Photogrammetry for flow measurements at hydropower plants with no operational restrictions or limitations

During refurbishments of hydropower plants, optimisation of the usage of the water, and changed operating conditions, flow-related variables usually need to be considered. This may be losses, discharge capacity, hydraulic loads, level variations, air swelling, splashing, icing, attraction flow, erosion, and sediment transport. Measurements of the water flow close to hydropower plants are normally time-consuming and therefore costly due to a complicated geometry, large volumes, transient effects, etc. It is therefore in place to evaluate efficient methods to measure fluid flow and in this project focus is set on photogrammetry.

In the first part of this project, between 2019 and 2022, a multi-camera photogrammetric technique, to measure the 3D velocity of free surface flows, was developed and validated in lab and in field. The differences in velocity measured by photogrammetry and other techniques boils down to a few percent in lab while the error in field is larger but still resonable. It is furthermore shown that the measurement can be based on natura features appearing on a surface. A main result is also that for a stationary installation the technique is ready to be used even for more chaotic flows in spill-ways, for instance. Now the aim is to extend the technique in two directions i) be able to do 2D velocity measurements with drones, ii) measure the bathymetry. This will result in five deliverables.

The objectives of this project, which will end at 2024, is to develop the new photogrammetric technique to make it more flexible and extend the areas of application. This will imply that the technique do not require extensive operational restrictions, security restrictions or expensive equipment. It also implies that focus is set on applied and plant-based research that has a close­-to-implementation profile for easier utilisation/commercialisation. In particular the objectives are to:

1. Show the potential of doing photogrammetry of river surface velocity by drones in 2D.
2. Determine if it is possible to map the bathymetry with the technique.