flood managed aquifer recharge (Flood-MAR) in California:
Proponents argue Flood-MAR provides much-needed flexibility and resiliency. While often discussed as an emerging climate adaptation strategy, forms of intentional winter flooding and aquifer recharge have actually been practiced for over a century by native tribes and farmers/ranchers seeking to boost summer water availability.
For example, the Scott Valley in Northern California has a long tradition of flood irrigation in the wet season to build alluvial groundwater storage that sustains irrigation needs in the dry summer months. With technical guidance and financial assistance, similar beneficial coordination of wet season precipitation with groundwater recharge could be expanded throughout the state. When integrated with sustainable groundwater plans, Flood-MAR can help stabilize water supply reliability.
As climate change and growing water demand intensifies California’s cycles of drought, water managers are desperately seeking new strategies to bolster our overtaxed water supply systems. One emerging approach is flood managed aquifer recharge, or Flood-MAR. This involves diverting high stormwater flows from wet winters to intentionally flood agricultural land, recharge basins, or historical floodplains. The goal is to allow more water to percolate underground, recharging critically depleted groundwater aquifers that millions rely on, especially in dry years.
Proponents argue Flood-MAR provides much-needed flexibility and resiliency. But critics counter that Flood-MAR risks running roughshod over ecosystems and sustainable groundwater management if not properly implemented. As local water agencies move forward with Flood-MAR projects, debates are heating up over its costs and benefits.
The Case For Flood-MAR
At first glance, the concept behind Flood-MAR seems like an elegant win-win. In a wet year with heavy winter runoff, why not put those “excess” peak flows to use replenishing our aquifers, instead of having all that water rush out to sea? Then when drought returns, we have more groundwater banked to sustain agriculture, communities, and ecosystems. Flood-MAR mimics natural floodplain processes in a more controlled manner while supporting water users. Properly designed projects also reconnect historical floodplains, bringing hydrological and ecological benefits.
Some of California’s most severely overdrafted groundwater basins have already seen aquifer levels rise and wells stabilize following pilot Flood-MAR projects, even during droughts. The potential is enormous – a recent PPIC analysis found that Flood-MAR could yield over 3 million acre-feet of additional annual recharge. That’s almost four times Los Angeles’ annual water demand! With ever-increasing variability between deluges and drought predicted under climate change, expanding Flood-MAR seems like a smart hedge.
Critics Raise Alarms
However, many ecologists and environmental advocates warn against embracing Flood-MAR too quickly. While sympathetic to the need for more groundwater storage, they argue that without strict safeguards for river health, Flood-MAR risks becoming just one more flashpoint of conflict between water users and the environment.
Seasonal flooding drives critical ecosystem functions – disrupting those delicate flows to maximize recharge may help refill aquifers on paper but devastate already declining native species. Fish need carefully timed winter-spring flows to migrate and spawn, while floodplain forests depend on occasional inundation. Such habitat is already scarce after a century of heavy damming and diversion on California’s rivers.
There are also concerns that by creating a new supply, Flood-MAR will foster unsustainable groundwater use instead of the cuts in pumping the Sustainable Groundwater Management Act mandates for stressed basins. Just as with canal-building in the last century, the “build it and they will come” rule may apply for recharge projects. Although Flood-MAR supplementation seems small compared to aquifers’ vast capacity, less recharge also disincentivizes the conservation essential for true sustainability.
Is California’s grand Flood-MAR experiment worth the risks? Can we avoid sacrificing rivers for aquifers? The keys likely lie in careful project selection, monitoring for impacts on both surface and groundwater, and integration with demand management rather than reliance on new supply. If supplemented by ecosystem protections and pumping governance, Flood-MAR could play a valuable role in transitioning to more robust regional water systems suited for a hotter, more variable climate. But without foresight, Flood-MAR may temporarily paper over unsustainability, not remedy it, gaining marginal supply while degrading the vibrant living rivers and fisheries cherished by so many Californians. The next decade’s water decisions are crucial – we must choose wisely.
Let me know if you would like me to modify or expand on any part of this draft pro/con piece. I aimed to surface some of the key tensions summarized in the source material. There is certainly more that could be said on both sides.
I used ai to smooth out the kinks for better reading.
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