Showing papers on "Hydraulic conductivity published in 1972"

watershed physics: Soil variability criteria

Abstract: Variability criteria for input parameters to the moisture characteristic and hydraulic conductivity models are developed. The parameters include the water contents at air entry and at 15 bars as well as the hydraulic conductivity used in matching the predicted values with the experimental values at saturation. The available data suggest that the water contents at 15 bars and at air entry have a normal distribution whereas the hydraulic conductivity has a log normal distribution. The distributions of water contents and conductivities for different soil series with depth and over an area are illustrated, and variability is expressed as the coefficient of variation. It is suggested that in watershed studies a soil be considered uniform with depth or over an area if the coefficient of variation with respect to water content does not exceed 15% at 15 bars and 10% at air entry and the logarithmic standard deviation for hydraulic conductivity used in matching is less than log 2. If the preceding conditions are met, the water contents at 15 bars and at air entry as well as the saturated conductivities may be averaged.

Modeling the pore structure of porous media

Abstract: A physicomathematical alternative to capillaric modeling of the pore structure of porous media is proposed. With this model, the hydraulic conductivity of porous materials is determined from a ‘pore domain’ characterization of the pore space by using an appropriate conductance theory for estimating the flux contribution of the various components of heterogeneous media. The proposed model is versatile yet mathematically tractable and is capable of analyzing fluid flow through porous materials of widely differing structure including anisotropic and structured media. A comparative study of the predictions of this model with those of a model proposed by E. C. Childs and N. Collis-George and now widely used in soil science is made for several media. The findings indicate that indiscriminate use of the latter model may be responsible for the gross overpredictions of hydraulic conductivity for some porous materials and also for the reported distortions in the relationships between conductivity and the degree of saturation for some soils.

An Improved Form of Soil-Water Diffusivity Function

Abstract: The soil-water diffusivity D(θ) is expressed by a functional form which becomes infinite as the soil-water content approaches a constant value, such as the saturated or near-saturated value. The function begins at the origin, and shows an approximately exponential rise in the intermediate soil-water content range. When combined with a previously suggested form of unsaturated hydraulic conductivity function K(θ), qualitatively reasonable forms for the relationship between water content and suction head can be inferred. A computer program was developed to determine the characterizing parameters in the function by a least-squares fit to experimental data for horizontal water absorption. The program used an optimum seeking technique with numerical solutions of the flow equations as obtained by Philip's method. For different types of soils and several bulk densities, the new functional form was compared with the commonly used exponential expression for D(θ), and was found to be more representative, particularly for soils which show a very rapid increase in D(θ) as saturation is approached.

Clays with Abnormal Interstitial Fluid Pressures

Abstract: Consideration of the stresses in clay rocks, and their compaction processes, leads to the conclusion that abnormally pressured clay sequences generally have been abnormally pressured since burial to a shallow depth--2,000 ft (600 m) or even less--in areas of gravity loading under sediments. Rubey and Hubbert's concept of equilibrium depth (ze) is reexpressed. [EQUATION] in which the ratio (1 - ^lgr)/(1 - ^lgre) is a dimensionless measure of the expulsion of fluids from the formation. Zones of abnormal fluid pressure are caused more by low hydraulic conductivity in a rock unit or sequence than by load or rate of loading. Hence the transition zone from normal to abnormal pressures at the top of a relatively impermeable sequence will have its mirror image at the bottom of the unit, if it overlies a sequence of sufficient hydraulic conductivity. The petroleum potential below an abnormally pressured clay sequence is similar to that above it.

Soil structure and its effects on hydraulic conductivity

Abstract: The influence of the soil structure on coefficients of radial and vertical conductivity is studied. Evaluation of the data shows that the flaky shape of clay particles and its orientation with reference to vertical and horizontal axes give more hydraulic conductivity in the horizontal than in the ve

