Vegetation and terrain drivers of infiltration depth along a semiarid hillslope.

An improved understanding of the drivers controlling infiltration patterns in semiarid regions is of key importance, as they have important implications for ecosystem productivity, retention of resources and the restoration of degraded areas. The infiltration depth variability (ΔInf) in vegetation patches at the hillslope scale can be driven by different factors along the hillslope. Here we investigate the effects of vegetation and terrain attributes under hypothesis that these attributes exert a major control in ΔInf within the patches. We characterise the ΔInf within vegetation patches at a semiarid hillslope located at the Jornada Experimental Range at dry antecedent conditions preceding two winter frontal rainfall events. We measured these events that are typical during winter conditions, and are characterised by low intensity (0.67 and 4.48 mm h-1) and a total rainfall of 10.4 and 4.6 mm. High precision geo-referenced wetting front depth measurements were taken at various locations within the vegetation patches using differential GPS. Vegetation and terrain attributes were analysed to explain the ΔInf among the vegetation patches. The infiltration depths in the periphery of the patches were in general considerably deeper than those in the centre. The observations suggest that the upslope margin of the patches received additional water in the form of runon from upslope adjacent bare soil. Patch orientation with regard to the slope dictated the effect of the rest of the patch attributes and the distance to the hillslope crest on ΔInf. We found that primarily patch orientation, followed by shape and size modulate lateral surface water transport through their effects on overland flow paths and water retention; something that would be obscured under more simplistic characterisations based on bare versus uniform vegetated soil discrimination.

Near surface water balance in the Northern Murray-Darling Basin.

The water balance allows the calculation of deep drainage from other components of the hydrological cycle. Deep drainage has been linked to outbreaks of dryland and irrigated salinity. Until recently, deep drainage was not considered to be an issue on the alluvial plains of the Northern Murray-Darling Basin. Recent simulation studies and calculations using the water balance suggest that substantial deep drainage occurs under irrigated agriculture. However, these estimates have large uncertainties due to possible errors in measurement, calculation and due to spatial variability. On a catchment scale the relative area under a certain land use as well as the connection to local groundwater and the influence of anomalies such as prior streams needs to be considered. This paper discusses the current state of knowledge on the water balance in the Northern Murray-Darling Basin and highlights the need for a concentrated effort to measure all the components of the water balance in this area, as well as the effect on shallow groundwater quality and levels.