The San Joaquin Valley East Side Perspective

Abstract

The East Side sub-watershed of the San Joaquin River Basin includes the area of five /irrigation districts, the Merced ID, the Turlock ID, the Modesto ID, the Oakdale ID and the South San Joaquin ID. These districts plus adjacent land irrigated with ground water cover approximately 240,000 ha (600,000 acres) of the east side of the San Joaquin Valley between the San Joaquin River on the south and the Stanislaus river on the north. The five irrigation districts hold the majority of the water rights to the flow of the Merced, Tuolumne and Stanislaus Rivers that provide excellent quality snowmelt water from the Sierra Mountains. Most of the snowmelt runoff generally occurs between April and July each year. Consequently, the districts have large storage reservoirs to capture the runoff for power generation and irrigation during the remainder of the year. Each river has required instream flows below the major reservoirs during some or all months of the year. The release of water from the reservoirs and from irrigation district canals currently dilutes the more saline water in the San Joaquin River that originates from the west side of the San Joaquin Basin during most of the year and particularly during the irrigation season regardless of the volume of flow. The Central Valley Regional Water Quality Control Board's (Regional Board) Salt and Boron Total Maximum Daily Load (TMDL) could in certain instances, require a reduction in the discharge of East Side water with salinity levels between 315 and 700 uS/cm (0.315 and 0.7 dS/m), during various times of some years. At the same time, discharges of water with higher salt concentrations and corresponding higher salt loads would be allowed from the West Side of the Valley. The elimination of the discharge of this good quality water to the San Joaquin River could require the release of additional water from New Melones Reservoir on the Stanislaus River in order to dilute the West Side discharges and meet the water quality objectives at Vernalis. This paper discusses the East Side perspective on the fixed load limits in the load based salinity and boron TMDL and the Dissolved Oxygen TMDL for the San Joaquin River.