Reflections on Exercise 4 There is a lot of stuff going on when we execute the Arc Hydro terrain processing and watershed delineation tools. Lets think a little bit about what this means

Duality between Terrain and Drainage Network Flowing water erodes landscape and carries away sediment Topography defines drainage direction on the landscape Threshold drainage area to define a stream: 4.5 km2 (20,000 15m DEM cells)

Catchments For every stream segment, there is a corresponding catchment Catchments are a tessellation of the landscape through a set of physical rules

Raster Zones and Vector Polygons One to one connection DEM GridCode Raster Zones 3 4 5 Catchment GridID Vector Polygons

Area goes to Line Connectivity For each catchment there is a unique drainage line GridID is same on both Catchment and Drainage Line

Watershed A watershed is the area draining to any point on the stream network A new kind of connectivity: Area flows to a line on a point

HydroID – a unique identifier of all Arc Hydro features HydroIDs of Drainage Points HydroIDs of Catchments

JunctionID – HydroID Relationship The JunctionID of a drainage area is the HydroID of its outlet point Can build and store relationships in the geodatabase to preserve these connections