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Model Development:
Utah Lake Water Quality Study

The selection and development of a water quality model of Utah Lake were initiated as part of the Utah Lake Water Quality Study. The primary objective of the model is to function as a decision-support and water-quality management tool to address eutrophication in Utah Lake.

Key objectives for the Utah Lake nutrient model:

  1. Provide a decision-support tool for Utah Lake, including the relationship of phosphorus and nitrogen to water-quality endpoints such as dissolved oxygen (DO), pH, and nuisance and harmful algal blooms, as well as the export of total phosphorus (TP), total nitrogen
  2. (TN), and organic matter to the Jordan River.
  3. Improve understanding of the nutrient dynamics in Utah Lake and the formation of nuisance and harmful algal blooms (cyanobacteria).
  4. Predict the effects of various nutrient-loading scenarios on the formation of nuisance and harmful algal blooms.
  5. Predict transition of Utah Lake from turbid state to clear state and clear state to turbid state.

A secondary objective of the nutrient model is to identify input and calibration data gaps and support the planning of data collection efforts.

Deliverables

The ULWQS Work Plan identifies the following goals for model application:

  • Water-quality endpoints for Utah Lake that would inform necessary nutrient reductions
  • Determinations of inflows, outflows, the influence of evaporation, discharges, and effects on the Jordan River
  • Loading analysis results to identify management strategies for addressing existing and future water-quality concerns resulting from human activities. The results will be used to indicate problem areas or ‘hot spots’ under existing and future land-use conditions.
  • Experimental work to help answer questions that current data or modeling may not be able to assess
  • Development of an assessment methodology for assessing high-frequency and continuous datasets. A broader sample set will allow a more comprehensive data analysis.
  • Determination of end goals for realistic expectations for Utah Lake

Accomplishments

Model Selection

A model selection process was undertaken with a select committee of stakeholders, the Utah Lake Modeling Group Members. The results of the model selection process are documented in the Utah Lake Nutrient Model Selection Report. The following selection criteria were considered in ranking each of the modeling platforms considered:

  • Complexity
  • Capabilities
  • Data requirements
  • Transparency
  • Flexibility
  • Compatibility

The recommended modeling platform is a three-dimensional hydrodynamic model coupled with a water-quality model. The selected hydrodynamic model is the Environmental Fluid Dynamics Code (EFDC) and the selected water-quality model is Water Quality Simulation Program (WASP). Both models are supported by the EPA and have been widely applied for numeric nutrient-criteria development and total maximum daily loads (TMDLs).

Model Development

The EFDC-WASP Utah Lake model is being built and calibrated by a research team from the University of Utah under the direction of Dr. Michael Barber in the Civil and Environmental Engineering Department. The model development is occurring under a research grant from the EPA Office of Research and Development. A Memorandum of Understanding was signed in September 2016 between the University of Utah, EPA Region 8, and DWQ that stipulates substantial interaction and coordination between agencies on model development. Once the Utah Lake model has been calibrated by the University of Utah team, it will be made available to DWQ for use in the water-quality study.

Model Application

The calibrated Utah Lake model is anticipated to support the development of site-specific criteria for nitrogen and phosphorus in Utah Lake. Depending on direction from the Science Panel, additional data collection and model calibration may be necessary prior to the application of the model.