An Ecogeomorphic Evaluation of the Post‐Flood Restoration of the Little Thompson River: A Colorado Front Range (USA) Stream

ABSTRACT River restoration is a multibillion‐dollar industry, but oversight, assessment requirements, and frameworks remain disparate. This study examines the case of the Little Thompson River (Colorado, USA), a mountain stream disturbed by a 2013 flood (500‐year recurrence interval) and subsequently reconstructed for flood mitigation. We compare the Little Thompson River Restored Site to a Reference tributary impacted by the same flood event, allowing for an assessment of stream recovery under different circumstances. Results suggest the Reference Site is in a quasi‐equilibrium with ecogeomorphic variables, while the Restored Site is not. The Restored Site had a step‐pool/pool‐riffle design but a plane‐bed slope (0.024 m/m). Grain‐size analysis showed a distribution ( D 50 = 55 mm and D 90 = 126 mm) not mobilized by typical flows (e.g., 2‐year), and most flows (> 2‐year) would not inundate the floodplain region. The Reference Site had expected (based on reference systems with similar watershed positions) pool‐riffle morphology and grain size (slope = 0.013 m/m; D 50 = 38 mm and D 90 = 108 mm), is mobilized by typical flows, and the floodplain region inundates at flows > 2‐year. Vegetation surveys showed that only Salix and naturally recruited Populus are prolific at the Restored Site, while the Reference Site has a denser and more diverse plant community. Our study suggests allowing for natural plant succession, primarily recruitment of Populus , complemented with low‐cost, effective, simple Salix plantings, and preserving seed banks where possible could aid future restoration projects. Our results raise questions about the efficacy of channel construction and revegetation efforts in post‐flood restoration of mountain streams and highlight simple recommendations for future restoration projects.