Monthly Archives: February 2017

SoCal Rain Update: Keep it Coming

After 5 long years of drought, a series of powerful storms in January and February 2017 finally brought heavy rain and snow to California. Let’s take another look at where we stand in Los Angeles, and at water supplies around the state. As always, remember that in California we measure precipitation from October through the following September; this period is called the water year.

Currently, downtown LA is at 18.50” of rain for the water year. This is about 3.5” greater than the yearly average, and well past any of the drought years.


February 2017 finally brought a storm that put the Central Coast in the bullseye, and the effect on Lake Cachuma, the largest reservoir for Santa Barbara County, was incredible. So far this winter, Lake Cachuma is up from 7% full to 42% full, and on one day in February gained nearly 30,000 acre-feet of storage. (One acre-foot is enough water to cover an acre of land with one foot of water, about what two average households in CA use in a year).


Precipitation indexes for the Sierra Nevada show it’s been a very wet year throughout the range. The north Sierra, corresponding to the Sacramento River drainage, has had 76.3”, already well above the water year average of 50.0”, and with all-time records within reach.


The central Sierra, corresponding to the San Joaquin River drainage, is also already well above the water year average, with 60.4” to 40.8”. It too is on pace to chase some of the wettest years on record.


The south Sierra, corresponding to the Tulare Basin (Kings, Kaweah, Tule, & Kern Rivers), is now well above the water year average, with 40.9” to 29.3”.


Let’s look over to the other side of California, the east Sierra, corresponding to the Owens Valley. Snow water content has not only already doubled the April 1 average (50.4” to about 24”), it’s already tied the wettest year on record. This is where the water in the LA Aqueduct comes from, so it’s good news for city water supplies, as we’ll have to buy less water from the State Water Project and Colorado River Aqueduct.


The juxtaposition of such a wet year following the worst drought in the state’s history has highlighted that California, especially southern California, is the land of extremes. Annual precipitation in SoCal is almost comically variable, with the wettest year having over 10 times as much rain as the driest year.


Variability is expressed using coefficient of variation (standard deviation divided by mean). LA’s coefficient of variation is 0.48.

To demystify the variability of SoCal rainfall, I thought it might be interesting to do a comparison between Los Angeles and Portland, widely considered to be a pretty rainy place. Here’s the average rainfall for each city by month.


Portland gets about 36” of rain every year to LA’s 15”, though surprisingly enough LA is, on average, wetter than Portland in the month of February. However, when we look at daily rainfall records, a striking pattern emerges.


The all-time daily record rainfall in Portland is 2.69”; in LA it’s over twice that much at 5.88”. It’s never rained 3” or more in one day in Portland; there are 31 daily rainfall records greater than 3” in LA. The 4” mark has been hit ten times and 5” three times. LA’s daily rainfall record is greater than Portland’s for 165 days out of the year, despite Portland getting nearly 2.5 times the annual rainfall and being wetter in nearly every month, and LA being so reliably dry in summer that 19 days have never seen measurable rainfall and the last 140 Julys having delivered a grand total of 1.55” of rain.

The last 6 years are a reminder that for SoCal the faucet can turn on just as quickly as it turns off – and vice versa. The forecast for the next week or so is dry and in fact once, water year 1996-97, LA had no measurable rain between March 1 and the end of the water year. So now that I’ve sufficiently jinxed things, you’d better hope extra hard for some more drought relief this year!


S is for Snake

Long-time riders will not be surprised that this blog has a dim view of Measure S, the NIMBY land use initiative on the March 7th ballot. Measure S would put a minimum two-year moratorium on any new housing that requires a zone change or general plan amendment – in the case of the latter, even for projects that are 100% affordable. The reasons Measure S is bad have been well explained, so I won’t revisit them here.

However, the level of deception being used by the Yes On S campaign is atrocious. That mendacity deserves to be remembered on its own. And anybody who still finds themselves unsure how to vote on S should ask: why do the proponents of S feel the need to lie so profusely?

Set aside the fact that the vast majority of funding for Measure S – well over $4 million – comes from an AIDS non-profit organization. There is a clear pattern in the Yes on S campaign of lying about the intent of the initiative and lying about support for it.

