BASINS is a multipurpose environmental analysis system for use by regional, state, and local agencies in performing watershed- and water-quality-based studies. It was developed to address three objectives: To facilitate examination of environmental information; To support analysis of environmental systems; and To provide a framework for examining management alternatives. Because many states and local agencies are moving toward a watershed-based approach, the system is configured to support environmental and ecological studies in a watershed context. It is designed to be flexible. It can support analysis at a variety of scales using tools that range from simple to sophisticated. BASINS was also conceived as a system for supporting the development of total maximum daily loads (TMDLs). Developing TMDLs requires a watershed-based point and nonpoint source analysis for a variety of pollutants. It also lets the user test different management options. BASINS makes watershed and water quality studies easier by bringing key data and analytical components 'under one roof.' Analysts can efficiently access provided national environmental information, apply assessment and planning tools, and run a variety of proven, robust nonpoint loading and water quality models. A geographic information system (GIS) provides the integrating framework. GIS provides techniques for analyzing landscape information and displaying relationships. Through the use of GIS, BASINS has the flexibility to display and integrate a wide range of information (e.g. land use, point sources discharges, water supply withdrawals) at a scale chosen by the user. BASINS comprises a suite of interrelated componenets for performing the various aspects of environmental analysis. The six componenets include (1) nationally derived databases with Data Extraction tools and Project Builders; (2) assessment tools (TARGET, ASSESS, and Data Mining) that address large- and small-scale characterization needs; (3) utilites to
facilitate organizing and evaluating data, including Watershed Delineation, Import, Land Use Reclassfication, and DEM Reclassification; (4) Watershed Characterization Reports that facilitate compilation and output of information on selected watersheds; (5) water quality models including TOXIROUTE and QUAL2E; and (6) the Nonpoint Source Model (NPSM) and postprocessor, which provide integrated assessment of watershed loading and transport, The assessment component, working under the GIS umbrella, allows users to quickly evaluate selected areas, organize information, and display results. The modeling component module allows users to examine the impacts of pollutant loadings from point and nonpoint sources. Working together, these modules support several specific aspects of watershed-based analysis by: Identifying and prioritizing water-quality-limited waters; Supplying data characterizing point and nonpoint sources and evaluating their magnitudes and potential significance; Integrating point source and nonpoint loadings and fate and transport processes; Evaluating and comparing the relative value of potential control strategies; and Visualizing and communicating environmental conditions to the public through tables, graphs, and maps.