DWR presents the draft list of Critically Overdrafted Basins at public meeting in Clovis
Staff give details on the background, the process for identifying critically overdrafted basins, the results and the next steps; public comment on the draft list closes on September 25
The Department of Water Resources has released for public comment a draft list of groundwater basins which have been identified as ‘subject to conditions of critical overdraft’. The evaluation and designation of critically overdrafted basins is one of DWR’s requirements under the provisions of the Sustainable Groundwater Management Act, signed by the Governor last fall. The 21 groundwater basins that made the draft list are located primarily in the San Joaquin Valley.
On Tuesday, DWR staff held a public meeting to discuss their findings and to provide an opportunity for the public and the local agencies to bring forward further information about the groundwater basins. On hand to explain the process to attendees were Mary Scruggs, Supervising Engineering Geologist; Tim Ross, Senior Engineering Geologist in southern region office; and Dane Mathis, Supervising Engineering Geologist in the Fresno office.
A note on the difference between “high priority basin” and “critically overdrafted basin”
There is a difference between a basin that is designated as a “high-priority basin” and one that is designated as a “critically overdrafted basin”. A high-priority basin is one that was identified through the CASGEM program which was implemented as part of the 2009 Delta Reform Act. A high-priority basin designation by CASGEM is based on factors such as population, irrigated acreage, the number of wells, and the degree to which those that overlie the basin depend on it. It is therefore more a measure of the importance of groundwater and not of the management of that basin; a basin can be designated as high-priority but still be adequately managed. Through the CASGEM process, 27 basins were designated as high priority, and 84 were considered medium priority.
On the other hand, a ‘critically overdrafted basin’ is based on the presence of one or more undesirable impacts as defined by the 2014 Sustainable Groundwater Management Act (SGMA): consistent chronic lowering of groundwater levels, water quality degradation, reduction in groundwater storage, seawater intrusion, land subsidence, and depletion of surface water. This designation is important because those basins that are identified as in critical overdraft are required to submit their groundwater sustainability plans by January of 2020, two years earlier than those basins not identified as in critical overdraft.
“Bulletin 118” is the official name for the state’s groundwater report which compiles basin maps and descriptions about the geology, water quality, and current management of the state’s groundwater basins. Bulletin 118 has been published by DWR inconsistently since 1952; updates were published in 1975, 1980, and 2003.
The 1980 update to Bulletin 118 included the first list of basins subject to critical overdraft; in the 2003 update, the same list was used. Ms. Scruggs said that by that time, some of the basin boundaries had changed, so the list might look longer, but it’s the same area. “So the Department has not updated critically overdrafted basins for nearly 35 years,” she said.
Ms. Scruggs clarified that the specific water code language is ‘basins subject to critical overdraft’ but they are using the term ‘critically overdrafted basins’ instead, “because in a way you could be subject to anything,” she said. DWR is required to publish the list of critically overdrafted basins in Bulletin 118; the interim update is expected to be published in late 2016.
Ms. Scruggs presented a slide from the 1980 report, noting that the map on the left show the basins identified at that time as critically overdafted; those areas had chronic lowering of groundwater levels, as shown by the hydrograph on the right. In Bulletin 118-1980, basins subject to critical overdraft were defined as those where ‘continuation of current management practices would probably result in significant, adverse overdraft-related environmental, social, and economic consequences.’
She then presented the list of the basins that were identified in 1980. She noted that the Ventura Central Basin was considered one basin in 1980, but by the 2003 list, the basin had been split into multiple subbasins, accounting for the additional number of basins in the 2003 update; however, the area is still the same.
Last fall the legislature and the Governor the Sustainable Groundwater Management Act which requires DWR to identify critically overdrafted basins; those basins designated as high or medium priority and considered critically overdrafted are required to submit their Groundwater Sustainability Plan by January 31st, 2020, which is two years before all the other high and medium priority basins. “The Department wanted to take care of this task, because we know that local agencies are forming their groundwater sustainability agencies, and so they will know where they are and they can be able to plan things out and get their plan in place,” she said.