It started innocuously enough, with the Yes on S campaign crowing about an endorsement from Leonardo DiCaprio. Eventually it was revealed that DiCaprio never endorsed S and the campaign walked back its claim, blaming it on a communications snafu.

However, about a week ago, many residents of Los Angeles found this flyer in their mail. It doesn’t come right out and say the mayor endorses S, but it sure implies that. Garcetti is strongly opposed to S. Oh, and the quote was not actually something Garcetti said. It was something they wrote, in a letter to him. NBD though, right?


Apparently uncertain of their ability to pass Measure S on NIMBY power alone, the backers have also stooped to trying to capitalize on well-placed concerns about housing in low-income neighborhoods, where many people are rightfully worried about eviction and displacement.


This is, to put it mildly, not true. Measure S will not encourage new construction of affordable housing, because Measure S does not contain any mechanism to do so. Measure S will not protect rent-stabilized housing, because Measure S says literally nothing about rent-stabilized housing. In fact, Measure S will probably destroy rent-stabilized housing, because Measure S is perfectly happy to allow rent-stabilized housing to be destroyed by projects that comply with the zoning.


Now we are entering rarefied space. Measure S does nothing at all about evictions. You know how many times eviction is mentioned in the text of Measure S? Zero.


Hard to top the chutzpah of the eviction flyer, but they managed to do it. Measure S doesn’t do anything for rent-stabilized housing or affordable housing, let alone housing the homeless. The sheer audacity of claiming that a moratorium on zoning changes and general plan amendments would somehow lead to helping get 1,200 veterans off the streets… I think I’m gonna be sick.

The campaign materials produced by Measure S do not present the true intent of the initiative at all and in many cases are outright lies… or, dare we say it, alternative facts? If someone is going to such lengths to hide their true intentions, you can be sure they don’t have your best interests at heart. If you truly care about affordable housing, rent-stabilized housing, or helping the homeless, you should be very wary of alliances with self-funding egomaniacs. They’ll betray your trust as soon as they don’t need you anymore.

Oroville, Again

A lot has happened at Lake Oroville in the three days since I posted an introduction to the State Water Project (SWP), to put it mildly.

At the time of that writing, Saturday afternoon, the lake level was at 902.02’, with water flowing over the emergency spillway sill at 901’, and releases from the damaged controlled spillway at 55,000 cubic feet per second (cfs). The lake level peaked at 902.59’ at 3am Sunday morning and then began to slowly decline. At 11am Sunday, the California Department of Water Resources (DWR) reported that flow over the emergency spillway had peaked at 12,600 cfs and since declined to 8,000 cfs, with the situation stabilized. At 4:40pm Sunday, an emergency evacuation was ordered, with the emergency spillway predicted to fail in as soon as an hour.

This photo from February 11 shows the emergency spillway not long after water began to flow over it. Note the roadway in front of the spillway. Very little erosion has occurred in this photo, though some channelization is visible bottom center.

This photo from February 12 shows the emergency spillway with erosion having progressed further uphill. Note the road has been washed out, and the channel has deepened and worked its way uphill.

Faced with this situation, DWR increased the releases from the controlled spillway, to try to save the emergency spillway. Releases were increased to 100,000 cfs, and after a few very tense hours, the lake level dropped below 901’ at about 8pm Sunday. Water stopped flowing over the emergency spillway, and the erosion stopped.

This photo from February 13 shows the damage to the emergency spillway. Note the people for scale. I do not know which channel was of the most concern but the large channel near the washed out road and white truck was not the closest to the emergency spillway sill. Top right, just left of the far end of the concrete spillway, are two workers in yellow vests standing by the channel that got closest. This photo shows a closer view, with that channel just behind the workers.

It’s obviously a huge relief that the lake level is below the emergency spillway and that the structure survived. It’s also a huge relief that the damaged controlled spillway has been able to maintain 100,000 cfs releases, which as of this writing (9pm February 14, 2017) have lowered the lake level to 883.60’, over 17’ below the surface of the emergency spillway sill.


