Generic autogenic behaviour in fluvial systems: lessons from experimental studies - From Depositional Systems to Sedimentary Successions on the Norwegian Continental Margin - page 3

(A) (B) (C) (D)

0 600 0 600 0 600

0 300

Abandoned area

Location of cross-
sections of
Figure 5

Zone of fractionated

Scour

sheet flow

Zone of
sheet
flow

Converging
flow

Fully confined flow

Delta covered by
single, continuous
sheet flow

Abandoned area

Zone of small-scale
channelised flow

12 h 00 35 h 36

36 h 16 38 h 27

(E) (F) (G)

0 600 0 600

0 600

Scour
holes

Flow spills over
channel walls

Channel widens

Bar

Situation reverted
to the situation
just before initiation
of the next incision
(Fig. B)

Bar

Abandoned area

41 h 00

42 h 00

64 h 00

Fig. 1. Shaded relief maps of an autogenic cycle. Run time is shown in the lower right corner. The scale of the plots is indi-
cated in the upper right corner; the position of panel (E) is given by the inset in panel (D). A. The initial jet transformed
into an expanding sheet flow. Single sheet flow producing smooth delta plain topography; B. With growth of the delta plain
sheet flow fractionates causing small-scale channelised flow near the shoreline; C. Progressive aggradation at the apex
increased the gradient of the delta plain up to the point when a scour hole was initiated along the centre line of the fan
delta; D. The scour hole developed quickly into a knickpoint that moved upstream connecting the scour with the feeder
channel; E. Backfilling starts with the deposition of a mouth-channel or mid-channel bar; F. Progressive backfilling while
the flow gradually started to exceed the confining channel walls and increasingly spilled over the margin in the course of
the backfilling process; G. When the entire channel had been filled, fractionated sheet flow and aggradation of the apex
were restored (from Van Dijk et al ., 2009).

Peakall et al . 1996) of a braid plain with character-
istic channel and mid-channel bar configurations.
The set up differed from those of Bryant et al .
(1995) and Van Dijk et al . (2009, 2011) in that the
feeder channel was uplifted, herewith creating
accumulation space (terminology sensu Blum &
Törnqvist, 2000) in the braid plain basin. Ashworth
and co-workers arbitrarily defined stream avul-
sion around the numerous mid channel bars by
the sudden, lateral shift of minimal 30 cm of a
channel, while the new channel position must be
maintained for at least a 15 min period. Each

avulsion starts off from a bifurcation, where the
mid-channel bar splits the active channel flow
over two branches following similar processes as
pictured in Fig. 1D and 1E. The experiments of
Sheets et al . (2002) and Hickson et al . (2005) con-
ducted at Saint Anthony Falls Laboratory had
multiple entries, which produced a kind of braid
plain showing autogenic processes probably more
akin to those occurring on stream-dominated coa-
lescing alluvial fans, each with characteristic
alternating channelised and sheet flow processes.
Sheet flow does occur in braided river systems, in