Pemberton Area Flood Protection Works 2004/05

Project Introduction:

The Pemberton Valley area experienced extensive flooding during a high rainfall event in October 2003. Rainfall records were set in the Squamish – Pemberton corridor with over 369 mm of rain over a four day period. The high rainfall/water event caused extensive erosion of stream channel banks, dykes and bridges in the Pemberton area. Cascade Environmental Resource Group Ltd. was retained to provide permitting and environmental monitoring services for restoration works for the Lil’wat First Nations (Mt. Currie), the Lower Stl’atl’imx First Nations (between Lillooet Lake and Harrison Lake), and the Pemberton Valley Dyking District.

Problem Statement:

A high rainfall event in October 2003 caused extensive erosion damage to road, bridge and property in the Pemberton area.

Solution Description:

In response to the damage and erosion caused by the high rainfall/water event in October 2003, a recovery plan was prepared for the BC Provincial Emergency Program. The plan identified many sites in the Pemberton area that were in need of immediate restoration. The sites included the repair of extensive erosion to channel banks, dykes and bridges; gravel extraction; as well as bridge and culvert replacements. A total of 17 projects were completed by Cascade Environmental Resource Group Ltd. over a two year period (2004/05).

Bank and dyke protection works entailed the installation of 800 mm riprap and filter gravel. All attempts were made to place the rock around vegetation to preserve critical riparian habitat. In projects along rivers with critical salmonid habitat (i.e. Birkenhead River) root wads were interlocked within the riprap. Bridge protection works also included the installation of riprap and filter gravel. Other restoration works included the replacement of blocked or damage culverts and the replacement of a damaged bridge at Rogers Creek. Extensive gravel extraction works were completed at Miller Creek (northwest of the Village of Pemberton) to remove approximately 4000 to 6000 m3 of bed material. The material was transported downstream during a debris flood event in October 2003.

Conclusion:

Bank, dyke and bridge protection; gravel extraction; and culvert and bridge replacement works were completed in the Pemberton area over a two year period in response to a high rainfall/water event in October 2003. To restore the sites to pre-flood conditions, Cascade Environmental Resource Group Ltd. completed the environmental monitoring and permitting for a total of 17 projects over a two year period.

Installation of riprap and root wads along Birkenhead River September 2004

Placement of riprap along Lillooet River near Pemberton August 2004