High-Frequency Sensing of Sediment Hysteresis to Understand Storm Event Dynamics Across an Urbanization Gradient

Abstract:

Storm events play a key role in the mobilization and delivery of sediment to stream corridors. Therefore, effective catchment management requires a profound understanding of how sediment source zones and transport pathways vary within and between storms across multiple land uses. We used high-frequency 15-minute turbidity data from 2002 to 2014 to identify key drivers of sediment dynamics during ~850 storms across five watersheds with different land uses, ranging from near-total rural to complete-urban. Hysteresis patterns were categorized and a variety of metrics (hysteresis index, flushing index) were used to quantify watershed-response to storm events. Further, a suite of hydrological and meteorological variables was analyzed to determine the impact of antecedent conditions, runoff, and precipitation on hysteresis patterns. Results indicate that Indian Creek and Mill Creek, the most urban watersheds, have the greatest proportion of CCW events, 55.97% and 62.23%, respectively. We attribute the CCW behavior to spills from combined sewer overflows and wastewater treatment facilities (WWTF) as well as the connectivity of more distal sediment sources in urban watersheds compared to agricultural systems. On the other hand, the more rural watersheds, Blue River, Kill Creek, and Cedar Creek, have a less proportion of CCW patterns, 35.98%, 36.36%, and 36.26%, respectively, indicating the more contribution of proximal sediment sources to the watershed outlet in these basins. Indian Creek, the most urban watershed, has also the largest average magnitude of flushing index (FI = 0.73) due to the rapid flushing of materials during storm events. Moreover, our results indicate that clockwise patterns are generally associated with higher total rainfall (p̅ = 0.08) and flood intensity (p̅ = 0.15) showing ample sediment supply in areas nearby the channels. The results of this study demonstrate the potential of high-frequency sensors to identify variations of active source zones and transport mechanisms of sediment through time and their relationship with hydrological, land use, and climatic conditions.