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I I I I I I I I I I I I I I I I I I I The channel, in its present condition, is adequate to contain the 100- year flood flows throughout most of this reach. The addition of low dikes at the downstream end of the reach will be required to completely eliminate flooding under lOO-year flood conditions. Downing Drive Crossing The existing Downing Drive bridge has sufficient discharge capacity ta pass the 100-year flood flow without overtappi ng. Washington Street Crossing The existing Washington Street bridge has sufficient discharge capacity to pass the lOO-year flood flow without overtapping. Culvert at Narth Valley Shapping Center - Plate 111-6 This culvert, which passes through the most expensive development along the Niver Creek, is the biggest bottleneck along the creek. It is a 9 foot by 6 foat reinforced box culvert with a discharge capacity of 700 cfs, about 165 cfs less than the 10-year flood flow. Increasing the discharge capacity of this culvert will be a very costly and inconvenient project because it passes under the shopping center parking lot. Due to the District's criteria that structures must pass a 10-year flood, and due to the frequent flooding and assaciated damage which occurs because of this culvert, its capacity must be increased. A significant portion of the construction cost for increasing the capacity of this culvert is due to the problems involved with working in a congested, urban area. Because of this, and because of the high damage potential of this area, it seems unreasonable to modify the existing culvert for any flow less than the 100- year flood flow. It is recommended therefare that the culvert be modiFi ed to pass the lOo-year flood flow by adding 0 secand culvert os shown on Plate 111-6. 111-7