Structure and Evolution of a Prograding Reservoir Delta in the Damodar River, India

The Damodar River is an ephemeral river with a braided stream pattern in many sections during the flood stage. Flood discharge is concentrated during summer monsoons. Damming of this river has produced two deltas, one corresponding to the live storage level ('upper delta') and the other at flood storage level ('lower delta'). The progradation of the upper delta over the topset beds of the lower delta coupled with fluctuations in lake level has produced a cyclic progradational deltaic sequence in the reservoir.

A significant zoning of the sedimentary structures is observed in the different parts of the delta. Parallel lamination is the major structure in the bottomset area; cross-stratification, ripple drift lamination and deformational structures predominate the foreset area; and horizotal and cross-stratification charactcrize the topset area. Cyclic sedimentation units with their characteristic sedimentary structures and grain size arc also characteristic of the topset area. The alluvial valley section is dominated by multiple units of a variety of cross-stratifications and some upper flow regime flat beds.