Living island solutions

The challenge
To capture and remove plastic and other solid wastes from rivers. Any solution must be ecologically benign, or even add something to the river environment.

 Figure 1: A willow tree smothered in plastic wastes after winter flooding.

Figure 2: Detail of plastic waste caught up on a willow branch. This provided the initial concept.

The (living) solution
 A floating boom made out of living materials such as willow and alder branches, reed mats etc. woven into mats and extended along a linear boom, that is placed in the river to capture floating and submerged wastes during winter flood events. The design is such that the boom closes into a circular island as it fills with waste. This is then drawn toward land by its own weight where it remains as the floods recede. Buoyancy is currently achieved using disposable plastic bottles found along the river bank.

Figure 3: The very first prototype made of woven alder and willow. It's now become a duck's nest.

Figure 4: The first island using a floating platform. Branches are placed thorugh the platform in bundles.

Initial tests carried out by dragging the boom behind a boat have shown that the system is capable of effectively collecting floating waste. More research is required into alternative designs and testing is required under differing flow conditions.

The benefits

• The materials are all locally available and biodegradable, being the waste product of coppicing/pollarding of willow and alder in the early spring;
• Jobs are created using mostly free materials;
• A living boom/island provides a habitat for wildlife as it grows during summer months;
• It is visually appealing;
• Living biomass also serves to improve water quality by absorbing nutrient loads;
• Collection using barges is cheap and easy;
• Disposal by incineration provides a feedstock for local combined heat and power (CHP) plants;
• Education and research into re-naturalisation are promoted.

More photos are available here 

Update 2nd April:

I built another, similar system using alder and willow branches in bundles placed through a large wooden pallet, which I found washed up on the river bank (see figure 2 above). The system became  submerged at the front when I towed it across the lake and the semi-submerged branches caught some items while bottles passed through the branches on the topside and were washed onto the pallet. It seemed to work okay (video to be uploded!) and is now tied up under a willow tree on the big lake. I hope that birds will use it as a nesting platform.

When I returned to the harbour I noticed that a pair of ducks were already making a nest on my prototype floating island! 

 Figure 5: A coot adds a small branch to the floating island prototype, showing the natural habitat that this produces.

The advantage of providing habitats is seen by their preference of floating natural material to the stern ladders of boats! The mess they create drives boateres mad, so this solution should be promoted in harbours for example.

We do need to experiment with different designs in terms of ease of construction, durability, growth potential, cost etc. Bundled branches are easy to fix and could be employed both horizontally in booms and vertically as with the island.

Update: Mentioned project on Guardian article about water and green growth.