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groundwater discharge[′grau̇nd‚wȯd·ər ′dis‚chärj]
a rise in the level of groundwater caused by an increase in the water table in rivers during construction of reservoirs, river dams, navigation canals, and other hydraulic-engineering structures. Groundwater discharge saturates soil by seepage of water through the bottom and banks of canals, by water loss from water-supply and sewage systems, or by silting of river channels; a natural cause may be a rise in sea level.
Groundwater discharge causes soils to become marshy and saline, lowers the productivity of meadows, fields, and forests, causes sanitation in the area to deteriorate, and destroys buildings. Land is classed as flooded by groundwater when the water table has risen to a level making the area unsuitable for use: 0.6–0.9 m for meadows, 0.8–1.4 m for plowed fields, 1.2–1.8 m for orchards, 1.5–2 m for small settlements, and 3–4 m for cities.
Drainage systems are built to protect land from groundwater discharge and may be horizontal or vertical drainage or combined drainage with machine pumping. The drains are located along the borders of the endangered land. In the USSR, drainage systems have been built to control groundwater discharge on agricultural lands in the Kostroma Lowland, flooded by the Gorky Reservoir, near the city of Mary (the Karakum Canal), in Moscow (the Pererva Dam), in Kazan and Dimitrovgrad (the reservoir of the V. I. Lenin Volga Hydroelectric Power Plant), and in Nikopol’ (the Kakhovka Reservoir).
REFERENCESKostiakov, A. N. Osnovy melioratsii, 6th ed. Moscow, 1960.
Zashchita territorii ot zatopleniia i podtopleniia. Moscow, 1963.
B. S. MASLOV