An Integrated Approach to Water Resource Planning in Southern California

California water providers are facing a number of challenges in maintaining reliable and clean drinking water supplies. Drought impacts have affected the availability, quantity and quality of the state's source waters and water providers must develop strategies to contend with these supply changes. To evaluate its long-term water supply challenges and solutions, Eastern Municipal Water District (EMWD) is developing an Integrated Resource Plan (IRP). The IRP provides a guide to leveraging the flexibility of their very complex supply system. The goal for the IRP is to seek fully integrated strategies utilizing EMWD's diverse range of supply and demand resources, including treated imported water, raw imported water, recycled water, local surface water, and groundwater systems. To aid in the evaluation of these operational strategies, a dynamic system model (System Model) of EMWD's integrated systems is being developed using the Powersim dynamic simulation software. The System Model parallel processes the dynamic operation of EMWD's treated water, raw water, recycled water and groundwater supply systems, including all imported water sources, regional and local treatment plants, and natural and artificial groundwater recharge components. Available raw and treated imported water, natural groundwater recharge, and treated and recycled water demands also serve as inputs to the System Model. Model programming allows inputs to be adjusted based on theoretical regional climate change impacts to assess the vulnerability of a water supply portfolio (e.g., combinations of water supply and demand options) to climate change. The System Model evaluates overall system performance of water supply portfolios against multiple planning objectives. The System Model is being used to develop a set of water supply and demand portfolios designed to meet these planning objectives. The most promising portfolios and their corresponding scores will be evaluated using decision analysis software which incorporates EMWD priorities for the individual performance objectives. This paper presents the integrated approach to addressing EMWD's future supply needs and the System Model used to compare the potential benefits and costs of potable and non- potable water supply and demand management options, and support decisions about how and when to implement various system improvements through the 2035 planning year.