Monitoring for sediment management

Sedimentary deposits are not wanted in hydroelectric plants as their necessary removal through emptying increases operating costs, and the sediment transported to power plants in waterways damages the turbines. The owner of the Grande-Eau plant in Aigle (Romande Energie SA) commissioned HYDRO Exploitation following the discovery of a large deposit in the headrace tunnel of the Farettes facility. Several proposals were submitted after a study was carried out. An innovative option was ultimately selected. It involved setting up a monitoring network that would measure the flow rate in the drainage basin, the turbidity at one of the water intakes, and the sedimentary deposits, including how they developed over time in the headrace tunnel.

Understanding, anticipating, and limiting the impact

The information obtained through monitoring not only helps us better understand the phenomena that cause silting, but also how it evolves and is affected by different weather conditions. It is most likely that the build-up of deposits in the Farettes tunnels is influenced by certain zones within the drainage basin and certain rainfall events. 

By analysing the data collected, it is possible to anticipate these build-ups, and modify the plant’s mode of operation in order to limit the impact they have.

The first phase of setting up the monitoring includes defining the location of the measuring points and the type of instrument best suited to the characteristics of the location, programming the modes for collecting the data, calibrating the sensors, and remotely transmitting the data. 

A multidisciplinary team was set up in HYDRO Exploitation to carry out these steps. The team was made up of engineers in civil engineering, computer science, automation and control, and geometrics. The measuring instruments are currently in place and operational.  

Recording a complete hydrological year

The aim of the second phase, which is under way, is to record a series of measurements covering a complete hydrological year. This will provide quantitative elements based on the weather conditions. The measurements are compared against events that drive the transport of solid particles: rainfall of varying intensities and/or snowmelt. This data is correlated with the mode of operation and observations from our operators at the plant. Distributing the measurements over the basin makes it possible to characterise the transfer of flows from upstream to downstream over a spatio-temporal basis. 

Our ultimate goal is to understand the phenomena, determine the relationship between cause and effect, and devise solutions to reduce the impact sedimentation has on the plant. 

Not all water is the right quality for storing

Alert criteria and proposals for operating instructions will be laid out in the third phase, which is scheduled to be completed by the end of 2023. These may include, in particular, weather alerts and preventative action at the water intakes most exposed to an extreme event. Not all water is the right quality for storing, especially if the detriment caused by water heavily loaded with sediment outweighs the production benefits. 

Finally, the information collected through this monitoring network will not only represent a valuable database on the projected sediment management, it will also be useful in the context of other studies and projects carried out on this plant.