The Lower Lake Clementine Dam on the North Fork American River in Placer County in Northern California. Photo taken March 31, 2016. By John Chacon / DWR

DR. JAY LUND: Why can’t we capture all the water in wet years?

Capturing and Managing Large Storms and Wet Winters in California—Prospects and Limitations

Capturing water from wet periods for use in drier seasons or years has been central to California’s water management since the early 1900s.  Reservoirs and aquifers are routinely used for this purpose by many agencies and regions.  How much more water can be saved in wetter times for later use?  How much would this cost?  What are the potential environmental costs (and benefits) of storing additional water?  Dr. Jay Lund, Vice Director of the Center for Watershed Sciences and an engineering professor at UC Davis, dove into those questions in the presentation for Sacramento State’s Office of Water Programs webinar series.

So why California can’t catch all the water in wet winters?  In most years, we have at least one storm where we can’t catch it all.  In the aftermath of those storms, it’s a question many folks ask.

California’s water system is very complex, and there’s a lot of partial understanding of the system, even by experts.  Many things go on in the state’s water systems, between the precipitation falling and the water coming out of the tap, including collection, storage, treatment, water quality control, regulations, and governance.

“Even the most expert person on California water doesn’t know everything inside that box, so it’s a big social activity as well as highly technical activity,” said Dr. Lund.

California is a wild place hydrologically.  Last year was one of the wettest years on record, preceded by one of the driest years on record.  Precipitation in California comes in big gulps and depends upon the number and frequency of the storms that arrive.

Precipitation is also highly variable between years.  The chart below shows the annual coefficient of variation for precipitation for thousands of stations across the United States.  The Eastern US has very little variability, but there is more interannual variability as you move west.  California, particularly Southern California, has an incredibly high precipitation variation from year to year.

“In California, we have more flood years and drought years per average year than any other state in the union,” said Dr. Lund.

California water is also challenged with the spatial and temporal distribution of water.  The map on the left shows that about two-thirds of all the runoff in the state comes off about 20% of the surface area, and about 90% of the runoff in the state comes off about 40% of the state’s surface area.  The areas shown in red represent 30% of the surface area of California and produce point .1% of the runoff.

The map on the right shows the infrastructure built for storing and delivering water.  Dr. Lund noted that the map is color-coded for ownership, illustrating the mix of federal, state, local, and private ownership.

“We have deserts and some pretty wet areas,” said Dr. Lund.  “This water is available, but not where we want it because it tends to be far from the large agricultural and urban areas.  It’s not at the times that we want it as it tends to be available in the wintertime when we would like it in the summer and the spring for irrigation of our lawns and of our crops.  So we have a big mismatch in space and time for our water.  California has become a heaven for infrastructure and water engineers because we’re always trying to move water in space and time to make that natural water distribution better match what humans want.”

The graph shows the total amount of groundwater and surface water storage available in California and how much we use.  About 150 million acre-feet of groundwater storage capacity is accessible in principle, although wells might have to be deepened to get to it.  There is about 42 million acre-feet of surface storage capacity.  The green shows the seasonal storage in an average year.

“For normal average seasonal storage, we depend more on the surface water storage than the groundwater storage, although certainly, we use a lot of groundwater seasonally,” said Dr. Lund.  “But in droughts, we rely more on groundwater than surface water.  And the longer the drought, the less surface water we have for the later years of a drought, and we’ve become more reliant on groundwater over time.”

Dr. Lund pointed out that the third bar shows the total amount of storage for all of the Prop 1 water storage projects is about 4 million acre-feet of storage.  “So even if we built everything that people propose for surface water storage, it doesn’t really add all that much storage to California’s water system.”

The map on the left shows the infrastructure and where the 42 million acre-feet of surface storage is located.  The map on the right shows the groundwater basins.  “So both surface water and groundwater storage are important, but, by far, the greatest capacity for storing water and water available in storage is in groundwater basins,” said Dr. Lund.

There certainly are groundwater overdraft problems.  The plot on the lower left from the USGS shows that most of the groundwater overdraft tends to be in the Tulare Basin.  “The other basins have some overdraft problems in places and at times,” said Dr. Lund.  “But probably 90% or more of the groundwater overdraft in California is in the Tulare basin.  And about 20% of the water use is in that basin.”

