Information
Sediment Budgets: Sources, transport pathways and sinks for cane lands and grazing lands in northern Queensland
Level 1 General description
Purpose:
Two studies were undertaken to monitor sediment sources, transport pathways and sinks in cane and grazing lands as a means to better target erosion control measures.
Methods (brief)
Cane land study:
This study was undertaken within a 5.4 km2 portion of the Ripple Creek sub-catchment in the Lower Herbert. Methods such as; paddock scale run-off flumes, grab sampling, cross-sectional measurements, and erosion pin arrays were implemented to monitor sediment movement within a 3.2 km2 alluvial clay plain.
Grazing land study:
This study was undertaken within a 13.5 km2 area of the Upper Burdekin River Catchment about 15 km west of Mingela, an area comprised of excessively grazed hill country on Granodiorite – derived red duplex soils. Methods such as; paddock scale run-off flumes, grab sampling, cross-sectional measurements, and erosion pin arrays were again implemented to monitor sediment movement within different landscape elements.
In addition, a modified SedNet sediment transport model was also developed to extrapolate the measurements of both studies in order to construct a watershed budget. The model is based on a conceptualisation of hydrological transport and deposition processes within a GIS spatial modelling framework.
Key findings (brief)
Cane land study:
In the wet seasons of 1999-2000 and 2000-2001 (when measurements were carried out) the rainfall was 2740 mm and 1349 mm respectively for the studied area with a long term average of 1807 mm. Water furrows and major farm drains were found to be the main source of sediments at a net erosion rate 19 t/ha and 9 t/ha respectively. Minor drains were found to be the most efficient sinks at a net deposition rate 35 t/ha. When accounting for the whole unit area cane fields and water furrows were concluded to be the most important source of sediment at 425 and 376 t, respectively, with headlands and minor drains being the main sinks at 105 and 74 t, respectively.
Grazing land study:
In the wet seasons of 1999 – 2000, 2000 – 2001, and 2001 – 2002 (when measurements were carried out) the rainfall was 789 mm, 367 mm and 576 mm respectively with a long term average of 600 mm. Rainfall was considered to be below average for two of the three monitoring years which was also reflected in the predicted values for average sediment export from Weany Creek at 874 tonnes per year corresponding to a unit area sediment discharge of 0.65 t/ha per year. Gully erosion was found to be the greatest source, accounting for 60% of sediment delivery mostly originating from a small band along the creek drainage lines. Sheet erosion from hillslopes was found to account for 35% of sediment delivery to the stream.
Related studies
Prosser, I., Rustomji, P., Young, W., Moran, C., and Hughes, A. (2001). Constructing river basin sediment budgets for the National Land and Water Resource, Audit, CSIRO Land and Water Technical Report 15/01.
Roth, C.H. Prosser, I.P., Post, D., Gross, J. and Webb, M. (2003). Reducing sediment and nutrient export from grazed land in the Burdekin catchment for sustainable beef production. Volume I. Main research report. Report submitted to MLA. CSIRO Land and Water, Townsville.