Modelling Water Exchange in the Flommen Lagoon, South Sweden

Abstract: The Flommen Lagoon in southern Sweden is surrounded by several natural reserves and is an important bird migration site on the edge of the continent. The protection of this area including water quality in the lagoon and flooding problems in the adjacent area has always been a concern. The objective of this study is to simulate the water level in the Flommen Lagoon and the water exchange between the Flommen Lagoon and the sea with regards to inlet properties, longshore sediment transport and the operation of the sluice gate on the lagoon inlet to minimize the impact of human activities and reach a suitable operation strategy of the sluice gate. An investigation was also performed about the impact of constructing a second inlet between the lagoon and the sea. According to the simulation results, the longshore sediment transport rate is larger in the south of the inlet than in the north which will result in sand accumulation around the inlet. The inlet geometry showed no significant influence on the lagoon water level but affected the water exchange rate. For the simulated time period, halve the cross-section area decreases the gross exchange rate by 39.2% and double cross-section area increases the gross exchange rate by 15.3%. The sluice decreases gross water exchange rate by 31.6%, but it plays an important role in protecting the golf courses around the lagoon from flooding. With two inlets, gross water exchange rate is 15.3% higher than with one inlet, and water level is also slighter higher.