An assessment of the water budget for contrasting vegetation covers associated with waste management

Abstract

Revegetation is critical to restoring hydrological function on waste disposal sites in order to minimize runoff and drainage and safeguard the water quality of the catchment. In this study, we determined the components of soil-water balance between late 2006 and the end of 2008 for three vegetation types established over sites used for waste disposal: (i) a juvenile plantation of mixed Australian woody species; (ii) a block of mixed tree seedlings; (iii) and an ungrazed grass pasture. These were compared against a nearby natural woodland taken as an analogue of a pre-existing hydrological state. Evapotranspiration (ET) was the major component of the soil-water balance in all the four vegetation types. In the plantation and woodland, ET accounted for 60–93% of the annual rainfall compared to 44–88% in the grass and seedling blocks. While the balance of rainfall was largely lost to runoff in the plantation and the woodland, it was split almost equally between runoff and drainage in the other two vegetation covers. The plantation maintained parity in its ET with woodland due to groundcover that contributed at least 70% of the water use, while seasonal growth and periodic mowing reduced ET from the grass. Over the 2 years, the height of the deep (~19 m above sea level) water table under the plantation and grass declined by an average of 0.3 m, while it rose by a similar magnitude in the woodland. The height of the shallow water table (~8 m above sea level) showed no consistent change. We conclude that, with a good groundcover of mixed herbaceous species, a juvenile plantation can restore hydrological function and minimize deep recharge of a waste disposal site to the status of that under a pre-existing undisturbed woodland.