This has allowed DWR to being making emergency repairs to the emergency spillway, in case it must be used again. This photo shows placement of rock in the channel that got closest to the emergency spillway sill. DWR also posted two videos, one from yesterday and one from today, showing the repair work. Emergency evacuation orders have been lifted, but residents are to remain vigilant under an evacuation warning, in case the situation changes.

It is very good news indeed that the emergency spillway survived. However, it is only mid-February and we still have a lot of winter to go, followed by spring runoff when an above-average snowpack melts. In another stroke of good fortune, the National Weather Service (NWS) Sacrament office is predicting the next storm, for Wednesday night and Thursday, to have lower snow levels (5000’-6000’) than originally expected (7000’-8000’). This will keep the precipitation as snow, rather than rain and melted snow that will immediately run down into Lake Oroville. This will allow DWR to keep lowering the lake level to create flood storage for the spring, and keep making repairs on the emergency spillway. Another series of storms is expected for Monday and Tuesday next week, but with snow levels between 3500’-5500’.

After the snow is gone, there are going to be a lot of questions to be answered. I’m not going to litigate the decisions made by DWR here; I’m sure there will be plenty of people to do that soon enough. I also want to say that I have great respect for the many DWR engineers and workers, the Butte County Sheriff, and many other public employees and safety officials that have worked hard to ensure public safety, and have had to make many extremely difficult decisions about how to proceed in a dangerous and dynamic situation.

As a civil engineer, things like this really hurt. Like many civil engineers, I went into this business because I believe it is a profession where I can put my natural skills to work in a way that improves people’s lives. I never want to see our works fail or put people at risk.

This is going to be a case study for future civil engineers, for that is what we must always do when something doesn’t work the way it should: ask ourselves why, figure out what went wrong, learn from it, and improve our designs and processes so that we increase public safety and public benefits in the future. I think there will be four main questions to be researched here:

  • What was the proximate cause of the damage to the controlled spillway?
  • Why was the emergency spillway damaged so critically by relatively modest flows (12,600 cfs) relative to its capacity (several hundred thousand cfs)?
  • What was the decision making process after the initial damage to the controlled spillway? Was all relevant information available to decision makers?
  • Was information available before the crisis that should have led to corrective actions, and if so, what stopped corrective actions from being taken?

In short there are several distinct things here: pre-crisis actions, controlled spillway damage, emergency spillway damage, and crisis management.

Again, none of this is to question the hard-working people who are doing everything they can to mitigate the crisis and have faced very difficult decisions. As engineers, we must seek to improve our understanding of our designs, how the natural world interacts with our designs, and how our decisions and processes affect those systems. My heart goes out to anyone affected by this situation, and I sincerely hope that we, as Californians, can pull through this and use the lessons to help make our state a better place.

The State Water Project: An Introduction

If you follow this blog’s twitter account, you know that engineering & water twitter has been closely watching the situation at the Oroville Dam in northern California. Many people know, conceptually, that much of the water we use in SoCal comes from northern California, but are not familiar with Oroville or the State Water Project. So, here’s a brief introduction to what the State Water Project (SWP) is, what it does, and what’s happening at Oroville now.

The SWP is an important source of water for SoCal, and Lake Oroville is the main reservoir. While popular conception hold that LA’s water comes from the east Sierra and Owens Valley via the LA Aqueduct, over the last 5 years, that facility has only delivered 29% of LA’s water. The SWP is the largest supplier of water to the city of LA, with 48% of LA’s water over the last 5 years coming from the SWP. So what happens at Lake Oroville is of interest to, well, anyone south of Lake Oroville.

The State Water Project: California Dreaming… Big

Everyone knows the split nature of California’s climate: the north is wetter, the south is drier. However, many people and much of the best farmland are in southern California. Over half of the state’s population lives in relatively dry climates south of the Transverse Ranges, which separate the southern quarter of the state from the rest. In addition, California experiences wide swings in annual rainfall, with droughts and floods often following on each other’s heels. In fact, 2014-15 was the driest water year in state history, but 2016-17 may prove to be the wettest.

