Drying front in a sloping aquifier: nonlinear effects

The profiles for the water table height h(x, t) in a shallow sloping aquifer are reexamined with a solution of the nonlinear Boussinesq equation. We demonstrate that the previous anomaly first reported by Brutsaert [1994] that the point at which the water table h first becomes zero at x = L at time t = t c remains fixed at this point for all times t &gt; t c is actually a result of the linearization of the Boussinesq equation and not, as previously suggested [ Brutsaert, 1994 ; Verhoest and Troch, 2000 ], a result of the Dupuit assumption. Rather, by examination of the nonlinear Boussinesq equation the drying front, i.e., the point x f at which h is zero for times t &ge; t c , actually recedes downslope as physically expected. This points out that the linear Boussinesq equation should be used carefully when a zero depth is obtained as the concept of an &ldquo;average&rdquo; depth loses meaning at that time.<br /

Estimation of wet surface evaporation from sensible heat flux measurements

A new method is proposed to estimate wet surface evaporation by means of measurements of sensible heat flux and of air temperature, relative humidity, and wind speed at one level only. This formulation is made possible by the linearization of the Bowen ratio, a common assumption in other methods, such as Penman’s model and its derivatives. The method will be useful in those cases where the sensible heat flux is more reliably acquired at field scales than the net radiation and the ground heat flux, which are needed in many operational methods because of energy budget considerations. Indeed, the ground heat flux is a notoriously difficult variable to measure on wet surfaces, such as lakes or wetlands, especially at the appropriate length scales, whereas sensible heat flux can be obtained from standard temperature variance methods or other instruments such as scintillometers. The proposed method was tested with field experimental data taken over Lake Geneva in Switzerland, where it showed excellent agreement with evaporation rates measured using eddy covariance techniques

A concise parameterization of the hydraulic conductivity of unsaturated soils

Abstract The parameter n in the well-known expression for hydraulic conductivity K K 0 S n e (where K 0 is its value at satiation and S e the eective saturation) is determined as a function of the exponent in the power form of the soil±water retention relationship. The result is validated with an extensive experimental database comprising some 43 soils, collected by Mualem.

Is Mongolia's groundwater increasing or decreasing? The case of the Kherlen River basin / Les eaux souterraines de Mongolie s'accroissent ou décroissent-elles? Cas du bassin versant la Rivière Kherlen

Abstract The average area-wide underground terrestrial water storage in the Kherlen River basin, a relatively pristine area in eastern Mongolia where human impacts have been minimal so far, has undergone a marked decline in the past decade; nevertheless, there is no evidence that any unusual or systematic long-term storage change has taken place over the past half century. This result follows from an analysis of daily streamflow records measured at three gauging stations on the river, namely at Baganuur, Undurkhaan and Choibalsaan. This absence of a clear trend in long-term groundwater storage is generally consistent with findings in previous studies regarding trends of other components of the hydrological cycle in Mongolia and neighbouring regions at similar latitudes, namely in northern Inner Mongolia to the east and Xinjiang to the west, and even further in the same direction in the adjacent areas of southern Central Asia of the Russian Federation and of Kazakhstan