Abstract
The purpose of this study was to evaluate the streamflow and water quality (SS, T-N, and T-P) interaction of the Nakdong river basin (23,609.3 km2) by simulating dam and weir operation scenarios using the Soil and Water Assessment Tool (SWAT). The operation scenarios tested were dam control (Scenario 1), dam control and weir gate control (Scenario 2), dam control and sequential release of the weirs with a one-month interval between each weir (Scenario 3), dam control and weir gate full open (Scenario 4), dam control and weir gate sequential full open (Scenario 5), weir gate control (Scenario 6), weir gate full open (Scenario 7), and weir gate sequential full open (Scenario 8). Before evaluation, the SWAT was calibrated and validated using 13 years (2005–2017) of daily multi-purpose dam inflow data from five locations ((Andong Dam (ADD), Imha Dam (IHD), Hapcheon Dam (HCD), Namkang Dam (NKD), and Milyang Dam (MYD))multi-function weir inflow data from seven locations (Sangju Weir (SJW), Gumi Weir (GMW), Chilgok Weir (CGW), Gangjeong-Goryeong Weir (GJW), Dalseong Weir (DSW), Hapcheon-Changnyeong Weir (HCW), and Changnyeong-Haman Weir (HAW)), and monthly water quality monitoring data from six locations (Andong-4 (AD-4), Sangju (SJ-2), Waegwan (WG), Hapcheon (HC), Namkang-4 (NK-4), and Mulgeum (MG). For the dam inflows and dam storage, the Nash-Sutcliffe efficiency (NSE) was 0.59~0.78, and the coefficient of determination (R2) was 0.71~0.90. For water quality, the R2 values of SS, T-N, and T-P were 0.58~0.83, 0.53~0.68, and 0.56~0.79, respectively. For the eight dam and weir release scenarios suggested by the Ministry of Environment, Scenarios 4 and 8 exhibited water quality improvement effects compared to the observed data.
Highlights
Water is one of the most important resources for human survival
The total release amount was subtracted from the total inflow from the upstream, the result was regarded as the actual release amount, and the module inside SWAT was modified so the result could be considered
Parameter estimation was applied to the model through a process of trial and error which involved selecting optimal parameters based on previous studies to simulate hydrological and water quality elements in a balanced manner
Summary
Experts who engage in water resources planning and management must address how to determine policy in accordance with future climate change and how to evaluate the resulting environmental effects [1]. In South Korea, the Four Major Rivers Restoration Project has been in place since the end of 2009 to prevent drought and flooding due to climate change, and to create healthy water ecosystems as well as various waterfront spaces. The Survey and Evaluation Committee of the Four Major Rivers Restoration Project proposed that to reduce algal bloom and improve water quality, it is necessary to simultaneously increase streamflow and lower weir water levels through the combined operation of dams, weirs, and reservoirs. In response to water pollution, related ministries such as the Ministry of Environment (ME) and the Ministry of Land, Infrastructure, and Transport (MOLIT) have reviewed plans for dam-weir-reservoir combined operations through the Dam-Weir Combined Operation Council, and they have performed partial release for some dams and weirs in the Nakdong River since August 2016
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