A geographic information system for watershed growing and hydrograph simulation

Defining watershed boundaries and hydrologic model parameters by conventional manual approaches requires significant time and expertise. To overcome these constraints, a geographic information system was developed to automatically generate the area and hydrologic parameters necessary to simulate streamflow for a watershed. The system uses digitized stream and elevation data that are available from federal agencies. These data are integrated with some unique terrain analysis techniques to produce a detailed network of flow paths for a watershed. The flow network is used to define the watershed boundary as well as the topology and physical properties for individual subareas. The subarea information is then combined with fundamental hydrologic and hydraulic techniques to produce a unit hydrograph for use in streamflow simulation. The system was tested on a variety of basins with actual storm events and performed as well as the manual methods currently used within NOAA. In addition to requiring minimal time and user input, the system is especially useful in ungaged areas. Also, the GIS provides a framework that allows easier application of more sophisticated physically based models. Overall, the system is a practical tool for hydrologic model applications where many watersheds must be considered.