Last week I reported on a forum sponsored by the California Department of Food and Agriculture regarding the need to significantly ratchet-up ground water recharge in California. There were some things I learned at the forum I thought I would pass on.
The Kern Water Bank has been in existence for a couple of decades. It comprises 7,500 acres of land near Bakersfield. That land has been configured with berms to be shallow ponds which slow water down to a point where it can recharge into the aquifer. Percolation rates are actually pretty low – 0.2-0.3 feet per day – but because of the large area the Water Bank covers, this past year 550,000 acre-feet of water were recharged into the ground by the Kern Water Bank.
The source for much of this water was surplus flows from the Kern River. I was surprised to find out that there are actually a total of 10 formal water banks in the San Joaquin Valley although not all are as far along as Kern. The water bank idea, as well as recharge efforts carried out by individual water districts face challenges in financing the projects, both for the infrastructure as well as the recharge water. It is no surprise that water flowing as surplus flood flow in creeks and rivers and available for free was grabbed by these folks much more aggressively than water that had a price tag associated with it. Measuring how much water made it into the ground was not done with precision by many of the participants. It was suggested that a 10% loss factor should be applied at a minimum when trying to calculate how much of the recharge water could be recaptured through pumping.
Don Cameron is the General Manager of the Terrranova Ranch in Southwest Fresno County. This 6,000 acre diversified farming operation has been the site of aggressive efforts to recharge water on fields, vineyards and orchards that make up the ranch. Don reported that during this past year they were able to put 13 feet of water per acre on wine grapes planted in sandy loam soil with no negative impacts on the vines. Their standing water underneath their ranch is at approximately 220 feet. The Terrranova Ranch has been in the fore front of testing the limits of groundwater recharge on farm land. You can learn more about what they are doing on their website: www.terranovaranchinc.com
Dr. Daniel Mountjoy, the Director of Resource Stewardship at Sustainable Conservation is another person who spoke at the forum. He is working with about 100 growers in California to evaluate and learn how much flood water can actually be put on a crop for recharge without risking that crop under a variety of scenarios. His goal is to develop a Groundwater Recharge Assessment Decision Support Tool that can be used by farmers to assist in making the decision about when, where, and how much water could be flooded onto a piece of ground without damaging its productivity. You can learn more about the work of Sustainable Conservation at their website: www.suscon.org
The Public Policy Institute of California has been looking at the state of the groundwater aquifer in the Central Valley for some time. They are the ones who estimated that from the year 2006 to 2016 the average annual overdraft in the San Joaquin Valley was 2.4 million acre-feet. I was able to ask their representative about this past water year and she said they have not yet finalized their research, but they do believe that not only was there no net overdraft this past year, but there was at least several hundred thousand acre-feet of recovery in the aquifer because of the wet winter and the more aggressive efforts to recharge that occurred.
Another tidbit we might not think about but would make a difference in certain locations and applications is the value of more accurate precipitation forecasting. A lot of potential recharge sites are also flood control facilities. The property damage that results from flooding can be catastrophic, so the managers tend to be very conservative in their operation of flood control facilities. Right now, weather forecasts 7 days out are 70% accurate, while 14- day forecasts are only 7% accurate. If the accuracy of forecasting could be improved, the managers could allow water to stay longer in those facilities permitting more percolation to occur rather than releasing that water to prepare for the next storm.
The whole issue of groundwater recharge particularly in the San Joaquin Valley, but also in urban Southern California where the Regional Boards have been using their regulatory authority to drive increased attention to hanging on to flood flows that for decades have been directed to facilities designed to move them efficiently and safely to the ocean is going to be increasingly important to all of us.
Geoff Vanden Heuvel
Director of Regulatory and Economic Affairs