Fraser Valley - Physical Geography

Physical Geography

After descending through the rapids of the Fraser Canyon, the Fraser River emerges almost at sea level at Yale, over 100 km inland. Although the canyon in geographic terms is defined as ending at Yale, Hope is generally to be considered the southern end of the canyon, partly because of the change in the character of the highway from that point, and perhaps also because it is at Hope that the first floodplains typifying the course of the Lower Fraser are found. Downstream from Hope, the river and adjoining floodplains widen considerably in the area of Rosedale, Chilliwack and Agassiz, which is considered the head of the Fraser Delta. From there the river passes through some of the most fertile agricultural land in British Columbia—as well as the heart of the Metro Vancouver region—on its way through the valley to its mouth at Georgia Strait.

During the last ice age, the area that would become the Fraser Valley was covered by a sheet of ice, walled in by the surrounding mountains. As the ice receded, land that had been covered by glaciers became covered by water instead, then slowly rose above the water, forming the basin that exists today. The valley is the largest landform of the Lower Mainland ecoregion, with its delta considered to begin in the area of Agassiz and Chilliwack, although stretches of floodplain flank the mountainsides between there and Hope.

Several of the Fraser's lower tributaries have floodplains of their own, shared in common with the Fraser freshet. Of varying size these include the Harrison River, Chilliwack River (Vedder River), Hatzic Creek and Hatzic Lake, the Stave, Alouette, Pitt and Coquitlam Rivers. Also incorporated in the Fraser delta region are the Nicomekl and Serpentine River floodplains and the Sumas River drainage, which flow to saltwater independently of the Fraser but help drain its lowland. The Fraser is tidal as far upstream as the town of Mission and, across the river, the City of Abbotsford, which is at the Fraser's closest approach to the international boundary, about 6 miles north of Sumas, Washington. Pitt Lake, one of the Fraser's last tributaries and among its largest, is so low in elevation, despite its mountain setting, that it is one of the largest tidal freshwater lakes in the world .

Oxbow lakes and side-sloughs are a common feature of the Lower Fraser's geography. The two main oxbows are those of Hatzic Lake and the Stave River on opposite sides of Mission, although that of the Stave has been silted in and part of it drained for a man-made lake. Around Fort Langley is an oxbow formation, mostly swamped in at the time of the fort's foundation, which was drained and made part of the fort's farm and remains farmland today. The system of sloughs and side-channels of the river is complicated, but important sloughs include those around Nicomen Island, Sea Bird Island and flanking the river from Rosedale to Sumas Mountain, on the western side of Chilliwack.