Regional exclusion barriers against cane toads – concepts, terrain challenges, new barrier designs. Route options in the East Kimberley .
Cane Toad Exclusion Consultancy "CTEC",
P.O. Box 1248,
fax (08) 8985 4266,
mobile 0408 678 367.
To successfully protect the Kimberley environment from cane toad invasion, the only appropriate control measure available in the near future is to build and maintain an effective regional exclusion barrier.
A reliable regional barrier for the Kimberley must be designed and tested to be effective across every type of terrain encountered, to create an unbroken line of effective defence stretching several hundred kilometres from the sea to the desert. Creative designs beyond standard fencing are required. The route, located in the vicinity of the Western Australian / Northern Territory border, must be carefully selected to optimise cost-effectiveness. Construction must be completed before any toads have migrated westward beyond it. The barrier must be secured against incursions by vigilant monitoring, and rapid and effective responses, to confidently eliminate any local invasions.
Terrain Challenges and New Barrier Designs.
New exclusion barrier designs, being developed by the CTEC design team and others, aim to stop effectively the migration of cane toads across the wide variety of terrains and incursion risk environments encountered along a regional barrier route. Barriers may be physical, chemical, biological or actively maintained. Design concepts, and their relative feasibility, will be briefly discussed for:
Terestrial (solid barrier fencing)
Flats, undulating ridges, hillsides (toads uphill or downhill), cliffs and waterfalls
Mud, sand, soil, rocky terrain
Grass, forest, mangroves
Saltwater, brackish or fresh
Sea, tidal estuaries, flood-prone river mouths (large or small) - Coastal Gauntlet, Venetian Boomerang
Rivers and creeks (toads upstream or downstream) - Weir Tier
- Waterholes, dams, lakes
- Shorelines - Toadstool Island, riparian environments
- Along or across minor or major roads – Stock/Toad Fence,Toad Grid
- Culverts - Toad Flap, fords, bridges - Weir
- Boat ramps, ports – Floating Boomerang Fence
Summary - most feasible terrains for cane toad exclusion barriers, and terrains best avoided. A summary table will be provided.
Terrain modifying factors are dynamic, and most exclusion barriers will suffer occasional damage, each incident risking possible migratory breaches by the toads. Incursion risk processes include: larger animals, tree or rock fall, flood debris, flood waters, fire, extreme winds, vehicles, vandalism, hitch hikers, estuarine bypass.
The longer-term security and risk mitigation of the exclusion barrier depends on:
- Comprehensive design for all terrains
- Engineering for worst-case scenarios
- Thorough field-testing of designs (eg. Solomon Line, Saddle Creek Delay)
- Quality assurance measures during construction
- Reliable monitoring of the barrier, particularly in the early years, involving: regular patrols, periodic maintenance inspections and remote surveillance - ToadNode.
- Monitoring for incursions, mainly using traps on the toad-free side of the barrier (terrestrial traps and Toadstool Islands )
- Rapid and effective responses to barrier damage or incursions (Toad Blaster, Toad Busters, portable traps)
Proposed regional exclusion barrier routes (for discussion):
- Darwin Peninsula
- The Solomon Line (proposed by CTEC)
- Victoria River Watershed (proposed by Jeff Hayley)
- Great Northern Highway to the Last Bastion (the simplest engineering)
- The Tourist Route (radical, but tourist marketable and possibly the cheapest)
The military concept of a multi-layered defence strategy could be applied to buy time, by building a temporary section of barrier ahead of the most advanced part of the front wave. This would also provide an opportunity to field test barrier designs and construction processes in all seasons before full construction on the permanent barrier route.