The Role of Erosion and Sediment Transport in Nutrient and Contaminant Transfer (Proceedings of a symposium held at Waterloo, Canada, July 2000). IAHS Publ. no. 263, 2000. 83 The effectiveness of grass strips for the control of sediment and associated pollutant transport in runoff HOSSEIN GHADIRI, BILL HOGARTH & CALVIN ROSE Faculty of Environmental Sciences, Griffith University, Nathan Campus, Queensland 4111, Australia e-mail: h.ghadiri@mailbox.gu.edu.au Abstract Grass filter strips have been used widely for erosion control on agricultural lands, but the mechanism of such action is not fully understood. A series of experiments was conducted in a 6 x 1 m flume and rainfall- runoff simulator to investigate the effects of filter strips on runoff hydrology and sediment and chemical transport using real and artificial grass strips. Changes in flow configuration caused by the strips were recorded at regular intervals during the 45-min runs. For the range of slopes and flow rates investigated, sediment deposition occurs largely in the backwater region ahead of the strips, the length of which is inversely related to flume slope. There was some deposition on the downstream side of the strips, but no sediment deposition or trapping took place inside the strips and between the grass stands. In the experiments with non-consolidated soils, the soil inside the strips was eroded away by channelized flow. Filter strips did not effec- tively reduce the transport of the finer fractions of the sediment load. Size distribution analysis conducted on the deposited sediment before and after the strips suggests significant enrichment of fine particles, sorbed chemicals and organic matter as a result of runoff passing through the grass strips. In this study, grass strips 20 and 40 cm in width did not effectively reduce downslope transport of pollutants by surface runoff. INTRODUCTION The use of cross-slope vegetation strips has long been recognized as a soil conserva- tion measure. Data from field and laboratory experiments indicate significant reduc- tion in the sediment load of runoff when passed through an even quite narrow vegetated strip (Kemper et al, 1992; Meyer et al, 1995; Magette et al., 1989; Raffaelle et al., 1997). The effectiveness of grass strips in reducing runoff sediment load and soil erosion has been attributed to the filtering capacity of strips as well as their ability to slow down surface runoff and enhance deposition. Such attributes are based more on common sense than on the outcome of scientific investigations. However, there has been a renewed interest in recent years in understanding the mechanics of flow through porous barriers and their effectiveness in reducing the transport of sediment and pollutants down slopes, or into receiving waters, from agricultural lands (Landry & Thurow, 1997; Hairsine, 1996; Magette et al, 1989). Because of the increasing interest in management of riparian lands to reduce the amount of nutrients and pollutants in runoff to streams, there is a need to study the