SENSITIVITY OF SIMULATED STREAM SALINITY TO SOIL CHLORIDE PROFILE

Removal of native vegetation and intensification of agriculture has le d to salinisation of soils and streams in the south-west of Western Au stralia. Four significant changes have typically been observed: an inc rease in streamflow volume; a relocation of deep groundwater levels; e xpansion of riparian wet zones; and an increase in stream salt loads. Can we predict stream salt loads following deforestation without data on the chloride profile, the vertical distribution of chloride in the unsaturated zone? This question is addressed in the context of the I k m(2) Wights experimental catchment which was clearfelled and converted to pasture. Time series data extending over 16 years for rainfall, sa ltfall, streamflow, stream chloride and deep groundwater levels were a vailable. Using the CATPRO lumped hydrosalinity model a generalised ch loride profile was parameterised and jointly calibrated to the streamf low, stream salinity and groundwater time series. It was found that th e chloride profile parameters were virtually unidentifiable. Although qualitatively different assumptions about the initial chloride profile produced different groundwater chloride concentration time series, th ey produced virtually identical stream salinity time series. It is sug gested that time series of groundwater chloride concentration observat ions will be necessary to better identify chloride dynamics in lumped models such as CATPRO.