Mechanical soil conservation with contour ridges: Cure for, or cause of, rill erosion?

Abstract

Based on the results of an erosion damage assessment in Southern Zimbabwe, where mechanical conservation work has been carried out since the 1940s, this paper describes the impact of mechanical conservation systems on processes leading to rill erosion. In a study of a catchment area, it was found that influxes of water from roads and waterways as well as contour ridges that were originally designed to control rill erosion had a major role in the formation of rills. Existing rills and depressions which cause water concentration, siltation of contour drains and overflowing of contour ridges were the main factors leading to excessive rill erosion. The study showed that particularly during a highly erosive year like 1992/93, the damage due to rill erosion can be excessive, causing an abrupt degradation. It is concluded that the present conservation system is insufficient to control rill erosion effectively and is often the cause of this erosion. Effective control of rill erosion is a pre‐condition for optimal implementation of land management systems such as conservation tillage. Therefore, an integrated approach to land husbandry must be developed jointly with farmers and promoted in order to improve crop production and sustainable management of natural resources. This should consider improved mechanical conservation as well as agronomic and biological soil and water conservation techniques.

Surface and subsurface flow effect on permanent gully formation and upland erosion near Lake Tana in the northern highlands of Ethiopia

“…Widths were measured at several points along a rill and averaged over the rill length (Herweg, 1996). From these measurements, different magnitudes of rill erosion were determined, including rill volumes, rates of erosion, density of rills, area impacted by the rills, and the percentage of area covered by the rills in relation to the total area of surveyed fields (Herweg, 1996;Hagmann, 1996;Bewket and Sterk, 2003). The rill magnitudes were calculated using the following equations:…”

Understanding the factors influencing rill erosion on roadcuts in the south eastern region of South Africa

“…The widths and depths of the rill were measured using a measuring tape and a 30 cm ruler respectively, at regular intervals (i.e. 0.01 m) along the sinuous length of the rill, and the averages were calculated (Hagmann, 1996;Sidle et al, 2004).…”

Sustaining reservoir use through sediment trapping in NW Ethiopia

“…Sediment discharge from a catchment is highly variable both temporally and spatially (Hagmann, 1996;Yeshaneh et al, 2014;Buendia et al, 2016), which is because the processes driving catchment sediment dynamics have proved to be highly variable in space and time (Liu et al, 2012). Over recent decades, there has been an increased interest in quantifying sediment loads of intra-annual (within a year) variability in addition to inter-annual (between years) in order to improve understanding of suspended sediment loads at a higher temporal resolution (Smith et al, 2003;Seeger et al, 2004).…”

“…Over recent decades, there has been an increased interest in quantifying sediment loads of intra-annual (within a year) variability in addition to inter-annual (between years) in order to improve understanding of suspended sediment loads at a higher temporal resolution (Smith et al, 2003;Seeger et al, 2004). This increased interest for intra-annual variability arose because it was shown that for many catchments only a small part of the catchment and only a few heavy rain storms on specific dates produced the bulk of annual sediment yield (Hagmann, 1996;Ziadat & Taimeh, 2013).…”

“…Only a small part of the catchment and only a few heavy rain storms on specific dates usually produce the bulk of annual sediment yield (Hagmann, 1996;Ziadat & Taimeh, 2013).…”