Mudslide Zone!

I’m sad at the thought of all those lives lost and people being flooded out in British Columbia. Also the estimated 2,000 farm animals drowning; they got feelings and get scared too. I saw fear in the face of one of my Golden Retrievers one time when attacked by a German Shepard. It was an eye opener.

The flooding and the mudslides didn’t have to be such a surprise.

The flooding at Sumos Lake in B.C. was predicted by the Indigenous people when their land was taken over by farmers in the 1940s. (Ref. 1) A prediction based on millennium knowledge of the land.

The location of potential mudslides could have been predicted too – if you had talked to a geotechnical engineer or a surficial geologist.

Surficial geologists map the different types of soils in an area as deposited by the glaciers many 1,000s of years ago. Eastern Canada has been mapped completely. I’m sure also much of Canada and British Colombia. The data is readily available and easy to understand.

The soils beneath and near the site of a proposed road or bridge – like those washed out – would normally be determined before design and construction. This is standard engineering practice for all structures in the built environment.

The geology maps tell the type of soils and the contours on topographic maps tell the steepness of slopes in the soils – in jargon free language. Maybe a little high school math is needed.

Geotechnical engineers analyse the physical properties of these soils and how strong and stable they are when used or found in different ways. This can include the stability of natural slopes alongside a highway.

The cause of mudslides is understood well enough that signs could be put up to alert a driver – like, “Mudslide Zone“. Signs similar to, “Construction Zone“.

The cause has everything to do with the type of soil, the natural slope of the soil surface, and water. Take out the water – the trigger – and the land and mud will stay put, as it has for 1,000 of years – unless shaken by an earthquake. Water increases the weight of the soil on the (mud) sliding surface and water decreases the frictional resistance of that surface – like in high school physics.

Geotechnical engineers and surficial geologists can tell you were to put the Mudslide Zone signs. Drivers don’t need to be surprised and some swept away. Farm animals don’t need to drown if we listen to Indigenous people.

References

  1. Hughes, John M., PhD, Vancouver, Personal communique, November 2021

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(Posted by Eric E. Jorden, M.Sc., P.Eng. Consulting Professional Engineer, Forensic Engineer, Geotechnology Ltd., Halifax, Nova Scotia, Canada November 21, 2021. Updated November 24, 2021 ejorden@eastlink.ca)   

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