Natural-Membrane Phenomena and Subsurface Waste Emplacement

Abstract: Commonly, shales are considered to be effective aquitards in the subsurface environment owing to their generally low hydraulic conductivity compared to materials such as limestones and sandstone that compose aquifer systems. However, recent laboratory and field studies indicate that clay minerals may behave as natural semipermeable membranes. A semipermeable membrane is capable of retarding the passage of charged species through its micropores when a driving force such as a hydraulic gradient is imposed across the membrane. Likewise, if a chemical, electrical, or thermal gradient is imposed across a semipermeable membrane, the result is a movement of H2O in response to the gradient in order to equalize the chemical potential of H2O on the two sides o the membrane. If liquid wastes are emplaced in a subsurface aquifer system which was previously in a state of dynamic equilibrium, the emplacement will likely upset the dynamic equilibrium; it may cause (1) chemical reactions with the existing fluid and rocks, (2) thermal changes, and (3) increased pressure on the aqueous phase. In addition to these well-recognized effects, if a shale capable of behaving as a membrane is expected to serve as an aquitard, its membrane characteristics must be taken into account. For example, if the chemical concentration in the aquifer is greatly increased as a result of waste emplacement, an osmotic cell may be set up between a nearby aquifer and the emplacement aquifer with the intervening shale acting as a membrane. A pressure increase beyond that anticipated coul result. Likewise, thermal and electrical osmosis could occur across the shale membrane with attendant pressure changes. If pressure is increased simply as a result of emplacement of waste, and if it exceeds the pressure required for osmotic balance, ultrafiltration can result. The effect would be to cause flow across the shale and increase the chemical concentration of the filtrate in the emplacement aquifer beyond the planned amount. In any plan to emplace liquid waste in an aquifer system, the possible membrane behavior of shale in this system must be taken into account. Whenever feasible, laboratory membrane tests which simulate field conditions should be conducted on cores of the shale prior to full-scale operation; the entire system, not just the emplacement aquifer, should be tested with a computer simulation model prior to initiation of waste injection.

Germination of wheat as affected by soil water stress

Abstract: Germination rate of wheat was determined at several water potentials (−0.8, −5.3, −7.8, and −15.3 bars) on two soils and a semipermeable membrane. Germination rate decreased as matric potential decreased. At a given water potential, germination rates were the same for both soils but germination on the membrane system was faster than on soils. Hydraulic conductivity was different on the two media, indicating that the hydraulic conductivity is an important component of soil water stress. Germination rate was not affected by decreasing water potential to −7.8 bars on each medium. At the −15.3-bar potential germination rate was considerably slower.

Water absorption by wheat seeds as influenced by hydraulic properties of soil

Abstract: Water diffusivity and hydraulic conductivity of wheat seeds were determined. At water contents approaching those required for germination, hydraulic conductivity of the seed was similar to those normally found in soils at the dry end of the available water range. Water uptake by seeds from soils indicated that both water potential and hydraulic conductivity of the soil influenced rate of water uptake. When seeds were buried in soil, water uptake rate was generally greater in the Chateauguay soil than in the Wellwood soil. This was a significant observation since at a given potential, hydraulic conductivity was greater in the Chateauguay than in the Wellwood soil. In view of these results it was concluded that seed hydraulic conductivity is a useful parameter in understanding water absorption by seeds from soil.

Effect of portland cement on soil aggregation and hydraulic properties

Abstract: THE EFFECT OF ADDITIONS OF SMALL QUANTITIES OF PORTLAND CEMENT ON THE WATER-STABLE AGGREGATES, THE SATURATED HYDRAULIC CONDUCTIVITY, THE SOIL-WATER CHARACTERISTIC, AND THE UNSATURATED SOIL-WATER DIFFUSIVITY OF A SILT LOAN SOIL ARE EVALUATED. CEMENT WAS INTIMATELY MIXED WITH AIR-DRY SOIL AT RATES OF 0.475, 0.95, OR 1.90% BY WEIGHT, AND THE MIXTURE WAS KEPT IN MOIST CONDITION FOR DURATIONS OF 1.33, 7,14, OR 28 DAYS. THE AGGREGATE ANALYSIS INDICATED A BENEFICIAL EFFECT OF CEMENT APPLICATION THAT INCREASED WITH THE RATE AND THE DURATION OF MOIST-CURING. THE AMOUNT OF WATER-STABLE AGGREGATES IN THE CEMENT-TREATED SOIL INCREASED AS MUCH AS THREEFOLD AND THE AGGREGATION INDEX AS MUCH AS EIGHT-FOLD AS COMPARED WITH THE MOIST-CURED NO CEMENT CONTROL. MOST OF THE BENEFICIAL EFFECT WAS ACHIEVED WITH 1% CEMENT AND 14 DAYS MOIST CURING. THE SATURATED HYDRAULIC CONDUCTIVITY OF THE TREATED SAMPLES WAS NOT MUCH DIFFERENT FROM THAT OF THE CONTROL INITIALLY, BUT AS THE WATER FLOW CONTINUED FOR 12 HOURS THE CONDUCTUVITY OF THE CONTROL DECREASED TO ONE-HALF ITS INITIAL VALUE, WHILE THE CONDUCTIVITIES OF THE TREATED SAMPLES INCREASED SLIGHTLY. THE WATER-RETENTION CURVE MEASURED FOR THE SOIL TREATED WITH 1.90% CEMENT SHOWED A SMALL DECREASE IN THE WATER RETAINED BETWEEN 50 CM AND 200 CM SUCTIONS. THE UNSATURATED SOIL-WATER DIFFUSIVITY OF THE TREATED SAMPLE WAS PRACTICALLY THE SAME AS THAT OF THE CONTROL. /AUTHOR/