This situation naturally led to the desire for civil engineering improvements to both prevent devastation from flooding in wet years and store water for human use during drought years. The SWP was conceived to help meet these goals. The map below shows the main components of the SWP.


The major components of the SWP are:

  • Oroville Dam: this dam is located on the Feather River, which drains a portion of the northern Sierra Nevada, and is the source of water for the SWP. Lake Oroville can store up to 3.5 million acre-feet of water, making it the second largest reservoir in the state after Lake Shasta. One acre-foot of water is enough water to cover an acre of land one foot deep – about 325,000 gallons.
  • California Aqueduct: this aqueduct conveys water from the delta to users in central and southern California. Water released from Lake Oroville flows down the Feather River and Sacramento River to the delta. From there it is pumped south out of the Clifton Court Forebay.
  • San Luis Reservoir: this is a large off-line reservoir in the southern Central Valley that can store 2 million acre-feet of water. “Off-line reservoir” means that it is not located on a major river – it was created by damming an existing valley and filled with water from the California Aqueduct. The creek that formed the valley, San Luis Creek, would never carry enough water to fill the reservoir on its own.
  • Distributary aqueducts: these aqueducts carry water from the main California Aqueduct to water uses. These are:
    • North Bay Aqueduct and South Bay Aqueduct, which serve the East Bay area.
    • Coastal Branch, which serves San Luis Obispo and Santa Barbara Counties, including a connection to Lake Cachuma, Santa Barbara’s main water supply.
    • West Branch, which serves the Los Angeles area and includes Castaic Lake and Pyramid Lake, the lakes you see from the 5 when you drive through the Grapevine.
    • East Branch, which serves the Inland Empire and includes Silverwood Lake and Lake Perris.
    • Second San Diego Aqueduct, which connects Lake Perris to San Diego County.

Because of the complicated geography and politics of water in California, the SWP includes some water agencies that don’t even have a physical connection to the project. For example, the Desert Water Agency (DWA) and Coachella Water Valley District (CVWD) serve Palm Springs and the Coachella Valley, which have no connection to the SWP. The DWA and CVWD buy SWP water and then swap it with the Metropolitan Water District of Southern California (MWD SoCal) for water from the Colorado River. So DWA and CVWD pay for SWP water, which is delivered to MWD SoCal, and in exchange, MWD SoCal gives DWA and CVWD water from the Colorado River Aqueduct.

Construction on the SWP started in the early 1960s and the major components were done by the late 1970s, though construction on various pieces such as the East Branch Extension continues up to the present day. The SWP is just one legacy of the leadership of Governor Pat Brown, who for his investments in water infrastructure, freeways, and education ought to be known as the father of modern California.

Ok, So What’s Going on at Oroville?

Lake Oroville is a dual-use reservoir – it is used both to store water for human use and to capture water from torrential rainstorms and snowmelt to prevent devastating flooding downstream. Every such reservoir has its storage divided into conservation storage and flood control storage. Under normal conditions during the rainy season, the reservoir is not allowed to fill up beyond the conservation storage level, so that if a big rainstorm or snowmelt event happens, there will be enough capacity to prevent flooding. Reaching the top of conservation storage is like the gas light coming on in your car: it means you need to start looking for a gas station, because you don’t want to run out of gas before you start looking.

Early this week, a large winter storm hit northern California. The storm was warm, meaning that it had high snow levels (the elevation in the mountains where the storm changes from rain to snow), so much of the precipitation went into the rivers right away instead of adding to the snowpack in the mountains. The warm temperatures and rain also caused some of the existing snowpack at low elevations to melt and flow into the rivers.

On Tuesday, Lake Oroville was near the top of conservation storage, and with a large amount of water on its way to enter the lake, state water managers increased water flow through the controlled spillway on the Oroville Dam. A controlled spillway is a structure on a dam that has gates that can be opened and closed by motors, allowing the agency in charge to control how much water leaves the reservoir. The Oroville controlled spillway had a theoretical maximum capacity of 250,000 cubic feet per second.

