Constraints to Water Transfers in Unadjudicated Basins: The Middle Rio Grande as a Case Study

摘要

Water transfers are viewed as a voluntary mechanism through which water can be reallocated in semi-arid areas in the southwestern United States. Despite the disproportion of marginal benefits received by various uses in the Middle Rio Grande of New Mexico, transfers are not frequent occurrences. This paper evaluates the process by which transfers are evaluated, and explores the notion that lack of supply of tradable rights constricts water markets.The Middle Rio Grande is a long, narrow, semi-arid region in New Mexico extending approxi-mately 160 river miles from the outlet of Cochiti Dam in the north to Elephant Butte Reservoir in the south. By most accounts, water in the region is grossly over-allocated, meaning there are far more claims to water than actual water. The basin must deal with significant hydrologic variance; the standard deviation of the Rio Grande's annual flow is nearly half of the mean. Shortages are frequent, and fights between uses are common, even in years of relatively high supply.In 2003, the Middle Rio Grande Water Assembly drafted a regional Water Plan (MRGWA 2003). The purpose of the plan was to evaluate water use and the water supply of the region. The plan also attempted to quantify the regional water deficit, meaning the amount of water consumed that is over the natural rate of recharge. The water plan estimates the regional deficit at roughly 55,000 acre-feet annually.The Middle Rio Grande is a fast-growing region, containing the booming cities of Albuquerque and Rio Rancho. Between 2000 and 2005, the population of Bernalillo Country grew 8.6 percent, to 603,562 inhabitants (US Bureau of the Census 2007). This growth is leading to an increase in water demand adding strain to the region's water supply.The presence of two endangered species has further complicated the water conundrum of the Middle Rio Grande. Therefore, the need to protect these species has created changes in the management of low stream flows. The Rio Grande Silvery Minnow (Hybognathus amarus), and the Southwestern Willow Flycatcher (Empidonax traillii) are both Federally protected species. These species have specific habitat requirements related to stream flows, and it is possible that transfers could be prevented, or at least delayed, because of species' needs. In Rio Grande Silvery Minnow v. Keys (2002), Judge Parker ordered a cessation of diversions from the Rio Grande until minimum stream flows were met at various locations in the Middle Rio Grande. A new Biological Opinion, along with new water operations are in place, but the possibility of water being reallocated from water users to endangered species still exists. At this time, individual transfers are not evaluated for their impacts on these species. Larger transfers and the cumulative impacts of transfers are considered by various member entities in the Middle Rio Grande Endangered Species Act Collaborative Program – a Federally-funded multi-jurisdictional governmental organization dedicated to the protection of the species.Albuquerque and its smaller neighbor Rio Rancho have investigated the use of large water projects, including trans-boundary water reallocations and ground water desalinization, as a mechanism to increase water supplies. Albuquerque has recently completed a surface water project that will allow it to withdraw non-native water from the Rio Grande, water that originates in the Colorado River Basin and is pumped into the basin via a tunnel system under the San Juan Mountains. When flows are adequate, the City can divert up to 94,000 acre-feet annually to meet a portion of its water demand. The city can consume 47,000 acre-feet, and the rest must be returned to the River system at the City's waste water treatment facility (U.S. Bureau of Reclamation 2004). Rio Rancho has explored the use of a deep saline aquifer approximately 2,500 feet below the surface (Clark 2009).In the absence of additional large water projects, reallocation from existing uses may be