REGIONAL MAPPING OF FLOODPLAINS USING LOW-COMPLEXITY HYDRAULIC MODELLING REVEALS PATTERNS IN FLOODWATER STORAGE

Floodplains provide many ecosystem services including sediment and nutrient storage, support to aquatic and riparian habitats, and groundwater recharge. Floodplains also have the potential to reduce flood risk to downstream communities by storing floodwaters and attenuating peak discharges. As we continue to value the diverse functions of floodplains, it becomes important to map their geographical extent to support restoration and conservation activities.

In the US, floodplains have typically been mapped in a regulatory context for limited geographic extents in developed settings, relying on mechanistic models (e.g., HEC-RAS) that require substantial resources to parameterize and calibrate. Low-complexity hydraulic models that simplify the characterization of water movement across the landscape, require fewer resources, and have recently enabled mapping of floodplains at broader regional scales.

We used a low-complexity modeling approach to map floodplains along ~5000 km of river in the Vermont portion of Lake Champlain Basin for reaches draining greater than 5.2 sq km relying upon high-resolution (1m), lidar-derived Digital Elevation Models available for the region (acquired between 2013 and 2017). In this presentation, we discuss how mapped floodplains compared to inundation extents and high-water marks observed during the Great Vermont Flood of July 2023. Leveraging basin-wide stream geomorphic data, we also highlight natural and anthropogenic factors influencing floodplain capacity to store floodwaters and the variability across geophysical regions and stream types.