Dams and reservoirs are functional assets of river basins, particularly in areas with strong seasonal variations in rainfall-runoff patterns, where they can regulate river flow to prevent flooding, as well as in areas with ever-growing water and energy demand due to growth of economy and population. However, it is obvious that any intervention in a natural system induces adverse impacts on the ecosystem. Additional negative impacts of dams and reservoirs can also be attributed to poor planning, mismanagement, inefficient operation and improper consideration (or negligence) of impact mitigation options and conditions.
The major environmental problem of dams in a river basin is the disturbance in natural flow dynamics and sediment transport, for example shortage in downstream flow and sediment supply leading to micro- to large-scale morphological changes and changes in species habitats. These changes do not only impact riverbeds, floodplains and settlements, but also aquatic and riparian habitats (e.g. wetlands and fish spawning areas) and ecological processes (e.g. fish migration cues). On the other hand, the reservoirs themselves suffer from sedimentation problems, and one of the main sediment-induced problems is storage loss. Globally, the total storage in reservoir is around 7000 km3. Due to sedimentation, we lose around 57 billion m3 per year (ICOLD 2009). The available water storage per capita is decreases since 1980. This means the solution we have so far is not sustainable.
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 in the reservoir and the river system (changing temperatures, sediment starvation, blocking fish migration, altering habitats, etc.). The shortage of sediment creates different bed characteristics which might not be suitable for aquatic life, particularly 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 river ecosystem and habitat suitability.
Deltares together with J-Power are aiming to improve the knowledge related to sediment management in rivers with reservoirs considering ecosystem of the river basin. A process-based tool has been developed and applied, namely a 2D-model (Delft3D) that is coupled with RTC-tools to mimic the real time dam operation of a single reservoir considering sediment transport and morphology. This has been used to optimize the sediment management in the reservoir and the river downstream. However, it is important to consider river ecosystem in relation to sediment management for rivers with a cascading system of dams. Consequently, it is vital to incorporate this in the modelling tool and test a large scale synchronized system operation of multiple reservoirs that at the same time integrate both sediments and ecological aspects.
The main objective of this project is to further deepen, broaden and integrate our knowledge and improve our tools (add-ons and coupling) to be able to link the dam and sediment management operation with ecology. Followings are some of the objectives of the proposed project:
1) To implement new functionality in our modelling tool to improve the morphological replication and prediction with dam operation that could be more useful to assess river environment and habitats
2) To improve and test our tool to replicate efficient and optimal sluicing and flushing operation of the system of reservoirs in a cascade
3) To improve and integrate our tools (morphology, dam operation and ecology) that could be used to address the problems of mitigating negative ecological effects and maintaining sustainable aquatic ecosystems.
4) To apply new developments (like Delft3D-Flexible Mesh and Delta-Shell) and make our tools more user-friendly
This allows quantitative assessment of implications and impacts of dam and reservoir operation and management scenarios on river morphology and ecology. This will help to determine the optimal management strategy for green and sustainable development of river system with reservoirs.
3. Expected results
Expected results are outlined as follows:
1) Update of Delft3D code with a new approach of spatial porosity and computation of consolidation
2) Delft3D4 model testing and application case with RTC, morphology and habitat suitability assessment
3) Implementation and validation of HABITAT model using Delft3D-Flexible Mesh and Delta-Shell
4) Memorandum with the results and a conference paper together with J-Power (and other contributors) → published in Riverflow2020.
River Flow 2020 Proceedings of the 10th Conference on Fluvial Hydraulics (Delft, Netherlands, 7-10 July 2020)
Omer, A., K. Sloff (2019): Environmental preservation and sediment management in Funagira Dam. Deltares-report 112003050-002-ZWS-0001.
Van Oorschot, M., Yossef, M., Jeuken, M. (2019). System understanding and ecological modelling of the Tenryuu River. Habitat suitability modeling of Ayu downstream of the Funagira dam and understanding the cascading system of the Tenryuu River. Deltares report 11203051-002-ZWS-0004.
van Oorschot, M., Harezlak, V., Jeuken, M., Omer, A., Kitamura, Y., Giri, S., ... & Buijse, T. (2020). Impact of dam operations on the habitat suitability of Plecoglossus altivelis downstream of the Funagira dam, Japan. In River Flow 2020 (pp. 2101-2109). CRC Press.
GIRI, S., HUANG, H., OMER, A., & KITAMURA, Y. MORPHOLOGICAL COMPUTATION OF A CASCADE SYSTEM OF DAMS USING DELFT3D-FM COUPLED WITH A REAL-TIME CONTROL TOOL. Proceedings of the 22nd IAHR-APD Congress 2020, Sapporo, Japan