Seepage scald in southeastern Australia

Abstract

This study addresses the problem of seepage scald in southeastern New South Wales. Limited information was available on soil and hydrological properties of these areas and a case study of the Yarralaw seepage scald was undertaken to answer questions concerning the scald's origin, the threat of scald expansion and possible offsite effects. The results have application to a number of similar sites in southeastern New South Wales. Scald formation was not related to any particular soil property inherent to the scalded area. Grassland and scald soil profiles were similar, with the major difference being the surface horizon. The grassland surface was relatively permeable but the scald surface was sodic, highly dispersive and compacted. As a result, it had lower permeability than the grassland. Soil salt loads were high only in the surface horizons of the scald. The water table in the lower catchment, even at its lowest level, was within 2 m of the ground surface. Upward capillary water movement is causing the salinity, but the salinity is confined to the scald because downward leaching in the grassland keeps the surface of these areas relatively salt-free. The areal extent of the Yarralaw seepage scald has been stable since 1962. High runoff conditions in the future may cause further scald expansion and it is important that reasonable measures be taken to prevent this. However, scald growth appears to be catastrophic in nature, with the majority of the damage occurring in a relatively short period of time in the early stage of formation. On the scald surface, the degradation is a progressive process but scald expansion appears to be catastrophic. This type of formation has important implications for management and emphasizes the need for seepage scald prevention.