Groundwater at the Delta Stewardship Council, part 1: Subsidence in the Central Valley and an update on CASGEM

DSC Groundwater panel 1Groundwater is taking a much-needed leading role in water policy these days, with the drought and several state-led efforts, such as the State Water Board’s groundwater workplan and the California Water Action Plan, that are focused on improving the management and monitoring of groundwater.  More recently, there has been an effort from the Governor’s office to convene a group of stakeholders to provide policy recommendations on groundwater management reform.

At the February 27 meeting of the Delta Stewardship Council, Delta Plan Manager Cindy Messer spoke of the reasons that the Council and the Delta Plan are addressing the state’s groundwater resources.  “Groundwater is a significant portion of the state’s water portfolio, and as stated in the Delta Plan, it makes up about 20% of both the agricultural and urban water supply for the state,” she said.  “There is a direct relationship between the health of the Delta and groundwater management, especially in the Central Valley.  If the Delta is in a healthy state, if water supplies are ample, then there is the ability to replenish groundwater aquifers and, in some cases, reduce the reliance of groundwater for water supply.  But when we find ourselves in a scenario as we’re in now in terms of the Delta’s health and decline, and when water supplies and exports are reduced out of the Delta, we find that the reliance on groundwater increases, and in some cases, speeds up some of the impacts, such as groundwater overdraft.”

Click here for more from the Delta Stewardship Council.

Our Delta Plan had an extensive discussion on groundwater management and sustainable groundwater, and we had four recommendations that dealt with that,” said Kevan Samsam, Supervising Engineer.  The four recommendations are:

  1. Update Bulletin 118:   The first recommendation is to update statewide groundwater plan, otherwise known as Bulletin 118, which hasn’t been updated since 2003.  “The reason that we put that in there was because knowledge of the groundwater situation is paramount,” he said, noting that the deadline in the Delta Plan is at the end of the year, and this date was chosen as the following year is the deadline for urban water management plans and agricultural management plans, and the information contained in Bulletin 118 would be useful knowledge to have as they prepare those plans.
  2. Groundwater management plans:  The second recommendation states that areas that get water from the State Water Project should implement groundwater management plans, he said.  “If we are exporting water from the Delta, the idea was to help supplement local groundwater sources, so it’s paramount that those people be an example of good groundwater stewards and not look at the SWP or the CVP as a additional source while at the same time deplete their limited groundwater resources.”
  3. Address critically overdrafted groundwater basins:  The third recommendation that says that we should recover and manage critically overdrafted groundwater basins, he said.  “It is paramount that we should be able to identify which basins are in danger, which ones are critical – I don’t believe that information is widely known, and those basins should be the priority for state and local efforts to adjust the problem.”
  4. Protect groundwater beneficial uses: The last recommendation from the Delta Plan is to protect beneficial uses of groundwater, something that is under the purview of the State Water Board, he said, noting that they currently are working on a groundwater workplan.

The California Water Action Plan also identified five priorities and actions that they would take similar to the Delta Plan, with completion of Bulletin 118 and CASGEM being a priority for them, said Mr. Samsam.  “The Governor’s office is going to work with the legislature to identify some policy recommendations to empower the locals but also to give power to the state to come in and help with sustainable groundwater management,” noting that the water action plan also addresses groundwater storage and recharge.

He then introduced the panel, which is comprised of Michelle Sneed, a hydrologist from USGS and the author of 2013 report on subsidence in Central Valley; Mary Scruggs, a supervising geologist with DWR and program manager for Bulletin 118 & CASGEM; Eric Oppenheimer, Director at the State Water Resources Control Board in charge of the Board’s strategic plan for groundwater; Walter Ward from Stanislaus County who heads a committee to deal with groundwater; and Andrew Fahlund from the California Water Foundation.

This panel will be covered in two parts:  Part 1 will cover Michelle Sneed and Mary Scruggs presentations; part 2 will cover Erick Oppenheimer, Walter Ward, and Andrew Fahlund’s presentations.

