Herman Bouwer

Bio: Herman Bouwer is an academic researcher. The author has contributed to research in topics: Water table & Aquifer. The author has an hindex of 6, co-authored 7 publications receiving 1463 citations.

A slug test for determining hydraulic conductivity of unconfined aquifers with completely or partially penetrating wells

Abstract: ~. help ed. steady Proc. With the slug test the hydraulic conductivity or transmissibility of an aquifer is determined from the rate of rise of the water level in a well after a certain volume or 'slug' of water is suddenly removed from the welL. The slug test is simpler and quicker than the Theis pumping test because observation wells and pumping the well are not needed. With the slug test the portion of the aquifer 'sampled' for hydraulic conductivity is smaller than that for the pumping test even though with the latter, most of the head loss also occurs within a relatively small distance of the pumped well and the resulting transmissibility primarily reflects the aquifer conditions near the pumped welL. Essentially instantaneous lowering of the water level in a well can be achieved by quickly removing water with a bailer or by partially or completely submerging an object in the water, letting the water level reach equilibrium, and then quickly removing the object. If the aquifer is very permeable, the water level in the well may rise very rapidly. Such rapid rises can be measured with sensitive pressure transducers and fast-response strip chart recorders or x-y plotters. Also it may be possible to isolate portions of the perforated or screened section of the well with special packers for the slug test. This not only reduces the inflow and hence the rate of rise of the water level in the well, but it also makes it possible to determine the vertical distribution of the hydraulic conductivity. Special packer techniques may have to be developed to obtain a good seal, especially for rough casings or perforations. Effective sealing may be achieved with relatively long sections of inflatable stoppers or tubing. The use of long sections of these materials would also reduce leakage flow from the rest of the well to the isolated section between packers. This flow can occur through gravel envelopes or other permeable zones surrounding the casing. Sections of inflatable tubing may have to be long enough to block off the entire part of the well not used for the slug test. High inflation pressures should be used to minimize volume changes in the tubing due to changing water pressures in the isolated section when the head is lowered. So far, solutions for the slug test have been developed only for completely penetrating wells in confined aquifers. Cooper et at. (1967) derived an equation for the rise or fall of the water level in a well after sudden lowering or raising, respectively. Their equation was based on nonsteady flow to a pumped,

Rapid field measurement of air entry value and hydraulic conductivity of soil as significant parameters in flow system analysis

Abstract: Field measurements of air entry value and hydraulic conductivity of soil are obtained with a covered cylinder infiltrometer equipped with standpipe and vacuum gage. Tests are normally completed in approximately 30 minutes. The resulting data are used to construct step functions relating hydraulic conductivity to (negative) soil water pressure for sorption and desorption. These functions may be used as simplified hydraulic conductivity characteristics to include negative-pressure flow in the analysis of subsurface water movement. Several field and laboratory studies demonstrate the validity of the concepts and the technique.

Predicting reduction in water losses from open channels by phreatophyte control

Abstract: 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 floodplain.

Delayed aquifer yield as a phenomenon of delayed air entry

Abstract: Delayed release of pore water from a pumped, unconfined aquifer is treated as a situation of restricted air movement in the vadose zone due to layers of high water content. This restricted movement produces below-atmospheric pressures in the pore air above the water table, which cause the water table initially to drop faster than the dewatered zone. The initial yield thus is less than the full specific yield, which develops after a certain water table drop. Equations are derived that relate delayed yield to air entry value and height above water table of saturated layers in the vadose zone. These equations agreed with results from a delayed yield experiment on a vertical soil column and produced ratios between initial and final yield that resembled those calculated by others from actual pumping tests. An axisymmetric flow system, simulated by interconnected jars with narrow standpipes, produced delayed yield drawdown curves that were amenable to Boulton's analysis.

Analyzing subsurface flow systems with electric analogs

Abstract: Subsurface movement of water in hydrologic or engineering systems can be analyzed with direct analogs. These are analogs that directly simulate the transmission and storage properties of the soil as relevant parameters in the water movement process. Principles and techniques for constructing and operating analogs include calculation of resistance and capacitance values for network analogs, simulation of fixed, free, and infinite boundaries, inclusion of unsaturated flow, solution of quasi-steady flow problems, analysis of diffusion-type flow systems, simulation of horizontal and vertical flow systems, instrumentation, and data conversion. Direct electric analogs are relatively simple to build and use, and they enable solution of flow systems not amenable to mathematical analysis. There is, however, a limit as to the complexity of flow systems that direct analogs can handle, and a point is reached, where digital computers are more appropriate.

