The permeability of fill must be great enough to allow for the percolation of water through the unsaturated zone, as well as to ensure sufficient groundwater flow (that is, internal drainage), to prevent water from rising to unacceptable levels. Permeability is controlled by grain size distribution and the density
of the fill.
Analysing permeability and then assessing the need for a drainage system should be made during the design stage of a reclamation project as it can have impacts on the final layout and costs of a reclamation.
Water from natural precipitation like rain or snow, overtopping and other sources can hamper the use of a reclamation if it is not readily drained away. This may cause ponding, flooding, and erosion. Natural drainage includes the infiltration of water into the fill combined with natural surface runoff and that is influenced by the permeability of the fill mass.
Natural drainage is defined as the infiltration of water from the surface into the fill mass combined with uncontrolled surface runoff (drainage). If the precipitation or overtopping is so intense that it exceeds the infiltration capacity of the fill mass, then ponding and natural surface runoff will occur.
If the ponding and runoff are too great and deemed unacceptable than an artificial drainage system may be necessary. Even during the construction phase process water may adversely affect the mechanical properties of the fill mass if the drainage capacity of the fill being placed is insufficient.
An artificial drainage system should then be designed and installed. A number of special measures can be taken to improve infiltration so that ponding water and surface runoff can be transported to a suitable location and discharged into open waters, like a river or sea, and not affect surrounding facilities.
This may already be needed during the construction period so that the site is accessible to equipment.