Michelle Sneed, hydrologist with the USGS and author of the report, Land Subsidence along the Delta-Mendota Canal in the Northern Part of the San Joaquin Valley, 2003-2010

Michelle Sneed began by saying that when she was first before the Delta Stewardship Council, they were just starting the project to study land subsidence using space-borne radar.  It was challenging in the Central Valley because of the land disturbances that go along with agricultural land practices, but the study was completed, she said.  This is the first part, which focuses on the Delta Mendota Canal; they are currently working on the second part, which is focused more on the California Aqueduct to the south of the study area, she said.

We were surprised to find about 1200 square miles of land affected by subsidence over a 2 year period,” she said.  “The rates of subsidence ranged anywhere from about ½” a year along the Delta Mendota Canal, but northeast of that canal, we found an area that subsiding about one foot a year since 2008, and we know from Reclamation and DWR surveys that those rates have continued through 2013.  So we know that at least 5 feet have happened since 2008.”

This is adversely affecting infrastructure, she said.  “The Delta Mendota Canal unfortunately is on the edge of this subsidence bowl, but in the middle of it are the East Side Bypass, which is a critical flood control channel, and also the San Joaquin River, and it happens to be where the San Joaquin River restoration work is going on.  It’s also affecting parts of the California Aqueduct and many other local canals.  Canals snake through this area.  This subsidence is permanent, and the subsidence occurred when groundwater levels declined and they declined to historically low levels meaning they are lower now than they ever have been since we started keeping records.”

The area of maximum subsidence is about 25 miles northeast of where it was historically, so they did not expect to find subsidence where they did.  “That was a big surprise – where it was located, how big was, and how fast it was subsiding – all of those were unexpected results from this study.”

Subsidence is important because it damages any infrastructure that crosses these areas, said Ms. Sneed.  “It’s not all subsiding the same; it’s subsiding differentially,” she said.  “The most sensitive infrastructure are canals because they are built on tiny little gradients, so they are built with very specific elevations.  The whole canal works together, meaning every point upstream has to be higher in elevation than every point downstream, and if you start messing one of those up in the middle, then you have to adjust the entire system to compensate for that.”

“If you don’t, you get lost conveyance capacity, and lost freeboard, which is the distance between the water surface and anything that crosses it like a bridge, for instance.  The panel and the water surface misalign, meaning sometimes the water will go over the top of the panel, start eroding behind the panel, and that’s bad for levees,” she said.

Sneed slides_Page_03It’s not just canals, but roads, railways, pipelines, and anything that crosses these areas, she said.  “We see the alignment for High Speed Rail is in horrible locations for subsidence at this time,” she said.  “The last time I saw them, they were going right through this area of about a foot a year.”

Subsidence also damages natural resources, she said.  The most common impact described is loss of storage capacity, she said, explaining that once an aquifer compacts permanently, it can’t store as much water as it used to.  She referred to the diagram on the slide, and said “Clay is big player in subsidence; it’s laid down in random orientations, and it’s a platy mineral – it’s like a pancake, and there’s lots of space between the pancakes, but when you lower groundwater levels to historically low levels, these units actually rearrange themselves and these pancakes become more like stacks of pancakes and you can fit a whole lot less water in between the pancakes, and they’ll never go back to random orientation.”

Subsidence can cause rivers to change course, pools to form in places they didn’t before, or new wetland areas to form, she noted.

Historically, there’s been a lot of subsidence south of the Delta Mendota Canal where the California Aqueduct is now, said Ms. Sneed.  “The subsidence was actually discovered because the Delta Mendota Canal started transmitting water in the early 50s, and almost immediately they discovered problems with the canal, and it was because of those findings that they said, keep the California Aqueduct closer to the Coast Ranges.  Where it comes out into the valley, we have problems.”

Sneed slides_Page_04When the California Aqueduct was completed and started transmitting water in the early 70s, then not as much groundwater pumping was necessary because farmers could get water out of the canal,” she said.  “Water levels came up and subsidence was essentially arrested.  It was only during droughts that we saw subsidence in this area again after 1970s.  So during 76-77, 87-92, 2007-09, and more recently also.  So the California Aqueduct essentially fixed the problem.”

She then presented a map and noted that the area she is talking about is shown by the red circle.  “Where the Delta Mendota Canal was previously affected by subsidence to the south, it’s now being affected by subsidence to the northeast,” she said.

