Geoscience Reference
In-Depth Information
Stage 1
Headward development of
'v' shaped axial gully
initiated by overland flow
on low permeability
materials possibly
related to periods of
former agricultural
activity.
Stage 2
Headward extension and
gully incision expose piping-
susceptible sediments to
overland flow generated
further up gully. Dessication
cracks provide water entry
points with the development
of vertical inlet pipes supplying
subhorizontal collector pipes,
which follow the principal gully
axis. Bulbous form related to
piping, pipe collapse and
slumping of saturated
sediments.
Piping-susceptible horizons
Non-susceptible horizons
Matorral scrub
Vertical 'funnel' pipe
Pipe outlet
Overland flow
Subsurface flow along
subhorizontal collector pipes
Stage 3
Disintegration of pipe system
by pipe enlargement, collapse
and continued erosion leaves fluted
susceptible horizons exposed on gully
sidewalls. Small vertical funnel pipes and
remnants of dissected pipe network. Axial gully
development on sideslopes of main gully. Patchy
vegetation colonization.
Case Fig. 5.3
Gully evolution and piping at the IBERLIM study site in central Spain. (From Ternan et al. 1998.)
