Optimal multi-reservoir system operations under inflow scenarios in Nam Ngum River Basin, Lao PDR

Abstract

The Nam Ngum River is one of the main rivers in Lao PDR. Many hydropower projects are currently operated, under construction, and in the planning stage within the Nam Ngum River Basin (NNRB). These hydropower projects are managed by different organizations which could lead to conflict in operation and hinder the achievement of national developments. The main objective of this research is therefore to develop an optimization model for maximizing hydropower production in the NNRB through optimal reservoir operation under the impact of climate change. The potential consequence of maximizing hydropower production that could lead to flooding was also considered in this study. The optimization model for the optimal multi-reservoir operation with the specified constraints is the main focus of this thesis. It was developed based on mixed-integer nonlinear programming (MINLP) through the General Algebraic Modeling System (GAMS). The optimization problems were solved by Basic Open-source Nonlinear Mixed-Integer (BONMIN) optimizer. To assess the impacts of climate change, the biased corrected precipitation projection under different scenarios obtained from the regional climate models (RCMs) was used. Due to the limitation of streamflow data, the Integrated Flood Analysis System (IFAS) model was used to simulate the present and future streamflow in the NNRB. The results showed that the optimal single reservoir operation using the optimization model could increase the annual hydropower production by 12.2% compared to the actual operation. When the optimization model was applied to the multi-reservoir system, it could increase the annual hydropower production by 20.2% (6.0% from NN1 and 14.2% from NN2) on average. It was also found that the optimization model could reduce the flooding days and also flood peak, amount of outflow volume, flow-through spillway by approximately 4.8%, 3.6%, and 4.7%, respectively on average. The future annual precipitation based on RCP4.5 and RCP8.5 scenarios increase by approximately 8.2% and 17.4% on average, respectively when compared to the observation. The increase of precipitation could lead to an increase in the future streamflow under both RCPs and the large flood events could occur and probably last longer than what occurred in the past. The present and future indicative reservoir operating curves were developed from maximum and minimum storage levels based on the optimal release for maximizing hydropower production and could be used to support decision-making on the release. The results suggest that the application of the optimization model could potentially contribute to better control of the release with the specified constraints in this study. For further research, the uncertainties from climate change scenarios and socio-economic development scenarios should be considered.