Hydrodynamics and depositional processes of the Solo and Porong Deltas, East Java, Indonesia

Abstract

The river outflow and depositional processes of the rivers Solo and Porong (East Java, Indonesia) have been studied. The input of sediment into the coastal waters by both the Solo and Porong river has resulted in the rapid development of two-delta-systems. The Solo delta is a mud-dominated, rapidly prograding elongate (single-finger) delta whereas the Porong delta is characterized as a lobate, multidistributary delta. In the wet season, river outflow generally has the character of a buoyant jet (Solo) or a friction-dominated plane jet (Porong). The excessive supply of sediment in the Solo delta in combination with decreasing flow velocities, as a result of entrainment and mixing, cause a rapid settling of suspended matter and deposition. Deposition rates in the Solo delta are also high because of the peculiar fact that maximum river outflow takes place around high tide. As a consequence, riverborne sediment is trapped by tidal and monsoon-induced flow beneath the plume. Bedload transport is of great significance for the Porong delta, and a substantial part of this sandy bedload is deposited in and in front of the present, main river mouth. The river mouth morphology is characterized by a braided complex of sandbars, which in the future may result in new channel bifurcations.