TURBIDITY RESPONSE TO DISCHARGE IN THE UPSTREAM REGION OF THE HITOTSUSE RIVER WATERSHED

Abstract

The objective of this study was to obtain a better understanding of high turbidity generation in the upstream region of the Hitotsuse River watershed, by focusing on analyzing the turbidity response to discharge in the river stream. This study revealed that there were 3 types of sources of turbid water in the study area, namely: Type 1 (Collapsed of mountainside), Type 2 (Outflow of collapsed soil), and Type 3 (Waterside erosion) . This study proposed the Turbidity Discharge Ratio as means for detecting the problem of turbid water generation. The results showed that the Turbidity Discharge Ratio was fluctuate during 1994-2003. Turbidity Discharge Ratio was very high, slightly after the occurrence of heavy rainfall triggered by a typhoon. This study clarified that the Turbidity Discharge Ratio tended to decrease due to the lesser amounts of fine particles transported to the river and the cumulative discharge about 200x103m3/s is required to reduce the Turbidity Discharge Ratio below 1.