A numerical investigation of dynamics of a shallow intermittently closed and open lake and lagoon (ICOLL)

We used a calibrated hydrodynamic model (Delft 3D FM) to investigate the dynamics of a shallow estuary in South East Queensland, Australia. Discharge boundary conditions required for the model can be obtained from in-situ velocity measurements, however, such surveys are expensive for the long time window necessary to explore the dynamics of the system. In line with this, a tidal rating curve empirical relationship was developed from limited observations to predict long time series of discharge, from the water level in gauging stations. We validated this relationship by identifying the correlation between the predicted and observed discharge, along with exploring the comparison between outputs generated using observed and predicted discharge boundary conditions. Predicted discharge shows a very good correlation with the measured discharge (R² = 0.86). Furthermore, the velocity outputs at many different locations within the channel using the predicted discharge showed a strong regression (R² = 0.88), compared with those obtained using observed discharge. Generation of predicted discharge allowed us to model long-term velocity variation in the channel. This work is the first examination of spatial dynamics of Currimundi Lake utilising residual velocity, enabling strong local flows to be identified.