bluuebunny/crossref_metadata_2025 huggingface dataset:
Identifying sediment sources in a gullied catchment using natural and anthropogenic radioactivity
Authors: Olley J. M. , Murray A. S. , Mackenzie D. H. , Edwards K.
Published: February 2004

The ratio of the lithogenic nuclides 226Ra and 232Th indicates that the major source of sediment in transport in a gullied catchment, located in the head waters of Whiteheads Creek, New South Wales, Australia, is the gully itself. This observation is supported by 7Be and 137Cs concentrations which indicate that the sediment is derived from erosion of either gully floor or gully wall material. While subcatchment 7Be and 137Cs data show sheet, rill, and gully erosion are occurring in the upstream catchments, sediment from these sources is either being trapped before entering the gully, or the volume of sediment is small compared to that derived from the gully itself. The differences in the 226Ra to 232Th ratio between the suspended solids collected on the rising stage and samples of sediment deposited during the falling stage at the outlet of the catchment, indicate a change in the source of sediment during storm events. The results presented here demonstrate the applicability of radionuclide tracers in providing quantitative estimates of the relative contributions of individual catchments to the sediment moving within a drainage network, and in determining whether or not the sediments are mainly derived from subsoil or topsoil sources.
Multiporosity/multipermeability approach to the simulation of naturally fractured reservoirs
Authors: Bai Mao , Elsworth Derek , Roegiers Jean‐Claude
Published: February 2004

This paper presents an array of deformation‐dependent flow models of various porosities and permeabilities relevant to the characterization of naturally fractured reservoirs. A unified multiporosity multipermeability formulation is proposed as a generalization of the porosity‐ or permeability‐oriented models of specific degree. Some new relationships are identified in the parametric investigation for both single‐porosity and dual‐porosity models. A formula is derived to express Skempton's constant B by Biot's coefficient H and relative compressibility ϕ*. It is found that the recovery of the original expression for Skempton's constant B is largely dependent on the choice of ϕ*, representing relative compressibility. The dual‐porosity/dual‐permeability model is evaluated through an alternative finite element approximation. The deformation‐dependent fracture flow mechanism is introduced where the rock matrix possesses low permeability and fracture flow is dominant. A preliminary study of the reservoir simulation identifies the strong coupling between the fluid flow and solid deformation.
Significance of soil surface moisture with respect to daily bare soil evaporation
Authors: Chanzy A. , Bruckler L.
Published: February 2004

The significance of the soil surface moisture (θs) with respect to daily bare soil evaporation (Ed) is analyzed using data from numerical simulations. This was performed by running a mechanistic model of heat and water flows in the soil. The mechanistic model was calibrated and validated on three different soils with contrasted hydraulic properties. Results show that θs does not allow an accurate estimate of the ratio of Ed to the daily potential evaporation (Epd). Added variables such as Epd and the wind velocity are necessary to improve the prediction of the Ed/Epd ratio. In a second attempt, a simple model of Ed is proposed. It is based on three empirical parameters and required the measurement of θs obtained at midday, Epd, and the daily wind velocity. For a given soil, a single set of the three parameters allows an accurate estimate of Ed under soil moisture and climatic conditions encountered through the year in temperate areas.
Surface‐based fractional transport rates: Mobilization thresholds and partial transport of a sand‐gravel sediment
Authors: Wilcock Peter R. , McArdell Brian W.
Published: February 2004

Twenty‐eight coupled observations of flow, transport, and bed surface grain size distribution were made in a laboratory flume using a wide range of flows and a sediment with a very poorly sorted, bimodal grain size distribution. These observations permit the transport rates of individual size fractions to be scaled by the proportion of each size immediately available for transport on the bed surface. The key to our observations is the use of a sediment in which each size fraction has been painted a different color, which permits reliable, repeatable, and nondestructive measurement of the bed surface grain size distribution from photographs of the bed surface. At a given flow, the fractional transport rates may be divided into two parts: a finer‐grained portion within which fractional transport rates are a function only of their proportion on the bed surface and total transport rate, and a coarser‐grained portion for which fractional transport rates also depend on the proportion of individual grains within a fraction that remain essentially immobile throughout the experimental run. We define the latter condition as one of partial transport and observe that the grain size separating partial and fully mobilized transport consistently increases with flow strength. Complete mobilization of a size fraction occurs at roughly twice the shear stress necessary for incipient motion ofthat fraction. Zones of partial and full mobility are quite distinct when fractional transport rates are scaled by the bed surface grain size distribution, although a region of partial transport is evident when these data and other experimental and field observations are scaled by the bulk grain size distribution of the sediment bed. Critical shear stresses for the incipient motion of individual fractions in our experimental sediment vary over an order of magnitude, a result strongly in contrast to many earlier observations, but consistent with our observations of incipient motion in sediments with bimodal grain size distributions.
Approximate analytical solution for soil chemical transfer to runoff: A modified boundary condition
Authors: Wallach Rony
Published: February 2004

