ESTIMATATION OF THE L-Q EQUATIONS FOR EACH SEA AREA IN THE SETO INLAND SEA

Abstract

 In the Seto Inland Sea (SIS), nutrient management plans are being considered for each sea area, and it is necessary to accurately estimate the amount of pollutant loads from the land area. In this study, we constructed a distributed runoff model and analyzed the characteristics and amount of pollutant loads from the land area to the SIS; in addition, the L-Q equations were estimated for each sea area from the model's result. The model simulated the discharge (Q) and pollutant load (L) in the normal and flood flow conditions of major large rivers with good reproducibility. We evaluated the amount of pollutant loads and identified that the pollutant loads in flood flow conditions contributed a large proportion, thus indicating the importance of considering the loads during the flood when the simulations in coastal areas were conducted. Estimations of the L-Q equations (L=_aQ^b, a and b are coefficients) from the distributed runoff model’s results showed that the coefficient b was less than 1 in normal flow conditions. In the flood flow condition, b became larger for COD and TP. In addition, the pollutant loads entering the sea area in the SIS were estimated with good accuracy by substituting the observed discharge data of major large rivers into the L-Q equations.