Economic Evaluation on Self Purification Capacity of the Tamnip Stone Weir Reservoir: Replacement Cost Approach Method

Abstract

This study investigates the changes in the concentration of pollutants before and after the removal of stone weir by using EFDC models. This paper analyzes the impact of Tamnip stone weir reservoir on the water quality of the main stream, which is directly affected by discharge water at the sewage treatment plant in Daejeon. This study further extends the field by performing replacement cost approach method to examine the economic benefits of water quality improvement. As a result of the EFDC model''s level calibration, it was analyzed that the level of RMSE was 0.4 m, NRMSE 0.11, and NSEC 0.01, which were properly calibrated. Furthermore, for verification, the model was properly calibrated with RMSE 0.10 m, NRMSE 0.10 and NSEC 0.01. To evaluate the adequacy of the water quality model, calibration was performed using the water quality measurement data at the W-2 point once a month. Water temperature, COD, T-N, and T-P all four water quality items had an R2 value of 0.8 or higher and the NSEC was between 0 and 1, therefore it is reasonable to perform analysis using simulations. Replacement cost approach method is performed using alternative cost in order to evaluate environmental technology effect from the perspective of economic benefit. According to the analysis of the effect of the Tamnip stone weir on river water quality, the water quality tends to deteriorate in all items of COD, T-N, T-P, NH₄-N, NO₃-N, and PO₄-P, although there are seasonal differences when the weir is removed. The reason for the water quality increase is because there was not enough time for biological self-purification during the Tamnip stone weir demolition. The significant increase in the water quality concentration from June to September is most likely due to the influence of temperature. Therefore, it is believed that removing the Tamnip stone weir located in the target section will have a significant impact on the water quality of the stream. In particular, the discharge water from the sewage treatment plant in Daejeon will be introduced within this section, which will have a positive effect on the water quality of the river. This study also sheds light on how economic benefits of environmental factors, such as water quality, could be measured by using replacement cost approach like alternative management facility or emission charges.