HYDROLOGY Our study reach extends along the Rio Chama from the Abiquiu dam to the confluence with the Rio Grande. Much like the rest of the Rio Chama watershed, this area faces myriad social and ecological challenges. Demographics are shifting as young people increasingly leave for cities, acequias are degrading due to higher flows and deferred maintenance, and the interests of the federal government, petroleum producers, and river-based recreation override the needs of the community and ecosystem. The watershed also has advantages: a 31-mile stretch of the river between El Vado and Abiquiu dams is protected as a Wild and Scenic River, administrative flow requirements virtually guarantee the river will not run dry, and strong social infrastructure advocates for the acequia system. The following will discuss the basic hydrology of the river so as to be able to take an informed approach to the social and ecological challenges and opportunities along the Chama.
RIO CHAMA WATERSHED The indicated stretch of the Rio Chama is primarily fed by the Colorado River as well as northern New Mexico snowpack and local thunderstorms (Platania, 1991). Precipitation on average is 9.8 inches per year at Abiquiu dam and 21.3 inches per year at the Chama weather station (OSE, 2009). The river flows heaviest in summer and fall, with lower levels in winter and spring. The Chama contributes about one third of the flow in the Rio Grande and also feeds 18 acequias via 12 diversions before the confluence (Harvey, 2018) and is the largest source of sediment in the Rio Grande (Parametrix, 2010). The river is fed by several smaller stream segments, many of which do not meet federal water quality standards for e. coli, turbidity, low dissolved oxygen, stream bottom deposits, high temperatures, and high levels of aluminum, ammonia, and phosphates (OSE, 2009); in fact, after the passage of the 1998 Clean Water Action Plan, the Rio Chama was designated Category I which indicates “a watershed in most urgent need of restoration” (Salvato & Crossey, 2013). Several fish species, such as the rainbow trout and Rio Grande sucker, are present in the river (Platania, 1991).
ANTHROPOGENIC CHANGES The Rio Chama is significantly altered from the “natural” state by several factors. The ever increasing encroachment of human settlements and infrastructure on the river is a factor, as in nearly every other environment, especially with regard to water quality and river geometry. Two major elements that have drastically altered the flow regime are the San Juan Chama Project (SJCP) and the addition of dams at Heron Lake, El Vado, and Abiquiu. In order to provide communities along the Rio Chama and Rio Grande in New Mexico, Texas, and Mexico with sufficient water, the SJCP diverts a portion of the Colorado River into the Rio Chama. This larger flow contributes about half of the total water in the Rio Grande below the Rio Chama confluence. For the 2017 water year (October 2016-September 2017), total discharge measured below El Vado dam was approximately 413,300 acre-feet; approximately one-fourth of this flow comes from the Colorado. This trans-basin water diversion has significantly increased river flows, adding an average of 100 acre-feet per year (AFY) from the Colorado River to the Rio Grande south of its confluence with the Rio Chama (Bean, 2018). The dams serve the dual purposes of flood control and water storage, preventing flooding during wet periods and allowing for the release of stored water during dry periods. Dams along the Rio Chama, particularly El Vado, have essentially cut peak flows in half through flood mitigation efforts. The reduction in heavy flows and increase in base flow has resulted in the Chama’s hydrograph being “squeezed:” although the river levels are higher overall, the peak flows (and associated flooding) are lower than before the SJCP (Parametrix, 2010). See the hydrograph here.
WATER QUALITY Contamination is a major problem along the study reach. The local geology, which is primarily sandstone, siltstone, conglomerate, shale, and limestone, can cause “problems with taste, odor, or other contamination of water from these aquifers” (OSE, 2009). Wastewater treatment plants serving Española and the Four Corners areas have been identified as point-source pollutants, as have the historically problematic Abiquiu treatment plant and the Los Ojos fish hatchery (OSE, 2009; Salvato & Crossey, 2013). Road and bridge runoff, streambank modifications, and most importantly septic systems have also been identified as major pollutant sources, leading to unacceptable levels of e. coli, nitrate contamination, and high temperatures among other issues along the study reach (OSE, 2009). Septic systems are particularly hazardous because they are widely used in the area and can result in higher levels of total dissolved solids, nitrate, parasites, etc. More information can be found here.
ECOSYSTEM SERVICES An essential consideration when evaluating the Rio Chama is the ecosystem services that it provides to human, animal, and plant life in the area. Surface water supplies 97% of the Chama planning region water, which includes local use as well as the much larger quantity of water promised to downstream users, a total known as the administrative water supply. In 2010, the total administrative water supply was 98,085 acre-feet (OSE, 2009). Much of the local surface water is used after being diverted along the 13 tributaries large enough to support agriculture, and the 23 small rural drinking water systems primarily rely on groundwater (ibid). The wells from which drinking water draw are stocked by alluvial aquifers that are “well-connected to the surface streams” (ibid). The acequia system supports local agriculture, and the acequias have deteriorated under the consistently elevated flow regime. Suggestions by the Rio Chama Acequia Association and others include starting winter releases earlier in the season in order to keep peak flows under 800 cubic feet per second (ibid). A major challenge with any proposition to alter river flows is how interconnected the ecosystem services are along the Chama. Riparian vegetation has suffered because the river no longer floods, but floods and high flows damage acequias.
References: Bean, Anjali, 2018. Opportunities to Enhance Environmental Flows on the Rio Chama. University of New Mexico.
Community By Design, Abeita Consulting, Southwest Planning and Marketing, 2009. Rio Arriba County Comprehensive Plan. Office of the State Engineer (OSE). http://www.rio-arriba.org/pdf/20/comprehensive_plan.pdf
Harvey, M. Lecture delivered at the University of New Mexico on 10/17/2018.
Parametrix, 2010. Restoration Analysis and Recommendations for the Velarde Reach of the Middle Rio Grande, NM. Middle Rio Grande Endangered Species Collaborative Program.
Platania, S.P., 1991. Fishes of the Rio Chama and Upper Rio Grande, New Mexico, with Preliminary Comments on Their Longitudinal Distribution. The Southwestern Naturalist. https://www.jstor.org/stable/3671919
Salvato, L., & Crossey, L.J., 2013. Hydrology and Water Quality of the Rio Chama River, Northern New Mexico: Establishing a Base Line to Manage Flows. American Geophysical Union.