Some of the groundwater basins have water quality issues.  The slide on the above right shows the nitrate contamination problems, particularly in the Tulare Basin.  “Nitrate contamination doesn’t really affect agriculture, but it does affect human consumption, and it’s projected to increase considerably over the coming decades.”

Requirements for water storage

To store water, five things are needed:

First, there has to be water available to store.

Second, there has to be a place to store the water, such as a reservoir or aquifer.

Third is conveyance to the storage location.  Water is not always available when we want it and where we want to store or use it, so water is moved from where it is to where we want it to be.  This is a challenge for California as most of the water is in the north, and most of the empty storage capacity is in the San Joaquin Valley.

Fourth is the ability to withdraw water.  You have to have the ability to get the water out of storage to use it.  This can be a problem with groundwater banks as the well capacity to withdraw water during drought can be limited.

Fifth is having the coordination and knowledge to combine all these pieces.  Typically, the water available for one location is controlled by one water right or another.  To move the water, we may need to move it through conveyance controlled by the State Water Project or Central Valley Project.  So, there needs to be coordination between the owners of the different components of the transaction, as well as the regulators of water, water rights, groundwater basins, and recharge ponds.

Lack of or high costs with any one of these items can prevent storage from occurring or limit the amount of storage available.

“It’s important to think of water storage as involving all five of these components,” said Dr. Lund.  “We often hear in our public discourse, just to focus on places of storage and storage capacity.  But I think engineers and most folks understand that if you don’t have water to put in it, and if that storage is in the wrong place, you won’t get much use out of it.”

So why can’t we catch all the water in the wintertime?

First, water is generally available infrequently and often in the wrong places.  We have plenty of water this year, but that’s not every year.

Second, new surface reservoirs, in particular, are costly, both in terms of finance and in terms of environmental impacts.  “If you’re going to build a large enough surface water storage project to capture all the flows available in winter, it has to be very large,” said Dr. Lund.  “But that means that the reservoir will not be able to deliver water in very many years.  It will be partly empty most years; it will mostly be for drought storage.  And so you will actually be able to make deliveries from that expensive capital facility fairly infrequently.”

Third, most of the empty aquifer storage is in the San Joaquin Valley, particularly the Tulare basin, which is far from where the water is.  Dr. Lund noted that the Tulare Basin is in overdraft partly because there’s not as much surface water there.  “So sometimes having available storage indicates that you don’t have enough water coming into storage, or as much as you’d like anyway.”

Fourth, moving water often requires diversions and conveyance, and when it involves the Delta, it can involve a lot of costs and be controversial on many levels.

Fifth, having infrequently used infrastructure raises water delivery costs.

“So the short answer to why we can’t catch all the water available in wet winters is physics: not much water available very frequently; economics: it costs a lot to build dedicated storage and dedicated diversions in advance for those unusual peaks when water is available; and politics because of the controversies and environmental impacts of this infrastructure and its operation.”

Economic limits of water storage

[Slide 12] The capital costs of a water storage project are paid for every year, even when the project is not delivering water.  And the economic value of having water delivered is finite.

“People like to talk about how water is our most valuable resource, but it isn’t really,” said Dr. Lund.  “Most of the time, it’s worth a few $100 an acre-foot, and this leads to one of my favorite quotes: there is rarely a shortage of water, but often a shortage of cheap water.”

The graph on the slide shows the annual cost of  $1,000 capital cost increases when the recurrence of the benefits is frequent on the left and infrequent on the right.  “If you have $1,000 in capital costs and a 5% interest rate, it’s pretty reasonable if, every few years, you get benefits from it.  But if you’re storing water for ten years, and then you get the benefits, you have to pay the capital cost for all of those ten years when no water is being delivered to get that delivery in an unusual year.”

Wind turbines illustrate a similar point.  Why are we allowing all that wind energy to go to waste?  Can we build wind turbines so that we don’t have to waste all that energy flowing across the state?  Why don’t we build so many turbines that we never feel the wind because the turbines are capturing almost all that wind energy?

