AQUA TERRA Consultants
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BASINS 4.0 Development

Client: U.S. EPA Office of Water, Office of Science and Technology, Washington, DC

The U.S. Environmental Protection Agency's (EPA's) Office of Water developed BASINS as a multipurpose environmental analysis system. As a multipurpose system, BASINS ( was designed to support watershed and water quality-based studies by facilitating examination of environmental information, by supporting analysis of environmental systems, and by providing a framework to examine management alternatives. BASINS encompasses a suite of watershed models, from sophisticated broad-spectrum watershed models to agricultural models, to planning and management level models, plus supporting tools and data, all within one package. From 1998 through 2009 AQUA TERRA Consultants has served as the prime contractor for development and support of BASINS.

The main interface to BASINS is provided through a Geographic Information System (GIS). Because GIS combines mapping tools with a database management system, it provides the integrated framework necessary to bring modeling tools together with environmental spatial and tabular data. Version 4.0 of BASINS is the first to be primarily based on a non-proprietary, open-source GIS foundation. By using open-source GIS tools and non-proprietary data formats, the core of BASINS becomes independent of any proprietary GIS platform while still accommodating users of several different GIS software platforms. The underlying software architecture provides a clear separation between interface components, general GIS functions, and GIS platform-specific functions. Separating these components and functions provides a future migration path for using core GIS functions from other GIS packages or for accommodating future updates to the already-supported GIS packages.

Beginning in 2004, BASINS development efforts focused on a new version of BASINS, known as BASINS 4.0. Major design goals for BASINS4.0 included removal of proprietary software (with the exception of the Windows operating system) as a prerequisite for use of the system and implementation of an extensible architecture allowing collaborative development efforts. BASINS 4.0 is built as an extension to MapWindow, a non-proprietary, open-source GIS (Figure 1).

Figure 1: The BASINS 4.0 Interface built upon an Open Source Foundation

The extensibility of MapWindow is one reason why it was identified as an excellent candidate GIS foundation for BASINS. MapWindow can be extended with plug-in components written in any Microsoft .NET language. The plug-in interface allows third-party developers to create plug-ins that become fully integrated into the BASINS interface. This means that third parties can write plug-ins to add additional functionality (models, special viewers, hot-link handlers, data editors, etc.) to BASINS and pass these tools along to other clients and cooperators.

The BASINS system includes a tool, known as the BASINS Data Download tool, for downloading and extracting a set of databases that facilitate watershed analysis and modeling. Some of the data downloaded using this tool have been preprocessed for use in BASINS. These data provide a starting point for watershed analysis, but users are encouraged to add additional data sets where locally derived data may be at a higher resolution or compiled more recently. Other data that can be downloaded using the Data Download tool have not been preprocessed and are extracted directly from the agency responsible for collecting the data.

Since version 3.1 the BASINS system has included a tool for dynamically downloading data from an additional set of sources. In addition to downloading the BASINS data from the EPA web server, the Data Download tool (Figure 2) provides links to the federal agencies where certain data types are hosted, as well as tools to download the data and convert them into forms usable by BASINS. Since data available on the web are not static, this tool allows a user to check for more recent data and update the BASINS project data as appropriate.

Figure 2: The BASINS Data Download Tool.

When the Data Download tool is started, a window appears listing all of the available data types that the tool may add or update. The list of data types is determined at run-time, so this list may expand as new data-type components are created. The user chooses as many of the data types as desired, and the tool accesses the specified data through the World Wide Web and adds the data to the BASINS project.

A key feature of BASINS Web Data Download tool's architecture is the separation of the list of data types into individual components. For each data type available for downloading, there is a unique Dynamic Link Library (DLL). This design allows the list of data types to be populated at runtime, but it also greatly enhances the maintainability of the Web Data Download program. Very often the way the data are hosted on a web site changes over time. With this design, if a data type's web storage is changed, only the DLL for that data type will need to be updated and distributed, not the whole Web Data Download program.

This tool provides great flexibility in pulling data from a variety of sources. Instead of distributing all BASINS data through a specially compiled BASINS data holding, the data can be retrieved from the source of the data directly. This design makes the BASINS system easier and less expensive to maintain, since it eliminates having another copy of each dataset in the BASINS data holdings. In addition, updates to the data are available directly to the user as soon as the agency producing the data makes the update available.

