Residents of the Chilliwack River valley in the Lower Mainland of BC recently experienced the latest in a series of devastating floods that left damaged homes, uprooted trees, dead fish, mud and angry evacuated residents in its wake. There have been several such floods, including one in 1990 when one house was completely washed away.

The Fraser Valley Regional District and the Province have long recognized the Chilliwack as a wild river and have undertaken many studies and upgrades of the flood and erosion protection works. Hay & Company was engaged by the Regional District this summer to develop options for upgrading the dyke in the Wilson Road area, the location worst hit by the November 6 flood. The river overtopped a low section of dyke constructed during a similar emergency in October 2003 and eroded half the width of an older dyke, threatening a house on the other side. When the flood struck, Hayco was requested to provide on-site services to implement emergency repairs and to gather information that could be useful in finalizing the final design of the upgraded works.

According to the Provincial River Forecast Centre, the Chilliwack River area received 61 mm of rain in 6 hours, 107 mm in 12 hours, and 153 mm in 24 hours. The total rainfall over the five day storm period was 328 mm. The river rose 1.3 m in about 12 hours and reached a peak discharge of at least 1000 cubic metres per second. The most recent estimate of the 200-year design flood is 1470 cu m/s.