The Los Angeles Stormwater Capture Master Plan: Harvesting Local Stormwater for Municipal Supply
The City of Los Angeles Department of Water and Power (LADWP) is responsible for providing the City of Los Angeles (City) with a safe and reliable supply of water. The City currently imports a large fraction of its water supply from the San Francisco Bay Delta, the Owens River Valley, and the Colorado River. The City intends to reduce the volume of imported water by 50% by 2024 to address sustainability issues with importing water from tenable supplies over large distances. One of the City’s key strategies to accomplish this is to use local stormwater to recharge aquifers and offset potable water use. Currently, the majority of precipitation that currently falls onto the City flows into storm drains and out to the ocean. The Stormwater Capture Master Plan was developed in order to determine how much additional stormwater could be captured for water supply, determine the most cost-effective combinations of projects, policies, and programs to accomplish this, and develop a strategy through 2035 to implement additional stormwater capture in the City.
Currently LADWP and its partners actively capture and recharge approximately 29,000 acre-feet per year of stormwater, and another 35,000 acre-feet per year infiltrating into the potable aquifers through incidental recharge. Through the work on LADWP’s Stormwater Capture Master Plan (SCMP), it has been demonstrated that an additional 68,000 to 114,000 acre-feet per year could be realistically captured through a suite of projects, programs, and policies over the next 20 years. Analysis of imported water costs and the value of local resources shows that stormwater projects have a value of $1,100 per acre-foot.
This talk will focus on the development of the City’s stormwater capture program. The modeling and technical approach used to develop and select various alternative projects, programs, and policies was a complex process involving a large range of site-specific variables around the City. This technical approach used to estimate opportunities, challenges, capture volumes, costs, and ancillary benefits associated with different stormwater harvesting techniques and develop a comprehensive plan for the City to maximize stormwater harvesting and minimize cost will be discussed. Many of the methods used to develop capture programs, evaluate site-specific obstacles and opportunities for infiltration, evaluate unit costs, and calculate captured stormwater volume could have wide application for other cities in California facing similar threats from drought, climate change, and population growth.