Two mass balance equations were used to model the transfer of dissolved chemicals from the soil solution to the surface runoff water and the transport of these chemicals to the field outlet. One mass balance equation was written for chemicals dissolved in the overland water, the other for chemicals within the soil profile. Chemical input into the surface water (upper boundary condition) was expressed as a rate‐limited convective mass transfer, depending on both soil surface and runoff concentrations. Isolating a slow and fast time scale and scaling the mass balance equations to the slow one yielded a parameter, ε, which multiplies the time derivative of the mass balance equation written for overland flow. In most cases ε ≪ 1, providing a singular perturbation problem that was solved by using the method of matched asymptotic expansion. The approximate solution, uniformly valid over the entire domain, was made up of two terms: a leading‐order solution and a first‐order solution, the latter of which was relatively small, even for ε = O(1). The leading‐order solution was compared with that for a simpler case, in which the convective mass transfer (upper boundary condition) depends only on the soil surface concentration. The comparison indicated those limited cases to which the simpler boundary condition can be applied resulting in a very small error. Although it is not possible to get a strictly analytical solution for a problem involving a modified upper boundary condition, the approximate analytical solution is easily obtained.
Optimal groundwater management: 2. Application of simulated annealing to a field‐scale contamination site
Authors: Marryott Robert A. , Dougherty David E. , Stollar Robert L.
Published: February 2004

Simulated annealing is used to analyze alternate design strategies for groundwater remediation at a contaminated field site. The simulated annealing optimization algorithm is combined with a field‐scale flow and transport simulation model for an unconfined aquifer to determine nearly optimal pumping schedules for a pump‐and‐treat remediation system at a proposed Superfund site in central California. A series of demonstration problems is presented using two different optimization formulations. The results of these experiments indicate that the method can be applied to realistic groundwater management problems. The computational expense of simulated annealing is large yet comparable to other nonlinear optimization techniques. A practical empirically based strategy is provided for selecting and adjusting the parameters necessary for successful optimization.
New control concepts for uncertain water resources systems: 1. Theory
Authors: Georgakakos Aris P. , Yao Huaming
Published: February 2004

A major complicating factor in water resources systems management is handling unknown inputs. Stochastic optimization provides a sound mathematical framework but requires that enough data exist to develop statistical input representations. In cases where data records are insufficient (e.g., extreme events) or atypical of future input realizations, stochastic methods are inadequate. This article presents a control approach where input variables are only expected to belong in certain sets. The objective is to determine sets of admissible control actions guaranteeing that the system will remain within desirable bounds. The solution is based on dynamic programming and derived for the case where all sets are convex polyhedra. A companion paper (Yao and Georgakakos, this issue) addresses specific applications and problems in relation to reservoir system management.
Rethinking rural water supply policy in the Punjab, Pakistan
Authors: Altaf Mir Anjum , Whittington Dale , Jamal Haroon , Smith V. Kerry
Published: February 2004

This paper provides an analysis of public policy relating to the rural water supply sector in the Punjab, Pakistan. Based on household survey data, it shows that rural water policies have not kept pace with the rapid economic development in this region and that in the absence of adequate public investment households find private sector alternatives to meet their water needs, often at high economic and environmental cost. Using the contingent valuation method for benefit estimation, it is also shown that household willingness to pay for reliable improved services is much higher than assumed. In fact, full cost recovery is quite feasible in many areas of the Punjab. It is recommended that rural water sector strategy be changed from a centralized, supply‐oriented focus to a decentralized, demand‐oriented policy.
On numerical modeling of capillary barriers
Authors: Oldenburg Curtis M. , Pruess Karsten
Published: February 2004

