Indicator: Soil erosion

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What the results tell us for Tumut

The most recent information about soil erosion in Tumut Shire was reported in the 1997 State of the Environment Report, which found significant evidence for land instability within the Tumut Shire. Such problems were generally most evident on steep cleared lands and areas adjoining watercourses. Land slip, slump, erosion and bank collapse were and still are all present in such locations within the Shire (Table 1). No new data were available for this report.

Extracts from the 1997 State of the Environment Report

Land instability was not only restricted to steep land, ridges and watercourses. On both undulating and gently sloping land in the Shire, water and wind erosion have occurred where inappropriate clearing has occurred or where there is a lack of windbreak vegetation. In many cases the erosion (particularly gully erosion) is historic, occurring relatively soon after clearing or development activities.

Some form of erosion other than gully erosion affected approximately 122810 hectares;, or 33%, of land in the Tumut Shire (Table 1), much of which was predicted to be sheet erosion. Clearing of trees and vegetation and the development of structures and roads within steep areas, or close to ridgelines and watercourses, is responsible for much of the sheet and other forms of soil erosion in the Tumut Shire.

More than 200 kilometres of erosion gullies were identified in the Tumut Shire, mostly outside Kosciuszko National Park. A relatively even distribution of minor isolated, minor continuous, severe and very severe gullies was reported, however very severe multiple branching gullies are the most prevalent form. Such gullying was characteristic of of soils underlain by sedimentary rocks such as shales, slates and some sandstones.

About the data

Gully erosion throughout the Tumut Shire was mapped by the NSW Department of Land and Water Conservation in the mid 1980's at a maximum scale of 1:25000, or 1:50000 when 1:25000 elevation mapsheets were not available. The severity of gully erosion was classified according to the extent to which gullies were connected, or ocurred in isolation, their depth, and whether or not they occurred in main drainage lines.

Maps showing the distribution of eroded areas at the time of mapping were published as part of the 1997 State of the Environment Report.

Description: What does 'soil erosion' measure?

Which data are collected?

• area and proportion of land affected by wind erosion
• area and proportion of land affected by sheet and rill erosion
• total length of erosion gullies

Why do we report this indicator?

Soil erosion is the physical loss of soil from an area by wind or water. As for other forms of land degradation, there are generally severe impacts on agricultural productivity, road and building infrastructure and water quality. In general, erosion has occurred as a result of clearing of vegetation on susceptible soils, and inappropriate land management practices. Erosion is of interest to State of the Environment reporting because it indicates a significant decline in the health of the land.

In the case of wind erosion, the effects can be seen as roads and fences buried by deposited soil, paddocks stripped bare of topsoil and occasionally as severe dust storms, although most loss occurs without anybody noticing, and the soil in many dust storms experienced in the Australian Capital Region has been transported hundreds of kilometres from its source.

Although sheet erosion is an important form of water erosion it is difficult to measure and the main form of water erosion in the Australian Capital Region is gully erosion. As soil is removed from the land, agricultural productivity declines, access across paddocks is reduced, stock endangered, crops buried. Damage to roads and other infrastructure can be severe. Further costs arise from increased sedimentation in dams and increases in the sediment load of streams.