased in runoff for Q-1'00 from pre to post-development conditions represents 24% (11.26 to 14.00 cfs}. -1 - Exhibit 4 shows a preliminary estimate of the size of detention facility for these conditions . Should the pond have an average depth of 0.5' the area required for it would not exceed i ,800 s.f. The logical location for this pond is shown in Exhibit 2. The pond stze estimate was obtained using Haestad Methods Pondpack V. 5.17 software. 3. CONCLUSION Since only a small area of Lot 6R is being proposed for development, since the remainder of the lot is owned by the same party , and since there are no current plans for developing the remainder of the lot, it is recommended that the construction of any detention facility be postponed until further development plans are prepared . It should however be made clear that current City Ordinance would require the detention pond facility. sized hereon if no additional development be contemplated. CHRISTIAN A. GALINDO, P.E. # 53425, R.P.LS. # 4473 September 8, i 998 '''''''''\\\\ _#°~~~:. .. ~~.!.~~ ..... : ~ _... * ···."'o:-· ,,,, ,... *... ···* ~ :; * :· ·~ * 'I.. ,,,,.. ............................... : ...... ~ ~C H F:I ST I AN A. GALINooi ~-···············-········-·· .. -·····-·····-ill t". • 25 . ,, ~""' ... 534 /cc-p ff~ -::; ... • •• .y I:-~-... ~ ~ rt~ '-'r -....:··.' G IST't..~~··· ~~ ,,;: t!f ,. ,, '··· •••• ,~ -i . lJ ~, ••••••• ~.\:> : ~ •·-. .., , t } P' A I t. \' - \. ( ~ •• ·~ \,.J f -,.._ .......... '-~'I:\\'\\'\·~~...,:-.... - 2 - x ~ 2.Ba.6 ~ GALINDO ENGINEERS AND PLANNERS, INC. 3833 South Texas Ave., Suite 213 Bryan, Texas n802 (409) 846-8868 281 .1 x x283.2 )( 2118 .7 EXHIBIT 1 N L. s SCALE , .. = 1 150 ' 1800 I ~ .. 1 .916 acr. ) 268 .6 ~ x w (X) w w ~ 8 L 0 (/) 0 \ c: tj -::r 0 ~ )( ~ Q) Ill 0 \ )> < (I) ~ en c: ~ ;::; N (I) ~ .... ~ I . TOTAL 2.418 ACR . w aJ V) .., ~ '< Q) ? ";;} )( . ~. Q) ~ Ill ·CALE ...... 1'' ::;:: 60' ...... (X) 0 1 720 ~ -~ ~ 0 CD -(X) >j ~~ (X) ~ (X) ~ en :I: (X) / m 0 =i / f\) / / Job: 30-98 Date: 09/08/98 RUNOFF CALCULATIONS -RATIONAL HETHOD ALLEN HONDA COLLEGE STATION, TX (County:Brazos) Tc : 10 .0 when calc. value < 10.0 ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------Section Soi 1 Type A Acres c Veloc . Length T cone. in mi I fps rt Cale. Used 5 yrs I I I 10 yrs 25 yrs 50yrs I 100yrs Q 5yrs Q Q Q Q 10 yrs 25 yrs $0yrs 100yrs ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ Pre-development Conditions 1 Grass 1 ~ Grass Total Haximum Development 1 Grass 1 Parking Total 2.163 0.400 1.400 0.255 0.400 1.400 2.418 2.163 0.450 1.400 0.255 0.900 7.000 2.418 450 150 5.4 10.0 7.693 8.635 9.861 11.148 11.639 1.8 10.0 7.693 8.635 9.861 11. 148 11.639 450 5.4 10.0 7.693 8.635 9.861 11. 148 11.639 200 0.5 10.0 7. 693 8.635 9.861 11. 148 11. 639 County : Brazos Constants for use in formula: l=b/(t+d)·e 2-yr 5-yr 10-yr 25-yr 50-yr 100-yr -------------------------------------------------------- b 65 .000 76.000 80.000 89.000 98.000 96.000 e 0.806 0.785 0.763 0.754 0.745 0. 730 d 8.000 8.500 8.500 8.500 8.500 8.000 6.66 7.47 8.53 9.64 10 .07 0. 78 . 0.88 1.01 1.14 1.19 7.44 8.35 9.54 10 .78 11.26 7. 49 8.40 9.60 10.85 11 .33 1. 77 1. 98 2.26 2.56 2.67 ---------------------------------------- 9.25 10 .39 11. 86 13. 