Prepared exclusively for Maven’s Notebook by Robert Shibatani
The “Miracle March” everyone was hoping for, unfortunately did not materialize.
Across California, federal CVP reservoir storage currently stands at 4.698 million acre-feet (MAF), representing a little less than 40% of total federal reservoir system capacity but, 57% of the 15-year average. When compared to this same time last month, however, total CVP storage was only 4.573 MAF, thus indicating an actual storage gain of 125,000 acre-feet (AF) over the past 30-days despite receiving little to no new precipitation.
How could this have happened? Particularly under supposed drought conditions?
The answer is simple. We exited the flood control season, allowing res-ops to transition to “refill” mode. Several notable reservoirs in fact gained storage during March. Shasta Reservoir, the State’s largest, gained 42,000 AF, Trinity Reservoir gained 21,000 AF, Oroville Reservoir on the SWP side gained 17,000 AF, even modest Folsom Reservoir gained 51,000 AF. New Melones Reservoir, however, the 3rd largest federal facility lost 46,000 AF.
California’s snowpack was significantly depleted over the month with statewide SWE dropping some 4.5 inches to 11 inches which is about 39% of normal for this date; interestingly, it was 64% of normal only 30-days ago. Across the northern, central, and southern regions, SWE values range between 30-44% of normal for this date.
Insofar as precipitation is concerned, the accumulated totals were dismal. The Northern Sierra Precipitation – 8 – Station Index stands at 33.2 inches gaining a paltry 1.3 inches for the month (with current totals representing only 75% of average). For the San Joaquin Precipitation – 5 – Station Index, the current 22.1 represents a meager 1.7-inch gain for March representing 67% of average for this date. For the Tulare Basin Precipitation – 6 – Station Index, the current 14.9 inches is only 63% of average, gaining only 1.4 inches over the month.
With the mid-month change in CVP/SWP operational priorities, system hydrology reacted as expected. While total delta inflow averaged 12,226 cfs for the month, it dropped from the mid-14,000s prior to March 15th, steadily declining to around 10,000 cfs over the latter half of the month. As reservoir releases from the upper Sacramento River reservoirs and Oroville Reservoir were scaled back, resulting change in Sacramento River flows at Freeport during this time became evident; flows were notably diminished from the mid-12,000 cfs to around 8,000 cfs.
Delta operations for the month of March had total Tracy pumping just under 70,000 AF through yesterday with Banks pumping around 29,000 AF. Total exports have been fairly constant around 1,500 cfs daily, but with the onset of the irrigation season, exports have ramped up to 4,800 cfs these past few days. Not surprisingly, a significant jump in daily E/I ratio was evident, calculated to be around 40%.
With March now officially behind us; the 2022 irrigation season is upon us, and exports are already ramping up. Statewide reservoir storage is low, though not yet dire. Unfortunately, there is no significant precipitation on the horizon and SWE is declining rapidly. While the terrestrial moisture reserves were capped off earlier in the season, unexpected warm spells have continually depleted these stores.
Prepared by Robert Shibatani
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. robert@theshibatanigroup.com
View more water conditions at DWR’s California Water Watch website.
