Gully erosion and its response to grazing practices in the Upper Burdekin catchment

[摘要] Execu Summary: Gully erosion is an important source of sediment to the Great Barrier Reef (GBR). Understanding gully sediment yields, and the effectiveness of grazing practices to reduce gully yields, is vital for defining the ecosystem significance of gully erosion, and identifying effective actions which large funding programs currently underway can take to reduce sediment delivery to the GBR. This study investigated the processes of gully erosion and the effectiveness of grazing practices in influencing resultant sediment yields in the Upper Burdekin catchment during 2009–2013. The study involved four research components; (a) the decadal erosion history of gullies on hillslopes and within alluvium, (b) processes and drivers of hillslope gully erosion at annual time-scales, (c) the effectiveness of gully erosion management, and (d) the potential to reduce runoff from grazing lands into gully networks. Since the 1980s, the hillslope gully networks in grazing land of degraded condition have been eroding at approximately half the rate averaged over the entire period since gully initiation, estimated at 1900. Recent gully activity was relatively lower in an area of better land condition and lighter grazing pressure, suggesting that grazing practices may be effective at reducing gully erosion in the long term. Large alluvial gully features were confined along the Upper Burdekin River. Sediment yield from mature hillslope gullies is primarily derived from upslope extension of the gully heads and widening of the channel immediately downstream of the heads. Runoff was a dominant control on head section erosion and net gully yield, suggesting that reducing runoff is an effective way to reduce gully sediment yield in this landscape. Runoff volumes can be 30% higher from degraded catchments relative to those in good condition, associated with smaller moisture stores. Deposition in the downstream valley sections considerably reduced the net gully yield, especially in dry years. Increasing vegetation cover should enhance this deposition. Consistent with studies elsewhere, we demonstrated that gully check-dams constructed of sticks wired together are an effective way to trap fine sediment on the gully bed, reduce gully sediment yield, and initiate revegetation of the gully bed, provided they are appropriately sized to the runoff volumes. Renovating Indian couch pastures in degraded grazing lands by re-seeding required more than 2 years to return back to pre-treatment levels of stability and infiltration capacity and was not an effective treatment to reduce gully sediment yields within the study duration.

[发布日期] 2013-12-20 [发布机构] CSIRO

[学科分类] 地球科学(综合)