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SUMMARYIntroductionSubaqueous sediments, rich in clay and organic matter have a high watercontent and are unaerated and almost impermeable just after emergence. Such a sediment is inaccessible due to the low bearing capacity. Plant growth is restricted to a pioneer vegetation of plants, which are able to provide the oxygen demand of their own roots. Due to evapotranspiration in periods with a rainfall deficit the water content of the sediment decreases irreversibly. By capillary forces the soil particles are drawn to each other, so the bulk density increases. As a result, the surface will subside and crack formation starts. Water transport to open-field drains and tile-drains is then possible via the cracks. This dewatering-process is known as 'ripening'. Ripening can be subdivided into a physical, a chemical and a microbiological part. The physical part of the process, which can be considered as the motor of the entire process, is the topic of this study.Knowledge about this process is necessary to be able to predict the qualities of not yet reclaimed sediments and their rate of subsidence. Since the start of the IJsselmeerpolder project, research has been carried out to increase this knowledge. In the first period emphasis was given to research concerning dewatering-measures that had to be taken to obtain a ripened soil as fast as possible. Also much research was focused on the subsidence-rates. A first attempt for a quantitative integrated approach of the physical ripening process was given by SEGEREN (1966).To improve this quantitative insight, including the process effecting factors a numerical simulation model has been developed, based on a conceptual approach.Description of the process of physical soil ripeningThe soil profile in the IJsselmeerpolders can be roughly characterised as a layer of Holocene, mostly rich in clay and organic matter, with a thickness from nearly nil to over 7 m, underlain by Pleistocene, mostly sandy deposits (figure 3 and 4). The cl, Op grond van vroeger onderzoek gedurende de ontginningsfase van de bestaande IJsselmeerpolders is een model ontwikkeld waarmee de fysische eigenschappen (met name veranderingen in verband met de waterbalans) van nieuw te ontginnen drooggemaakte gronden tijdens de rijpingsfase (die naast een fysische ook een chemische en een biologische component heeft) kunnen worden voorspeld