- Watershed Modeling System

Engineering Computer Graphics Laboratory, Brigham Young University


The Watershed Modeling System (WMS) was developed at the Engineering Computer Graphics Lab (ECGL) in cooperation with US Army Corps of Engineers Waterways Experiment Station (WES) and the Federal Highways Administration. The focus of WMS is to provide a single application which integrates digital terrain models with industry standard runoff models such as HEC-1 and TR-20. WMS can be used to develop hydrologic data from TINs or grids using many of the same techniques described in other sections of this CD, in particular GH-Terrain. In this way, hydrologic data developed in Arc/INFO, ArcView, or WMS can be directly linked to many common hydrologic models. While TINs or grids developed in Arc/Info or ArcView may be exported to WMS for further hydrologic data development, the primary way in which data is shared between the GIS and WMS is through three shapefiles: a polygon shapefile for basin boundaries, a line shapefile for stream networks, and a point shapefile to identify outlet locations. The watershed delineation tool in GH-Terrain, developed by ESRI, can be used with the Arcview Spatial Analyst extension to automatically generate these three shapefiles, including population of their attribute fields with important hydrologic parameters. These data can then be used in WMS to create an initial model for any of the hydrologic programs supported by WMS. Data entry for the hydrologic model, including Rainfall, job control, or any other parameters not defined as attributes in the shapefiles, can be completed using WMS's hydrologic modeling interface. WMS can be used to post-process and then export results back to the GIS software.

Figure 1. The Watershed Modeling System imports ArcView shapefiles for use in creating HEC-1, TR-20, and other hydrologic models.

WMS- Watershed Modeling System

From its very inception GIS has been an excellent tool for data storage and management. With the creation of GRID in Arc/Info and the Spatial Analyst in ArcView, GIS has become more useful for hydrologic data development as well. And yet much of this data, both stored and developed in the GIS, remains locked to hydrologic modelers. Even though GIS holds much promise as a tool for performing spatial hydrologic runoff modeling (particularly on a regional basis), much of the analysis performed must be done using industry standard, lumped parameter models such as HEC-1 and TR-20. While much of the input required to run these models can still be developed using GIS, some parameters such as rainfall, time steps, and other model-specific parameters can not, and typically are not efficiently entered and stored in the GIS.

Unlocking GIS Data for Use with Hydrologic Models

In order to "unlock" hydrologic data developed/stored in GIS for use in hydrologic models a link consisting of three primary shape files has been developed as a joint effort by ESRI and ECGL. The link provides a common gateway to transfer data from a GIS to a hydrologic modeling system such as WMS. These three shapefiles consist of:

In addition to the geometry stored in the shapefiles, any number of hydrologic modeling related attributes may be stored as part of the shapefile. These attributes may be developed using the Spatial Analyst or manually entered.

These three shapefiles can then be imported into any program designed for hydrologic modeling. The combination of outlet points, stream network, and sub-basins will uniquely define the watershed structure, and attributes can be used to set up any hydrologic model for which the application is designed to support.

Linking the GIS Data with Hydrologic Models

In order to demonstrate how hydrologic models can be developed from these three shapefiles, an interface to import them has been created in the WMS, an application which already supports the processing of digital terrain data for use in the development of hydrologic models such as HEC-1 and TR-20.

As the shapefiles are read by WMS, key words for database item names such as area, slope, curve number etc. are checked against several defined names in order to automatically "map" these variables for use within WMS. If the shapefiles were created using the customized scripts for the ArcView Spatial Analyst (described in more detail below) then they will be created with the proper item names to automatically map in WMS. If the item names to match the pre-defined names then the user can manually map the item names in the database (dbf) file to their corresponding use in WMS using the dialog shown below.

Once the mapping has been defined the shapefiles are read in and converted to a digital and topological representation of the watershed as shown in the next figure.

As mentioned above, any variables read in through the shapefile interface can be mapped to their corresponding values in WMS. As a minimum, basin areas and stream lengths will be defined. Since WMS was designed specifically for hydrologic modeling applications it is not important that all parameters be computed in ArcView prior to exporting the shapefiles for use in WMS. Missing data can be defined inside of WMS and properly formatted for any of the supported models. The hydrologic analysis can then be done in WMS and results sent back through the same three shapefiles for storage/query from ArcView.

Using ArcView's Hydrologic Modeling Extensions for Watershed Data Development

In order to facilitate the development of hydrologic data from grids in ArcView some sample extensions have been created by the ESRI development team. Some of the scripts were included as a sample application with the initial release of Spatial Analyst 1.0. These functions have been combined with several other commands in order to provide a more complete tool for developing hydrologic data in preparation of using industry standard hydrologic models such as HEC-1 and TR-20. Some of these scripts have been gathered together and automated in the watershed delineation tool contained in GH-Terrain. The scripts include the following capabilities:

Initially, the following attributes for the three different shapefiles will be exported:

For stream line shapes

For outlet point shapes

For polygon basin shapes

Other attributes for the different shapes will likely be added as the project progresses.

While WMS has been used to show how the resulting shapefiles can be linked to hydrologic models, the format is open and can be processed by any program designed specifically to interface to rainfall/runoff programs.

Hydrologic Models Supported by WMS

Other Tools available in WMS

More Information

More information, and a free demonstration version of WMS can be downloaded from the WMS home page. Pay attention to information on this site for availability and location where hydrologic modeling extension scripts for the ArcView Spatial Analyst can be downloaded.

More information on linking this tool to GIS can be found in a paper prepared by Dean Thomas

These materials may be used for study, research, and education, but please credit the authors and the Engineering Computer Graphics Laboratory, Brigham Young University. All commercial rights reserved. Copyright 1997 Engineering Computer Graphics Laboratory.