Bank Height Estimates and Flood Models - Challenges, current practices and recent developments

Estimating river bank heights is crucial for the accuracy of global flood models. Bank heights determine river-floodplain connectivity, and are used to parametrise channel capacity. Poor bank height estimates can lead to incorrect timings and locations of flood overtopping and erroneous channel capacity, resulting in unsatisfactory flood predictions.

In the current implementation of global flood models, bank heights are estimated by extracting elevations from global Digital Elevation Models (DEMs) at river edges. These elevations, even with the latest DEMs, are often noisy and thus need to be heavily filtered and smoothed. Additionally, the surface water masks used to define river edges often do not match the time of acquisition on the DEMs, leading to inconsistencies. These simple methods for estimating bank heights were introduced during the early stages of global flood model development and have not been revisited in depth. With the emergence of new global DEMs (ALOS AW3D, Coperncius, FABDEM), improved surface water masks from multi-temporal, multi-sensor satellite data and novel image processing techniques, we revisit this problem. We present a new method to estimate bank height across scales, comparing estimates derived from global DEMs with high-quality LiDAR. We map the bank height estimates onto a new FABDEM based river network. Using examples from the UK and USA, we demonstrate the impact of bank height estimates on flood inundation.