1. Lab 3 hydrological application using GIS

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

3. 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

4. 675649 524837 585522 30 675649 524837 585522 30 Slope: Hydrologic Slope - Direction of Steepest Descent

5. Flow Direction Arrows Based on Direction of Steepest Descent ElevationFlow Direction

6. 32 16 8 64 4 128 1 2 Eight Direction Pour Point Model ArcGIS Flow Direction Encoding

7. ArcGIS Flow Direction Raster Encoding

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

9. Delineating Surface Water Drainage

10. Calculating Uniform Depth of Precipitation using Theissen Polygons

11. 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

12. Areal Estimation Thiessen Polygons