Prepared Exclusively for Maven’s Notebook by hydrologist Robert Shibatani

As we near the end of WY 2021-22, much of the central and southern State are heading into a blistering end-of-summer heat wave over the upcoming Labor Day weekend.  This will certainly not help reservoir and river conditions.  Over the month of August, reservoirs continued their late summer decline.  Folsom Reservoir led the way losing some 144,000 acre-feet.  Shasta was next, losing 91,000 acre-feet.  San Luis, New Melones, and Trinity reservoirs lost 73,373, 69,100, and 56,000 acre-feet, respectively.  Millerton and Lake Berryessa each lost about 34,000 acre-feet over the month.

Current reservoir storage for Shasta, Trinity, New Melones, Folsom, San Luis and Millerton reservoirs stand at 1,592,000, 608,000, 642,000, 447,000, 180,000 and 252,000 acre-feet, respectively.  These storage levels are indeed low, yet relative to each of their longer-term averages, the current storage levels are not overly worrisome.

Total federal CVP water storage was 3.721 million acre-feet (MAF) as of yesterday.  Current federal storage relative to total storage capacity is about 31.3%, or less than a third.  As noted, however, relative to previous years, current federal storage is about 60% for this date of the WY.

No measurable precipitation occurred over the month.  It looks as though end-of-WY precipitation totals will show the American River basin has having a normal precipitation year (e.g., 98% of average), but all other basins will show below average accumulations (e.g., the Stanislaus River basin at New Melones at 73%; Sacramento River at Shasta at 68%, Trinity River at the fish hatchery at 61% and the San Joaquin River at Huntington Lake at 61%).

Oroville Reservoir was storing 1.316 MAF as of yesterday (e.g., 37% of total storage capacity, but 77% of its 15-year average for this date).

Export pumping has averaged 5,372 acre-feet per day from the Tracy Pumps (federal CVP) and 1,205 acre-feet per day from the Banks Pumping Plant (SWP).  Total Delta inflow for August averaged 10,530 cfs per day, with typical major contributions from the Sacramento River declining from about 11,000 cfs in early August to about 8,000 cfs by the end of the month, yesterday.  Delta outflow 7-day average was about 3,300 cfs over the month.  The E/I ratio averaged 31% for the month.

As of yesterday, reservoir releases from the four primary northern California reservoirs into the Sacramento River totaled 11,646 cfs from Trinity, Shasta, Oroville and Folsom reservoirs.  For Trinity and Folsom reservoirs, these releases were above their 15-year median values for this time of year.

For September, projected hot temperatures will continue to deplete reservoir storage.  End of WY carryover is expected to be alarmingly low.  Numerous September EOM reservoir release and instream flow targets from ESA requirements will likely be missed this year.  Fall and early storms and rains are very much in high anticipation.

Robert Shibatani, a physical hydrologist with over 35-years combined experience as an international expert witness on reservoir-operations, climate change hydrology, commercial flood damage litigation, and water supply development.  He is Managing Partner for The SHIBATANI GROUP International, a division of The SHIBATANI GROUP Inc. and resides in Sacramento, California.

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