Red-bellied black snake out of its natural habitat
The need to control fauna movement
Development for commercial, industrial, educational and residential use is commonly adjacent to a creek line or lagoon, with an appropriate riparian corridor of regenerated natural habitat.
Public recreation areas such as soccer fields are also commonly located on low lying flood prone land adjacent to natural habitat.
Any development area adjacent to a natural habitat area poses a risk of unwanted fauna visitors such as snakes.
Road kill of fauna is also a real threat to species in a local ecological community. Some species such as the endangered green and golden bell frog migrate seasonally and are at high risk of being killed by road traffic.
Under the New South Wales State Biodiversity Conservation Act 2016 one of the questions in the five part test for EECs is:
(b)(ii) is likely to substantially and adversely modify the composition of the ecological community such that its local occurrence is likely to be placed at risk of extinction.
There is thus a need to protect fauna species from road traffic on perimeter roads that are required for bushfire protection purposes in new developments. Such road is commonly the line of interface between a development and natural habitat. The warm surface of a road or footpath is very attractive for frogs and reptiles to bask on at night.
The solution is a low maintenance, robust structure that allows fauna to return to natural habitat but prevents small fauna entering dangerous (to them) urban or constructed hostile habitat such as a perimeter road.
Concept
A solid barrier is provided to enable easy small ground fauna movement in one direction but prevent or dissuade movement in the other direction.
Retaining walls are generally constructed in a form that allows small fauna, including snakes, to climb up and over.
Design example
See below for an example of how the barrier enables a dynamic response to variable terrain and boundary line.
Where a retaining wall is part of the design this barrier can be installed at the base of the wall.
Cross section
Location
The interface of a development area and a retained or regenerated natural area is generally long and sinuous. A creek line or other riparian area is rarely straight so this barrier is most suitable and flexible for installation.
Construction
A concrete pipe cut to split lengthways, forming a “C” section.
Bury the pipe to one third and back fill the convex side to the top of the pipe.
The concave side is left open for two thirds the height of the pipe.
The concave side of the pipe faces the natural habitat area.
For example, a pipe 900mm in diameter will have 300mm buried and 600mm as an exposed concave pipe wall. Larger diameter pipe may be appropriate in some areas.
Bends in the wall can be achieved by angle cuts at the end of pipe sections to enable butting up of one pipe to the next and thus preclude gaps. Any gaps will be prone to erosion of fill from behind the wall. A butted angle join will be very robust and provide stability against slippage from up slope and retain integrity of the barrier.
Function
Small ground fauna (e.g. snakes, frogs) approach the pipe from the concave side and are unable to climb the curved wall. Fauna approaching from the filled convex side (area of development) can jump down to the lower level into natural habitat.
Larger fauna such as kangaroos and deer may jump over the barrier but can easily return to the natural habitat.
Maintenance
Most small fauna can climb. Any shrubs or fallen branches will enable fauna to get over the barrier. An annual pass by a labourer with a brush cutter is all that is required to make a metre wide path along the low side of the barrier.
Benefits
Fauna exclusion fences are commonly specified of a drift fence design that is fragile and acts as a complete barrier to fauna movement in two directions. That design also requires intensive maintenance since large fauna such as deer and kangaroos break it down.
Flooding is unlikely to affect a Wild Snake pipe barrier whereas a flood is likely to completely destroy a standard mesh fence.
The height needs to be low enough to not be a safety hazard for people walking.
A simple post and rail fence along the top of the barrier can be installed where necessary.
Plan view (Wild Snake Half Pipe as red dashed line)
These are design options for a potential development adjacent to a creek line.
Option 1
Option 2
Alternate design from Department of Transport and Main Roads State of Queensland (Department of Transport and Main Roads) 2010.
Fauna Sensitive Road Design Manual.
Volume 2: Preferred Practices
6. MEASURES TO ACHIEVE FAUNA SENSITIVE ROADS
6.11 Barriers: Fencing
Frog exclusion fence Figure 6.11.9(b) page 75
This design is:
a) more expensive to install, and
b) not robust so will require replacement.