Characteristics of Runoff Pollutant Loadings and Their Annual Estimation in the Rivers Flowing into Lake Teganuma

Abstract

The Ohhori and Ohtsu Rivers are the two major rivers flowing into Lake Teganuma. To gain an understanding of SS, BOD, COD, nitrogen and phosphorus loads flowing into the lake, pollutant loadings were observed at downstream points of the two rivers. According to the runoff characteristics of the observed pollutant loadings, pollutant load could be separated into “dry weather load” and “wet weather load”. The wet weather load is caused by direct runoff of rainfall and could be represented by a regression equation using depth of runoff, antecedent precipitation factor and peak rainfall intensity as independent variables. As a result of annual pollutant load estimation, the ratio of annual wet weather load to annual total (dry+wet) was about 70 percent for SS, about 30 percent for BOD and COD, and 10-20 percent for T-N and T-P. Moreover, the ratios between dissolved and particulate constituents in dry and wet weather loads for COD, T-N and T-P were clarified. Furthermore, the runoff characteristics of constituents of T-N, i.e., nitrite, nitrate and so on, were investigated.