Lake Washington Sigma-Zed Application
Study Area Characteristics
Lake Washington is the second largest natural lake in the State of Washington, USA. It is a lake with steeply sloping sides and also has long-term, high quality vertical temperature records. This makes it an ideal case to test the Sigma-Zed layering approach. DSI has developed a hydrodynamic model of this water body with 1,183 cells and 55 layers to assess the accuracy for prediction of the epilimnion and hypolimnion. The horizontal plan view of the lake is shown in Figure 1. Model output is compared with data measured at the buoy at the lake’s center.
The extremely accurate simulation of vertical variation of temperature by EFDC+ using Sigma-Zed is demonstrated below. This compares the vertical profiles of model output (blue) with measured data (red) for temperature for the new Sigma-Zed (Figure 2). In contrast Figure 3 compares the vertical profile of model output (blue) with measured data (red) for the conventional Sigma Stretch approach. The Sigma-Zed clearly performs better and has a run time shorter than Sigma Stretch (3.5 hours vs 12 hours for a one year simulation).
A paper using this example was presented at the 11th International Conference on Hydrodynamics (ICHD 2014), October 19 – 24, 2014, Singapore, and may be downloaded from this website (click here). This paper uses Lake Washington as a demonstration and verification of Sigma-Zed and EFDC+.