Evaluation of Hydrologic Alteration and Opportunities for Environmental Flow Management in New Mexico

How Cadmus performed extensive review spanning the breadth of the state

Cadmus was retained by the U.S. Environmental Protection Agency (EPA) to conduct an assessment of the hydrologic and ecological health of representative streams and rivers in New Mexico, including an evaluation of hydrologic alteration using continuous streamflow records.

Challenge

From small mountain headwaters to major river systems, New Mexico’s waters provide a source of drinking water, irrigation for crop and pasture lands, and a multitude of recreational opportunities for residents and visitors. The use of such resources has not come without costs. Municipal, agricultural, and industrial water use in the state has led to significant modification of New Mexico’s rivers. Additionally, river modifications, groundwater pumping along river corridors, and land-use changes have contributed to major changes in the natural flow pattern, or hydrologic alteration, of New Mexico’s streams and rivers.

The ecological implications of hydrologic alteration are diverse. New Mexico’s sensitive riparian and wetland ecosystems are shrinking and under increasing stress from water shortages, with native vegetation outcompeted by invasive species such as saltcedar. Populations of native fish species have dwindled as a result of habitat degradation, loss, and fragmentation. Rivers such as the Rio Grande and Pecos River, which once supported a diverse array of habitat and wildlife, have been reduced to simplified pipelines for the transport of water from one user to the next. These issues are compounded by water quality changes caused or aggravated by hydrologic alteration (e.g., concentration of salts, sediment, and other pollutants). Together, these impacts can affect state and local economies, and the well-being of New Mexico’s residents, through increased costs for addressing polluted waters or endangered species, and the loss of recreational opportunities.

Solution

Though hydrologic alteration has been well-documented for several of New Mexico’s largest rivers, no one had undertaken a comprehensive review of hydrologic alteration in the state prior to this project. Cadmus’ work offers a first step towards that goal by presenting an analysis of hydrologic alteration for 32 New Mexico stream sites spanning the breadth of the state and covering a range of hydrologic conditions:

• High-elevation headwater streams.
• Perennial and ephemeral snowmelt-dominated rivers.
• Ephemeral desert washes.
• Major river systems.

Using geospatial data and existing field data, Cadmus performed trend analysis of long-term flow records to identify changes in eight streamflow metrics that characterize the magnitude, frequency, duration, and timing of high- and low-flow conditions.

Each of the study watersheds was ranked according to the presence of current hydrologic alteration and vulnerability to future hydrologic alteration. The results of this analysis will inform environmental flow protection efforts in the State of New Mexico.

The final report is available to view or download on EPA’s website.