Abstract

The Citarum River forms four different delta types at four main distributaries. The distributary which flows north builds a cuspate type of Bungin delta. The distributary flowing toward the northwest branches into two distributaries forming the arcuate type of Wetan delta in the northern part, and the cuspate-lobate type in the western part. The distributary that flows toward the southwest builds a bird foot type of Gembong delta. The delta modelling study with respect to oil exploration was made on the latter delta.

Interpretation of old maps nad aerialphotographs reveal that the formation of the Gembong Subdelta commenced 150 years ago and become static since 1971.

There are three channel mouths in the study area which from north to south are Muara Kuntul, Muara Gembong and Muara Mati.

The present condition of the channel mouths are as follows: Muara Kuntul is in an abandonment stage, Muara Gembong is static, whereas Muara Mati is in a very weak constructive phase.

The thickness of the delta front sand deposits appears inadequate for an ideal study; however, a sedimentation model can still be made based on surface sample characteristics.

The sedimentary sequences characteristic of the environments and stratigraphic relationships between the major sediment types are obtained from a number of borings made in the delta plain region.

Five types of sand deposits are observed i.e. channel, channel mouth bar, interdistributary bar, destructive zone shoal and chenier each of the deposits have characteristics identifible both in the field and in the laboratory.

Isolith maps of the sand bar show that the sands are thinning toward the youngest deposit, indicating the gradual decreasing of constructivity of this delta from time to time.