“It’s just not economical to do it,” said Dr. Lund.  “The frequency and the magnitudes of winds have to be high enough and frequent enough to justify the expense of building a turbine.  It’s the same thing with capturing water as with capturing energy out of the sky.  There are ecosystem limits to our ability to capture it all. … Capturing all the water in the winter would cause quite a bit of harm to most of the ecosystems; high flows flowing out to sea are needed occasionally to clear out habitats, reset them, and disrupt invasive species and predators.”

Particularly with a warming climate, Dr. Lund said storing water for ecosystems, both for providing cold water for species and flows in dry years, will become increasingly important.  “We normally think of the environmental impacts of water storage as being negative, but there will certainly be increasing cases that we’re going to have to consider where the stored water has environmental values.  And we have several projects that are working on that.”

Increasing water capture

So, while we can’t capture all the flows, we can capture more water.  Dr. Lund suggested focusing mostly on opportunities where water is available frequently, storage capacity already exists, such as empty groundwater basins or already constructed reservoirs, and infrastructure that makes moving water in and out easy.  Look for opportunities with existing infrastructure, such as unlined irrigation canals, which can serve essentially as linear recharge basins.

Look for “multi-benefit” project opportunities that provide additional ecosystem, recreation, water supply, or flood benefits.  Water trading, improved water operations, and forecast-informed reservoir operations can get more water from the same infrastructure or with less expensive infrastructure expansions or modifications.  Cooperation among the regulators and the owners of the different pieces of infrastructure and the different water rights will be important.

Solutions for California’s water problems

Dr. Lund said that there’s no silver bullet for California’s water problems, although there are plenty of silver bullet vendors pushing their solutions, such as desalination, surface water storage, recycled water, or conservation.

“We’re moving away from that, hopefully in a big way, to looking at taking advantage of the existing system and using a portfolio approach of different supply and demand management actions to make better use of infrastructure and capital costs and provide opportunities for multi-agency and multi-sector benefits.”

The hydrology varies greatly across the state’s various regions, and every drought impacts the regions differently; some regions may be wetter in some droughts and drier in others.  So, having the flexibility to trade water and move it around can help reduce the need to construct large, expensive infrastructure and mitigate environmental impacts.

“We have to do these portfolio approaches where you’re managing supplies and demands all together in different ways,” he said.  “Even across multiple agencies, you need more data, more knowledge, better modeling, and it will require some shifting of institutional capabilities.”

In California, water problems are changing over time; the water problems the state faced 100 years ago and the water problems today have quite a bit in common, but they’re also fundamentally different.  The structure of the economy has altered water demands; agricultural water use has changed along with the economic value of supplying those demands.  Sometimes, the institutions were structured to solve water problems as they existed 50 years ago, and we need to modify the institutions and the governance of the problem so that problems can be solved or better understood.

California has an extensive network of water infrastructure that really functions as one large network that is mostly governed locally.  “It’s more than just storage and conveyance,” said Dr. Lund.  “It has water demand management, local sources, water quality issues, water treatment, pumping costs – all kinds of things that are going on.  And it really gives us a lot more opportunities to have very extensive diverse variable portfolios of activities to manage these problems as they vary over wet and dry conditions.  And it’s going to vary even more with changes in climate.”

Portfolio approaches have been quite successful, and most of the major water agencies have tried to adopt them.  But it takes extra time to organize them and for them to be successful.

The slide below lists the various activities that can be used in a portfolio approach.

There are many activities for water supply, such as different sources, storage capacities, operational strategies, conjunctive use of surface water and groundwater, and strategies for water allocation and demand management.  And because water systems often involve millions of people and hundreds of agencies, there needs to be incentives to encourage people to work well together.  These can include pricing and markets, subsidies, norming, and shaming.

The slide at the lower left shows how San Diego has diversified their water portfolio over time, reducing their dependence on the Metropolitan Water District and improving their water supply reliability.  Portfolio activities can be at the local, regional, and statewide levels.  The goal is to have an integrated mix of various activities over time so they work well across agencies, users, and individual actions.

Water demand

The slide from Josue Medellin at UC Merced shows the total number of acres of crops in California, ordered by the share of statewide employment and revenues from those crops.

