This survey was accomplished to compare the characteristics of water quality and algae at the Daechung Dam with those at its regulating reservoir from the year 2003 to 2005. In the case of Daechung Dam, three sites, such as the area near dam body, the Mooneui intake station, and Chudong intake station, were selected averaged data were used for the comparison. The water quality of the Daechung Dam are an follows; temperature is from 4 to 25℃(average 15), pH is from 7.3 to 8.6(average 7.9), DO is from 5.7 to 13.0mg/L(average 9.9), BOD is from 0.7 to 1.7mg/L(average 1.1), COD is from 2.5 to 4.4mg/L (average 3.1), SS is from 1.1 to 9.8mg/L(average 3.2), total coliform is from 0 to 37MPN/100mL(average 11), total phosphorus is from 0.008 to 0.074mg/L(average 0.022) and total nitrogen is from 1.087 to 2.175mg/L(average 1.492). The water quality of regulating reservoir are an follows; temperature is from 1.0 to 24.0℃(average 13), pH is from 6.7 to 8.2(average 7.6), DO is from 5.9 to 13.2mg/L(average 9.2), BOD is from 0.3 to 1.8mg/L(average 0.8), COD is from 2.4 to 5.3mg/L(average 3.8), SS is from 1.2 to 50mg/L(average 9.0), total coliform is from 0 to 260MPN/100mL(average 56), total phosphorus is from 0.005 to 0.224mg/L(average 0.04) and total nitrogen is from 1.123 to 5.227mg/L (average 2.3). The water quality of regulating reservoir had been the Class Ⅱ raw water criteria ein years ago, but it has been improved to Class I recently. Whereas the water quality of the Daechung Dam has been maintained as Ⅱ except COD.

This study focuses on analyzing the inflow characteristic of contaminants of city water that flows into a main water system like a reservoir, and intends to provide basic data which can be efficiently reflected on water quality management policy and decision making of a reservoir. The conclusion obtained from the analysis of the inflow of a main water system by analyzing the inflow property of city water contaminants is as follows. In the case of Chungju-cheon stream which is the city water, pollution load from the basic outflow is low when it rains, and with high load of basic outflow during the dry season, due to the discharge of pollutants from the city, the quality of water becomes worse. In the case of Chungju-cheon stream, average BOD is 4.53mg/ℓ when it rains, and the contaminants increase and flow in about 7.8% compared to the average BOD during the average ‧ droughty season. The average SS concentration in water is 798.67mg/ℓ and increased 97.2% compared to the average ‧ droughty season.