Sneed slides_Page_05She then presented a slide of a time series of data that are in this new area of subsidence.  “The study was initiated because during the last drought, there was concern about subsidence that was occurring, and that there would be more reliance on groundwater resources,” she said.  “But as it turns out, while the area south of the Delta Mendota Canal still only seems to be affected during droughts, this new area that is northeast of the Delta Mendota Canal near a small community called El Nido, is subsiding at the same rates, whether it’s a drought or whether it’s a record year of water, so we didn’t expect to find that either.”

Sneed slides_Page_06She presented a map of the area, and noted that there are many canals that cross the area, including the Delta Mendota Canal, the California Aqueduct, the East Side Bypass, San Joaquin River, and the Chowchilla Bypass.

Sneed slides_Page_07We were focused on the Delta Mendota Canal, and as we were processing the satellite data, we could see that we were on the edge of something, but our focus was on the Delta Mendota Canal,” said Ms. Sneed.  “We had limited resources, but it was about the same time that we received a call from DWR saying that they were doing leveling and GPS surveys and it looks like there’s about a foot a year of subsidence – can that be right?” 


Sneed slides_Page_08So, we processed another interferogram, the satellite data, and confirmed not only that yes we were seeing a foot a year of subsidence, but also that it was huge, and it was going from I-5 to 99 from Merced on the north to Mendota on the south – a much larger area than what we had suspected that was subsiding –  the smaller areas about a foot a year and towards the edge, it’s more like ½” a year.”

Sneed slides_Page_11She then presented a slide of a cross-section made using the data along the East Side Bypass, depicting the elevation changes.  “There’s a huge hole in the middle, so now, when water is flowing out – remember this is a flood control channel – it’s going to have to fill up that hole first and all the elevations lower than the next segment downstream, so that is going to exacerbate flooding in this area and diminish the capacity of the East Side Bypass to move water out,” she said.

These are historically low groundwater levels, and there are reasons for this, she said.  “We have found that there’s been a conversion from row crops to permanent crops, and there’s also been a conversion from rangeland to permanent crops, so these are areas that have never been irrigated before,” she said.  “Much of these conversions are happening by very large companies, and not the farmers that have been there for a very long time.”

Sneed slides_Page_12She then presented a schematic of the Central Valley’s aquifer system, and pointed out that there are two systems, a shallow system and a deep system, that are separated by a very thick, confining layer of clay.

Sneed slides_Page_13She then presented some graphs of groundwater levels and noted that the shallow system was not quite at historical lows, although this data was collected in 2010 and things have likely changed.  “The deep system has absolutely hit historic lows, and they are continuing to decline,” she said.  “This is just in this one area of the valley.  There are stories like this all over the valley.”

Sneed slides_Page_14They studied GPS stations in the area, and they found that there were different behaviors in the different GPS stations.  “One near Los Banos, for instance, has a fairly steady rate of subsidence, but the rate increases a bit during drought,” she said.  “South of there near Mendota, we see that there’s subsidence really only during droughts but the rest of the time, it’s pretty flattened out.  Then on the east side of the valley near Madera, we see that there’s a very fast rate of subsidence, it also occurs during droughts, during non-droughts, and there’s no discernible rate change, so this is happening anyway.  All of these are on the very edge of the subsidence bowl.  Of course, we don’t have any monitoring right inside; it always turns out that way.”

Sneed slides_Page_15She then presented a slide that showed where the GPS stations were in relation to surface water supplies.  “The east side near Madera, since they don’t have access to surface water, that’s why it doesn’t matter if there’s a drought and not enough water’s coming down the canal; they don’t have access to it anyway, so they pump essentially the same, year after year,” she said.  “Whereas near Mendota, P304, that’s near the Delta Mendota Canal, they get surface deliveries, but when surface water deliveries are curtailed, they get subsidence because they have to pump more.”

Sneed slides_Page_16She then presented two slides, one showing where subsidence has been historically and where it is now.  “We also know of another subsidence area that’s in the south near Corcoran and Pixley, and we’re trying to find the funding to do the work down there,” said Ms. Sneed.

