Bed-material transport estimated from channel morphodynamics: Chilliwack River, British Columbia

This study investigates the relation between channel changes, as mapped fro m aerial photography, and bed-material transport along Chilliwack River, Br itish Columbia. Detailed mapping of channel features was completed for five dates between 1952 and 1991 using an analytical stereoplotter. Data were t ransferred to a geographic information system (GIS) to analyse changes duri ng four consecutive periods. Erosion and deposition volumes along channel r eaches were estimated by multiplying measured areal changes by the bed-mate rial depth along each reach. Bed-material transport rates are related to mo rphologic changes using a sediment budget approach. The highest rate of tra nsport for the four study periods is estimated as 55 000 +/- 10 000 m(3) a( -1) between 1983 and 1991. These rates are compared with estimates from sho rt-term (1-2 year) changes along the lower reach to investigate variations in sediment flux that may otherwise remain undetected. Significant morpholo gic change occurs roughly once every 5 years when flows are large enough to erode and entrain large volumes of bed material stored within the contempo rary floodplain. In the absence of large floods, transport rates decline an d vegetation begins to establish new floodplain. Copyright (C) 2000 John Wi ley & Sons, Ltd.