Funagira Dam                                                                                                                                        Left: maximum suspended sediment concentrations (104 mg/l) during flushing compared between

                                                                                                                                                                 scenarios with different reservoir water levels. Right: response curve for feeding P. altivelis provided by J-Power.

Introduction

The construction of dam operating regimes always presents a trade-off between power generation, water supply and/or flood protection on the one hand and ecological quality of the reservoir and the river downstream of the dam on the other hand. 

Sedimentation in reservoirs decreases their lifespan and has severe impact on the reservoir purposes. The trapping of sediment, in reservoirs, creates shortages in sediment supply downstream. This has implications for river morphology and creates ecological problems (changing temperatures, sediment starvation, blocking fish migration, altering habitats, etc.). The shortage of sediment creates different bed characteristics which might not be suitable for fish. The use of sediment management practices, such as flushing or sluicing to transport more sediment to the downstream, has not been fully investigated with respect to their consequences in improving habitat suitability. 

However, with the expansion of building reservoirs in cascading systems, sediment management becomes less effective and costly. The synchronization of sediment management in cascading systems needs to be explored further. To assist managers in selecting the most cost-efficient eco-friendly dam and reservoir management regime, knowledge and development of tools to diagnose the challenges and to provide the managers with integrated solutions is needed. 

Deltares together with J-Power are aiming to improve the knowledge related to ecology and sediment management in rivers with reservoirs. A 2D-model (Delft3D) has been developed and coupled with RTC-tools in order to mimic the real time dam operation of a single reservoir. This has been used to optimize the sediment management in the reservoir and the river downstream. However, because of the need to synchronize and optimize downstream ecology in combination with sediment management for river with cascading dams, it is vital to look for large scale system operation measures that integrate sediment and ecological aspects. A tool that covers the full pathway of sediments including its physical processes, and that integrates the ecological aspects on a system scale, does not exist yet in the world. Nevertheless, the increased need for sustainable operation of hydropower cascades does call for such a tool.

Objective

The aim of this research is to further deepen and broaden our knowledge and develop our tools (add-ons or coupling) to be able to link the dam operation with respect to ecology and sediment to:

1)    Efficiently flush the reservoirs (to increase their lifetime) in a cascade,

2)    Reduce erosion problems and increase the sediment supply within and downstream of a dam cascade and,

3)    Create a good and sustainable habitat and ecosystem downstream by integrating the habitats requirements in the dam operation.

 

This allows an assessment of the ecological and sediment implications of dam and reservoir management scenarios to determine the optimal cost-efficient management strategy, for green and sustainable development of rivers systems with reservoirs.  

Expected results

-       HABITAT model application for Funagira reservoir and the river downstream

-       Python scripts for improved workflow in HABITAT, and including meta-information;

-       New formula implemented in Delft3D sed-mor module.

-       2D morphodynamic and water quality model of Funagira reservoir and downstream reach that can be coupled to habitat model.

-       Python scripts will be uploaded to the HABITAT wiki.

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