Colliery Dams – studies on dam failure

What’s happening with the Colliery Dams? Do the dams need to be repaired or not? Two areas of concern have been identified for the Colliery Dams:

  • Would the dams survive an earthquake
  • Would the dams survive a flood

It has been determined that the Colliery Dams will not fail in a seismic event. The dams are in much better condition than previously thought.

Now the concern is what would happen if there was a flood.  At the September 15th Committee of the Whole meeting Councillor Kipp raised some interesting points:

  • Dam Inspection report: January 21, 2012 = no risks.
  • Dam Inspection report: August 12, 2012 = problem.
  • City spent $1 million between 2012-13 to study problems.
  • City spent $2.47 million to conduct studies related to a seismic event.
  • Now city would like to spend approximately $400,000 on a Hydraulic study

This would mean that the cost of the safety studies on Colliery Dams will total approximately $4 million dollars.

At the September 15th meeting it was decided to hold off on approving the Hydraulic study until a number of concerns could be addressed and included.

It the Hydraulic study goes ahead it would determine the rate of erosion in a flood situation and what would happen if the lower dam overtopped. This study would answer questions such as: how would the embankment hold up? Would the core concrete wall inside fail? Where would the water go?

Colliery Dam embankment
Colliery Dam embankment – would this area fail if water went over it?

A scale model would be built of the Colliery dams to see how the embankment behind the dams would hold up. Then an overtopping event would be conducted to see what would happen.

Colliery Dam Spillway
Colliery Dam Spillway – would the water go over the sides?

The scale model would cost about $100,000 to build. From that model engineers would find out how best to armour the dam for a failure event. The explanation as to why the scale model is so expensive is because in doing the tests the scale model will get destroyed and they would have to rebuild the model again.

The Colliery Dam Technical Committee disbanded at the end of August 2014 and by September 8th they decided upon a Hydraulic Study which could lead to options of either overtopping repairs or expanding the spillway size or leaving the dams as they are.

Many people spoke at the September 15th Committee of the Whole meeting and had several questions that remain unanswered such as:

  • What about the back fill?
  •  What would happen to the fish?
  • Why can’t the water level be lowered prior to the wet season?
  • Why was a drain pipe filled with concrete?
  • Why was there no updated drilling done on the bank?
  • Why has no soil profile been taken so far?
  • Why was only a sonic sample taken?
  • How can we make a model of the dam if we haven’t done soil samples?
  • Have there been any water/drainage flow studies done of the area?
  • Have there been any rainfall studies done?

One speaker commented on the concrete core shown in green in the drawing below:

“…it shows that the concrete core is narrow from top to bottom…they are built tapered, thicker at the bottom, we paid $500,000 for a study…they drilled two holes 30 feet from the concrete straight down…if they drilled the hole 10 feet away from the wall then they might have discovered the footing of the dam and found that the dam core is tapered… no dam in the world looks like this…it’s just wrong.”

Take a look at the diagram below:

Colliery Dams Hydraulic study
Flood event: what would happen? Green represents concrete core which speaker noted is the wrong shape

The city was going to hold a public open house in September but it was cancelled.

Repairing the dams will mean another multi-million project. Are these dam repairs really necessary? Is this overreaction? Ironically, if these dams were still in the hands of a coal mine operator, it would be doubtful if the same scrutiny would be applied.

Colliery Dam repair options
Colliery Dam repair options – either $3+million or $8.2 million to repair

Note that Option 1 for a Hydraulic Study has increased to $400,000 to cover model building.

Why hasn’t the City given the same attention to the miles of coal tunnels under the City of Nanaimo and Protection Island? When Duke Point was being blasted in the early 80’s, many homeowners complained of sinkholes on their property. It was proven by the engineer that the root cause of the sinkholes was the old coal tunnels. What about the new five star hotel slated to be built next to the Number One coal shaft? Who would be liable if there was a failure?

The Colliery Dams were completed on May 1, 1911. The dams have stood for 103 years. They withstood a 7.3 earthquake that shook Nanaimo and Vancouver Island on June 23, 1946.

Why can’t the City just let the dams be? A simple drain would most likely solve the problem. It’s as if the taxpayers are being held hostage on this project.