Engineers present Frelighsburg's own "Bridge of Sighs"
The MRC official admitted that a proper study of the causes of the flooding should have been done, and was not done
A taller bridge? It was like saying that lifing the Bridge of Sighs would keep Venice from flooding!
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EDEN MUIR, FRELIGHSBURG, 2009/09/11.
At the September 3, 2009, town hall meeting, our engineers were reminded that the Pike River passes
under five bridges before it arrives at the center of Frelighsburg. These spans increase from 8
feet at Lake Carmi, to 65, 70, and even 90 feet as the river grows in volume. (Image 2.) When the swelling flood waters
hit the Adélard-Godbout bridge however, they are forced through a 38-foot bottleneck, causing the river
to back up and flood the upper village. The engineers were skeptical. They responded that they only consider
local conditions when they calculate the "design flow" of a bridge; the rest
of the river valley and watershed was apparently not of interest to them.
A citizen posed the obvious question: Why not significantly expand the space between the new bridge's support
piers so that more water could flow through? An examination of the site shows that perhaps 10 feet of bridge length
could be gained, simply by pushing the piers further apart. No buildings or land would have to be sacrificed.
The engineers replied that they would not do this because their computer model (Image 4.) indicates that neither the
existing nor the proposed bridge has any significant connection to the upstream flooding. Citizens objected that
they had often witnessed the bridge acting as a dam, impeding the flow of the flood waters. In fact,
it is clear that even the moderately flooded river is much wider than the bridge span and the water has some
difficulty squeezing through. (Image 3.)
The engineers, however, were not moved. They presented their spreadsheet as proof that the bridge only causes a
3/4-inch rise in our annual floods, and only a 4 3/8-inch rise in a 100-year flood. They insinuated that
citizens had contributed to the flooding by dumping fill in the river, but
refused to say exactly where or how.
In fact, the new design does slightly increase the open area under the bridge. Multiplying the span by the
height, the current bridge opening has a 39.7 m2 cross-sectional area. The new bridge is higher and
slightly longer, with 49 m2 of space for water to pass underneath.
However, most of this increase is provided
by raising the underside of the bridge.
Several citizens tried to make the engineers understand that additional space higher up will not prevent
flooding -- if the water goes so high that it touches the underbelly of the bridge, then the town would
already be suffering catastrophic flooding upstream. The water would already be flowing past Marché Tradition
and across rue Principale as it has in the past.
The entire park would already be under 4 feet of water. (Images 5, 6.) The
engineers did not seem to want to address this obvious but fundamental gap in their reasoning.
The river's flow speed is 2 m/second, so the volume of water that can pass in one second
is 39.7 m2 X 2 m/sec
or about 80 m3. In theory, the new bridge would increase this
flow to 98 m3/sec. The engineers claim that 88 m3/sec represents
a 25-year flood level, so the new design is adequate. (This was moments after insisting that there was no relation between
the bridge and the flooding.) But again, most of this new space for water to pass is up
high, and if the water level ever climbs that high we are already "up the creek"! What we need is a wider opening
lower down.
Telling us that the taller bridge opening is going to help is akin to telling the Venetians that by lifting
the famous Bridge of Sighs by a few inches the annual flooding of Piazza San Marco will be averted! (Image 1.)
In the end, the meeting was a sad reminder of the gulf between engineering bureaucrats armed with
computer-generated calculations and the thoughtful and earnest long-time residents who have been
eyewitnesses to decades of property damage from flooding. The concerned taxpayers sighed in resignation. They were
simply seeking
a practical solution, but they were basically dismissed as cranks, and received no support from their
elected municipal representatives.
The MRC representative however, did admit that a proper study of the entire river valley and
the causes of the flooding should have been done during the 2-year period of design and discussion
between the mayor and the engineers, and was not done. Then, perhaps realizing how preposterous it sounded for a
MRC official to recommend a study just days before the construction was to start, he added that it was
only the municipality, not the MRC, that could do so. The mayor, who sat next to him, said nothing.
One of the engineers, obviously impatient and frustrated with the townspeople for questioning the
bridge design, resorted to the politician's favourite refuge: security. Their overriding concern, she explained, was public
security, suggesting that the bridge was an imminent danger. There were more sighs of
exasperation, and one resident muttered that if the structure were truly about to collapse, then why did the highway department
allow 700 huge truckloads of gravel and asphalt to rumble over the bridge in the last few weeks as they resurfaced Richford Road?
The construction of our $1.4 million bridge is now underway. Will the slightly increased bridge opening help to alleviate our
periodic flooding? The proof, as they say, will be "in the
pudding." You can be sure that just like in Venice, Italy, there will be a crowd assembled at the bridge
at each major flood, planning the brass plaque to mark the maximum water level.
Note: Data provided here are from notes taken at the Sept. 3 meeting.
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