摘要:

The rate of evapotranspiration from thinned and unthinned stands of Douglas fir was measured using energy and water balance methods. At high values of soil water storage in the root zone the evapotranspiration rate was approximately 80% of the equilibrium evaporation rate. Below a critical value of soil water storage the ratio of the evapotranspiration rate to the equilibrium evaporation rate (E/Eeq) tended to decrease linearly with decreasing soil water storage. The critical values of soil water storage in the root zone were 11.8 and 8.3 cm for the thinned and unthinned stand, respectively. Below these critical storage values, there was approximately 3.5 cm of water remaining in both root zones that was extractable by the trees. The relationship betweenE/Eeqand the fraction of extractable water in the root zone for both stands was very similar for sunny days. In this relationship,E/Eeqbegan to decrease when there was approximately 40% of the extractable water remaining in the root zones of both stands.

ISSN:0043-1397    

DOI:10.1029/WR015i001p00164

年代:1979

数据来源: WILEY

摘要:

The Río Blanco crosses a coastal plain south of Veracruz in Mexico, and discharge measurements suggested that the river was recharging the groundwater system. The estimated evapotranspiration is very close to the mean annual precipitation, so estimates of effective recharge by infiltration of precipitation are very imprecise. The variations in the stable isotopic composition (D and18O) of surface and groundwater samples are used to estimate the relative importance of the two sources of recharge to the groundwater system. The data indicate that recharge by infiltration of precipitation is the dominant source of recharge. This conclusion is based upon measurements from individual wells and also on the base flow of rivers originating in the plain, thus providing an estimate integrated over the area drained by the rivers

ISSN:0043-1397    

DOI:10.1029/WR015i001p00171

年代:1979

数据来源: WILEY

摘要:

A numerical model based on the equation describing the unsteady groundwater flow on impervious sloping bedrock has been herewith formulated. The case which has been studied concerns the groundwater flow from one canal to another with a sudden rising of the canal level as an upstream boundary condition, while the downstream level remains constant. Initially, at timet= 0, both levels are equal. The numerical model uses the finite element technique with Galerkin's method. The stability and accuracy of the method have been proven by comparison of numerical results with the Crank‐Nicolson scheme. The algorithm developed for the finite element technique gives the same results as the one for the finite difference scheme. The effect of inclination of lower impervious boundary on outflow rate has been studie

ISSN:0043-1397    

DOI:10.1029/WR015i001p00176

年代:1979

数据来源: WILEY

摘要:

Nine different methods of weighting interblock hydraulic conductivity values used for modeling one‐dimensional water transfer in homogeneous unsaturated soil are tested for their influence upon the accuracy of the finite difference solution. On the basis of these results the most suitable weighting relation is selected. In a first stage the numerical results obtained by the models using the various conductivity weighting formulas are compared with the quasi‐analytical solution developed by Philip for a clay soil. In a second stage the models are used to simulate a laboratory experiment carried out on a sandy soil. In both cases, rather drastic boundary conditions are applied. It appears clearly from these tests that the weighting errors are of critical influence on the accuracy of solution. As proposed in this note, the geometric mean taken over two adjacent hydraulic conductivity values is the only weighting method that generates little weighting error. The latter weighting relation is found to be preferable in terms of flexibility, precision, and feasibil

ISSN:0043-1397    

DOI:10.1029/WR015i001p00181

年代:1979

数据来源: WILEY

ISSN:0043-1397    

DOI:10.1029/WR015i001p00189

年代:1979

数据来源: WILEY

ISSN:0043-1397    

DOI:10.1029/WR015i001p00191

年代:1979

数据来源: WILEY