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<br />Drainage System from ll_th A~enue .~~)__!~~~l.!:"ie~_Bouleva~~! <br />(Master Plan Drawing Nos. 21, 22. 23, 24): The existing <br />drainage facilities in this--j::eac},ha~Jce--iIini ted capaci t:y. <br />A new system with a combina1:ion of open channels and box <br />cU1VE!rts having the capacity for the 10-year storm event <br />has been designed to replace the existincJ facilities. The <br />undistrubed portions of the existing facilities would remain <br />to serve the local drainage. Information shown On thEl dl:aw- <br />ings includes: (1) typical channel and box culvert cross- <br />sections; (2) right-of-way requirements; (3) flood boundaries <br />for the 10-year and 100-year storms under existing channel <br />conditions and improved channel conditions with future basin <br />development; (4) existing uLLli ties and drainage facilities; <br />(5) adjacent bank elevations after irnpJeovements; (6) watE,r <br />surfe.ce profiles for the 10--year and 100"'year st:orm events <br />after improv(~ments; and (7) other requirEld notes. CircuJ.ar <br />pipe is also a feasible alternative and should be investigated <br />in dE!tail in final design. <br /> <br />The E.tage and discharge informatIon at var:ious locations. are <br />listE!d in Table 9. <br /> <br />Drairage System from Montview Boulevard b~ Stapleton Airport <br />(Mast.er Plan Drawing Nos. 2~;' and '26")-,---'Ttle existirlg dl:airlage <br />system from lo1ontview Bouleva:~d tc:,-ap'proximately 23rd Jwenue <br />is a 370-ft long, 3' x 6' concrete box culvert in parallel <br />with a 370-f1: long 6' x 9' corruqated metal pipe followed <br />by a 900-ft long 10.5-ft circular corrugated metal pipe. <br />The capacity of this drainage facility is approximately 500 <br />cfs. This existing drainage facility would remain for drain- <br />ing a. portion (500 cfs) of the lO-year design flow (1:;65 cfs). <br />A box culver1: under Mon1:view Boulevard followed by an opEm <br />channel has been designed to convey the rest of the desicrn <br />flow (1065 cfs). <br /> <br />Under the 10-'year storm event:, the natural ponding arE,a <br />located south of th,,, Staplet:on Ai.rport would have an <br />apprc.ximate pool elevation of 5302.2 fee t, according to t:he <br />flood routinq resul.ts, because the 10 B--inch Rep under <br />Stapleton Airport has the capacity for only 900 cfs, whidl <br />is less than the 10'-year storm flow. Since the lOB-inch <br />RCP is 2150 :Eeet long, and t:he major head loss is due t.O <br />friction, modification of inlet condition:3 would not, <br />for all practical purposes, incrEase the pipe capacity. <br />There fore, improvincr the channel beb,,,en :2 3rd Avenue and <br />Stapleton Airport from its existinq capacity of approxi- <br />mately 500 c:Es to 900 cfs will reduce the frequent flooding <br />in th is reach. <br /> <br />--3].- <br />