An Efficient Technology for Reservoirs Dredging
WODCON XXIII - Dredging is changing - The Practice. The Science. The Business.
F. Aldà, A. Ranaldi
"The subject of reservoir dredging has been a matter of continuous study and development due to the immense impact that the conditions of the reservoirs have on the everyday lives of human society. Whether it's for irrigation, power generation or water storage, the consequences of having sediment accumulate in these reservoirs and therefore reduce their capacity can impact food supply chains, water availability and power generation, as well as limiting the capacity that these structures have to perform their duty. Under the current conditions, it is estimated that by 2030, 50% of the worldwide reservoir capacity will be lost due to sedimentation related issues and if no solutions are in place to tackle this issue it could have catastrophic consequences in future years. For this reason. it is mandatory for reservoir management entities as well as government agencies to have a reliable solution that can manage the sediment and dispose of it, maintaining maximum capacity in the reservoirs and mitigating the risks of downstream problems. These solutions must not only account for the sediment already within the reservoirs but also be able to manage the incoming rate of sediments entering the area. For this reason, it is important to define the most critical points for each reservoir and develop a solution that can fit within these requirements case by case. Conventional methods involve the emptying of the reservoir for extraction of the sediments through earth-moving machines, but this operation has proven to be very expensive and inefficient due to the high costs involved and the necessity to stop any operation depending on the reservoir. Another common alternative is that of using turbidity currents that flow along the bottom of the reservoirs. These can help carry the sediments downstream and out through discharge valves at the dam. This method whoever depends on the occurrence of the turbidity currents and is limited to removing the incoming sediment and not the sediment already present in the reservoir. Several other methods are used, but most of these are limited by a cost factor and low efficiency at which they dispose of the sediments. Dredging has surfaced as a very interesting alternative to common methods to remove sediment, since it allows that the reservoir is kept fully operational during the dredging activities as well as providing the opportunity to handle and dispose of the sediment with minimum turbidity and at the best convenient location for each project. There are several alternatives to the placement of the dredged material such as the use of geotextiles in which the dredged slurry is pumped inside porous bags where the solid is contained and the water is returned to the dredging area. This method can be used to provide support to the reservoir shores by using the geotextiles as reinforced containment structures. Another alternative is that of directly pumping the material downstream so that it can be naturally carried away. This has proven to be the most environmentally sustainable practice as it simulates the natural flow of sediments before the reservoir was even built, as long as the concentration of the removed sediments do not exceed the natural sediment load of the downstream waters. One important factor to consider when dredging reservoirs is the depth, as it can be considerable especially for reservoirs used for hydroelectrical power generation. This will be a crucial parameter when defining the most suitable solution for the reservoir as it can greatly affect costs and requires specialized equipment. Different dredging technologies have been developed to manage these issues, such as those manufactured by"