The environmental history and geomorphic impact of 19th century placer mining along Fraser River, British Columbia

One possible source of part of the 171,000 to 229,000 m³ of gravel that accumulate annually in the gravel bed reach of Fraser River in the Lower Mainland is sediment dumped into the river by 19th century placer gold mining activity. Historical data suggest that, following the Fraser Gold Rush of 1858 and the Cariboo Gold Rush of the 1860s, a substantial placer gold extraction industry was established and continued into the beginning of the 20th century. Gold production figures and typical gold concentrations can be combined as a proxy to estimate that around 50 million m³ of sediment were excavated by mining activity. Excavations caused by mining are still present in the modern landscape. The areas covered by 456 mine excavations were mapped between Hope and the Cottonwood Canyon along Fraser River. A subset of 58 mines was surveyed and strong regression relations predicting mine volume from mine area were found and used to produce estimates of the volume of excavated material. This allows estimation of the total excavated volume of sediment: 45,900,000 m³. Small mines (