Impact of climate change on persistent turbidity in the water supply system of a Metropolitan Area

Persistent turbidity, a long-term resuspension of fine particles in aquatic system, is one of the major water quality concerns for the sustainable management of water supply systems in metropolitan areas. Turbid water has undesirable aesthetic and recreational appeal and may have harmful effect on ecosystem health, in addition to increasing water treatment costs in drinking water supply systems. These concerns have been more intensified as the strength and frequency of rainfall events increase by climate change in the Asian monsoon climate region, including Korea. The aim of this study was to assess the impact of potential climate change on the persistent turbidity of the Han River systems that supplies drinking water to approximately 25 million consumers dwelling in the Seoul Metropolitan areas. A comprehensive numerical and statistical modeling suit has been developed and applied to the systems for the projection of future climate, responding hydrological and soil erosion processes in the watershed, and sediment transport processes in the rivers and reservoirs systems. The down-scaled 100 years of climatic data from General Circulation Model (HadGEM2-AO) based on the IPCC's greenhouse-gas emissions scenario RCP4.5 were used for the forcing data of the watershed and river-reservoir models. As the results, an extreme flood event that may incur significant persistent turbidity was projected to be occurred five times in the future. The threshold of a flood event that is classified as an extreme event was based on the historical flood event that occurred on July of 2006 when turbid water had persisted within the Soyang Reservoir and discharged to the downstream of the Han River systems over the year until May of the following year. A two-dimensional river and reservoir model simulated the transport and dynamics of suspended sediments in Soyang Reservoir, and routed the discharged turbid water to the downstream of Paldang Reservoir, in which most of the drinking water offtake facilities are located. The statistical features of the extreme flood events, their impact on the persistent turbidity on the downstream rivers and reservoirs, and consequently on the water supply system of the Seoul Metropolitan areas will be presented in the special session.