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I I I I I I I I I I I I I I I I I I I EVALUATION OF ALTERNATIVES The project alternatives were evaluated based on how the project meets the design issues, project costs, and permitting issues associated with the project alternatives. Flood Attenuation The alternatives studied in this report will reduce the storm water detention capacity of the reservoir, which will result in a decrease in the flood peak attenuation historically enjoyed by downstream entities during storm events. The increase in storm peak discharge over historic conditions would mostly be evident during rainstorm events and not during snowmelt events which are generally of longer duration, larger volume, and lower peaks. The City does not have a legal obligation to provide storm water detention and attenuation of flood peaks to downstream residents. For all Alternatives considered except for Alternative C, a remnant reservoir pool would remain and some flood attenuation would be provided. In the event of a flood, all alternatives except Alternative C would have similar impact on downstream properties; Alternative C would provide no flood attenuation. Sand Deposition, FreezinQ and Water RiQhts Issues All alternatives are designed to address the sand deposition, freezing and water rights issues. Alternatives A, B, D, E, F, and G provide a remnant reservoir pool to function as a sediment pond upstream from the pipe intake. The pool provided for Alternatives B, D, E and G is on-stream, and its operation will be impacted by sediment deposition more quickly than the pool for Alternative A and F, which is effectively off-stream. For Alternative C, a sluice gate would be provided to flush out sediments accumulated behind the diversion dam. Alternatives B, C and D would be provided with a new turnout box, which includes a small sediment trap and sluice gate/bypass back to the stream channel. Alternatives A, B, 0, E, F and G would be provided with a modified intake standpipe, which could include a 27