Emergency flood protection work fast-tracked to avoid potential flooding

Removal of unsuitable dike fill material by contractor

The 2006-2007 winter season was unusual for portions of British Columbia, which experienced very large snow-pack accumulations. The Upper Fraser, Mid-Fraser, and South Coast, as well as the North and South Thompson all had above normal snow-packs.

Due to the widespread, heavy snow accumulations across a range of elevations, the British Columbia River Forecast Centre predicted above normal spring runoff in most basins, including the Fraser, Nechako, and Thompson. The flood risk continued to increase well into the spring with late season snowfalls. The conditions were in place for major flooding, with the severity depending largely on the weather patterns during the freshet period.

Two additional conditions exacerbated the situation. Firstly, based on the results of improved hydraulic models, the Fraser Basin Council had released a report that recommended increasing the Flood Construction Levels on the Lower Fraser River. Secondly, the devastation caused by the Mountain Pine Beetle increased the uncertainty of the hydrologic response of the river to the spring freshet.

In response to these threats, the Provincial government announced the 2007 Urgent Mitigative Flood Works (UMFW) program. The objective of this emergency program was to increase the level of flood protection afforded to the public within the province of British Columbia.

The City of Port Coquitlam engaged Associated Engineering to prepare applications for funding for diking improvements along the Pitt River Dike Right Bank and the Coquitlam River Dike Left Bank. Both dikes protect a total area of 1200 ha, approximately 2300 structures, and a population of over 20,000 people. A dike breach would be an environmental, economic, and public safety disaster.

The Coquitlam River project, founded on peat and nearly 3 kilometres long, included the installation of approximately 1000 millimetres of fill material along the entire length in order to raise the dike to the new flood construction level.

The Pitt River project, over 10 kilometres long, included the installation of 500 millimetres of fill material along the entire length. A 300 metre long section within an industrial area posed significant challenges as existing structures encroached on the dike. In addition, much of the original dike including the impervious core, constructed in the 1970?s was absent. The compromised dike at this location would not withstand the design water levels of nearly 4 metres.

Deep soil mixing machine on dike crest. Rip rap slope stabilization on left side and a new river side impervious core on right side of photo.

Project Engineer, Andrew Wiens, advises, "This project was particularly challenging because it had a hard, non-negotiable deadline - the spring snowmelt. The tight schedule and the complex and evolving scope added additional technical and management challenges during the project. The significant consequences and the possibility of a dike breach, particularly after identifying flood protection deficiencies, required that we carefully manage the project schedule and advise the client and the Inspector of Dikes (Ministry of Environment) of the possibility of a major public disaster."

The Associated Engineering team, consisting of Project Manager Wayne Zhan, P.Eng., and Senior Water Resources Engineer, John van der Eerden, P.Eng., had to consider existing structures and the need for public protection while dealing with the business. In order to the remediate the dike and keep the structures, we used a variety of construction methods, including deep soil mixing, impervious liners, retaining walls, and slope stabilization. This prevented the demolition of the major industrial buildings.

The total cost of this fast-track, design-build project was $5 million. Design and construction was completed on budget and on schedule within 2 months.

Due to the complexity of the project and the tight schedule, Senior Diking Experts Guna Gunadasa and Aubrey Brown were retained to assist on the projects. Other team members included John Tait, Jonathan Borch, Guillermo Quijano, and Mark Spence.