FLOOD00275

• County: Adams
• Community: Westminster
• Title: Bruchez Farms Property - Big Dry Creek at Wadsworth Parkway
• Date: 1/1/1998
• Prepared For: Bruchez Farm
• Prepared By: Wright Water Engineers Inc
• Floodplain - Doc Type: Floodplain Report/Masterplan

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14

Decrease In Depth

Figure 3 indicates that for a flow of 5,000 cfs, the water surface elevation wlll be

reduced about two feet If the entrance to the existing concrete arch rallroad culvert

is improved as shown in Figure 4.

With the Ketner Reservoir improvements In place, the pea~ flow rate upstream of

tho railroad 10 oi,5<tO efo. Uoing Flgur" 3, thla flow rat" tranelat"s to a water sur-

face elevation of 5362.8, based on the Improved Inlet curve. This is the same elev-

ation given by the the 1986 stUdy results. All this means Is that the HEC-2 model

formUlation is not as accurate as the hand calculated depth-outflow relationship. ~/

The HEC-2 model uses only the orifice equation to estimate the upstream depth.

STORAGE YOLUf1E UPSTREAf1 OF THE C&S RAILROAD

There is another Improvement that should be made to the models used In the 1986

FHAD study. The existing HEC-I model does not incorporate the storage volume that

presently exists upstream of the railroad culvert, which wlll tend to reduce the

depth of water upstream of the culvert.

If the 10o-year flood event had occurred at the time that the 1986 study was being

conducted, the water surface elevation upstream of the rallroad culvert would not

have been 5365.0, but would have been several feet lower.

This is because a portion of the runoff volume would have been temporarily detained

upstream of the rallroad culvert. This water would be used to form the temporary