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The federal Endangered Species Act is a powerful tool in the process of protecting western rivers. The endangered status of the Rio Grande silvery minnow is attributed to hydromodification, primarily over-diversion in the Middle Rio Grande Project service area, where an average of 12 af of water are diverted to serve crops requiring 2-3 af of water. As many as 60 linear miles of the Rio Grande had zero flows in 1996.
Albuquerque's Water Resources Strategy calls for increased surface water diversions that, if not mitigated, are likely to result in further risk to the minnow. Additionally, increased depletions threaten to destabilize New Mexico's already shaky record of compliance with its Compact delivery obligations.
Environmentalists and agency stakeholders have convened a working group seeking strategies for "keeping the river wet", in effect protecting and even augmenting, Elephant Butte inflows.
Some important elements of the upstream search for sources of water are:
Irrigation efficiency improvements-Perhaps the basin's brightest hope is that so much of the Rio Grande's water is so inefficiently used; 90% of the basin's farms flood irrigate (USGS, 1993). On- farm uses are not measured, nor are net depletions. A reasonable expectation is that 10-20% of existing diversions can be foregone by a combination of district efficiency improvements and on-farm conservation measures. If these are not implemented, or if they prove unsuccessful, the Middle Rio Grande Conservancy District may be pressured to curtail a portion of their water use. In any case, serious revamping of MRGCD's water operations, which has been based on the law of capture, is a virtual certainty.
Upstream Reservoir Storage-Evaporation from Elephant Butte averages 180 kaf per year, principally due to its location in an area that averages 80 inches per year of evaporation. Reducing the volume of water in storage at Elephant Butte could conserve some of this amount. For example, evaporation losses at Abiquiu Reservoir average about half of those at Elephant Butte.
In addition, conjunctive use scenarios (groundwater-surface water co-management) proposed for the Albuquerque groundwater basin offer the intriguing alternative of utilizing this aquifer to store Compact water presently held in Elephant Butte.
Federal Water Operations-Streamflow is determined by a combination of water delivery obligations and water management decisions. Historically, the timing of Compact deliveries has been weighted to the off-irrigation season (October-March) to reduce evaporation losses and avoid subjecting Compact water to interception, as would occur in the summer irrigation season.
Recognizing the environmental restoration benefits to be gained from modifying water operations, both the Army Corps of Engineers and USBR are poised to commit to managing water releases to more closely mimic the natural hydrograph. The agencies (including the NMISC) are jointly conducting a Water Operations Review to guide future Rio Grande water operations from El Vado, NM to Ft. Quitman.
A broad partnership (including the U.S. Geological Survey) is in the process of creating an "Upper Rio Grande Water Operations Model" (URGWOM) to calculate water supply effects of various operational scenarios. These efforts, which coincide with Endangered Species Act mandates to address the silvery minnow's grave difficulties, promise a greater degree of intentional balance among water uses and more flexible water management that explicitly includes the environment.
San Juan-Chama Project-This is an interbasin diversion (of ~100kaf, annually) water from the San Juan River to the Rio Grande. Project water is stored at Heron reservoir, with a capacity ~600 kaf the past, SJ-C water has been used to offset depletions of native water and tributary groundwater, and thus has been available to the river. Now Albuquerque and Santa Fe have announced plans to divert their SJ-C entitlements (~53 kaf collectively). Approximately 43 kaf is still not scheduled for consumptive use and some portion of this may be available for purchase as environmental water. Rio Grande Restoration is seeking a purchaser for 5-10 kaf of the SJ-C to test the "beneficiality" of instream uses under NM state water law and begin implementation of a "source to sea" protection program for streamflow (Harris, 1999).
There are several other potential sources of streamflow embedded within the SJ-C Project: (1)There's still ~5 kaf of "uncontracted for water" and (2) flexibility within the firm yield of the project (which has diverted as much as 40 kaf more than contracted for in a given year). The City of Albuquerque's aquifer storage and retrieval plan includes a strategy to curtail its SJ-C diversions in favor of the river, at certain drought thresholds. The City of Santa Fe is organizing the SJ-C contractors, who may consider organizing a drought water bank.
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