Research on dynamic alluvial channels has recognised the influence on
river channel change of both discharge and sediment supply, although it
has proved difficult to measure the latter. This paper presents the
first accurate data from a dynamic alluvial channel mat describe the
interrelated effect on channel morphological change of both discharge
and sediment supply variations over different timescales. Reliable
information on the spatial patterns of erosion and deposition were
obtained using combined photogrammetry and tacheometric survey of the
meltwater stream of a glacierised catchment over a 5 week period. Over
the full time-period, the morphological evidence suggested the passage
of a wave of sediment. Counter-intuitively, the period of aggradation
was associated with increasing diurnal peak and base flow discharge
magnitude, while degradation occurred during a period of steady peak
diurnal discharge. This suggests that the channel change was controlled
by variation in upstream sediment supply. Over a shorter timescale,
information on diurnal changes in morphology reveals that although
discharge was responsible for some aspects of channel change, this was
modified by the effects of upstream sediment supply. Consideration of
the spatial patterns of erosion and deposition at the within-reach
scale reinforces this point, with spatial aspects of morphological
change being driven by discharge and sediment supply fluctuations, but
modified by spatial feedbacks associated with internal channel
morphology. The implications of these findings for fluvial
geomorphology in general are considered.