No abstract

ab s t r ac tTo improve the water quality of the four major rivers in Korea, Ministry of Environment of Korea (MOE) has introduced the Total Maximum Daily Loads (TMDLs) management system since 2002 and BOD was selected as one of the target materials during the first period (2004)(2005)(2006)(2007)(2008)(2009)(2010). For an effective watershed management, it is necessary to have one or more quantitative measures that can be used to evaluate the relationship between pollutant sources and their impacts on water quality. Such measurable quantities are termed water quality indicators. Once an indicator is selected, target values for that indicator must be established to distinguish between the impaired and unimpaired state of the water-body. Various factors such as available data, application, management conditions and cost will be considered for the selection of an appropriate watershed management indicator. This paper introduces various factors required for choosing target water quality indicators and establishes reasonable target values during the second TMDLs period (2010)(2011)(2012)(2013)(2014)(2015).

The allocation of margin of safety (MOS) at a uniform rate to all areas of the unit watershed makes it very difficult to keep the load allotment stable in the area for lack of reduction measures like forest land. This study developed an equation to calculate margin of safety differentially according to the regional characteristics. The equation was formulated on the basis of the regional characteristic factors such as a load contribution factor for land use type and a site conversion factor for the unit watershed. The load contribution factor represents a contribution of loads from a particular land use. The site conversion factor was derived from the site conversion ratio of a unit watershed. Margin of safety for the non-point pollution load in the land use sector decreased by 20~25% in three river basins. The margin of safety in the unit watersheds with low site occupation ratios decreased in high rate, while in the unit watersheds with large urban area decreased in low rate. With the application of the differential margin of safety considering regional characteristics, not only the reduction of pollution loads can become lighter but also it can be easier to develop plans for Total Maximum Daily Loads (TMDLs) even where the reduction measures are not available.

The land use of the unit watersheds should be maintained appropriately in order to keep the load allotment stable for the management of Total Maximum Daily Loads (TMDLs). This study classified the land area in four types and analyzed the use of each land type and its changing pattern by calculating the occupation and conversion ratios for the unit watersheds in three river basins. The forest land showed the greatest occupation ratio with 63.0%, followed by the farm land with 23%, the other area with 8.0% and the site area with 6.0% in 2003. The occupation ratio of the site and the other area increased by 0.4% and 0.2% respectively, and that of the farm and the forest land decreased by 0.4% and 0.2% respectively in 2007. The conversion ratio for the site area ranged from 1.65% to 1.97%, for the farm land from -0.47% to -0.33%, for the forest land from -0.10% to -0.04% and for the other area from 0.17% to 1.97%. It can be inferred that the decrease in the farm and the forest land contributed to the increase in the site area and that the increase in the other area was mainly made by the decrease in the forest land. It could be more effective to take into account the changes in the site area and in the forest land in the process of developing the TMDL plans.

A B S T R A C TDetermining impairment of water bodies in the light of watershed characteristics is useful in selecting applicable water quality indicators as target pollutants for the watershed management. This study investigated impaired water bodies using frequency analysis on a stream zone basis in Geum river basin in Korea. The river basin was divided into three stream zones by its characteristics. Selected water quality parameters discussed in this study were pH, DO, BOD, COD, SS, T-P, T-Coli, and F-Coli. Excess ratios of the water quality parameters were used to discriminate water bodies that did not meet water quality standards. Excess levels were used to classify the water quality degradation. Contributions of the tributaries were also estimated to identify the major contributors to the stream zones. The upstream zone showed that the indicators for impaired water bodies were BOD, COD, T-P, and T-Coli which indicated especially high excess level. The downstream zone revealed that COD, T-P, and T-Coli were the indicators and the M/D stream zone revealed that the indicators were BOD, COD, and T-P. The major contributors in the upstream are Okcheon, Juwon, Bonghwang, and Pumgok tributaries. In the downstream, Nonsan, Seokseong, Gab, Yudeung, and Daejeon were the major contributing tributaries and in the M/D stream zone, the major contributors were Iksan, Gobu, and Jeongeup tributaries.