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Pre -Development Hydrology <br />IQ,,,=011 x18x0.11=0.02cfs I <br />1Q„2=0.30x1.8x 0.64=0.34cfsl <br />IQ =0.27 x18x 007=0.03 cfsI <br />IQ, =0.26x 18 x 0.64 - 0.30 cfs I <br />Post -Development Hydrology <br />Drainage New New Runoff Runoff Composite Post - <br />Drainage Developme <br />Area Pervious Impervious Coefficient Coefficient Runoff <br />Are Size (SF) Surface (SF) Surface(SF) (Pervious) (Impervious) Coefficient nt Discharge <br />(Q.PD, cfs) <br />A-1 4740 2868 1872 0.1 0.9 0.42 0.10 <br />A-2 27669 14691 12978 0.1 0.9 0.48 0.63 <br />A-4 27972 13408 - I 14564 0.1 0.9 0,52 0.70 <br />I Qam=0.11x 2.1 x042=0.10efs1 <br />IQrnv=0,48x2.1x0.64=0.63cfsI <br />IQrn. = 043 x 2.1 x 0.07 = 0.06 cf.I <br />IQ,.=0.52 x 2.1 x0.66=0.70 c'fsl <br />Orifice Sizing <br />Drainage <br />Existing <br />Exisu ng Runoff <br />Runoff <br />Composite <br />Existing <br />Drainage <br />Area <br />Pervious <br />Impervious Coefficient <br />Coefficient <br />Runoff <br />Discharge <br />Areas <br />S¢e (SF) <br />Surface ISE <br />Surface (SF) (Pervious) <br />iImpervious) <br />Coefficient <br />(QEX, cfs) <br />A-1 _ <br />4740 <br />4675 <br />65 0.1 <br />0.9 <br />0.11 <br />0002 <br />114 <br />A-2 1 <br />27669 <br />20891 <br />1 6778 0.1 <br />0.9 <br />0.30 <br />D 34 <br />A-3 I <br />2978 <br />2328 <br />1 650 0.1 <br />0.9 _ <br />0.27 _ _ <br />0033 <br />A-4 <br />27972 <br />22272 <br />1 5700 0.1 <br />0.9 <br />0.26 <br />0 30 <br />IQ,,,=011 x18x0.11=0.02cfs I <br />1Q„2=0.30x1.8x 0.64=0.34cfsl <br />IQ =0.27 x18x 007=0.03 cfsI <br />IQ, =0.26x 18 x 0.64 - 0.30 cfs I <br />Post -Development Hydrology <br />Drainage New New Runoff Runoff Composite Post - <br />Drainage Developme <br />Area Pervious Impervious Coefficient Coefficient Runoff <br />Are Size (SF) Surface (SF) Surface(SF) (Pervious) (Impervious) Coefficient nt Discharge <br />(Q.PD, cfs) <br />A-1 4740 2868 1872 0.1 0.9 0.42 0.10 <br />A-2 27669 14691 12978 0.1 0.9 0.48 0.63 <br />A-4 27972 13408 - I 14564 0.1 0.9 0,52 0.70 <br />I Qam=0.11x 2.1 x042=0.10efs1 <br />IQrnv=0,48x2.1x0.64=0.63cfsI <br />IQrn. = 043 x 2.1 x 0.07 = 0.06 cf.I <br />IQ,.=0.52 x 2.1 x0.66=0.70 c'fsl <br />Orifice Sizing <br />4 x 0.34 <br />D2= .. 