drainage or ‘beach face dewatering’ involves
the localized lowering of the water table beneath and
parallel to the beach face. This has been demonstrated
to cause accretion of sand above the installed drainage
system. Sand is in continual movement on a wet beach
face due to wave and tidal action in the ‘swash’
zone. Under specific conditions, beach drainage systems
can halt beach erosion and promote sand accretion by
adjusting the dynamic equilibrium that exists on sand
The accretion or erosion of a beach is influenced by
a number of hydrodynamic forces in a beach surf zone.
The effects and interaction of these sediment transport
mechanisms have been studied since the 1940’s.
It is well understood that lowering the water table
in granular soils improves their stability and eliminates
the tendency for them to move (ie, ‘well-pointing’).
A number of theories have been proposed to explain the
empirical evidence for sand deposition from beach drainage
(ie, backwash reduction, seepage reduction, liquefaction
reduction) and these continue to be studied around the
It is evident that lowering the water table in the beach
face eliminates buoyancy factors and reduces the lubricating
effect between the grains, restoring the frictional
characteristics of the sand. In addition, the percolation
of 'swash water' into the beach means less backwash
energy, which encourages suspended sand to settle out
on the beach face.
Water table lowered by beach drain (not to scale)
side effect of the system is that the collected seawater
is very pure because of the sand filtration effect.
It may be discharged back to sea but can also be used
to oxygenate stagnant inland lagoons or used as feed
for heat pumps, desalination plants, land-based aquaculture,
aquariums or seawater swimming pools.
This is achieved by installing a drainage system in
the beach that lowers the beach face water table, intercepting
the flow of swash, tidal and inland ground water. Collection
pipes are buried in the beach parallel to the coastline
to create an unsaturated zone beneath the beach face.
This unsaturated zone is achieved by draining the seawater
away by gravity to a collector sump and pumping station.
The sump and buried pumping station can be located at
the back of the beach, where they are not readily visible.
A typical pumping station might consist of two submersible
electric pumps located in a buried concrete chamber.
The only visible feature of the system may be the pump
station control panel that regulates and monitors the
pumps, sends data and receives control signals.