Pumping an Artesian Source for Water Table Control

Abstract: Pumping tests conducted on an artesian aquifer in the Red River Valley of North Dakota indicate that water table control can be provided for the overlying water logged and saline agricultural lands at an estimated pumping cost of $0.34 per acre ($0.84 per ha) per yr. Because the fine-textured overburden is more than 100 ft (30 ms) thick and has a very low vertical hydraulic conductivity, continuous pumping (year around) will be necessary. By reducing the artesian pressure, the upward flow of saline water will be stopped, the water table in the leaky overburden will be reestablished at a greater depth, and salts can be leached from the root zone by precipitation. Even though the water pumped from the artesian aquifer is saline, the amount would be small enough that its discharge into the Red River of the North at probable low flow would not make the river water unsuitable for domestic use.

Hysteresis of flux‐gradient relations for saturated flow of water through clay materials

Abstract: Summary The relation between flow velocity (v) and hydraulic gradient (7) was studied for two porous materials. The volume of the sample was allowed to change during experiment. For the kaolinite, the relation between v and I is non-linear, the hydraulic conductivity k becomes dependent on time and varies for both increasing and decreasing 7. After some time, k tends to some constant value. For bentonite, k remains constant as 7 increases. However, when I starts to decrease, k decreases accordingly. Hysteresis in the relationship between v and 7 remains unchanged with time. The observed deviations from Darcy's law may be due to deformation of the voids.

On the tensor concept of unsaturated anisotropic hydraulic conductivity

Abstract: Unsaturated hydraulic conductivity can be regarded as a second order tensor, the coefficients of which depend on soil moisture suction or soil moisture content General equations for the three-dimensional anisotropic unsaturated flow of water in porous media must involve nine coefficients of the hydraulic conductivity tensor, all of which are, in general, nonzero Equations for horizontal anisotropic unsaturated flow can be reduced to an orthotropic form with principal hydraulic conductivities Kx′,Ky′, and Kz′ provided the principal axes of the conductivity tensor do not rotate when the moisture content or the soil moisture suction changes This condition is fulfilled only for a certain constant ratio of hydraulic conductivities in different directions that is independent of the soil moisture suction or soil moisture content In this case the flow velocity is given by the simple Darcy type equation without the cross coefficients of hydraulic conductivity A simple experimental method is proposed to determine the diagonal and cross coefficients of the hydraulic conductivity as functions of the soil moisture suction for horizontal unsaturated steady flow in anisotropic porous media