Ms. Scruggs noted that the Department of Water Resources is also tasked with identifying critically overdrafted basins in water code section 12924. “It’s been in there for a long time, but we’ve just never had the funding to be able to do it,” she said. “These results are required to be published in Bulletin 118.”
The process for evaluating basins
Tim Ross then discussed the process for determining which basins were in overdraft, noting that the process involved determining a hydrologic base period, evaluating groundwater basins, notifying basin managers and counties that are on the preliminary list, and then releasing the list to the public.
He began with the determination of the hydrologic base period. “When DWR looks at critical overdraft, we want to make sure that we’re looking at a time period where the water supply is averaged over a long period of time,” he said. “So we attempted to make the longest time period that we could that includes wet and dry years, cycles of climatic change, and a base period that has the same mean precipitation as long term mean. Here we’re assuming that precipitation is a proxy for water supply, and since we’re doing this on a statewide basis, we’re looking at the whole statewide system, so we’re going to choose a system that we can apply throughout the state.”
Mr. Ross said the brought the time period as close as possible to the present drought. “In the water code, it says that we should not use overdraft during a drought period to show critical overdraft or show that there’s chronic lowering of groundwater levels,” he said. “One of the things that you’re doing in conjunctive use is that you’re storing water when you have it, and you’re storing groundwater when you have it to store, and using it during a drought period when you don’t have that surface water available, so your basin is going to experience lowering groundwater levels simply by managing that basin in a conjunctive way. So the water code says we shouldn’t be holding that against groundwater managers specifically because it’s during a drought.”
They consulted with the state climatologist, and determined the best base period to work with to be 1989 through 2009 water years; CASGEM data is not included in this is because CASGEM data was started to get reported in 2011, so this is past the base period, he said.
Mr. Ross then presented a slide of the state’s precipitation record, noting that the data starts around 1895 up to the present. He noted that the graph is not directly of precipitation but of the cumulative departure from precipitation. “So if we have a below mean or below average rainfall during a particular year, you will see the slope drop; in a year where we have above average precipitation, you’ll see a rise, so in general, if the slope of a line is going down, it’s a drought period; if the slope is going up, it’s a wetter than average period,” he said.
“We wanted to include dry periods and wet periods, and we wanted to try and pick when the water was at more or less an equilibrium situation where the same number of years after a particular wet period,” Mr. Ross continued. “Another key is that we want the average or mean precipitation over that time period to be very close to the mean for the whole record, and in this sense, in this case, the deviation is less than 1% of the long-term mean precipitation. So we feel that this is a good record to show changing water conditions or cycles of water conditions that we’re averaging.”
To begin, DWR did an initial evaluation of all groundwater basins using groundwater elevation data available in DWR database, he said. “Unfortunately, out of the 515 basins, there were over 400 of those groundwater basins and subbasins that did not have enough water level elevations during that time period to evaluate groundwater basins for water level decline,” he said. “The more recent data from CASGEM doesn’t fall within our base period, so we could not use those, and the water levels again evaluated for the basins was what was available to DWR in our database. We don’t have a complete record for the whole state, but a lot of local agencies have more information than we do, so we had to back up and change that a little bit. So due to the limited data in 400 of these basins, DWR reevaluated our process for identifying critically overdrafted basins.”
The first step then was to put all of the basins identified in the 1980 and 2003 updates to Bulletin 118 on a preliminary list. DWR also reviewed published reports and investigations by DWR, USGS, local agencies and others, as well as utilizing the local knowledge of issues in the regional offices to identify additional basins to added to the preliminary list. Local agencies were then invited to provide additional data or information to DWR to use for reevaluating basins to either remove basins from the list or identify new ones to be added.
