Abstract
The writers carried out certain investigations in order to estimate the amount of groundwater discharge through the Watarase River valley near Kiriu City in Gumma Prefecture.
They surveyed the geology of the flood plain by means of electric resisti-vity methods using apparatus of the Electro-Technical Laboratory type and check the results by test borings (Fig. 1).
The Watarase River valley is underlain by Tertiary formations and dilu-vial and alluvial deposits. The alluvial deposit, with a maximum depth of 20 meters. is divided into an upper and a lower layer. The upper layer, composed of loose sand and gravel, is the most productive aquifer; the -diluvial deposit has some confining aquifers.
From the groundwater contour map (Fig. 1), obtained from observation of 30 wells, it was found that groundwater generally furnishes the river water throughout the valley, but locally influent seepages occur in some places.
The writers calculated the gradient of the groundwater flow and evaluated -the permeability coefficient by Tienis' method as modified by Muskat.
Using the data arrived at by the above methods, they calculated the amount of groundwater discharge through a valley section at 1.253m)sec.