However, as flows ramped up, a sinkhole appeared in the lower portion of the spillway, and water releases had to be stopped to allow inspection. After assessing options, it was determined that because of the large volume of water entering the lake, it was necessary to continue to allow water to flow through the damaged spillway to keep the lake from rising too quickly. Water flowing through the spillway has caused additional erosion, although yesterday and today the discharge appears less muddy. Hopefully, this is an indication that the channel has cut down to bedrock, and erosion has slowed down.

As water flows downhill, erosion will tend to cut back uphill. This is why Niagara Falls is at the head end of a long gorge; the falls have cut the gorge back upstream from the Niagara Escarpment since the end of the last ice age. It is critical that erosion on the controlled spillway at Oroville not be allowed to proceed uphill and damage the spillway gates, which would negatively impact the ability to control releases down the spillway. That is why the damaged spillway is only being allowed to operate at a reduced capacity.

Because inflow is currently greater than outflow, the lake level is rising. However, this is NOT a threat to the Oroville Dam itself, because there is an emergency spillway that the water will flow over first. The dam crest elevation is at 922’, while the emergency spillway sill is at 901’. The emergency spillway is an uncontrolled weir, so once the lake reaches elevation 901’ water starts to flow down the emergency spillway. This happened at about 8am this morning and as of 3pm February 11, 2017, the lake elevation is at 902.02’, so water continues to flow over the emergency spillway. In a noon press conference, the state announced that it expects this flow to continue for 36-56 hours.

The emergency spillway is an unlined, unimproved channel, which means water that flows over down it is just flowing over dirt, vegetation, and rocks. This means some erosion will occur and enter the Feather River downstream.

What’s Next?

Because it’s only mid-February, winter is only part way over, and more rain and snow storms may be on the way. The state will face challenges with water coming into the lake over the next few months as additional storms hit, and then as spring and summer temperatures melt the snowpack. At the moment, it does not appear there will be enough time to much in the way of repairs before more rain and snow arrive. Resource managers will face difficult decisions between increasing flow on the damaged spillway and allowing additional flows over the emergency spillway.

It’s important to emphasize that as of this writing (3pm February 11, 2017), there is no threat to the Oroville Dam itself, no flooding occurring downstream, and no imminent public danger. Everyone should pay attention to information from the California Department of Water Resources, the Butte County Sheriff, and the California Office of Emergency Services for updates on changing conditions.

After the rainy season and spring snowmelt is over, the state will face a busy summer construction season at Oroville, including repairs to erosion and/or improvements to the emergency spillway, and repairs to the existing damaged controlled spillway or replacement with a new controlled spillway.

Is the SWP the Same Thing as the Central Valley Project?

No, though they are related. The SWP is operated by the state of California, while the Central Valley Project (CVP) is operated by the federal Bureau of Reclamation. The main CVP components are:

  • Shasta, Trinity, and Whiskeytown Lakes in northern California, which store water for use in the Central Valley.
  • Tehama-Colusa Canal, which distributes water for use in the northern Central Valley.
  • Friant Dam and Millerton Lake on the San Joaquin River, and the Friant-Kern Canal, which distribute water from the San Joaquin River for use in the southeastern Central Valley.
  • Delta-Mendota Canal, which distributes water from the delta for use the San Joaquin River drainage basin below Friant Dam.
  • San Luis Canal, which is shared with the SWP, and distributes water for use in the southwestern Central Valley.


In addition, there are interconnections between the SWP and the CVP such that if the south Sierra has a very wet year, water from the Tulare Basin rivers (Kings, Kaweah, Tulare, and Kern Rivers) can be sent to the SWP.

What Are All Those Grey Squares on the SWP Map?

Curious readers may have noticed several reservoirs and other facilities on the SWP map shown in grey. These are facilities that were proposed as part of the SWP but never constructed.

The undeveloped facilities in northwestern California are of the greatest consequence. The project as originally proposed included dams on the Klamath River and Eel River, which would have created the Ah Pah Reservoir and the Dos Rios Reservoir. At 15 million acre-feet and 7.5 million acre-feet, respectively, each of these reservoirs on their own would have dwarfed Lake Shasta and Lake Oroville. These facilities would have been located in the wettest part of California. An additional reservoir, the Glenn Reservoir, would have been located east of the coastal mountains, with water directed there via tunnel from Dos Rios.


