Sediment management for catchments with hydropower dams under uncertainty in future projections. (2020)
Type of ContentTheses / Dissertations
Thesis DisciplineCivil Engineering
Degree NameDoctor of Philosophy
PublisherUniversity of Canterbury
The sustainability of hydropower reservoirs in catchments undergoing rapid development in the Mekong River Basin depends on the projected level of sedimentation. Excess sedimentation of reservoirs can be mitigated by using appropriate sediment management, but uncertainties in sediment predictions need to be addressed to better inform the selection of sediment management options. It is necessary to understand the magnitude of uncertainty in future sediment in response to land use/ land cover (LULC) change, climate change and sediment model parameterization. It is also necessary to evaluate the implication of catchment and reservoir-level sediment management options and costs under uncertainty in sediment projections.
Hence, this study aims to evaluate the uncertainty in sediment projections due to LULC, climate and model parameterization, and the implication of sediment management options and costs for catchments with hydropower dams. The following specific questions were investigated: a. How do future climate scenarios and model parameterization affect the uncertainty in flow and sediment projections? b. How do LULC change scenarios affect the uncertainty in flow and sediment projections? c. How do combined future climate scenarios, model parameterization and LULC change scenarios affect the uncertainty in flow and sediment projections? What is the major source of uncertainty in flow and sediment projections? d. What is the implication of sediment management options and associated cost under the greatest source of uncertainty in sediment projections?
The Sekong, Sesan and Srepok (3S) sub-basin of the greater Mekong River Basin was used as a case study.
The Soil and Water Assessment Tool (SWAT) was used to simulate flow and sediment. Uncertainty in future climate scenarios was addressed using three Global Climate Models (GCMs) and three Representative Concentration Pathways (RCPs). Model parameter uncertainty was analyzed by calibrating SWAT model using three different optimal objective functions. For evaluation of LULC change uncertainty, twelve LULC change scenarios were generated applying Land Change Modeler (LCM), and combining three LULC demands, two transition potential models and retaining or not protected areas. The catchment-level sediment management options of terracing, vegetative filter strips and no tillage were evaluated using SWAT. The reservoir-level sediment management option of flushing was assessed using the Sediment Simulation Screening Python Model (PySedSim). Costs of sediment management options were assessed via the economic value of loss in hydropower production and the avoided cost of dredging.
The evaluation of uncertainty in flow and sediment projections associated with future climate scenarios and model parameterization suggests that the dominating source of uncertainty in flow and sediment can vary spatially and temporally for large basins. In short-term period projections (2030s), model parameterization dominates the uncertainty in flow and sediment, while in long-term projections (2060s) selection of climate scenarios dominate. Model parametrization uncertainty needs to be incorporate in climate change impact studies and efforts should be made to reduce the uncertainty due to model parametrization through a careful calibration and validation.
The assessment of uncertainty in flow and sediment in response to LULC change alone suggest uncertainty is primarily driven by LULC demand, resulting in large variability of flow and sediment projections.
The evaluation of uncertainty in flow and sediment in response to future climate scenarios, model parametrization and LULC change suggest that for a basin undergoing rapid LULC change uncertainty in future flow and sediment is dominated by the choice of LULC change scenarios. Hence, LULC change uncertainty should not be neglected in evaluation of climate change impact on basin hydrology.
Uncertainty in future sediment loads in response to LULC change can result in high variability in loss of reservoir capacity and cost of sediment management. Terracing performed best among the catchment-level management options in reducing the magnitude and variability in loss of reservoir capacity, but it is the most expensive option to implement. Flushing, although effective in increasing the life span of reservoir, was found less cost effective compared to catchment-level management options. The research outcome suggests that the best catchment- management option for reservoir sustainability may not be the best in terms of cost. Further, catchment-level management options do not address the issue to sediment starvation downstream, hence integrated sediment management approaches (i.e, combining both catchment-level and reservoir-level) may be required to reduce the adverse effect on reservoir storage and permit sediment flux downstream of the reservoir.