FLOOD00591

• County: Weld
• Community: Greeley
• Stream Name: Cache La Poudre River
• Title: Floodplain and Floodway Analysis
• Date: 2/20/1994
• Prepared For: CWCB
• Prepared By: Brown & Caldwell
• Floodplain - Doc Type: Floodplain Report/Masterplan

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BC Brown and Caldwell
~ Consultants

7535 East Hampden Avenue
Suite 403
Denver. CO 80231-4838
[phone]
FAX [phone]

January 20, 1994

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Mr. Larry Lang, P.E.
Colorado Water Conservation Board
721 State Centennial Building
1313 Shennan Street
Denver, Colorado 80203

City of Greeley, Colorado
Request for Letter of Map Revision
Cache La Poudre River

Dear Mr. Lang:

The City of Greeley is presently designing improvements to their Water Pollution Control
Facility (wpCF) located adjacent to the Cache La Poudre (Poudre) River between Ash Avenue
and U.S. Highway 85 in Weld County, Colorado. The WPCF is presently located within the
regulatory floodway of the Poudre. The floodplain and floodway are defmed by the Flood
Insurance Study (PIS) of the Federal Emergency Management Agency in a report entitled "Flood
Insurance Study, City of Greeley, Colorado" dated January 1979.

Brown and Caldwell has undertaken a program to analyze the existing floodplain and floodway
of the Poudre adjacent to the WPCF and to detennine floodway regulatory compliance
concerning construction of the new facility improvements.

Since 1979, the date of the PIS study, considerable changes have been made which impact the
floodway. Most notably are the construction of replacement bridges crossing the Poudre at Ash
Avenue and at 8th Street. These bridges cause a reduction in the floodway and lower the 25-,
50-, and 100-year water surface profIles. Additionally, the lOG-year floodway is greatly
reduced. The magnitude of the changes justifies an application for a Letter of Map Revision
(LOMR) to redefme the regulatory floodplain and floodway.

The accompanying documentation provides a basis for requesting a LOMR. This would remove
large areas of the WPCF from the floodway. Additionally, the lowered lOO-year flood profIle
would place plant components that are on naturally high ground out of the floodplain. The
resultant regulatory boundaries world pennit most of the contemplated plant modifications,
required to meet discharge criteria, to be constructed without violating floodway ordinances.

21-7387