Vegetated filter effects on sedimentological connectivity of agricultural catchments in erosion modelling: a review

Abstract

The sedimentological connectivity of agricultural catchments may be affected by anthropogenic structures (land management practices) established to reduce sediment exportation from agricultural plots to water streams. Distributed erosion models may in theory provide information about where and how these structures should be installed in catchments to reduce sediment exportation. The interaction between sediment exportation and land management practices is very complex from both theoretical and experimental points of view. Vegetated fi lters are a widely used land management practice. They interact with water fl ow, change turbulence conditions, and ultimately affect sediment transport and deposition processes. Experimental results have shown that the effi ciency of sediment trapping in vegetated fi lters is infl uenced by fl ow characteristics, sediment size, and vegetation type, as well as by the slope and width of the fi lter in the streamwise direction. At the catchment scale, the spatial organisation of management practices is crucial for the global sedimentological connectivity. Present-day erosion models propose different approaches to simulate the infl uence of management practices on soil loss and sediment export for agricultural catchments. Some of them use the Sediment Delivery Ratio (SDR) or P-factor to describe sediment transport from source to sink areas. Others, such as in the TRAVA and VSFMOD, rely on process-based descriptions involving changes in roughness and infi ltrability along fl ow paths to study the effect of management practices. From the literature review conducted herein, we identifi ed the lack of an approach of intermediate complexity, that would be more physically relevant than SDR and P-factor approaches, but simpler and easier to spatialise than TRAVA and VSFMOD-type models.

Managing ditches for agroecological engineering of landscape. A review

“…We assumed that similar characteristics influence sedimentation within ditches. As mentioned above, vegetation generates friction and roughness, which decrease the flow velocity and enhance the sedimentation potential (Fiener and Auerswald 2003;Gumiere et al 2011;Hösl et al 2012;Needelman et al 2007), which has been evidenced by Moore et al (2010), who detected a lower proportion of suspended solids in the water column of a vegetated ditch than those in the water column of a non-vegetated ditch. The ditch morphology and the water level fluctuations also influence the flow velocity .…”

“…If gullies are connecting the adjacent field and the ditch, the sediment loads in the overland flow can reach very high concentrations (Lecce et al 2006;Tucker and Bras 1998). However, if ditches are connected to the adjacent fields by intact grass strips, the sediment loads may be consistently attenuated before reaching the ditch (Gumiere et al 2011;Huang et al 2002;Tucker and Bras 1998). Sidewall erosion is deemed to be a minor source of suspended sediments that are transported throughout vegetated ditches (Lecce et al 2006).…”

“…Clay-sized particles, which tend to stay in suspension in the water column, are predominantly removed by infiltration (Fiener and Auerswald 2003). Infiltration is driven by both the vegetation cover, which, by reducing the flow velocity, enhances the potential infiltration time, and the ditch soil characteristics, namely, its porous structure (Fiener and Auerswald 2003;Gumiere et al 2011;Hösl et al 2012;Liu et al 2008;Needelman et al 2007). …”

Improved APEX Model Simulation of Buffer Water Quality Benefits at Field Scale

“…Reported trapping effectiveness was lower than the Iowa study: 15% to 23% for runoff, 28% to 30% for sediment, and 22% to 26% for TP loads over five years. These two unique field-scale studies document the potential for significant variation in the performance of upland buffers, possibly due to variations in slope, vegetation density, flow rate, soils, buffer width, and placement characteristics (Gumiere et al, 2011). From a literature review, Gumiere et al (2011) concluded that sediment removal was maximized when vegetated buffers were placed at the downstream edge of agricultural fields, close to the outlet.…”

“…These two unique field-scale studies document the potential for significant variation in the performance of upland buffers, possibly due to variations in slope, vegetation density, flow rate, soils, buffer width, and placement characteristics (Gumiere et al, 2011). From a literature review, Gumiere et al (2011) concluded that sediment removal was maximized when vegetated buffers were placed at the downstream edge of agricultural fields, close to the outlet. The use of models to evaluate the effects of spatial organization of buffers is essential, as field experimentation for such evaluations is very expensive and difficult to apply.…”