Effect of Channel Restoration on Flood Wave Attenuation

Re-establishment of floodplain hydraulic function is increasingly a goal of restoration programs, yet the approximate magnitude of possible change to attenuation due to reach-scale restoration remains poorly quantified. The efficacy of channel restoration on flood attenuation was examined using restored reaches and synthetic reaches representing median dimensions of channel restoration projects in North Carolina (e.g. ∼ 1 km in length). An industry standard dynamic flood routing model (UNET in HEC-RAS) was utilized to route floods in impaired and restored reach models. Our study showed that the predominantly small scale of current channel restoration will provide minimally quantifiable enhancement to flood attenuation. Sensitivity analysis demonstrated that attenuation of peak discharge is overall most sensitive to channel and valley slope, channel and floodplain roughness, and channel and valley length in decreasing order, but is dependent on flood magnitude. Floods of intermediate magnitude (between 2 and 50 yr return interval) were impacted most by restoration.