From the Stanford Model to BASINS: A Summary of Model Evolution

In the early 1960's the Stanford Watershed Model (SWM) was instrumental in introducing the civil engineering profession to the concept of continuous hydrologic modeling. With wide distribution and application of the SWM in the late 1960’s, civil engineers recognized the value of digital continuous simulation for hydrologic applications. By the early 1970’s the developers of SWM expanded and refined SWM to create the Hydrocomp Simulation Program (HSP), which also included general nonpoint source loadings and water quality simulation capabilities. Hydrocomp had demonstrated the utility of quantity/quality simulation by modeling a range of water quality constituents in a large basin. During the early 1970's EPA sponsored development of the ARM (Agricultural Runoff Management) and the NPS (Nonpoint Source) pollutant loading models to address pollution from agriculture, urban, and other land uses; the SWM approach was selected as the hydrologic foundation for an expanding suite of models of nonpoint pollution impacts. In the late 1970's EPA recognized that the continuous process simulation approach contained in all these models would be needed to analyze and solve many complex water resource problems. Grant money from the agency to Hydrocomp resulted in the development of the Hydrological Simulation Program - FORTRAN (HSPF), a non-proprietary system of simulation modules in standard Fortran that handled essentially all the functions performed by HSP, ARM and NPS, and was considerably easier to maintain and modify. HSPF simulates the hydrologic and associated water quality processes on pervious and impervious land surfaces and in streams and well-mixed impoundments. Since the first public release (Release No. 5) of HSPF in 1980, the model has undergone a continual series of code and algorithm enhancements producing a succession of new releases, leading up to the most recent Release No.12 in 2001. Since 1981, the U.S. Geological Survey has been developing software tools to facilitate watershed modeling by providing interactive capabilities for model input development, data storage and data analysis, and model output analysis including hydrologic calibration assistance. The ANNIE, WDM, HSPEXP, and GenScn products developed by the USGS have greatly advanced and facilitated watershed model application, not only for HSPF, but also for many other USGS models. In 1994 efforts began to develop EPA's Better Assessment Science Integrating Point and Nonpoint Sources (BASINS) modeling system. The BASINS system combines environmental databases, models, assessment tools, pre- and postprocessing utilities, and report generating software to provide the full range of tools and data, integrated into a single modeling package, needed for performing watershed and water quality analyses. HSPF was incorporated into BASINS as the core watershed model. Since 1998 BASINS has benefited from considerable efforts to integrate and enhance the strongest features of HSPF and the USGS software products (including GenScn) within a common framework. Today HSPF/BASINS serves as a focal point for cooperation and integration of watershed modeling and model support activities between the USGS and the EPA. The Model Core: Process Algorithm Development Hydrologic simulation began in the 1950s and 1960s with the advent of the digital computer. The purpose was to predict streamflow, given observed precipitation and other meteorological variables, at time scales short compared to catchment storm response times. The first models were spatially lumped, meaning that the models represented the effective response of an entire catchment, without attempting to characterize spatial variability of the response explicitly.