GUEST COMMENTARY: Our Enduring Water Supply: Are the Answers to California’s Water Problems Obvious?

Written by Robert Shibatani

Is there a water supply problem in California?                   

To answer such a question, much depends on who one asks.  For in the politically ideological and highly volatile world that is California water, we would likely hear many answers to such a question, each steeped in their own biases, background, and seeming agendas.  All these opinions would have merit, but to what extent would they be based on reality and more specifically, hydrologic reality?

Armed with this information, the media, regulators, and the general public will each gladly offer their opinions (this author included).  And they will do so covering a wide range of beliefs.  For the outside observer, the challenge comes in the ability to sift through the growing detritus of water-related information in order to come up with some semblance of truth.  Sadly, that quest often falls short, and the observer walks away with only a marginal view of the real problem. 

Let’s start with first principles. 

Before agreeing that there is problem, perhaps identifying what problem we’re referring to might help.  So, what is the acknowledged problem?  Most people will likely respond that there is an inadequate supply of water available to all users, during all seasons, in all years.  Fair enough.  So, what’s causing this alleged shortfall?  Here is where you will hear a wide range of reasons including, insufficient rainfall, a warming and/or drying climate, unscrupulous water usage leading to wastage, unfair allocation amongst water right holders, and overly zealous regulators among others.  All are potentially valid reasons depending on specific circumstance, and each possess some merit.  But they all ignore a fundamental shortcoming in water resources and that is the need to first establish baseline hydrology and to only make determinations after the baseline is verified.  In any water resources management framework, whether in the UK, Middle East, Southeast Asia, or California, or whether the issue is instream flow, water quality regulation or water supply, authenticating baseline hydrology must come first

All too often, however, inherent baseline hydrology is ignored.  In fact, the urge to immediately dive into an issue before the baseline hydrology is even corroborated happens all too often.  What results is that the ensuing debates, perceptions, and ultimately established policies become based on incomplete, outdated or, incorrect hydrologic information.  In many cases, the specific water yield quantity at issue is never even identified.  Whether the issue involves a new instream flow objective, water quality dilution target, or preemptive release volume in a reservoir flood rule curve, one rarely asks the fundamental question, “What’s the targeted volume of water we have to work with?” 

This is why defining water balances is so important in any water resource investigation.  Water balances quantify system accretions and depletions, a process that provides quick context to water status before any in-depth analyses are undertaken.

So, what does California’s long-term water balance, say about our water supply? 

Most people recognize that the State of California receives plenty of water every year, even if you consider the interannual variability between water-year (WY) types.  While the long-term trends are shifting due to climate change, on average, California receives about 200 million acre-feet (MAF) of precipitation annually.  An overwhelming portion of this incident water, however, California water managers never touch. 

Much of the annual precipitation is largely unavailable for use because it is either lost to evaporation (E) and terrestrial transpiration (ET), deep seepage losses to inaccessible groundwater (DS) and to direct runoff to the ocean either as unchannelized dispersed flow or uncontrolled river and streamflow.  This total quantity amounts to about 60% of the incident precipitation.  The remaining 40% is often referred to as our “managed yield”, since this is the portion that we actively manage.  

That managed yield, let’s say 80 MAF, is allocated proportionally between the three main beneficial users; urban, agricultural, and the environment (e.g., Wild & Scenic Rivers, Refuges, managed wetlands, minimum instream flows).  Depending on WY, the proportional allocation between these three user groups shift depending on natural demands and regulatory priorities.

The surprising fact for many are the quantities used by cities, relative to that used in agriculture and for environmental purposes.  In a “normal” WY, urban uses account for maybe 12% of the managed yield while agricultural use and that dedicated for the environment account for perhaps 40 and 50%, respectively.  While the exact numbers will fluctuate in any WY, the point is that in any given year, urban use, compared to agriculture and the environment is minimal.  Many Californians, and yes, legislators, still do not realize this. 

From such data, two facts emerge.  One, that the annual incident precipitation and resultant hydrology is more than adequate to meet State water demands.  And two, the allocated hydrology is strongly skewed away from consumptive uses.  The often end result is that despite ample quantities of rainfall, not enough water is left available afterwards to meet State consumptive demands later in the season.  But is this an accurate depiction of California’s water supply dilemma? 

Even a casual review of the State’s water resource status confirms that we regularly endure two hydrologic extremes: too little water and too much water, with both often occurring in the same WY.  This leads to the popular axiom:

“It is impossible to have protracted drought conditions and widespread flooding in the same region and in the same water year”

 Unless any one of three possible conditions regarding one’s infrastructure apply:

“1. they are undersized,
2. they are inappropriately operated, and/or
3. there simply isn’t enough of them”

In California, all three conditions are applicable.  Consequently, we regularly endure both water “shortages” as well as flooding. 

