Over the years many of the southern Delta channels have degraded due to the accumulation of sediments. In recent years, areas such as Middle River, Old River, Paradise Cut and Sugar Cut/Doughty Cut have lost significant capacity. This loss of capacity creates serious problems for may beneficial uses, and especially agricultural diversions.
Delta channels historically accumulated sediment at times and had sediment washed out during high flows at other times. When channel reaches became clogged, the local Reclamation Districts (“RD”) or diverters were able to dredge the problem areas to reestablish channel capacity. This not only helped maintain adequate depth for diversions, but also helped maintain flood flow capacity and in-water habitat. However, endangered species law and related environmental regulations now make any such dredging too costly for any RD or landowner to undertake.
The situation is complicated by the operations of the State Water Project and federal Central Valley Project export pumps in the southern Delta. Those export pumps lower water levels in the southern Delta below that which would naturally occur in this tidal system. By causing such additional lowering of water levels, less water comes in on the flood tide which decreases the amount of water available for diversions and for diluting the salts of the poor quality San Joaquin River water.
The sediment also interferes with the export operations themselves, decreases riverine habitat and as mentioned above adversely affects the transportation of high flows through the system. Because so many beneficial uses are impacted, a diverse group of interests are exploring how to pursue a Delta dredging project. The group includes South Delta Water Agency, the Department of Water Resources, the Bureau of Reclamation, the State Water Resources Control Board Delta Watermaster, Westlands Water District, the San Luis Delta Mendota Water Authority and the State Water Contractors. Many other interests support or are participating in the effort including fishery agencies and local interests. The parties Joint Problem Statement is included herein.
Using monies provided by SDWA, SLDMWA and Central Delta Water Agency, the group has retained a consultant who is in the process of analyzing the problem and estimating where and how much sediment needs to be removed. There are many issues involved in this initial analysis and the group is also exploring mitigation/habitat actions and coordination with other entities and efforts.
Absent significant dredging in certain channel reaches in the southern Delta, many local farmers will be unable to divert water under their water rights which would lead to a catastrophic chain of events and severely harming the area as well as the entire State.
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