South St. Vrain Creek Restoration at Hall Ranch Longmont, Colorado
With the goal of re-establishing its floodplain connectivity, the restoration of St. Vrain Creek enhances aquatic habitats, restores riparian health, and improves stream resiliency. The multi-objective design incorporates features to mitigate future flooding and moderate sediment loads from inundating the Town of Lyons.
Restoring a Floodplain for More Resilient Habitats and Community Flood Mitigation
Central to the design development was a thorough understanding of sediment dynamics and hydraulics. Sediment dynamics were assessed by modeling and comparing reach-scale capacities. The restoration involves approximately 3.2 miles of South St. Vrain Creek, extending from the canyon mouth to the Old St. Vrain Road bridge near the Town of Lyons. Channel hydraulics were assessed by 2D modeling of the study area using the Sedimentation and River Hydraulics 2D (SRH-2D) model, developed by the Bureau of Reclamation. The model informed the design with an understanding of the complex linkages between main channel and floodplain flow, including floodplain benches, overflow channels, and more than a dozen large wood structures throughout the reach. The project team worked with stakeholders to collect feedback and turn concerns into project goals. Otak led the channel restoration design, 2D hydraulic modeling, geomorphology, and sediment transport analyses for this CDBG-DR grant-funded restoration project.