GISHydro97 - Terrain

Introduction

Terrain analysis describes a set of methods for doing calculations on a digital elevation model of the land surface to derive drainage patterns and delineate streams and watersheds. There are standardized tools in the Arc/Info Grid system to perform these functions, and these have also been incorporated into the Spatial Analyst extension available for Arcview Version 3.0. This page describes several programs that use terrain analysis functions.

ArcView3-based Watershed Delineation Application

An ArcView 3-based watershed delineation application is being developed by Dean Djokic and Zichuan Ye of the Applications Programming group at ESRI for the Texas Natural Resources Conservation Commission. Some testing of this tool is being done by Seann Reed of the Center for Research in Water Resources, University of Texas at Austin. This application provides interactive tools for delineating areas draining to points, areas draining to stream line segments, and areas draining to and from polygon features. The application uses functionality provided by the ArcView Spatial Analyst Extension and therefore this extension is required to use the application. The application includes a customized GUI which adds to but does not modify the standard ArcView GUI and functionality. In addition to watershed delineation tools, the application also includes utilities for managing point, line, and polygon shapefiles, and pre-processing tools for setting up input data.

This application is still under development. A tutorial demonstrating the use of this application is included on the GisHydro97 CD-ROM along with sample files needed to run the application.

****NOTE: The original "Application Tutorial" distributed on the GISHydro97 CD-ROM has been outdated. The link below is to a more recent exercise that was updated on 10/11/97. Please contact the Application Developers (see bottom of this page) for the most recent version of software and documentation. (10/1/97)

• Application Tutorial

Links to Class Exercises and Educational Tools

There are two online exercises related to terrain analysis that are part of a GIS course taught by David R. Maidment in the Department of Civil Engineering, University of Texas at Austin. Exercise 2 describes watershed and stream delineation using Arc/Info Grid and Exercise 6 uses ArcView 3 with the Spatial Analyst.

• Exercise 2. Delineation of Watersheds and Streams
• Exercise 6. Spatial Hydrology of the Urubamba River System

A list of all these class exercises is provided under the Class Exercises Module on this CD-ROM.

Ferdi Hellweger has created a Web Grid Calculator using Java that illustrates some of the concepts like "flow direction" and "flowaccumulation" used for terrain analysis.

Link to Web Grid Calculator (On this CD)
(Includes instructions to make this version work.)


Link to Web Grid Calculator (On the Internet)

Special Considerations for Terrain Analysis

There are two important aspects of terrain analysis that are not handled in the methodology described by class Exercise 2 above or by the Watershed Delineation Application.

• Burning-in Streams: When using digital elevation models (DEMs), it is often the case that the relief is not accurate enough to delineate the stream networks in flat areas. In such cases, it is useful to "burn" digitized streams into the DEM so that the elevation model reveals a more accurate representation of the drainage network. A simple methodology for burning-in streams is to rasterize the digitized stream network and then assign all stream cells a value of zero while maintaining the elevation of land surface cells. There may be problems with this method that need to be corrected manually if the digitized streams being used are not at the same scale as the DEM. Burning streams is a very useful technique for identifying stream locations in flat areas where high resolution DEMs are not available, but this technique should be used with caution. A somewhat more sophisticated program for burning in streams called AGREE is provided by Ferdi Hellweger.
  

Link to AGREE Documentation


• Identifying Inland Catchments: The Arc/Info Grid FILL function or an equivalent ArcView 3 Spatial Analyst function eliminates pits in the land surface. Filling pits is typically the first processing step taken after a DEM is projected into the chosen map projection. Pits are cells or groups of cells which are completely surrounded by cells of higher elevations. Some pits are artificial while others represent real inland drainage basins. It is sometimes difficult to distinguish between real pits and artificial pits automatically by using the DEM alone. Two criteria that are useful for identifying real pits are the pit depth and area. An Arc/Info Grid procedure for identifying inland basins using these criteria is provided by Francisco Olivera.
  

Link to Inland Basin Procedure

Primary Contact(s)

This page was created by:

Seann M. Reed
Center for Research in Water Resources
University of Texas at Austin
seann@crwr.utexas.edu
http://www.ce.utexas.edu/prof/maidment/gishydro/seann/seann.htm

I will post information on my web site about when and where the final version of the AV3 Delineation Application can be obtained. Other questions regarding this application should be directed to Dean Djokic or Zichuan Ye.

AV3 Watershed Delineation Application Developers:

Dean Djokic
ddjokic@esri.com
-or-
Zichuan Ye
zye@esri.com

These materials may be used for study, research, and education, but please credit the authors and the Center for Research in Water Resources, The University of Texas at Austin. All commercial rights reserved. Copyright 1997 Center for Research in Water Resources.