In evaluating the basins, they looked for evidence and extreme evidence of undesirable impacts which would be caused by lowering of groundwater levels, he said. “Consistent chronic lowering of groundwater levels would be one indicator,” he said. “Water quality degradation is another; water quality can change as groundwater levels go down and you may be pulling in lower quality water from different areas. There is also reduction in groundwater storage, seawater intrusion, land subsidence, and depletion of surface water.”
Mr. Ross noted that only four of the six were issues that have been documented in reports: lowering of groundwater levels, groundwater quality degradation, land subsidence, and seawater intrusion. “Any one of those [undesirable impacts] can put you in a category of critically overdrafted,” he said. “Most of those basins show more, but there are a few basins that show just one in a really big sense.”
In July, the groundwater managers and the respective counties for all of those basins and subbasins on the preliminary list were contacted and given the opportunity to present additional data for reevaluation of critically overdrafted status. “We wanted to give them a heads up as we’re on a pretty fast timeline, so we wanted to allow them as much time as possible,” he said. “Some basins and subbasins were removed from the preliminary list based on information they provided to us, and then on August 19, we presented a draft list of critically overdrafted basins and a summary of the process to the California Water Commission.”
Mr. Ross noted that DWR is still meeting with local agencies and during the public comment period, information may be provided that could potentially add or remove basins from the list.
Results and next steps
Dane Mathis then presented the results and the next steps.
He presented the statewide map and regional maps showing the distribution of the 21 basins that are currently on the draft list. Nine new basins were added: the Soquel Valley basin, the 180/400 foot basin in the Monterey/Salinas area; the Los Osos Valley, and the Paso Robles area, all in the Central Coast area. Also added were three additional basins in San Joaquin Valley: The Merced, Delta-Mendota and Westside; basins and then the Indian Wells Valley and Borrego Valley in the southern region.
“These are just draft results and we still continue to receive public comment and work with local agencies,” Mr. Mathis emphasized. “These are as of August 6th and they will be updated over the next 30 days with public comment.”
Twelve out of the eighteen basins listed in Bulletin 118-1980 and the 2003 update continued on the list, and nine new ones were added, he said. They are all high and medium priority basins as designated by the CASGEM process. These 21 represent about 40% of the total area of the 127 basins designated as high and medium priority. There is one in the North-Central Region, fifteen in the South-Central region, and 5 in the Southern region, he noted.
Mr. Mathis then quickly summarized the process. “We included the previously identified 1980 basins to start with. We established the non-drought hydrologic base period to evaluate groundwater conditions and adverse impacts. We consulted readily available information; we didn’t do exhaustive studies for each basin because we don’t have the time nor the data to do that. We identified these new critically overdrafted basins, they have these adverse impacts within that base period, and we worked with local agencies.”
Mr. Mathis noted that the Sustainable Groundwater Management Act required the entire basin to be identified as in critical overdraft, even if they have localized impacts, such as land subsidence.
“So there could be more out there,” he said. “There could be basins that are actually in overdraft, but perhaps not in this critical overdraft condition. We only tried to identify the obvious ones, and we welcome comments from the public and the local water agencies on the basins as we work through the draft list. If you want to submit data, we’re looking for that water level data that’s within that’s hydrologic base period, 1989 – 2009.”
Mr. Mathis noted that the public comment period runs for 30 days and ends on September 25; they will accept any data and information from agencies as well as public comment through that time. They will review the information and refine the list, likely by October. After that, it will be officially incorporated in the next issuance of Bulletin 118, scheduled for the end of 2016.
For the draft list and maps …
- Draft List
- Statewide Draft Map
- Central California Draft Map
- Southern California Draft Map
- Public Meeting Presentation
To submit comments …
Comments can be submitted by email to DWR at email@example.com or sent hardcopy, postmarked by September 25 to:
California Department of Water Resources
Attn: Sustainable Groundwater Management Section
P.O. Box 942836
Sacramento, CA 94236
For more information …
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