This finding should be no surprise given the State’s extensive flood history and ongoing flood management initiatives.  We have accepted flood risk as a water management reality.  In fact, it remains one of the most damaging and life-threatening natural disasters in California.  Since 1992, for example, every county in California has been declared a federal disaster area due to flooding at least once.

All of this leads to the question “are we wasting water, either deliberately or unknowingly?” 

It’s a tricky question to answer since much depends on how forcefully one applies the definition of “waste”.  If by deliberate action or inaction one allows water in one’s control to be lost (e.g., to the ocean, deep groundwater, or out-of-State) then, in my view, it should be considered waste.  This is not a legal determination; however, it is simply my definition based solely on hydrologic principles.

California likely views water waste differently, though I cannot conceivably think of a good reason why, since floodwater should not be treated any differently.  Water is a public trust; it has value for which beneficial use designations have been established.  Temporality should not affect its benefit to society, particularly when one is dealing with a highly abbreviated time period from which to establish that benefit.  In other words, the same floodwaters cast aside in February quickly gain value following snowmelt and over the ensuing months. The short passing of time should not in itself warrant reclassifying the beneficial use status of any water supply.     

From a pure water quantity perspective, the volume of controlled (i.e., through dam releases) or uncontrolled (i.e., through direct runoff) water that leaves the State and discharged into the Pacific Ocean, deep groundwater or out-of-State is significant.  To find out how significant, several years ago, I monitored all releases from Folsom Reservoir from December through May to track the scope of these losses using an accrual template similar to the one shown below, Table 1.

Table 1.
Folsom Reservoir Daily Operations
Source: USBR – Central Valley Operations, 2021 – Reservoir Operations Monthly Reports, Folsom Reservoir


Depletions included releases through the power penstocks, upper/lower river outlets, and over the ogee spillway via the tainter gates.  Specifically, I monitored daily encroachment into the reservoir’s flood conservation pool and verified corresponding “spills”.  Over the 6-month period, the reservoir “spilled” over 330,000 AF (i.e., equivalent to over one-third of total reservoir capacity).

All of this water went unnoticed by the public, media, and most regulatory agencies but the point was simple; to demonstrate that even in a non-flood year, a significant quantity of water was being legally released from the local region’s primary water storage facility to the Pacific Ocean.   For the 2018-2019 WY, the reservoir “spilled” over 913,000 AF, equal to about 93% of the reservoir’s total capacity. This occurred between January and May. 

What does this tell us? 

It reaffirms two critical facts.  First, that California’s hydrology is more than adequate to meet current and future consumptive demands.  Second, that flood- and stormwater represent the untapped water reserves the State needs to fully develop, if it truly feels it is water-short.

Interestingly, in the broader water resources management context, it prompts us to ask why we have chosen to pursue more expensive, technologically challenging, and regulatorily complex water supply options than turning to storm- and floodwater.  After all, flood waters are a ubiquitous, reliable, waste-free, and gravity delivered supply.  Moreover, floodwater can be acquired with largely straightforward storage and conveyance engineering.  Floodwater, for example, does not have the same pumping energy or waste disposal concerns as desalinated water.  It seems we are deliberately choosing “dirtier” water supply options (e.g., desalinated water and recycled water) requiring waste product disposal than floodwater which does not. 

If all this appears strikingly simplistic, its because it is.  So, why does it at least appear that integrating flood control and water supply has gained so little traction over the years?   

There are many reasons.  These reasons span the full gamut of socio-politics, ideology, and financial or commercial realism.  A great topic perhaps for a subsequent discussion.  For now, this note was simply intended to put into proper context any notion that the State is inherently water short.  It is not.  In fact, one of the first questions I ask when a water user seeks assistance in acquiring a new water supply is, “Do you have to deal with floods on a regular or periodic basis?” Depending on the answer to this question, the array of possible solutions can be quickly narrowed.  For California, the answer is simple, the only question is whether we have the wherewithal to capitalize on a seeming untapped bounty.  After all… 

The hydrology is on our side…. as this rainy season will once again demonstrate… 

Note: The views expressed herein are those of the author and should not be attributed to Maven’s Notebook.

About the Author

Robert Shibatani is an international expert witness on reservoir-operations, climate change hydrology, commercial flood damage litigation, and water supply development.  He is a physical hydrologist with over 35-years combined academic, legal, consulting and water advisory expertise and is the Managing Partner of The SHIBATANI GROUP International, a division of The SHIBATANI GROUP Inc. and resides between Toronto, Canada and Sacramento, California.

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