Computer Program for Project Formulation: Hydrology (TR-20) Revisited

The TR-20 computer program originally developed for the Soil Conservation Service in 1964 has been completely rewritten recently. The TR-20 rewrite involves a system of programs including not only a new watershed scale surface water hydrology model with expanded features but also a data converter for old input data, a HEC-RAS cross section reformatter, an input editor, a graphical post processor and eventually a Geographic Information System (GIS) based input generator. The rewritten TR-20 model has a more physically based input philosophy than previous versions and is based on the approach in the AnnAGNPS (Annualized AGricultural Non-Point Source Pollution) model. Most of the maximum number limitations have been removed from the model as well. Input has been expanded to include the flow path for time of concentration and curve number weighting calculations from Urban Hydrology for Small Watersheds (TR-55) as options. The data converter converts as much of the old input data as practical to the new format. The HEC-RAS reformatter can provide the needed stream cross section rating information in the TR-20 input format. The GIS based input generator can be used to develop input from Digital Elevation Models, soils, and land use information data layers. Converted data or GIS generated input can be used in conjunction with reformatted data as a starting point in the input editor to complete the input data. The post processor provides graphical display of model input/output that can be incorporated into reports or other documents.