A capillary barrier arises in unsaturated conditions at the contact of a fine layer of soil overlying a coarse layer of soil. If such a contact is tilted, infiltrating moisture in the fine layer will be diverted and flow down the contact as capillary diversion. Capillary barriers can occur naturally in layered heterogeneous systems, or they can be engineered for the purpose of diverting infiltration, for example, away from hazardous wastes. Recent theoretical analyses of capillary diversion have revealed some simple relations for the behavior of an idealized capillary barrier. Meanwhile, laboratory experiments and field investigations have shown much more complicated behavior. We have attempted to bridge the gap between the simple theoretical results and the more complicated laboratory and field observations by means of numerical experiments. Numerical modeling of capillary barriers presents significant challenges because of the potential for gravitational instability which can give rise to strong space discretization and grid orientation effects. We have examined the ability of different finite difference techniques, such as harmonic weighting, upstream weighting, and higher‐order differencing, to represent flow exclusion and leakage effects at capillary barriers. The numerical experiments show that analytical results previously obtained are reasonable, but that leakage occurs upstream of the theoretical breakthrough point. Furthermore, in the breakthrough region and downstream from it, the behavior is considerably more complicated than assumed in the theoretical analysis. Numerical experiments, with careful consideration of space discretization and grid orientation effects, reveal that the initial breakthrough allows sufficient leakage at the contact to partially dry the upper layer, making the barrier active again downstream. Finite difference schemes specifically designed to handle transient multiphase flows can adequately reproduce the broad features of flow diversion and leakage at capillary barriers.
A numerical model for flow in meandering channels with natural bed topography
Authors: Demuren A. O.
Published: February 2004

A finite‐volume numerical model is presented for the calculation of three‐dimensional turbulent flow in meandering channels with natural bed configuration. The governing equations are written in a general curvilinear coordinate system so that all singly connected geometrical configurations can be accommodated. For simplicity, the Cartesian velocity components are retained as dependent variables. The numerical procedure is very general so that it can deal with complex cross sections and separated flow. Turbulence closure is through the standard k‐ϵ model. Computed results show good agreement with experimental data in meandering channels with rectangular and natural bed configurations. This work provides a hydrodynamic basis for the study of the mechanisms for the formation of river meanders.
A management model for specification of groundwater withdrawal permits
Authors: Mueller Frederick A. , Male James W.
Published: February 2004

The Massachusetts Water Management Act was enacted in 1986 to preserve the State's water resources. The intent of the Act was to allow for sustained economic growth while protecting the natural environment by minimizing the occurrence of low stream flows. As a result of the act, a permit must be obtained for new water withdrawals (including increases on existing withdrawals) of more than 0.1 million gallons per day (0.00438 m3/s). The permits specify the degree to which applicants may withdraw water, and reserve the right to curtail use during low flow seasons. A linear programming model is presented that is capable of assisting regulatory agencies in specifying details of permits for groundwater use. The model links ground water withdrawals with surface streamflow, considering consumptive use and interbasin transfers. The optimization minimizes the depletion of streamflow below a standard while honoring the statistical distribution of allowed withdrawals permitted each applicant. The results specify the amount and timing of allowed withdrawals throughout the year.
Property rights and water markets in Australia: An evolutionary process toward institutional reform
Authors: Pigram John J.
Published: February 2004

In the past decade far‐reaching reforms have taken place in the Australian water industry. Extensive restructuring of water administration has been accompanied by increased evidence of willingness by public agencies to consider alternative institutional arrangements to the traditional regulatory approach to water allocation and use. In irrigated agriculture, a market‐based system linked to enforceable property rights to water is seen as preferable to rule‐based management of water resources. However, significant social and economic considerations and political realities constrain the unfettered operation of water markets. The challenge facing the irrigation industry in Australia is to put in place institutional arrangements which reflect the most appropriate mix of incentive‐based and regulatory mechanisms for water management.
Water resources issues in the developing countries
Authors: Brookshire David S. , Whittington Dale
Published: February 2004

The focus of this special section are the problems and issues regarding water development in developing countries. A significant number of the populations in developing countries do not have access to satisfactory water supplies. This problem is especially acute in the rural areas. The planning process has routinely failed to lead to successful projects. Often the projects do not pass the simplest of benefit‐cost analyses. Further, the institutional framework that is developed for the administration of the projects is often flawed. The papers in this special section address these issues.
Water resources planning in a strategic context: Linking the water sector to the national economy
Authors: Rogers Peter , Hurst Christopher , Harshadeep Nagaraja
Published: February 2004

In many parts of the developing world investment in water resources takes a large proportion of the available public investment funds. As the conflicts for funds between the water and other sectors become more severe, the traditional ways of analyzing and planning water investments has to move away from project‐by‐project (or even a river basin‐by‐river basin) approaches to include the relationships of water investments to other sectors and to overall national development policies. Current approaches to water resources investments are too narrow. There is a need for ways to expand the strategic thinking of water sector managers. This paper develops a water resources planning methodology with the primary objective of giving insights into the linking of water sector investments and macroeconomic policies. The model optimizes the present value of investments for water resources development, while embedding a macroeconomic model into the framework to allow for an examination of the interactions between water investments, the growth in the agricultural sector, and the performance of the overall economy. A case study of Bangladesh is presented which shows how strategic thinking could lead to widely differing implications for water investments than would conventional water resources systems planning models.
Design principles in long‐enduring irrigation institutions
Authors: Ostrom Elinor
Published: February 2004

