Steps and pools are characteristic bedforms that dominate the channel morphology of steep mountain streams, regulating the flow and sediment dynamics feeding into lowland rivers and larger water bodies. In summer of 2012, several catastrophic wildfires spread across the Rocky Mountains of Colorado and burned numerous watersheds containing step-pool channels. These events provide opportunities to monitor the impacts of wildfire as a major disturbance on step-pool streams, and to ultimately develop predictive understanding of the resilience and potential recovery of such systems. This project seeks to quickly establish baseline conditions in step-pool channels before significant changes occur in response to the Waldo Canyon Fire. The Waldo Canyon Fire started on 23 June 2012 and was fully contained on 10 July 2012. It burned 18,247 acres of an area just northwest of the city of Colorado Springs, mostly on national forest land. Channel conditions in burned step-pool streams within the Pike National Forest will be documented at selected reaches. Temporary benchmarks installed in the study sites will provide bed elevations. Physical measurements include longitudinal profiles, cross-sections at pools, suspended sediment, and turbidity. Benthic macroinvertebrate samples will also be collected for analysis of wildfire impacts on benthic communities, particularly in relation to the impacts of changes in sediment regime in the streams.
The project will generate information that can be used by environmental managers who manage water resources for communities such as Colorado Springs while also working to protect residents from flood and sediment hazards. Because step-pool streams are important habitats for many sensitive aquatic species, results of this study are also expected to have implications for ecological management. The project will engage graduate and undergraduate students, and develop a collaboration with the US Geological Survey.
Mountains of the western United States are becoming more susceptible to wildfire as a result of warming climates. These trends have growing impacts on human society, evidenced in increasing numbers of structures destroyed by wildfire and related costs of damages and firefighting. Changing climate-fire regimes have significant indirect effects on hydrologic and geomorphologic processes. Because of the acute reduction of vegetation and organic matter, soils burned by fire are greatly altered, leading to elevated runoff, erosion, and flood potential years after fire. This RAPID (rapid-response) project established a monitoring program to track the recovery of step-pool mountain channels following the 2012 Waldo Canyon Fire of Colorado. At eight sites within the burn area in Pike National Forest (and three unburned reference sites), field surveys over two years revealed how the river channels responded to post-fire storm events. Sampling and analysis of benthic macroinvertebrates also documented changes in stream quality after fire. Results show that the first post-fire storm events widened and downcut many areas of the burned channels by more than one meter and obliterated the step-pool bedforms. The abundance, richness, and percent of sensitive taxa also decreased drastically within burned channels compared to the reference unburned sites. Channels that were able to retain a step-pool structure exhibited less ecological impact and facilitated recovery more readily. Although the morphology and ecological character of the burned channels appear to be recovering after two years, however, the ultimate trajectory of that recovery remains unclear. Particularly in areas where the processes of hydrologic, geomorphologic, and biologic recovery interact with human activities, longer timeframes are needed to decipher the effects of wildfire on river systems, and ultimately on human society. The data and findings from this project will assist with planning and mitigation efforts to reduce hazards from future wildfires, which are inevitably increasing. The project also facilitated collaboration among academic institutions, government and non-government agencies, as well as private organizations. The project further enabled training of graduate and undergraduate students in field and laboratory techniques. It also served as the basis for one M.S. student’s thesis.
