Jake Sahl, Water and Wildlife Program Assistant, San Francisco
NRDC recently published a paper highlighting the water supply strategies of five Southern California agencies that plan to significantly reduce their reliance on water imported from the overstressed Bay-Delta and Colorado River systems. This approach makes sense for most water agencies in California as they examine their future water needs and the costs and benefits associated with various supplies. As part of my recent Master’s degree work at the Bren School of Environmental Science and Management, a team of my fellow students and I examined future water supply options in the Ventura River Watershed. Like these Southern California water agencies, we concluded that water-use efficiency and conservation measures could provide the most cost-effective and reliable solutions to predicted water supply shortages in the Ventura River basin, just like many other areas of the state.
The Ventura River Watershed is located roughly 90 miles north of Los Angeles, California in Ventura County. It is a small, coastal watershed, covering an area of roughly 228 square-miles. This watershed is remarkable in that, unlike the vast majority of Southern California watersheds, it does not currently import any water from outside sources. This means that the only water available to residents, businesses, and industries in the watershed is that which falls within the basin as precipitation. Consequently, a finite amount of this precious resource must be divided among a variety of important uses, including maintaining adequate flows within the stream network to support populations of endangered Southern California steelhead trout. This creates challenges for water resource managers, but also presents a unique opportunity. Because it does not use any imported water from California’s network of increasingly over-allocated remote supplies, the Ventura River Watershed is not threatened with many of the same water supply reliability challenges faced by districts heavily dependent on the Delta and Colorado River. It has the potential to serve as a model of sustainability for other Southern California water resource managers.
But over the past decade, water supplies within the basin have become increasingly stressed leading some to propose ending the Ventura River Watershed’s self-reliance by connecting to the State Water Project. This would mean that residents could import water from the San Francisco Bay-Delta, a system that is already stressed and overtapped. However, water from this system is less than reliable as yearly allocations often exceed the amount of available water. An alternative option is to invest in improved local water use efficiency and conservation measures.
To assess the costs and benefits of these approaches, my colleagues at Bren and I used the Water Evaluation and Planning (WEAP) System to construct a hydrologic model of the Ventura River Watershed. We used this model to quantify the potential of several water resource management strategies to mitigate the effects of increased water demand and decreased supply resultant from population growth, land use change, and climate change. Strategies considered in our study fell into two categories: consumer based, and infrastructure based. Consumer based strategies included constructing Native Plant Gardens in single-family homes, installing greywater re-use systems in homes, and increasing residential water rates. These strategies focus on altering end-user tendencies, with the goal of decreasing overall water demand within the watershed. Infrastructure based strategies considered in our study included constructing distributed infiltration basins to increase stormwater capture, constructing a wastewater treatment plant for use in golf course irrigation, and replacing impervious roads with pervious materials. These strategies increase infiltration to groundwater and increase water re-use, adding to the available supply of water within the watershed. Distributed infiltration basins (curb-cuts, bioswales, etc.), for example, capture stormwater runoff from city streets, parking lots, and lawns before it reaches the stream network. By capturing this water and allowing it to infiltrate into the groundwater system, water that would normally flow out to the ocean is being stored for later re-use during dry months. This strategy also improves in-stream water quality by reducing urban pollutant input.
We analyzed each of the strategies based on six different criteria: (1) cost-effectiveness, (2) ability to increase water supply, (3) ability to decrease water demand, (4) ability to improve water quality, (5) ability to improve ecosystem health, and (6) suitability for Proposition 84 funding, a program that supplies grant money for watershed enhancement projects. We found that installing native plant gardens and greywater systems in single family homes were the most effective strategies overall. These strategies have the potential to earn homeowners money in the long-run by lowering water bills, while also increasing overall supply, decreasing overall demand, and improving water quality. We also found that increasing water rates is an effective strategy for decreasing demand, and constructing decentralized infiltration basins is the most cost-effective means of increasing the available water supply. All of these options were found to be more cost-effective than paying to connect to the State Water Project and model results show that, when applied in concert, these conservation and water-use efficiency measures have the potential to offset increased demand associated with a warmer climate.
Results from our study are extremely exciting, especially when viewed in the larger context of California water issues. Many reports and studies suggest that, rather than increasing reliance on the State Water Project to provide for California’s growing demand, local conservation and efficiency measures should be implemented. These measures are often not only less expensive per acre-foot of water gained than the infrastructure costs associated with improvements to California’s massive water transport system, they also provide a more reliable source of water. Given the uncertainty of future precipitation within California (and the Western U.S. in general) it makes much more sense to design systems that efficiently use the water that is available, rather than designing systems that rely on water that may or may not be there. Such efficiencies increase the robustness of any water supply system and can help insulate California from the potentially severe decreases in available water in the coming decades.