Crafting institutions related to the supply and use of irrigation systems require skills in understanding how rules, combined with particular physical, economic, and cultural environments, produce incentives and outcomes. If the users and suppliers of irrigation systems design their own institutional arrangements to cope with the physical, economic, social, and cultural features of each system, the variety of institutional arrangements could be immense. Examining specific rules of particular systems, however, is like focusing on specific blueprints of successful irrigation projects around the world. Recent theoretical and empirical work on institutional design has attempted to elucidate the core design principles used in long‐enduring, self‐organized irrigation institutions throughout the world. By “design principle” is meant a characteristic that helps to account for the success of these institutions in sustaining the physical works and gaining the compliance of generations of users to the rules in use. By “long enduring” is meant that the irrigation system has been in operation for at least several generations. Eight design principles identified in prior research are discussed and analyzed.
Water and poverty: Implications for water planning
Authors: Fass S. M.
Published: February 2004

Although it recognizes the tangible economic benefits to health and income that may derive from greater safety of supply and improved time savings in procurement, planning for improvements of urban water systems in developing countries has overlooked other ways in which water may influence health and income among the poor. In these populations the price of water may further affect health and labor productivity, both directly through its impact on nutrition and indirectly through its impact on housing size and quality and on residential density. What at first might seem a straightforward equity issue in planning may thus be an issue of economic efficiency as well. Failure to account for the fuller range of tangible benefits associated with improvements in water supply may lead to underestimation of returns to investment and therefore to economically inefficient investment.
Sustainability of potable water services in the Philippines
Authors: Bohm Robert A. , Essenburg Timothy J. , Fox William F.
Published: February 2004

Financial sustainability of rural water systems in the Philippines is evaluated based on a comparison of willingness to pay for improved water and the costs of service delivery. Willingness to pay estimates indicate that user fees are unlikely to be sufficient to cover the full cost of service and subsidies are necessary, at least for a major portion of capital costs, or the water systems will become unsustainable because of insufficient resources. Sustainability is more probable when care is exercised in selecting villages for improved water services. Economies of scale lead to lower unit costs in larger villages. Willingness to pay is greater for household connections than for public faucets. Willingness to pay increases with income and wealth, family size, education, and dissatisfaction with traditional water sources.
Rent‐extracting behavior by multiple agents in the provision of municipal water supply: A study of Jakarta, Indonesia
Authors: Lovei Laszlo , Whittington Dale
Published: February 2004

A framework is presented for the analysis of rent‐extracting behavior by multiple agents involved in the provision of municipal water supplies in Jakarta, Indonesia. It is shown that such behavior can dramatically affect the terms and conditions under which water service is offered to the public. A water supply system based on limited numbers of public taps, relatively few house connections, and water vendors can generate substantial monopoly rents that can be appropriated by both public and private agents. Most professionals involved with water supply projects in developing countries typically assume that the objective of municipal water authorities is to serve the public interest. In fact, agents involved in the water delivery system may pursue strategies designed for private gain, which can have important and pervasive implications for how a water system is actually designed and operated. Proposals to change the technical, engineering aspects of a water distribution system can thus threaten the interests of powerful groups. Effective public policy and donor involvement in the water sector must be based on an understanding of the structure of water markets and the political power supporting existing institutional arrangements.
Transmissivity of a heterogeneous formation
Authors: Dykaar Bruce B. , Kitanidis Peter K.
Published: February 2004

The objective of this paper is to derive the transmissivity of an equivalent homogeneous medium having the same macroscopic flow behavior as the actual heterogeneous formation. We apply generalized Taylor‐Ans moment analysis in order to determine the phenomenological coefficient of transmissivity for the case of saturated flow confined in a heterogeneous permeable formation with variable thickness. The generalized Taylor‐Aris moment analysis yields a two‐step procedure for determining the constant two‐dimensional transmissivity tensor from the three‐dimensional spatially variable conductivity tensor: solve a flow problem and then perform an integration. For the special case that the conductivity is locally isotropic and the impermeable confining surfaces are parallel, the equations governing transmissivity are discretized using a pseudospectral Fourier‐Galerkin scheme. The resultant system of linear algebraic equations is solved efficiently, using preconditioned conjugate gradients, in order Nt In (Nt) operations, where Nt is the number of spatial discretization points. The numerical method is used in several examples to compute the transmissivity of lognormally distributed hydraulic conductivity, and the results are compared with the transmissivity found using the usual depth‐averaging approach and another method suggested in the literature. The numerical results show that the averaging volume required to obtain an effective value of transmissivity is about 10 horizontal integral scales. When the flow field has a significant three‐dimensional character, the standard method of finding transmissivities by depth averaging can lead to significant errors in the prediction of global scale flows. It is shown that depth averaging consistently overestimates transmissivities. An example illustrates how in the case of tilted strata, anisotropic transmissivities arise and how the degree of transmissivity anisotropy depends on the angle of the dip and the horizontal to vertical integral scale ratio.
Comparison of steady flows from infiltration rings in “Green and Ampt” and “Gardner” soils
Authors: Youngs E. G. , Elrick D. E. , Reynolds W. D.
Published: February 2004

