Image below: Stream culvert (northern stream crossing, Córrego do Geraldo) under two lane road, Itirapina Ecological Station, São Paulo, Brazil. Note that this is not a suitable crossing structure for large mammals. The stream is funneled into a narrow culvert resulting in consistent high water velocity and this is likely a barrier for many aquatic species. There is no semi-aquatic or terrestrial habitat inside the culvert and the culvert dimensions are too small for e.g. capybara (Hydrochoerus hydrochaeris)). Also note that fencing is only installed above the retaining wall of the culvert. The fencing on the other side of the road is only a little longer; perhaps several dozens of meters.
Image below: Cross marking the location of a human fatality as a result of a collision with a capybara (Hydrochoerus hydrochaeris), northern stream crossing, Itirapina Ecological Station, São Paulo, Brazil
Image below: Wildlife trail (probably mainly used by capybara) at fence end of northern stream crossing (east side road, south of culvert) leading to the two lane road, Itirapina Ecological Station, São Paulo, Brazil
When there is an opportunity to change this stream crossing and associated fencing, it should ideally include:
1. A larger structure that is wider than the stream. Ideally the structure is "bottomless" (e.g. a bridge) so that the stream characteristics inside the structure are similar to those upstream and downstream of the structure.
2. Allow for sufficient space in the structure to also provide semi-aquatic and terrestrial habitat.
3. Make the structure tall enough to allow for large mammals (e.g. capybara) to cross through the structure.
4. Extend the fencing at least a few hundred meters on both sides of the structure if capybara are the target species (capybara tend to stay close to streams). Habitat generalists such as the maned wolf may require additional structures away from streams and much longer road sections with wildlife fencing (at least several kilometers long) and associated safe crossing opportunities.
5. Design the fence (e.g. height) based on the requirements for the target species. The strength, the jumping, climbing, or digging abilities of the target species should form the basis for the design of an effective fence.
Developing good relations between transportation agencies and natural resource management agencies can help implement effective mitigation measures. When the time comes to replace the culvert with another structure, the new structure and associated measures (e.g. wildlife fencing) can be designed appropriately from the earliest planning phases onwards.
Click here for images of wildlife fencing.
Click here for images of multifunctional underpasses.
Click here for images of wildlife underpasses.
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