感潮河川における工場廃水の分散

Abstract

It is conceivable that concentration of industrial drainage diffused into a tidal water is remarkably fluctuated depending on the ebb and flow. The present work is an attempt to estimate a general pattern, of the fluctuation, which is one of the primary problems for controlling water pollution in tidal rivers and estuaries. Data used for example were obtained from the lower reach of the Edo River on the eastern border of Tokyo (Fig. 2) in winter of 1961, the season when the natural flow of the river is minimum.Fig. 1 shows a mathematical model of the water course proposed for analytical computation of the diffusion, where A represents a drainage outlet with an area 2 (b2-b1)×ε, and b is the breadth of the river. If drainage with a constant concentration, Si, is discharged at a certain rate into the river, the drainage concentration, X (xyt), may be expressed in the following equation.(1)where X0 is concentration of polluted matters flowing from the upper stream into this area.(Error function)Kx, Ky…… coefficient of diffusion in the directions x and y.During pollution surveys conducted along the Edo River on 11 and 12 January 1961, COD (ppm) was observed for stations 2.4 km and 4.4 km lower stream from the drainage outlet of a paper pulp mill. The natural flow of the river then and there averaged 3.4 cubic meters per second. Theoretical values of COD were computed by the following equation simplified from Equation (1):X(xt) =2.58+10.48F0 (xt)±1.43 (2)Comparison of the computed values of COD with the observed values indicated that 64 per cent of the observed values falls within the range of the computed values of COD (Tables 4 and 5). In Fig. 5 diurnal changes of COD at those stations based on Tables 4 and 5 are compared with changes of velocity of the tidal flow and the water level of the river. It is evident from Fig. 5 that COD at the upper station has a diurnal cycle from 4.3 to 3.5 ppm in accordance with the tide. Although COD at the lower station remains within a smaller range, the average level of COD there is very often higher than that of the upper station.