A memo to the South Delta Water Agency Board of Directors by SDWA Counsel and Manager John Herrick highlights some of the problems with science in the PPIC report. The analysis, he says, “appears to be based on a fundamental lack of understanding of the hydrodynamics, hydraulics, diversions, and water quality data of the area.”
The report uses the Water Analysis Model (WAM) to estimate water quality in the southern Delta and to conclude that water quality will improve with an isolated conveyance facility. But the WAM model isn’t designed to capture the small changes in salinity that can have significant adverse effects on agriculture. The report averages water quality from different parts of the Delta and averages tides, which actually affect different channels in different ways.
The PPIC report estimates water quality from some (but not all) areas of the South Delta using unidentified sampling stations. The report excludes from analysis the channels that have the worst source of water quality.
Averaging salinity during the irrigation season ignores the fact that maximum salinity at the wrong time can ruin a crop. The report also underestimates average salinity in the southern Delta.
Salt enters the southern Delta from the San Joaquin River, where it collects and is concentrated. Water and salt typically leave the southern Delta only through the export pumps. Sacramento River water entering the southern Delta on its way to the export pumps dilutes San Joaquin River salts. If you put in an isolated facility and decrease the amount of Sacramento River water passing through, fewer salts will leave the area and the water quality will get worse.
It’s as simple as that.