Abstract

Automating Hydro-Enforcement on Sub-Meter Terrain Grids
Track: Water Resources
Authors: Brian Quinn

Local government enforcement of creek protection ordinances often relies on accurate, detailed, and objectively determined flow line features. Creek protection issues can exist well upstream of typical NHD features.
Since 2009, County of Marin compiled topographic and bathymetric data into a single comprehensive model, using ESRI Terrain Dataset to yield a 45-cm gridded surface useful for contouring, hillshade, and many cartographic uses.
To automate refinement of county NHD flowline features, ArcHydro-style grid analyses of this terrain were performed, and the harmonization of synthetic flow lines with existing mapped creek features became a priority. When ephemerals are mapped below 1/3-acre catchments, a great many small areas of DEM-fill must be drained; every culvert under every road must be represented. With ArcInfo 10 Spatial Analyst and Python scripting, we automated the detection of nearest drain points to minima within filled areas, solving about 2500 per hour, greatly reducing need for manual hydro-enforcement.