摘要:

A procedure is presented for calculating seepage from a stream due to uptake of groundwater by vegetation or evaporation from soil in the floodplain. The calculation requires that the relation between evapotranspiration rate and water table depth be known. If these relations are available for a given floodplain before and after removal of phreatophytes, the reduction in seepage losses from the stream due to phreatophyte removal can be computed. To simplify the calculation process, the curves relating evapotranspiration rate and water table depth, which are generally sigmoid, can be approximated by step functions of the same area. Potential water savings by phreatophyte control are calculated for step functions that are representative of deep‐rooted vegetation, shallow‐rooted vegetation, and bare soil. In addition to the depth from which groundwater can be evaporated before and after phreatophyte removal the water savings are affected by the vertical distance between the water level in the stream and the floodpl

ISSN:0043-1397    

DOI:10.1029/WR011i001p00096

年代:1975

数据来源: WILEY

摘要:

To estimate cheaply the infiltration/runoff of typically unsteady rainfall events for purposes of watershed modeling, a method known as ‘time compression’ has been tested against hysteretic Darcy computations. This method assumes that for a given soil the maximum infiltration rate is simply a function of the cumulative infiltration, regardless of the rainfall versus time history. Hysteretic characteristics from soils measured by Topp (1971) were employed in the Darcian calculations. The appraisal proved generally encouraging for application of this approximation to watershed modeling. The maximum infiltration rate was uniformly underestimated to a moderate degree in the early minutes of a downpour commencing late in an unsteady ev

ISSN:0043-1397    

DOI:10.1029/WR011i001p00102

年代:1975

数据来源: WILEY

摘要:

A theory of water movement in the combined mole‐tile drain system based on the transient state condition was developed. Two general equations were derived to describe the height of the water table at any location in the system at any elapsed time after the drainage process begins. One of the equations is applicable for the stage in which the water table is above the mole drains, and the other equation is for the stage in which the water table falls below the mole drains. The two general equations were simplified for the point located at midpoint between the tile drains and mole drains in the system. In the derivation, assumptions regarding the flow condition of groundwater and shape of the water table profile at certain boundaries were made. Field experiments were then conducted, and the test data were used in verifying the equation for the first stage. A reasonably good agreement between the theoretical analysis and field data was obtained for this type of researc

ISSN:0043-1397    

DOI:10.1029/WR011i001p00111

年代:1975

数据来源: WILEY

摘要:

A deterministic hydrologic watershed model that simulates the watershed discharge and soil moisture status continuously throughout the crop season was developed for drainage watersheds with depressional storage. The model simulates the processes of interception, surface storage, infiltration, surface runoff, soil profile storage, percolation to the water table, subsurface tile drainage, soil moisture redistribution, evapotranspiration, and routing through depressions, tile mains, and the drainage ditch. The resulting outputs are daily evapotranspiration, soil moisture status in the crop root zone, and watershed discharge. The model simulated the watershed discharge and soil moisture status of the 24‐mi2East Fork Hardin Creek watershed near Jefferson, Iowa, for the 1964 crop season as well as could be expected with the input data that were available. Discrepancies between the measured discharge and the predicted discharge were in part due to spatial variations in precipitation over the watershed, which were not accounted for in the model input dat

ISSN:0043-1397    

DOI:10.1029/WR011i001p00120

年代:1975

数据来源: WILEY

摘要:

A numerical model is described for solving axisymmetric infiltration problems. The model uses saturation‐capillary pressure data and a modified Burdine equation to develop reasonable estimates of relative hydraulic conductivity. A specially designed infiltrometer and a field data collection system, which provide infiltration capacity, saturation‐time, and saturation‐capillary pressure data, are also described. The numerical solutions were fitted to the field data to define the hydraulic properties of the soil. Close agreement was found between the numerical model solutions and the field measurements for two sites on the Reynolds Creek Experimental Watershed in southwestern Idaho. A feasible method was developed for determining the hydraulic properties of surface soils under natural condi

ISSN:0043-1397    

DOI:10.1029/WR011i001p00127

年代:1975

数据来源: WILEY

摘要:

Air pressures in the unsaturated soil and hydraulic heads beneath a shallow water table were measured during border irrigations. Air pressures rose during the irrigation, thereby increasing the hydraulic heads. The increased hydraulic heads were not uniformly distributed under the border strip but varied in the cross‐slope and with‐slope directions and thus caused groundwater redistribution. Cross‐slope and with‐slope variations in air pressures also caused variations in infiltration and groundwater r

ISSN:0043-1397    

DOI:10.1029/WR011i001p00139

年代:1975

数据来源: WILEY

摘要:

The differential equation derived by Childs for groundwater flow over a sloping bed, the streamlines being assumed to be parallel to the slope, is integrated for the case of ditches and uniform rainfall. Expressions are obtained for the maximum vertical water table height, the location of this maximum and of the watershed, and the water table shape. Calculated water table heights are in much better agreement with previously published experimental data than those calculated from an earlier theory based on the assumption that streamlines are horizontal. Thus Childs' revised assumption is confirmed. An approximate solution for the form of the water table under small rainfall rates is also derived.

ISSN:0043-1397    

DOI:10.1029/WR011i001p00144

年代:1975

数据来源: WILEY

摘要:

New equations are given, based on an extended theory, that take into account the following factors: the compressibility and anisotropy of the main aquifer; the partial penetration of the abstraction well; the depth at which the drawdown in an observation well is measured; the existence of a low‐permeability layer, hereafter called ‘the aquitard,’ above the aquifer; and the saturated and unsaturated zones above the water table. A practical method of evaluating the formation constants for an aquifer from pumping test data is fully discussed. Type curves based on the new equations are used to analyze data from a pumping test in the thick Bunter sandstone formation of Shropshire (Great Britain). A correction for the water derived from storage within the abstraction well is found to be nece

ISSN:0043-1397    

DOI:10.1029/WR011i001p00148

年代:1975

数据来源: WILEY

摘要:

In some situations associated with geothermal activity, groundwater motions are affected by convection currents due to large temperature gradients. In such cases, usually saline hot water is located in the deep layers of the aquifer from which salt and heat are transferred to the upper layers. In part 1 of this study the parameters of the two‐dimensional flow field stability were determined. In this paper, further analysis of the phenomenon in three dimensions is presented. It was found that the convection cells have the shape of rolls whose axes are perpendicular to the steady state flow velocity. However, there is also a possibility of overstability of the flow field caused by rolls whose axes are parallel to the steady state velocity. The parameters of these two kinds of instability were determined in this stud

ISSN:0043-1397    

DOI:10.1029/WR011i001p00154

年代:1975

数据来源: WILEY

摘要:

An analytic solution is derived yielding the potential distribution in a bounded confined aquifer pumped by a well that is radially extended at the bottom. An exact solution for the rate of discharge is found by which the effect of local radial extension on the increase of the pumping rate is studied. Solutions have been evaluated numerically, and the results are presented graphically in terms of dimensionless parameters. The results show that production rate is doubled in some cases by extending the bottom of the well.

ISSN:0043-1397    

DOI:10.1029/WR011i001p00159

年代:1975

数据来源: WILEY