Pontecosi is a tiny dot on the map of Garfagnana, an area of Tuscany, Italy, that is rich in history and natural attractions. The village is visited mainly by hikers and mountain bike enthusiasts who enjoy adventuring in the local hills, which are covered in chestnut woods. The artificial lake of the same name also attracts families and anglers, who come here to relax on its shores. The lake was created in 1924 by the damming of the Serchio River in order to produce electricity. This tranquil place is known to few; however, it is now attracting the interest of hydroelectric experts from all over the world thanks to a project launched recently by Enel Green Power. A unique experiment At Pontecosi, EGP is testing an innovative system for the continuous removal, in controlled concentrations, of the sediment that builds up on the bottom of reservoirs. The project uses a small electric vessel measuring 5 meters in length and 2 meters in width, equipped with a system that uses powerful jets of water to separate the deposits of mud, clay and gravel left by the currents on the bottom of the lake. A pump sucks up the deposits into a system that then flushes them out downstream from the dam in quantities that have been studied meticulously to replicate the natural flow and dynamics of the river. The entire system contributes to the maintenance of the natural equilibrium of the river basin, is extremely quiet, doesn’t produce emissions because it uses electric energy, and helps to tackle a problem that limits the efficiency of a large number of hydroelectric power plants around the planet. The test conducted in Italy could well turn out to be a hi-tech, low-impact solution worth replicating elsewhere. The problem of sediment Dams are extremely useful because they can ensure important reserves of water for local communities, they enable the development of ecosystems in which many species of flora and fauna make their homes and they facilitate the production of clean energy with zero emissions. According to the latest data from the IEA, hydroelectric power now boasts an installed capacity at global level of more than 1,300GW. It is the most used renewable energy source: the latest report by IRENA, the International Renewable Energy Agency, states that hydroelectric power makes up more than 46% of clean electricity produced around the globe. The build-up of materials transported by rivers, however, can seriously limit the efficiency of hydroelectric plants. Various studies have shown that every year, sediment reduces the hydraulic capacity of hydroelectric reservoirs by between 0.5% and 1%. Unless mitigating measures are adopted to control the phenomenon, its effects in the coming years could even impact the planet’s reserves of fresh water. Furthermore, accumulations of sediment increase the load on structures, can potentially damage mechanical equipment, reduce reservoirs’ capacity to contain floods and have a negative impact on the production of energy. Many possible solutions The issue of sediment build-up is well known to experts and has led to the development of numerous methods to limit it that intervene upstream from the reservoirs: for example, by controlling erosion and maintaining and replanting the vegetation on river banks, or by creating bypass tunnels or external storage reservoirs away from the main flow of the current, without altering the flow of the transported material. A further strategy is the removal of sediment using traditional systems of dredging that, while effective, have a number of disadvantages, such as significant environmental impact, high energy costs and the production of polluting emissions. And it is on this front that that the method being tested by Enel Green Power in Lake Pontecosi could provide the solution. The phases of the EGP project Initiated in November 2019, the project was launched following an in-depth analysis of various approaches adopted around the world for the continuous removal in controlled concentrations of sediment, conducted with a focus on environmental sustainability among the main parameters considered. In the spring of 2020, due to the Covid-19 pandemic, activities were suspended until December 1, when the project recommenced with the aim of concluding the experimental phase by the end of 2021. A successive evaluation of the results will serve to help plan a three-year campaign at Lake Pontecosi to remove a quantity of between 50 and 60 thousand cubic meters of deposits per year. Before beginning the work of removing the deposits, EGP’s experts conducted an in-depth study of the type of sediment found in the lake, the dynamics of its build-up and the overall balance in the Serchio river basin, which transports suspended material in quantities of around 20 thousand cubic meters a year. Ongoing improvements These studies enabled EGP to determine how to make the system work without altering the natural balance of the course of the river upstream from the dam. For this purpose, an automatic control system was created to manage the quantity of sediment to be removed by regulating the speed of the pump and positioning the mouth of the suction system. The new testing session that started on December 1 was able to implement a series of improvements to achieve a perfect match between the planned and the actual quantity of sediment removed from the lake. It is an important step forward in understanding in detail how the system works and making it applicable to any other artificial reservoir in the world.
