Prediction of surface flow hydrology and sediment retention upslope of a vetiver buffer strip

Abstract

Vegetated buffer strips are widely used to reduce fluxes of eroding soil and associated chemicals, from hillslopes into waterways. Sediment retention by buffers is time-dependent, with its effectiveness changing with the deposition process. Our research focuses on settling of sediment upslope of stiff grass buffers at three slopes, under subcritical flow conditions. A new model is developed which couples the hydraulics, sediment deposition and subsequent adjustment to topography in order to predict water and sediment profiles upslope of a buffer with time. Experiments to test the model were carried out in the Griffith University Tilting-Flume Simulated Rainfall facility using subcritical flows at 1%, 3% and 5% slopes. Water and sediment profiles were measured at different times as Vertisol sediment was introduced upslope of a vetiver grass strip. A region of increased flow depth (backwater) was produced upslope of the strip which increased in depth and decreased in length with increasing slope. Backwater height could be predicted from flow rates and thus could be used as an input for the model in the absence of experimental data. As slope increased, sediment was deposited closer to the grass strip, moving into the grass strip itself at 5% slope. The grass strip was less effective in reducing sediment in the outflow as slope increased and differences between slopes were significant. Model prediction of water and sediment profiles compared reasonably well with measured data, giving low root mean square errors and high coefficients of model efficiency. Masses of deposited sediment were generally simulated within 20% of measured values. However, simulated particle size distributions of deposited sediment were less accurate. ª

Effectiveness of grass strips in trapping suspended sediments from runoff

“…Under the experimental conditions, fl ow retardation took place at a certain distance ahead of each grass strips, especially on the gentle slope, and most sediment deposited in the backwater region. Hussein et al(2007aHussein et al( , 2007b also reported that backwater region increased overall STE, and more than 90% of infl ow sediment was deposited upslope of a vetiver grass strip at 1~5% slopes and subcritical fl ow rates ≤0·001 m 3 m…”

Land-Use Suitability in Northeast Iran: Application of AHP-GIS Hybrid Model

“…Grasslands are also used to control the erosion of highly erodible lands [43,44]. Grasses are used in crop rotations and in strip cropping systems to slow surface water flow [45], to increase infiltration [46,47], and to reduce sediment running off tilled fields [48]. Despite this, it seems that the lands of study area were more suitable for agriculture than for grassland.…”

Modelling Sediment Trapping by Non-Submerged Grass Buffer Strips Using Nonparametric Supervised Learning Technique

“…The length and depth of backwater for the same flow rate and vegetation type and density changes substantially with slope. Therefore, it is almost impossible to have sediment trapping upstream of the grass buffer strips in slopes more than 12% (Ghadiri et al, 2001;Hussein et al, 2007b).…”

“…A few physically-based models have been developed to predict the efficiency of vegetated buffer strips in sediment removal (Deletic, 2001b;Hussein et al, 2007b;Munoz-Carpena et al, 1999;Newham et al, 2005). Some currently available models are not completely process-based and their sediment transport and deposition sub-models are not very well validated (Munoz-Carpena et al, 1999;Newham et al, 2007).…”

“…Some currently available models are not completely process-based and their sediment transport and deposition sub-models are not very well validated (Munoz-Carpena et al, 1999;Newham et al, 2007). Some of the existing models neglect one of the two major zones of "upstream" or "within the grass strips" in their assumptions (Deletic, 2001b;Hussein et al, 2007b). The existing models are limited to some specific conditions or cannot accurately predict the efficiency of grass strips in removing sediments.…”