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ItemThe behavior of stratified pools in the Wimmera River, AustraliaWestern, AW ; ONeill, IC ; Hughes, RL ; Nolan, JB (AMER GEOPHYSICAL UNION, 1996-10-01)Numerous inland Australian streams contain density-stratified or saline pools, which are usually located on channel bends. Saline pools consist of a layer of saline water underlying a layer of fresh water. Saline pools generally form as a result of saline groundwater seeping into the stream and collecting in scour depressions during periods of low flow. Inflows of saline river water can also collect in scour depressions. Field and laboratory investigations of saline pool mixing by overflowing fresh water reveal that mixing depends on a balance between interfacial shear and buoyancy forces acting on a thin dense layer flowing up the downstream slope of the scour depression, and on the bend sharpness. Convection associated with surface cooling also causes mixing. A model for saline pools formed by groundwater inflows and mixed by fresh overflows is proposed and applied to several saline pools in the Wimmera River.
ItemPreferred states in spatial soil moisture patterns: Local and nonlocal controlsGrayson, RB ; Western, AW ; Chiew, FHS ; Bloschl, G (AMER GEOPHYSICAL UNION, 1997-12-01)In this paper we develop a conceptual and observational case in which soil water patterns in temperate regions of Australia switch between two preferred states. The wet state is dominated by lateral water movement through both surface and subsurface paths, with catchment terrain leading to organization of wet areas along drainage lines. We denote this as nonlocal control. The dry state is dominated by vertical fluxes, with soil properties and only local terrain (areas of high convergence) influencing spatial patterns. We denote this as local control. The switch is described in terms of the dominance of lateral over vertical water fluxes and vice versa. When evapotranspiration exceeds rainfall, the soil dries to the point where hydraulic conductivity is low and any rainfall that occurs essentially wets up the soil uniformly and is evapotranspired before any significant lateral redistribution takes place. As evapotranspiration decreases and/or rainfall increases, areas of high local convergence become wet, and runoff that s generated moves downslope rapidly wetting up the drainage lines. In the wet to dry transitional period a rapid increase in potential evapotranspiration (and possibly a decrease in rainfall) causes drying of the soil and 'shutting down' of lateral flow Vertical fluxes dominate and the 'dry' pattern is established. Three data sets from two catchments are presented to support the notion of preferred states in soil moisture, and the results of a modeling exercise on catchments from a range of climatic conditions illustrate that the conclusions from the field studies may apply to other areas. The implications for hydrological modeling are discussed in relation to methods for establishing antecedent moisture conditions for event models, for distribution models, and for spatially distributing bulk estimates of catchment soil moisture using indices.
ItemThe Tarrawarra data set: Soil moisture patterns, soil characteristics, and hydrological flux measurementsWestern, AW ; Grayson, RB (AMER GEOPHYSICAL UNION, 1998-10-01)Experiments investigating the spatial variability of soil moisture conducted in the 10.5 ha Tarrawarra catchment, southeastern Australia, are described. The resulting data include high-resolution soil moisture maps (over 10,000 point measurements at up to 2060 sites), information from 125 soil cores, over 1000 soil moisture profiles from 20 sites, 2500 water level measurements from 74 piezometers, surface roughness and vegetation measurements, meteorological and hydrological flux measurements, and topographic survey data. These experiments required a major commitment of resources including 250 person days in the field, with a further 100 person days in the laboratory preparing for field trips and checking and collating data. These data are available on the World Wide Web (http://www.civag.unimelb.edu.au/data/).
ItemObserved spatial organization of soil moisture and its relation to terrain indicesWestern, AW ; Grayson, RB ; Bloschl, G ; Willgoose, GR ; McMahon, TA (AMER GEOPHYSICAL UNION, 1999-03-01)The degree of spatial organization of soil moisture, and the ability of terrain attributes to predict that organization was analyzed. The measured soil moisture patterns exhibited a high degree of organization during wet periods due to surface and subsurface lateral redistribution of water. The shape of the distribution function of soil moisture changed seasonally and was influenced by the presence of spatial organization. A correlation analysis found that ln(a), where a is the specific unslope area, was the best univariate spatial predictor of soil moisture during wet periods and up to 22% during dry periods.