Quantification of nutrient load caused by floods, as revealed by daily sampling: A case study of Hii River

Abstract

The purpose of this study was to examine the percent contribution of nutrient loads caused by flood events to the total annual nutrient load. We conducted daily sampling at Kandachi Bridge from July 1, 2010, to June 30, 2011, to determine the relationship between the amount of rainfall and flow volume. We examined the relationship between precipitation and flow rate and obtained a good relationship between the volume of one rainfall and runoff height using the storage function method (R = 0.87). During the study period, three rainfall events with precipitation exceeding 200 mm were observed. The rainfall from these three events accounted for 41.3% of the total annual rainfall. The increased flow caused by these three events accounted for 34.8% of the total annual flow. Total nitrogen and total phosphorus loads caused by these three events accounted for 40.7% and 62.2%, respectively, of the total annual loads. The reason that the percent contribution of phosphorus loads exceeded that of nitrogen loads is the high dependency of phosphorous loads on flow rate.