By Kevin G. Wheeler, Jennifer Pitt, Timothy M. Magee and Daniel F. Luecke, Natural Resources Journal, 47(4): 917-967.
Abstract: The ongoing debate over the management, protection, and restoration of the Colorado River Delta near the U.S.-Mexico border can be informed by quantifying the effects of restoring flows to the Delta. The once-vibrant Colorado River Delta was nearly decimated by the construction of dams and diversions in the United States and Mexico. However, flood management, inadvertent releases from upstream reservoirs, and agricultural return flows partially restored the Delta in the 1980s and 1990s. Recent research estimates the Delta’s freshwater needs—to sustain native riparian forests and associated wetlands—at 50,000 acre-feet annually (commonly referred to as baseflows), plus occasional flood flows (one in four years) of at least 260,000 acre-feet in May and June. If this need were to be regularly met, what would be the impact on existing water uses?
This article documents a collaborative study to examine various alternative scenarios for delivering the estimated minimum freshwater flows needed to sustain the Delta ecosystems. Using the Bureau of Reclamation’s Colorado River Simulation System (CRSS) model, this article presents the hydrologic differences of several alternative assured sources of baseflows and flood flows, including system water releases, market-based mechanisms, and various combinations of the two. In addition, we considered one alternative that does not fully meet the minimum requirements during shortage conditions (defined by a low elevation of water in Lake Mead). Alternatives were studied specifically to determine their effects on Colorado River water storage and deliveries, with particular attention to changes in water available to current consumptive users. On one extreme, making additional system water releases for the Delta from Lake Mead would reduce expected deliveries in Arizona by 2.7 percent, in Nevada by 1.7 percent, and in California by 0.2 percent by the year 2060. In contrast, leasing water from existing uses for the Delta could have a slightly beneficial effect on other existing uses in the United States. This article does not seek to advocate one particular alternative over another, but to provide an understanding of the impacts of these alternatives.