Since the Klamath and Eel Rivers are not currently connected to the SWP, these dams would have greatly increased the water available to the SWP. However, they would have destroyed some of California’s last free-flowing river segments, and would have had enormously negative consequences for fish and other wildlife. The large environmental impacts resulted in these projects being canceled, and they are unlikely to ever be revived.

The other two unbuilt large reservoirs are the Sites Reservoir and Los Banos Grandes Reservoir. The Sites Reservoir would be able to store between 1.2 million and 1.8 million acre-feet, with Los Banos Grandes adding another 1.7 million acre-feet. Together, they would equal another Lake Oroville of off-line reservoir storage, increasing SWP storage by over 50%. Since they would be off-line reservoirs, not located on main rivers, the impact of these facilities might be less.

The last major unbuilt piece of the SWP is the Delta Peripheral Canal, or as we know it today, the Delta Peripheral Tunnel. The purpose of this facility would be to channel water from the Sacramento River (released from Lake Oroville, Lake Shasta, or the Sites Reservoir) around the delta to the pumping facilities that send the water south via the California Aqueduct. This would reduce the environmental impact on the delta and increase the reliability of SWP water deliveries.

With climate change possibly making droughts and floods more likely, and causing precipitation to fall as rain instead of snow, there may be renewed interest in the Sites Reservoir, Delta Peripheral Tunnel, and maybe even Los Banos Grande Reservoir.

Sustainability as Penance

An article in City Lab on a vegetable shortage in the UK reminds me of an old idea that I never really seemed to be able to articulate, so I figured I’d finally give it a shot.

There’s a weird vibe about arguments on sustainability sometimes, where it feels like it’s more about impugning the morality of the behavior in question rather than about some technical definition of sustainability. This dubious definition of sustainability has a habit of popping up when people have a preconceived negative opinion of the user in question (LA is bad and unsustainable for importing Owens Valley & State Water Project water!) but not when they don’t (when was the last time you heard about the water shortage on the Delaware River?).

Food is perhaps the most frequent victim. In the article above, it is suggested that poor harvests in Spain due to bad weather are revealing an “unsustainable” food supply system in the UK. It is noted that 50 percent of the UK’s vegetables and 90 percent of its fruit are imported. Further, it is suggested that perhaps UK residents should just eat in-season locally available vegetables like winter roots and leeks, cabbage, Brussels sprouts, and kale (three of which are cultivars of the same plant).

First, let us note that sustainability here has been arbitrarily defined: produce from Spain, not sustainable; produce from the UK, sustainable. Sustainability should be defined by some assessment of our ability to keep producing things without destroying the productive capacity of the system; instead it is defined by arbitrary borders. Why are Spain and the UK the units of analysis rather than something larger (the EU, for example) or something smaller (the constituent countries of the UK, parliament districts, etc)? Why not go full rugged individualist, and say that any produce you consume that you didn’t grow on your own land isn’t sustainable?

Second, there’s a tone of judgment – why do you silly people demand zucchinis and eggplants, instead of just being satisfied with cabbages? Well, aside from this having nothing to do with sustainability, why shouldn’t people in the UK get to enjoy a variety of vegetable and fruit? Most produce in the US is grown in California, because of places with very favorable climates like the Salinas Valley, Central Valley, and Imperial Valley, and available resources for irrigation. Why shouldn’t people in other states get to enjoy that productivity?

Third, it’s quite possible that moving to a system where people are only allowed to consume locally produced food would have a larger environmental impact. Transportation costs and carbon emissions are a small portion of the total costs and carbon emissions of making food. Increasing agriculture on marginally productive land just because it’s close to population centers might increase impacts because a larger amount of land would have to be put into production.

Finally, the unsound footings of this definition of sustainability are laid bare if we try to apply the concept to something other than food. For example, much of the world’s iron comes from mines in remote desert portions of Australia. It would be crazy to argue that all the steel in California should have to come from in-state iron mines, which would be more destructive. It would also be crazy to argue that iron miners in the Pilbara should only get to eat whatever food can be grown in the Australian desert.

