The tranquil sea coast in the heading is deceptive.
Many forensic engineering problems are caused by water or water is a factor in the problem. And – at the risk of annoying you, I must tell you that experienced forensic engineers like heavy rain when investigating a flooding or drainage problem.
They’ll also use somewhat unconventional methods to gather data to solve the problem – this blog site is partly about forensic methods. And think outside the box when analysing the data.
There’s no shortage of flooding and drainage problems in eastern Canada in the spring.
We are almost always interested in how rain and melt water are flowing across a site and around, beneath, and into structures. We can do detailed topographic and contour surveys – which can take days, and determine drainage patterns and watercourses the text-book way.
Or we can wait and hope for heavy rain – sorry, and note and measure the location of the water as it flows across the site and in the vicinity of the structures. I often do the latter. It’s very accurate.
Also, we note in some problems where it’s not flowing – this was relevant in one problem I investigated a few weeks ago.
We’re interested in discharge too. I went to one site four times in 24 hours to measure the discharge in a drainage channel – I was interested in how quickly the site drained after a rain storm. Quite quickly as turned out.
Noting where water was not flowing was relevant in another problem I looked at a couple of years ago. Unfortunately, I was retained after $140,000 was spent in misguided investigation. Getting out on a rainy day and noting where water was not flowing would have saved an awful lot of money.
Sadly, sometimes there’s no heavy rain when a drainage problem is being investigated. Or greater flow is needed than can be expected from typical rainfalls for the season. Fire hoses and water trucks can be used to generate flow. I planned this for one investigation.
The scene in the heading is Prospect Bay, Nova Scotia, Canada, photographed by J. Knoll, Halifax.
Other days are not as nice as this scene along the 1,000s of kilometres of Atlantic sea coast – almost as long as Canada is wide. Nor are the 1,000s of rivers and streams that flood – and they certainly have flooded this late winter, early spring, 2014.
The rivers and lakes are still flooding this morning after the heavy rain yesterday as the land sheds the rainfall and melt water in runoff to our watercourses. And the lakes are overtopping their banks – there are more than 4,000 lakes in Nova Scotia. That’s just the water you can see on the ground surface.
There is also the ground water – the water table, that you can’t see. Water that is just below the ground surface or quite deep, and fluctuating up and down all the time – certain to be well up and high after the rain this year.
Ground water flows through the ground much like a river flows on the land; welling up behind obstacles buried in the ground – e.g., foundations and basement walls, like river water wells up behind a boulder in a stream.
Forensic engineers use monitoring wells to measure how ground water flows and drains beneath a site, and also measure ground water discharge. They are looking for similar parameters to those for surface water.
It’s been said that if you could take the water out of the ground, out of the soils and rocks beneath our feet, you would reduce foundation and ground engineering problems to a fraction.
The camera operator in the heading is filming the re-enactment of a fatal MVA from a sea king helicopter during a forensic engineering investigation. The sea and snow – frozen water, were factors in the fatal accident. For this forensic investigation, I set up a full scale test site at Shearwater airbase in eastern Canada complete with:
- A traffic lane,
- An obstacle in the lane,
- A vehicle,
- Monitoring devices to track vehicle behaviour on striking the obstacle, and,
- Film crews to record the tests.
The surveyor in the heading is checking the adequacy of the underpinning of a structure during a forensic investigation.
Surveyors also carry out topographic surveys of sites with drainage problems. But, noting and measuring where the water is draining during heavy rain can often give us all the data we need and much quicker and more accurately.