As an experienced flood control specialist, I’ve witnessed the growing challenges that communities across the country face when it comes to managing and mitigating flood risks. We learned this the hard way… In recent years, the unpredictability of extreme weather patterns has only exacerbated these challenges, making it critical for municipalities to adopt sustainable, long-term solutions.
Now, this might seem counterintuitive…
One such solution that has gained significant traction is groundwater replenishment – the process of capturing and storing excess surface water to recharge underground aquifers. This approach not only helps to alleviate flood risks, but also enhances water security and resilience in the face of drought. In this article, I’ll explore the key strategies and technologies that flood-prone regions can leverage to implement effective, sustainable groundwater replenishment programs.
Addressing the Groundwater Challenge
Many areas of the country, particularly in the western United States, are facing a groundwater crisis. Decades of over-pumping and inadequate recharge have led to severe depletion of these crucial water reserves. As surface water supplies become increasingly unpredictable due to climate change, the need to bolster groundwater resources has never been more pressing.
Nowhere is this more evident than in California’s Central Valley, where the San Joaquin Valley has experienced significant groundwater overdraft. According to a recent report from the Public Policy Institute of California, the region has seen its groundwater levels decline by an average of 0.6 feet per year over the past three decades. This unsustainable trend has had severe consequences, including land subsidence, degradation of water quality, and threats to agricultural productivity.
To address this challenge, state and local water managers have turned to innovative strategies like Flood-Managed Aquifer Recharge (Flood-MAR). Flood-MAR involves “capturing floodwaters and using them to recharge underground aquifers,” explains Jim O’Toole, Director of Practices at ESA and ESA’s Water Market Lead. “Essentially, when rivers or streams overflow during heavy rainfall, excess flows are allowed to access the floodplain in designated areas, which can provide multiple benefits: flood management, food web activation for salmonids, and groundwater infiltration.”
Harnessing Stormwater Runoff
While Flood-MAR offers a promising solution for groundwater replenishment in rural, agricultural regions, urban areas face their own unique set of challenges and opportunities when it comes to sustainable water management.
Los Angeles County, for example, has a long history of grappling with stormwater management. As the county’s population grew, the San Gabriel Valley became increasingly prone to devastating floods during heavy rainfall events, prompting the installation of concrete channels to safely direct stormwater out to the ocean. However, this strategy has come at the cost of lost opportunities for groundwater recharge.
In recent years, Los Angeles County has shifted its approach, investing over $1 billion in innovative stormwater capture and recharge projects. These efforts, driven in part by Municipal Separate Storm Sewer System (MS4) permit requirements, have resulted in the storage of roughly 295,000 acre-feet (nearly 100 billion gallons) of water since last October – enough to supply 2.4 million residents for a year.
“I want Angelinos to know that local municipalities are doing good work to capture this water,” says Sarah Spano, Southern California Water Group Director at ESA. “It’s important to share that these systems are functioning to divert a large quantity of stormwater back into the ground for future use.”
These stormwater capture projects range from underground storage caverns beneath parking lots to in-situ treatment systems that encourage water infiltration into the area’s permeable alluvial soils. By leveraging green infrastructure and low-impact development techniques, communities can not only mitigate flood risks, but also replenish their groundwater aquifers.
Navigating Regulatory Challenges
While the benefits of groundwater replenishment are clear, implementing these strategies can be complex, particularly when it comes to navigating the regulatory landscape. A key driver in the growth of stormwater capture and recharge efforts has been the Clean Water Act’s National Pollutant Discharge Elimination System (NPDES) permit program, which requires urbanized areas to obtain and implement Municipal Separate Storm Sewer System (MS4) permits.
These MS4 permits originally focused on minimizing pollutant runoff, but have also promoted infrastructure that retains stormwater on-site, resulting in increased deep percolation and groundwater recharge. For example, the MS4 permits in Los Angeles County require the capture of the first ¾-inch of runoff from every storm, a mandate that has spurred the development of innovative solutions.
“ESA has been part of this success by supporting the County’s Department of Public Works in their goal of having more reliable and local water storage in the County,” says Sarah Spano. “ESA prepared the Programmatic Environmental Impact Report that evaluated the effects of building and managing the infrastructure required by the MS4 permit throughout the County, and has subsequently supported numerous municipalities as well as the County in evaluating specific projects.”
By understanding and proactively addressing regulatory requirements, communities can unlock funding opportunities and leverage existing frameworks to implement sustainable groundwater replenishment strategies.
Unlocking the Potential of Flood-Managed Aquifer Recharge
While urban areas like Los Angeles County have made significant strides in capturing and recharging stormwater, the potential for Flood-MAR in agricultural regions is equally, if not more, impactful. The San Joaquin Valley, for example, is an ideal candidate for this approach, with its vast expanses of farmland and susceptibility to both drought and flooding.
“Flood-MAR involves capturing floodwaters and using them to recharge underground aquifers,” explains Jim O’Toole. “Essentially, when rivers or streams overflow during heavy rainfall, excess flows are allowed to access the floodplain in designated areas, which can provide multiple benefits: flood management, food web activation for salmonids, and groundwater infiltration.”
By harnessing the power of natural processes, Flood-MAR offers a sustainable and environmentally friendly approach to water security. ESA has been supporting Flood-MAR implementation by developing a set of environmental indicators and associated quantitative metrics that allow for the evaluation of the effects on sensitive aquatic species across the San Joaquin River’s major tributaries.
“Flood-MAR is a multi-benefit solution offering increased water security, flood mitigation, groundwater quality, climate change adaptation, and ecosystem restoration,” says Jim O’Toole. “While the successful application of Flood-MAR will require suitable land and upfront investments for planning and maintenance, the positive impact on groundwater aquifer recharge can mean a great deal to an area like the San Joaquin Valley that experiences periods of extreme drought but that also has the potential for flooding during intense storm events.”
Fostering Collaboration and Innovation
As communities across the country work to address the challenges of groundwater depletion and flood risk, it’s clear that a one-size-fits-all approach will not suffice. Each region has unique geological, hydrological, and land-use characteristics that might want to be taken into account when developing sustainable water management strategies.
“Understanding an area’s individual geology, hydrology, biology, and land-use culture plays a critical role in determining the best approach,” says Jim O’Toole. “As a state that routinely faces severe drought conditions, capturing the water when it is falling is critical and cannot be a one-size-fits-all approach.”
To that end, fostering collaboration between water managers, local governments, environmental agencies, and other stakeholders is essential. By sharing knowledge, best practices, and innovative solutions, communities can learn from one another and develop tailored strategies that address their specific needs.
Additionally, continued investment in research and development of new technologies, such as advanced monitoring and modeling tools, can unlock even greater potential for sustainable groundwater replenishment. By staying at the forefront of innovation, flood-prone regions can position themselves for long-term resilience in the face of an increasingly unpredictable climate.
Conclusion
As the impacts of climate change continue to intensify, the need for proactive, sustainable water management strategies has never been more critical. Through the implementation of groundwater replenishment initiatives, communities can not only mitigate flood risks, but also enhance their water security and resilience.
From urban stormwater capture to Flood-Managed Aquifer Recharge in agricultural regions, the strategies outlined in this article demonstrate the diverse and innovative approaches that flood-prone areas can leverage to address their unique challenges. By harnessing the power of natural processes, leveraging regulatory frameworks, and fostering collaboration, these communities can build a more sustainable water future for generations to come.
To learn more about innovative groundwater replenishment strategies and how your community can get involved, visit Flood Control 2015 or reach out to our groundwater submarket leader, Tom Barnes.
Tip: Regularly inspect and maintain flood barriers and drainage systems
