Abstract
The lagoons along the Saudi Arabian coast of the Red Sea are rich in biodiversity. The Presidency of Meteorology and Environment of Saudi Arabia with the collaboration of the International Union for Conservation of Nature and Natural Resources has declared some of these lagoons as sensitive sites. These lagoons differ widely from each other and the current velocities and flushing time are a function of size, shape, tidal range and size of inlet. The water column conditions of Rabigh Lagoon and the flushing times of Shoaiba, Obhur, Ras Hatiba, Rabigh and Yanbu lagoons are determined. The water column conditions are based on the change in potential energy relative to the potential energy when the water column is mixed, and depend on the balance of heat at the air-sea interface, wind and tidal mixing. A negative potential energy change dv/dt develops stratification and positive potential energy change tends to mix the water column. In Rabigh Lagoon, the water column remains mixed throughout the year except in September-October, when a weak stratification develops. The flushing time of the lagoons varies from a few days to about a month. The marine environment in arid zone lagoons is under stress due to high temperature and salinities. However, the present-day flushing time scale may not exert an intolerable stress on the ecology of these lagoons. The relative important of local wind in the flushing of these lagoons can vary substantially. The changing environment of these lagoons due to rapid urbanization, industrialization and utilization of the coast may change their conditions. These lagoons are highly productive but are also stressed by anthropogenic inputs and human activities and need continuous monitoring.