Assessing environmental flows of coordinated operation of dams and weirs in the Geum River basin under climate change scenarios

Abstract

The International Panel on Climate Change (IPCC) has predicted frequent and severe droughts and floods caused by irregular climatic conditions in the future, making water resources management difficult. Within the field of integrated watershed management, the concept of ‘environmental flow’ is being increasingly studied. In Korea, the Four Major Rivers Restoration Project was carried out as part of the plan to manage future water resources, particularly in response to climate change. In order to improve comprehensive water resources management, there is an interest in integrating into the operation of the existing dams the multi-functional weirs constructed under the said project. To date, there is an absence of studies comprehensively considering climate change, run-off volume, reservoir operations, and environmental flow, with most of the existing studies focusing only on one or the other of these factors. In this study, we presented a method to evaluate the river environment that considers all the said factors. To evaluate how environmental flow is influenced by the changes in river flow due to climate change and hydraulic structure operation, the Streamflow Synthesis and Reservoir Regulation (SSARR) was used as the hydrological model, HEC-ResSim was used as the hydraulic structures operational model, and the Global Environmental Flow Calculator (GEFC) was used as the method to evaluate environmental flows. RCP climate change scenarios, provided by the Climate Change Information Center (CCIC), a branch of the Korea Meteorological Administration, were applied to analyze the future watershed runoff characteristics of the Geum River Basin under different hydraulic structure operation modes. This study concludes that efficient use of water resources can be achieved through the integrated operation of the dams and multi-functional weirs in times of water shortage. Comparing the results of modelling under a no‑carbon reduction scenario on one hand, and a scenario in which emissions were reduced on the other hand, differences were found in flows during floods, in the mean annual runoff ratio in accordance with the environment management class, and in the environmental flow rating. It appears that a new water resources management plan is required to respond to climate change as indicated by the shift of the flow duration curve to a lower environmental management class (EMC) under climate change scenarios.