Assessment and Mitigation of Akagera River Avulsion

Between 2015 and 2016 an avulsion occurred at Lake Rweru, which changed the course of the Akagera River about 50 km upstream of the dam site. Previously, the Akagera River bypassed Lake Rweru. However, since the avulsion the Akagera River flows into the lake. There are concerns that this might have negative impacts on downstream river flows at RRFHP.

The objective of this study is to analyse the impacts of the avulsion on the flow conditions and electricity generation at the hydropower plant. The study uses a combination of field surveys as well as advanced hydraulic and hydrological modelling tools.

AFRY provides the modelling and hydropower expertise in this study, whereas project management and field work is covered by the partner Hydroc (Germany).

The methodology and results are discussed and presented at workshops in Rwanda and Burundi.

Facts to Project

Client: Nile Equatorial Lakes Subsidiary Action Plan (NELSAP)

Services:

• Collection of hydro-meteorological data from national authorities.
• Field measurements to collect river cross sections, bathymetry at avulsion zone, flow velocity and sediment transport data.
• Sediment assessment before/after the avulsion and sediment transport to the hydropower plant.
• Detailed 2D hydraulic modelling of the inflow-outflow relationship between the river channel and Lake Rweru.
• Hydrological analyses with a rainfall-runoff model to assess inflow to the hydropower plant from Akagera River as well as lateral inflow from Ruvubu River. Consideration of evaporation losses at Lake Rweru.
• Impact assessment of avulsion on electricity generation at the hydropower plant for 40 year scenarios with/without avulsion.
• Outline of possible mitigation measures.

Project period: 2019 - 2020

Location: Rwanda, Burundi and Tanzania