Uichiro Matsubayashi

A method for determining air–water interfacial area in variably saturated porous media

Abstract The air–water interfacial area (a0) was estimated using the surfactant adsorption concept in unsaturated porous media. A column composed of several stainless steel rings was used to carry out saturated/unsaturated experiments in three glass beads media (0.25, 0.50 and 0.75 mm) using sodium dodecylbenzene sulfonate (SDBS) and NaCl as the reactive and nonreactive tracers, respectively. SDBS sorption onto the glass bead surfaces was determined by miscible displacement and was found to be zero. The medium was made unsaturated step by step with recycled surfactant solution from saturated conditions to achieve homogeneous surfactant concentration in the liquid phase. This also helped to form a stable air–water interface and pressure–saturation relationship inside the soil column. After establishing equilibrium in the system, the rings were dismantled and total surfactant mass from each ring was extracted and analyzed by the two-phase Hyamine 1622 titration method. The number of surfactant monomers adsorbed onto the air–water interface per unit area was determined by Gibbs isotherm. The air–water interfacial area was then estimated based on the amount of SDBS onto the air–water interface divided by the number of SDBS monomers per unit area. The results obtained by this technique for different porous media revealed that the estimated a0 followed the general concept of a decreasing trend with increasing Sw and grain size. Surface areas of the solid, obtained by extrapolating the curves from the experimental data (a0∼Sw) at Sw=0, were also found closer to the areas calculated by the geometrical method.

Hydrograph separation and flow analysis by specific electrical conductance of water

The use of the specific electrical conductance of water to separate flow hydrographs into event (new) and pre-event (old) waters has been studied through the analysis of background events and flow process phenomena in a study basin. Runoff ratio analysis shows that background events, such as periods of no rainfall or no flow, influence the percentage of old water occurring in the hydrograph. Comparison of one result with a separation using δ18O as tracer shows that the separation model of Matsubayashi et al. (1991) produces reasonable results. The analysis of the conductance-discharge (C-Q) relationship showed that there were fast flows in a majority of the wet season hydrographs.

Characteristics of the dispersion coefficient in miscible displacement through a glass beads medium

Abstract The importance of understanding the process of solute transport in soils is well documented in several fields of study, including water supply, environmental protection and agriculture. However, researchers still disagree on some topics, especially the nature of the unsaturated dispersion coefficient. Miscible displacement experiments, carried out using glass beads as the porous medium show that while the saturated dispersion coefficient increases linearly with pore water velocity, under unsaturated conditions, the dispersion coefficient increases linearly but more rapidly with pore water velocity up to a limiting moisture content. Beyond this moisture content, the unsaturated dispersion coefficient decreases and approaches that of the saturated condition. These phenomena are discussed in relation to variation in pore water velocity and the mixing length of flow paths inside the porous medium. Mixing length in this sense is characteristic of the porous medium within which the concentration of the solution conforms to the surrounding concentration. The dispersion coefficient is expressed as the product of mixing length and standard deviation of the pore water velocity which is estimated from the ψ-θ and K -θ relationships. The mixing lengths are found to be almost constant (about 0.23 cm) in the lower moisture content range (0.16–0.27 cm 3 cm −3 ), but decrease at moisture contents greater than 0.27 cm 3 cm −3 . Mixing lengths are also smaller in saturated than in unsaturated conditions. Despite the apparent increase in pore water velocity and its variance at higher moisture content, the decrease in the dispersion coefficient can be attributed to a decrease in the mixing length. This study shows that the dispersion phenomenon, both in saturated and unsaturated conditions, can be described successfully using mixing length theory.

Correlation of Optimal Salinity as Function of Water/Oil Ratio in Brine/Surfactant/ Alcohol/Oil System

Results of investigation on the effects of water/oil ratio (WOR) in groundwater on phase behavior of the system containing brine, an anionic surfactant, alcohols and different oils were presented. The results showed that the effect of WOR and salinity on the phase behavior of this system is analogous. Increasing the WOR also changes the system from Winsor I → Winsor III to Winsor II. The higher the WOR, the lower the salinity required to produce the middle-phase microemulsion, but the narrower the salinity range for the three-phase region. The WOR term was correlated with the function of optimal salinity (S*) through the coefficient of WOR (k a ). This correlation can be used to select the surfactant/alcohol formulation potentially effective for aquifer remediation.

Estimation of Air-Water Interfacial Area in Unsaturated Porous Medium: A New Experimental Approach

Air-water interfacial area (a 0 ) was estimated using a surfactant (surface-active agent) adsorption concept in unsaturated porous medium by a new experimental technique. Sodium dodecylbenzene sulfonate (SDBS) was selected as anionic surfactant and a glass bead of size 425–600μm (d 50 =0.50mm) was chosen as the porous medium. Sorption of surfactant onto the solid surfaces was evaluated by miscible displacement under water saturated conditions using nonreactive NaCl and reactive SDBS, and was found to be zero for the glass bead surfaces. The number of surfactant monomers adsorbed onto the air-water interface per unit area was determined by Gibbs isotherm. The main experiment was done in a column composed of several rings where the medium was made unsaturated step by step from the saturated condition to allow the surfactant monomers to be adsorbed at the air-water interface in a regular fashion. After the column reached equilibrium and became homogeneous, the rings were dismantled and the total amount of surfactant in each ring as well as the surfactant concentration in the aqueous phase was determined by the two-phase Hyamine 1622 titration method. Finally, based on these estimated parameters, the air-water interfacial area was determined and the values obtained were found to support the general concept of decreasing a 0 with increasing water saturation, S w . The surface area of the solid (75cm2/cm3), estimated from extrapolation of the experimental data (a 0 ~S w ) at S w =0, was found to be close to the geometrically calculated area (76cm2/cm3), which proves the validity of the method.

ON THE EFFECT OF THE GEOGRAPHICAL FEATURES TO THE RUN-OFF IN MOUNTAINOUS FOREST AREA

Understanding of the terrain effects on hillslope runoff processes is important to formulate the accurate runoff model. In this study, observations were, therefore, made to understand the spatial distribution of volumetric water contents, thickness and hydraulic conductivities of various soil layers, and response of volumetric water contents considering both concave and convex configurations of land surface in Kanedaira catchment. Observations showed that the response of volumetric water content of all points in concave part and surface of the convex part were similar to runoff response. However concave configuration had produced faster runoff than that by convex one.