Integrated Physical Modelling of the Lake George, NY Watershed

Lake George is located in the Adirondack State Park region of upstate New York, about 350 km north of New York City. It is a glacial, oligotrophic water body and is unique among fresh water lakes because of its ecology, geographic orientation, historical importance, and tourism-driven economic impact. Further, this narrow, dimictic lake (51.5km long with an average width of 2.1km, surface area of 117 km2, volume of 2.28 km3, maximum depth of 76m and average depth of 21m) of unusually high clarity has been experiencing ecological changes in recent years with the influx of invasive species and increasing levels of salt (NaCl) from road de-icing agents and the accompanying deterioration of water quality. In addition, the morphology of an anoxic zone within the lake is not fully understood.

To begin to address these questions, we have developed a coupled system to physically model the atmospheric, hydrological, and hydrodynamic aspects of the lake and the surrounding region. To enable these capabilities very high-resolution bathymetric and topographic surveys were conducted. The coupled models are also associated with a real-time multi-modal observing system composed of in-situ sensors for atmospheric, stream and lake measurement.

Atmospheric forcing is considered for both lake circulation and runoff models with hydrological forcing of the lake as well. To address the former, we build upon the on-going work with IBM Deep Thunder. It is based, in part, on the ARW core of the Weather Research and Forecasting (WRF) model. It is run operationally twice daily (initialized at 00 and 12 UTC) nested to 1-km horizontal resolution with high vertical resolution in the lower boundary layer for regional coverage for 48 hours. A number of model and remote sensing data sets are ingested to enable appropriate initial and boundary conditions. Three-dimensional variational data assimilation is performed around each analysis time using MADIS and EarthNetworks WeatherBug observations, which is being extended with a new mesonet in the Lake George watershed.

For the runoff, a two-dimensional hydrological model has been implemented, which has been scaled to utilize 2m-resolution topographic data derived from the aforementioned survey. It supports fully dynamic routing with flow driven by both precipitation and snow melt, including over 400 stream networks with a total length of over 1000 km. The model has been extended for the transport of dissolved salt.

For the lake circulation, we build upon the on-going work with IBM DeepCurrent, a three-dimensional, hydrodynamic model with a vertical hydrostatic approximation implemented at high-resolution for Lake George (approximately 20 m horizontal, and 2.8 m vertical). It also utilizes data derived from the aforementioned bathymetric survey. The model has been extended to address chlorine ion transport as an indicator of water quality given the tendency of sodium to bind with soil en route to the lake.

There is an inherent scale gap between each of these models, which needs to be addressed in order to create a one-way coupled system. Hence, the atmospheric model is being extended to include downscaling into the very large eddy regime (i.e., O(100 m) horizontal resolution) with no boundary-layer parameterization.

We will present an overview of each of these models along with the results to date, including the model coupling. We will also discuss on-going issues such as model verification as well as computational, visualization and data management challenges. In addition, we will outline recommendations for future work, including additional data assimilation in the coupled models.