Abstract
Flood-restoration and flood-resilience within an urban corridor
We evaluated the effectiveness of a river engineering project conducted for flood-restoration and flood-resilience within an urban corridor (Resilient St. Vrain Project; Longmont, Colorado, USA) by characterizing: 1) vegetation-channel-flow relationships, 2) geomorphic complexity and bed mobility, and 3) the ability of the St. Vrain to withstand future 100-year flow events. As such, we collected physical and ecological parameters within the reconstructed and re-vegetated channel that reduced the footprint of the floodplain and increased the conveyance capacity within a narrower active 100-year flood zone. We found the functional traits of the revegetation plan to have variable outcomes regarding diversity and roughness, depending on the implementation location and time, reflected by varying Shannon’s diversity index in different reaches as well as certain areas with high vegetation roughness (n > 0.25). Certain woody species demonstrated characteristics expected to enhance sediment aggradation because of high rigidities and/or high densities. The revegetation strategy relied exclusively on a one-time irrigated planting strategy and a plan to remove any naturally recruited vegetation (whether native or exotic) indefinitely. There is uncertainty about the ecological function of the riparian corridor under such a strategy.
Shear-stress divergence from hydraulic modeling predicts locations of grain-size changes and depositional areas. We found channel slope and grain size to be adjusting to the reconstruction. Slope was as designed (0.003) for the entire study area, but with some local variations likely responsible for grain-size patterns as the profile adjusts. Grain size and topographic surveying indicate certain areas of fine-grained deposition, but a coarser grain size than expected for a pool-riffle setting overall. Slope was as designed (0.003) for the entire study area, but with some local variations (concave-up sections near Price Road and pools near Dickens Farm) likely responsible for grain-size patterns as the profile adjusts. Nevertheless, the channel design has the capacity to carry a 100-year flood.
Biography
Sharon Bywater-Reyes, Associate Professor of Environmental Geoscience
University of Northern Colorado
As an associate professor of Environmental Geoscience at the University of Northern Colorado, Dr. Bywater-Reyes studies and teaches about rivers and Earth surface processes. She received her Bachelor’s Degrees in Geology and German from Southern Oregon University, Master’s Degree in Geology from the University of Wyoming, and Ph.D. in Geosciences from the University of Montana. Her research is multifaceted, considering interactions among geology, hydrology, geomorphology, biota, and disturbances. Using field, remote sensing, experimental, and numerical approaches she studies: 1) controls on water quantity and quality; 2) natural and anthropogenic controls on sediment routing; and 3) controls on river form and function. She teaches introductory geology, hydrology, soils, and geomorphology. In her spare time, she likes to spend time outside, with her family, exercising, and crafting.