41 14 .00 MODIFIED RATIONAL METHOD ----Graphical SUrrmary for Maxirrun Required Storage ALLEN HONDA COLLIDE STATION After Develo~t EXHIBIT .4 ********************************************************************** * * * RE'IURN FREQUENCY: 5 yr * 'C' Adjustment: 1.000 Allowable outflow: Required Storage: 7 .44 cfs * 589· cu.ft. * * * * STORM DURATION = Tc for Max.Storage * *--------------------------------------------------------------------* * Peak Inflow: 8.42 cfs Inflow .HYD stored: SIN .HYD * ********************************************************************** F L 0 w c f s 0 0 0 I •I• Tc= I = Q= 10.00 7.693 8.42 minutes. in/hr cf s Area (ac): Weighted C: Adjusted c: Required Storage -----------589 cu.ft. I I• 0 0 0 0-0 I I' I I I I I I I I Q= 7.44 cfs. (Al 1 ow. OUtfl ow} NOT TO· SC.ALE ------------------------ -----------------------'------------------------' 11.17 minutes 2.42- 0..45 0'.45' MODIFIED RATIONAL METHOD ----Graphical SUTl'Tary for Maximum Required Storage ---- ALLEN HONDA COLLIDE STATION After Develoi:rnent ********************************************************************** * * * RE'IURN FREQUENCY: 10 y.r Allowable outflow: 8.35 cfs. * * 'C' Adjustment: 1.000 Required Storage: 662 cu.ft. * * * * STORM DURATION = Tc for Max.Storage * *--------------------------------------------------------------------* * Peak , Inflow: 9.45 cfs Inflow .HYD stored: lOIN .HYD * ********************************************************************** F L 0 w c f s I •I • 0 0 0 0 Tc= 10. 00 minutes, I = 8 . 635· in/hr Area (ac): Q = S. 45 cfs Weighted C: Adjusted C: Requ.d.red Storage -----------662 cu.ft. I I• I I I I 0 0 0 I I• I I Q= 8.35 cfs (All ow. Out fl ow} N()l.l' TO SCALE ------------------------ '-----------------------:------------------------ 11.11 minutes 2.42 0.45 0.45 MODIFIED RATIONAL METHOD ----Graphical SUrrrnary for Maximum Required Storage ··-·.:.. __ ALLm HONDA OOLLEGE STATION After Developnent ********************************************************************** * * * RE'IURN FREQUENCY: 25 yr * 'C' Adjustment: 1.000 Allowable outflow: Required Storage: 9.54 cfs * 753 cu .ft . * * * * STORM DURATION = Tc for Max.Storage * *--------------------------------------------------------------------* * Peak Inflow: 10.79-cfs Inflow .HYD stored: 25IN .HYD· * ********************************************************************** F L 0 w c f s I •I• 0 0 0 0 Tc= 10.00 minutes I = 9.861 in/hr Area (ac): Q = 10.79-cfs Weighted C: Adjusted c: Required Storage -----------r53· cu. ft ~ I I • 0 0 (j 0 I I• I I • I I I I I I Q= 9.54. cfs (All ow. OUtfl ow) NOT TO SCALE ------------------------ -----------------------:------------------------ ll .16 minutes ,'<' 2.42 Q...45 0.45· MODIFIED RATIONAL METHOD · ----Graphical Sunmary fer Maximum Required Storage ·~--- ALLEN HONDA COLLIDE STATION After Developnent ********************************************************************** * * Al lowahle outflow: 10 .78 cfs * * RETURN ~CY: 50 yr * 'C' Adjustment: 1.000 Required Storage~ 854 cu.ft. * * * * STORM WRATION = Tc for Max. Storage * *--------------------------------------------------------------------* * Peak Inflow: 12. 20 cfs Inflow .HYD stored: 50IN . .HYD * ********************************************************************** F L -------· --·--(}- w c f s I I I I _I -------1 I I I I I I I I I I I I I I 0 0 I • I • 0 0 Tc= I :: Q' :: 10.. 0(} 11.148 12.20 minutes in/hr cf s Area (ac): Weighted C: Adjusted C: Required Storage -----------854-cu.ft. I I• o o o Q= 10 .. 78 cfs o. (Allow.outflow) NOT TO SCALE ------------------------ ----------------------------------------------- 11 17 minutes 2. 42" 0.45 0.45 MODIFIED RATIONAL METHOD ----Graphical Surrmary for Maxirrun Required Storage ·~~-- ALLm HOODA COLLIDE STATION After Developnent ********************************************************************** * * * RETURN IBEQUENCT: 100. yr Allowable OUtfl ow: 11. 