Ephemeral streams are a key component of nutrient transport, hydrologic function, and ecological productivity in southwestern rangelands. Though geomorphic change is integral to watershed evolution, significant erosion or sediment deposition can be both an indication of and precursor to poor watershed health and upland vegetation degradation. This study had two primary objectives: (1) identification and quantification of geomorphologic changes of ephemeral stream reaches in the Altar Valley, a 610,000 acre rangeland southwest of Tucson, Arizona, between 2011 and 2016 and (2) assessment of the geomorphological impacts on ephemeral reaches following the construction of a natural gas pipeline in 2014. Using multi-temporal LIDAR data, the Automated Geospatial Watershed Assessment (AGWA) GIS tool, and ground-truthing, the study assessed the four main criteria impacting erosion rates in rangelands: climatic events, upland vegetation, soil characteristics, and slope. The experiment design included weekly or bi-weekly cross section measurements upstream, downstream, and across the pipeline right-of-way of ten study washes of varying size, upland vegetation cover, and channel bed material. Preliminary results of the disturbance study suggest increased sediment deposition downstream of the pipeline right-of-way when compared to the control upstream cross-sections. Variability in geomorphic response was linked to upland vegetation, channel bed material, and individual ephemeral stream treatments. ��Identification of stream reaches with significant geomorphic changes and their contributing upland areas can be used as a tool to inform land managers on locations of priority management.
Oral presentation and poster titles, abstracts, and authors from the Society for Range Management (SRM) Annual Meetings and Tradeshows, from 2013 forward.