Supply and dispersion of water and suspended matter of the rivers Solo and Brantas into the coastal waters of East Java, Indonesia

Abstract

Major elements and a trace metal have been used to trace the fate and origin of water and suspended matter (SPM) of the rivers Solo and Brantas into the coastal waters of East Java. The transport, dispersion and distribution of water and SPM definitely has a seasonal character and is principally a wet-season phenomenon. In that season, monsoon and tide-induced coastal currents result in eastward fluxes of water and SPM. These longshore fluxes along the northern coastline of Java and Madura almost completely reduce the transport into an offshore direction (Java Sea). In the Strait of Surabaya, the amount of SPM from the Solo river clearly exceeds the contribution of the Brantas system. Both flow patterns and the magnitude of supply—the Solo is a suspension-load river— are responsible for this dominance. In the Porong delta, there is little exchange of estuarine SPM. In the dry season, estuarine mixing processes operate in the lower parts of the deltas, modifying the chemical characteristics of the water masses and SPM. SPM of the Solo river again represents the largest share in the total amount of SPM. Especially in the Strait of Surabaya, resuspension of particles originating from the Solo delta is the major process that determines the presence of SPM.