EVALUATION SYSTEM OF COD, TN, TP GENERATION AND INFLOW IN A WATERSHED AREA INCLUDING POPULATION, INDUSTRIAL AND RAINFALL EFFECTS: PROTOTYPE MODEL APPLIED TO OSAKA BAY AND HARIMA-NADA SEA

Abstract

 We developed a new system to evaluate the amounts of COD (Chemical Oxygen Demand), TN (Total Nitrogen), and TP (Total Phosphorus) generated in watersheds and their inflows into rivers and coastal ocean. This system calculates the generated amounts from point and non-point sources, classified by municipalities into categories such as residential, industrial, livestock, and others, and estimates the inflow amounts by considering the delivery ratio. Additionally, it predicts changes in generated and inflow amounts based on variations in population, industry, land use, and rainfall. The system was applied to the Osaka Bay and Harima-Nada watersheds. For system validation, we compared the observed and calculated values of COD, TN, and TP time series in the Yamato River, and the calculated values generally reproduced the observed values. Moreover, predictions of generated and inflow amounts for changes in population, industry, land use, and rainfall in Osaka Prefecture indicated that population decline and industrial structural changes from FY 2004 to FY 2045 significantly reduced the generated amounts. Additionally, changes in rainfall conditions greatly affected the extreme values and periods of inflow amounts.