WC134 JanFeb 2024 - Magazine - Page 10
STORMWATER
The log jam size could increase significantly during a large
flood event. The log jams could affect river flow hydraulics and
act as a dam and create an impoundment in the river. Therefore, if it breaches during an extreme event, it could create a
wave of water and debris propagating downstream. Should
this happen, the flood wave and the loose logs could endanger
the downstream infrastructures and landowners. For example,
a major log jam release at Box Canyon may damage the dike
network protecting residential and industrial areas of Revelstoke. Therefore, it was recommended to remove the log jam
to reduce the risk of further damage downstream.
The approach to incorporate this kind of information,
factors outside of the original study area, depends on the
nature and magnitude of the factors beyond the study
boundary. It needs some engineering judgment and/or analysis
to decide which factors may play a meaningful role in the
results. For example, in the case of the Revelstoke study,
the impact of HKD on the flood levels at the project site
was incorporated even though it is located a few hundred
kilometres downstream. However, if the log jam was formed
a few hundred kilometres upstream of the project site, the
impacts would be reduced if there was a large enough body
Delivering the
Measure of Possibility
Flow & Level Measurement
Application Solutions
● Contacting and non-contacting measurement options
● Ultrasonic and radar technology
● Portable measurement devices and 昀椀xed installations
Contact our friendly
team for more information:
northamerica@pulsarmeasurement.com
PULSARMEASUREMENT.COM
10
WATER C AN ADA • JANUARY/ FEBRUARY 2024
of water located between the log jam and the study area to
attenuate the surge of water associated with a log jam release.
Dam breaches, landslides, avalanches, and debris flows are
some of the other factors that may affect the hydraulics of
the flow downstream and, therefore, have to be evaluated and
incorporated into the analysis if needed.
There can be challenges with this, even when evaluating these
factors is a necessity:
• RESTRICTED BUDGET Sometimes, clients may lack the funds to
investigate and integrate factors outside the project’s boundaries.
When this is the case, addressing these factors might be relegated
to recommendations.
• LIMITED ACCESS There may be instances where the area in question is difficult or impossible to access, necessitating assumptions
that can introduce uncertainties.
• LIMITED OR NO MEASUREMENTS AND/OR HISTORICAL RECORDINGS
Usually, the available historical recordings or information from
previous events could help to calibrate the models, remove, or
mitigate the hazard, and prevent or reduce the consequences of
similar hazards in the future. For example, available flood extend,
or water levels from previous floods can help calibrate the model,
or the collected footage of the Box Canyon log jam shows that
it’s been a returning issue for a long term that should be removed. However, in the Illecillewaet River log jam, there was no
known measurement of the height of the log jam or water levels
upstream and downstream of that. The lack of measurements,
which may cause uncertainties in the analysis, is usually the case
when the areas of concern are remote.
• LACK OF AWARENESS OF THE ISSUE If the client and local people
are not aware of the issue and if there’s no evidence in aerial
photos, past reports, news archives, or during site visits, it may be
overlooked in the analysis. It’s imperative to collaborate closely
with the client, ensuring all conceivable variables are factored
into the flood assessment. A comprehensive evaluation not only
maps potential risks but also suggests the most effective actions
to bolster community resilience. Relying merely on historical
data and anecdotal information is insufficient. Whenever feasible,
there should be an on-ground examination of factors upstream,
as these could amplify the repercussions of a severe weather
occurrence.
Studying potential flood impacts is invaluable for communities as they work to understand what resilience measures can help
limit the severity of this kind of extreme weather event. However,
we must recognize that there are factors beyond the scope of the
directed study that can have severe impact during a flood event.
By taking the time to look beyond the available data, having
conversations with community members and researching historic
events, we can appreciate all elements that can impact the severity of a flood event, regardless of where they originate from.
To learn more about how WSP helps communities understand
the potential impact of severe weather events, visit: www.wsp.
com/en-ca/hubs/climate-change-resilience-and-sustainability
