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.
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.”
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.
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.