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Service Areas ~O. g.lO. and 11. No Major improvemelltsareproposed for tllese service <Irea5. 48-lnch o~tfall on North 7th Avenue is adequate for existing and development. 105 ..---=--- Th, future facility to prevent oackwater floo~ing and signlflCdlltly reduce discharge peaks downstrean. Detention storage upstredm would dlso reducebackWdterflooding in Service Area 6. Tile Jowerpeak flows downstream resulting from s~ch 5torage WQul~ slgnif1cantly reduce the head necessary to push water through the culvert and bridges beneath the .~. ]hway and railrOdd tracks. Pioneer Ditch Imorove~ents ThePioneerOitchshouldberoutinelyclearedofsmall trees, brush. and other debri s throughout Its length. tn the ~pper reaCh, the dftch has almost enough cross-section area to carry the 5-year flood. However, most ~ri!:'lolry crossings, as for exa~ple. the 48.inch culvert beneath Highway 14 are grossly under s1ze. If these were replaced with adequately sized hydraulic structures. and tile right- angle bends on Franklin and North 7th Avenue were smoothed out, the ditch would function more efficiently during flood events. Recommended design flows for various recurrence interval floods are summarized in Tablel7. As a minimum. all hydraulic structures should be designed to saft!iy pa"" tht!10-j'ear f1ecd. In the lower reach of Pioneer Ditch (North 7th Avenue and Franklin to High"ay 138). the ditch should be erllar'1oo. At the proposed dete~ti:m storage site the ditch should ha~e a minimum cross-sectional area of 210 ft2 below elevation 3,922. Even if the size of t~e ditch were increased, 5 ~nd la-year recurrence interval floods would cause miner floooinginservicearea7. Howevllr,ifdetentionstoragewerea]so provided at a location north of the ditch opposite the drainage lateral Chat currently services Areas 7 and 8. backwater flooding would be less likely to occur. The proposed capacity of this reservoir would be approximately 150 Acre-feet. It would have a surface area of approximately 25 acres as seen in Figure 18. Excavation of tllis area below the flow line of Pioneer Oitch "ould create a pond, which would provide an u '.'f"~ ,~~ ~"~~~''''~'1 "M~"'at~c~ area ~e" !Io:e city J..rQ.... .~ ..,,~ .~........_ . _"' _ A number of OPtions i"xist forooerating the proposed detention pond during times of flood. For example. it could be designed to 5 f . <,..,,, fer lat.... ....le~~.. in t~e store f>torm runoff frcr:'. crv ce r.reJ~ ~,; ~ . _ . . " ",-. ~i,h flows iro the dj teh could spill into t!lis storage altc". ,," Ditch Relocation For many years, the existing PiOneer Ditch has served its purpose well as a drainage ditoh. The grade and alignment of this channel was or'ginally selected to prOvide the most efficient use of the land for f~rming. However. with recent urban development the ditCh is befng increasingly relied upon to function as a flOOd channel in addition to serving its original purpose of maintaining a lower water table. Because the bends and extre~.ely flat gradient considerably limit its abflity to effiCiently carry s~orm runoff, the o~erflow and b<lckwater flOOding previously discussed Will continue to be a persistent problem for the City. Realignment of the dftch between Highway 14 and Division Avenue as shown in Figure 18. would reduce bend losses, shortero the ditch by approximately 25 percent. and ir.crease the gradient. Because the new ditch segment would confonn more closely to the natural Sand Creek channel andfJoodplain, the flood1.ay area would be easier tOlllaintain. ThefJoodwdy could serve a dllal purpose. as for example. a direct transportati onllnk around the City between Highway 14 and Highway 138. Taole 17 sUfIlna.ri~es estimated flood discharges in the Pioneer Ditch assuming tnat all trtdjor flood control structures were in place. This water would caLIse tnereSldualdamage(S79,700.00peryear}Shcwnin Fi!iure14 If portions of the ditch were relocHed and enlarged as discussed above. residual da~ges could be Significantly reduced. More- over, the floo~ay shown in Plates 2 - 19 could also be reduced. allowing more efficient land use. :.JIll Ie realignment and enlargeeentof the dftchwOuld O('a costly altcr:1Jtive. the improved hy<lraulic efficiency and othl'r mitiqat,ng results merl t serious cons idl'rJtion by t.~e CI ty of Sterl lng. The area through Which the realigned ditch lo(luld be cons:r"cted is largely undevel oped. h~nce the transi tion could take place as part of.l long-term planning process. '"