Andrew La Croix, Shahin Dashtgard, Korhan Ayranci, John Clague, Philip Hill

The Fraser River Delta (FRD) is a major sedimentary system and is home to one of Canada’s largest metropolitan areas, Metro Vancouver. It is also an ecologically important region that is culturally significant to several First Nations groups. In this review, we summarize the state of knowledge about the geological evolution of the FRD and link hydrodynamic processes with sedimentary products across the continuum of environments from the river to the delta slope. We discuss the implications of sedimentation for natural hazards and highlight knowledge gaps. This review also serves as background for continued research on the FRD.
The FRD consists of four main zones: river, delta plain, tidal flats, and delta slope. The river zone includes the Fraser River and its various distributary channels from the landward limit of tidal modulation to the terminus of the distributary channels at the seaward limit of the tidal flats. The delta plain borders the modern Fraser River’s distributary channels. Intertidal marshes and tidal flats rim the seaward portion of the delta plain and include both “active” and “abandoned” areas. Active tidal flats are situated on the western margin of the FRD and receive sediment directly from the Fraser River; these include Roberts Bank and Sturgeon Bank. Abandoned tidal flats receive virtually no sediment from the Fraser River and occur along the southern boundary of the FRD at Boundary Bay and Mud Bay. The tidal flats transition seaward into more steeply dipping foresets of the subaqueous delta slope. South of the Main Channel the upper delta slope is predominantly sand, and north of the Main Channel the upper delta slope is predominantly mud. The lower delta slope both south and north of the Main Channel consists of mud, and these sediments grade into flat lying, muddy sediment at the base of the Strait of Georgia.
The FRD experiences a range of natural hazards including subsidence and flooding, earthquakes, liquefaction, and tsunamis. Many parts of the FRD are subsiding, which amplifies the effects of rising sea level. Approximately 250 km of dikes along the river, distributary channels, and landward side of tidal flats protects the populated delta plain from river floods and storm surges. Rare subduction-related earthquakes and large crustal and subcrustal earthquakes produce sudden land level changes that can trigger tsunamis, submarine slope failures, and/or liquefaction of unconsolidated delta sediments. With increasing knowledge of the sedimentation on the FRD and its evolution, it may be possible to devise novel methods to protect the populated FRD from some of the worst impacts of these hazardous events.