A slug test for determining hydraulic conductivity of unconfined aquifers with completely or partially penetrating wells

Abstract: ~. help ed. steady Proc. With the slug test the hydraulic conductivity or transmissibility of an aquifer is determined from the rate of rise of the water level in a well after a certain volume or 'slug' of water is suddenly removed from the welL. The slug test is simpler and quicker than the Theis pumping test because observation wells and pumping the well are not needed. With the slug test the portion of the aquifer 'sampled' for hydraulic conductivity is smaller than that for the pumping test even though with the latter, most of the head loss also occurs within a relatively small distance of the pumped well and the resulting transmissibility primarily reflects the aquifer conditions near the pumped welL. Essentially instantaneous lowering of the water level in a well can be achieved by quickly removing water with a bailer or by partially or completely submerging an object in the water, letting the water level reach equilibrium, and then quickly removing the object. If the aquifer is very permeable, the water level in the well may rise very rapidly. Such rapid rises can be measured with sensitive pressure transducers and fast-response strip chart recorders or x-y plotters. Also it may be possible to isolate portions of the perforated or screened section of the well with special packers for the slug test. This not only reduces the inflow and hence the rate of rise of the water level in the well, but it also makes it possible to determine the vertical distribution of the hydraulic conductivity. Special packer techniques may have to be developed to obtain a good seal, especially for rough casings or perforations. Effective sealing may be achieved with relatively long sections of inflatable stoppers or tubing. The use of long sections of these materials would also reduce leakage flow from the rest of the well to the isolated section between packers. This flow can occur through gravel envelopes or other permeable zones surrounding the casing. Sections of inflatable tubing may have to be long enough to block off the entire part of the well not used for the slug test. High inflation pressures should be used to minimize volume changes in the tubing due to changing water pressures in the isolated section when the head is lowered. So far, solutions for the slug test have been developed only for completely penetrating wells in confined aquifers. Cooper et at. (1967) derived an equation for the rise or fall of the water level in a well after sudden lowering or raising, respectively. Their equation was based on nonsteady flow to a pumped,

Modeling infiltration during a steady rain

Abstract: Few of the infiltration models in current use are suitable for the situation in which the rainfall intensity is initially less than the infiltration capacity of the soil. In this paper a simple two-stage model is developed for infiltration under a constant intensity rainfall into a homogeneous soil with uniform initial moisture content. The first stage predicts the volume of infiltration to the moment at which surface ponding begins. The second stage, which is the Green-Ampt model modified for the infiltration prior to surface saturation, describes the subsequent infiltration behavior. A method for estimating the mean suction of the wetting front is given. Comparison of the model predictions with experimental data and numerical solutions of the Richards equation for several soil types shows excellent agreement.

Artificial recharge of groundwater: hydrogeology and engineering

Abstract: Artificial recharge of groundwater is achieved by putting surface water in basins, furrows, ditches, or other facilities where it infiltrates into the soil and moves downward to recharge aquifers. Artificial recharge is increasingly used for short- or long-term underground storage, where it has several advantages over surface storage, and in water reuse. Artificial recharge requires permeable surface soils. Where these are not available, trenches or shafts in the unsaturated zone can be used, or water can be directly injected into aquifers through wells. To design a system for artificial recharge of groundwater, infiltration rates of the soil must be determined and the unsaturated zone between land surface and the aquifer must be checked for adequate permeability and absence of polluted areas. The aquifer should be sufficiently transmissive to avoid excessive buildup of groundwater mounds. Knowledge of these conditions requires field investigations and, if no fatal flaws are detected, test basins to predict system performance. Water-quality issues must be evaluated, especially with respect to formation of clogging layers on basin bottoms or other infiltration surfaces, and to geochemical reactions in the aquifer. Clogging layers are managed by desilting or other pretreatment of the water, and by remedial techniques in the infiltration system, such as drying, scraping, disking, ripping, or other tillage. Recharge wells should be pumped periodically to backwash clogging layers. Electronic supplementary material to this paper can be obtained by using the Springer LINK server located at http://dx.doi.org/10.1007/s10040-001-0182-4.

Class—A Canadian land surface scheme for GCMS. I. Soil model

Abstract: A new GCM land surface scheme is introduced, incorporating three soil layers with physically based calculations of heat and moisture transfers at the surface and across the layer boundaries. Snow-covered and snow-free areas are treated separately. The energy balance equation is solved iteratively for the surface temperature; the surface infiltration rate is calculated using a simplified theoretical analysis allowing for surface ponding. Snow cover is modelled as a discrete ‘soil’ layer. The results generated by CLASS are compared with those of an older model incorporating the force-restore method for the calculation of surface temperature and a bucket-type formulation for the ground moisture. Several month-long test runs are carried out in stand-alone mode. It is shown that the surface temperature in the old scheme responds more slowly to diurnal forcing and more quickly to longer term forcing than that modelled by CLASS, while its one-layer representation of soil moisture proves incapable of reproducing changes in the surface fluxes owing to surface variations of moisture content. Finally, the lumped treatment of snow and soil in the old scheme results in an extremely fast disappearance of the snow pack under certain conditions.