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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18

ADDITIONAL HEC-1 RUNS

The above data on Improved Inlets and available storage were used in the existing

HEC-l model to determine their effects on the water surface elevation upstream of

the railroad. ThIs study represents a refinement of the current FHAD analysis. The

same assumptions were used as in the original FHAD study: fully developed, unde-

tained flows and the same floodway criteria. This study does reflect the reduced

outflows from Ketner Reservoir after completion of the recent construction and the

Inclusion of the effects of floodway storage. These changes represent a more de-

tailed, In-depth study of the flood elevations during the 10o-year event at a speCific

location on Big Dry Creek. The results of these changes are shown in Table 3.

During this study, the UDFCD and the city of Westminster redefined what .adequate

assurances. in regards to Standley lake means. In the original FHAD study, the

HEC-l model Included a constant outflow of 430 cfs from the principal spillway plus

an outflow hydrograph from the emergency spillway which peaked at 1,043 cfs. The

sum of these two peak flows Is about 1,470 cfs. Using the new definition of 'ade-

quate assurances., there Is assumed to be a constant outflow of 1,470 cfs from

Standley Lake.

In addition, the UDFCD and the city of Westminster also requested a study of what

Increase In the water surface would take place upstream of the railroad If land not

owned by the Bruchez family were excluded from the floodway storage volumes.

The results of the change In assumption for .adequate assurances. and reduced

storage volume are also shown In Table 3.