USING DEBRIS-FLOW HAZARD DATA TO PLAN AND IMPLEMENT LANDSCAPE-SCALE WATER SOURCE PROTECTION IN THE RIO GRANDE WATERSHED

The Rio Grande Watershed in New Mexico (NM) has experienced several recent wildfires in forested tributaries that have negatively affected water supply infrastructure jeopardizing water supply delivery for downstream water users. Although the exact location, extent, and severity of wildfire or subsequent rainfall intensity and duration cannot always be known, probabilities of fire and debris-flow occurrence for given locations can be estimated with geospatial analysis and modeling. Potential probabilities and estimated volumes of postwildfire debris flows in unburned and previously burned mountainous areas of the Rio Grande Watershed were estimated using empirical debris-flow models developed by the U.S. Geological Survey (USGS) in combination with fire behavior and burn probability models developed by the U.S. Department of Agriculture Forest Service. This prewildfire assessment approach is valuable to resource managers in order to facilitate wildfire management, planning and mitigation before an event occurs.

To lessen the severity of wildfires and their impacts to Rio Grande water supplies, The Nature Conservancy has established the Rio Grande Water Fund. The Rio Grande Water fund engages a diverse group of upstream land managers and downstream water users in a process of assessing wildfire risk and securing necessary funds for forest restoration planning, implementation, and monitoring. A critical parameter used to assess wildfire risk to downstream water supply is debris-flow hazard within upstream forested watersheds. In 2015 and 2016, the USGS conducted prewildfire debris-flow hazard assessments along upstream watersheds of the East Mountains near Albuquerque and the Jemez Mountains near Los Alamos; two critical mountain ranges which contribute to the Rio Grande in NM. The output of these debris-flow hazard analyses has been used by the Rio Grande Water Fund stakeholders to prioritize available funding for forest restoration treatments which reduce catastrophic wildfire risk and subsequent debris-flow impacts to water supply.