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Delta Doozy: Hydrology - Not Pumping Restrictions - is the Primary Driver of Water Supply Allocations
Delta Doozy: Hydrology - Not Pumping Restrictions - is the Primary Driver of Water Supply Allocations
22 February 2016

Discussions about California water supplies have too often become a fact-free discourse that fail to advance an informed discussion. The State Water Contractors’ “Delta Doozy” series was launched in order to distinguish the facts from the fiction and promote constructive dialogue.

This week’s Doozy comes from a blog by attorney Doug Obegi of the Natural Resources Defense Council on February 16, 2016. Citing a graphic presented at a recent meeting of the Metropolitan Water District of Southern California, Obegi states the following about potential allocations of State Water Project supplies:

“But as the graphic from Metropolitan below demonstrates, hydrology - not pumping restrictions - is the primary driver of water supply allocations.”

Some Facts for the Record: The graphic reveals that pumping restrictions in the Delta will be the primary reason why water supplies for 25 million Californians are severely limited if California is fortunate enough to have a wet remainder of the year. The terms “50 percent exceedance” and “25 percent exceedance” refer to hydrologic conditions that happen half the time and wetter conditions that happen only 25 percent of the time. Supplies to Metropolitan would only improve by 3 percent under wet conditions compared to average under the pumping restrictions. Why? The window to move supplies in wetter years is largely in the winter and spring, when the restrictions for delta smelt are in effect.

According to the latest estimates by the California Department of Water Resources (DWR), wet conditions (25 percent exceedance) for the remainder of the year will produce an estimated 20.8 million acre-feet of runoff in the Sacramento River watershed compared to 16.3 million acre-feet of water under average conditions. That is 4.5 million acre-feet more runoff in a wet 2016, yet it would produce only 120,000 acre-feet of additional supplies for the State Water Project (half going to Metropolitan). Put another way, a 28 percent increase in available supplies in a wet winter would only translate into a 3 percent improvement in deliveries to Metropolitan.  

According to this same DWR Allocation Study on Jan. 22, public water agencies would be receiving 29 percent more water than currently allocated were it not for the restrictions. That is more water than these agencies can expect to receive this year under the restrictions no matter how much more it rains.

To suggest that hydrology is the primary driver of water supply allocations, given the existing restrictions, simply isn’t true in wet years.

For more information, SWC’s Water Update series provides regular updates on the total amount of water flowing into the Delta compared to how much water the state and federal water projects export.