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IMPROVE~ENT ALTERNATIVES For this study, five b~sic alternative i~provernent designs were evaluated. Each alternative is divided into three reaches described earlier and covers the entire study area. Improvement alternatives selected, however, all indicate the importance of continuous i~provements through Reaches A and B. Therefore, improvements and costs of inprovements were jointly evaluated in these reaches. This flow will spill back to Dry Creek reach through the reservoir spillway. required to contain this reduced flow Meadow Lane. about mdiway through the The only further improvements is an improved culvert at Once property damages were evaluated, the different alternatives were tailored to alleviate areas experiencing the greatest flood damage. The design alternativ~ studied for the most part were the least expensive in terms of construction and implementation costs. The five alternative improvement designs considered are described below. I I I , , I I I i I I I I Reach E: Channel improvements to direct the overflow from Terry Lake to the poudre River were designed. The Larimer and Weld County Canal was routed through a siphon under Dry Creek and a new channel was constructed south to the poudre bypassing the existing Dry Creek. An improved culvert is needed to replace those existing upstream and downstream of College Avenue. A bypass channel around the Alta Vista area and new culvert under Hospital Road is required. Future development in areas between College Avenue and Alta Vista and between LeMay Avenue and Vine Road will provide channelS to contain residual lOO-year flows. Alternative ~l Reach C: An improved grass-lined channel designed for ~ lOO-year flow of 1,400-cfs through the Valley Airpark area was evaluated, channeling flows south to the poudre River. Improved culverts were designed for the airport runw~y and two local streets in this reach. T1I" Cache I... poudre ~eservoir Inlet C3.n31 '""s routed The lOO-year flood event was the basis for this alternative. Flood watcr from ahove the study area was diverted to Terry Lake dm1 the overflow fro~ the lakc was channeled to the ?Qudre River along a bypass route south of the Larimer and Weld County Canal. Improvements through the rest of the study area were designed for local runoff from the lOO-year event. through a siphon taking it beneath Dry Creak. Areas north of the Valley Airpark are currently undev~loped and no improvements W0re considered. Reach A: Just upstream (rom the beainning of this rC3ch, 2,700-cfs is diverted to Terry Lake through improvements to the intake canal that feeds the lake. Improvements to Terry Lake are required to receive this flood water and this analysis showed that a peak flow of 600-cfs would have to bo released even with these improvements because of storaqe linitations in the reservoir. Alternative #2 The lOO-year flood event was the design frequency for this alternative. Flood water was channelized through Reach A to be diverted near the Larimer and Weld County Canal crossing of Dry Creek along a bypass route to the Poudre River. Improvements to Dry Creek betow the canal were desiqncd for residual runoff from the lOO-yeat event below t~c diversion. -25- -26-