Undesired Results Caused by Recovery of Ground-water Levels

Abstract

The land subsidence and the sea-water intrusion have proceeded naturally from overdraft of ground water in the urban, industrial regions and the coal-fields in Japan.
For the prevention of these damaging effects the laws and the ordinances have controlled the volume and rate of ground-water withdrawal in many urban and industrial zones. And the coal-mining is now closed in many fields. The ground-water levels have been recovering as a result of the conservation of the ground-water resources. But undesired results e. g. re-issue of springs, re-wetting or upheaval of groung surface have produced because of the recovery in several zones and fields.
The region of ground-surface upheaval coincides with a region where subsidence produced on a large scale. The observation records of ground-water level and subsidedence show that the ratio of upheaval to recovery in artesian pressure head is about 1 or 2 to 1,000, and that there is time lag between its recovery and the corresponding upheaval in a zone having a greater percentage of unconsolidated clay.
An amount of the upheaval is able to calculate as the expansion of elastic artesian aquifer due to the recovery of its pressure head applying Lohman's formula (1961). in Kawasaki-shi, the value of the calculation is nearly equal to that of releveling of bench marks and of observation records.
Producing of undesired results due to overdraft or control of ground water suggests that it is important to maintain withdrawal of water within the limits of safe yield.