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940 Apollo Rd - Pond Design
POND Design: 100 Yr. Elev. Normal Elev. Bottom Elev. POND VOLUME Elev. Sq. Ft. 848 36,620 846 30,490 844 25,360 843 22,750 842 14,570 840 12060 838 5,490 Cu. Ft. 67,110 55,850 24,055 18,660 26,630 17,550 NURP Design (Dead Storage): Total drainage area (ac.) = 20.62 848.00 843.00 (area = 22,750 sf) 838.00 Walker Std. (wet volume reqd. below normal elev.) = 2.5" rainfall CN (post development) = 89 Direct runoff (in.) for a 2.5" rainfall (per SCS and CN) = 1.45 Runoff volume (regd. wet storage vol. < normal) (cf) = 108,886 Actual proposed volume below normal elev. (cf) = a qq C r— Rord (t Pt/ Pi4G-e- 1 Cu. Ft. 100 yr. live storage (848 -843) = 147,010 NURP dead storage (843 -838) = 62,840 Reqd. 100 yr. live storage = 145,320 Regd. NURP dead storage = 108,890 Max. 3:1 slopes above and below normal elev. Except 10:1 bench for 1st 10' below normal elev. REc 1I, DUKE APOLLO SITE, EAGAN, MN 3/8/99 DRAINAGE CALCULATIONS INPUTS: Drainage area (ac.) Drainage area (ac.) Tc (min.) Tc (min.) CN (soil B; woods & pasture; good) <before> CN (soil B; 4.93 ac. green @ 61) <after> Rainfall, P (in.; 24 hr.) Initial abstraction (in.); Ia Initial abstraction (in.); Ia la /P Ia /P OUTPUTS: <before> <after> <before> <after> < before> <after> <before> <after> Qu (unit peak discharge; csm /in.) <before> 520 430 Qu (unit peak discharge; csm /in.) <after> 750 750 ..... (cfs per sq. mi. per in. runoff) Runoff, Q (in.) (1) <before> 1.68 Runoff, Q (in.) (1) <after> 4.74 (1) S= (1000 /CN) -10 Q =((P- 0.2S) ^2)/(P +0.8S) Runoff volume, Vr (ac. ft.) < after> 8.14 Qp (peak discharge; cfs) (2) <before> 28.1 Qp (peak discharge; cfs) (2) <after> 114.4 (2) Qp =Qu * Drain. area in sq. mi. * Runoff(Q) IPOND CALCULATIONS /FLOOD ROUTING: Qo = peak pond outflow discharge (cfs) ( =Qp before) Qi = peak pond inflow discharge (cfs) ( =Qp after) By: Peter Knaeble, PE (Terra Engineering, Inc.) 100 Yr. 10 Yr. 2 Yr. 20.62 20.62 20.62 20.62 20.62 20.62 25 25 25 15 15 15 (per SCS info.) 57 57 57 (per SCS info.) 89 89 89 6.0 4.2 2.8 (for Mpls. area) 1.51 1.51 1.51 0.25 0.25 0.25 0.251 0.359 0.539 0.041 0.059 0.088 0.71 3.01 250 (based on Tc & la /P per Fig. 7.1 -5) 750 (MPCA BMP blue book) 5.17 2.96 9.8 0.19 1.72 1.5 72.8 41.6 28.1 9.8 1.5 114.4 72.8 41.6 Qo /Qi 0.25 0.13 0.04 VsNr (= Storage VoI. /Runoff Vol.) 0.41 0.52 Vs (required pond storage volume; ac. ft.) 3.34 2.69 1.66 Vs (required pond storage volume; cu. ft.) 145,324 117,205 72,098 (per SCS TR -55 methodology) ( =0.2((1000/CN) -10)) (compute) i SCS METHOD I ISCS TR -55 METHOD I 0.56 (input based on Qo/Qi Fig. 7.2 -1) (if Qo /Qi < 0.10; set VsNr = 0.56) (MPCA BMP blue book)