the set of field investigations carried out for the purpose of compiling hydro-geological maps and evaluating the overall hydrogeological conditions of an area.
In the process of hydrogeological surveying studies are made of the rocks forming water-bearing levels, complexes, and zones, the filtering properties of these rocks, and the persistence in area and thicknessof water-storing and water-resistant rocks, as well as the amount of pressure and the types, quality, and regime of underground water. The values of basic hydrogeological parameters are given, and evaluations are made of the geological, geomorphological, hy-drological, climatic, and other factors affecting the recharge and formation of underground water.
Hydrogeological surveys vary, depending upon the scale and purpose of the survey. A small-scale hydrogeological survey (1:1,000,000-1:500,000) is carried out in order to compile survey hydrogeological maps in regions that have been little studied from a hydrogeological point of view for the purpose of an overall appraisal of the water-bearing properties of the rocks and the quality of the groundwater. In medium-scale hydrogeological surveys (1:200,000-1:100,000), conducted for compiling government (general) hydrogeological maps, water-bearing complexes, levels, or zones are mapped and studies are made of the water-bearing properties of rocks, of the quality and regime of underground water, and of geological phenomena connected with the activity of underground and surface water. Large-scale hydro-geological surveys (1:50,000 and greater) are conducted in order to solve specific problems at the stages of engineering and operational planning (to choose sectors for water collection, to prospect for reserves of underground water, and to study the watering capacity of deposits). During large-scale hydrogeological surveying water-bearing levels, zones, layers, and lenses are mapped. Medium-and large-scale surveys are accompanied by drilling operations, measurement of the flow of sources, and observations of the level and chemical composition of underground water. Geophysical methods, aerovisual observations, and deciphering of aerial photographs are employed.
REFERENCESKamenskii, G. N. Poiski i razvedka podzemnykh vod. Moscow-Leningrad, 1947.
Metodicheskoe rukovodstvo po gidrogeologicheskoi s”emke mas-shtabov 1:100,000-1:500,000 i 1:200,000-1:100,000. Moscow, 1961.
Metodicheskoe rukovodstvo po proizvodstvu gidrogeologicheskoi s’emki v masshtabakh 1:50,000 i 1:25,000. Moscow, 1962.
Metodicheskie ukazaniia po gidrogeologicheskoi s”emke na za-krytykh territoriiakh v masshtabakh 1:500,000, 1:200,000, i1:50,000. Moscow, 1968.
A. M. OVCHINNIKOV