ABSTRACT:

Accurately predicting the magnitude and timing of overbank flooding is crucial for protecting communities. Floodplains attenuate floods and can reduce downstream impacts, yet large-scale routing models such as the National Water Model (NWM) represent floodplains as confined compound channels, potentially limiting the ability to model attenuation. Recent advances in topographic datasets now allow more realistic representation of floodplain geometry, but the benefits of this added complexity on flood prediction are untested and likely vary across hydrogeomorphic settings. We evaluated the influence of topographically derived cross-section geometry (FULL topography) on flood hydrographs across the Lake Champlain Basin, USA, by developing reach- and basin-scale Muskingum-Cunge routing models using both NWM and FULL topography, driven by NWM Retrospective hydrologic inputs. At the reach scale, FULL topography reduced peak discharge by <10% and celerity by 30-50% relative to the NWM. Celerity reductions were largest in wide, well-connected, low-gradient floodplains with large drainage areas, while peak discharge reductions were greatest in headwater reaches. FULL topography improved flood prediction in ~45% of test cases, primarily where floodplain and wetland area was extensive and the NWM overpredicted peaks. Results highlight the potential for floodplain topography to improve routing performance and begin to inform development of spatially heterogeneous flood routing frameworks.

ABSTRACT:

In June 2021, a catastrophic forest blowdown brought measurable amounts of large wood into valley bottoms and river channels across the Wombat State Forest, Victoria, Australia. Large wood loads, reach-scale morphologic characteristics that might influence large wood recruitment and storage, and sediment and water storage behind large wood pieces and jams were recorded in select creeks across the Wombat State Forest in July 2022. This resource includes two datasets of large wood data collected at the reach and piece scale in the Wombat State Forest.