Hydrologic Maps

maps depicting the distribution of water on the earth’s surface, characterizing the regime of bodies of water, and making it possible to evaluate the water resources of individual land areas. Hydrologic maps include maps of river networks and their density and lake content, runoff maps, and maps of sources that feed bodies of water, glacier regime, water turbidity in rivers, and the mineralization and chemical composition of natural waters. In addition, hydrologic maps may show characteristic phenomena such as desiccation, freezing, and floods. There are also maps of the components of the water balance, evaporation from land and water surfaces, and the runoff coefficient, as well as maps of hydrologic regionalization and the use and prospects for use of water. The specific features of the regime of lakes and reservoirs are depicted on special maps that are similar to sea charts.

The basic hydrologic maps show runoff (average, maximum, and minimum). In evaluating the water resources of a territory the most substantial role is played by maps that show distribution of the average (normal) runoff over many years. The streamflow of individual rivers is shown on a map of streamflow rate by means of a scaled strip that corresponds to the amount of streamflow in various directions. Streamflow rate maps depict individual rivers. The runoff from a territory and its moisture are shown well by maps of the discharge in second-liters per square kilometer and by maps of the depth of runoff in millimeters per year, month, or season. When there has been little hydrometeorological study of a territory, hydrologic maps are the most reliable sources of information on its water resources.

A runoff map was prepared for the first time in the USA in 1892 by F. Newell. In the USSR the first runoff map, which showed the spring high-water period of tributaries of the Dnieper, was published by P. N. Lebedev in 1925. In 1927, D. I. Kocherin compiled for the first time a map of the average runoff over many years in the European USSR, and in 1937, B. D. Zaikov and S. Iu. Belenkov published a runoff map of the USSR. The first runoff map of the entire world was done by M. I. L’vovich in 1945. The distribution of the average runoff in the USSR is most completely depicted on maps drawn up by B. D. Zaikov (1946) and V. A. Troitskii (1948) and in the Physico-geographic Atlas of the World (1967).