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

3.1.2.          Underpasses
Both pipe and box culverts are installed where roads cross drainage lines to allow water to flow under the
road. Pipe culverts have curved surfaces and often have a wet base whereas box culverts have flat surfaces
and often remain dry between runoff events. Both types of culvert have been used as wildlife crossings for
various small to medium sized terrestrial species and are one of the more economical wildlife crossing
structures (Glista et al. 2009). New culverts can be designed and installed with fauna crossing as well as flood
conveyance in mind and existing culverts may be modified to encourage use by fauna to cross roads.

Wildlife underpasses are large, open passages often associated with roads crossing waterways or other
roads. Underpasses can use the natural landscape to allow passage for larger terrestrial fauna and species
associated with riparian vegetation (Glista et al. 2009). The construction of an underpass is expensive and
the use of this type of crossing is likely to be used only when a bridge is deemed necessary.

Efficacy
The installation of culverts and underpasses has lead efforts to mitigate the road-kill and barrier-effect of
roads and traffic. There is much support for the use of underpasses with exclusion fencing to facilitate safe
road crossing for a range of fauna species, especially when they are positioned on migration paths, are large
enough to accommodate the target species and where human noise and activity are minimised (Taylor &
Goldingay 2003). Some examples include:

•    Clevenger et al. (2001) investigated culvert use by small and medium-sized mammals along roads in Banff
     National Park, Canada. A variety of mammals were recorded using the culverts. Traffic volume, noise
     levels and road width were the most significant factors affecting culvert use.
•    Mata et al. (2008) evaluated the utility of different types of crossing structures along a motorway in
     north-western Spain and found crossing structure type and width to be the most important factors in
     their selection for use by vertebrates. Larger-bodied animals favoured more open passages, while small
     mammals and herpetofauna favoured culvert-type structures.
•    Culvert crossings designed for amphibians and reptiles have been installed in numerous locations across
     North America, Europe and Australia (Cunnington et al. 2014). Several studies have shown that
     amphibians and reptiles use culverts (Rodriguez et al. 1996; Yanes et al. 1995; Lesbarrères et al. 2004;
     Mazerolle & Desrochers 2005).
•    Veenbaas and Brandjes (1999) reported mammals using 100% and amphibians using 77% of monitored
     wildlife passages along waterways under highways in the Netherlands during the 1997-98 survey. For
     mammals, underpasses with the largest diameters were used most frequently and passages with
     extended banks were used by more species.
•    Bond and Jones (2008) studied the effect of crossing structures associated with the Compton Road
     upgrade south of Brisbane in 2004, confirming underpass use by a wide range of small and medium-sized
     mammal species.
•    Dexter et al. (2016) examined whether retrofitting existing road structures at six sites facilitated safe
     passage for koalas across roads. The study found that road crossing events were restricted to a relatively
     small subset of individual koalas, with crossing events being generally uncommon among the resident
     tagged populations. Of that subset, structure use varied but the study highlights the importance of these
     individuals in relation to population connectivity and of appropriately placed crossing infrastructure
     and/or fauna fencing. Relatively low rates of structure use by koalas do not necessarily equate to poor
     connectivity or conservation outcomes, as a relatively low rate of dispersal success is sufficient to
     maintain the population viability of local subpopulations (Taylor & Goldingay 2009; Dexter et al. 2016).
•    Where suitable structures are available, koalas will willingly incorporate structures into movement
     patterns (Dexter et al. 2016; RTA 2009; AMBS 2012).
Koala Infrastructure Audit & Feasibility Report                                                          Page 11

Noosa Council
17SUN-0087/1700860