Investigation of saline water intrusions into the Curonian Lagoon (Lithuania) and two-layer flow in the Klaipėda Strait using finite element hydrodynamic model

摘要

This work is focused on the application of a modelling system to simulate3-D interaction between the Curonian Lagoon and the Baltic Sea coastalwaters and to reflect spatiotemporal dynamics of marine waters in theCuronian Lagoon. The model system is based on the finite element programmepackage SHYFEM which can be used to resolve the hydrodynamic equations inlagoons, coastal seas, estuaries and lakes. The results of a one year (2009)3-D model simulation with real weather and hydrological forcing show thatthe saline water intrusions from the sea through Klaipėda Strait aregradually decreasing with distance from the sea and become negligible(average annual salinity about 0.57‰) at a distance ofabout 20 km to the south of Kiaulės Nugara island. Analyses of thesimulation results also show this area to be highly heterogeneous accordingto the vertical salinity distribution. While in the deeper KlaipėdaStrait (harbour waterway) differences in average salinity between nearbottom and surface layers varies in the range 2–2.5‰,in the rest of the Curonian Lagoon it is less than 0.5‰. The exchange flow showed vertical structure, but was horizontally uniformwith the presence of a two-directional flow that from time to time changesto either saline water one-directional flow to the Curonian Lagoon or freshwater one-directional flow to the sea. Two-directional flow durationdecreases with a distance from sea entrance in Klaipėda Strait fromaround 180 days yr?1 close to the sea entrance to 50 days yr?1just behind Kiaulės Nugara island. One-directional outflow duration isincreasing with a distance from the sea entrance from 100 to 225 days yr?1. One-directional inflow duration occurs in the range of 70–100 daysyr?1. The analysis of the ratio of buoyancy layer thickness to waterdepth (h_b/H) and the Wedderburn number identified the main importance ofwind action on the flow structure. Strong winds from the North and NWdetermine a barotropic inflow which is mostly responsible for the salt waterintrusion into the Curonian Lagoon. Absence of wind or cross-strait windregimes allows the maintenance of a two-layer flow typical of estuarinedynamics.