12=2.6" <br />V 0.611xrz 2x32.2 x3.5 <br />4 x 0.03 <br />D3= I x12=0.9" <br />', 0.611xrz 2x32.2 x2.75 <br />�-4x0.30 <br />D4='10.611 xrr 2x 32.2 x4.0 .12 _ 2.4 <br />Discharge Calculation Method. Rational Method <br />Q=CiA,wherei=1.8in/hr(10year10 minute) and i=2.1m/hr <br />(30 year 10 minute) <br />Post -Development Stormwater Storage. Attachment O <br />Volume Stored=(Q' -Q )x3/2Tc,Tc=10mmutes <br />Detention Volume Summary Table <br />Storage Volume Basin Surface SeRock Total <br />Required Surface ace Volume Detention <br />(CF) Are. (SF) (CF) Volume Volume (CF) <br />(CF) <br />66 122 34 49 83 <br />266 567 190 227 417 <br />26 109 28 43 71 <br />-03_03353__0303 --992- _-2720303 --397- __0303669_- _I <br />V1=(0.10 -002)x 3/,x 10 x 60=66 ft3I <br />V2 = (0 63 - 0 34) x 3/yx 10 x 60=266 ft3 <br />1173=(0.06- 0.03) x 3f7 x 10 x 60=26 ft31 <br />V4 = (0.66 - 0.30) x 3/2 x 10 x 60 = 320 ft3 <br />Orifice Sizing Calculation: <br />where <br />rz <br />Q=4C4Dz 2gh <br />Q=flow rate <br />4Q <br />D <br />Orifice <br />Drainage <br />Q(Existing <br />Cd <br />g <br />h(ft) <br />Diameter <br />At <br />Discharge) <br />(inch) <br />A-1 <br />0.02 <br />0.611 <br />32.2 <br />2.75 <br />0.7 - <br />A-2 <br />0.34 <br />0.611 <br />32.2 <br />3.5 <br />2.6 <br />A-3 <br />003 <br />0 611 <br />32.2 _ <br />2.75 _ <br />0.9 <br />A-4 <br />0.30 <br />0 611 <br />32.2 <br />4 <br />2.4 <br />01= <br />4 x 0.02 <br />x12=0J" <br />�. 0.611 xa 2x 32.2 x2.75 <br />4 x 0.34 <br />D2= .. 12=2.6" <br />V 0.611xrz 2x32.2 x3.5 <br />4 x 0.03 <br />D3= I x12=0.9" <br />', 0.611xrz 2x32.2 x2.75 <br />�-4x0.30 <br />D4='10.611 xrr 2x 32.2 x4.0 .12 _ 2.4 <br />Discharge Calculation Method. Rational Method <br />Q=CiA,wherei=1.8in/hr(10year10 minute) and i=2.1m/hr <br />(30 year 10 minute) <br />Post -Development Stormwater Storage. Attachment O <br />Volume Stored=(Q' -Q )x3/2Tc,Tc=10mmutes <br />Detention Volume Summary Table <br />Storage Volume Basin Surface SeRock Total <br />Required Surface ace Volume Detention <br />(CF) Are. (SF) (CF) Volume Volume (CF) <br />(CF) <br />66 122 34 49 83 <br />266 567 190 227 417 <br />26 109 28 43 71 <br />-03_03353__0303 --992- _-2720303 --397- __0303669_- _I <br />V1=(0.10 -002)x 3/,x 10 x 60=66 ft3I <br />V2 = (0 63 - 0 34) x 3/yx 10 x 60=266 ft3 <br />1173=(0.06- 0.03) x 3f7 x 10 x 60=26 ft31 <br />V4 = (0.66 - 0.30) x 3/2 x 10 x 60 = 320 ft3 <br />Orifice Sizing Calculation: <br />where <br />rz <br />Q=4C4Dz 2gh <br />Q=flow rate <br />4Q <br />D <br />Cu = dischargecoeffiment(0.611), <br />g = gravitationla acceleration (32.2 ftlsz), <br />_ <br />Carz 2gh <br />h=depth of orifice <br />77qEXHIBIT B4 <br />B K F F BASIN DETENTION CALCULATIONS <br />t2LE? <br />t <br />ENER <br />o NNFlRSIEW +L�� Inc. Drawn: KH Checked: JM Approved: JM <br />SAN JOSE, CA 95112 9wdwbw.bkEcom Job No.: 20176020 Date: 3/23/2018 <br />