Habitat Benefits of Aquifer Recharge

from Bruce Van Allen:

So now we get to the habitat benefits of recharging our aquifers.
A good example would be Bean Creek, which comes down from the Scotts Valley basin as a major tributary of the San Lorenzo River. Bean Creek has suffered greatly from groundwater depletion in the Santa Margarita. The creek’s “base flow” (roughly its average flow not counting storm-season peaks) barely supports life in the manner to which its riparian habitats were accustomed. This is mostly because as the Santa Margarita aquifer has been depleted, less water seeps from it into the creek. If the aquifer is re-filled, both the higher elevation of the groundwater and the underground water pressure within it will increase flows of some of the aquifer’s water to the creek through the ground.

Increasing Bean Creek’s base flow will allow its recovery as an important habitat for fish, and will help revive the stream-side food chains for all manner of bugs, birds, amphibians, and mammals, as well as plant life in and along the creek. Finally, higher base flow in Bean Creek means higher base flow in the San Lorenzo River

For those of us who have focused for years on habitat recovery in the upper and lower reaches of the San Lorenzo, nothing we want rates as important as higher non-winter flows, and not only for the big migrating fish — Steelhead and Salmon — but for all aspects of the riparian ecosystems. Even if our region didn’t have a human water supply challenge, re-filling the San Lorenzo watershed’s upstream aquifers would be a major goal. But getting the funding, water rights adjudications, and political agreements to do so only for habitat’s sake has seemed beyond reach. So we have settled for measures (again upper and lower river) that, yes, can make a difference for local and migrating wildlife. However, without more water flowing all year, our efforts have a small chance of really bringing the river back to its once-key role in the health of the regional ecology of the Santa Cruz Mountains, the coastal plain, and the Monterey Bay.

There would be similar, if smaller, ecological benefits to restoring the mid-County Purisima aquifer to its capacity. The Purisima, and especially the locations where injection wells would probably be located, is downstream of the mountain streams and the land above it is heavily urbanized. But increasing its storage would benefit the remaining coastal creeks and lagoons, potentially enhance the lives of larger trees throughout the area, and possibly make the mix of fresh- and seawater offshore more like it once was, to the benefit of marine life and birds. Intruding seawater may have ecological consequences we don’t yet recognize, so fortifying the freshwater in the ground is an important goal even aside from protecting a source of human water supply.

I hope you sense my (cautious) excitement that what turns out to be the optimal solution for human water supply could actually provide a major gain for habitat and wildlife in our region.
-Bruce Van Allen

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