How hydropower can deal with sediments
Sediments get deposited in storage lakes and increase the erosion of hydraulic turbines. To keep hydropower plants operational for as long as possible, researchers are developing new methods of monitoring sediments in real time.
Hydropower is the most important source of renewable electric energy worldwide, but it’s not uncommon that it has to face a serious challenge: Many storage lakes and stretches of river upstream of run-of-river hydropower plants are filling up with sediments transported by the inflowing rivers.
Without adequate countermeasures, the storage volume continuously diminishes and eventually completely vanishes, having negative effects on hydropower production. A storage power plant would turn into a run-of-river plant, losing its main asset of supplying peak energy when demand is high. Further negative effects of sediments are an increasing wear of hydraulic machinery such as turbines and pumps, as well as of auxiliary infrastructure like weirs, desanding facilities and flushing channels, resulting in increased operation and maintenance costs. The hydro-abrasive wear of turbines adversely affects their geometries, which leads to reduced efficiencies and the loss of power production.
Need for countermeasures
There are a multitude of countermeasures to cope with sediments. They all have in common that they require either high investments or an appreciable amount of water that can no longer be used for energy production, thereby reducing revenues. Nevertheless, to keep hydropower facilities economical, environmentally friendly and socially acceptable over the long term, there is no alternative to finding sustainable solutions to cope with sediments. Moreover, water protection acts in many countries today require sediment continuity to be re-established in river systems where sediments are partly or fully trapped upstream of weirs, dams or other engineering structures across a river (see also this blog post).
Interesting solutions that have already proven to be technically feasible and environmentally favorable include the following:
– Constructing sediment bypass tunnels around dams
– Venting turbidity currents
– Regularly flushing through low-level dam outlets
– Removing sediments using hydro-suction
A new approach
In my view, another approach that deserves further research and development is to continuously pass fine sediments to downstream stretches of river via the power waterways and turbines. This method keeps the sediment flux similar to what it was before the construction of the hydropower plants. Despite increasing the wear on hydraulic machinery, this method seems promising for a number of mainly Alpine reservoirs where alternative solutions are either cost-prohibitive or unfeasible due to legal restrictions. To counter turbine wear, special coatings may significantly reduce hydro-abrasion.
To keep hydropower plants operational for as long as possible, researchers are developing new methods of monitoring sediments in real time, while also expanding their knowledge on how sediments are transported, deposited, and removed and how machinery is subject to sediment-induced wear. Furthermore, real-time and continuous monitoring of suspended sediment characteristics such as concentration and particle size allows for short-term decision-making by the operators. One option is to “switch off” power production during floods when certain threshold values are exceeded and the hydraulic machinery would be eroded disproportionately.
Sediment-management gets more important
As part of our research in the SCCER-SoE [1], we are focusing on the erosion of turbines, on sediment bypass tunnels and flushing channels. We also develop prediction models and measuring techniques for the real-time monitoring of bed load and suspended load, applying both experimental and numerical methods. Many countermeasures can be taken to minimize the negative effects of sediments, but in our experience they need to be optimized site-specifically. Therefore, improved knowledge of the relevant processes and measuring techniques serves as a basis to develop sediment-management solutions that are tailored to the specific sites.
With ageing reservoirs and ongoing glacier retreat, sediment management at hydropower schemes is becoming even more important. However, glacier retreat also offers important new possibilities for further hydropower development, in line with the Swiss Energy Strategy 2050.
This article is also available in the external page blog of the SCCER-SoE.
Further information
[1] The Swiss Competence Center for Energy Research – Supply of Electricity (external page SCCER-SoE)
