AQUA TERRA Consultants
Back to Project List

HSPF Application Assistance For The Patuxent River Nonpoint Source Assessment Study and Development of a Watershed Model of the Patuxent River Basin


  • State of Maryland, Department of Health
  • Mental Hygiene, Office of Environmental Programs, Maryland Department of the Environment, Baltimore, MD
  • U.S. Geological Survey, Office of Surface Water, Reston, VA

For more than a decade, AQUA TERRA principals and staff have been providing watershed model development and application assistance to government agencies charged with evaluating nonpoint source pollution in the Patuxent River Basin. Four contracts with the three agencies listed above have resulted in AQUA TERRA providing nearly continual services that support comprehensive watershed management.

In 1984 the Maryland Office of Environmental Programs initiated a comprehensive, coordinated monitoring and modeling program for the Patuxent River Basin to identify critical regions of nonpoint source load generation, evaluate water quality conditions resulting from both point and nonpoint source contributions, and analyze the impact of alternative management practices and land use policies. The HSPF model was selected to provide the framework for the program, and we were selected to provide expert assistance in model use and application throughout the 7-year project.

Our scope of activities included: review and analysis of available data for model application; assistance in site selection and design of the monitoring program; development of a simulation plan; training in HSPF operations, calibration, verification, and interpretation of model results; direct assistance and participation in the model calibration and verification for both water quantity and quality; and guidance in model use for analysis of alternative management practices and land use conditions.

In 1986, the USGS Watershed Data Management System (WDMS) was selected as the modeling data management tool for the project, and the development of a Patuxent River Watershed Data base Management (WDM) file was initiated to include all the meteorologic, hydrologic, water quality, and land use information needed for the HSPF application. Under a separate contract with the USGS, AQUA TERRA implemented the HSPF/WDM linkage which allows HSPF to directly use WDM files during model operation. The HSPF/WDM linkage has subsequently been tested and used in the hydrologic calibration of subwatersheds within the Patuxent River Basin.

Since 1986, the Maryland Department of the Environment has undertaken a comprehensive monitoring and modeling program of the Patuxent River basin. The principal objective of this program is the development of a tool that will permit identification of critical regions of nonpoint source pollution in the basin, evaluation of the effectiveness of corrective measures in reducing water quality impacts, and prediction of the water quality impacts of various land use policies. This project involved a cooperative effort sponsored by the State of Maryland, with the assistance of the U.S. Geological Survey, to develop a calibrated model of the Patuxent River basin using the Hydrological Simulation Program - FORTRAN (HSPF). The resulting Patuxent River Basin Model is a finer scale version of the Patuxent portion of the EPA's Chesapeake Bay Watershed Model; the basin and the river are represented by 21 land segments and 34 stream/reservoir reaches. Land uses simulated in each segment include forest, four residential/urban categories, eight crop categories, and pasture. The model simulates hydrological and nutrient processes on the land surface and soil profile as well as in streams, rivers, and reservoirs. Inputs to the instream model include the nonpoint loadings generated by the land model, point sources, atmospheric deposition, and water supply diversions.

The project also demonstrated several innovative software tools designed to facilitate watershed modeling. Development of the Patuxent model involved the use of the following modern computational techniques: model segmentation, land use, and soils-related parameters were developed from a Geographic Information System; the hydrology calibration was performed using an "Expert Advisor" program designed for HSPF by the U.S. Geological Survey; and the model is operated by an interactive graphical interface ("Scenario Generator") that facilitates simulation of the calibrated model to represent a range of scenarios. The interface includes a map of the basin and capabilities to modify the model inputs, execute the model, and display results.

AQUA TERRA directed the basin segmentation, assembled the model database, performed the hydrology calibration, developed the AGCHEM model of the cropland areas, performed sediment and water quality calibration, and completed nutrient management and forest scenario runs. AQUA TERRA also developed the Scenario Generator interactive interface.

Back to Project List