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Evaluating the effects of groundwater management strategies

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It looks like the earth is breathing. The land beneath Southern California appears to rise and fall in two animated graphics created by geophysicists at Caltech. Researchers recently analyzed satellite radar data in order to better understand the effects of groundwater extraction and replenishment on the land. Their findings reveal just how much the ground fluctuates as water is pumped in and out of aquifers.

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The study, titled “Quantifying Ground Deformation in the Los Angeles and Santa Ana Coastal Basins Due to Groundwater Withdrawal,” is based on radar data collected by European Space Agency satellites over an 18-year period and compiled into 881 radar images that track vertical ground motion down to the millimeter.

“What we see through the rising and falling of the ground surface is the elastic response of the land to regular changes in groundwater level,” says lead author Bryan Riel (MS ’14, PhD ’17). “Because we have data over a long period of time, we were also able to isolate long-term surface deformation signals, including subsidence of the land that seems to be caused by compaction of clay layers in response to background variations in groundwater withdrawal.”

via Gfycat

Researchers explain that the fluctuation of ground levels also tells the story of Southern California’s groundwater management. The oscillation of ground levels—which is far more dramatic in earlier years than today—reflects changes in the state’s aquifer management strategy over time. In fact, the decrease in variability suggests that groundwater management regulations, such as those outlined in the Sustainable Groundwater Management Act (SGMA), a 2014 bill signed by Governor Jerry Brown, have been effective in preventing overdraft and subsistence.

“At the beginning of the study period, we see big sinusoids—higher highs and lower lows. Toward the later half of the study, that flattens out a bit, indicating that water control districts were more actively managing aquifers, and making sure to put water back into them instead of just taking it out,” explains Caltech geophysics professor Mark Simons. 

via Gfycat

For decades subsistence has been an issue in the San Joaquin Valley of Central California. Depleted aquifers have led to soil compaction that has caused the ground in the area to subside by as much as 28 feet, according to the United States Geological Survey. The Caltech study confirms that with careful aquifer management, water districts can prevent resource depletion and soil compaction.

What groundwater management strategies does your district employ? Is subsistence an issue in your area?

Groundwater management, aquifer recharge, and water reuse are just a few of the exciting topics that we look forward to exploring at the Western Water Summit, a conference presented by Forester Media February 6–8 in San Diego, CA. We invite you to attend! Click here to register.  WE_bug_web

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  1. Laura, interesting animation. Is this plumping up and drying down of clay lenses? But, simultaneously, do the dewatered gravel layers also behave in this manner? That would be the critical question and I don’t think that the gravel/sand lenses respond in this way. That may be an unfortunate reality. Accordingly, this may be why we see the dramatic drop in surface elevation within the San Joaquin Valley, mainly a deep gravel fill from the ancient weathered Sierra. This takes on an additional issue in that, if the data are accurate that the system is drying down, then there is less chance to see recharge. As this drying down ensues, the vegetation on the Sierra slopes changes and the chance of wild fire goes up, thus the ability to hold snow pack may shift to that of faster release down slope and thus a more narrow but higher amplitude peak in out flow, hence a greater tendency to see loss to the ocean rather that soaking in.
    Then we should also see the impacts on coastal aquifers shifting into greater tendencies toward seawater intrusion as inland pumping is unlikely to change. The Oxnard basins and their seawater intrusion are a classic example of bureaucratic failure. The reality of over-pumping was evident way back around the initiation of the Twentieth Century. Sailing ships could anchor off the coast and fill water barrels from the upwelling fresh water, homes along the coast had pressured water on the second story. Then, through the invention of gasoline and natural gas fueled internal combustion engines, wells were developed to irritate the Oxnard Plain and it was not long before the flow to the second story ceased and the off-shore watering point failed. The latter, abundantly demonstrating that the aquifer was open to the influence of the ocean. Once the water table dropped below sea level, the gradient reversed. By the mid 1980s, there were about 26 square miles of the aquifer’s inland area now invaded with seawater. Thus we have something like at least 80% of a century of information that there was an issue, yet the sequentially ineffective politics of the situation failed to effectively correct the situation. It will take about 4 times the intruded saltwater volume to flow through the aquifer to flush it. That is an unlikely outcome—-where will that water come from if we are facing a long drying cycle?
    My guess is that politicians will, nonetheless, grasp upon these findings of the rise and fall of surface to argue that the situation of subsidence is self correcting and thus can be, as an issue, put on the back burner. They once assumed that all was well with the State Water Project and thus invented paper water, upon which politicians eagerly pounced to allow rapid expansion of development in the southern portions of the state. To pull the system back out of that issue and to get the chestnuts out of the fire, we see the people in the San Diego area now going on toilet to tap.
    Water scientists need to become more involved in the politics of water, we cannot leave it to politicians.

  2. Once again: My 70+ years of observations confirmed. Non-native man is the definitive icon of a lunatic DNA strain that is permitted regenerative progeny with no limitations. His ultimate success will be total self destruction. “We have met the enemy and he is us”.

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