USING AN HISTORIC ANALYSIS TO INFORM HABITAT RESTORATION EFFORTS: A CASE STUDY OF THE STRAWBERRY RIVER, UTAH

An historical analysis of a degraded river system can aid the selection of appropriate management objectives and restoration strategies by characterizing natural system variability and identifying sources of degradation. In this study, we analyze a decades-long aerial photograph record to calculate historic bank erosion rates, planform characteristics, and riparian cover of the Strawberry River, Utah, a site of ongoing riparian and instream habitat restoration. We use this analysis in conjunction with pre- and post-project channel surveys and streambed samples to evaluate restoration goals and strategies. Erosion rates have declined over the past two decades, concurrent with the removal of livestock grazing and the return of natural flows. Contrary to perception, erosion rates of the past decade were actually lower than historic rates. Furthermore, we show that channel width and sinuosity peaked during the period of no riparian cover, but have remained relatively static over the past two decades. Streambed samples support the finding that present-day bank erosion rates are not excessive relative to historic rates; the percentage of fine sediment in the substrate is insufficient to have a significant biological impact. Taken together, these results show that bank erosion rates were not high prior to restoration and bank erosion is not currently contributing fine sediment to spawning gravels in this system. We show how quantitatively evaluating perceived sources of degradation and assessing current conditions can potentially increase restoration effectiveness.