So what can be done about this? “Scientifically what we would say is that groundwater levels have to be above those historic lows, because that is the trigger that causes subsidence when water levels go below that level,” she said.  “If they stay above, we don’t have subsidence, and that’s a matter of either reducing groundwater withdrawal or enhancing groundwater recharge. It’s a water balance question.”

Sneed slides_Page_17Long term monitoring of water levels and subsidence is critical, Ms. Sneed emphasized.  “Historical data is really important so we can put current data in context,” she said. “Where are we now compared to where we have been? That could be a way to gauge if we have to worry about subsidence here or not. Where are our water levels in the context of the past?  And that’s really what we need to track these conditions for any kind of decision support activities.”

For more information:

Mary Scruggs, Supervising Engineering Geologist with the Department of Water Resources

Item_11_Groundwater_Panel_Scruggs_Presentation-1_Page_02California has 515 groundwater basins,” began Mary Scruggs.  “They are defined as alluvial basins in Bulletin 118 and they vary significantly throughout the state: different precipitation, different demands, different geographic and geologic conditions.”

Item_11_Groundwater_Panel_Scruggs_Presentation-1_Page_03Groundwater use varies throughout the state as well, she said.  “Different demands throughout the hydrologic regions account for 35 to 46% of the water supply based on the 2013 groundwater update, depending on a wet or a dry year,” she said.  “About 75% of the groundwater use is for ag; and about 22% is for urban and the rest is for managed wetlands.  Groundwater is about 16.5 MAF per year, on average from 2005-2010.”

Groundwater is managed differently than surface water, she said.  “In California water law and management, surface waters are managed under permitting system, and groundwater is regulated at the local level through adopted groundwater management plans, local ordinances, or litigation,” she said.  “The state encourages groundwater management and local water management.

Legislation for groundwater management is nothing new, she said, noting that AB 3030 in 1992 brought first groundwater management plans; AB 303 initiated local groundwater system grants in 2002, and also in 2002, SB 1938 which identified required elements in a groundwater management plan, as well as recommended elements and it made getting funding for grants reliant on having groundwater management plan.

Click to visit the CASGEM website.

In 2009, SBX7-6 was passed as part of the California water package, and it became what we call CASGEM, California Statewide Groundwater Elevation Monitoring Program and it required statewide seasonal and long-term groundwater elevation monitoring statewide, she said.  In 2011, there was an amendment to the CASGEM program to allow modified groundwater elevation monitoring for certain conditions, she noted.

Groundwater management is managed at the local level either through an adopted groundwater management plan, court-adjudicated basin or local ordinances or joint power agreements,” she said.

Because groundwater provides so much of our water supply, data is critical, she said.  “We need to evaluate levels and trends, we need to identify where our recharge areas are, we need to find out where the pumping and discharge areas are and how that interacts, we need to track groundwater storage changes over time, we want the elevations of the conditions of the basin, we need to understand the hydraulics and connectivity, surface water and groundwater, as well as within the basin,” said Ms. Scruggs.  “The data is used to address impacts.  Subsidence is a huge issue in some areas, but there can also be saline intrusion, seawater intrusion, overdraft, etc.”

The critical data that we need for monitoring are the groundwater levels and flow directions, she said.  “You need to get a trend analysis. – a couple points doesn’t tell you the trend,” she said.  “You also don’t know where you are historically where that level is so you need long and short term as it will also fluctuate seasonally and long term.  You want to look at the groundwater storage calculation; how is groundwater storage increasing or decreasing or is it stable.  You want to get a water balance for groundwater budgets, what’s going in and what’s recharge annual, and you also want information off of well logs such as is there continued drilling, are they set, what aquifers, etc.”  She noted that most of this information comes from the local level.

Additional information would include annual groundwater reports and assessments, reports on conjunctive management projects, identification of critical recharge zones, and assessment of adverse conditions, such as subsidence or salt water intrusion.  “Unfortunately, if you have some of these adverse conditions, they can be permanent of difficult to address, so you really want to try and get into prevention mode,” she said.

