Abstract
It is impossible to evaluate the water quality in Yodo River, without considering the transverse diffusion and mixing of three rivers (Uji River, Kizu River and Katsura River). Therefore we made up a mathematical model to simulate the behavior of pollutants in Yodo River.
In our diffusion model we introduced the water flow rate as a variable in stead of the river width. As a result the specific diffusion coefficient (α) is expressed an Kyuh2 (Ky : diffusion coefficient, u : velocity, h : depth). Using the hydraulic data of Takahama point in Yodo River, Ky is about 0.1.
The large scale “Kizugawa Sagan regional sewerage”, which covers six municipalities, is being constructed and its treatment waste water is discharged into the left bank of Uji River. The calculation about the distribution of the effluent from the sewage treatment plant indicated that the raw water quality of Kuzuha waterwoks, located at the most upper Yodo River, would be worse. When the planning is achieved and the water flow rate in Yodo River is low, the increase of TOX formation potential (TOXFP) 524% and that of NH4-N 1572% at Kuzuha, compared with the present concentration. In the case of which there is no sewerage planning, that of TOXFP is 27% and NH4-N 4%. Alternative plan, the small scale one, were simulated as well and its result suggested that the water quality would be less influenced.
