Streamflow Conditions and Annual Availability for Streams of the San Juan–Chama Project, Southern Colorado

The Albuquerque–Bernalillo County Water Utility Authority (ABCWUA) supplements the municipal water supply for the Albuquerque metropolitan area with water diverted from the Rio Grande that is derived from the San Juan–Chama Project (SJCP). The U.S. Geological Survey, in cooperation with ABCWUA, has compiled historical streamflow to characterize streamflow conditions and annual flow variability of three streams within the SJCP. Nonparametric statistical methods were applied to calculate summary statistics of streamflow and trends in streamflow conditions. The study area included the Rio Blanco, Little Navajo River, and Navajo River. The variability in seasonal distribution of streamflow was more strongly controlled by the variability in the total annual discharge than by long-term trends in streamflow. Streamflow indicators, including the date of the start of snowmelt-derived runoff, the date of selected percentiles of annual discharge, and the center of mass of the annual discharge, occurred at later dates in years with higher annual discharge. In general, years with higher annual discharge had a smaller percentage of annual discharge in March, a larger percentage of annual discharge in June, and a larger monthly discharge in June compared to years with reduced annual discharge. Additionally, snowmelt-derived runoff occurred later in the year and had a longer duration in years with higher annual discharge. Streamflow conditions at the Navajo River varied nonmonotonically over time and were likely a function of complex climate pattern interactions. Streamflow conditions at the Navajo River varied over time such that annual discharge was generally lower than the median during a negative Pacific Decadal Oscillation (PDO) interval and higher than the median during a positive PDO. Study results indicated that the median of the sum of the streamflow available above the minimum monthly bypass requirement for the SJCP from 1975 to 2010 for the three streams within the SJCP was 126,240 acre-feet.