The state of Water quality was observed and discharge BOD loads was classified into Six pollution source groups by monthly loads and discharge source at the Nam-River watershed in Jinju city form January 2006 to December 2009 as follow:
1. Water quality survey results of the Nam-River watershed in Jinju city
From January 2006 to December 2009, the water quality of the Jangbakgyo at the end of Nam-River watershed in Jinju city was investigated. The results show the average BOD5 was estimated 3.0 mg/l in 2006, 2.7 mg/l in 2007, 2.9 mg/l in 2008 and 3.6 mg/l in 2009. This results was exceeded target water quality of 2.0 mg/l, so that water quality should be properly managed.
Also discharge volume of Namgang-dam has influence on change of water quality at Nam-River watershed in Jinju city because of geographical trait of the downstream of Namgang-dam. In carrying out Total Maximum Daily Load, we need to have proper supplementation for the trait.
2. Discharge BOD loads of each pollution source group at the Nam-River watershed in Jinju city
The Nam-River watershed in Jinju city was classified by six pollution source groups to estimate BOD loads so that loads of industry, cultivation and reclamation, etc were not large. And, population, livestocks and land use, etc had the largest loads at the Nam-River watershed in Jinju city.
The discharge BOD loads of pollution source group was as follow: The land use had larger discharge BOD loads than loads to occupy 45.2 % ∼ 50.5 % of total water system and to contribute to loads the largest. This was because agricultural farming drainage supplied non-point pollution source such as fertilizer, compost and agricultural chemicals, etc. The non-point pollution source can be managed the best by preliminary prevention before occurrence to reduce. And management of non-point pollution source's foundation and study will be required.
3. Discharge BOD loads of each discharge source at the Nam-River watershed in Jinju city
From 2006 to 2009 at the Nam-River watershed in Jinju city, discharged BOD loads was classified by discharge source. The results show the non-point pollution source has been increased, while the point pollution source has been decreased.
The non-point pollution source discharged BOD loads shows higher contribution rate than 70 % of total watershed, we have to mange non-point pollution source about discharge BOD loads by discharge source.
4. Monthly estimated discharge BOD loads of discharge source at the Nam-River watershed in Jinju city
The BOD loads at the Nam-River watershed in Jinju city had very much big difference between summer season of June to August and winter season of December to February. The BOD loads at summer was high because of rapid increase of loads of land use because of non-point pollution source of rainfall strength as well as rainfall frequency: In June to August when it rained much, in particular, at the rainy season, loads of land use rapidly increased.
Current method that relies upon sewage disposal plant to reduce loads had limit on reduction plans, and discharge BOD loads should be definitely reduced at summer when total discharge BOD loads increases rapidly. Therefore, to manage water quality of the Nam-River watershed in Jinju city effectively, loads should be managed by dividing season into summer and winter: And, considering characteristics of rainfall in Korea, non-point pollution source is difficult to manage it, and non-point pollution source at summer should be definitely managed to improve water quality of rivers, lakes and marshes. Also the investment for this should be increased.