Prepared Exclusively for Maven’s Notebook by Robert Shibatani

October 31, 2020

The first month of the new 2020-2021 water-year (WY) has not brought any new hydrological inputs to the system; it has been a dry October.  Across both the CVP/SWP, precipitation to date has been negligent.  A La Niña is currently underway and is expected to continue throughout the November through January period.  At this time, given the strong La Niña signatures, below normal precipitation is anticipated although depending on where the composite line ultimately rests, increased storm activity and above normal precipitation could occur over the northern portion of the State.  This could have significant implications to CVP storage potential.

As with many years, we endeavor to rely on stored carryover storage from the preceding year(s) and this WY is no different.  Across the northern CVP reservoirs, storage as a percentage of the 15-year average stands at 96%.  The good news is that of the four primary reservoirs, Shasta, Oroville, Trinity and New Melones are all holding storage at 90, 94, 97 and 113% of their 15-year averages for this time of year representing some 6.4 million acre-feet under storage or 43% of the total storage capacity for those noted reservoirs.  This means that there is notable storage space available should operators choose some level of encroachment this fall and winter.

With no significant precipitation events on the horizon, reservoir operators are once again forced to play a very conservative game.  Fortunately, unlike other years, carryover is almost as good as one can reasonably expect for this time of year.  We will be watching releases closely and so far, releases appear to be trending close to their 15-year medians with the possible exception of Goodwin Dam that has experienced periodic ramp ups to 1,450 cfs.  The real test for reservoir storage will occur should a series of early winter storms force operators to make a hard decision regarding maintaining water levels at the rule curves or allowing encroachment into the flood storage pools.

Prepared by Robert Shibatani

Robert Shibatani, a physical hydrologist with over 35-years combined academic, legal, consulting and water advisory expertise, is 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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