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6.A. - Page 56 of 69 <br />Pre -Development Hydrology <br />Q.,=0.65X1.7X0.73=O.SScfs <br />Past -Development Hydrology <br />Drainage <br />Existing <br />Existing <br />Runoff <br />Runoff <br />Composite <br />Existing <br />Drainage <br />Area <br />Pervious <br />Impervious <br />Coefficient <br />Coefficient <br />Runoff <br />Discharge <br />Areas <br />Sire (SF) <br />Surface (SF) <br />Surface (SF) <br />(Pervious) <br />(Impervious) <br />Coefficient <br />(Q_EX, cfs) <br />A-1 <br />31877 <br />13206 <br />18671 <br />0.3 <br />0.9 <br />0.65 <br />0.81 <br />Q.,=0.65X1.7X0.73=O.SScfs <br />Past -Development Hydrology <br />QPni=0.72X2.2X0.73=1.16efs <br />Discharge Calculation Method: Rational Method <br />Q=CIA, where ip-=1.7 in/hr (10 year 10 minute) and iP-e1= 2.2 in/hr (30 <br />year 10 minute) <br />Post -Development Stormwater Storage: Attach ment O <br />Volume Stored = (QPD - QEX) x (3/2)Tc, Tc =10 minutes <br />Detention Volume Summary Table <br />Pipe <br />Rock <br />Orifice <br />Storage Volume <br />Basin <br />Post - <br />Drainage <br />New <br />New <br />Runoff <br />Runoff <br />Composite <br />Required <br />Drainage <br />Detention <br />Volume <br />Developme <br />(inch) <br />Area <br />Pervious <br />Impervious <br />Coefficient <br />Coefficient <br />Runoff <br />Areas <br />(CF) <br />319 <br />1 694 <br />152 <br />243 <br />Discharge <br />nt t Disc <br />Size (SF) <br />Surface (SF) <br />Surface (SF) <br />(Pervious) <br />(Impervious) <br />Coefficient <br />cfs) <br />A-1 <br />31877 <br />9385 <br />22492 <br />0.3 <br />0.9 <br />0.72 <br />1.16 <br />QPni=0.72X2.2X0.73=1.16efs <br />Discharge Calculation Method: Rational Method <br />Q=CIA, where ip-=1.7 in/hr (10 year 10 minute) and iP-e1= 2.2 in/hr (30 <br />year 10 minute) <br />Post -Development Stormwater Storage: Attach ment O <br />Volume Stored = (QPD - QEX) x (3/2)Tc, Tc =10 minutes <br />Detention Volume Summary Table <br />V1 = (1.16 — 0.81) X 3/2X10x60=319 ft3 <br />Pipe Storage Volume =193 ft * pi * 0.512 sf = 352 CF <br />Rock Section Volume =694sf * 0.35=243 CF <br />Orifice Sizing Calculation: <br />where <br />Q =ir Cd � Q = flow rate <br />Cd — discharge coefficient (0.611), <br />D = 4Q g = gravitational acceleration (32.2 ftlsz}, <br />Cd 2gh h = depth of orifice <br />Orifice Sizing <br />Pipe <br />Rock <br />Orifice <br />Storage Volume <br />Basin <br />Total <br />Cd <br />Storage <br />Section <br />Diameter <br />Required <br />Surface <br />Detention <br />Volume <br />Volume <br />(inch) <br />(CF) <br />Area (SF) <br />32.2 <br />4 <br />Volume (CF) <br />(CF) <br />(CF) <br />319 <br />1 694 <br />152 <br />243 <br />394 <br />V1 = (1.16 — 0.81) X 3/2X10x60=319 ft3 <br />Pipe Storage Volume =193 ft * pi * 0.512 sf = 352 CF <br />Rock Section Volume =694sf * 0.35=243 CF <br />Orifice Sizing Calculation: <br />where <br />Q =ir Cd � Q = flow rate <br />Cd — discharge coefficient (0.611), <br />D = 4Q g = gravitational acceleration (32.2 ftlsz}, <br />Cd 2gh h = depth of orifice <br />Orifice Sizing <br />4 x 0.81 <br />D1=x12=3.9" <br />0.611x 2x32.2 x4 <br />1730 N. FIRST ST. Subject EXHIBIT 85 <br />SUITE 600 BASIN DETENTION CALCULATIONS <br />..71 SAN JOSE, CA 95112 Job No. 20166162 <br />BKF 408-467T-9100 By Date 06725-1.9 Chkd. <br />Elr ilenr73u�rereee JPlrvaifnl; 408-467-9199 {FA419e 7 of 7 SHEET EX—B5 OF <br />REV: 07-25-19 DZ <br />60 <br />Orifice <br />Drainage <br />Q(Existing <br />Cd <br />g <br />h (ft) <br />Diameter <br />Areas <br />Discharge) <br />(inch) <br />A-1 <br />0.81 1 0,611 <br />32.2 <br />4 <br />1 3.9 <br />4 x 0.81 <br />D1=x12=3.9" <br />0.611x 2x32.2 x4 <br />1730 N. FIRST ST. Subject EXHIBIT 85 <br />SUITE 600 BASIN DETENTION CALCULATIONS <br />..71 SAN JOSE, CA 95112 Job No. 20166162 <br />BKF 408-467T-9100 By Date 06725-1.9 Chkd. <br />Elr ilenr73u�rereee JPlrvaifnl; 408-467-9199 {FA419e 7 of 7 SHEET EX—B5 OF <br />REV: 07-25-19 DZ <br />60 <br />