HecRas model for Bywater-Reyes et al. (2026) Resilient St Vrain Assessment

Dataset associated with Bywater-Reyes et al., 2026, Lessons Learned from a Post Flood-Reconstruction Project of an Urban Stream (Resilient St. Vrain, Longmont, Colorado, USA), Geomorphology HecRas model To assess sediment transport dynamics (Objective 1), vegetation-flow dynamics (Objective 2), and capacity to transport the 100-year flood (Objective 3), we constructed a 1D hydraulic model in HEC-RAS 6.5 following the procedure described in Merwade (Merwade, 2016). We combined topography from in-stream RTK surveys, SfM, and as-built topography data provided by the contracted engineering company (CH2M). Roughness was mapped spatially based on grain-size and vegetation parameters as follows. Vegetation polygons were extracted from thresholded NDVI, by visually matching the minimum threshold to observed vegetation regions (NDVI = 150). Overbank areas were assigned a Manning’s roughness of n = 0.035 whereas within-channel areas were assigned 0.040. Extremely rough areas (e.g., riprap/engineered tubing structures) were designated as inefficient flow areas. Vegetation roughness was scaled to the values found from vegetation surveys for each reach according to equation 4, where C_D and y were set equal to 1 for simplicity. Boundary condition was set to normal depth with the reach-average slope (0.003). Five flows were modeled, ranging from a low-flow to the engineered flow ranging from 430 to 20 m3/s, corresponding to a recurrence intervals of 2 through 100 years (Table 2). Measured downstream stage from the State of Colorado Gauge (SVCLOPCO) was 1.83 m for discharge equivalent to PF5, which was within 10% of modeled values, providing support for model performance (Segura & Pitlick, 2015).