Analyzing Sedimentary Rocks to Evaluate Paleo Dimensions and Flow Dynamics of Permian Barakar River of Rajmahal Gondwana Sub-Basin of Eastern India

Abstract

The cross strata and planar strata of sedimentary rocks are used in estimating paleo dimensions and flow dynamics of Permian Barakar River of eastern India. Quantitative estimates indicate that mean bed form became thinner i.e., from 1.363 m to 0.928 m to 34.21 m–23.33 m, as the Barakar River flowed with flow velocity of between 90 cm/sec and 157 cm/sec from Fox Ridge situated to the south on a steeper slope which becomes gentler downstream. The friction factor (0.036) is on higher side indicating low flow resistance while bed shear stresses remain competent, even during low paleo-discharges to transport coarse-pebble bed. Rouse number, Z, is decreased from Brahmini (3.38) to Hurra (1.71) implying predominant bed-load in upstream and local transition to mixed load in the downstream. Bed load formed 17.74 to 15.62 percent in upstream and reduced to 10.14–7.94 percent in downstream suggesting bed load channel for the former and mixed load channel for the latter corroborating estimated Rouse Number (Z) values. The trunk Barakar River on an average was about 2260 km long, 817 m wide and 13.63 m deep with channel belt width in between 6310 and 2205 m. The river channel sinuosity was in place of sinuosity 1.361 in the south-southwest part and progressively became more sinuous in the northern and northeastern part of the basin (1.728) with maximum sinuosity of 1.955. The catchment area of the Barakar River lies between 10,700 to 422,600 km2 and paleo-discharge between 22,070–4510 m3/sec with the maximum 66,000 m3/sec and whose mean annual flood was in the range of 170,600–42,260 m3/sec. These parameters suggest that initially multi-thread and broad Barakar River became narrow and single thread in downstream and had its outlet in the northeast (Sikkim, Assam and Bangladesh) towards the Tethys Ocean during Permian times.