Use of laser-scan technology to analyse topography and flow in a weir pool

The development of laser-scan techniques provides opportunity for detailed terrain analysis in hydrologic studies. Ground based scans were used to model the ground surface elevation in the area of a stream gauge weir over an area of 240 m<sup>2</sup> at a resolution of 0.05 m. The terrain model was used to assess the possibility of flow bypassing the weir and to calculate stream flow during filling of the weir pool, prior to flow through the weir notch. The mapped surface shows a subtle low-lying area at the south end of the structure where flow could bypass the weir. The flow calculations quantify low-flows that do not reach the weir notch during small rain events and flow at the beginning of larger events in the ephemeral stream

Effect of Eucalyptus plantations, geology, and precipitation variability on water resources in upland intermittent catchments

Land-use change and climate variability have the potential to alter river flow and groundwater resources dramatically, especially by modifying actual evapotranspiration. Seven catchments with intermittent flow dominated by either winter-active perennial pastures (4 catchments) or Eucalyptus globulus plantations (3 catchments), located in 3 geologic settings of southeastern Australia, were studied for over 6 years to determine the primary controls on water resources. Groundwater levels in the pasture sites were stable through the 2011–2016 study period, while levels in the plantations declined in the same period. Streamflow occurred mainly during winter. Annual streamflow showed no difference clearly attributable to pasture versus plantation land use. The presence of grass buffers along streams enhances groundwater recharge and saturation-dependent overland flow, reducing the impacts of the plantations on streamflow. Site water balances indicated that the average annual actual evapotranspiration was 87–93% of precipitation for pasture catchments and 102–108% of precipitation for plantation catchments. Actual evapotranspiration greater than precipitation at the plantations was attributed to uptake of groundwater by the root system in parts of the catchments. Thus, change to groundwater storage is a critical component in the water balance. Actual evapotranspiration from pasture catchments was higher than previously estimated from global pasture and cropping data, instead matching global precipitation versus actual evapotranspiration curves for treed catchments

Nitrogen supply, rotation and variety are critical predictors of the water use efficiency of wheat in grower's paddocks in Victoria

ictorian grain crops rarely reach their water limited yield potential. Few Australian studies have systematically ranked the relative importance of various genetic, environmental and grower management attributes on this gap under commercial conditions. Wheat crops growing in 136 paddocks in the Victorian Mallee, Wimmera and High Rainfall Zone were monitored from 2013 to 2016 to assess the relative importance of 53 environmental, genetic/cultivar and grower management attributes on water use efficiency (WUE). Growing season rainfall ranged from Decile 1 to 10 and grain yields from 0 to nearly 10 t/ha in the study and WUE averaged 11.5 kg grain/mm/ha. Conditional forest analysis identified grower management as the key determinant of WUE, with N supply, previous crop rotation and variety as the most important factors. The results indicate the need to focus future extension messages and research priorities on N management, rotation and variety selection to maximise WUE