Information
Level 2 Detail of experimental conditions (what might be found in a journal paper or project brief in Hydstra)
Description of study
What?
This study collected runoff, bedload and sediment concentration data from six woodland sites over unbound catchments in grazed and exclosed pastures. The importance of cover, soil moisture status, rainfall intensity, rainfall event size, and pasture type in determining rates of runoff, bedload and sediment loads was also studied. The aim was to quantify runoff and soil movement in grazed woodlands.
When and Where?
Over a five year period, runoff, bedload and sediment concentration data were collected from unbounded catchments in grazed and exclosed pastures at six woodland sites. The sites were located east of Greenvale, in the Dalrymple Shire, north-east Queensland.
Sites were dominated by Eucalyptus drepanophylla and E. Erythrophloia and contained a variety of native or naturalised grass pasture. Cover was categorized into three pasture types:
1. BOPER sites dominated by B. Pertuse;
2. HECON sites characterized by native, perennial tussock grasses of which Heteropogon contortus was a common component; and
3. MIXED sites contained both perennial tussock grasses and B. Pertusa.
The six sites were characterised by neutral duplex red soils derived from granodiorite around Carters Towers. Slopes ranged from 1.5 - 5 %. Average rainfall ranged from 600 – 675 mm with >85% recorded in Nov – Apr.
How?
At each site, the BOTANAL method was used to estimate pasture yield and composition two times per year. Cover was directly estimated within the quadrants and used for yield estimation (50 quadrants each 0.5 m x 0.5 m).
The GRASP model, modified to incorporate tree water use, was used to interpolate pasture biomass between sampling dates and estimate soil water deficit in the upper 50 cm of the soil profile. Pasture biomass was used to estimate cover at each rainfall event using regression equations.
Each site had two treatments: a 4 ha block fenced to exclude domestic stock (enclosed treatment) and an adjacent 4 ha block open to stock (grazed treatment).
In each treatment, two 10 m wide rectangular gerlach troughs were placed perpendicular to the slope, extending to the top of the slope, and offset so that catchments did not overlap. Catchment areas varied from 205 – 1200 m2 with length of slopes ranging from 25 – 120 m.
A tipping bucket mechanism connected to a data logger measured runoff. Data collected from the two troughs were combined to provide results from each treatment. A conversion between the number of tips and volume runoff was determined by pumping a range of water flow rates through the tipping bucket mechanism and measuring the resulting tipping rates. Runoff was calculated by converting the tipping rate to a volume for each interval throughout each event. Each bucket mechanism required separate regression relationship to convert tipping rates to volumes.
In each treatment, total rainfall and maximum intensity over 15 minutes were recorded using a data logger. Mechanical counters on tipping buckets were used at the southern sites as backup for data loggers and standard rain gauges were located within each treatment.
Bedload was collected as large soil particles settled out from runoff water in the troughs every two weeks in summer and every month in winter.
Runoff water was sub-sampled into 10 L reservoirs which were emptied at the same time soil was collected. Filtering the water and weighting the dried sediment gave the suspended sediment concentration.
Total sediment load was estimated using equation: sediment load = (runoff x sediment concentration) / 1000
Project administration
Site identifier code: na
Principal investigator: J.C. Scanlan
Principal data manager: -na
Principal organizations: Department of Lands and Department of Primary Industries?
Data custodian: DPI
Key co-operators: DPI
Data access policy: Research has been published but base data is not archived
Planned pathway for data: completed study, no evidence of formal database records.
Data warehousing: for ongoing studies -na
Planned data upload frequency: for ongoing studies -na
Key references and sources of this data synthesis
These data summaries have been extracted from:
- Scanlan JC, Pressland AJ, Myles DJ. 1996. Run-off and soil movement on mid-slopes in north-east Queensland grazed woodlands. Rangel.J. 18 (1):33-46.
Keywords:
Greenvale, soil movement, runoff, bedload, sediment, perennial tussock grasses, stoloniferous grasses, grazed pastures, exclosed pastures, sustainable land use