FLOOD02508

• Designation Number: 292
• County: Adams
• Community: Westminster
• Stream Name: Big Dry Creek
• Basin: South Platte
• Title: Flood Hazard Area Delineation - Bruchez Farms Property, Big Dry Creek at Wadsworth Parkway
• Date: 1/1/1988
• Designation Date: 3/1/1988
• Floodplain - Doc Type: Floodplain Report/Masterplan

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15

pond that. according to the 1986 study, would be 25 feet deep at the time the peak
discharge rate was approaching the culvert.

However, this is not what would physically occur at the site. The depth of water
upstream from the culvert entrance will only rise to the height necessary to permit
the peak outflow rate to pass throuah the culvert as lIlustrated in Figure 5, I. e.,
the peak of the outflow hydrograph. The shaded area is the volume of storage up-
stream of the culvert being utll1zed. The greater the available volume of storage,
the greater will be the reduction In peak flow rate.

Total ExIsting Volume

Using the available topographic mapping, the total volume of storage presently

existing upstream of the culvert was determined. The total available storage at

2-foot Intervals is l1sted In Table 2. If the water surface elevation upstream of the

railroad culvert were 5364, about 300 acre feet of runoff would be temporarily

stored upstream of the culvert.

Existing Volume Within the F100dway

At some point In the future, the land outside of the floodway upstream of the

railroad culvert could be filled. This would reduce the amount of storage available

for the temporary detention of flood water. For this reason, the volume of avail-

able storage upstream of the railroad culvert was recalculated, assuming that the

land outside the floodway had indeed been filled. These results are also l1sted in

Table 2.