A water quality modeling study of the Nakdong River, Korea

A water quality modeling study was performed for water quality management of large river systems where autochthonous sources and denitrification play an important role in biochemical oxygen demand (BOD) and nitrogen dynamics. The model was based on the USEPA's QUAL2E and several modifications were made in the computer code to overcome limitations of QUAL2E. This paper outlines changes which were made in the model in addressing some of water quality problems and demonstrates the model application to the Nakdong River, Korea. The changes include the modification of computational structure and the addition of new constituent interactions, such as conversion of algal death to BOD, denitrification, and dissolved oxygen (DO) change caused by fixed plant. To validate the program modifications, both QUAL2K and QUAL2E were applied to the same reaches of river and the results were compared. The water quality parameters included in the model were DO, BOD, nitrogen and phosphorus series, and chlorophyll-a. Both QUAL2K and QUAL2E model represent the field data quite well except for some parameters of QUAL2E. In BOD, DO, and total nitrogen, there are significant discrepancies between the results of two models, where QUAL2K displayed better agreement with the field measurements than QUAL2E due to QUAL2K's ability to simulate the conversion of algal death to BOD, fixed plant DO, and the denitrification.