Distribution of grain size and resulting hydraulic conductivity in land reclamations constructed by bottom dumping, rainbowing and pipeline discharge

Abstract

Spatially constant porosity and hydraulic conductivity are usually applied in hydrological studies related to land reclamations. However, the grain sorting and the degree of compaction within land reclamations differ per placement method. A study area at Maasvlakte II, the Netherlands, and the four other land reclamations that could be found in the literature are considered that were constructed by a combination of bottom dumping, rainbowing and discharging the sand-water mixture by pipeline. The structures of the porous media are derived for each placement method and validated by comparison with semi-variograms of cone-penetration tests. It is found that all placement methods lead to some degree of heterogeneity, so that the hydraulic conductivity in these land reclamations is not constant. This is due to the degree of segregation of the grain sizes that differs between placement methods. Segregation even varies within a specific placement method because of its characteristics and site-specific circumstances such as settling depth, grain-size distribution and angularity resulting from grain type. If land reclamations are considered for aquifer storage and recovery for freshwater supply, it should be considered that the recovery efficiency will be affected by both the properties of the material in the borrow area and by the placement methods including their spatial configuration as applied during construction of the reclamation.