ISSN:
1752-1688
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Architecture, Civil Engineering, Surveying
,
Geography
Notes:
: In the past, much effort has been put into the development of sophisticated mathematical models to describe settlement and consolidation of water deposited sediments. Such models often aim at completeness and accuracy in modeling the physical processes involved. However, as a result of the generality of the descriptions, the models often fail to compute local circumstances satisfactorily. In specific cases, the empirical approach may prove to be highly competitive and reliable. In large water bodies in the central part of the The Netherlands, the alluvial “IJsselmeer-deposit” is a common type of fresh water sediment. Its deposition and settlement started in 1932, when anthropogenic activities changed the physical and chemical conditions of the lakes drastically. Five representative cores of this sediment were taken in deep zones of the lakes. Periodic water depth surveys over the last sixty years at these locations provided information on the net sedimentation rate and the total thickness of this Ijsselmeer-deposit at known time intervals. In order to calculate a time-equivalent of the depth scale, correction factors for soil consolidation are introduced. A decrease in the total thickness of individual sediment layers is proportional to the decrease of its volume, which is derived from in situ characteristics. Correction factors are based on a simplification of various stages of compression (i.e., O percent, 30 percent, and 45 percent). A factor n, which represents changes of water content of the sediment as a dependence of clay content, is derived for each layer, allowing an inverse calculation procedure to determine the initial, uncompressed thickness of each layer. Hence, a fairly reliable time scale in depth can be reconstructed. Furthermore, the radionuclide activity was measured in some cores and the degree of organic and inorganic pollution was determined in numerous layers of all cores. Cs-isotopic tracers (137Cs, 134Cs) give a good reconstruction of the last six decades of physical changes of the sediment and the degree of pollution, assuming post depositional redistribution and transformation of pollutants to be negligible. The results showed close coherence to calculated time-scales.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1752-1688.1994.tb03318.x
Permalink
