Late Holocene development of a tide-induced elongate delta, the Solo delta, East Java

Abstract

The Solo River, East Java, is a typical monsoonal river. The discharge and transport of appreciable amounts of sediment is mainly restricted to the wet season (December–March) and has resulted in the rapid outgrowth of an extensive delta system. The Solo delta is characterized as a highly mud-dominated and rapidly prograding single-finger delta, a specimen of a high-constructive, elongate delta type. The presence of firmly built natural levees, more or less ‘channelizing’ river outflow, the role of flow inertia and the rapid deposition of sediment in front of the main river mouth explain the very strong longitudinal growth of the delta and determine its long, rather straight and narrow shape. The presence of these pronounced natural levees is clearly a natural response to river outflow conditions, since maximum river output is observed at high tide. This phenomenon results from the interference of tidal components in the waters surrounding the Solo delta. The tidal model, a conceptual model, assumes that the tidal motion is capable of introducing a temporary increase in deltaic river slope during high tide by creating a local difference in the high water levels North and East of the delta. The lateral dispersal of sediment is limited and mainly depends on the transport in distributary channels. Natural crevasses are rather scarce and do not have a stable character.