26 cf s * * 'c' h:ijustment: · i.ooo Required storage: 889· cu.ft. * * * * STORM DURATION = Tc for ¥...a.x.StoFage * *--------------------------------------------------------------------* * Peak Inflow: 12.74 cfs Inflow .HYD stored: lOOIN .HYD * ********************************************************************** F L -0 w c f s ....... .I I 1 1- I ·I I J , I 0 I I • c : 0 Area (ac): Tc= I = (\--. "" - 10.00 11.639 12.74 minutes in/hi cfs Weighted> C~ Adjusted C: I • I • 0 Required-storage : -----·--------------as9: · c\i: ft. I I• I I • I I 0 0 0 0 I I• I I 1 I Q= 11.26 cfs (Allow.outflow} ------------------------ '-----------------------:------------------------ 11.16 minutes 2.42 0'. 4S. 0.45 ' ' GALINDO ENGINEERS AND PLANNERS, INC. 3833 South Texas Ave., Suite 213 Bryan, Texas 77802 (409) 846-8868 September 8, 1998 Mrs. Veronica Morgan, P.E. Assistant City Engineer City of College Station Colleg.e Station, TX Subject: Drainage Study Allen Honda Parking Lot Lot 6R, Block "B" Eastmark Subdivision "' Phase ~I College Station, TX Dear Veronica: Pleased find enclosed the referenced report for your review. This reports covers the proposed expansion of the parking lot of the Allen Honda facility located at the northwest comer of the intersection of Southwest Parkway anc:t the S.H. 6 East Bypass. Sincerely, GAUNDO ENGINEERSAND PLANNERS, INC. ras 1an A. Galindo, P .E.,. R.P.L.S. President cc: W. S. Scarmardo, Architect -------~-----~ GALINDO ENGINEERS AND PLANNERS, INC. 3833 South Texas Ave., Suite 213 Bryan, Texas 77802 (409) 846-8868 1. TRACT DESCRIPTION ALLEN HONDA PARKING LOT COLLEGE STATION, TX DRAINAGE REPORT The parking lot is to be located at the southwest corner of Lot 6R, Block "B", Eastmark Subdivision, Phase II. The total area of this lot is 2.418 acres , of which the proposed parking lot is to cover 0.255 acre. Lot 6R is in turn part of the total acreage owned by he developer, acreage that includes Lots 7R, SR, SR, 11 and 12R, Block "B" of the referenced subdivision. Exhibit 1 shows the general location of this property. The general runoff flow direction is to the northeast side of the property where an "area wide" detention-facility could be located. However, since there are several lots involved in this study onLy the specific lot, Lot SR, has been studied. Lot SR has a total area of 2.418 acres .. The adopted Flood Insurance Study does-not identify the existence of a ·1-00-flood plain affecting. this tract (Map # 48041 C 0144 C, JulY. 2 , 1992}. 2 . STORMWATER RUNOFF The site currently is currently vacant. Exhibit 2 shows the tract, its topography and· the proposed. location of the parking lot. This. Exhibit also sl'lows the possible location-of-a detention pond sl'lould one be built in connection with-the development of this parking lot. This pond maY. have to be moved· should the terms of the platted private parking. easement ma}! not altow it at this tocation . Two drainage sections were defined for this project. Section 1·, 2.1S3 acres, will remain non- developed at this time. Section 2 will contain the prop.osed parking lot and it covers 0.255 acr-e. Exhibit 3 shows the runoff calculations for 5·, 10, 25, S.O and 100-~ear rainfalls . Runoff detention estimate was made for the 100-year return period . The increased in runoff for Q-100 from pre to post-development conditions represents 24% (11.26 to 14.00 cfs). -1 - Exhibit 4 shows a preliminary estimate of the size of detention facility for these conditions. Should the pond have an aver-age depth of 0.5' the area required for it would not exceed 1,800 s.f. The logical location for this pond is shown in Exhibit 2. The pond size estimate was obtained using Haestad Methods Pondpack V. 5.17 software. 