Geology Reference
In-Depth Information
Fig. 19.1
Illustration of the
interaction between ephemeral
gully development and tillage
erosion/deposition. Left:
evolution of (ephemeral) gully
volume over time if no tillage
operations take place. Note the
digressive increase of gully
volume (based on review by
Vanwalleghem
et al
., 2005c).
Right: evolution of (cumulative)
ephemeral gully volume over
time, if gully channels are filled
in annually by tillage operations.
1997; Nachtergaele
et al
., 2002b; Poesen
et al
.,
2006). However, in cropland areas, ephemeral
gullies are usually filled in by tillage (tillage ero-
sion and tillage deposition) within less than a
year of their initiation. During subsequent storms
(years), the infilled soil material is usually eroded
again by concentrated flow, thereby increasing
the plan-form concavity of the site. The newly
created plan-form concavity increases the proba-
bility of concentrated flow erosion. So ephemeral
gully erosion and tillage erosion reinforce each
other (Poesen
et al
., 2003). Gordon
et al
. (2008)
recently demonstrated through modelling that
total soil erosion rates in several geographical
regions (Belgium, US) could be 250% to 450%
greater when ephemeral gullies are tilled and,
hence, reactivated annually as opposed to no-till
conditions. These results demonstrate that rou-
tine filling of ephemeral gully channels during
tillage practices may result in markedly higher
rates of soil loss compared with allowing these
gullies to persist on the landscape, demonstrating
a further advantage of adopting no-till manage-
ment practices (Fig. 19.1).
In various parts of Europe, landscapes heavily
dissected by gullying (badlands) have been lev-
elled, thereby causing strong soil profile trunca-
tion in the intergully areas and infilling of gullies
with this material (e.g. Revel & Guiresse, 1995;
Poesen & Hooke, 1997; Borselli
et al
., 2006). Such
land levelling operations have often resulted in
renewed gully incision of the levelled land, as well
as in shallow landsliding causing large soil losses
(Clarke & Rendell, 2000; Borselli
et al
., 2006). In
other words, important interactions exist between
concentrated flow erosion and tillage erosion
(Poesen, 1993) as well as with erosion caused by
land levelling.
The significant interactions between gully
erosion on the one hand and hydrological (i.e.
infiltration, drainage) as well as other soil erosion
processes (piping, mass wasting, tillage erosion
and erosion by land levelling) on the other, need
to be better understood for improving our predic-
tions of hydrological response and land degra-
dation rates under different environmental
conditions. This improved understanding is the
basis for taking appropriate and effective meas-
ures to control soil erosion.
Acknowledgements
The authors thank the many colleagues for fruit-
ful discussions on gully erosion and for stimulat-
ing visits to their gully sites. Financial support