The field‐saturated hydraulic conductivity Kfs can be obtained from measurements of the long‐time steady flow rates from ring infiltrometers by assuming either that the soil is a “Green and Ampt” soil that has a relationship between hydraulic conductivity K and soil water pressure ψ, such that K = Kfs, 0 > ψ > ψf; K → 0, ψƒ < ψf, or that the soil is a “Gardner” soil with an exponential relationship K = Kfs exp(αψ), where α is a constant. It is shown that infiltration into a Green and Ampt soil from a surface source with zero head is the same as that for a Gardner soil with α → ∞ (gravity dominant) and with a surface source at a head |ψfs|. The shape factor G calculated for Gardner soils using a numerical solution of Richards's equation is used to calculate Kfs and α from ring infiltrometer tests based on Q = [aH/G + a/(αG) + πa2]Kfs, where Q is the steady state flow rate, H is the constant ponded head, and a is the ring radius. The equivalent G factor for Green and Ampt soils calculated using electric analogue solutions of Laplace's equation is shown to agree very well with the numerical solution. The slope of the linear relationship between the shape factor and the depth of insertion of the ring divided by the radius of the ring is shown to have a slope approximately equal to 1/π.
Helium isotope fluxes and groundwater ages in the Dogger Aquifer, Paris Basin
Authors: Marty Bernard , Torgersen Thomas , Meynier Vincent , O'Nions R. Keith , de Marsily Ghislain
Published: February 2004

Helium isotopic and rare gas measurements in the Dogger aquifer of the Paris Basin have shown the helium concentration and helium isotopic ratio to be first‐order homogeneous with only slight differences in relation to specific chemical water types. Helium in the Dogger aquifer contains quantities of 3He 3–4 times in excess of radiogenic production/accumulation from natural decay of U, Th series elements. Calculations of cosmogenic production/accumulation of 3He cannot account for the observed excesses, and 3He excess is attributed to the addition of a mantle‐derived He magmatic component. Calculations of the isotopic fluxes of helium out of the Dogger (4He flux, 2×10−7 mol 4He m−2 yr−1; 3He flux, 1.8×10−14 mol 3He m−2 yr−1 (±50%)) suggest that the helium residence time and the groundwater residence time in the Dogger aquifer are 4 Myr (±50%). This age estimate is at least 10 times as great as estimates derived from hydrologic models but is more consistent with the geochemistry of the water.
Evaporation and the field scale soil water diffusivity function
Authors: Parlance Marc B. , Katul Gabriel G. , Folegatti Marcos V. , Nielsen Donald R.
Published: February 2004

Simplifications to the depth‐integrated soil water transport equation lead to an Ito stochastic differential equation where the evaporation is related to the stored water by the nonlinear soil water diffusivity function. From the derived equation the diffusivity function was estimated from daily stored water measurements obtained at the field scale using nonlinear filtering theory for a period of 100 days. Comparisons with daily evaporation measured with a sensitive 50‐ton lysimeter indicated that the proposed method may be used to determine soil water diffusivity functions at the field scale under natural conditions when applied water and evaporation are the primary controlling physical mechanisms in the hydrologic budget.
Identification of the underlying distribution form of precipitation by using regional data
Authors: Cong Shuzheng , Li Yuanzhang , Vogel John L. , Schaake John C.
Published: February 2004

A method of identifying the underlying distribution form for precipitation is proposed in this paper. This method is different from the classical hypothesis‐testing method and is based upon using regional data. Two fundamental assumptions are made: (1) the distribution forms of rainfall at all stations in a studied area are the same, and the thirdLmoment ratios, τ3, at all stations are also the same; and (2) the unknown underlying distribution form is one among five commonly used distributions: i.e., generalized extreme value (GEV), gamma (GAM), lognormal (LON), generalized Pareto (PAR), and generalized logistic distribution (LGI). Using the proposed method, one can not only choose a distribution form for the given data, but also know the probability that the identification is correct. For a parameter within the range commonly occurring in practice, this probability is reasonably high. Therefore the proposed method would be valuable and informative.
Effect of rainfall‐induced soil seals on soil water regime: Wetting processes
Authors: Mualem Y. , Assouline S. , Eltahan D.
Published: February 2004

