WSP04963

• File Number: 8220.105.I
• Description: Colorado River-Water Projects-Navajo-Environmental Studies
• State: CO
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 4/1/2002
• Author: BOR
• Title: Navajo Dam EIS-Summer Low Flow Test Report-San Juan River New Mexico and Utah
• Water Supply Pro - Doc Type: Report/Study

I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I

A ttachment A

Hydrology

This analysis was done to evaluate proposed flow recommendations (Flow Recommendations
for the San Juan River [Flow Recommendations]) (Holden, 1999) of the San Juan River
Basin Recovery Implementation Program (SJRBRlP), Operating criteria for Navajo Dam
were developed to demonstrate how the dam might be operated to meet the Flow
Recommendations. These suggested criteria determine the timing and size of release flows
to maximize the ability of the river to meet the Flow Recommendations, These proposed
criteria could reduce releases from Navajo Reservoir to 250 cubic feet per second (cfs) for a
portion of time during the non-spring runoff period when fish releases or flood control
releases are not being made, This analysis addresses hydrologic impacts that may affect water
diverters in the San Juan River from Navajo Dam to the Animas River confluence under these
low-flow conditions. Impacts to the trout fishery and the riparian environment are addressed
in other sections,

In a 6-day test, July 9,2001 through July 15, 2001 (Summer Low Flow Test [Test]), average
releases from Navajo Dam were reduced from a previous rate of approximately 500 cfs to a
target minimum of approximately 250 cfs. All releases during the test were made through the
Navajo Hydroelectric Plant via the Navajo Dam main outlet works penstock, Release criteria
for the Test included flows as low as 250 cfs at Navajo Darn, provided that a minimum flow
of 500 cfs was maintained in the San Juan River in the critical habitat area. During the Test,
six Geological Survey (GS) river gauging stations were monitored to ensure the 500 cfs
minimum flow was not violated. The minimum flow recorded in the recovery area was
609 cfs at Shiprock on July 15. Daily flow data from the six gauging stations are shown in
table 1. Flow rates shown are mean daily values and are provisional data only, Figure 1 is a
graph of the data in table I.

To evaluate impacts between the San Juan River GS gauge at Archuleta and the Animas River
confluence, flow measurements were collected over a three-day period, July 10-12, The
San Juan River, canal diversions from the river, canal flow at various points along the canal,
and canal wasteways were measured, When necessary, flow data were collected through
interviews with water usets, All flow measurements, reported flow, and observed or
estimated flows are summarized in table 2. Data types are station number, station name,
description, river mile, flow measurements, average of the measured flow, and field personnel
(who performed measurements) and are arrayed by rivers, canals, personal contacts and
observations, and Hammond Data Sheets, Maps 1 and 2 show the location of measurement
points and irrigated areas. Table 3 summarizes inigated acres by canal subset by return flow
points that coincide with river measurement locations,

Summer Low Flow Test Report. April 2002

A-l
00605