Some places, like California and parts of Spain, are good at growing lots of food. Other places, like the UK, are good at other things. There’s nothing wrong with this; letting people do what they’re good at is a good thing. It doesn’t help people in the UK to deprive them of a greater variety of food, and it doesn’t help Murcia to deprive it of a place to sell the food it can grow. This is literally the entire point of trade.

SoCal Rain Update: One Step Forward

After 5 long years of drought, a series of powerful storms in January 2017 finally brought heavy rain and snow to California. The short-term impacts of the floods and mudslides have been well covered in the news, but many SoCal residents are wondering if the storms have made a major impact on the drought. Let’s take a look at where we stand in Los Angeles, and at water supplies around the state. As always, remember that in California we measure precipitation from October through the following September; this period is called the water year.

Currently, downtown LA is at 14.33” of rain for the water year. This is just 0.60” short of the yearly average, and already well past any of the drought years. In fact January 2017 alone brought more rain to LA than 3 of the 5 drought years, including last year’s completely ineffectual El Niño.


The six-year total for 2011-12 through 2016-17 is currently at 53.12”, which is 0.13” less than the record driest six-year period of 1958-59 through 1963-64. Over the last 10 years, we have a rainfall deficit of about 37”. So while this year has been good so far, to start making up lost precipitation from the drought, we still need the storms to keep rolling through over the next few months. Looking a little more broadly at SoCal, we can see that much of the region has fared better than LA.

Looking at major reservoirs in the state, almost all are doing very well. It already seems likely that the state will go into the summer with water storage facilities nearly full, and there’s still a lot of winter to come. Remember this the next time someone tells you there’s no reason to create more storage!


Taking a closer look at some southern California reservoirs of interest, Lake Cachuma, the largest reservoir for Santa Barbara County, was down to 7% of capacity last fall. This put cities in the area on severe water restrictions and prompted the city of Santa Barbara to reactivate its desalination plant. While this year has certainly replenished Lake Cachuma more than any of the drought years, it doesn’t seem like enough to ease restrictions yet.


Over in the southern Sierra Nevada, Lake Isabella has finally received some much needed rain as well. This reservoir, on the Kern River above Bakersfield, is the largest in the Tulare Basin other than Pine Flat on the Kings River. Capacity is 568,000 acre-feet, so it’s nowhere near full, though storage is currently kept below maximum due to ongoing seismic improvements to the dam.


Looking at departure from normal precipitation to date for the water year across SoCal, we can see there’s been some drought relief in the south Sierra, the Coast Ranges, and the SoCal mountains.


Precipitation indexes for the Sierra Nevada show it’s been a very wet year throughout the range. The north Sierra, corresponding to the Sacramento River drainage, has had 53.2”, already past the water year average of 50.0”, and on record pace (though the breakneck pace of January precipitation would be hard to match).


The central Sierra, corresponding to the San Joaquin River drainage, is also already past the water year average, with 42.9” to 40.8”. It too is on pace to match some of the wettest years on record.


The south Sierra, corresponding to the Tulare Basin (Kings, Kaweah, Tule, & Kern Rivers), is just past the water year average, with 30.2” to 29.3”. It’s been a very wet year for the south Sierra, though it might be hard to keep up with 1968-69.


Looking over to the other side of California, the east Sierra, corresponding to the Owens Valley, snow water content has already passed April 1 averages, with 34.7” to about 24”. This is where the water in the LA Aqueduct comes from, so it’s good news for city water supplies, as we’ll have to buy less water from the State Water Project and Colorado River Aqueduct.


Peering into the next 7 days, the forecast calls for another round of solid storms for northern and central California.


Totals for the far south Sierra and SoCal look relatively modest for the next week… let’s hope that, like in January, this powerful NorCal storm is a prelude to strong rainstorms for us!

Editorial: all of the data used for this post came from public sources (National Weather Service, CA Dept of Water Resources, LA Dept of Water & Power). A lot of useful data is created and made available free to the public by government agencies that are going to have their budgets under attack in the coming years. So, you know… call your reps to protest when that happens!