Under CASGEM, we prioritized the California groundwater basins according to what was in the water code under the CASGEM program, she said, noting that the inventory of groundwater management plans was updated with the groundwater enhancements included in the California Water Plan 2013.

bulletin118-coverBulletin 118 hasn’t been updated since 2003 due to lack of funding, but even so, Bulletin 118 still provides useful information, she said.  “It provides a standard framework, it defines the groundwater basins that we’re talking from a common entity, it also has information on basin descriptions, physical settings, and properties, although the degree of information of that varies depending on the basin,” she said.  “Some basins, there is a lot of information and it’s very well known, other basins, small and remote, don’t have a lot of things in between.  It also provides basic information on groundwater, how groundwater is managed, and how it works and operates – the science of it.”

Groundwater is action item number 6 in the California Water Action Plan, which is to expand water storage capacity and improve groundwater management, she said, noting that specific provisions address providing essential data to enable sustainable groundwater management, and to expand and fund CASGEM.  There is some funding in fiscal year 14-15 in the governor’s budget right now to continue with CASGEM, she said.

Another item for groundwater is to update Bulletin 118.  It’s also asking for a systematic evaluation of major groundwater basins,” said Ms. Scruggs.  “There is no funding in the upcoming fiscal year for updating Bulletin 118, and we haven’t had funding for Bulletin 118 since it was finished back in 2003.”

DWR has been trying to combine and collaborate and leverage efforts under groundwater to move forward, so we’ve taken the CASGEM program and the California Water Plan update 2013 and worked together to build upon it, she said.  “We’ve advanced statewide understanding of groundwater using these efforts,” she said.  “We’ve done what we can but clearly there’s more work to be done.”

CASGEM is a voluntary program, and  it’s the first statewide program for groundwater elevations, she said.  The state is working with local agencies to monitor and become monitoring entities; and the data collected is made publicly available, she said.  “DWR is also required to do other work such as prioritize the groundwater basins, conduct groundwater basin assessments, and provide status reports to the legislature,” she said.  “The CASGEM data augments the information and groundwater work that’s in other DWR programs.”

Item_11_Groundwater_Panel_Scruggs_Presentation-1_Page_14Ms. Scruggs then gave some statistics on what the CASGEM program has accomplished so far.  Over 3700 CASGEM wells have been added to the water data library, along with over 100,000 groundwater historical records.  “Some of those are historical records that agencies, when they became CASGEM monitoring entities, they added their historical data for those wells, so we’ve got a much longer time period,” she said, noting that there are 71 designated monitoring entities.

Item_11_Groundwater_Panel_Scruggs_Presentation-1_Page_15She then presented a map of the proposed prioritization of the state’s groundwater basins, noting that they are process of working to finalize the list.  The high priority basins are in orange, the yellow are medium, and light and dark green are low and very low.  “We ended up with 46 high priority basins, and 80 medium priority basins, 126 total, which is about 25% of the groundwater basins,” she said.  “The remaining 75% are low or very low.  And of those high and medium priority basins, that covers 92% of the groundwater use overlying the groundwater basins, and 89% of the population overlie, so we figure we did a pretty good job of trying to capture where groundwater is being used and what it’s being used for.

The prioritization covers 8 criteria, but it’s predominantly measured more on groundwater reliance,” she said.  “Our prioritization does not reflect groundwater management, so it’s based on the criteria, it is not a reflection of is the basin managed well or not well.”

How will we use this prioritization?  With 515 basins, we need to figure out where we’re going to start, she said.  With high and medium priority basins, we will be focusing on groundwater level monitoring, she said, as well as work on allocating resources, she said.

Next steps for CASGEM are to finalize the prioritization and look at which basins are the high and medium basins are designated, and which do not yet have monitoring or a monitoring entity, she said.  Currently, 58% of the high and medium priority groundwater basins are monitored under CASGEM; 8% are partially monitored, and 34% are not monitored at all, she said.

Future efforts for CASGEM starting with next fiscal year, we want to continue with the designation for the areas that are not designated,” she said.  “We want to evaluate the extent of groundwater monitoring, we want to identify regional trends, identify the basins subject to overdraft and start conducting groundwater basin assessments.  We also want to update the Bulletin 118 boundaries, there are some areas where work’s been done and the boundaries that are set up in Bulletin 118 are different, so we need to talk to locals and we need to finalize that.”