“About half the acreage provides about 85 or 90% of the revenues and jobs in agriculture in the state,” said Dr. Lund.  “I’d love to see a similar plot for water use in urban areas where half the water use in most urban areas is for landscape irrigation, which has relatively few jobs and relatively little economic importance compared to flushing toilets and industrial and commercial uses.  But it gives you some confidence that if you manage the demand side properly, you can suffer some fairly sizable water shortages without causing grave damages to your economy in the agricultural and urban sectors.”

Resistance is futile …

“We’re going to see some changes in California in the future,” he said.  “It’s really based on the physics and economics of the situation.  No matter how much we want not to have this happen, it’s going to happen, so we should prepare for that.  Some things are not within our management control.”


California’s water system was designed to capture water in wetter seasons for drier years and seasons; we can do more of this, especially aquifer recharge.

“We’re still going to have major water shortages even if we capture all the economically feasible water with additional aquifer recharge and surface water storage,” he said.  “We’re still going to have water shortages given our climate.   Climate warming will make capturing water harder and a bit more valuable.  Because more of the flows will occur in the winter when we also have flood control concerns and less flows in the spring, it will give us more incentives to try to move much more of our drought storage from surface reservoirs into groundwater.”

“There are economic and environmental limits to capture all the water, even a bit more.  It’s important, and I think feasible, to capture a bit more water.  But don’t be greedy about it.  Don’t have expectations that are unrealistically high.”


QUESTION:  More funding is needed to address California’s water problems.  What are some current and potential funding solutions?

DR. LUND: “Everyone would always like to have someone else pay for the solution to the problems that they’re experiencing. But of the roughly $40 billion a year that we spend in California on water systems, 80% of that is from local revenues, and maybe about 10%, each from the state and federal sources. So, really, we have to look mostly at beneficiaries paying for water infrastructure and water storage.  That’s a good model for accountability and ensuring that money is well spent because the beneficiaries will be paying for most of it.  I think you have to look at water rates to pay for most of this.  People are always proposing water bonds, but that’s a fairly inefficient way to get things done.  I would much prefer other methods of regularly coming up with money to fund state activities.”

QUESTION: Last year, farmers complained that the California and local governments moved too slowly to take advantage of the storms.  What has been done to improve the speed of approval?

DR. LUND: “This is a very diverse state with thousands of local governments that manage water. What impresses me when I get out in the field is that this is not a new problem for most of the local governments that manage water systems.  They’re always very keen on trying to store as much water as they can.   So there will be occasions where they have regulatory problems or mis-organization locally.  But for the most part, the problems they’re facing are economic; it’s not worth building infrastructure to capture all that water where there are infrequent opportunities when it’s available.”

“There will be some hundreds of thousands of acre-feet that you can capture with a little better regulatory attention and coordination of state and local activities.  But that’s always going to be a struggle because every wet year is a little bit different.  It’s a little different time of the year and a little different place.  We’re always going to be moving water around, so that coordination part of storage for water is always going to be a challenge.”

“I know that the local folks are always scrambling and looking for opportunities to bank more water, to get the water from where it’s in excess to where we can put it underground or in a reservoir someplace.  They work very hard at that and pretty creatively.  But sometimes, it’s just a lot to do in a short period of time.  Sometimes, the state can get out ahead of it, or the regions can have some agreements on water rights, water exchanges, conveyance capacity, and operations to be better able to react more quickly.  So a lot depends very locally on just how prepared they are.  But it’s not that these people are lazy or unaware of a concept here.”

QUESTION: How does the shift of precipitation from snow to rain due to climate change affect the desirability of storage?

DR. LUND: “I think it increases the value of storage because you now have more water available in the wet season and less water available in a longer dry season; the spring becomes more of a dry season when you don’t have snowpack.  So that would give you some greater value for storing water from the wet season to the dry season.  The cheapest way to do that, in many cases, will be to move some of your drought storage from surface reservoirs into groundwater.  Because that way, you’re better utilizing existing storage capacity.”

The problem is we’ve already built many reservoirs fairly large, and to go back in and expand them gets really expensive.  Not only have things gotten more expensive in the construction field and the regulations but also the locations of many of our reservoirs already have been economically sized, so if you were to expand those reservoirs, you’d have to do special construction – expensive construction, such as saddle dams, that raise the construction costs.  The larger you build the reservoir, the harder it is to fill it up in general.”

