Floating Wetlands Protecting Shorelines

Posted on August 30, 2017

Written by Terry Wearmouth

The forces of nature can be relentless and the power of wave action is a huge source of energy. Nature has learnt to survive or diminish the power of waves in many ways. Next time you are near the sand dunes take some time to admire the complex ways the dune plants hold the dunes in shape and repair the dunes after storm events by re-trapping the sand.

Some water bodies are not so fortunate and we can expound on two examples where we are making a difference using clever technology.

One example is in the Mississippi delta region of Louisiana and New Orleans and the other is here in NZ on Lake Ellesmere in Canterbury.

The change in salinity in the Mississippi delta due to less fresh water exiting the river system and more salt water encroaching the delta is causing huge wetland marsh loss. As the wetlands’ health diminishes the wave action is eroding the levees. In fact tens of thousands of hectares of marsh have been lost at the rate of one rugby field every hour. As you are reading this, these levees are under huge pressure. We have had reports this week from Louisiana that Hurricane Harvey is like nothing they’ve seen before. Jason Martin (Martin Ecosystems) commented that “everyone is ready for Harvey to just get out of here!”

We have been researching and developing a solution to mitigate this erosion.

Kauri Park (Waterclean Technologies) work closely with Martin Ecosystems in Baton Rouge together developing natural wave breakers to protect shorelines from further erosion and help nature restore itself. This technology is known as Floating Treatment Wetlands.

Like the amazing work that is happening in Louisiana, we have installed Floating Treatment Wetlands on Lake Ellesmere. Lake Ellesmere is a very complicated ecosystem that is not in a good state of health. There are many reasons for this and currently of lot of opinions are pointing to the agricultural sector. What many are unaware of, that up until around the time of the “Wahine” storm, Lake Ellesmere had huge macrophyte (submerged plants species), forests growing around the perimeter of the lake.

These acted as giant kidneys filtering nutrients and trapping sediments, but also more importantly dispersed the wave action energy before the forces could destroy the shoreline. The loss of these macrophytes during the late 1960’s has contributed to the decline of the lake health. Great work is being investigated by the Te Waihora Co-Governance group in trying to re-establish the macrophytes.

The picture below demonstrates the level of erosion happening within Lake Ellesmere. This is the mouth of the Selwyn River at the south western part of the lake.

The sediments from the shoreline erosion continue to become water borne and take with them any nutrients that they contain. This sediment will continue to wash and mobilise with each reasonable wind event meaning the murky waters are not conducive to macrophyte re-establishment.

The Floating Breakwaters in Lake Ellesmere will be positioned a reasonable distance from the shorelines to provide a number of benefits:

  • Reduce wave energy. These specially designed and anchored wave breakers can disperse up to 80% of the wave energy. This wave action depletion will stop that continuing shoreline erosion.
  • Reduce suspended solids between the wave breakers and the shoreline with the aim of being able to re-introduce the critical macrophytes.
  • Reduce nutrients in the water body that vectors with algae therefore reducing algae levels.
  • Provide safe habitat for bird life away from predation.
  • Provide habitat for fish as the platform provides protection from above and a food source amongst the vast root column.

During July the lake rose 600mm over 48 hours. This is a staggering 1.2 billion litres of water. The floating wetland is designed for double this amount of water level change.

We will keep you updated as this exciting project develops and as we go through the storm events of the next few months.