PATTERNS OF STEADY GROUNDWATER MOVEMENT IN BOUNDED UNCONFINED AQUIFERS

Patterns of steady groundwater movement in bounded unconfined aquifers, predicted from the analysis of horizontal seepage, are presented for various areal geometries in the form of maps showing lines of equal value of the seepage potential together with those of the horizontal seepage rate obtained from the gradient of the seepage potential. The situation considered is that of a steady uniform flux through the water table due to rainfall or evaporation with a uniform seepage potential at the aquifer's boundary such as that imposed by water-filled ditches sunk to a horizontal impermeable barrier. The maps reveal that there can be large areas where the horizontal seepage beneath the water table is practically uniform. They also show that the flow into or out of an aquifer varies along the boundary depending on the geometrical shape. Thus, for straight boundaries meeting at angles less than pi/2 the flow becomes zero at the corner but is finite for larger angles with the calculated result being infinite in some situations. Such variations of seepage rate for different boundary shapes influence leaching and soil erosion.