QUESTION: Do we have the physical capacity and ability to store runoff in aquifers?

DR. LUND: “If all of our surplus water were available in the Tulare basin, we would not have a groundwater overdraft problem down there.  We would be able to use that 100 million acre-feet of empty groundwater storage to mitigate droughts.  But most of that surplus water in the wet years is available up in the Sacramento Valley.  And to get it across the Delta and down into the Tulare Basin is the real is a real challenge, both economically physically and legally regulatory perspective.”

QUESTION: Is storage in aquifers and the subsequent pumping more expensive than surface storage?

DR. LUND: “Surface storage is more expensive to construct. If you have pumped storage, you have to you have to pay to pump the water in, but then you get a little bit of hydropower back out. But for the most part, the operating capital cost of aquifers is very small, and you might have some capital costs to increase the recharge capacity,  such as recharge basins.  Then you have to pay to take the water out when you pump it out with the wells.”

QUESTION: What are the biggest challenges, maybe the top three, you think we need to be addressing in the next 20 years?

DR. LUND: with how that’s going, but it’s a long road to go.  Second, ecosystem management, and we’re really doing a terrible job.  We’re investing a moderate amount of money, but we’re not really quite highly organized or understand how effective that has been.  And it’s going to become a harder challenge with climate change.  I think the hardest one is the ecosystem.

Third is the Sacramento San Joaquin Delta; there’s a lot going on with sea level rise and changes in ecosystems and flooding of islands and all kinds of things.  It’s a mess in many dimensions.  And the fourth one is the rural water systems that have problems with safe drinking water.  There is a nitrate contamination problem in the Tulare basin and in many rural areas.  This is the problem of high groundwater drawdown during drought years, leaving households and small community well supplies stranded.  There are problems with the lack of economies of scale in those small systems in rural areas and financially keeping them viable.”

“Those are the four big problems that I see.  Everybody has problems, but for urban and most agriculture, they’re pretty well organized and pretty well funded.  They would always like to have more money, but I think ecosystems, the Delta, groundwater management, and small rural water systems are the biggest problems that the state really is struggling with.”

QUESTION: Wetter areas have more opportunities because solutions are more economical and physically possible.  What about areas with drier areas?  How can they better solve water problems if they are worse off geographically and would have to pay higher costs?

DR. LUND: “Traditionally, what the drier regions did was they tried to bring in water. I think we’re not going to see too much expansion of that strategy for the drier regions.  Certainly, on the urban side, we’re seeing declining per capita water use, which is really helping in a lot of cases.  So, we have a larger fraction of our economy using a smaller fraction of the water.  That really, really helps a lot.  With agriculture, the drier parts of the state are going to see some losses of irrigated agricultural land.   There will be a little bit of dryland farming, which is really hard to make a go of in much of the state, and some dryland grazing, which is not nearly as valuable as irrigated crops.  So the drier areas are going to have to reconcile with being dry more than they have in the past.”

QUESTION: What are the technical issues with storm prediction and modeling?

DR. LUND: Well, the fundamental one is we’re really never going to have weather predictions up more than, say, 10 or 11 days that are any good. Just the nature of the equations of fluid motion in the atmosphere is highly subjected to chaos after about 7 to 10 days. So today, we have pretty good forecasts, maybe three to five days out, sometimes seven days out, to sort of see really big events coming.  Maybe even a little bit longer than that, but there are just limits to how far ahead we’re going to be able to forecast.  And it’d be nice if we could forecast once a month out, but months and months out, or forecasts might get a little better than they are today.  But then they’re not going to be substantially better, I think, for operational purposes, most operational purposes than what we’ve got.

QUESTION: For a fuller picture, shouldn’t the chart from Josue Medellin add in economic value of much higher value dairy and livestock aspects for which feed crops are just inputs?

“That’s a reasonable a reasonable concern.  Even with that,  those very feed crop things are like $9 billion of the $50 billion agricultural economy, so it’s pretty sizable.  50% of what I had there was field crops.  But I don’t think that 50% is what feeds the dairies and and the beef industry so much.  So, if you want to make that correction, go right ahead.  But you still have a sizable amount of lower value field crops out there.”

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