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e e r- -~ EJr~.,..~f /,#_ ~A~,.A. - SetA'~ s-..1fIt"~. ~,,.I, .~_I,.,.. ~..~I'//1 /1"1#1,'1' ~ . v. Drainage Outfall into HCFCD Ditch The Harris County Flood Control District requires that flow into an HCFCD ditch be concentrated and have an incoming velocity of 3 ft/s. Upon recommendation by HCFCD, the conduits for outflow into the HCFCD ditch were designed to contain a three-year flood event (three-year flows were calculated in Section III of this attachment and are shown on Attachment No. 9). The overflow ditctles w~re designed to contain overflow, of a 25-year flood event, not contained by the conduit. The following calculations for the outflow conduits are based on the Manning equations for full pipe flow: Of* = Q.463 D 8/3 S 112 n Vf* = 0.590 D 2/3 S 1/2 n The flows in the outflow conduits are not considered to be under pressure and therefore the calculations are conservative. ': ,.:..L....The..:flow.('OJ.). into ttie 'HeFCi) ij'itch fronr,""ditch'2 -is"lO..2"cfs'-(.r-efer.,to Attachment No. 8e). Given: 03 = 10.2 cfs Vf = 3 fps n = 0.024 (Texas Hwy. Dept.- Hydraulic Manual, Corrugated Metal Pipe) Assume one pipe will be used Minimum pipe size allowed = 24" (HCFCD Specification) Area = 10.2 = 3.4 ft 2 .-r-' ' ..... ;..~.. .....:...-./;p ..... .... ". '0' '..:.. n' '0 ~. .... ..I..... "'0 .... '.... '. ..' .. .'. ..... ",.. ..0. .". ':'.0 ...., ...... '"i I" .. .... "0 . . .'. '.: . .........;. ..: ....... .... D (pip~) = 4 (3.4 ft 2t = 2.08 ft = 25.0 in Use D=' '30" CMP Vf = 3 = 0.590 1JQl2/3 (S) 1/2 0.024 1I2T -21- .'.. "00.: .............. .... :.... ..... ... I":' I' . . . .. 00. : : I . 'I. ". ':",. "0 " '"0 :' ...... ... ..: 00- , . '.., ~'/"'- ji,