Thursday, August 22, 2013

Update Report from Roblyn Hunter
Letter to Acting City Manager Howat
Key Info from the Inundation Study

The saga of the Colliery Dams continues. We had an extremely lucky break with Doug White, Chief of Snuneymuxw First Nations intervening at the July 8th Council meeting. As a result we now have a different process, but we are unsure what that will look like. Ian Howat has said that the Colliery Dam Park Preservation Society will be included in the decision making as short and long term mitigation is being considered. We are now waiting for this opportunity. 

One concern we have is that we were told that the same inundation study is being re run inputting different information. Even if they were to change the standard to 1:5,000, and if they use the conceptual costs from KCB, it would be financially unacceptable to the community. We will continue to press for accountability for information, money spent on studies, and pursuing common sense methods and options.

My letter to Ian Howat with copies sent to council members and Snuneymuxw representatives

Dear Ian Howat,
Thank you for inviting us to a meeting with you this last Friday August 16th. It was encouraging to be told that your staff will be looking at all options regarding the Colliery Dams and that we will be invited to participate in that planning. We would like to re affirm that we would very much like to participate.

As per our conversation I am sending some information that you were not aware of and I believe is extremely important in going forward. First I have included the description of the software models that were used in the inundation study for the Colliery Dams for you to look over which you will find below. You will find a description of the model used for the Westwood Inundation study on page 11 of the 2004 Westwood Inundation study, under the heading Hydraulic modelling. You will quickly see the difference is the addition of 2 dimensional modelling for the Colliery dams study.

To see the mapping differences please see page 18 – 21 for the Westwood study and compare this to pages 59 – 95 in the Colliery study. Considering that Westwood has more than 10 times the water you will quickly understand the reason we question the study used for the Colliery dams.

Please refer to: and if you scroll down you will find the hydrology maps for both Westwood and Colliery. These maps are similar and were used for the initial estimates in the 2010 seismic study for the Colliery dams of approx 10 people dying. This is comparable to the West wood study; far different to the 2012 inundation modelling.

With this information I think it highly irresponsible to re run the same model for the Colliery dams without first questioning its assumptions and considering how we are going to fix all the dams in Nanaimo to the highest standards that this modelling requires.

I also question that in one breath mode of failure is the reason for assessing this high risk (the middle dam in its current state toppling into the lake causing all its water to be released which in turn causes the lower dam to fail.) and in the next breath saying it isn't mode of failure but using the assumption that all the water is released instantaneously regardless of the state of the dams. If it is the latter then I would suggest that all the dams in Nanaimo need to be assessed as they hold far more water and would show a much greater degree of catastrophe. If it is the former then we should be fixing the middle dam and then reassessing the classification. If the possibility of the middle dam toppling into the lake is removed then the lower dam would not fail.

Given the information I have just presented, to go ahead with rerunning the inundation study is not only irresponsible but a waste of taxpayer dollars. It may show a small change in numbers, might even show a 1:5,000 standard, but as we know, if we are going by the KCB conceptual costs, the dollars are still higher than most of us are willing to agree to. Why waste money when we already know the outcome.
We have strongly insisted that tax payer dollars not be used to continue with dam demolition since last November, but this was ignored, we insisted that a fresh set of eyes be used to consider the options, but this was ignored. It is with a great deal of concern that I ask you to reconsider rerunning this model as it doesn't make a lot of sense and will be a further waste of tax payer dollars. I ask you to put a stop to further waste.
If we are to be welcomed into the planning this would be a good first step. Our intention is to assist in finding a safe, cost effective method for keeping dams in our park. We have many incredibly skilled and brilliant minds in our community that would be willing to assist for the love of our lakes. No tax dollars needed. I hope that you will take full advantage of this offer.


Roblyn Hunter

Taken from the Colliery Dams inundation study:


The selection of appropriate software for the analysis of potential dam breach scenarios requires careful consideration. A variety of hydraulic conditions will exist while the flood wave travels throughout the inundation area. These conditions include sub-critical and super-critical flows.

Another important consideration relates to the hydraulic analysis of the Chase River channel, as well as the adjacent floodplain. Immediately below the Lower Dam, the Chase River channel has significant conveyance capacity. However, this conveyance capacity rapidly diminishes upstream of Howard Avenue.

Hydraulic analysis of the Chase River channel, while flows are below the top of bank, can be completed by using a 1-dimensional river modelling program such as HEC-RAS or Mike-11. 1-dimensional river modelling programs calculate water levels and flow rates based on input cross-section data. The direction of flow for these models follows the river alignment, which is perpendicular to the input cross-sections. These models are unable to account for lateral outflows and alternate flow paths above the top of the cross-sections; this inability results in the label ‘1-dimensional model’.

Once the river channel capacity is significantly exceeded, as would be the case during a dam breach condition, then the conveyance and attenuation of the flood wave becomes an important condition. Nonuniform floodplain areas, such as the Chase River floodplain, downstream of the Lower Dam cannot be completed with confidence using a 1-dimensional modelling program. As a result, a 2-dimensional analysis of the floodplain area is required. 2-dimensional models do not use cross-section data and instead rely on a rectangular grid or, occasionally, a triangular irregular network, where each grid cell or triangular cell has been assigned a specific elevation. Models utilizing a triangular cell system can also account for the slope and aspect (slope direction) of the cells, which can result in computational efficiencies over a rectangular grid network. As a result of the cellular elevation system that describes the topography of the study area,the model can account for flow in any horizontal direction. This ability earns this type of model the label ‘2-dimensional’. Notably, these models assume a uniform vertically averaged velocity.

Computational effort within the floodplain using a 2-dimensional solution is significantly affected by the resolution of the grid. Reducing the grid size results in increased computational effort and longer model run times for a fixed duration simulation. For example, a grid resolution of 1 m by 1 m would take approximately 4 times longer to run than a 2 m by 2 m grid. Generally, floodplain areas can be accurately modelled using a grid size that is significantly larger than what would be necessary to model a river channel such as the Chase River. As a result, this project would benefit significantly, in terms of computational effort, from the use of a 1-dimensional river model and a 2-dimensional floodplain model where flow can be exchanged dynamically throughout the simulation.

The Danish Hydraulic Institute (DHI) produces a wide variety of hydraulic modelling programs including 1-dimensional, 2-dimensional and 3-dimensional platforms. Many of their programs are able to dynamically exchange flows within a single simulation. In addition, the software programs are recognized internationally by engineers and scientists, and have been in use for several decades.

As a result, we selected Mike-Flood, produced by DHI, which allows for the dynamic coupling (flow exchange) of the following programs:

Mike-Urban (a 1-dimensional pipe and minor watercourse program). (Not used)

Mike-11 (a 1-dimensional major watercourse and river modelling program).

Mike-21 (a 2-dimensional program capable of modelling flows in floodplains, as well as lakes and oceans).

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