Vegetative filter strips to control sediment movement in forest plantations: validation of a simple model using field data

A field study of sediment movement through vegetative barriers was carried out to assess the sediment-trapping effectiveness of vegetative barrier typ es typically used in forest forest plantation management in south-east Quee nsland, Australia, and to develop a simple methodology for predicting sedim ent movement through these barriers. For sites at the centre of Queensland's 110 000 ha Pinus plantation and 45 000 ha Araucaria plantation program, small field flumes (plots) were establ ished on a range of vegetation types and slope gradients, and sediment-lade n flows passed through them. Sediment trapping in the plots was assessed by comparing paired samples taken from the inlet and outlet of the plots at p re-determined sampling times. Measurements included total sediment and equi valent size distributions of sediment particles (the latter measurements be ing based on settling velocities). For plots that did not erode, the degree of sediment trapping, if based on total sediment only, was quite variable. However, if rates of transport wer e considered in terms of the various size fractions, results were very cons istent. A simple conceptual approach equating the vegetated area to a sedim entation pond allowed deposition to be calculated on the basis of settling velocity, flow depth, and residence time within the vegetated area. Estimat ed transport rates of sediment through the vegetated areas were in close ag reement with measured transport rates, confirming the efficiency of this ap proach. The results highlight a number of issues for management of sediment movemen t from forest estates.