| |
|
 |
Lillooet River Corridor Engineering Study
The Pemberton Valley, one of the fastest growing regions in
Canada, is subject to regular flooding. This is caused, in part,
by several large tributaries that discharge into the Lillooet
River near Pemberton, British Columbia.
Objectives
Kerr Wood Leidal (KWL) was retained to provide a long-term management
plan for the Lillooet River. Work included assessing existing
geomorphic and hydrologic conditions, and updating the flood
profile.
Assessing the River's Geomorphology
In the late 1940s, extensive engineering works were implemented
to reclaim agricultural land and prevent floods. KWL assessed
the impacts of these drastic changes on the morphology and present
alignment of the river. Much of the analysis was based on channel
maps created by KWL from historical air photographs and existing
cross-section survey data.
KWL also determined how much gravel is transported into the
lower reaches of the river annually. This is critical in designing
flood protection works because sediment accumulations tend to
compromise the level of flood protection provided by dykes.
Identifying Areas at Risk
Water levels for a 200-year return flood were determined using
Mike 11, an hydraulic model well suited to the complex hydrology
of the river. Over 100 cross-sections were surveyed and input
into the model. Modelling results identified areas where existing
dykes were too low and areas requiring flood protection.
Reducing the Flood Risk
Using its hydraulic and geomorphic analysis, KWL is developing
a river management plan for the Pemberton Valley. The plan will
identify areas in need of flood protection and rank proposed
works according to input from the local community, the Mount
Currie Band, the Pemberton Valley Dyking District, and government
officials.
KWL is also completing a gravel management plan to identify
the volumes, location, and timing for gravel removals. The plan
will prevent the channel bed from rising, reduce the flood risk,
and help maintain the ecological character of the river. |
|
|
|
 |
|
