Lab 3 hydrological application using GIS

Deriving Runoff CharacteristicsArcGIS Flow Diagram

Load DEMLoad DEM

Fill sinksFill sinks

Compute flow directionCompute flow direction

Compute flow accumulationCompute flow accumulation

Define a pourpointDefine a pourpoint

Generate watershedGenerate 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

67 56 49

52 48 37

58 55 22

30

67 56 49

52 48 37

58 55 22

30

45.0230

4867

50.0

30

5267

Slope:

Hydrologic Slope - Direction of Steepest Descent

Flow Direction ArrowsBased on Direction of Steepest Descent

Elevation Flow Direction

32

16

8

64

4

128

1

2

Eight Direction Pour Point Model

ArcGIS Flow Direction Encoding

ArcGIS Flow Direction Raster Encoding

Flow AccumulationNumber of Cells Contributing Flow

Flow AccumulationValue = 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