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HomeMy WebLinkAboutSDP200400019 Assessment - Groundwater 2004-03-24 r HENELY MIDDLE SCHOOL ADDITIONS AND RENOVATIONS STORM WATER MANAGEMENT ANALYSIS March 2004 By Frank Slinsky Timmons Group Project: Henley Middle School Additions & Renovations Location: Crozet, VA Calcs by: FS Date: 3/22/2004 EXISTING RUNOFF TO OUTFALL 'A' RATIONAL METHOD (up to 200 ac) Time of Concentration: Overland (Seelye): Length 200 ft (up to 200 ft) Slope 8.8 c-factor 0.40 Travel time 8.3 minutes Channel Flow (Kirpich): Length 917 ft Max Height above outlet 22.0 ft (200 ft to outfall) Travel time 7 minutes Tc= 14.8 minutes Intensity: Albemarle IDF Curve: Intensity (2 yr) i2= 3.4 in/hr Intensity (10 yr) iio= 4.7 in/hr Intensity (25 yr) i25= 5.5 in/hr Drainage Area: A= 4.5 acres Coefficient of Imperviousness: Surface Runoff Watershed C x A Coef. "C" Area "A" Developed 0.71 4.52 3.209 0.000 0.000 Sum 4.52 3.209 Cw= 0.71 (Sum CA)/(Sum A) Peak Runoff Q2 = 10.91 cfs Q1a = 15.08 cfs Q25 = 17.65 cfs Project: Henley Middle School Additions & Renovations Location: Crozet, VA Calcs by: FS Date: 3/25/2004 POST-DEVELOPED RUNOFF TO OUTFALL 'A' RATIONAL METHOD (up to 200 ac) Time of Concentration: Overland (Seelye): Length 200 ft (up to 200 ft) Slope 3.0 c-factor 0.40 Travel time 10.1 minutes Channel Flow(Kirpich): Length 822 ft Max Height above outlet 25.7 ft (200 ft to outfall) Travel time 5 minutes Tc = 15.6 minutes Intensity: Albemarle IDF Curve: Intensity (2 yr) i2= 3.3 in/hr Intensity (10 yr) iio= 4.6 in/hr Intensity (25 yr) i25= 5.4 in/hr Drainage Area: A= 3.5 acres Coefficient of Imperviousness: Surface Runoff Watershed C x A Coef. "C" Area "A" Developed 0.88 3.54 3.115 0.000 0.000 Sum 3.54 3.115 Cw= 0.88 (Sum CA)/ (Sum A) Peak Runoff Q2 = 10.28 cfs Qio = 14.33 cfs Q25 = 16.82 cfs Project: Henley Middle School Additions & Renovations Location: Crozet, VA Calcs by: FS Date: 3/22/2004 EXISTING RUNOFF TO OUTFALL 'B' RATIONAL METHOD (up to 200 ac) Time of Concentration: Overland (Seelye): Length 200 ft (up to 200 ft) Slope 10.4 c-factor 0.40 Travel time 8.0 minutes Channel Flow(Kirpich): Length 1370 ft Max Height above outlet 38.3 ft (200 ft to outfall) Travel time 8 minutes Tc = 16.3 minutes Intensity: Albemarle IDF Curve: Intensity (2 yr) i2= 3.3 in/hr Intensity (10 yr) iio= 4.6 in/hr Intensity(25 yr) i25= 5.4 in/hr Drainage Area: A= 10.8 acres Coefficient of Imperviousness: Surface Runoff Watershed C x A Coef. "C" Area "A" Developed 0.56 10.83 6.065 0.000 0.000 Sum 10.83 6.065 Cw= 0.56 (Sum CA)/(Sum A) Peak Runoff Q2 = 20.01 cfs Q10 = 27.90 cfs Q25 = 32.75 cfs Project: Henley Middle School Additions & Renovations Location: Crozet, VA Calcs by: FS Date: 3/25/2004 POST-DEVELOPED RUNOFF TO OUTFALL 'B' RATIONAL METHOD (up to 200 ac) Time of Concentration: Overland (Seelye): Length 200 ft (up to 200 ft) Slope 10.4 c-factor 0.40 Travel time 8.0 minutes Channel Flow (Kirpich): Length 1370 ft Max Height above outlet 38.3 ft (200 ft to outfall) Travel time 8 minutes Tc = 16.3 minutes Intensity: Albemarle IDF Curve: Intensity (2 yr) i2= 3.3 in/hr Intensity (10 yr) i1o= 4.6 in/hr Intensity (25 yr) i25= 5.4 in/hr Drainage Area: A= 11.6 acres Coefficient of Imperviousness: Surface Runoff Watershed C x A Coef. "C" Area "A" Developed 0.63 11.59 7.302 0.000 0.000 Sum 11.59 7.302 Cw= 0.63 (Sum CA) / (Sum A) Peak Runoff Q2 = 24.10 cfs Qio = 33.59 cfs Q25 = 39.43 cfs _ ______ .._ ____ _ .___ .... . . _ __._..__ ... . ._ ._._____ _ ... _ _.._ _ . .__ . . . _____ _ ____ - • . . . ________ .... . .. ._._____. _ __._ . __ __ _c. .0:___._____ A AL5EM ' _ ._.__ - --- • - - - -- - • - --- • - • • . .... . . .. _ . _._ ___._ . . . __. . _ _. . _ ____ . . . . - - -- • -- - - • --- - - 8 7 . • . . • . 1. . . . . . .. . . _ _ .• _ _ _ . . . ... . _. . . : _CO:.ht.9. _OE" • - - - - • • • - - .. . . _ ___ _._. . _ . __ .. . . • - _____ _. _ . . . . __ ___ i. . . . . . . . . . . . _ . . . . . . . . .. . . . . . . . . . _ 0 J. . . . . . _......._. .- 1. ... ... :. . _ . . _ . __ . 6 i ........... ".... -:.:.. -"..... ..._. •... .. .. ....::-...__:-.. i.. '.. ...--..... _.....i......7_____. i . • • • . . _ . . . - -- - . . . ___ . _ . . . 1 _ . . ___ _ _ -. • • . . . . . . .. . _ 5 _ . . . . . _ • . • . . 41 i . : - - - . -. . ...: . ....: . _... ... :.._ . ..... i T._ . . . < . _ __ . . _ . u_ . . . _ .. . . . . .. __. . . ._____._ . . -: - -. - . -. 1_ . . -. .- %I. • • : - • %1 it . . ____ tl ---- - ' • - •' b- - • --• . alil:- IIH1i':��� � a - • 20 30 .-==4 0 I O5S : : 6 : : :T v -- - , , ,