BASINS continues to have new data sources added to it. The most notable recent addition is access to an updated meteorological database. BASINS previously accessed a meteorological database containing just fewer than 500 stations across the U.S. through the year 1995. It now accesses a database with over 15,000 stations, with over 6,500 of them containing hourly precipitation records through the year 2006. A total of seven meteorological constituents are stored on the database, though not every station contains all of them. Markers indicating distinct constituents are displayed in the GIS interface to help visualize the constituents found at each station (Figure 3).

Figure 3: GIS representation of constituents available at meteorological stations

Several other new data sources are being made available for download and use in BASINS in 2008. These include NHDPlus (EPA & USGS's enhanced hydrography dataset -, TerraServer (satellite and aerial imagery -, NLCD 2001 (national land cover dataset from the Multi-Resolution Land Characteristics Consortium -, and Modernized Storet (EPA's water quality, biological and physical dataset -

With its open-source plug-in framework and growing number of data sources, a number of new models and analysis tools have been and are being added to BASINS 4.0. On the modeling side of the system, a plug-in for EPA's DFLOW model has been developed and was released in early 2008. Likewise, plug-ins for EPA's Water Quality Analysis Simulation Program (WASP) model and Stormwater Management Model (SWMM) have also recently been developed.

BASINS 4.0 analysis tools that process timeseries data share a common data selection interface (Figure 4). This interface allows the user to filter all available timeseries by any available attribute. In the figure, eighty-nine timeseries are available for analysis. In the 'Scenario' column, the 'OBSERVED' value has been selected. In the 'Location' column, two locations have been selected. This leads to two matching data sets. These are summarized in the 'Matching Data' frame.

Figure 4: Select Data User Interface Example

Clicking on entries in the 'Matching Data' frame selects data sets and includes their summary in the 'Selected Data' frame. Attributes used for selection are specified through the dropdown list. They may be added or removed from the form using the 'Attributes' file menu item. Attributes shown in the figure are part of the metadata for the dataset. Additionally, computed attributes (Mean, Maximum, etc) may be used for selection. BASINS basic analysis tools may be used to produce summary reports and graphics.

One of the more recently added specialized analysis tools is the Climate Assessment Tool (CAT). CAT provides a flexible set of capabilities for representing and exploring climate change and its relationship to watershed science. Tools have been integrated into the BASINS system allowing users to create climate change scenarios by modifying historical weather data, and to use these data as the meteorological input to the Hydrological Simulation Program - FORTRAN (HSPF) watershed model. A capability is also provided to calculate specific hydrologic and water quality endpoints important to watershed management based on HSPF model output (e.g. the 100-year flood or 7Q10 low flow event). Finally, the CAT can be used to assess the outcomes of a single climate change scenario or to automate multiple HSPF runs to determine the sensitivity or general pattern of watershed response to different types and amounts of climate change.

Figure 5: The BASINS Climate Assessment Tool (CAT)

Users can modify historical climate data using standard arithmetic operators applied monthly, seasonally or over any other increment of time. Increases or decreases in a climate variable (precipitation, air temperature) can be applied uniformly, or they can be selectively imposed on only those historical events that exceed (or fall below) a specified magnitude. This capability allows changes to be imposed only on events within user-defined size classes and can be used to represent the projected effects of 'intensification' of the hydrologic cycle, whereby larger precipitation events intensify, instead of events becoming more frequent. In addition, users are able to create time series that contain more frequent precipitation events. These capabilities provide users with an ability to represent and assess the impacts of a wide range of potential future climatic conditions and events. An example of the CAT window is shown in Figure 5.

Another data analysis tool recently added to BASINS is the USGS Surface Water Statistics (SWSTAT) software. SWSTAT is a software package for statistically analyzing time-series data. A user interface to some functions of SWSTAT has been written as a BASINS plug-in. The available functions include frequency distribution, trend analysis, and n-day annual time series.

BASINS scripts allow the user to customize and extend the system without the complexity of writing a plug-in. Portions of a script are shown in Figure 6. This script summarizes gridded precipitation data at specified points. Output is a text file that is further processed. Scripts allow repetitive tasks to by quickly accomplished. BASINS Watershed Characterization Reports are implemented using scripts.

Figure 6: The BASINS Climate Assessment Tool (CAT)