Prediction and Evaluation of Pollutant Runoff Loads into the Regulation Pond at Isahaya under Rainfall Condition

At Isahaya of Nagasaki in Japan, a big project for constructing a sea-dyke and reclaimed land has just been finished, and the inner part of Isahaya bay becomes an enclosed water body. Then, in order to avoid eutrophication in the pond, integrated water management over a watershed for the water region called regulation pond should elaborately be pursued. For reducing the pollutant runoff loads from the watershed, washoff rate of each pollutant from non-point sources should be made clear, based on the hydrological condition of watershed. So, considering the geographic condition shown by GIS data, pollutant runoff rates from non-point sources are investigated considering a time series of rainfall, i.e. the antecedent and current ones. For the above-mentioned purpose, field observation of water quality has been progressed, especially under the rainfall condition. In addition, authors already proposed the mathematical mode (Noguchi et al., 2005, 2006), which can evaluate the pollutant runoff rates from diffuse sources if model parameter will appropriately be identified. In this paper, observed data of total nitrogen (T-N) as pollutants are shown. Furthermore, efficiency of the above-mentioned model has been discussed for prediction and evaluation of runoff loads