7 September 2016

Why maintaining forest roads is important – a large landslide triggered by a small culvert failure

Posted by dr-dave

The reasons why maintaining forest roads is important – a large landslide triggered by a small culvert failure

Carolyn Cook of the Six Rivers National Forest in California has posted online an amazing powerpoint presentation showing the chain of consequences that can occur when there is inadequate maintenance of drainage (and in particular if a culvert) on forest roads.  She has kindly agreed that I can post about it here – the original file can be obtained from here.  I have posted below some of the slides from the presentation.

The events occurred at Bluff Creek in the Six Rivers National Forest in January 2006.  It started with inadequate maintenance of a large (48 inch = c.1200 mm) culvert:

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Culvert failure on Bluff Creek, via Carolyn Cook of Six Rivers National Forest

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The stream then diverted down the road, incising a channel en route:

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The diverted channel via Carolyn Cook of Six Rivers National Forest

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About 300 m down the road the flow diverted off the road and into the forest:

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The flow diverting into the forest via Carolyn Cook of Six Rivers National Forest

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The new channel incised into the soil to create a gully, and then flowed over the break of slope onto the lower slopes:

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The new, deeply incised gully via Carolyn Cook of Six Rivers National Forest

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On the lower slope it triggered a landslide that covered 3 acres (about 12,000 square metres):

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The newly triggered landslide via Carolyn Cook of Six Rivers National Forest

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This landslide permanently destroyed a newly-constructed road that had cost about US$750,000:

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The destroyed road via Carolyn Cook of Six Rivers National Forest

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The landslide and gully then delivered a large volume of sediment to the river, damaging the ecosystem:

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Sediment being delivered to the river, via Carolyn Cook of Six Rivers National Forest

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This is a dramatic example of the ways in which a lack of maintenance on low cost roads can have dramatic consequences on landslides.  This pattern is repeated again and again in, for example, Nepal where forest roads are constructed without managing the drainage.  I continue to believe that this is a major factor in the high level of loss of life in the Himalayas and other mountain chains.  But even in a developed country like the USA, poor basic road maintenance leads to massive environmental damage over long distances. and loss of amenities such as other forest roads:

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The damaged forest road, via Carolyn Cook of Six Rivers National Forest

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Other posts on a similar theme:

And of course this classic Youtube video of the failure of a culvert:

Acknowledgements

Thanks to Carolyn Cook of Six Rivers National Forest for putting together this brilliant example, and for allowing me to use it, and to Ellen Hardy of U.S. Forest Service Rocky Mountain Regional Office in Golden, Colorado for bringing it to my attention and putting me in contact with Carolyn.