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<br />e <br /> <br />e <br /> <br />.... - <br /> <br />EJr~""/,1 ,,#_ ~A~"k - setA'~ s:..1JIIt,'/'. <br /> <br />~,,.I,.~~I,;,,, <br /> <br />~A~111/ /'1"1#1"/ <br /> <br />V. Drainage Outfall into HCFCO Ditch <br />The Harris County Flood Control District requires that flow into an HCFCD <br />ditch be concentrated and have an incoming velocity of 3 ft/s. Upon <br />recommendation by HCFCD, the conduits for outflow into the HCFCD ditch were <br />designed to contain a three-year flood event (three-year flows were <br />calculated in Section III of this attachment and are shown on Attachment No. <br />9). The overflow ditches were designed to contain overflow, of a 25-year <br />flood event, not contained by the conduit. <br /> <br />The following calculations for the outflow conduits are based on the Manning <br /> <br />equations for full pipe flow: <br /> <br />Of* = 0.463 D 8/3 S 1/2 <br />n <br /> <br />Vf* = 0.590 D 2/3 S 1/2 <br />n <br /> <br />The flows in the outflow conduits are not considered to be under pressure <br />and therefore the calculations are conservative. <br /> <br /> <br />'1. 'The" "flow . ("03) into tHe 'HCFCO ditch from .''ditch '2 -is ,,10.2' cfs' (.referto <br />Attachment No. 8C). <br /> <br />Given: <br /> <br />Q3 = 10.2 cfs <br />Vf = 3 fps <br />n = 0.024 (Texas Hwy. Dept.- Hydraulic Manual, Corrugated Metal <br />Pipe) <br /> <br />.......... "".:"'''''". <br /> <br />Assume one pipe will be used <br />Minimum pipe size allowed = 24" (HCFCD Specification) <br /> <br />Area = 10.2 = 3.4 ft 2 <br />.'- <br /> <br />. '. -.;.' ".. <br /> <br />, '.~ . ., . <br /> <br />.,;.' '. .... '..' <br /> <br />D (pipe) = 4 (3.4 ft 2) = 2.08 ft = 25.0 in <br /> <br />Use D= 30" CMP <br /> <br />Vf = 3 = 0.590 ~2/3 (S) 1/2 <br />0.024 1m <br /> <br />-21- <br /> <br />., :', ,'. . ;- t" <br /> <br />'. .., ":"'~';.' Vf' <br />