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March
2000 Newsletter
The
Flood Threat to the Expressway
In
February, Glenn Rivers wrote a Spectator feature on the
threat that flooding poses to the proposed Red Hill Expressway.
The expressway's Senior Project engineer, Gary Moore, replied
to this article in a letter containing several flaws and
misunderstandings. Unfortunately, the Spectator did not
allow Mr. Rivers to rebut, so we printing his comments on
Moore's claims:
1.
By artificial channelization, I never implied a concrete
channel. I am well aware of the plans for "natural channel
design". This boils down to the meaning of the words. I
consider the artificial construction and or realignment
of a stream channel "artificial channelization", regardless
of the materials used to construct it.
2.
Gary Moore claims that the use of "natural channel design"
will slow down the velocities of the flood water. This is
correct, but this does not help prevent the flooding of
the expressway. In fact, just the opposite is true. If the
flow velocities in the creek are lower, the flow will have
to be higher and deeper to maintain the same discharge.
This actually increases the danger of flooding on the expressway.
3.
Gary Moore mentions that areas are or will be set aside
to store floodwater during peak flow conditions. I am already
aware of this. I know about the large storage facility on
Hannon Creek. The region's flood calculations are already
based on this facility being in place. It must be realized
that even if more smaller storage facilities are built along
the valley, their effects will be partially or totally cancelled
out by the loss of the natural floodplain storage which
will be buried under the earth fill upon which the expressway
will be built.
4.
My 2% risk statement was based on the information given
to me by phone from a regional official, stating that the
50 year flood was being used as the design criteria. It
is difficult to get the right figures when the region continues
to withhold information about the expressway's design. Whether
it is the 50 year or 100 year flood that is being used for
the design criteria, this is still a substantial risk: e.g.
a 1% exceedence probability per year for the 100 year flood.
Furthermore, Gary Moore did not address my caution about
the flood climatology of Red Hill Creek being based on historical
weather data, without allowance for the affects of changing
climate.
5. Gary Moore mentions the Provincial Standards for 400
series highways in Ontario. However, the Redhill Expressway
is faced with a different situation than many other roads.
In many cases, if Provincial Standards dictate that a road
must withstand a flood of a given size, we are usually talking
about a simple bridge or culvert crossing, and not a situation
where a road runs parallel to a stream, sharing its floodplain
for a substantial length. This latter situation is arguably
more critical than the former, and perhaps warrants a more
stringent safety factor than can be provided for in the
Provincial guidelines.
6.
At the end of Gary Moore's rebuttal, he claims that other
scenarios such as the "Hurricane Hazel Flood" have been
"considered". Earlier in his rebuttal he claims that the
design flood is the 100 year flood. This is bound to confuse
the reader. The Hazel flood is much bigger than the 100
year flood. To suggest (even implicitly) that the expressway
is safe in a Hazel magnitude event is misleading if the
design storm is the 100 year flood. If "considering" scenarios
such as Hazel magnitude events simply means calculating
the velocities and flood levels of the flows, that says
little about the safety of the expressway, which would certainly
be overtopped.
I
stand by my opinion that the proposed Red Hill Expressway
faces a significant flood risk, and reiterate that this
is another reason not to build the road here.
Glenn Rivers
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