A Study on the Rough Estimation of Drainage Discharge in the Ohuchi-Area of the Right Side of the Yoshii River

Abstract

The water level in the river is banked up at the upstream by completion of the headworks and consequently the neighboring underground water level rises. In such a case, to prevent the rise of underground water, some works such as sheet piling or grouting along the river and the drainage work within the area should be considered.
In this report, we tried to estimate the rough drainage discharge to hold the present underground water level (before the headworks are completed) in the relatively wide area.
In calculation, we used the fundamental equation of underground water (1), substituting the velocity of the drainage discharge into ε₂ (velocity of the water which goes out of the underground).
As an example, we chose the Ohuchi-area (the right side area of the Yoshii river) and obtained the following results:
To hold the present underground water level,
(1) It is required to drain 350 mm/day within the Ohuchi area without any water stopping works along the river.
(2) When the present permeability 1.0×10^-3m/s is assumed to become small to 7.0×10^-4m/s by sheet piling or grouting along the river, it is required to drain 250mm/day within the Ohuchi area.
(3) When the present permeability 1.0×10^-3m/s is assumed to become small to 5.0×10^-4m/s, it is required to drain 220 mm/day within the Ohuchi area.
(4) When the present permeability 1.0×10^-3m/s is assumed to become small to 3.0×10^-4 m/s, it is required to drain 130 mm/day within the Ohuchi area.