Item_11_Groundwater_Panel_Scruggs_Presentation-1_Page_21She then presented a map depicting groundwater level change, noting the before CASGEM, this information was not available.  “These are changes of 25 feet and it’s from spring of 2012 to spring of 2013, and it shows significant drops in the groundwater statewide,” she said.  “The California Water Plan did a lot of groundwater updates  They did descriptions, they looked at groundwater conditions, changes in storage, hydrographs, land subsidence, and others, and did an inventory of the groundwater management plans and assessed them.”

Item_11_Groundwater_Panel_Scruggs_Presentation-1_Page_23She then presented a slide of the Tulare Lake basin with five hydrographs from various parts of the basin.  She noted that all five of these areas react differently.  “There are recharge areas, there are other areas where there’s declining groundwater levels, and other areas where it’s fluctuating back and forth so one hydrograph doesn’t explain it,” she said, noting that the water plan has regional reports that give information on a regional scale.

Item_11_Groundwater_Panel_Scruggs_Presentation-1_Page_24Another thing that was new to the California water plan was the change in storage, and in this is was done for the Central Valley, she said, presenting a slide showing the change in groundwater storage.   “It’s total loss of 5.4 to 13.2 MAF over the 5-year period of 2005-2010 in the Central Valley, so a huge drop/change in groundwater storage,” Ms. Scruggs said.  “We wouldn’t have been able to do this without  the water plan update, and we’ll be able to do better analysis and refine with the CASGEM data.”

Key messages from the California Water Plan include:

  1. The state is highly dependent on groundwater for about 40 percent of supply
  2. Groundwater extraction varies by hydrologic region (average 16 MAF)
  3. 1980 DWR Bulletin 118: 11 basins subject to critical overdraft; 31 basins with evidence of overdraft‐ 30 years later ‐ many show signs of continued depletion and impacts not adequately  addressed
  4. There is renewed land subsidence
  5. Only 17% of B118 basins are covered by groundwater management plans that include all the SB 1938 CA Water Code requirements
  6. Although significant efforts have been made to improve ground water management, bolder actions are needed.

Item_11_Groundwater_Panel_Scruggs_Presentation-1_Page_25Other recommendations in the California Water Plan include promoting public education, better understanding of groundwater basins, improving collaboration and coordination so that we can get information and build on it, encourage sharing of groundwater information (sometimes difficult), continue to strengthen and expand CASGEM, continue to assess groundwater management plans against the criteria in SB 1938, develop guidelines for groundwater management, and develop tools for conjunctive water management, as well as increase statewide groundwater storage areas, she said.

As for actions, we want to advance integrated water management as we don’t want the transferring of problems from one region to the next, Ms. Scruggs said.  “We want locals and regional entities to step up and take responsibility and work together on their water management issues,” she said.  “Things can be managed best when they are working together at the local level.  IRWM plans should also address risk appropriately and address the all of it.”

Sometimes groundwater is not always looked at, and we want to be developing standards for a sustainable groundwater resource,” she said.  “We are too reliant on the resource not to have that.  There should be legislation considered to provide additional authority needed for some local agencies to step up and be able to put in controls or stop pumping or whatever.  Some of them don’t feel that they have that authority so if everyone’s getting along and taking care of it, it works fine, but when people start pumping too much and pumping too far, how does it stop.”

In closing, we look forward to continuing to implement these actions and we want to point out that funding is needed at both the state and local level to address groundwater management issues,” Ms. Scruggs concluded.  “We’ve received some but there’s more to do and the locals need it as well.”

For more information:

For more information on this meeting of the Delta Stewardship Council:

Coming in part 2:

Eric Oppenheimer, Director at the State Water Resources Control Board in charge of the Board’s strategic plan for groundwater will give an update on the State Water Board’s groundwater workplan, Walter Ward from Stanislaus County who heads a committee to deal with groundwater will talk about their efforts to get their groundwater under control, and Andrew Fahlund from the California Water Foundation will discuss their efforts to garner stakeholder input which will be used to make groundwater policy recommendations.

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