Road ecology blog: Drainage from road under wildlife fence at underpass, São Paulo, Brazil

January 06, 2015  •  Leave a Comment

Drainage from road under wildlife fence at underpass, SP-270 about 70 km south east of Presidente Prudente, São Paulo, Brazil. Drainage can be hard to combine with a wildlife fence as it may result in an opening in the fence allowing certain species to access the fenced road corridor. In the images below the drainage is positioned right above multifunctional underpasses (water, wildlife). There are pros an cons associated with this approach:

 

Pros:

1. This may reduce intrusions of wildlife into the fenced road corridor as it is harder for wildlife to access the gap under the fence.

2. Depending on the construction it may be harder for vegetation to eventually block the gap under the fence and plug the drainage gutter.

 

Cons:

1. If it is a multi-functional underpass including for water, I would recommend against draining run-off from the road directly into a stream, or river. Pollutants (e.g. from road surface, particles from tires) and sediments are likely to be present in the run-off. In my opinion it is best to not drain road run-off directly into streams and rivers. It is better to drain road run-off into (artificial) depressions where it can percolate into the soil. The soil and microbes can then filter out or break down the pollutants and sediments before they get into the stream.

2.  If it is a multi-functional underpass including for water, I would recommend against draining any unnaturally concentrated water directly into a stream. Concentrating water and dumping it into a stream or river increases peak flows and increases the risk of flooding down stream. This is especially important when rain events are severe (heavy downpours) and when such events may become more common in the future(climate change). It is better to drain road run-off into (artificial) depressions where it can percolate into the soil. As a consequence it takes more time for the water to reach the stream and the water does not reach the stream all at the same time.

3. In other situations the underpass may not have a stream or river, and the structure may be only or mostly intended for wildlife. However, when it rains, it results in a temporary "waterfall" at the entrance of the underpass. I really do not know if this affects wildlife use or not. "Falling water" may deter wildlife during a rain storm, but a puddle (after a rain storm) may be an attractant. However, because of the pollutants in road run-off it is not advisable to encourage wildlife to drink this type of water.

4. In a "dry" underpass a hard (potentially artificial) surface is needed to prevent erosion where the water hits the ground. However, the surface in front of and inside an underpass should preferably match the natural soil of the surroundings though. 

 

Click here for more images of erosion and erosion control measures.

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Drainage from road under wildlife fence SP-270 about 70 km south east of Presidente Prudente, São Paulo, BrazilDrainage from road under wildlife fence SP-270 about 70 km south east of Presidente Prudente, São Paulo, BrazilDrainage from road under wildlife fence SP-270 about 70 km south east of Presidente Prudente, São Paulo, Brazil Drainage from road under wildlife fence SP-270 about 70 km south east of Presidente Prudente, São Paulo, BrazilDrainage from road under wildlife fence SP-270 about 70 km south east of Presidente Prudente, São Paulo, BrazilDrainage from road under wildlife fence SP-270 about 70 km south east of Presidente Prudente, São Paulo, Brazil


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