William Scott

Values of unsaturated water content determined with neutron moisture measurements (NMM) reveal different water profiles below different plantings. In the extremes, calibration requires a linear and logarithmic response (using the Lambert-W function) along with the normal submersion in a drum of water. Nevertheless a post-calibration with a hydraulic push sampler was used for confirmation. Data were collected at six pastures near the Western Australia coast near Geraldton, with four replicates through the profile. The sites have mostly sandy soils and receive 300–500 mm of rainfall annually. Findings generally showed that, if there was sufficient water, as in 2006, the perennials were able to use the water evenly throughout the vertical profile. Otherwise, with low rainfall, as in 2009, perennials struggle to survive and use less water than the annuals. Modelling of the soil water movement, plant growth and calibration/recalibration is and will be used to get a maximum likehood fit. Clearly, in desert conditions and little or no vegetation, rainfall tends to build up deep in the profile, increase salinity in groundwater, and create waterlogging. Any vegetation is helpful; perennials more so; provided they have sufficient water and are not significantly harvested.

Soil core samples were collected at Ashfield to determine the extent of Acid Sulfate Soils (ASS), and pin-point hot spots. ASS are major problems to environmental health, to people and infrastructures, from acidity and the movement of toxic heavy metals. Field and laboratory testing were used; (Field pH), Chloride to Sulfate ratios (Cl:SO4), as well as the Suspension Peroxide Oxidation Combined Acidity and Sulfate (SPOCAS) suite. Statistics show that Field pH measurements are sufficient in the detection of ASS; SPOCAS tends to confirm the results of the conservative Field pH measurements. Cl:SO4 ratios do not detect ASS in the same way as SPOCAS and cannot be considered as surrogates for Field pH or SPOCAS techniques. A decision tree presents a basis for analysing ASS, which might be used by an Environmental Health Officer.

Historic observations of sea-level on Macquarie Island recorded an ∼ 6 min oscillation with a perceived beat of ∼ 3 h, interpreted as two counter-rotating edge waves of slightly different frequencies. Alternative evidence is presented here that the oscillations are consistent with the fundamental shelf period of Buckles Bay; an envelope characteristic of local coast and shelf features. New data from a shore-mounted tide gauge, analyzed using fourier and wavelet techniques, show an ∼ 6.6 min phenomenon occurring in bursts every 1-4 h. A simple model shows that the fundamental resonant frequency may spread and comply with maximum and minimum coast and shelf features.

A method is developed to estimate the stress at the surface in a portable wind tunnel for wind erosion studies. The boundary layer height and the pressure gradient are used in a simple expression from the Kármán Integral Momentum Equation. Values of friction velocity u* are within 10% of experimental values obtained through correlation techniques, including measurements of differential pressures with the Murdoch Turbulence Probe MTP and the X-wire, hot-wire anemometer XWA. Wind velocity and stress profiles reveal logarithmic trends and a 'constant stress layer' near the surface in the DAWA portable wind tunnel. Realignment of the statistics with the mean wind is essential.

The force of wind on the ground created by turbulent eddies is commonly used to describe the horizontal flux of material during wind erosion. Here we present the Murdoch Turbulence Probe, an instrument for use in both clean and eroding flows which uses pressure differences to measure the three components of wind velocity. Correlation techniques calculate the forces near the ground and turbulence statistics in nearly real time, including turbulent velocity fluctuations from less than 0.1 Hz to 200 Hz, mean flow velocities, Reynolds stresses as well as the integral length and time scales. In the portable wind-tunnel used by Agriculture Western Australia, turbulence statistics were recorded over stable surfaces and in blowing sand from the initiation of erosion up to the time the sand supply was exhausted. Estimates of the friction velocity derived from the turbulence probe were compared with estimates obtained from the wind speed profile measured with a rake of pitot and static tubes. The Murdoch Turbulence Probe appears to work well in sandblasting conditions. Relative turbulence intensities ranged from 0.11 to 0.2 and are in close agreement with values in the literature. The ratio of the turbulence to the friction velocity (3 to 3.2) is at the high end of the reported range. The Reynolds stress measurements agree closely with predictions of the threshold friction velocities of the sand and estimates from the wind speed profile with a von Kármán constant of about 0.3, lower than the commonly accepted value of 0.4. We suggest that the wind-tunnel profile represents the 'outer layer' of the boundary-layer that may best be described by a 'Wake Law' or 'Defect Law'. At about 54 mm above the surface, the friction velocity decreases from 0.64 m/s to 0.39 m/s and the mean velocity increases from 9.6 m/s to 11.6 m/s as the supply of sand is depleted. In addition to the friction velocity, other scales may be necessary to characterise the overriding effect of the wind and in extending wind-tunnel results to the field.

