Constraining accretion rates in a tide-dominated, freshwater river (Pitt River, Canada) and implications for lateral accretion of channels in the tidal-fluvial transition

A vibracore-based investigation of channel and floodplain deposits in the Pitt River Valley (PRV) was conducted to spatially and temporally confine the evolution of the PRV floodplain and the tide-dominated Pitt River. Sedimentological and ichnological assessment of cores is supplemented by geochronological and palynological analyses. The lateral migration rate of a Pitt River meander is quantified using Carbon-14 age dates of organic detritus at the base of a channel-margin core and the position of the core relative to the present-day channel profile. The Pitt River meander bar is shown to laterally migrate between 0.16 and 0.28 metres per year. A comparison of this rate to previous studies reveals that channels modulated by tides are capable of migrating at a rate equivalent to slowly meandering purely fluvial systems, and tidally affected channels migrate at less than 1.5% of the channel’s width each year.