Sinkholes (dolines) in Bhander Limestones around Rewa, central India, and theirenvironmental significance

The Bhander Limestones of the Vindhyan Supergroup (Precambrian), exposed around Rewa in northeastern Madhya Pradesh, Central India, show excellent development of sinkholes (dolines) of various shapes and sizes. They are commonly funnel-, bowl-, trough-, oval-, and irregular-shaped. The diameter of the dolines varies between 0.40 m and 10 m with a depth up to 2.5 m, and the surface area between 0.13 m3 to 80 m3. Density of the dolines varies from 20d/km 2 to 1550 d/km3. Sinkholes in the area are mainly solutional and collapse types. Solutional sinkholes have formed primarily due to pronounced karstification of limestones around some favourable points, generally at the intersections of joints, while collapse sinkholes are the product of cavities lying near the surface. Sinkholes either appear singly or form doline fields and long- Irawn-out rows on joints. Normally, sinkholes of the high topographic areas are in line with those of low topographic areas, direction of which commonly matches with the prevalent joint direction. Groundwater in karst aquifers is potable and suitable for various uses. However, shows of pollution in groundwater are noticed in the vicinity of streams and sinkholes that are interconnected and structurally aligned. It is observed that the pollutants are carried to groundwater through an intricate network of interconnected sinkholes. These sinkholes receive pollutants from those streams and associated depressions which are used for disposal of industrial and municipal effluents. Those areas where sinkholes are well interconnected have been identified, and it is suggested that non-disposal of the industrial and municipal effluents in such areas would prevent groundwater pollution, ensure fresh water supply and maintain aquatic environmental balances in the area.