Two major river systems flow through the Chilliwack area; the Chilliwack (a.k.a. Vedder) River and the Fraser River, while many smaller rivers, creeks and streams flow into these watersheds.  

The Chilliwack River

The Chilliwack River originates in the North Cascades provincial park in Washington, U.S.A; it flows into Chilliwack Lake and then the Sumas River and finally the Fraser River. The Chilliwack River changes its name once along its course, known as the Vedder River after the bridge at Vedder Crossing.

Before 1873, the Chilliwack River flowed into the Chilliwack, Luckakuk and Atchelitz Creeks at Vedder Crossing.  It is believed that due to feuding amongst the farmers of South Chilliwack (now Sardis) and Sumas (now Greendale) who were concerned about the river flowing into their low-lying fields, the Chilliwack River was diverted entirely into the Vedder Creek and resulting in its present-day course.  At that time, the Vedder flowed into Sumas Lake (today Sumas Prairie) until the lake's draining which began in 1922. Whether the river diversion was the result of a natural log jam, was man-made, or a result of both these factors, is debatable.

The Chilliwack River is subject to springtime runoff and flooding. Potential log jams upriver are also concerns for those who live along the river bank. [image: P4762 Chilliwack River]

The Fraser River

The Fraser River is the fifth largest river in Canada. It originates in the Rocky Mountains in Mount Robson Provincial Park and flows into the Pacific Ocean at Vancouver.  The Fraser River is a major watershed for the Rocky Mountains and poses a constant threat of flooding because of an unpredictable spring freshet; a mixture of heavy rains and spring thawing that cause the river to overflow.  [image: P2527 Mt. Cheam and Fraser River]

History of Flooding

Carved out by glaciers over thousands of years, the Chilliwack Valley is situated on a natural floodplain. A high risk of flooding in the Chilliwack valley is due to the combination of the two major river systems, low-lying land and the potential of heavy precipitation, warm springs and mountainous snowpack.  As long as people live here, the rivers will need to be managed as naturally, the rivers will spill their banks when the conditions present themselves.

There are two major floods in Chilliwack's history that are well known to Chilliwackians. These floods happened in 1894 and 1948, although there have been other, smaller floods and many flood threats in other years. Chilliwack has seen extensive dyking and river management to prevent floods from occuring in Chilliwack.