Ecosystem-based Groundwater Recharge to Help Farmers and Fish: Why California Needs 10,000 More Dams
National Oceanic and Atmopsheric Administration
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Instream structures such as wood jams, living vegetation, beaver dams, certain geomorphic features and other obstacles that slow the downstream movement of surface water and sediment are essential to the restoration of streams and the recharge of alluvial aquifers. In particular, such ecologically functional dams help restore complex fluvial ecosystems with high groundwater recharge potential and multiple and synergistic ecosystem goods and services. We provide an overview of how ecologically functional dams can be used to increase groundwater recharge of alluvial aquifers and provide examples from pilot studies in California and Oregon where such ecologically functional dams have been used to increase groundwater levels in agricultural landscapes, providing water that benefits both farmers and the taxa that utilize fluvial ecosystems. Despite the promise of such ecosystem-based groundwater recharge efforts, numerous regulatory and policy obstacles cast doubt as to whether such an approach can be used on a widespread basis, despite the fact that many of the technological challenges have been addressed. Many of the regulatory and policy obstacles derive from the fact that surface water management has historically been focusing on mitigating flood damage rather than sustaining natural groundwater recharge rates. Thus streams and rivers have been viewed as drainage networks rather than groundwater recharge networks, and managed accordingly, such that much of the surface water that historically would have contributed to recharging alluvial aquifers has instead been managed for rapid transport out to sea. We conclude that new approaches to stream restoration and surface water management are needed that take into account society’s economic and ecological imperatives to create resilient, structurally complex and dynamic fluvial systems that can substantially increase groundwater recharge rates in agricultural landscapes.