Towards a Simple Gaussian Model to Describe Multiple Source Areas during Wind Erosion Events

Wind erosion is a broad-scale process in inland Australia. When conditions are conducive to wind erosion, dust storms can entrain fine sediment over large areas of the continent, however closer examination indicates that the dust source areas are often spatially discrete. The fine sediment entrained from these sources, is transported as dust plumes, which may coalesce at some point downwind. While some progress has been made in estimating the dust load in these plumes (Knight, McTainsh & Simpson 1995), the accuracy of these estimates is limited by the size and shape of the source region assumed. In addition, soil loss per unit area is a more appropriate measure of soil erosion than total plume load, but estimating loss per unit area requires accurate estimation of source areas. The new model developed hopes to overcome these limitations by working from the source area downwind, rather than back-tracking to estimate the source area as done by Knight et al. (1995). As a result of this, the new model is quite distinct from that of Knight et al. (1995), in that it no longer assumes that entrainment is uniform across a single source area, and consequently that the concentration profile is uniform across the source area. The new model uses a Gaussian plume model (Zannetti 1990), with the dispersion parameters based on the Hanna, Briggs & Hosker (1982) estimates for rural areas. As a first approximation, the model describes dust loads emanating from sources of different strength and spacing along a crosswind line. This configuration is indicative of spatially discrete sources, with different soil erodibility and cover protection, producing different source strengths. Initial results from the model indicate that the nature of the downwind dust concentration profile is dependent on the following factors: downwind distance from source, source strengths,and crosswind source separation. A detailed discussion of the relationship between the above factors is presented. As a result of this discussion a number of conjectures are made about the nature of the physical system.