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Australian National University (1996)

The spatial variability of groundwater recharge at the local scale

Lane, Patrick Norman James

Titre : The spatial variability of groundwater recharge at the local scale

Auteur : Lane, Patrick Norman James

Université de soutenance : Australian National University

Grade : Doctor of Philosophy 1996

Résumé partiel
Traditionally, groundwater recharge has been thought to be greatest on ridge areas with thin, coarse soils. However well tested hillslope hydrologic theory shows that redistributive processes within the vadose zone act to concentrate water downslope of ridges. This water is potential recharge. If soil hydraulic properties and vegetation are uniform, topography is the most important variable in hillslope water movement. Surface and subsurface flow convergence driven by hillslope geometry is of particular significance. The aim of this study was to test the hypothesis that the spatial and temporal variability of recharge is controlled by hills lope hydrologic processes driven by topographic gradients. Two subcatchments were instrumented to observe soil water pathways and fluxes. These sub catchments, Begalia A (5.3 ha) and B (9.9 ha), displayed contrasting topographic geometries. A was characterised by long, relatively planar slopes, and B by shorter, steeper converging slopes. Hillslope hydrologic theory predicts a greater incidence of flow convergence and therefore saturated or near saturated conditions in the B subcatchment. Four experimental plots were constructed in each subcatchment. Soil moisture dynamics, surface runoff generation, lateral and vertical subsurface flows, evapotranspiration, groundwater responses and recharge were measured or estimated. The experimental data inferred there were different recharge mechanisms operating in the two subcatchments. The B plots all recorded vertical saturated fluxes from the soil profile into the aquifer bearing material throughout the four to five month wet period in the two measurement years. In contrast, such flows were observed at only one plot AA, in the A subcatchment. This plot was situated near a ridge crest where surface runoff and groundwater responses clearly showed the existence of a macropore system

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