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COMMENTARY - SHEETS 19 & 20 I I I I I I I I I I I I I I I I I I I These sheets are a plan view of the Little Dry Creek floodplain as it extends to Clear Creek. In the 100-year flood event and present channel conditions, all but 300 cfs of the 4600 cfs peak flood flow is out of the channel at 64th Avenue, following and over- flowing 64th Avenue all the way to Tejon Street. With the construction of the proposed channel improvements, all the 100-year flow would be contained within the 25-year channel, but there would be no freeboard and minor spillages from the channel would be probable. The remainder of the 100-year run off which spills out of the channel at the upstream railroad crossing (Sta. 48 + 32, Sheet 17), is intercepted by the existing gravel pits south of 64th Avenue. No attempt has been made in this study to determine how much water would actually enter the pits and to what elevation(s) the water surface would rise. As is pointed out on the sheet, an alternative to constructing the concrete lined channel from 64th Avenue to Clear Creek is to construct a channel to divert flood waters directly into these gravel pits. Cost comparisons and legal constraints need to be determined for this approach during final design as they have not been included in this st udy. The existing floodplain should be regulated and property owners who would be adversely affected by the 100-year flood should be encouraged to acquire flood insurance. Residents in the vicinity of the 100-year floodplain should be notified annually of the potential flood hazards. Since the improvements are designed for the 25-year event, the continued enforcement of floodplain regulations and an ongoing program of floodplain management will be necessary after the proposed improvements are built to compensate for larger floods.