Vadose zone

About: Vadose zone is a research topic. Over the lifetime, 5781 publications have been published within this topic receiving 130825 citations. The topic is also known as: unsaturated zone.

Numerical Analysis of Coupled Water, Vapor, and Heat Transport in the Vadose Zone

Abstract: Vapor movement is often an important part in the total water flux in the vadose zone of arid or semiarid regions because the soil moisture is relatively low. The two major objectives of this study were to develop a numerical model in the HYDRUS-1D code that (i) solves the coupled equations governing liquid water, water vapor, and heat transport, together with the surface water and energy balance, and (ii) provides flexibility in accommodating various types of meteorological information to solve the surface energy balance. The code considers the movement of liquid water and water vapor in the subsurface to be driven by both pressure head and temperature gradients. The heat transport module considers movement of soil heat by conduction, convection of sensible heat by liquid water flow, transfer of latent heat by diffusion of water vapor, and transfer of sensible heat by diffusion of water vapor. The modifications allow a very flexible way of using various types of meteorological information at the soil–atmosphere interface for evaluating the surface water and energy balance. The coupled model was evaluated using field soil temperature and water content data collected at a field site. We demonstrate the use of standard daily meteorological variables in generating diurnal changes in these variables and their subsequent use for calculating continuous changes in water contents and temperatures in the soil profile. Simulated temperatures and water contents were in good agreement with measured values. Analyses of the distributions of the liquid and vapor fluxes vs. depth showed that soil water dynamics are strongly associated with the soil temperature regime.

Hydrologic response of a steep, unchanneled valley to natural and applied rainfall

Abstract: Observations from natural rain storms and sprinkling experiments at a steep zero-order catchment in the Oregon Coast Range demonstrate the importance offlow through near-surface bedrock on runoff generation and pore pressure development in shallow colluvial soils. Sprinkling experiments, involving irrigation of the entire 860 m 2 catchment at average intensities of 1.5 and 3.0 mm/h, permitted detailed observation of runoff and the development of subsurface saturation under controlled conditions. A weir installed to collectflow through the colluvium at the base of the catchment recovered runoff equal to one third to one half of the precipitation rate during quasi-steady irrigation. Three key observations demonstrate that a significant proportion of storm runoffflows through near-surface bedrock and illustrate the importance of shallow bedrockflow in pore pressure development in the overlying colluvial soil: (1) greater discharge recovery during both the experiments and natural rainfall at a weir installed approximately 15 m downslope of the weir at the base of the catchment, (2) spatially discontinuous patterns of positive pressure head in the colluvium during steady sprinkling, and (3) local development of upward head gradients associated withflow from weathered rock into the overlying colluvium during high-intensity rainfall. Data from natural storms also show that smaller storms produce no significant runoff or piezometric response and point to a critical intensity-duration rainfall to overcome vadose zone storage. Together these observations highlight the role of interaction betweenflow in colluvium and near- surface bedrock in governing patterns of soil saturation, runoff production, and positive pore pressures.