Hydrodynamic modeling and management alternatives in a Mediterranean, fishery exploited, coastal lagoon

Model development is described, related to the restoration efforts of Vassova Lagoon, a small and shallow, fishery exploited coastal lagoon, located in the region of eastern Macedonia, N. Greece. This lagoon has been configured and is used for fisheries, by having dredged through tidal channels and installed fish entrapment devices. Decreases in fish production have been related to poor seawater circulation, limited water renewal and related water quality problems. The aim of this study is to evaluate the current situation of the lagoon and propose alternative management scenarios for improvement of water flow and lagoon ecosystem. The SWMM-EXTRAN mathematical model has been adapted, calibrated, verified, and applied to describe the current situation of the lagoon, and evaluate alternative scenarios for increasing tidal flushing and water residence time. Data necessary for model validation have been collected in the field. Among the tested restoration alternatives were the following: widening and/or deepening the lagoon inlet; constructing a second inlet; widening and/or deepening the tidal channels inside the lagoon. The combined influence of opening the existing communication channel of Vassova Lagoon with the adjacent Eratino Lagoon was also considered for each scenario. The implications of the various scenarios on lagoon's fisheries management are discussed. The alternative of constructing a second tidal inlet channel, 5 m wide, and keeping the Eratino Lagoon channel open provided most tidal flushing and increased internal and inlet flow that favors recruitment of juvenile fish. This alternative was proposed for implementation.