In this study, we have investigated the water quality and flow rate at the 3 sites of main stream and 11 sites of the branch stream of Hwang river from January, 2007 to 2010, and analyzed the effects on Hwang river with the purpose of using the data for as the fundamental information for water quality improvement and water resource management in the water system of Hap-Cheon dam Upper Stream.
1) The flow rate at 3 sites of the main stream and 11 sites of the branch stream increased during the rainy season between June and September, and continuously decreased during the dry season starting from autumn to winter. The BOD water quality status at each site of the main stream was stable in between 1.6~2.5 mg/L with no large variation, so that it was between ‘Good’ and ‘A Little Good’ by the life environment standards. On the other hand, BOD of the inflow branch streams such as Panmuncheon, Nabulcheon, Gajoacheon and Yongacheon was between 2.0~4.0 mg/L to be ‘Good’ to ‘Usual’ by the life environment standards and it was much dependent on the precipitation. The average COD of the branch streams, Poonggye bridge, Kimcheon and Gaebong bridge was 3.3 mg/L, 3.5 mg/L and 5.5 mg/L, respectively, which were relatively high. The COD of the main stream was relatively stable with no large variation. The SS of the branch streams had large variation, while that of the main stream was relatively stable. The T-N of Gaebong bridge was about 2~3 times higher than that of the main stream. The T-P, the target substance of the second year’s total water pollution loads, of Gaebong bridge was relatively higher than other sites. Other investigation items showed similar tendency.
2) The results of correlation analysis with Pearson correlation coefficient showed that BOD and COD, BOD and T-P, and COD and TSS at the 3 sites of the main stream had high correlation with each other. At Site 12, BOD and COD, BOD and T-P, and COD and TSS showed high correlation with the correlation coefficients of 0.697, 0.302 and 0.401, respectively. At Site 13, the correlation coefficients were 0.621 for BOD and COD, 0.216 for COD and TSS. Also, the correlation coefficients at Site 14 were 0.578 for BOD and COD, 0.211 for COD and TSS. At Site 11, the correlation coefficients were 0.917 for BOD and COD, 0.728 for BOD and T-P, and 0.458 for COD and TSS, showing high correlation.
3) We have also analyzed the correlation between Chl-a and major factors at the 3 sites of the main stream. At Site 12, the correlation coefficient of Chl-a and the water temperature was -0.182, and that of Chl-a and T-P was -0.011 correlation coefficient of minus showed. Chl-a and BOD was 0.219, and that of Chl-a and COD was 0.297 correlation coefficient of plus showed. At Site 13, the correlation coefficient of Chl-a and the water temperature was -0.218, and that of Chl-a and pH was -0.098 correlation coefficient of minus showed. Chl-a and BOD, COD was 0.268, 0.336 correlation coefficient of plus showed. At Site 14, the correlation coefficient of Chl-a and pH was 0.024, and that of Chl-a and COD was 0.320, Chl-a and TSS was 0.180 showing their high correlation Water quality analyzed results. At Site 11, the correlation coefficient of Chl-a and the water temperature was -0.157, that of Chl-a and BOD was -0.017, that of Chl-a and TSS was 0.177, Chl-a and T-P was 0.074.
4) The N/P ratio at all the 3 sites of the main stream was higher than 16 by DIN/DIP and T-N/T-P, indicating that phosphorus is acting as the limited nutrient.