The effects of a rainfall‐induced soil seal on wetting processes are studied in the cases of two different soils: Hamra (sandy loam) and loess (loam). The soil seal is identified as the disturbed upper layer where the average hydraulic properties have been changed during rainfall from the initial properties that were identical to those of the undisturbed soil bed. These properties are derived by applying the seal model of Mualem and Assouline (1989), calibrated for the two soils. Determination of the seal thickness, bulk density, retention curve, and hydraulic conductivity function made it possible to solve systematically the flow equation for different boundary conditions, allowing the simulation of the wetting processes within the seal layer as well as the undisturbed profile underneath. The infiltration curves and the water content profiles during and after rainfall are derived for three rainfall intensities. The water content and the capillary head profiles, as well as the variation of these variables with time, at different depths under the soil surface, were also calculated. Smaller amounts of the rainfall infiltrate as the rainfall intensity increases. The infiltration rate diminishes faster as the rainfall intensity increases. The idea of a single infiltration curve as a function of the cumulative rainfall seems to be invalid. Each rainfall intensity yields a different infiltration curve. A rough validation test of the model yielded predicted infiltration curves closely bounded by the experimental results. The final infiltration rate after 50 mm of rainfall also seems to be a function of the rainfall intensity, with the higher rate obtained for the higher rainfall intensity as experimentally observed in other studies. Unlike the explanations found in literature, this study suggests that a shallower saturated zone within the seal layer is the reason for this phenomenon. This study points out that the disturbed layer which forms the surface seal is not saturated from the very beginning of rainfall. It has a significant water‐holding capacity and, thus, takes time to reach saturation. Furthermore, under rainfall of high intensity, the seal layer reaches saturation only at its upper zone close to the soil surface. The lower part may remain unsaturated even after 50 mm rainfall and is larger for the soil of coarser texture.
A composite L1 parameter estimator for model fitting in groundwater flow and solute transport simulation
Authors: Xiang Y. , Sykes J. F. , Thomson N. R.
Published: February 2004

This paper proposes a composite L1 parameter estimator to solve the inverse problems in groundwater flow and solute transport modeling. The estimator is formulated using a weighted L1 norm as the error measure between the vector of the observed hydraulic heads and solute concentrations and the corresponding vector of the heads and concentrations computed from a finite element model for steady state groundwater flow and solute transport in a two‐dimensional areal confined aquifer system. The parameters currently considered are the hydraulic conductivities, the dispersivities, the porosities of the aquifer system, and the solute source concentration(s). The gradients of the state variables with respect to the parameters are computed analytically using a formulation stemming from the finite element model for the state variables. The solutions to two hypothetical groundwater parameter estimation problems are presented to illustrate that the proposed estimator does have the property of being fairly accurate and, more significantly, being robust in handling observation data containing certain outliers.
A model of household choice of water supply systems in developing countries
Authors: Madanat Samer , Humplick Frannie
Published: February 2004

Studies of pipe water demand in developing countries have traditionally analyzed household connection decisions to the pipe water system. On the other hand, empirical observations have revealed that often, after connecting, households do not use their pipe water supply, or augment it with alternative sources. Due to deficiencies in pipe water quality, pressure, or availability, households invest in coping strategies in the form of alternative supplies and storage facilities. Because these strategies have important economic implications, there is a need to develop an understanding of households' water demand that goes beyond connection decisions. This paper presents a model system of household water supply choices. The system accounts for the fact that households may use different supply systems for different uses of water. Moreover, the relation between households' choices of water supply and their connection decisions is explicitly modeled. The approach is illustrated using data from Faisalabad, Pakistan.
A dynamic model of soil salinity and drainage generation in irrigated agriculture: A framework for policy analysis
Authors: Dinar Ariel , Aillery Marcel P. , Moore Michael R.
Published: February 2004

This paper presents a dynamic model of irrigated agriculture that accounts for drainage generation and salinity accumulation. Critical model relationships involving crop production, soil salinity, and irrigation drainage are based on newly estimated functions derived from lysimeter field tests. The model allocates land and water inputs over time based on an intertemporal profit maximization objective function and soil salinity accumulation process. The model is applied to conditions in the San Joaquin Valley of California, where environmental degradation from irrigation drainage has become a policy issue. Findings indicate that in the absence of regulation, drainage volumes increase over time before reaching a steady state as increased quantities of water are allocated to leaching soil salts. The model is used to evaluate alternative drainage abatement scenarios involving drainage quotas and taxes, water supply quotas and taxes, and irrigation technology subsidies. In our example, direct drainage policies are more cost‐effective in reducing drainage than policies operating indirectly through surface water use, although differences in cost efficiency are relatively small. In some cases, efforts to control drainage may result in increased soil salinity accumulation, with implications for long‐term cropland productivity. While policy adjustments may alter the direction and duration of convergence to a steady state, findings suggest that a dynamic model specification may not be necessary due to rapid convergence to a comon steady state under selected scenarios.
Household demand for improved sanitation services in Kumasi, Ghana: A contingent valuation study
Authors: Whittington Dale , Lauria Donald T. , Wright Albert M. , Choe Kyeongae , Hughes Jeffrey A. , Swarna Venkateswarlu
Published: February 2004

