A simple and efficient method was developed to determine soil macroporosity and hydraulic conductivity for dual-porosity models from measurements of unconfined infiltration rates. The utility of this method was demonstrated by analyzing unconfined infiltration tests conducted with a tension infiltrometer at ponded conditions and at negative 3, 6, and 15 cm of water-supply pressure. The conductivity of soil macropores (pores > 1 mm in diameter) was 3.6 times the conductivity of the soil matrix. This contrast in the magnitudes of the hydraulic conductivity may justify the use of dual-porosity models of water flow and solute transport. Positive but small correlation between soil macroporosity and hydraulic conductivity of the soil matrix was identified. Soil macroporosity remained constant near the surface but it decreased with soil depth. The narrow range of 0 to −15 cm of water pressure may govern water flow and contaminant transport under field conditions because of the rapid decrease of conductivity with...

A small body of knowledge exists on the root water uptake (RWU) and evapotranspiration in humid environments having a mixture of natural vegetative cover. In this paper, we assess the impacts of atmospheric conditions and land cover on RWU from a natural vegetative cover. An intensive field investigation was carried out to monitor water table fluctuations along two flow transects comprising an upland grass area and a lowland riparian zone. Calibration and validation of the soil hydraulic parameters using the two-dimensional variably saturated ground water flow model, HYDRUS-2D, confirms the reliability of the model to simulate satisfactorily the large-scale daily fluctuation of RWU. Simulation results revealed that the actual RWU during the wet season is about 40% higher than RWU in the dry season due to high water table levels and temperatures prevailing throughout the wet season. Simulation results using HYDRUS-2D, which was modified to accommodate variable surface boundary conditions and heterogeneous ...

Stormwater biofiltration systems can include a submerged layer containing a solid organic carbon substrate, such as wood chips, to promote biological denitrification. The objective of this research was to evaluate the effect of biofilter depth and dispersion on the performance of submerged wood-chip biofilters. Tracer and reactive column studies were performed on biofilters with varying depths (30, 45, and 60 cm), which were evaluated with stormwater at varying hydraulic retention times. The results from every tracer test (n=9) indicated that dispersion affected constituent transport. Shorter columns and/or higher hydraulic retention times resulted in dispersion dominated transport, which contributed to greater constituent bypass through the biofilters. Even though a wood-chip biofilter is considered a porous medium, dispersivity values in this layer were an order of magnitude larger than dispersivities of natural porous media (e.g., sand). These results provide evidence that less media volume is ...

The capillary length (λ_s) and time (t_s) are dynamic scalars that emerge routinely in the infiltration problem when gravitational and pressure gradients forces are involved. During drainage, however, capillary gradients oppose gravity and retain soil moisture close to surface. In this case, the pull of capillary gradients increases with drainage time and offsets gravity resulting in a quasi‐hydrostatic pressure distribution and negligibly small drainage flux in the profile. In this paper, it is proposed to anchor the dynamic concept of field capacity—the attainment of a small negligible drainage flux—in the physics of soil moisture redistribution as influenced by gravity and capillary forces. Similar to infiltration, this dynamic approach grounds the concept of field capacity in soil hydrology and allows its estimation from readily measured intrinsic physical characteristics such as λ_s, t_s, and K_s. Finally, we exploit an analytical solution by Broadbridge and White (1988, https://doi.org/10.1029/WR024i001p00145) to track the drainage front as soil water redistributes in an initially saturated soil profile. While initially large, the downward migrating drainage front decelerates with time reaching near steady state condition at t ≈ 1,000t_s. Quasi‐hydrostatic pressure matric head and water content profiles develop above the drainage front.