Posted by: Deirdre Des Jardins | December 6, 2018

Why more storage won’t help conflicts on the Lower San Joaquin River

1 New Melones Dam, owned by US Bureau of Reclamation Source: Wikipedia

The United States Congress is currently considering an extension of the controversial 2016 Water Infrastructure Improvements for the Nation Act or WIIN Act. Section 1 of the extension would appropriate an additional $134 million per year for the next five years for new dams, for a total of $670 million. One of the main reasons cited for providing additional funding for new dams in California is the State Water Resources Control Board’s proposed updates to the Bay-Delta Water Quality Control Plan. But new dams won’t help reduce the conflicts with the State Water Resources Control Board’s new Lower San Joaquin River flow objectives, because none of the proposed new dams are on the tributaries to the lower San Joaquin River which are affected by the proposed LSJR flow objectives. (The proposed emergency spillway modifications at New Exchequer would increase storage slightly, but at the cost of affecting the safety of the dam.)

According to the Water Board’s Technical Report for the Scientific Basis for the San Joaquin River flow objectives, three huge new dams on the tributaries to the Lower San Joaquin River were built in the late 1960s and early 1970s. New Exchequer Dam was completed on the Merced River in 1967, New Don Pedro on the Tuolumne River in 1970, and New Melones on the Stanislaus River in 1978.

With New Exchequer Dam, the dams on the Merced River can store 120% of the median annual flow of the Merced, or the entire flow in 65% of years. With New Don Pedro Dam, the dams on the Tuolumne River can store 170% of the median annual flow of the Tuolumne, or the entire flow in 80% of years. and with New Melones Dam, the dams on the Stanislaus River can store 260% of the the median annual flow of the Stanislaus, or the entire flow in 95% of years. So the conflicts on the Lower San Joaquin River do not stem from inadequate reservoir storage, but rather from the ability to divert and store the entire annual flows of the three tributaries to the Lower San Joaquin in most years.

Major dams on Lower San Joaquin River Tributaries

 

Stanislaus River

Tuolumne River

Merced River

Median Annual

Unimpaired Flow

(1923-2008)

1.08 MAF

1.72 MAF

0.85 MAF

Total Reservoir Storage

2.85 MAF

2.94 MAF

1.04 MAF

Reservoir Storage as % of median flow

264%

171%

122%

% of Years Unimpaired Flow < Total Reservoir Storage

95%

80%

65%

Major Dams

New Melones

(1978, 2.4 MAF)

Tulloch, Beardsley, Donnells

(1957-8, 203 TAF)

New Spicer Meadows

(1988, 189 TAF)

New Don Pedro

(1970, 2.03 MAF)

Hetch Hetchy

(1923, 360 TAF)

Cherry Valley

(1956, 273 TAF)

New Exchequer

(1967, 1.02 MAF)

 

The Water Board’s permits for New Exchequer, New Don Pedro, and New Melones dams were issued over 40 years ago. The conflicts between human uses of water and ecosystem needs have grown enormously in the past four decades. Diversion data from 1984 to 2009 shows that the some of the highest diversions, as a percent of flow, occur during the critical February to June period when San Joaquin Chinook salmon are rearing and migrating. The Water Board looks at ecosystem flows as a percentage of estimated unimpaired flows on the river. From February to June, 79% of the unimpaired flow Tuolumne River has been diverted, 74% of the Merced River, and 60% of the Stanislaus River.

1984-2009

  Stanislaus River Tuolumne River Merced River
Median Annual % of Unimpaired Flow 58% 40% 46%
Median Feb-Jun % of Unimpaired Flow 40% 21% 26%

The Bay Institute produced these graphs of flows on the Lower San Joaquin River and its tributaries from 1995 to 2016. Except for the extremely wet year of 2017, the Lower San Joaquin and its tributaries have been almost dried up from February to June since 2012.   This is the critical time for migration and rearing of a number of fish, including Chinook salmon.

 

 


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