DEVELOPMENT OF HYDRODYNAMIC, WATER QUALITY AND EUTROPHICATION MODELS - Integrating GIS, Remote Sensing, and Mathematical Modelling for Surface Water Quality Management - page 142

The analysis of the velocity currents and wind speed shows a clear match between the directions of the
current and the wind which indicates the main effect of the wind on the lake hydrodynamics. Figure
(7-15) shows the analysis of the wind and velocity vectors.
Figure (7-15): Comparison between wind and current velocities in the U direction
In this case the model outputs show that the drainage water inflows to the lake do not change the
general circulation pattern inside the lake as generated by the wind: their influence is limited to the
areas near their inlets.
Model Calibration
In order to calibrate the model, real data were used as boundary conditions and the results were
compared with field measurements (that is, the water level at a fixed location upstream of the exit
channel). The main calibration factor was the bed roughness coefficient. The hydrodynamic model
was run for different roughnesses distributed over the grid. The roughness at the exit channel was
increased from 0.05 to 0.09, and the main area of the lake different ranges of roughness coefficients
were applied, namely 0.05-0.07-0.09. The roughness coefficients in the 2D model were determined to
give a good representation of water levels measured at the exit channel to the sea, which has a value of
0.6 m. The roughness coefficient selected for the main water body was n=0.07m, while at the lake exit
to the sea the roughness was increased to 0.09 to account for the exit bridge. Different roughness grids
were tested and the target calibration parameter, namely the water level at the exit channel, was
calculated with the selected roughness grid.
7.5. 2 D WATER QUALITY MODEL OF SHALLOW LAKE SYSTEM
The water quality model for the shallow lake system has two main components. The first component is
a 2D water quality model that consists of the main water quality parameters which are foreseen to be
the main pollution indicators in the lake system. The second component is a eutrophication screening
model. The development of these two models was determined by the complexity of the lake system
and the interaction between the different lake components, namely the main water body, the vegetation
and the fisheries. The aim of the 2D water quality model is to develop the temporal and spatial
variations in the concentrations of main parameters in the lake. The eutrophication screening model is
based on the modelling of CHL-a, which is considered a direct indicator of the eutrophication
condition of the lake and is the main algae species existing in the lake water body. Figure (7-16)
shows the water quality modelling and its components.