Effectiveness of grass strips in trapping suspended sediments from runoff

Abstract

Little information is available concerning the performance of grass strips for erosion control from steep cropland. An experiment was conducted on 5-m-long grass strips with slopes of 3°~15° that were subjected to silt laden runoff and simulated rainfall, to investigate the sediment trapping processes. The grass strips had three treatments including intact grass control (C), no litter (dead grass material covering the soil surface was removed) (NL), and no litter or leaves (only 2~3 cm grass stems and roots were reserved) (NLL).Generally the grass strips had a high effectiveness in trapping sediment from steep cropland runoff. Sediment trapping effi ciency (STE) decreased with increasing slope gradient, and even for a 15° slope, STE was still more than 40%. Most sediment deposited in the backwater region before each grass strips. The removal of grass litter or/and leaves had no signifi cant infl uence on STE. The sediment median size (D 50 ) in infl ow was greater than that in outfl ow, and the difference (ΔD 50 ) decreased with increasing slope. A positive power relationship between STE and ΔD 50 can be obtained. Grass strips were more effective in trapping sediments coarser than 10 or 25 μm, but sediments fi ner than 1 μm were more readily removed from runoff than particles in the range of 2 to approximately 10 μm.Grass litter had less infl uence on fl ow velocity than leaves because the deposited sediment partially covered the litter layer. Mean fl ow velocity and its standard deviation were negatively correlated with STE, and they can help make good estimation of STE. Results from this study should be useful in planting and managing forage grass to effectively conserve soil loss by runoff from steep slopes on the Loess Plateau of China.

Diagnosis on the Riparian Vegetation in the Downstream Reach of the Gyungan Stream for Creating Vegetation Belt

“…및 38%가 제거되었다 (Dunn et al, 2011). 그 밖의 많은 연구 에서도 강변 완충대가 발휘하는 비점오염원 물질의 제거능이 밝혀진 바 있다 (Agouridis et al, 2005;Dahlin et al, 2005;Dorioz et al, 2006;Haycock and Pinay, 1993;Lee et al, 2003;Oteroa et al, 2011;Pan et al, 2008;Pan et al, 2010). 이러한 영양염류 제거 과정은 그것이 문화적 부영양화를 크게 줄일 수 있게 때문에 생태학적으로 중요하다.…”

Sustaining reservoir use through sediment trapping in NW Ethiopia

“…only grass stems and roots. STE ranged from 42-69%; 41-72% and 37-59% for the C, NL and NLL treatments, respectively, and thus Pan et al (2010) concluded that grass litter and leaves had no significant influence on STE of the local grass. …”

“…For example, hedges of switch grass and Vetiver (Vetiveria zizanioides (L.) Nash) caused backwater depths of up to 40 cm and trapped >90% of sediment coarser than 125 µm in areas of concentrated overland flow (Meyer et al, 1995). The effect of grass litter and leaves on ST was also studied on the Loess Plateau, China (Pan et al, 2010) where perennial local grazing grass, black rye (Loliumperenne L.) were tested on slopes of 3-15 0 applying three treatments: C-control with intact grass, NL-no litter i.e. without grass covering the soil surface and NLL -no litter or leaves i.e.…”

“…The sediment trapping efficacy (STE) of many grass species is well known. For example; Lemon grass (72-92%), Elephant grass (62-84%), Paspalum (65-88%) and Sugarcane (56-82%) in Uganda (Wanyama et al, 2012); Vetiver grass (65%) in Australia (McKergow et al, 2004); Switch grass (92%) (Lee et al, 2000) in the USA; Centipede grass (24-73%) in Japan (Shiono et al, 2007); Black rye (42-69%) in China (Pan et al, 2010) and Vetiver (62%) and Desho (43%) in the lowland part of Ethiopia (Welle et al, 2006). However, still many grass species that could potentially serve as vegetative barriers have not been studied for their STE, including the locally used grass species in the northwestern Ethiopian highlands, Desho (Pennisetum pedicellatum), Senbelet (Hyparrhenia rufa), Sebez (Pennisetum schimpri) and Akirma (Eleusine floccifolia).…”

“…For example; Lemon grass (72-92%), Elephant grass (62-84%), Paspalum (65-88%) and Sugarcane (56-82%) in Uganda (Wanyama et al, 2012); Vetiver grass (65%) in Australia (McKergow et al, 2004); Brome grass (70-85%) (Robinson et al, 1996) and Switch grass (92%) (Lee et al, 2000) in the USA; Centipede grass (24-73%) in Japan (Shiono et al, 2007); Black rye (42-69%) in China (Pan et al, 2010) and Vetiver (62%) and Desho (43%) in the lowland part of Ethiopia (Welle et al, 2006). The STE of Desho grass was tested by Welle et al (2006) in the lowland part of Ethiopia but not in the highlands where it performs best (MOARD, 2010).…”