3. CONCLUSION Since only a small area of Lot 6R is being. proposed for development, since the remainder of the lot is owned by the same party, and since there are no current plans for developing the remainder of the lot, it is recommended that the construction. of any. detention facility be postponed until further development plans are prepared. It should however be made clear that current Ctty Ordinance would require the detention pond facility sized hereon if no additional development be contemplated. CHRISTIAN A. GALINDO, P.E. # 53425, R.P.LS. # 4473 September 8, 1998 '''''''''\\\\ ~-... t OF I ''-t, .:: "'.. ~' .. ············ ~..t ,, -v.. .. ·· * ·· .. -1.r. It. : *"' .·· · .. u· "'1~ ~ . ·~ ~ ,..,.*: ·.7' "• ,#' : ~*'l ~·······························:······l ~CHR I STIAN A. GALINooi ~·············-··-·········-·· ... -·············-ii! ~ . . , :I~ --0 ••• 53425 .: ~I" 'i. ~--· .. .-? .t-~<0 ·.: /;;·:: ri /. ... ;,....,_,· ...... GIST£.~ .... ~v .,;: t:; <· '" ··... ..•' r_"\, ..,.. 'e · "':-i, ....... ~.s• : ';~. '"''v ?f AL tY .,:':" l ~ .. :• ........ . ~~\\\. , ..... ,.~ ..... -..;: . 2. GALINDO ENGINEERS AND PLANNERS, INC. 3833 South Texas Ave., Suite 213 Bryan, Texas n802 (409) 846-8868 EXHIBIT 1 2&1 .l N x L, x X.2all s ~ 2M.' ~ SCALE , .. = 150' 1 1800 / 268.6 x B L O 1.916 acr. N 0 TOTAL 2.418 ACR. CAl-E : 1" = 60' 1 : 720 \ ~ ::c m =i / I\) / w ~ Q) w w ~ CJ> 0 c t::j -::T 0 ~ )( ~ D> en )> < C1I ~ CJ> c ~ ;:; C1I "' ~ ~ w m V} .., ~ '< D> ? ~ )( D> ~ en ....., ....., Q) 0 "' -~ ~ 0 ~ Q) ~ ~ ,f'l en I Q) Q) ~ en Q) 0 Job: 30-98 Date: 09/08/98 RUNOFF CALCULATIONS -RATIONAL METHOD ALLEN HONDA COLLEGE STATION, TX (County:Brazos) ' Tc : 10.0 when calc. value ( 10 .0 :::::::::::::::::::::::::::::::::::::::::::::::::::::::;::::·::::::::::::~:::::::::::::::::::::::::::::::::: :::::::::::::::::::::::::::::::::::::::: Section Soil Type Acres c Veloc. Length T·conc. in mi I fps rt Cale. Used 5 yrs I I I 10 yrs 25 yrs 50yrs I 100yrs Q 5yrs Q Q Q Q 10 yrs 25 yrs SOyrs 100yrs ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ Pre-development Conditions 1 Grass 1 ~ Grass Tota 1 Maximum Development I Grass I Parking Tota 1 2. 163 0.400 1.400 0.255 0.400 1.400 2.418 2. 163 0.450 1.400 0.255 0.900 7.000 2.418 450 150 450 200 5.4 10.0 7.693 8.635 9.861 11. 148 11.639 1.8 10.0 7.693 8.635 9.861 11. 148 11 .639 5.4 10 .0 7.693 8.635 9.861 11. 148 11.639 0.5 10.0 7.693 8.635 9.861 11 . 148 11 .639 County: Brazos Constants for vse in formula: l=b/(t+d)·e 2-yr 5-yr 10-yr 25-yr SO-yr 100-yr b 65 .000 76.000 80.000 89.000 98 .000 96.000 e 0.806 0.785 0. 763 0.754 0.745 0.730 d 8.000 8.500 8.500 8.500 8.500 8.000 6.66 7.47 8.53 9.64 10.07 0.78 0.88 1.01 1.14 1.19 7.44 8.35 9.54 10.78 11.26 7.49 8.40 9.60 10.85 11.33 1.77 1.98 2.26 2.56 2.67 9.25 10.39 11 .86 13.41 14.00 ~ - MODIFIED RATIONAL METHOD ----Graphical SUrrmary for Maximum Required Storage ALLEN HONDA COLLEGE STATION After Developnent EXHIBIT .4 ********************************************************************** * * * REIURN FREQUENCT : 5 yr * 'C' Adjustment: 1. 000- Allowable Outflow: Reqt:ri.red St orage: 7 .44 cfs * s.ss cu. ft. * * * * STORM OORATION = Tc f O·r Max . Storage * *--------------------------------------------------------------------* * Peak Inf low: 8.42 cfs Inf low .HYD stored: SIN .HYD * ********************************************************************** F L 0 w c f s I •I • 0 0 0 Tc= 10.00 minutes.. I = 1 .693 in/hr Al:ea (ac): Q = 8.42 cf s Weighted C: Adjusted C: Required: Storage -----------&S9 cu.ft . I I• I I I I 0 0 0 0 I I• I I I I I I I I Q= 7.44 .cfs (Al 1 OW·. Out fl OW) NOT TO SCALE ------------------------ -----------------------:------------------------ 