The northern border of the islands lies at a water depth of -8 metre. The islands will be constructed as so called polders on top of the extreme soft subsoil of this bay. Polders are low lying areas surrounded by dykes with a drainage system consisting of surface and subsurface drains, retention basins and a pumping system. The project consists of approx. 57 million m3 sand reclamation for the construction of dikes and polder area. The dikes are protected with several layers of rocks to ensure a lifetime of at least 50 years. The land level in these polders will be around mean sea level, whereas the dikes are being constructed to a level of between 3 and 6 metre above mean sea level.
The Kapuk Naga Indah land development project is part of a larger land development program stretching along the coast of Jakarta in westerly direction, north of Banten. Witteveen+Bos is involved in the land development programme for North Jakarta for almost 25 years.
The services for the development of Kapuk Naga Indah consists of (modelling) studies to determine hydraulic and morphological impact, sand logistics and tsunami impact. Conceptual, detailed designs and the tender documents have been prepared for all three islands. Witteveen+Bos assisted the client in the tender process and technical assistance during the construction. Construction of the first artificial island started in 2012.
The hydraulic and morphological impact study focussed on the effect of the construction of the islands on the outflow of rivers and canals close to the future islands. The outflow of these rives and canals should not be obstructed by the new development, the so-called back water effect. Besides that, calculations were made on possible sedimentation and erosion near the islands.
The sand (logistics) study was made to determine the effects on time, costs and quality of the various possible sand borrow areas to be used for the reclamation works. A tsunami study was carried out to determine the chances and impact of a tsunami wave arriving at the KNI location. Origin (location and source) and magnitude of an earthquake, the resulting tsunami wave and the wave development from the source location to the project location were determined and modelled, to find out if and what kind of measures should be taken to protect the development against this phenomenon.