Level 2 Detail of experimental conditions (what might be found in a journal paper or project brief in Hydstra)

Description of study

What?

Data was collected from runoff plots at ‘Springvale’ a cattle grazing property located 75 km west of Emerald in central Queensland.

When and Where?

The study commenced in 1987 with the installation of 9 bounded runoff plots within the catchment which were ungrazed and 4 outside of the catchment which were grazed by cattle. Pasture cover on the plots varied from bare to 70% and tree basal area was from 1 to 11m²/ha on sandstone, mudstone and eroded mudstone derived soils.

Climate in the region is classified as subtropical with a moderately dry winter. From October 1987 to September 1994, the study period, mean annual rainfall was 610 mm. Rainfall is abundant in the six warmer months of the year. Annual average evaporation is at least twice average rainfall across all months of the year.

Vegetation on the site is dominated by silver-leaved ironbark (Eucalyptus melanophloia) and is open woodland with a grassy understorey dominated by a variety of tussock grasses. Grass growth was inhibited within thick patches of silver-leaved ironbark (up to 400 trees/ha) and ground cover was predominately leaf litter and twigs. Tree canopy cover within these patches was <30% and had little direct effect on hydrology and erosion compared to soil water use by trees and tree litter input and the effect on grass growth and cover.

Main soil types found on mudstone are moderately deep, texture-contrast soils (Sodosols) or shallow poorly formed eroded soils (Leptic Rudosols).

The main soils on sandstone are shallow to moderately deep, texture-contrast (Chromosols) or gradational soils (Kandosols), and some elements of moderately deep sands (Orthic Tenosols), and very shallow to shallow, often stony soils (Rudosols) on steeper slopes. Land slope is varied across the catchment ranging from 1% in the lower slope areas to 20% on the hills and ridges.

Each plot had varied pasture conditions including high cover ungrazed, under trees, medium cover, grazed, eroded and bare scalded with a range of cover conditions on mudstone and sandstone derived soils.

How?

Runoff plots were aligned perpendicular to the slope, with a Gerlach trough installed at the bottom to collect bed load soil and collect runoff. Runoff rate and volume were measured via tipping buckets installed at one end of each Gerlach trough. Mechanical counters were attached to the tipping buckets as a backup to measure total runoff tips. Each plot was bounded to prevent non-contributing surface run-on entering the plot proper. Runoff in millimetres was accumulated for the service period from the logger data.

Suspended Sediment

Development and testing of a tipping bucket integrating suspended sediment sampler demonstrates that its performance across the typical discharge range is linear in terms of a flow proportion (Silburn & deVoil, pers comm.). Thus a single suspended sediment sample is flow-weighted and representative of the entire runoff event. The suspended sediment sample is accumulated in a container, collected at the end of a service period and then analysed in the NRM&W Emerald laboratory for Total Solids by APHA method 2540B. As this is a discharge- integrated sample for the preceding interval runoff event, simple calculation of a sediment load in t/Ha is possible by the following formula:

t/Ha_suspended = mg/L_suspended * mm_event ÷ 100000

Bedload

At the end of each service period, bed load material was manually removed from the Gerlach troughs and weighed.  Sub-samples were then collected, weighed and oven dried for moisture content correction.  The weight of the oven dry sediment was converted to an equivalent soil loss on an area basis:

t/Ha_bedload = kg_bedload ÷ Ha ÷ 1000

Total Soil Movement

Simply:

t/ha_total = t/ha_suspended + t/ha_bedload

Silburn et al (2011) measured runoff and erosion over a 7 year period on 12 hillslopes each with varying pasture conditions and soil type to determine the level of influence each variable had on runoff and erosion quantities.

Silburn (2011) fitted a simple event sediment concentration model to suspended and bedload sediment concentrations measured on hillslope runoff plots.

Silburn (2011) modelled USLE soil erodibility K factors and cover-soil loss relationships using data derived from the study.

Owens et al. (2003) modified GRASP model to include the USDA curve number runoff method from PERFECT with the aim of providing a more general model than the regionally derived Scanlan runoff approach used previously and to improve runoff and water balance prediction. This study provides important new runoff parameter values for modelling water balance and degradation of hard setting soils under pasture.

Project administration

Site identifier code: CQGF

Principal investigator: Silburn DM; Ciesiolka, CAA

Principal data manager: Silburn DM

Principal organizations: Department of Natural Resources, Mines and Water

Data custodian: Department of Natural Resources, Mines and Water

Key co-operators: DERM QScape, Paddock to Reef Monitoring, Modelling and Reporting Program and eWater CRC Catchments and Climate projects.

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 N/A

Planned data upload frequency: for ongoing studies N/A

Key references and sources of this data synthesis

These data summaries have been extracted from

1. Owens JS, Silburn DM, McKeon GM, Carroll C, Willcocks J, deVoil R. (2003). Cover-runoff equations to improve simulation of runoff in pasture growth models. Australian Journal of Soil Research 41: 1467-1488.
2. Silburn DM, Carroll C, Ciesiolka CAA, deVoil RC, Burger P. (2011). Hillslope runoff and erosion on duplex soils in grazing lands in semi-arid central Queensland. I. Influences of cover, slope, and soil. Soil Research 49:105-117.
3. Silburn DM, Carroll C, Ciesiolka CAA, deVoil RC, Burger P. (2011). Hillslope runoff and erosion on duplex soils in grazing lands in semi-arid central Queensland. II. Simple models for suspended and bedload sediment. Soil Research 49:118-126.
4. Silburn DM. (2011). Hillslope runoff and erosion on duplex soils in grazing lands in semi-arid central Queensland. III. USLE erodibility (K factors) and cover–soil loss relationships. Soil Research 49:127-134.

Keywords:

South-east Queensland, hydrology, sediment, nutrients, hillslope, runoff, erosion

Level 1, level 3,  level 4, level 5