FLOOD10343

• County: La Plata
• Stream Name: Pine River
• Basin: San Juan/Dolores
• Title: Pine River Flood Plain Study
• Floodplain - Doc Type: Correspondence

Colorado Water Conservation Board
Department of Natural Resources
721 Centennial Building
1313 Sherman Street
Denver, Colorado 80203
Phone: [phone]
FAX: [phone]

STATE OF COLORI\DO

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, ..

.,

Bill Owens
Governor

MEMORANDUM

Greg E. Walcher
Executive Director, DNR

Peter H. Evans .
Acting Director, CWCB

To: Ms. Bet Lotosky
Floodplain Management Services
Albuquerque District
U.S. Army Corps of Engineers

From: Tom Browning $-
Flood Control and Floodplain Management Section
Colorado Water Conservation Board
Department of Natural Resources

Date: February 25, 1999

Re: Pine River Floodplain Delineation Study

I have reviewed the meeting minutes for the Pine River hydrology meeting held on February 4,
1999 at the offices of the Bureau of Reclamation in Durango, Colorado. After doing some additional
research and reviewing available data, I would like to recommend a slight change to the Vallecito
Reservoir assumptions that were discussed. It was initially agreed that for the purposes of the
floodplain study a constant reservoir release of3,100 cfs would be assumed as the maximum discharge
from the outlet works. It was also assumed that no spillway discharge would be considered.

My recommendation is to include some amount of discharge from the reservoir spillway in
addition to the constant reservoir release from 3,100 cfs. Specifically, I would like to assume a flow
depth of 2 feet at the spillway crest beneath radial gates during a major flood event (i.e. gates are
opened at 2 feet). This relates to a spillway discharge of approximately 2,000 cfs according to the
Vallecito Dam spillway discharge curves provided by the Bureau of Reclamation. Therefore, the
assumed total discharge from the outlet works and the spillway would be 5,100 cfs during a major
flood event.

For the Pine River drainage area below the dam, I fully support the methodology as agreed
upon at the meeting and as outlined in the meeting minutes.

Please call me at [phone] if you wish to discuss this matter in further detail.

xc: Stan Powers, USBR - Durango Office
Butch Knowlton, La Plata County OEM

c:/seca/projects/pine river fp studylhydrology memo-I.doc