Hydrology-geomorphology links in the Kapuas river system

Projectleiders: Ton Hoitink, Wageningen Universiteit en Robert Delinom, Indonesian Institute of Sciences.

The Kapuas is the largest river system in Indonesia and the world’s longest river on an island, stretching more than 1100 km in a relatively pristine region dominated by lowland forest and peatlands. The length of the river, the complex geomorphology of the lowland channel network and the hydrological links with the adjacent peat bogs and inland wetlands render the Kapuas river system represent a challenging subject for scientific study. The overall objective of this research project is to establish and understand the interlinked processes governing the hydrology and geomorphology of the Kapuas River, its delta, the Kapuas Hulu wetland region and the peatlands connected to the river. This will yield new scientific insights in the fields of hydrology and geomorphology, which can be linked to aquatic ecology and form a solid basis for science-based water resources management and river engineering in the future. The knowledge gained in the project will be used to reveal the main factors controlling drought in peat forests and wetland areas, including the associated wildfires, and to analyse problems of flooding and salinity intrusion in the downstream lowland region.

At the basin scale, the project will study processes governing the terrestrial water cycle, subsurface hydrology, land-sea surface water interactions and the factors controlling river channel morphology, using a set of models that include the Community Land Model (CLM) and a multi-scale hydrodynamic model. The interlinked models will be tested, calibrated and validated with existing remote-sensing information and new measurements from surface and subsurface level gauges, soil moisture stations, rain gauges, and two discharge monitoring stations in the river equipped with horizontal acoustic Doppler current profilers. The initial aim for the models is to simulate and understand the hydrological functioning of the Kapuas River basin and historic and projected events of floods and droughts. Subsequently, the models will be used to simulate basin-scale sediment runoff and transport in the river channel network, and to establish the links with river channel morphology.

At a local scale, the project will focus on wetland functioning, hydrogeology of peat forests, water and sediment division at channel junctions, and the morphology of complex river bends. The CLM and an integrated sediment transport module will be used to establish the vulnerability of the Kapuas Hulu wetlands to changes in the hydrological regime and in sediment runoff, in terms of the pristine aquatic ecology. Regarding the hydrogeology of peat forests, emphasis will be placed on drought development in order to specify the conditions leading to forest fires. Focusing on the river delta, two key channel junctions will be analysed in detail so as to understand the processes controlling the distribution of water and sediment over distributary channels. To this end, a local-scale morphodynamic model will be set up to explore the impacts of changes in discharge regime and sediment runoff on channel junction morphology. Finally, processes forming sharp river bends will be the subject of study, assimilating results from high-resolution flow simulations with geographical information and with the outcomes of the hydrological studies.