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I I I I I I I I I I I I I I I I I I I Flood Hazard Page six Upstream Development Development and the associated increase in impervious area can cause an increase in runoff. However.. looking at the entire 255 acre basin and the development since about 1975 when the subject home was built. it does not appear that the impervious area has increased substantially. It is even more difficult to demonstrate that development of the approximate 14 acre Mountain View Park Subdivision just upstream of Kelley Road has, by itself. caused flows to increase substantially. At the downstream end of the Mountain View Park subdivision is a detention pond claimed to have been constructed by the developer. It appears to be a detention pond mostly as a result of the barrier formed by Kelley Road. The usual purpose of a detention pond is to limit runoff from the subdivision to some acceptable level of historic flow. Based on recent calculations by the developer's engineers. the outflow from the pond is controlled by a combination of flow through the existing culvert and weir flow over the road. During a 5-year event (17.2 cfs inflow), water will pond behind Kelley Road to an approximate elevation of 8372.0 feet. Since the low point of the road is 8374.3, no water is expected to pass over the road. Flow through the existing culvert was calculated at 8.2 cfs. During a 100-year event (150.1 cfs inflow). water will back up behind Kelley Road to an approximate elevation of 8374.5 which means water will flow at least 0.2 feet deep over the road. Approximately 22 cfs will pass through the existing culvert and 102.3 cfs will pass over the road. According to the current drainage requirements of the City of Woodland Park, the detention pond is acceptable. It prevents 5-year flows from overtopping Kelley Road. Furthermore. in a 100-year event the pond reduces the combined flow through the culvert and over the road to about 80% of the inflow.