WATSONVILLE – When an excessive amount of groundwater is pumped from wells, it can result in subsidence of the ground above the wells, causing buildings to collapse and pipes to burst.
A new report prepared for Pajaro Valley water managers, however, shows that from 2015 to 2018, the land above the valley aquifer only subsided by 2 inches – good news as coastal communities battle severe drought.
Just above the coastal central valley mountain range, the “land subsidence” in the over-pumped water basins is much more serious. Some areas of the fertile valley have reached a subsidence rate of almost a foot per year, causing substantial damage to roads, canals, pipelines and other infrastructure both above and below the ground.
In 2017, the State Department of Water Resources recommended the analysis of land subsidence to water managers in the Pajaro Valley because its basin is severely exposed, which means that much more water is pumped that the rain cannot naturally replenish.
The US Geological Survey used satellite imagery to determine the extent of subsidence that had occurred in recent years. Next, the USGS compared the results to water levels in the Pajaro Valley aquifer.
“We saw that the groundwater levels were generally rising throughout the valley,” said Justin Brandt, a USGS geophysicist. “As long as they don’t have the water levels starting to drop again, they’re in pretty good shape.”
Managing aquifer levels is especially vital for the California coast as prolonged periods of severe drought and other effects of climate change increase over the coming decades. When aquifers are exposed, salt water invades watersheds and ends up ruining them.
Since its inception in 1984, the Pajaro Valley Water Management Agency has focused its efforts on restoring and maintaining its aquifer. And the results of the USGS report show the effort is paying off.
âWe have been working hard to achieve sustainable groundwater resources for some time,â said Brian Lockwood, general manager of the local water agency. âIt’s a long-term challenge.
A game changer was providing recycled urban water to coastal farmers for irrigation so they didn’t have to pump so much groundwater. Since the mid-1990s, the water agency has also measured private wells and educated farmers and residents of the Pajaro Valley on sustainable water use.
Although the threat of subsidence appears to be diminishing, the Pajaro Valley aquifer is still not out of the woods.
Conservation alone will not bring the basins out of their overexploited state. This therefore makes projects that directly raise the water table, such as the Harkins Slough reclamation project, indispensable.
The two-decade-old project diverted surface runoff, which would otherwise flow into Monterey Bay, and filters the water before letting it flow into a shallow aquifer for short-term storage.
âConservation is a key part of sustainability,â said Sierra Ryan, manager of water resources for Santa Cruz County. âBut we cannot stay our way out of climate change.“