FLOOD03719

• County: Adams
• Community: Thornton
• Stream Name: Big Dry Creek
• Basin: South Platte
• Title: Floodplain Information Report
• Date: 4/15/1988
• Prepared For: Thornton
• Prepared By: McLaughlin Water Engineers, Ltd.
• Contract/PO #: &&
• Floodplain - Doc Type: Floodplain Report/Masterplan

I I
II
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I

GOLFP2.H2
Proposed conditions run from just downstream of 136th Avenue (Section 959+20) to
upstream of 1-25. All starting water surfaces are from GOLFE.HEC. The existing 136th
Avenue bridge is modeled. The file CHNBRP.H2 contains the proposed 136th Avenue
bridge. The flood events modeled are 2-year, lO-year, FEMA 100-year and UDFCD 100-
year.

The modeling procedure utilizes the split flow option of HEC-2, with diverted flow onto
the practice range returning at Section 963+20. All water surface profiles match with
existing conditions at Section 1005+64, upstream of 1-25.

PR.H2
Driving range model of the spilled 100-year UDFCD flow of 3,606 cfs. The run is
started using the water surface at Section 963+20. The FEMA 100-year flow split of
2,130 cfs is also included.

1251.H2
The improved 1-25 bridge. The starting WSEL at Section 1001+50 is from the proposed
condition 100-year WSEL. The Q used for the bridge is 11,480 cfs from Greiner's FHAD.

GOLFFl.H2
This file contains the 100-year FEMA flood, with floodway downstream of 136th Avenue.
Channel encroachment occurs along the right overbank downstream of Washington Street
and along the left overbank upstream of Washington Street. The encroachments upstream
of Washington Street change the flow over Washington Street as computed by the split
flow option. The floodway table is attached.

EASTFW.H2
This file contains the 100-year FEMA flow and floodway for the east side of Washington
Street, starting at Section 937 +60. The 100-year and encroached conditions flows are
different due to encroachments on the west side of Washington Street.

A-2