WC134 JanFeb 2024 - Magazine - Page 9
testimonies, reviewing aerial photos, and contacting archiving
centres. Although this additional data is not directly used in
the flood modelling exercise, it helps build a more profound
understanding of the flood risk within the study area by
identifying the causes and consequences of historical flood
events. This information is paramount to confirm the results of
any flood assessment.
All of these combined can provide the overall foundation needed
for the flood assessment. However, there can be gaps in the information, especially for factors that lie outside the community itself. The
best way to observe these gaps is with a physical site visit, allowing
the engineer to see the study area, and gain observational data on
how some of the landscape may have changed.
Factors outside the study area
In the case of the flood inundation study that we worked on for
WAT E R C A N A D A . N E T
the City of Revelstoke in the interior of British Columbia, the
study area defined by the municipality was only part of the
Illecillewaet River at the city. However, the Illecillewaet River
drains into Arrow Lake, which is impounded by the Hugh
Keenleyside Dam (HKD). The operation of HKD affects the
water level in Arrow Lakes and the Columbia River at the
confluence of Illecillewaet River. This may cause some backwater conditions in Illecillewaet River in the study area. This
situation was thus considered within the hydraulic model that
we developed.
It was during our discussions with the client that we recognized a second factor that needed consideration; the Box Canyon
log jam. The log jam formation is not a new issue, and it has
been reported at the Box Canyon before, for example, during the
July 1983 flood. The river’s valley is very narrow at this location,
making it prone to debris accumulation and log jams.
WATER C AN ADA • JANUARY/ FEBRUARY 2024
9
