Sediment management works in reservoirs

From the antiquity still, man searched for ways to exploit the enormous volume of the aquatic resources to his profit. Water supply, irrigation, flood control and later, hydropower production are only a few of the needs that were covered with the hemming of water via the dams. Over the years however, the basic obstacle becomes only bulkier: the loss of the biggest part of reservoirs’ beneficial volume, due to the accumulation of sediments in them. Furthermore, because of the environmental approach that local communities have over the past years, the phenomenon of environmental degradation, resulting from the construction of a dam and occuring downstream of the reservoir, must be resolved as well. For the confrontation of the problem, the complete comprehension of the mechanisms, which lead to his birth, is essential. In the basin under review, soil erosion first takes place, then follows the transport of the eroded materials and finally the deposition of them in the reservoir. Those three mechanisms function in succession and contribute, each one in a different degree, in the loss of the reservoir’s beneficial volume. The finding of an effective method of confronting the problem is in the foresight of the scientific community. The methods of managing the sedimentation can be separated in three categories, with the most effective and applicable to be considered that of hydraulic flushing. According to the experience and knowledge that has been acquired by the application of the method worldwide, it is believed that this is the one that can lead to an reintroduction up to 100% of the volume of a reservoir. The conditions, of course, for its effective application are relatively strict, without however this meaning that they can only be satisfied in a small number of reservoirs worldwide. Another solution in the problem of the accumulation of sediments is the construction of a reservoir bypass system. This method is based on the construction of a bypass tunnel, but unfortunately does not find wide application due to its increased cost, as well as the high cost of its maintenance. However, after studying and planning such a system in an under-study reservoir in Greece, it was proved that the cost of this method is indeed increased, but at the same time does not exceed only but a small percentage of the total cost of the construction of the dam. It is worth, of course, to be marked that the under-study reservoir is of a special purpose and does not represent the biggest percentage of the constructed reservoirs. It is consequently, a relatively simplified case. The problem of the accumulation of sediments is the most serious and important problem that is related with the exploitation of the aquatic resources. Consequently, it is equally important and necessary for a widely applicable solution to be found. After the study of the reservoir bypass system that was mentioned before, there is a sense that even in Greece, the problem can finally find an economically applicable solution, opening a new page in the combating of the environmental impacts, following the construction of a new dam, and the loss of the reservoirs’ beneficial volume at the same time.