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Modification of the Channel BOD Simulation Scheme in SWAT for Korean TMDL Application

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org

Citation:  Transactions of the ASABE. 54(5): 1739-1747. (doi: 10.13031/2013.39839) @2011
Authors:   N. W. Kim, A. H. Shin
Keywords:   Bottle BOD5, QUAL2E, SWAT-KQ, TMDL

Many streamflows in Korea are discontinuous or intermittent due to stream hydraulic structures, such as dams and diversions constructed to control streamflow and for water use. This is primarily because rainfall is concentrated in the summer. These hydraulic drop structures can enhance the stream re-aeration process, whereas a reduced flow upstream of a structure can promote algae proliferation. Therefore, these phenomena need to be incorporated into a water quality simulation process. SWAT is one of the most popular watershed models and adopts QUAL2E as the channel water quality simulation module. The QUAL2E module has a DO-centered water quality simulation structure because the model was developed based on continuous stream conditions. However, because the flows of many streams in Korea are discontinued due to stream hydraulic structures, flow discontinuity phenomena need to be considered for more accurate algae or nutrients simulation. In addition, bottle BOD5 is the primary BOD indicator that is measured and incorporated into the Korean TMDL program. This is in contrast to CBOD, which the current SWAT model deals with. In this study, a modified QUAL2E model to simulate algae growth kinetics in detail was incorporated into the SWAT model to allow for an increase in internal organic matter and bottle BOD5 simulation. The reliability of BOD simulation was improved, and the modified model was applied successfully to a watershed under the TMDL program to estimate the BOD pollutant loads over a wide range of flow conditions. Overall, the modified SWAT, namely SWAT-KQ, can be a useful tool to improve BOD simulation and help enhance the TMDL program.

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