Lab 3 hydrological application using GIS

Deriving Runoff Characteristics ArcGIS Flow Diagram Load DEM Fill sinks Compute flow direction Compute flow accumulation Define a pourpoint Generate watershed

Filling Sinks DEM creation results in artificial sinks in the landscape A sink is a set of one or more cells which has no downstream cells around it Unless these sinks are filled they will isolate portions of the watershed Filling sinks is the first step for processing a DEM for surface water systems

Slope: Hydrologic Slope - Direction of Steepest Descent

Flow Direction Arrows Based on Direction of Steepest Descent ElevationFlow Direction

Eight Direction Pour Point Model ArcGIS Flow Direction Encoding

ArcGIS Flow Direction Raster Encoding

Flow Accumulation Number of Cells Contributing Flow Flow Accumulation Value = Number of Cells Flowing Into Flow Direction

Delineating Surface Water Drainage

Calculating Uniform Depth of Precipitation using Theissen Polygons

Areal Estimation The Thiessen polygon approach is a geometric method for assigning areal weights to each gauge based on a nearest neighbor approach. Thiessen polygons are constructed by: (1) Connecting each gauge in a triangulated network (2) Intersecting each triangle edge by a perpendicular bisector (3) Deriving polygons from the bisector edges and watershed boundary

Areal Estimation Thiessen Polygons