Wildlife and Roads: Decision Guide Step 2.1.4

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2.1.1: Identify Species to Benefit from Potential Mitigation

2.1.2: Identify Ecological Processes (Water Flow, Animal Movement, Other)

2.1.3: Identify Landscape and Topographic Features That May Affect Movement and Mitigation

2.1.4: Identify Engineering and Maintenance Concerns

2.1.5: Weigh Cost Concerns with Potential Benefits

2.1.6: Identify Appropriate General Wildlife Crossing Type

2.1.7: Other Mitigation Options

2.1.8: References

2.1.4 Identify Engineering and Maintenance Concerns

The collaborative work of engineers, planners, and ecologists is critical in this step of the selection process. There are many factors that constrain the selection of the type and placement of crossings. For example, the road grade is an important consideration and may influence the decision to install a bridge or culvert. Soil type and bedrock stability are considerations. The design of a bridged crossing is also dependent on engineering concerns as much as wildlife preferences. While wildlife prefer to cross under bridges that have gradual slope sides (such as those with a 2:1 ratio), engineers need to be considered to see if this slope is possible. Terrestrial wildlife and streams can be accommodated in the same structures but wildlife ecologists need to work with engineers to provide information on wildlife preferences, while engineers need to be consulted on structural issues. There needs to be sufficient upland along a crossing, enough room for the target species to pass under the planned height and openness of the passage, and if rip-rap rocks are placed to stabilize the stream bed, their size needs to be considered so that they could be negotiated by the animals that would use the passage. Through iterative processes, engineers, planners, and ecologists working together can come to a solution that satisfies both engineering and wildlife considerations. If an overpass is selected as the mitigation of choice, landscape topographic features can be used to some degree to minimize costs. McGuire and Morrall's paper (2000), found in section 2.1.8 in References, can be helpful: it describes some engineering concerns that were dealt with in the 24 wildlife passages that were built along the Trans Canada Highway in Banff National Park. Terry Brennan, the USDA Forest Service Highway Program Leader in Arizona has written an article for the Wildlife Crossings Toolkit site, entitled, "The Severn Dwarfs: Often Ignored Highway Project Issues." These issues are all important to the final plans for construction of mitigation. The article can be downloaded at: http://www.wildlifecrossings.info/sa017.htm.


2.1.1: Identify Species to Benefit from Potential Mitigation

2.1.2: Identify Ecological Processes (Water Flow, Animal Movement, Other)

2.1.3: Identify Landscape and Topographic Features That May Affect Movement and Mitigation

2.1.4: Identify Engineering and Maintenance Concerns

2.1.5: Weigh Cost Concerns with Potential Benefits

2.1.6: Identify Appropriate General Wildlife Crossing Type

2.1.7: Other Mitigation Options

2.1.8: References