Level 2: Details of Experimental Conditions and Methods

When and Where

The study was carried out in the Burdekin River Catchment, a major catchment of the Great Barrier Reef (approx 130,000 km2) west of Townsville. The study commenced in 1999.

The general description of the site is as follows:

• Site on Dotswood military training area (TFTA section);
• Site with no grazing over the past 20 years; and
• General site condition excellent, except for occasional permanent military vehicle tracks.

Soil Type

The soils from the sites are varied but generally old and weathered with a large proportion of duplex soils. With the exception of soil derived from basalt (Vertosols or Ferrosols) most of the soils are low in fertility and due to their textual properties, are particularly prone to crust and hard setting. The six sites are located on duplex or gradational soil types that are common within the Upper Burdekin River Catchment.

Soil Description for High Range (site 4):

• Brown and Yellow Chromosols (Bluff Series);
• Sand 86-89%
• Clay 5-7%
• Bulk Density 1.36-1.57g/cm³;
• OM content 0.6-1.4% C;
• Moisture 0.08-0.14% volume;
• Ground Cover 75-100%; and
• Biological Activity 3-4.

Landscape Features

Features of High Range include:

• Narrow leaf Ironbark is the dominant tree species;
• Kangaroo grass and Black Speargrass are the dominant grass and legume species; and
• Granite and Granodiorite (Geology).

How

Six sites were selected on duplex and gradational soil types typical of large parts of the catchment. Individual plots reflecting the main classes identified were selected with two to four replicates per class, resulting in about ten to sixteen plots per site.

The rainfall simulator consisted of 1m² capillary tube (inner diameter 0.5 mm) drop forming chamber mounted on a 4 m high aluminium tower. The tower is attached to a trailer that supports the equipment to conduct the rainfall simulation.

The rainfall intensity varied between 30 and 75mm h^-1. The targeted intensity for this study was 60 mm h^-1 for 30 minutes, which represents a storm event having a 1 year return period for northern Queensland.

Metal runoff plot frames 0.4m by 0.6 m in size were placed in the middle of the rainfall plot, thus allowing a 0.2m to 0.3 m buffer zone around the plots. An angle grinder was used to cut slots into dry ground to enable insertion of the frame into the soil without disturbing surface features.

The soil features recorded from the experiment include the following:

• Estimate of ground cover (green material and litter);
• An assessment of microreleif and plot slope; and
• Range of macroscopically visible crust.

In addition the following criteria were recorded as proposed by (Tongway and Hindley, 1995), this includes:

• Presence and type of crust;
• Extent of cryptogams;
• Extent and nature of surface lag and gravel cover;
• Presence of pedestals;
• Degree of litter incorporation;
• Presence of macropores; and
• Extent of surface casting.

Soil cores were taken from within each plot after the event for bulk density measurements at depths of 1 to 5 cm. Soil moisture was measured at the same depth as bulk density for each plot.

Level 1, level 3, level 4 and level 5