Summary
The HAND (Height Above the Nearest Drainage) tools compute the vertical distance from each cell to the nearest drainage cell and provide rasters useful for flood mapping and hydrologic analysis. HAND rasters are typically derived from a DEM and a stream/drainage raster and can be used to identify low-lying areas relative to channel elevation.
Tools
| Tool | Description |
|---|---|
| Catchment Hydraulic Geometry | Computes reach length average hydraulic geometry and synthetic rating curve flow for river reaches within specified catchments using Height Above Nearest Drainage (HAND) concepts. For each stage height, it calculates wetted area, bed area, volume, cross-sectional area, wetted perimeter, hydraulic radius, and discharge based on Manning’s equation. Inputs include HAND raster, catchment ID raster, slope raster, stage height table, and a catchment list with slope, length, and optional roughness. Output is a table of hydraulic properties for each catchment and stage. |
| Inundation Depth | Generates an inundation depth map for river reaches based on forecasted flows and precomputed hydraulic properties. It uses the Height Above Nearest Drainage (HAND) raster, catchment IDs, and a synthetic rating curve to interpolate stage from flow, then computes cell inundation depth as max(stage − HAND, 0). Inputs include HAND and catchment rasters, optional mask, a flow forecast table, and hydraulic property table from catchhydrogeo. Outputs a raster file of inundation depths and optionally a CSV of reach depths. |