A contingent valuation survey was conducted in Kumasi, Ghana, to estimate households' willingness to pay for two types of improved sanitation services: improved ventilated pit latrines and water closets connected to a sewer system. Over 1200 randomly selected households throughout the city were interviewed. Most households were willing to pay more for improved sanitation service than they were currently paying for their existing sanitation system (mostly public and bucket latrines), but in absolute terms the potential revenues from households are not large, of the order of US$1.40 per household per month (about 1–2% of household income). The results of the study confirm the conventional wisdom that conventional sewerage is not affordable to the vast majority of households without massive government subsidies. On the other hand, it appears that only modest subsidies are required to achieve relatively high levels of coverage with on‐site sanitation (improved ventilated pit latrines). This is because improved ventilated pit latrines are much cheaper than conventional sewerage and because most households are willing to pay about as much for a ventilated pit latrine as for a water closet connected to a sewer. Several tests were conducted to check the accuracy of respondents' answers to contingent valuation questions. The findings indicate that contingent valuation surveys can be successfully carried out in cities in developing countries for public services such as sanitation and that reasonably reliable information can be obtained on household demand for different sanitation technologies.
Use of output from high‐resolution atmospheric models in landscape‐scale hydrologic models: An assessment
Authors: Hostetler S. W. , Giorgi F.
Published: February 2004

In this paper we investigate the feasibility of coupling regional climate models (RCMs) with landscape‐scale hydrologic models (LSHMs) for studies of the effects of climate on hydrologic systems. The RCM used is the National Center for Atmospheric Research/Pennsylvania State University mesoscale model (MM4). Output from two year‐round simulations (1983 and 1988) over the western United States is used to drive a lake model for Pyramid Lake in Nevada and a streamfiow model for Steamboat Creek in Oregon. Comparisons with observed data indicate that MM4 is able to produce meteorologic data sets that can be used to drive hydrologic models. Results from the lake model simulations indicate that the use of MM4 output produces reasonably good predictions of surface temperature and evaporation. Results from the streamflow simulations indicate that the use of MM4 output results in good simulations of the seasonal cycle of streamflow, but deficiencies in simulated wintertime precipitation resulted in underestimates of streamflow and soil moisture. Further work with climate (multiyear) simulations is necessary to achieve a complete analysis, but the results from this study indicate that coupling of LSHMs and RCMs may be a useful approach for evaluating the effects of climate change on hydrologic systems.
Optimal management of a groundwater system for seasonally varying agricultural production
Authors: Cunha Maria da Conceição Morais de Oliveira , Hubert Pierre , Tyteca Daniel
Published: February 2004

We discuss the problem of programming the optimal operation of an aquifer system hydraulically linked to a river, using a set of predesigned hydraulic structures, in order to meet agricultural requirements. The focus is on two fundamental aspects: (1) the choice of a model that adequately reflects the physical, dynamic behavior of such a system and possesses characteristics allowing for the treatment of the problem through optimization techniques, and (2) the formulation of the problem as an optimization program. The model includes a physical component, based on the influence coefficient (impulsional response) concept and the principle of superposition, and an agricultural production function, elaborated in such a way as to reflect the dynamic process of plant development, that is, the seasonal life cycle of the crops and the effect of changing hydrological conditions on the latter. Results obtained on a test scenario illustrate the approach.
The regulation of groundwater quality with delayed responses
Authors: Kim C. S. , Hostetler John , Amacher Gregory
Published: February 2004

This research develops a dynamic model of input regulation in the presence of externalities that do not occur simultaneously with input use. The model is formulated to study the regulation of firms that apply fertilizer, where leachate from the application of fertilizer accumulates in groundwater over time. In the model we show the derivation of an optimal nitrogen user fee and the consequences of regulatory design when time lags between nitrogen application and nitrate contamination are present. This research also responds to the need of developing a general solution algorithm for an optimal control model when the control variable exhibits a delayed response. A multistage solution algorithm presented in this paper is different from other studies in that a typical relationship is not assumed for the state and adjoint variables.
Stochastic modeling of solute flux in a heterogeneous partially saturated porous formation
Authors: Russo David
Published: February 2004

