The Valley Citizen is committed to bringing as much science as possible to the ongoing dialogue about water in the San Joaquin Valley. Stanislaus County’s resident geologist is an internationally acclaimed consultant on geohydrology and geology. Dr. Horacio Ferriz also teaches a wide range of courses at California State University, Stanislaus. He has an earned PhD from Stanford University. Dr. Ferriz generously offered the following interview via email.
Valley Citizen: Your biographical information lists you as the Stanislaus County geologist. Have you been consulted by the county about groundwater pumping in eastern Stanislaus County?
Dr. Ferriz: Yes. I have my desk a few steps away from that of Mr. Walt Ward, County Manager of Water Resources, and we have a chance to talk about current issues. Mr. Ward has asked my opinion about very specific matters, such as the best information to include on a water database for the County, or the type of sediments that are likely to behave as aquifers on eastern Stanislaus County. Of course you realize that water resources management is 50% a technical issue, 25% a legal issue, and 25% a political issue. I mention this because historically, in California, the owner of the land has the legal right to extract groundwater to put it to a beneficial use. You or I might think that this right should be curtailed during times of drought, but the law is the law, and can only be challenged through the time-honored and battle-tested court system.
Valley Citizen: Given almonds need three acre feet a year to be productive, in your professional opinion, how sustainable are the 30,000+ acres in the foothills without tapping surface water?
Dr. Ferriz: Well, assuming 10% porosity in the aquifer, you would have to drain 10 ft of the aquifer for every foot of water, or 30 ft of draining for the three feet required. So, for every year you irrigate the crop, the water level would drop 30 ft. The saturated section of the basin is about 1,000 ft thick, but let’s say that we are prudent and would like to operate it over a 100 ft range. If this is the case, then we should be able to water the orchards for 3 years using groundwater. It may not be much, and if our surface water supplies fail for more than 3 years, then it may be necessary to think about letting them die. This is a back of the envelope calculation, so clearly it would be a good idea for farmers to keep track of the static water level in their wells (it would be an even better idea to share the data with the County, so we can put the big picture together).
I should point out that a lot of the new orchards in eastern Stanislaus County are being supplied with surface water by Oakdale Irrigation District, and that as far as I understand this year OID was able to supply the full allotment. It is the progress of the next three years that will be of crucial importance to the well-being of the economy of the County and its residents!
Valley Citizen: A Superior Court Judge just ruled that pumping groundwater affected flows on the Scott River. How likely is it that large pumps (300-350 HP) near rivers, lakes, and reservoirs affect flows and water levels in those rivers, lakes, and reservoirs?
Dr. Ferriz: It really depends on whether the wells are screened in the unconsolidated sediments of the river or lake, or in the rocks on which the stream sediments rest. Thinking about the Stanislaus or Tuolumne Rivers, a well within 2,000 ft of the river, and screened on the young, unconsolidated sediments, is very likely to affect the base flow of the river (base flow is the flow of groundwater into the river). In contrast, wells that are more than 2,000 ft from the river or lake, and are screened into the harder sedimentary or metamorphic rocks is not very likely to affect base flow.
Since you mentioned the decision of a Superior Court judge, I have to say that the legal process through the courts is the mechanism that is available for people to try to right a perceived wrong. I am definitely not in favor of this solution, but I have inherent trust in the legal process. Me, I would first talk with that person or company who you have an issue with, and see if a solution acceptable to both can be achieved by negotiation. Educate yourself in the process (my class in Development of Water Resources at CSU Stanislaus this Fall term would be a great place to start), and consult with your County Geologist or your County Manager of Water Resources. If negotiation, civil conversation, and your own willingness to compromise fail, well then you may consider the legal process.
Valley Citizen: Wouldn’t wells screened on the young, unconsolidated sediments near rivers, lakes and reservoirs be more productive and reliable than those screened into harder rocks and thus more attractive to growers?
Dr. Ferriz: Yes, those growers who have the good luck of farming within a few thousand feet from a river, lake, or reservoir could probably drill shallow wells that are very productive. And yes, those wells would eventually be recharged from those bodies of water. Is this “taking” surface water without a permit? Unfortunately the law is unclear in this respect, and court decisions have gone both ways, depending on whether a party is directly injured or not.
Next: Mass balance, subsidence, sedimentation, and more…
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