The concept of effective length in hillslopes: assessing the influence of climate and topography on the contributing areas of catchments

Abstract

Abstract:This paper introduces a concept of 'effective length' in hillslopes to define the effective area influencing the runoffproducing saturated zones of a hillslope or catchment. This effective area of a catchment usually is less than that given by its physical boundaries, particularly in regions where the total potential evaporation exceeds total rainfall on an annual basis. In this paper, expressions for effective lengths in hillslopes with different scale, shape and soil properties are derived for given climatic conditions. The influence of these variables on effective length is investigated. It is shown that, for a given rainfall frequency and soil parameters, the effective length changes with the planform geometry and profile shape of a hillslope; it is also a function of the ratio of available travel opportunity time to the hillslope's scale response time. The application of the concept to three natural catchments, subdivided into a number of simple hillslopes, is described. It is shown that, for these three test catchments and over 24 years of record, rarely would the entire catchment areas contribute to flow at the respective outlets. The implications of the concept of effective length for several land-use practices, such as clearing for forest for greater water yield, and planting trees for salinity control, are discussed.

Evaluation of catchment contributing areas and storm runoff in flat terrain subject to urbanisation

“…As in other studies (Aryal et al, 2003;Beven, 1997) the results reported here suggest that runoff can be generated in a large area of the catchment, but its contribution to outflow from the catchment may be limited from various part of the catchment. However in addition to "effective slope length" (Aryal et al, 2003) or "dynamic contributing areas" (Beven, 1997), this can also be associated with a compensating effect of surface depressions in flat landscapes, when only "excess of runoff" generated within a depression under a single rainfall event can be passed down gradient.…”

“…However in addition to "effective slope length" (Aryal et al, 2003) or "dynamic contributing areas" (Beven, 1997), this can also be associated with a compensating effect of surface depressions in flat landscapes, when only "excess of runoff" generated within a depression under a single rainfall event can be passed down gradient. This also could be considered as extreme case or macro-scale of surface roughness.…”

Slope shape effect on runoff and soil erosion under natural rainfall conditions

“…The effects of length (Kinnell 2000, 2007, Rejman & Brodowski 2005, Bagarello & Ferro 2010 and slope gradient (Bracken & Kirkby 2005, Assouline & Ben-Hur 2006, Moreno de las Heras et al 2010) on soil loss and runoff were studied extensively, with the general conclusions that eroded materials and runoff increase with higher slope steepness (Young & Mutchler 1969a, Wischmeier & Smith 1978, Liu et al 1994, Gabriels 1999, Chaplot & Le Bissonnais 2003. Moreover, a clear reduction in runoff for each unit of slope length was observed as slope length increased (Gascuel Odoux et al 1996, Aryal et al 2003, Parsons et al 2006. However, few research has been conducted on the influence of slope shape on runoff and soil erosion.…”

Rural land management impacts on catchment scale flood risk

“…However, there are problems with the use of this term, including no constrained definition and the difficulty of quantifying it (Bracken and Cloke, 2007;Michaelides and Chappell, 2009 as active areas which actually connect to the river network. This has also been referred to as "effective hillslope length" (Aryal et al, 2003) and "dynamic contributing areas" (Beven, 1997). Therefore, landscape position is important as areas of the landscape closer to the river channel are more likely to connect.…”