Written by Alex Sandu and Simon Bluestone with MWH (Broomfield, Colo.)

From flood control to water quality concerns, the stormwater paradigm has continued to shift in California. Now, as a result of increased water demand and scarcity issues, the state is searching for ways to leverage stormwater as a supply. The struggle lies in meeting flood control and environmental requirements while finding ways to bolster supplies with stormwater capture and beneficial use.

One solution — already successfully executed in Los Angeles County for more than 40 years — is recharging groundwater basins with stormwater. The Los Angeles County Department of Public Works augments the area’s potable water supply with about 270 million m3 (220,000 ac-ft/yr) of mixed stormwater and reclaimed water. If purchased from the Metropolitan Water District of Southern California, this water would be worth approximately $120 million.

Despite this longstanding example, the beneficial use of stormwater in California actually is a new and evolving concept with a unique set of challenges. These challenges are underpinned by jurisdictional, regulatory, and economic constraints.

First, under current regulatory and administrative regimes, stormwater stakeholders often have competing interests. For example, California stormwater permits now commonly hold a lead permittee liable for numeric effluent discharge standards, creating enforcement challenges between co-permitees.

In addition, capturing and using stormwater can cost more than using traditional supplies. “However, this downside is, at least partially, offset by several key advantages. Stormwater capture delivers “better bang for the buck,” including better flood control as well as cleaner beaches and waterways. Using stormwater also diversifies the water portfolio and therefore increases the security of potable water supplies.

California already faces water scarcity issues, which are forecast to worsen with climate change. Snowpack — projected to decline 20% to 40% by 2050 — provides much of the state’s water supply. Therefore, climate change is critical to forecasting water and infrastructure needs accurately, and stormwater will become an increasingly valuable supply component.

Because of these drivers, California has begun to address challenges associated with stormwater use.

A number of institutions are collaborating actively with various stakeholders to develop stormwater solutions. For instance, a task force of the Southern California Stormwater Committee brings together multiple stakeholders — water purveyors, flood control districts, and federal agencies — to develop strategies for reducing runoff pollution problems, providing flood control, and using stormwater effectively as a water supply.

In addition, Ventura County and the City of Los Angeles promulgated municipal building codes that require new and redevelopment projects to integrate low-impact development practices, thereby providing incentives associated with multiple benefits as part of integrated sustainable local water resource development solutions.

Both examples show that flexibility, innovation, and collaboration are required to advance stormwater management policies and practices in a more integrated manner, from the state to local level.