Conveyance in a two-stage meandering channel with a mobile bed

A series of experiments are reported on the conveyance of over-bank mobile bed meandering channels, using the UK Flood Channel Facility at HR Wallingford. The sides of the inner channel were fixed whilst the bed was formed of graded material with a d50 of 1.6 mm. The floodplains were either smooth or, for most experiments, artificially roughened using expanded metal strips. Three floodplain planforms were used, these being straight, sinuous and narrow berms parallel to the inner channel. Inner channel discharges were measured using integrated point values from a 3-D Acoustic Doppler Velocimeter. Most discharge calculation methods for meandering channels employ a horizontal division between the main channel and floodplain meander zone. The results of several of these were compared with the observed data and were shown to be unsatisfactory when the floodplain is rough. This led to the development of a method using vertical interfaces between the inner channel and floodplains, based upon a force-momentum flux balance for the inner channel. This vertical interface method is shown to give improved results for both total and sub-sectional discharges in cases where the floodplain is rough.