Site selection of the largest earth rockfill dam project in United States history

The Metropolitan Water District of Southern California is currently constructing the largest earth/rockfill dam project in United States history: the $1.9-billion Eastside Reservoir Project. Metropolitan undertook a detailed site selection study that led to approving the 7.5 square-mile, 800,000 acre-foot reservoir in Domenigoni Valley southwest of Hemet, California, in western Riverside County. The site selection study began with the identification of all possible storage sites in the area. Originally, there were 13 potential sites. Initial screening reduced these to five. More detailed screening led to three feasible sites. Final screening led to the current site. In addition to the number of sites, Metropolitan considered various reservoir sizes at different sites and different combinations of sites that individually did not have enough storage capacity to meet the total need. The study team used a quantitative decision model to compare sites on the basis of selected decision criteria reflecting the major goals of practicability, operations and water quality, and environmental and social impacts. The team weighted the criteria to reflect differences in their importance. Further weighting permitted calculating a single overall quantitative score (incorporating the scores on each criterion) for each site. At each screening phase, the team carried forward the sites with the best scores for further study.