A review of salinity management for coastal reservoirs with the aim of storing flood drained into sea

Document Type : Review Article


1 Assistant Professor of Hydraulic Engineering in Shahid Rajaee Teacher Training University

2 Director of River and Coastal Engineering Unit, Iran Water and Power Resources Development Company, Elahieh, Tehran, Iran.


Introduction - The importance of providing fresh water as one of the principles of achieving sustainable development is not hidden from anyone. Unfortunately, in many developing countries such as Iran, access to fresh water is associated with many problems. The water in aquifers, which supply water to one-third of the world's population, is being consumed more than nature can recover them. On the other hand, almost all large surface water storage dams were built in gorgeous sites. Despite spending a lot of money and innovations in the construction of surface reservoirs, according to UN surveys, more than one billion people currently lack adequate and clean drinking water. Therefore, water shortage will become one of the main constraints on economic development in the near future.
In recent years, population growth and rapid economic development have exacerbated the problem of water shortage, especially in coastal areas, to the point that meeting freshwater demand has become a serious challenge for coastal communities. A coastal reservoir is defined as a water storage structure constructed at river estuary or other coastal area to store fresh water and control water resources. One of the obvious advantages of coastal reservoirs is providing additional fresh water storage capacity for water supply networks. In areas under water stress, coastal reservoirs, which are often the basis of local economic development, can help reduce water scarcity. Many coastal reservoirs have been developed in China, South Korea, Hong Kong and Singapore. Despite the importance of coastal reservoirs, there is a little scientific research on these structure in the authorities and many issues in this regard have not yet been resolved. In the present review study, the most important issues and problems related to these structures are presented. Finally, different new topics for future studies are presented.
Methodology - Accordingly, while introducing coastal reservoirs, their advantages and disadvantages and the appropriate potential that Iran has for the construction of these reservoirs were discussed. In the following, the studies performed on the reservoir dynamics and the mechanism of salinity transfer and diffusion, were mentioned. The most important concern about the performance of this method of water supply is the control of salinity entry into the reservoir, which requires the adoption of special measures in reservoir operation policies. In the study of different authorities, while introducing this important challenge in the two periods of washing and operation parts, 6 boundary conditions controlling the performance of the reservoir were presented. These boundaries are water level, side, Intertidal zone, inlet rivers, reservoir bed and dam. Also, the factors affecting hydrodynamics and salinity transfer in coastal reservoirs such as meteorological conditions, sediment and intertidal zone, upstream rivers, saltwater-freshwater mixing rate, seawater leakage, exchange between coastal reservoir and groundwater, coastal reservoir and lateral side groundwater, coastal reservoir and underlying groundwater, coastal reservoir and submarine groundwater and finally subsidiary functions of coastal reservoirs were investigated. Then, special attention was paid to salinity as the main factor affecting water quality in reservoirs and studies on salinity transfer in coastal reservoirs or wetlands in three parts: desalination, salinization or seawater infiltration and numerical simulation. Finally, the titles of new projects that could be done by researchers in the future were introduced.
Results and discussion - Coastal reservoirs enable the storage of excess river flood waters near the coast for future use in areas known to be drought-prone or at those times of the year when water supplies become scarce. Construction of a coastal reservoir does not involve many risk factors and disadvantages like relocation which would be there in inland dam construction. The construction of coastal reservoirs in Iran, especially the southern coasts can solve the problem of water shortage in in these areas. On the other hand, it seems that due to the problems of building inland reservoirs such as suitable topography in some southern part of the country, the use of these reservoirs is the only solution.
Conclusion – Coastal reservoirs need to be rationally utilized. In the present study, with considering different findings from previous studies, several avenues for future research on coastal reservoirs were presented. Hydrodynamics of reservoir water and adjacent groundwater, especially the hydrodynamics near the six boundaries as discussed in this paper. Methods of washing the salty water and sediment, Morphological changes and coastal sedimentation at the vicinity of coastal reservoirs, Sediment transport in the reservoir, Operation of sluices and the influence of dams, Integrated three-dimensional models of water in the reservoir, access channel, groundwater and river and Transfer of contaminants such as heavy metals into the reservoir are some important topics which should be considered in future researches.


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