Hydrodynamic models are computer-based programs designed to simulate processes and movements in water bodies. Scientists and policymakers use the robust information produced by hydrodynamic models to improve our understanding and develop policies for the protection and future management of water bodies. Current environmental issues in Lake Champlain that are or could be informed by hydrodynamic models include excess nutrients, changing temperature dynamics, flooding, harmful algae blooms, pathogens, contaminants, and invasive species. Existing hydrodynamic models are currently used to forecast flood risk and to determine how seasonal water current and nutrient dynamics affect the occurrence of harmful algae blooms, among other applications.

In Lake Champlain, hydrodynamic models have been developed and utilized for a variety of purposes. This document summarizes early modeling efforts focused on Lake Champlain and describes five hydrodynamic models used to describe the hydrodynamics of the lake.

2019 Report of Activities highlights LCBP projects that were in progress or concluded between October 1, 2018 and September 30, 2019. It includes a comprehensive listing of external contracts managed by LCBP, and key LCBP tasks implemented by staff during this time period. The LCBP received federal funding in FY 2019 from the U.S. Environmental Protection Agency, the Great Lakes Fishery Commission, and the National Park Service.

The Farm-P Reduction Planner tool (Farm-PREP) is designed to help farm management planners to quantify the reductions in farm-scale P losses achieved through modifications to field-level practices. Farm-PREP includes an optimization tool that will identify potential combinations of practices across multiple farm fields that will enable a targeted reduction in P loss. The tool has now been expanded for use throughout the entire state of Vermont, both within and outside of the Lake Champlain Basin. The tool has been further tested and significant enhancements have been made through a stakeholder feedback process. Farm-PREP Training workshops held throughout Vermont exposed a broad group of agricultural professionals to Farm-PREP, both providing education and serving as a platform for further user feedback.

The goal of this project was to develop a robust APEX model capable of representing edge-of-field P loads (both via surface transport and tile drainage) and to use this model to investigate the impacts of innovative manure management technologies on P loads. This work addresses the need for quantification of P loads from tile drain flow under various conditions, as well as provides a basis for comparing P load from tile flow and surface runoff, and for evaluating factors influencing P movement in tile drainage. It also provides a quantitative assessment of the potential value of manure management technologies in reducing P loads from agricultural fields. Innovative manure management may play a role in improving water quality outcomes at the farm and basin-scale.

A phosphorus loading study was conducted for the Vermont portion of the agriculturally dominated Mckenzie Brook watershed, which drains several small subwatersheds directly to the southern portion of Lake Champlain. Water quality (7 sites), streamflow (2 gages), and precipitation (12 gages) monitoring was conducted from April – November in both calendar years 2017 and 2018. 342 total and dissolved phosphorus samples were collected in 2017, which was characterized by above normal spring-summer rainfall and normal to below normal monthly totals that fall, with a significant 2.59 inch event in early July. 281 total and dissolved phosphorus samples were collected in 2018, which was much drier with above normal rainfall in April and November but well below normal for most of the intervening months and many periods of zero flow. A watershed model based on the curve number approach was developed that includes soil moisture accounting routines, which was calibrated and validated to estimate daily mean streamflow at ungaged sampling sites. Poor and inconsistent concentration-discharge correlations necessitated the use of the Beale Ratio Estimator to estimate flow-weighted daily mean concentrations and total April – November loads for year at each site. In general, the sampled phosphorus concentrations were high, with some extremely high concentrations even at low flows. This study provided useful insight into the hydrologic and geochemical dynamics of this region, and results serve as a point of reference for reducing phosphorus concentrations and loads through implementation of agricultural best management practices moving forward.