Information

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

Description of study

What?

Runoff and soil movement were measured for three pasture utilisation treatments (high, medium and exclosed) and replicated at the ‘plot scale’ (80-160 m2) and a high and medium utilisation rate for two timbered ‘mini-catchments’ (0.4 - 0.5 ha) (Figure 1). Treatments were implemented in spring 1994 and the runoff sites were instrumented soon thereafter. The Glentulloch site had an additional timbered exclosure; however late installation and ongoing operations failures make much of the data unreliable.

When and Where?

From 1994 to 2000 the investigation occurred at “Glentulloch”, Injune, 100 km north of Rockhampton.

The Glentulloch grazing site is predominantly undulating with a poplar box (Eucalyptus populnea) overstorey on shallow silty duplex  soils with semi-permeable medium to heavy clay  subsoil.  Pastures are predominantly Bothriochloa decipiens and Aristida spp. on 3-5% slopes.

How?

Rainfall

Rainfall intensity and depth were recorded using tipping bucket pluviometers (1 minute interval) connected to a data logger. Pluviometers were located adjacent to each plot and manual raingauges were located adjacent to each plot and mini catchment to account for the spatial variability across the sites.

Runoff

Runoff plots were replicated for each of the three treatments for a total of six plots per site and two timbered mini catchments. Plots were aligned perpendicular to the slope, with a Gerlach trough installed at the bottom to collect bedload soil and runoff. Runoff rate and volume were measured via tipping buckets installed at one end of each Gerlach trough. Mechanical counters were attached to the buckets as a backup to measure total runoff tips. Average plot slopes were 3-5% and each plot was bounded on all sides to prevent non-contributing surface run-on entering the plot area.

For the mini-catchments (0.25 - 0.5 ha), surface runoff was measured using Parshall flumes fitted with capacitance or pressure water levels measuring sensors and chart recorders for backup. Artificial boundaries were constructed around each mini-catchment. Average slopes for the catchments ranged from 4.5-7.5%.

Time series logger data were processed through the in-house Datalog v5.6 package prior to capture in Hydstra. Datalog allowed management and editing of individual logger files; application of a calibration to convert from abstract units (eg. ‘tips’) to real-world units of measure (i.e. millimetres of rainfall and runoff); plus summarisation of data for intervals such as a service period.

Event-based soil movement was determined by separately measuring the bed and suspended load component of surface runoff. Due to the remote location of the sites, several discrete runoff events may have been combined into one service interval however due to the nature of the sediment sampling equipment these analyses are still quite valid on a cumulative basis.

The division between bed and suspended sediment is unique for each differing Gerlach trough configuration as the deposition of all water-borne sediments is dependant upon the hydraulic characteristics of each structure. The configuration used for this project may not be compatible for comparisons with other projects at a constituent level; however within the project comparisons of bed or suspended components between treatments remain valid while of similar trough construction. The calculation of a total soil movement allows independence from the measuring structure and permits direct comparisons with other projects’ soil movement data.

Reporting of event- based data is at the end of a service period, i.e. data represents the preceding interval.

Suspended Sediment

Suspended sediment that accumulated in containers, collected at the end of a service period, were analysed in the NRM&W Emerald laboratory for Total Solids by APHA method 2540B. As this was discharge- integrated sample for the preceding interval runoff event, simple calculation of a sediment load in t/ha was possible by the following formula:

t/hasuspended = mg/Lsuspended * mmevent ÷ 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/habedload = kgbedload ÷ ha ÷ 1000

Total Soil Movement

Simply:

t/hatotal = t/hasuspended + t/habedload

Total Runoff

Runoff in mm was accumulated for the service period from the logger data.

The mechanical counter total for the service period was also multiplied by the tipping bucket’s static tip volume for a minimum runoff estimate where the data logger had failed.

Table 3. Plot characteristics including, utilisation, treatment and plot area (Waters 2004)

Site

Utilisation

Treatment

Plot Area (m2)

AT130500

Composite pluvio (pl)

Cleared

84.0

AT130501

High Rep 1

Cleared

157.9

AT130502

Medium Rep 1

Cleared

142.1

AT130503

Exclosure Rep 1 (pl)

Cleared

84.0

AT130504

High Rep 2

Cleared

142.8

AT130505

Medium Rep 2

Cleared

162.4

AT130506

Exclosure Rep 2 (pl)

Cleared

100.3

AT130507

High mini-catchment

Timbered

5340

AT130508

Medium mini-catchment

Timbered

4384

AT130509

Exclosure

Timbered

96.8

*pl – pluviometer installed

Ground Cover/utilisation rate

Projected ground cover was recorded at every site visit which was generally on a monthly basis. Ten replicates were recorded for each plot and averaged to give the percentage ground cover. Detailed species composition and biomass data were also collected annually at each plot.

Utilisation rates (75%, 50%, 0%) were managed by measuring the quantity of standing dry feed in autumn every year and adjusting cattle numbers  on each paddock to suite.

Data analysis

Annual rainfall, runoff and soil loss were calculated from July to June to enable comparison of annual totals over the entire wet season. For Glentulloch years one and two data were omitted from individual event analysis. This was because treatment effects were not well established and soil surface disturbance due to trough installation was dominating runoff and soil loss as opposed to treatment effects.

Project administration

Site identifier code: na

Principal investigator: David Waters

Principal data manager: -na

Principal organizations: Meat Research Corporation; Department of Primary Industries; Department of Natural Resources, Mines and Water

Data custodian: Department of Environment and Resource Management (DERM)

Key co-operators: Aristida

Data access policy:

Planned pathway for data: completed study, evidence of formal database records (Hydstra)

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:

  1. Grazing management implications and runoff and erosion processes in semi-arid Central Queensland. ISCO 2004 – 13th International Soil Conservation Organisation Conference;
  2. Aristida/Bothriochloa pastures under Eucalypt Woodland (Hydstra brief); and
  3. Interview with David Waters.

 

Level 1, level 3, level 4 and level 5