Hydrogeological Maps

maps representing the conditions of the occurrence and distribution of underground water.

These maps contain data on the quality and productivity of water-bearing levels, on the dimensions, form, and position of old foundation beds of water-pressure systems, and on the interrelationship of geological structure, terrain, and underground water. They are compiled on the basis of hydro-geological surveying, taking into account geological and tectonic maps. Hydrogeological maps depict the distribution of various water-bearing levels and their complexes, the sources and their flow, wells, boreholes, sinkholes, the roof or base of water-bearing strata, and the depth at which underground waters are found and their chemical composition. Hydrogeological maps are accompanied by cross sections on which the geological structure of the region is represented— the lithological composition of the water-bearing levels, facies changes, water-resistant strata, the depths of occurrence and amount of pressure of the water-bearing levels, the position of the free and piezometric surface of underground waters, and the mineral content and flow of the waters.

Small-scale hydrogeological maps (smaller than 1:500,000) depict the most important characteristics of the hydrogeological structure of an area, the boundaries of hydrogeological basins, and the areas of recharge, pressure, and discharge of underground waters. Regions with a primary development of various types of underground waters are identified. Small-scale hydrogeological maps are sometimes compiled from data found in literature and archives, without conducting a hydrogeological survey. Medium-scale hydrogeological maps (1:200,000-1:100,000) provide additional quantitative indicators characterizing the condition of the underground waters during a fixed interval of time. Large-scale hydrogeological maps (larger than 1:50,000) are employed to solve specific problems in the stages of engineering and operational planning. Such problems include choosing areas for water collection, revealing reserves of underground waters, studying the watering capacity of deposits, and establishing the conditions for draining or irrigating an area.

Three types of hydrogeological maps may be distinguished: general maps, maps of the principal water-bearing levels, and maps having a specially designated purpose. General maps represent water-bearing complexes and levels and their characteristics, the age and petrographie composition of the water-storing rocks, the abundance of water, hydro-geological test holes, typical wells, major springs, and data on the level of the water and its chemical composition.

Maps of the principal water-bearing levels indicate the areas of distribution of the water-bearing levels that are planned for use in a central water supply, the composition of the rocks making up these levels, and the depth at which the levels occur. These maps also indicate the free or pressurized water level and the abundance of water at these levels, as well as the degree of water mineralization. Maps for specially designated purposes are compiled to solve problems of water supply and to estimate reserves of underground waters, to determine the watering capacity of mineral deposits, to delineate sites of mineral waters, and so forth. Hydrogeological maps usually have an appended explanatory text with a description of the region’s hydrogeological conditions. There are also maps that divide an area into hydrogeological zones, hydrochemical maps, and maps indicating the reserves of underground waters.