FLOOD02650

• County: La Plata
• Stream Name: Animas River
• Basin: San Juan/Dolores
• Title: Hydrology Addendum to FIS La Plata County Unincorporated Areas
• Date: 5/21/2002
• Prepared For: La Plata County
• Prepared By: Montgomery Watson
• Floodplain - Doc Type: Floodplain Report/Masterplan

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measures 162 feet in height and has a crest length of 4,0 1 0 feet. The reservoir has a storage capacity
of 129,700 acre-feet.

The USBR constructed the dam to provide irrigation water to the Pine River Project and is
part of the Upper Colorado River Storage Project. The USBR's Operation and Maintenance Branch,
Water and Land Division, Durango Area Office, is responsible for the safe and proper operation and
maintenance of the dam and reservoir. The Pine River Irrigation District is under contract with the
USBR to operate the dam under criteria developed by the USBR. The U.S. Army Corps of
Engineers is responsible for providing and approving the operating criteria for flood control subject
to the provisions of Section 7 of the 22 December 1944 Flood Control Act (58 Stat 890). The USBR
is responsible for the administration of flood control operations.

Normal releases from Vallecito Dam are made through the outlet works that have a
maximum capacity of3,100 cfs. The spillway is controlled by three 37-by-19-foot radial gates; the
spillway has a peak discharge capacity of 30,000 cfs. Operating criteria are designed to minimize
the occurrence of releases greater than 2,500 cfs which is considered for operating purposes to be
the downstream channel capacity. Below Vallecito Dam, the Los Pinos River flows south through
La Plata County for approximately 35 river miles until it reaches the ColoradolNew Mexico State
line. The Los Pinos River continues to flow south until it outlets into the Navajo Reservoir on the
San Juan River in northwestern New Mexico.

HYDROLOGIC ANALYSIS

Three U.S. Geological Survey (USGS) stream gages exist near the watershed under study;
these gages are listed in Table 1. Flow recorded at the Los Pinos River at La Boca stream gage is
regulated by Vallecito Reservoir 24 miles upstream. The flow also reflects diversions for irrigation
of about 33,000 acres upstream of the gage location. Flow recorded at the Spring Creek at La Boca
stream gage is affected by regulation because nearly all of the irrigation in this basin is water diverted
from Los Piiios River which causes a considerable change in the annual pattern of natural flow.

TABLE 1
USGS STREAM GAGES
Gage Name USGS Drainage Area Gage Period
- Gage Number (Square Miles) Elevation of Record
Los Pmos River at La Boca, CO 09354500 510.0 6144 1950to
Present
Spring Creek at La Boca, CO 09355000 58.0 6160 1950 to
Present
Vallecito Creek near Bayfield. CO 09352900 72.1 7906 1962 to
Present

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