A framework for the modeling of solute flux and related entities in partially saturated, heterogeneous porous formations was presented by combining a general Lagrangian formulation (Dagan et al., 1992), relating the travel time moments of the solute pulse to the velocity field, with the stochastic theory of Yeh et al. (1985a, b) for steady, unsaturated flow, relating the statistical moments of the velocity field to properties of the heterogeneous formation. First‐order approximations of the travel time covariance were derived for unidirectional, vertical mean flow in partially saturated, heterogeneous porous formations of three‐dimensional structures. Hypothesizing lognormal distribution for the one‐ and two‐particle travel time probability density functions, the effect of mean water saturation and statistical parameters of the porous formation properties on expected values, and variances of the solute discharge S and accumulated mass M passing through a given horizontal control plane located at an arbitrary vertical distance from the solute source, as a function of time were evaluated. Assessment of the uncertainty in the predictions of S and M and possible application of the results of this investigation to assessment of groundwater contamination hazards were discussed.
Simulation of fluid distributions observed at a crude oil spill site incorporating hysteresis, oil entrapment, and spatial variability of hydraulic properties
Authors: Essaid H. I. , Herkelrath W. N. , Hess K. M.
Published: February 2004

Subsurface oil, water, and air saturation distributions were determined using 146 samples collected from seven boreholes along a 120‐m transect at a crude oil spill site near Bemidji, Minnesota. The field data, collected 10 years after the spill, show a clearly defined oil body that has an oil saturation distribution that appears to be influenced by sediment heterogeneities and water table fluctuations. The center of the oil body has depressed the water‐saturated zone boundary and the oil appears to have migrated laterally within the capillary fringe. A multiphase cross‐sectional flow model was developed and used to simulate the movement of oil and water at the spill site. Comparisons between observed and simulated oil saturation distributions serve as an indicator of the appropriateness of using such models to predict the actual spread of organic immiscible liquids at spill sites. Sediment hydraulic properties used in the model were estimated from particle size data. The general large‐scale features of the observed oil body were reproduced only when hysteresis with oil entrapment and representations of observed spatial variability of hydraulic properties were incorporated into the model. The small‐scale details of the observed subsurface oil distribution were not reproduced in the simulations. The discrepancy between observed and simulated oil distributions reflects the considerable uncertainty in model parameter estimates and boundary conditions, three‐phase capillary pressure‐saturation‐relative permeability functions, representations of spatial variability of hydraulic properties, and hydrodynamics of the groundwater flow system at the study site.
Preferential flow mechanism in a water repellent sandy soil
Authors: Ritsema Coen J. , Dekker Louis W. , Hendrickx J. M. H. , Hamminga W.
Published: February 2004

Dry water repellent soils are difficult to wet, forcing water and solutes to flow via preferential paths through the unsaturated zone. A tracer field experiment was used to investigate the mechanism of preferential flow and transport in a water repellent sandy soil. Water and solutes are distributed by lateral flow within the, relatively wet, thin humose topsoil toward preferential flow paths below this zone. This flow in the upper layer, which is of major importance in the spatial distribution of water and solutes in field soils, is generally not considered, and is introduced here as “distribution flow.” The preferential flow paths are separated by dry soil bodies, which are highly persistent due to their extremely water repellent character and their low hydraulic conductivity. In the wettable zone, below 45 cm depth, water and solutes diverge toward areas below dry soil bodies. Despite this process, the spatial variation in solute concentrations in this zone remained relatively high.
Modification of fluvial gravel size by spawning salmonids
Authors: Kondolf G. Mathias , Sale Michael J. , Wolman M. Gordon
Published: February 2004

Salmonids (salmon and trout) winnow fine sediment from streambed gravels during construction of the nest or “redd” used for spawning and incubation of fertilized eggs. The gravels and interstitial fine sediments excavated during this process are exposed to currents and differentially transported: gravels move a short distance, while the fine sediments are swept further downstream from the redd. To quantify the resultant modification of particle size distributions in redds, we sampled redds and adjacent undisturbed gravels to document changes in size distributions. These data were compiled with previously published observations to analyze the general nature of size modification during spawning. The final percentage finer than 1 mm in the gravels, P1f, is related to the initial percentage finer than 1 mm, P1i, by the equation P1f = 0.63 P1i. Hydraulic variables (water surface slope, mean column velocity, depth, shear stress, unit stream power) explained little of the variance and did not appear in the optimal models. Because fisheries biologists are called upon to evaluate gravels as potential spawning sites, these findings should prove useful in such evaluations.