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

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SECTION I
EXECUTIVE SUMMARY

This report was prepared for the City of Thornton to investigate hydraulic conditions
along Big Dry Creek due to the proposed construction of the Thornton Municipal Golf
Course, located at 136th Avenue and Washington Street. The report presents
information sufficient for:

1. Review by the Federal Emergency Management Agency (FEMA) for a Conditional
Letter of Map Revision to alter the 100-year floodplain designation;

2. Review by the Urban Drainage and Flood Control District (UDFCD) for floodplain
modification; and

3. An estimate of capital construction costs necessary for a cost-effective and
efficient stream crossings and stream bank protection program.

Two additional separate reports will address utilities and wetlands mitigation associated
with golf course construction. The Utilities Report was used to determine Quail Creek,
Lake Erie Basin Tributary 4, Tanglewood Creek, and storm sewer outfall locations for
riprap location and sizing along the Big Dry Creek. The Wetlands Report was used in
conjunction with floodplain hydraulics to establish compatible cross sections for wetland
mitigation, streambank protection, and golf course landscape aesthetic appeal.

Section U - Hydrologic Data
Previous reports were used to establish storm water flows for the 2-, 10-, and 100-year
events in the Big Dry Creek basin for future residential, commercial, and industrial
development and for existing conditions. Future conditions are used by the UDFCD. The
future flows used in this report are 3,650, 5,620, and 11,190 cfs for the 2-, 10-, and 100-
year events, respectively. Upstream of 1-25, within the City of Westminster, a flow of
11,480 cfs was used.

For existing conditions used by FEMA, a 100-year flow of 8,839 cfs was used to provide
a hydrologic match at Interstate Highway 25 (1-25) with the flow used in a recently
completed Flood Insurance Study (FIS) for Westminster. This flow was not used in
previous FIS studies