PEM Technology

The PEM solution involves permeable independent drain tubes installed vertically into the beach. Each tube is 2½ in. by 6 ft. They form a grid stretching from the dunes to the water line.

A typical number of tubes will be 70-100 per mile of beach each placed 1-3 feet below the surface, however the exact design of the installation will vary from site to site.

The tubes act as “connectors” between different layers of ground water in the beach. With PEM installed water is able to drain from the beach via the layer with the lowest resistance (typically a coarser layer), this leads to a reduction in ground water pressure. Air entering from the top of the PEM replaces the water. 

Improved drainage will reduce pore pressure and increase the inter-granular friction, and the sand grains will stay on the beach in stead of being washed back to the sea.

The result is a beach where waves sink in more easily, leaving more suspended sand on the beach than they take back to sea. Over time the beach will build up.
 

PEMs are placed subsurface and are invisible except after an unusually heavy storm, where they may be visible during a short period of time.

PEMs are independent modules and the effect of one module is not dependent on other modules.

No power is needed to operate the PEM.

Under most conditions the PEM system causes a new equilibrium profile to be formed with a wider and higher beach profile. This, together with a flatter foreshore breaks the waves farther away from the water line and reduces the risk of dune erosion.

Provided there is good water circulation activity (strong winds or tide), the new equilibrium profile will normally be built in 6-9 months.

For the PEM system to function properly, sand has to be suspended in the water that flows ashore. If this is not the case new sand may have to be added. A combination of beach nourishment and the PEM system to maintain the sand is a viable solution.

PEM is a “soft” solution applying a small change, just enough to tip the balance in the beach, resulting in the accretion of sand.

Click here to see a White Paper written by an independent Consulting Engineer.

To view examples of PEMs in combination with hard structures see Projects.

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