Ds. Gabbard et al., LANDSCAPE POSITION, SURFACE HYDRAULIC GRADIENTS AND EROSION PROCESSES, Earth surface processes and landforms, 23(1), 1998, pp. 83-93
Different hydraulic gradients, especially due to seepage or drainage,
at different locations on a hillslope profile may have a profound effe
ct on the dominant erosion processes. A laboratory study was designed
to simulate hillslope processes and quantify effects of surface hydrau
lic gradients on erosion for a Glynwood clay loam soil (fine, illitic,
mesic Aquic Hapludalf). A 5 m long, 1.2 m wide soil pan was used at 5
and 10 per cent slopes with an external watering tube to vary the soi
l bed's hydrological conditions. Different combinations of slope steep
ness with seepage or drainage gradients were used to simulate the hydr
ologic conditions on a 5 m segment of a hillslope profile. Runoff samp
les were taken during rainfall only and rainfall with added inflow. Re
sults showed that, under drainage conditions, interrill processes domi
nated and rilling was Limited. The surface contained scattered crescen
t-shaped pits after the run. Under seepage conditions, rilling process
es dominated and the inflow introduced at the top of the soil pan furt
her accelerated the headward erosion of the rills. Erosion rates incre
ased by as much as 60 times under seepage conditions representative of
the lower backslope when compared to drainage conditions that general
ly occur at the upper backslope. This indicated that rills and gullies
on backslopes and footslopes may be catalysed or enhanced by seepage
conditions rather than form from flow hydraulic shear stress alone. An
understanding of spatial and temporal changes that affect both hillsl
ope hydrology and erosional processes is needed to develop accurate pr
ocess-based erosion prediction models. This knowledge may lead to diff
erent management practices on landscape positions where seepage occurs
. (C) 1998 John Wiley & Sons, Ltd.