Research on dynamic alluvial channels has recognised the influence on
river channel change of both discharge and sediment supply, although i
t has proved difficult to measure the latter. This paper presents the
first accurate data from a dynamic alluvial channel mat describe the i
nterrelated effect on channel morphological change of both discharge a
nd sediment supply variations over different timescales. Reliable info
rmation on the spatial patterns of erosion and deposition were obtaine
d using combined photogrammetry and tacheometric survey of the meltwat
er stream of a glacierised catchment over a 5 week period. Over the fu
ll time-period, the morphological evidence suggested the passage of a
wave of sediment. Counter-intuitively, the period of aggradation was a
ssociated with increasing diurnal peak and base flow discharge magnitu
de, while degradation occurred during a period of steady peak diurnal
discharge. This suggests that the channel change was controlled by var
iation in upstream sediment supply. Over a shorter timescale, informat
ion on diurnal changes in morphology reveals that although discharge w
as responsible for some aspects of channel change, this was modified b
y the effects of upstream sediment supply. Consideration of the spatia
l patterns of erosion and deposition at the within-reach scale reinfor
ces this point, with spatial aspects of morphological change being dri
ven by discharge and sediment supply fluctuations, but modified by spa
tial feedbacks associated with internal channel morphology. The implic
ations of these findings for fluvial geomorphology in general are cons
idered.