Hydrological effects of land use change on small catchments at the Narayen research station, Queensland

Abstract

The hydrological effect of a change in land use, where trees were killed and improved pasture was established, was examined in an open grassy woodland on duplex soil derived from granite. Two pairs of small catchments at the Narayen Research Station, Queensland, were instrumented to measure rainfall, runoff, soil water and meteorological variables. The treated catchments stored up to 26 mm more soil water in the 0-1 m depth than those in their original condition. Evapotranspiration over a period, calculated from rainfall, runoff and soil water storage change, was similar for both treated and untreated catchments. This result was attributed to compensating factors following death of the trees which removed interception of rain and solar radiation, caused an increase in wind velocity at ground level, and allowed enhanced grass growth in the areas previously under tree canopies. A water balance model did not provide a satisfactory calibration for the detection of runoff changes resulting from the treatment. The ratios of the annual runoff from catchment pairs, although variable, did not show drastic changes as a result of treatment. So, provided a good grass cover was maintained, it seems unlikely that the treatment would greatly alter runoff. The chloride balance in the undisturbed woodland under the present climate suggests that any changes due to treatment are unlikely, but indicates that in these soils soluble ions are readily lost from the system.