Field assessment of surface runoff, sediment yield and soil erosion in the opencast mines in Chirimiri area, Chhattisgarh, India

Chirimiri Coal field is located in the Koriya district of Chhattisgarh state of India. It lies in the valley of the Hasdeo River and is spread over 125 km2 area. Ever increasing problem of declining forest resources and water quality is a cause of concern particularly due to excessive soil erosion resulting in soil sediment deposition from the overburdened dump. Dwindling resources has compelled the policy makers to search for alternatives such as waste lands and mined areas to improve soil and water resources for use in agriculture and allied sectors while maintaining the local ecology and hydrology. Most Opencast mines release huge amount of mining wastes in the form of overburden dump (OBD) materials that are prone to soil erosion and also create problems of sedimentation and deteriorating water quality, affecting agriculture. Historical daily rainfall data for 21 years and daily surface runoff as estimated by SCS-Curve Number method were analysed. Sediment yield was estimated at lower end of erosion face of OBD and near drainage outlet of opencast mine. Assessment of soil erosion from OBD materials was made byRevised Universal Soil Loss Equation (RUSLE) method and was compared with direct field measurements by placing plastic sheets in downstream portion of OBD. As a result monsoon rainfall constitutes 91.6 percent of the annual rainfall and surface runoff constitutes 31.7 percent of monsoon rainfall. The surface runoff was found to be 4133 m3/ha while the sediment yield of drainage effluent was negligible. The soil loss from OBD as estimated by the RUSLE method (62.7 t ha−1 yr−1) was quite close (+13.2 percent) to the direct field measurement 54.44 t ha−1. The sediment samples from OBD were found acidic in nature and exhibited low values of Electrical Conductivity (EC), Organic Content (OC), Water Holding Capacities (WHC), and Available Nitrogen (N), Phosphorus (P) and Potassium (K). For controlling soil erosion of OBD, mechanical and vegetative measures have been suggested along with installation of sediment traps inside and outside the mines. There is good scope to backfill the mines with the OBD in the form of well laid out terraces to support plantation. This can be eventually used for leguminous fodder/grass production.