|Citation||Northwest Hydraulic Consultants. 2008. Fraser River Hydraulic Model Update: Final Report. Prepared for BC Ministry of Environment.|
|Organization||Ministry of Environment|
|Abstract/Description or Keywords||In 2006, northwest hydraulic consultants (nhc) developed a MIKE11 hydraulic model for
the Fraser River, covering the reach from just upstream of Mission to the Strait of Georgia.
Using the model, a new design profile was computed and found to be up to 1 m higher than
the previous design profile developed in 1969. The results affected the profile for the
upstream reach from Laidlaw to Mission developed in 2001 by UMA Engineering Ltd. The
two models were merged into a single model and a design profile computed, corresponding
to a reoccurrence of the 1894 flood.
The 2007 snow-pack was well above normal and considering the increase in the design
profile there was concern of potential flooding in the Fraser Valley. The British Columbia
Ministry of Environment (MOE) retained nhc to run the new hydraulic model in real-time to
forecast flood levels between Laidlaw and the Strait of Georgia. An intensive program of
water level and flow data collection was carried out by Water Survey Canada (WSC), MOE,
Fraser Valley municipalities and others to monitor river conditions and assess model
performance during the daily forecasting as well as collect additional information for model
fine-tuning. The model performed well but it became evident that there were problems with
previously reported discharge data published by WSC. Also, that the Laidlaw – Mission
(upper) model was not entirely compatible with the Mission – Georgia Strait (lower) model.
An unprecedented amount of water level and flow data was collected during the 2007 flood
and following the freshet the project described in this report was undertaken to resolve the
discharge data issues, update the two models as necessary, merge them and refine the
previously developed design profile.
Both the Hope and Mission stage-discharge curves were revised by WSC in 2007. Using
corrected discharges the lower model was calibrated to the 2007 flood and validated to the
2002 flood. A slight reduction in roughness coefficients was warranted for flows under
/s. However, roughness coefficients for the design profile were unaltered in the
Mission-Douglas Island reach since they were previously derived using a historic model and
the 1948 flood, to ensure proper representation of channel conditions at very high flows. No
network changes were required to the fully hydro-dynamic lower model. The design profile
was essentially unaltered, with a maximum flood level reduction of 0.16m in the Coquitlam
The upper model was recalibrated to the 1999 flood and validated to the 2007 flood.
Significant changes were made to the model network. These modifications were undertaken
to allow operating the model hydro-dynamically rather than using the diffusive wave
algorithm. Roughness coefficients were revised, Harrison Lake was added to the model and
several other changes were made. The changes resulted in increases and decreases in the
design profile of up to 0.28 m.
A number of dikes were raised prior to the 2007 freshet. The dike crest elevation assessment
completed in 2006 was repeated using the updated design profile and available as-built dike
|Regional Watershed||Lower Fraser|
|Sub-watershed if known|