Water Well Manual (USAID).pdf - The Water, Sanitation and Hygiene

may be seen in some river valleys and gorges. These sections may also indicate
whether water-table or artesian conditions exist in an aquifer. The cross-
sections of Fig. 3.2, drawn from the geologic map of Fig. 3.1, illustrate many
of the important features mentioned above.
Fig. 3.2 GEOLOGIC CROSSSECTIONS FROM THE MAP OF FIG. 3.1.
Water surface
Aerial Photographs
Aerial photographs, skillfully interpreted, provide valuable information on
terrain characteristics which have considerable bearing on the occurrences of
ground water. Features which indicate subsurface conditions such as
vegetation, land form and use, erosion, drainage patterns, terraces, alluvial
plains, and gravel pits are apparent on aerial photographs. The skillful
interpreter of aerial photographs can determine the most promising areas for
ground-water development.
INVENTORY OF EXISTING WELLS
The hydrologist next makes a study of all available information on existing
wells.
Well logs which are records of information pertaining to the drilling and
construction of wells would be the main sources of information. From these
logs he may obtain such information as the location and depth of the well;
30