ON THE PREDICTION OF SALINITY INTRUSION IN DANSHUI ESTUARINE SYSTEM

摘要

The main parameters that affect the flow conditions and intrusion of salt water in an estuary system are tides and seasonally variation of water discharge. A laterally twodimensional averaged numerical model called MIKE11XZ (MIKE11 Reservoir) is used to simulate the hydrodynamics and salinity intrusion of Danshui River estuarine system. The model uses k-ε turbulence closure scheme. A series of comprehensive field data is used for calibration and verification of the model. The friction coefficient is calibrated and verified using water surface elevation and velocity measurements. Then the dispersion coefficient is calibrated and verified through comparison of salinity concentration in different layers and stations. Reasonable agreement is obtained between the model results and observed data. The model application is investigated with different discharges and the effect of discharge variation on salinity intrusion is studied. The results show that when the river discharge decreases from mean flow to Q_(90), the salinity intrusion increases about 8 km, 7.5 km and 6.5 km in Tahan Stream, Hsintien Stream and Keelung River, respectively. On the other hand, due to the presence of the topographic sills at upriver end of the tributaries, when the fresh water discharge becomes less than Q_(90), the salinity does not intrudes further up. The results also show that the fresh water discharge is the main parameter that affects the salinity intrusion in this system. Finally, simple equations are suggested to predict the salinity intrusion due to fresh water discharge in different tributaries.