Digital twins of regulated river stretches

Digital twins of rivers can be used as an advanced hydraulic- and ecological modelling tool that can provide powerful means for evaluating impacts of various river management scenarios such as river flow regimes and habitat restoration on fish populations.

Flow fluctuations resulting from load-following (i.e., hydropeaking) can be controversial, in part because they may affect downstream fish populations through both acute processes such as scouring or stranding and cumulative changes in habitat quality. Assessing these effects are keys for well-informed decision-making regarding the trade-off between producing fossil-free electricity and conservation of aquatic biodiversity.

In order to accurately predict the ecological response in a water course, in-depth knowledge of the hydraulic conditions are required such as the dynamic variations in water depth and local flow velocities. Gathering the required amount of hydraulic data experimentally for a range of different flow scenarios in the field is not feasible and therefore hydraulic models that can simulate both steady flows and dynamic flows for an entire river reach is the preferred method of choice. By expanding the digital twins to also include Individual-Based Models (IBMs), the population of relevant fish species can be simulated on an individual fish basis and their response to different flow scenarios can be predicted.

Three potential case-studies with interesting environmental applications and different stages of relicensing within the NAP process have been identified and will be utilised in this project.

1. Bredforsen in Dalälven, as a Natura 2000 site has important and unique riparian floodplains and forests with an significant population of Grayling.
2. Kungsådran presents the only possibility for fish to ascend the river Dalälven until reaching the dam in Älvkarleby and consists of an experimental area isolated from the main channel, limiting habitat access for Atlantic Salmon.
3. In the upstream parts of Luleälven there are two parallell river stretches where one has a much more established population of Grayling and the other (Akkats-Letsi) could benefit from environmental measures.

The results from the three case-studies will be compiled and general suggestions regarding hydropeaking conditions, environmental flows and possible hydraulic measures will be given in relation to their effect on river hydraulics and the response of the population of target fish species.