Last year I wrote an article about groundwater and how it is so critical to farmers and cities in the state. We pump the water out of the aquifers, which are like a big bladder that holds the water that percolates from the surface through the soil, sand, and rocks. It is like a bank that you deposit and take out what you need. The problem is that we take out more than we put in. The big danger is the collapsing of these water caves, which like a house of cards falling, are almost impossible to open up that space again.
So, a lot of work is being done to recharge these aquifers. The big problem has always been how do we measure what is happening underground in these aquifers? It would take thousands of some sort of meters to gauge the removal or addition of water and where it goes because it is not just one big bowl under vast areas like the San Joaquin Valley or our local water banks. We are finding there are many below-ground individual pockets throughout the state lands.
“Scientists are now coming up with a way to map the “Pulse” of groundwater flow through California’s Central Valley,” which is the title of a report by Brittany Hook for the UC San Diego News Center. The Valley has gone through many upheavals over the years, with large drops in the Valley floor. Some places have seen the surface drop over 30 feet, power pole heights because of drawing too much out of the water bank.
The problem has been recording the timing and movement of water flow because of the lack of reliable data. UC San Diego Scripps Institution of Oceanography and the School of Global Policy and Strategy, and the U.S. Geological Survey have been working together to use advanced satellite information. The group, for the first time, is getting an idea of the recharging of the groundwater in the southern part of the great Central Valley – the San Joaquin Valley. Based on satellite observations, the Central Valley changes by a plus or minus 2.75 inches, five and a half-inch yearly spread, based on what is happening below in water storage. During drought, and no doubt we are in one now, ground in the southern valley can sink over a foot, 13.7 inches, in a year. How would you like your house to sit on the ground like that?
Using satellite-based InSAR (interferometric synthetic aperture radar) from the Sentinel-1 missions and ongoing Global Positioning System (GPS), scientists can visualize the movement of water in the subsurface. The mapping can monitor and measure the sinking in the Valley when a large amount of water is being removed from the aquifers. Less water equals lower surface heights which they can now watch. Also, these new mapping techniques can measure the rising of the land from more water getting into the underground storage. As the “bladder” shrinks, so does the land, and when filling pushes up the surface because it is hemmed in below and to the sides, so the path of least resistance is up.
Mapping the timing across the valley, researchers were able to find where the uplifts are related to river and stream runoffs from the Sierra Nevada Mountain Range. Then moving away from the mountain runoff, they can check the uplift changes that would show possible pathways of the groundwater flow like an underground river. This can build up a library of the changes in dry and wet years to better map what is going on below.
Current guidelines assume that everyone is sitting on one big underground pool of water and getting an equivalent amount of water. So, finding these uneven distributions of groundwater recharge and where it is going is causing water agencies to think about the need to coordinate efforts to reach sustainability. With more experience, this methodology can be used to study regional underground storage all over the world. That would include locally in our Avila Valley, Edna Valley, Paso Robles, and Santa Maria, which are mostly dependent on rain and how and where to grab some of the water, and where to put it for underground storage before it ends up in the ocean.
