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Nutrient and Flow Modeling of the Minnesota River |
Client: Minnesota Pollution Control Agency, St. Paul, MN
AQUA TERRA Consultants is providing on-going services for the Minnesota Pollution Control Agency in support of a multi-agency analysis of water quality conditions in the Minnesota River Basin. The U.S. EPA Hydrologic Simulation Program - FORTRAN (HSPF) is being used as a framework to identify and quantify the relative pollutant contributions from both point and nonpoint sources, and to help evaluate the effects of alternative agricultural BMPs on pollutant loadings and water quality of the main stem of the Minnesota River. The Minnesota River is considered the State's most polluted river, with 533 km of main stem and 44,000 km2 of drainage area. Water quality problems are typical of many agriculturally dominated Midwestern states, with low dissolved oxygen, high turbidity, elevated ammonia, and fecal coliform standards violations common during the summer low flow conditions. The HSPF model simulations for the Minnesota River Basin will provide the basis for developing integrated point and nonpoint source management strategies for restoring the water quality of the Minnesota River by means of nutrient and sediment load reductions.
For this effort, AQUA TERRA has provided expertise on all aspects of HSPF model application, including simulation plan development, database development, watershed segmentation, model input development, model calibration, and scenario assessment. The study area has been divided into ten sub-watersheds. Hydrology, sediment, nonpoint source loads (including atmospheric deposition) have been simulated for eight different land uses within model segments of each sub-watershed. In the river reaches sediment, nonpoint source loads and point sources are received and integrated into the instream water quality processes which are being simulated on an hourly time step. In addition to flow, sediment, nutrients, and fecal coliforms are modeled sequentially from the land surface to the main stem, and throughout the main stem of the Minnesota River.
To date, AQUA TERRA,s services have focused on modeling support to MPCA, HSPF application to the LeSueur Watershed, development of software for scenario evaluation, and refinement of preliminary model calibrations (hydrology and water quality) by MPCA staff.
AQUA TERRA applied HSPF to the LeSueur Watershed as an example, or template, for subsequent extension to the rest of the entire Minnesota Basin within the State boundaries so that similar assessments can be performed on a basin scale. As of late 1997, seven of the ten sub-watersheds have been modeled with preliminary calibrations for both hydrology and water quality. Model calibration work is continuing on the remaining sub-watersheds, to set the stage for integration of the sub-watershed simulations with the Minnesota River main stem for complete basin-scale calibrations and assessments.
To facilitate the evaluation and comparison of alternative watershed and water quality management alternatives, the calibrated LeSueur Watershed model and database were implemented within an interactive computer framework called 'GenScn', an acronym for GENeration and Analysis of model simulation SCeNarios. GenScn allows the user to interactively create simulation scenarios that represent alternative management practices, analyze the scenario results, and compare their impacts on flow, concentrations, and loadings throughout the watershed. AQUA TERRA developed documentation that describes the implementation of the LeSueur Watershed GenScn, along with an overview of the LeSueur Watershed model based on HSPF, and demonstrates the use of GenScn to evaluate selected agricultural BMPs. Although the GenScn implementation is currently limited to the LeSueur Watershed, MPCA plans to extend it to include the entire Minnesota Basin as the model development and calibration proceeds.