Conditioning digital elevation models for use in the evaluation of river networks and height above the nearest drainage for flood inundation mapping

Presentation for AWRA Geospatial Technologies Conference held Virtually August 4-13, 2020. This presentation on August 12. https://www.eventscribe.com/2020/AWRAGIS/

Flood inundation is difficult to map, model, and forecast because of the data needed and the computational demand. Recently an approach based on the relative elevation, or Height Above Nearest Drainage (HAND), which is derived from a digital elevation model (DEM), has been suggested for both flood mapping and obtaining reach hydraulic properties and synthetic rating curves. These products are only as good as the underlying DEM from which they are derived and better DEMs offers the potential for improving model representations of streams and parameters derived from DEMs used in hydrologic and flood inundation modeling and mapping. This presentation will review the approach for using relative elevation in flood modeling, describing how HAND is calculated, how it is used to map flood inundation for stream reach catchments and how it is used to determine stream reach properties, identifying shortcomings and giving ideas for improvements. As we obtain more detailed information on bathymetry, topography and hydrography it is important to establish a consistent data model for the river bed that is used in HAND related work that aligns and reconciles elevation and hydrography. This presentation will discuss approaches for using hydrography to remove DEM obstacles, the segmentation of streams used in deriving HAND reach average hydraulic properties and ideas for quantifying reach average roughness based on HAND and flood inundation mapped from remote sensing of previous floods with measured discharges.