This paper presents a model of the uplift by wind of heavy (i.e. saltating and unaffected by turbulent diffusion) soil particles. Detailed trajectories are not calculated, although trajectory heights are required and this necessitates taking account of the drag on particles. Quantities required as input are (a) the mass-concentration at a height equal to the roughness length above the surface for each size class, (b) the roughness length of the undisturbed surface, and (c) the friction velocity which is assumed to be controlled by the overlying wind and unaffected by erosion. The model is combined with a previously bublished model for lighter particles and applied to hypothetical size distributions for a range of friction velocities. Mean-diameter profiles and horizontal fluxes are obtained and found to agree well with observations by various workers.

A pedon scale study was conducted to investigate the degree of chloride leaching from a de-watered saline soil profile in the non-irrigated wheatbelt region of south-western Australia. Within the surface 250mm of the soil profile was a dispersed layer acting as a hydraulic throttle. Soil water tensions and chloride concentrations were obtained over a two-year period over depths ranging from 0.2m to 1.5m. In the first year the soil surface remained untouched. In the second year, the throttle layer was fractured by ripping to a depth of 250mm. Rainfall, runoff and potential evaporation were also measured at the site. These data were used to calibrate and run the MACRO solute transport model using three surface treatment management scenarios: I. the soil surface remains unchanged (`Do nothing'); II. the soil surface is continually ripped; III. the soil surface is ripped followed by surface scaling. The time period required, effectively, to leach the chloride from the profile, to a depth of 1.5m, was predicted. Effective leaching would take at least 400 years and possibly in excess of 200,000 years for Treatment I, 5 years for Treatment II and 90 years for Treatment III. Macropores that were observed within the sub-surface soil profile played no significant role in the leaching of the chloride. However, the rip fractures were treated as macropores by the MACRO model and as such allowed greater infiltration of water that resulted in the mobilisation of chloride within the rest of the soil profile.

Measuring wind erosion is difficult as it requires the coincidence of a rare wind event with soil conditions that allow erosion. The measure must include a scale and an indication of the force of the wind on the ground, usually the dynamic roughness and the Rouse Number. There is not necessarily a distinct 'threshold velocity'; the relative force of the wind and the 'fluffiness' of the soil determine whether erosion will occur. Grain sizes, density and shape should be characterised by mass-mean fall velocity. The relative importance of stable/unstable surface elements may be determined by analysing the wind profile. Lastly, a model of suspension with saltation has evolved; it suggests that saltation is not distinctly different from suspension and that there is no distinct 'saltation layer'.

The two-dimensional, steady, turbulent Navier-Stokes Equations are explored for the case of a logarithmic profile. A general, analytical solution technique is presented, using potential functions; it contains two arbitrary functions. Example solutions are derived with the symbolic manipulator Maple; they show various shear stress profiles derived from a single form for the velocity profile. These stress variations occur within an ‘equilibrium profile’ and are affected by boundary conditions and upstream effects. Shear stress and dynamic roughness values derived from velocity profiles should be used with caution.

A theoretical approach to the treatment of wind erosion data, particularly from a wind tunnel, is presented. Considerations are given to the utilisation of a real data set in validation of the model, data that will be presented in a forthcoming paper. Following this, the physics of particle suspension, saltation and the turbulent boundary layer are examined. Two different mathematical models evolve: one considers only suspension, another evokes Bagnold's observation that eroding material merely shifts the velocity profile and the effect of the airborne material on the effective density of the air parcel. These produce a final, relatively simple expression that credibly fits the data of Gerety and Slingerland. A critique of the approach reveals it to be an adequate expression of the known mechanisms of suspension and saltation. Derived algebraic forms for integrated collectors show several of the same "logarithmic power" dependences. Importantly, the results show little influence of saltation itself on the profile. It appears that the saltation process is responsible for a feedback such that the eddy diffusion process for particle movement is effectively enhanced. The combination of an appropriate correction of the pitot data (following Scott and Carter) and a complete mass balance has removed the "kink" from the velocity profile and also the need to consider the saltation process itself in the particle mass balance.