2019-03-12 P&E Agenda - Item 5 - Attachment 2 - Koala Infrastructure & Feasibility Report

Design considerations
• Several factors affect the ability of a crossing structure to facilitate wildlife movements (Glista et al. 2009)
        o Location is vital, especially for smaller, less mobile species
                  ▪ crossing structures should be placed in areas of suitable habitat
                  ▪ passages implemented near continual disturbance (e.g., excessive human presence) are
                      less frequently used by several wildlife species
        o Dimensions of structures are also important in designing passageways for vertebrates
                  ▪ size and shape may determine crossing success
                  ▪ relative openness may be more important than overall size
• Sediment and debris may be deposited during flow events and culverts must be maintained to allow free
   passage for water and fauna.
• Thought must be given to flow conveyance when retrofitting existing culverts. Each culvert must be
   checked to ensure that retrofitting will not significantly impact design flows prior to any retrofitting
   exercise.
• When considering multi-species applications, culverts and exclusion fencing facilitate safe passage across
   a road for a range of wildlife species but are not effective for frogs (Taylor & Goldingay 2003). Cunnington
   et al. (2014) found that culverts alone do not reduce anuran mortality as anurans do not detect the
   presence of the culvert and will continue across the road surface. However, installation of anuran-proof
   fencing along both sides of the road reduced anuran mortality.
• Vegetation at the culvert entrance is important for encouraging use by small mammals and in providing
   protection from predators (Taylor & Goldingay 2003; Clevenger et al. 2001). In the Australian context,
   vegetation cover at passage entrances appears to make passages more attractive to native prey species
   and less attractive to feral predators (Finegan 1997; Hunt et al. 1987).
• The inclusion of a natural substrate within a crossing structure can provide continuity of habitat and may
   encourage animals to pass (Glista et al. 2009).
• Road-related factors have the greatest influence on mammal passage at culverts, whereas structural and
   landscape attributes of culverts are lesser predictors of culvert use (Clevenger et al. 2001; Yanes et al.
   1995; Rodriguez et al. 1996).
• It is important to have at least one culvert or passage within an individual's home range to ensure cross-
   road connectivity and gene flow (Gerlach & Musolf 2000), it is therefore important to understand the
   average home range size of target species to inform the frequency of crossing infrastructure (Clevenger
   et al. 2001).
• Use of the relatively large underpasses could be enhanced for smaller species by the inclusion of small
   mammal-specific features including hollow logs and pipes along the open floor of the underpass and
   raised shelves could be incorporated into existing culverts and underpasses to encourage increased use
   by small species (Bond & Jones 2008).
• Bliss-Ketchum et al. (2016) studied the effect of ecological light pollution on animal usage of a bridge
   under-road passage structure. The study suggested that artificial light within the underpass was a barrier
   to use by some species but not for others. Manipulation of spectra may facilitate use by fauna and
   artificial light could be used to influence movement (Bliss-Ketchum et al. 2016).

3.1.3.          Overpasses
Overpasses for wildlife are a ‘green’ bridge used in areas where an underpass is not feasible and designed
primarily for fauna that are unlikely to use a culvert crossing. Overpasses can maintain the connectivity of
horizontal ecological flows across the landscape, are open, quieter than underpasses and culverts, maintain
ambient conditions (rainfall, temperature and light) and can serve as both passageways for wildlife and
Koala Infrastructure Audit & Feasibility Report                                                            Page 12

Noosa Council
17SUN-0087/1700860