Infiltration characteristics of furrow irrigation in a heavy-textured soil

Abstract: The objective of this thesis is to study the rate and pattern of infiltration of soil water, under the conditions of heavy texture and shallow depth in a tropical furrow- irrigated soil. The analysis is the result of a series of field-experiments and is supported by theories that has been proposed by others.The experiments were carried out in the Cojedes-Sarare Irrigation Project, Portuguesa State, Venezuela. Furrows with a length of 200 m, spaced at w = 0.70 m, and with an average slope of 0. 18 % were used. Three series of experiments were set out: (i) First series with variable inflow and surface roughness; (ii) Second series with variable initial soil moisture content; (iii) Third series with variable furrow length. Replicates of the treatments were distributed at random.Five irrigations were applied to the land during the period from January to March, 1970. Subsequently in the first series of experiments, first, third and fourth irrigations for three roughness conditions and four sizes of flow were tested. The second irrigation was used for the second series of experiments. The fifth irrigation served for the third series of experiments.During the first series of experiments, the following measurements were taken: (i) rate of advance of the water front (distance x in m at time t in min); (ii) furrow section parameters (top width T and depth h ); (iii) furrow inflow Q and outflow Q out . During the second and the third series of experiments, only the simultaneous inflow and outflow were recorded.Advance and infiltration functions were obtained for the period of advance of the water front (first stage), and infiltration functions for the period of wetting the root zone (second stage). Exponential equations were obtained by computer analysis for single furrow trials. Then, by averaging coefficients and exponents of the equations of the replicates, general equations for each treatment were found.The data of x as a function of t showed a good fit with the equation x = p t r . The coefficient p increased significantly with the flow size Q and the exponent r showed a trend to decrease although not significantly, with increasing Q . The coefficients of variation of p and r were rather high. Therefore a single furrow advance trial may not suffice to express the average field advance of the water front under the given conditions.The advance curves showed that the differences in roughness were great between the first irrigation with loose furrows and those irrigations after two or three applications have taken place. The roughness conditions appeared to be identical for third and fourth irrigations.With distance-averages of the furrow section parameters h and T , for three water front advance stages ( x = 87.5 m, x = 137,5 m and x = 175.0 m), the average section a f , and the average wetted perimeter P were obtained for a parabolic section of the furrows. The surface volume V f = a f p t r , and the area of infiltration A i (net area A in = P pt r and gross area A ig = w pt r ) were then arrived at.The infiltration functions were found for each treatment during the first stage, as V i = f(t) by using single furrow data of V i = Q t - V s ,. As the average infiltration depth I cum = V i / A i , the equations for I cum = f(t) were obtained. Equating these functions with the equation I cum = F at b +1/ ( b + 1) ( b + 2), the parameters a and b of the Kostiakov equation ( I = a t b ) were derived. For the second stage (when x = L = 175.0 m), the infiltration function was obtained by simultaneous measurements of the inflow and outflow, as infiltration flow: Q i = Q - Q out , from which the parameters of the infiltration equations, were found.The increase of infiltration with inflow size was clearly shown from the data analysis of both stages as being the effect of a larger volume of water. The parameters of the infiltration equation for the first stage altered in successive irrigations.Some emphasis was put on the unit inflow function q0 to relate flow sizes for both stages with length of run and infiltration. Equations for the unit inflow q 0 = Q / A i and for unit infiltration flow q i = Q i / A i per unit area, were obtained for each treatment. Then a generalized type of equation was introduced which relates the unit inflow function with the average depth of water infiltrated during the advance time at the furrow intake. An equation to predict the length of advance is included x = φ( Q ) t 0.927 , for the surface roughness and soil conditions under which the experiments were carried out. The representation of q 0 = f(t) and q i = f(t) for both stages, in a composite figure with the advance function as a function of time, provides an illustration of the infiltration process, usable for the design and management of furrow irrigation under the conditions of the experiments.The relationship between the exponent of time in the advance equation and the exponent of time in the infiltration equation was analysed with the data from the experiments. This analysis confirmed that r increases when ( b + 1) decreases. This agrees with findings in the literature, such as the relationship proposed by FOK and BISHOP (1965) Values for the surface storage coefficient C 1 = D / D 0 , and infiltration coefficient C 2 = I cum / I cum0 to solve the balance equation for predicting advance were also obtained.The second series of experiments, in which infiltration rate was measured during the second stage, as a function of the initial moisture content, showed that the value of the coefficient a of the Kostiakov equation increased not significantly as the initial content of soil moisture decreases.The third series of experiments - measurements taken during the second stage - showed that upon the increase of furrow length, the coefficient a of the infiltration equation decreases and the exponent b increases.Water losses by deep percolation and by run-off at the end of the run, were finally analysed on the bases of the equations found and the data available. The analysis was made for the case of constant inflow for both stages (third irrigation), and for the case of reduced inflow during the second stage (fourth irrigation).The data analysis showed that infiltration is a very variable factor affected by the conditions of the soil and the surface of the channel bed, as well as by the size of the flow, furrow length and stage of irrigation. Soil cracking upon drying was found to be a relevant factor in the entry of water into the soil. Because deep percolation losses are certainly very small under the indicated physical conditions, irrigation efficiency will be rather high if provisions are made to use a cut-back stream, during the second stage, in order to lose a minimum of water by run-off at the end of the run.

Influence of surface soil conditions on drying in early spring

Abstract: Changes in water content of adjacent plowed and unplowed surface soils were measured in early spring in the field. The plowed plots on sand and clay soils lost more water than unplowed plots. The major decrease in water content of the clay soil was in the 0–7-cm layer, whereas the sand lost as much water from the 7–15-cm layer as from the 0–7-cm layer. The medium-grained soil showed greater drying from the unplowed than from the plowed surface. The higher bulk density of this soil may account for this observation. Differences in net radiation measured above plowed and unplowed surfaces were too small to account for the measured differences in water loss. There was evidence that the drier surface was due to lower hydraulic conductivity of the plowed surface, but increased turbulent transfer from the rougher surface could also be involved.

