Simultaneous Solute and Water Transfer for an Unsaturated Soil

Abstract

The simultaneous transfer of solute and water during infiltration was studied both in the field and numerically. An apparent diffusion coefficient of about 0.07 cm2/min provided maximum solute concentration values agreeable with field data over a 17‐hour period. The advance of a solute front introduced as irrigation water is shown to be nearly independent of the initial soil moisture content but highly dependent on the moisture content maintained at the soil surface during infiltration.

In Situ Field Testing of Processes

“…Note that the core top was wet to 20 mm when the experiment was ended, although the moisture front is shown at the 18 mm location in Panel (b) of Figure 6-63. This observation of a nonreactive solute front lagging behind the moisture front agrees with the findings in moist soils (Warrick et al 1971[DIRS 106150], pp. 1216, 1221Ghuman and Prihar 1980 [DIRS 106099], pp.…”

Vadose zone lag time and potential 21st century climate change effects on spatially distributed groundwater recharge in the semi-arid Nebraska Sand Hills

“…If we assume that the movement of moisture through the vadose zone is vertical (where the vertical coordinate z increases downward), gravitydriven, and steady, such that a unit hydraulic gradient exists (∂H/∂z = −1), as is conventionally specified (e.g., Rasmussen, 2001;Sisson et al, 1980;Warrick et al, 1971), we obtain the following expression:…”

“…Studies of Warrick et al, 1971, Wilson, 1974and Wilson and Gelhar, 1981, and Rasmussen (2001 showed that the pressure-based (kinematic) velocity exceeds the tracer-based (advective) velocity by a factor in excess of two to four, depending on moisture content, choice of conductivity-water content relation and solute transport parameters. The tracer-based velocity is greater than Darcy's velocity as follows from Eq.…”

“…This velocity is used if one is interested in the timing of arrival of capillary pressure changes at the water table resulting from the changes in pressure and pressure gradients at the land surface (Philip, 1957;Warrick et al, 1971;Wilson, 1974), referred to as the kinematic wave approximation (Sisson et al, 1980) or kinematic velocity (Rasmussen, 2001). The pressure-based velocity is the most relevant when calculating lag times associated with GR.…”

“…The simplified approach to modeling the vertical movement of moisture through the vadose zone has been investigated by Philip, 1957, Warrick et al, 1971, Wilson, 1974, Sisson et al, 1980, Wilson and Gelhar, 1981, Smith, 1983and Rasmussen, 2001, and Cook et al (2003, among others. In contrast to tracer-based advective velocity, these studies calculate lag times using the velocity of the capillary pressure wave response due to a small perturbation of hydrologic conditions in a uniformly wetted soil profile.…”