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<br />:J~~::fC: ENGINEERING CONSULTANTS, INC. <br /> <br />Mr. l. Scott Tucker <br />July 11, 1973 - DG 855/73 <br />Poge Th ree <br /> <br />AI ternatives for Drainage Improvement <br /> <br />The alternatives for improvement, or 'do-something' alternatives, are described <br />in Chapter V. Our studies indicated that a major detention pond on Niver Creek at <br />88th Avenue and a smaller one on Tributary L at Interstate-25 were unquestionably the <br />best improvements that could be made anywhere in the basin. The land at these two <br />sites is vacant, and no environmental problems should arise because most of the land is <br />'de facto' flood plain anyway; the structural costs of throttling devices to control the <br />flow would be small, and no major dikes or re-routing of highways would be required. <br />These detention ponds would provide dramatic reductions in flood peaks at all fre- <br />quencies throughout the downstream reaches; for example, a 100-year storm after full <br />development would discharge about 2,700 cfs at 84th Avenue without detention, while <br />with detention the corresponding value would be only 1,300 cfs. The downstream re- <br />ductions would be proportionately less, of course, but would stj II be significant. We <br />conclude that there is nothing else you could do in the Niver Creek Basin that would <br />be as beneficial as these detention facilities. <br /> <br />. <br /> <br />In addition, we have evaluated the effects of upstream and downstream drainage- <br />way improvements, above and below the detention ponds. These improvements include <br />additional culvert capacity in the upper basin, additional culvert or channel capacity at <br />the North Valley Shopping Center, and bank stabilization and protection works in the <br />York Street-Steele Street reach. The downstream portion of these improvements can, of <br />course, be made much more economically if the detention ponds are installed, because <br />the required peak discharges will be smaller. We have evaluated three alternative <br />combinations of these improvements, designated as follows: <br /> <br />Alternative A: <br /> <br />Detention at 88th Avenue, <br />p I us Lpstream Improvements <br /> <br />Alternative B: <br /> <br />Upstream and Downstream Im- <br />provements, but no Detention <br /> <br />Alternative C: <br /> <br />Detention at 88th Avenue, plus <br />Upstream and Downstream Im- <br />provements <br /> <br />. <br />. <br /> <br />A PLANNING RESEARCH CORPORATION COMPANY <br />