Presenter/s: Daniel Scott
Symposium Session: 2020 - 04 Observe Stage 0
Topics covered: beavers, lessons learned, monitoring, and sediment transport
Stage 0 Restoration seeks to restore natural fluvial processes to valley bottoms to sustain a spatially heterogeneous and dynamic morphologic state that can then support a robust and resilient fluvial ecosystem. While monitoring the ecological response of Stage 0 restoration is feasible and effective, the multi-channel, dynamic, and wood-rich state produced by restoration complicates monitoring of the geomorphic response that underpins fluvial ecology. We address these monitoring challenges by testing a geomorphic complexity-based monitoring approach that integrates both spatial and temporal data from a Stage 0 restoration site on Deer Creek, Oregon. We present the geomorphic and wood dynamics outcomes immediately following restoration, the moderate-term geomorphic trajectory pre- and post-restoration, and short-term wood jam dynamics post-restoration.
Our monitoring framework seeks to capture how restoration influences: valley bottom spatial heterogeneity; variability, or dynamism, in valley bottom morphology through time; and the trajectory of geomorphic response before and after restoration. We accomplish this by mapping high- and low-altitude aerial imagery to quantify valley bottom metrics of spatial heterogeneity. We contextualize these measurements of spatial heterogeneity by conducting this mapping over a period covering 11 years pre-restoration and 3 years post-restoration, which allows us to evaluate both the dynamism of channel morphology from year to year and the moderate-term trend in geomorphic response both pre- and post-restoration. Because the geomorphic response to Stage 0 restoration depends on wood jam dynamics, we also apply the recently developed Wood jam Dynamics Database and Assessment Model (WooDDAM; a standardized field protocol and online database for monitoring and understanding wood jam dynamics) to survey wood jam characteristics and dynamics along Deer Creek. We use the broader WooDDAM database, consisting of hundreds of observations of wood jam dynamics, to contextualize and explain wood jam dynamics in Deer Creek.
We find that valley bottom-focused metrics, such as the ratio of active channel to valley bottom area and the Shannon equitability index (a measure of the relative distribution of morphologic patches across the valley bottom) are most representative of the ecogeomorphic processes targeted by Stage 0 restoration, such as channel migration, avulsion, widening, vegetation establishment on deposited surfaces, and vegetation recruitment to the channel. They are also more robust to data quality issues and mapping errors than more traditional metrics such as braiding indices. We use data and observations from Deer Creek to make recommendations on how to effectively monitor the geomorphic response of other Stage 0 restoration projects. We also present results from monitoring of Deer Creek, demonstrating that monitoring must both capture relevant indicators of processes and account for flow history. We present this research to help improve monitoring and understanding of the geomorphic effects of complex, valley bottom-scale river restoration.