11.17' minutes 2.42- 0.45 0·.45. MODIFIED RATIONAL METHOD ----Graphical SUrmary for Maximum Required Storage ALLEN HONDA COLLEGE STATION After Develo~t ********************************************************************** * * * RETURN FREQUENCY: 10 yr * 'C' Adjustment : 1.000 Allowable outflow: Required Storage: 8 .35' cfs * 662' cu.ft. * * * * STORM IX:JRATION = Tc for Max.Storage * *--------------------------------------------------------------------* * Peak Inflow: 9.45 cfs Inf low .HYD stored: lOIN .HYD * ********************************************************************** F L 0 w c f s 0 O' 0 Tc= 10. OCf minutes I = 8 . 63,5 inf hr Area, (ac): Q = 9·. 45' cfs Weighted C: Adjusted C: I •I• Required Storage ------------6627 cu,. ft. _, I I• 0 0 0 Q= 8. 3'5, cf s 0 (All ow. OUtfl ow) (} NOT TO SCALE ------------------------ 11 17 minutes 2.42 0.45 0.45 MODIFIED RATIONAL METHOD ----Graphical Sumary for Maximum Required Storage ·_·:._ __ ALLEN HONDA COLL.Em: STATION After Develoµnent ********************************************************************** * * * RETURN FREQUENCY: 25 yr * 'C' Adjustment: 1.000 Allowable Outflow: 9. 5-4 cfs * Required storage: 153' cu.ft. * * * * STORM IXJRATION = Tc for Max. S_1;orage * *--------------------------------------------------------------------* * Peak Inflow: 10.79 cfs Inflow .h'YD stored: 25IN .HYD * ********************************************************************** F L --.. 0 ~ w : c f s 0 I •I • 0 0 0 Tc= I = Q = 10·.00 9·.861 10. 79 minutes in/hr cf s Area (ac)': Weighted C: Adjl:lSted C: Required storage -----------7·53 cu. ft. I I• I I I I 0 0 0 0 I I• Q= 9'.54 cfs (All ow. OUtfl ow) NOT TO· SCALE ------------------------ '-----------------------:------------------------ 11.16 minutes- 2.42 0..45 0.45 MODIFIED RATIONAL METHOD ----Graphical SUmnary for Maximum Required Storage·_:. __ _ ~ HONDA COLLroE STATION After Develo~t ********************************************************************** * * * * RETURN ~CY: 50· yr 'C' Adjustment: 1.000 Allowable outflow-: Required St-0rage: * l:0.78 cfs * 854 cu.ft. * * * STORM OORATlON = Tc for Max. Storag.e * *--------------------------------------------------------------------* * Peak Inflow: 12. 20 cfs Inflow .HYD stored: 50IN .HYD * ********************************************************************** F L -() w c f s I ' I I I ' I I I I I I I I 1 I '-------· I I I ., I 0 0 0 Tc= 10.00· minutes I = ll.148 in/hr Area (ac}: -o = 12.20 cfs. Weighted C: Adjusted C: I • I • Required storage -• ---------------------85.4 cu. ft. 0 I I• I .I. I I 0 Q= 10·. 78-cfs (Al 1 ow. OUtfl ow) NOT TO SCALE ------------------------ 11 17 minutes. 2.42 0-.4& 0-.45 MODIFIED RATIONAL METHOD ----Graphical SUmary for Maximum Required Storage -~~-- ALLm HONDA COLLroE STATIOO After Developnent ********************************************************************** * * * RETURN FREQUENCY: 100> yr Allowable outflow: 11.26 cfs. * * 'c' Adjustment: . 1. 000 Required Stor(l9e: 889--cu. ft. * * * * STORM IXJRATION = Tc fo~ Max.Storage * *--------------------------------------------------------------------* * Peak Inflow: 12. 74 cfs Inflow .HYD stored: lOOIN .HYD * ********************************************************************** I I I I ., -· I I F l L ~ -0 -1--·- w c f 5 , 0 0 Tc= I = Q -. - I • I • 10. 00 minutes i1~. 63-s-in/hr -- _1i-.14 cfs Area (ac): - Weighted c: Ad-justed c: Re9llred S.tor(l9e -=--------------889 cu. ft. 0 I I • I I • I t 0 0 O' 0 I I • I I I I Q= 11.26 cfs (All ow. OUtfl ow} ------------------------ -----------------------:------------------------ 11.16 minutes ZA2 ().. 45' 0-.45