Estimating the Water and Salt Budgets of a Stratified Estuary

Small tidal range, low salinity, moderate temperature and salinity stratification during summer which becomes weaker during winter, abundant fresh water inflow and connection through a shallow sill with the adjacent sea are the characteristic features of some estuaries along the coast of the Baltic Sea. In this study the flow and transport of salt in the upper and lower layers of the outlet of an estuary of this type were determined. First the magnitude of the terms of the transport equations was estimated using the analogy between the transport of salt and heat. Then the important terms of the transport equation were computed with a model which is based on the measured slope of the water level and on the water budget of the estuary. Testing was carried out by comparing the measured and computed salt contents of the estuary. The operation of the model on Pohjanpitäjänlahti bay in southern Finland was found to be satisfactory.