Seepage from Trenches through Nonhomogeneous Soils

Abstract: Infiltration from shallow trenches of arbitrary cross-sectional shape and through a layer of nonhomogeneous soil was studied analytically. The soil layer is underlain by a bed of gravel that is represented mathematically by a line of constant pressure. The basic flow equations were derived and the corresponding boundary value problems constructed by use of the perturbation theory. The effect of an exponential variation of the hydraulic conductivity on the quantity of seepage and the free surface is determined. A comparison with the case of constant permeability is made for different layer thicknesses. A triangular trench was chosen to indicate the effect of trench dimensions on the amount of seepage through layers of nonuniform permeability. Curves are presented to illustrate this effect.

Chemical additives to reduce frost heave and water accumulation in soils, with discussion and closure

Abstract: SOIL WATERPROOFING CHEMICALS ARE KNOWN TO REDUCE FROST HEAVE IN SOILS, PARTICULARLY WHEN SOILS ARE DRIED; THE PRESENT STUDY DEMONSTRATES THAT THESE CHEMICALS WORK IN MOIST SOILS AS WELL. THE MECHANISM AND LIMITATIONS ARE PARTLY DEFINED IN THIS PAPER. A MODEL SOIL WATERPFOOFING COMPOUND, 4-TERT-BUTYLCATECHOL (TCB), WAS STUDIED AS REPRESENTATIVE OF THE GENERAL GROUP. WATER ABSORPTION TO GROWING ICE LENSES WAS MEASURED AS AN INDICATION OF FROST-HEAVE RATES. CAPILLARY CONDUCTIVITY WAS ALSO MEASURED AND CORRELATED TO HEAVE AND TREATABILITY. AS LITTLE AS 0.01 PERCENT TCB PRODUCED MINIMUM ICE LENS GROWTH AND CAPILLARY FLOW IN SOME SOILS. A-4 SOILS RESPONDED WELL TO TREATMENT, WHEREAS SOILS CONTAINING MORE THAN 50 PERCENT CLAY DID NOT. A SIMPLE HYDRAULIC CONDUCTIVITY TEST SHOULD BE CONSIDERED AS A MAJOR SOIL FROST-SUSCEPTIBILITY CRITERION. /AUTHOR/

Selected Methods of Aquifer Test Analysis

Abstract: Changes in groundwater levels due to a well discharging at a constant rate are used with various formulas to determine hydraulic properties of aquifers and their confining bed and to detect the presence of aquifer boundaries. These formulas are generally solved by graphical methods.

Effect of Exchangeable Sodium on Hydraulic Conductivity of Soils

Abstract: Clay, clay loam, silty clay loam, silty ham, loam and loamy sand soils of U. P. were incubated with Na2CO3 (0, 15, 25, 35, 45, 55 & 65 per cent of CEC) in order to obtain increasing levels of exchangeable sodium. An increase in exchangeable sodium percentage was accompanied by a marked decrease in hydraulic conductivity. The fractional changes in hydraulic conductivity [K/Kmax) were 0.85 at 5.01 E.S.P., 0 52 at 14.43 E.S.P., 0.21 at 24.50 E.S.P., and 0.06 at 29.88 E.S.P.

Infill of Nuclear Rubble Chimneys by Ground Watera

Abstract: This paper presents some of the preliminary results of a theoretical analysis of the ground-water infill rate of a rubble chimney produced by an underground nuclear explosion. The study was conducted to evaluate effects that various features of the hydrogeology regime have on rate of infill. This model for infill is based on the analogy of a rubble chimney to a small diameter gravity well. The infill history is approximated by integrating production from a series of steady state infill rates based on Dupuit-Forchheimer assumptions. The model has been used for parameter sensitivity analysis. Of the aquifer characteristics, changes of the hydraulic conductivity have the greatest effect on infill; the radius of influence is most sensitive to changes in the specific yield. The effect of infill rate of using a rubble porosity that decreases with depth is small, although initial infill is more rapid. The hydrogeology data from two events where infill data are available have been used with this model for verification. For both BILBY and GREELEY events, agreement between measured and calculated infill data are good. BILBY data suggest that substantial dewatering of the rubble in the chimney occurred before much ground water entered the chimney. Comparison of the GREELEY data indicates that dewatering of the rubble is minimal but that porosity of the rubble near the surface was higher than originally anticipated.