摘要:

The information and data used to support decision making under uncertainty in water resources situations can often be characterized as being very limited or weak. The representation of knowledge in conventional Bayesian decision analysis is in the form of precisely specified distributions and is the same no matter how weak the information source for this knowledge. A Bayesian analysis therefore may inadvertently impart too much precision to the input information and to the results. The concept of imprecise probability addresses this problem of excessive precision and a number of methods incorporating this concept have emerged. One such method, developed by Dempster and Shafer, accommodates greater imprecision by allowing the specification of probabilities on intervals. Theoretical aspects of the Dempster‐Shafer methodology and its application to inference and decision analysis are described. A water resources example of an application of the Dempster‐Shafer approach is presented, and the results contrasted with those obtained from the closest equivalent Bayesian sch

ISSN:0043-1397    

DOI:10.1029/92WR01818

年代:1992

数据来源: WILEY

摘要:

A dynamic optimization model for irrigation management and investment of an individual field is formulated. The model is applicable to situations where soil salinity is a current or potential problem and where drainage flows incur costs. The crop rotation is prespecified and several alternate irrigation systems are available for investment. These differ in application uniformity and cost. The field is assumed to be spatially variable in soil salinity and infiltrated water. The joint distribution of these two variables evolves over time in response to annual volumes of irrigation water and type of irrigation system. Social net benefits are defined as crop revenue net of irrigation costs, production costs, and environmental/disposal costs associated with percolation of water below the root zone. The optimization problem is to choose annual applied water volumes and investment in irrigation systems to maximize the present value of social net benefits.

ISSN:0043-1397    

DOI:10.1029/92WR01747

年代:1992

数据来源: WILEY

摘要:

Optimal decision rules and dynamics are characterized for the irrigation management model in the previous paper (Knapp, this issue (a)). For a constant crop and irrigation system, the decision rules are concave inE[s] and SD[s]. That is, seasonal water applications first increase as these variables increase, and then possibly decrease. Optimal water applications are observed to be decreasing in the correlation coefficient, although the effect is small. Optimal water applications and soil salinity follow a cyclical time path with a multicrop rotation. The decision rules for applied water are also found to vary for the same crop depending on place within the crop rotation. A range of irrigation systems are efficient depending on prices and other parameters. Investment dynamics are generally a constant type of irrigation system with possibly an initial transition period of another system type. More complex investment behavior is observed with constrained water supplies.

ISSN:0043-1397    

DOI:10.1029/92WR01746

年代:1992

数据来源: WILEY

摘要:

Water demand is characterized for the cotton‐cotton‐tomatoes rotation considered in the previous paper (Knapp, this issue (b)). Demand is found to be price inelastic. However, currently low water prices imply that fairly moderate increases in water prices can result in large water savings. A marginal cost curve for source control of drain water emissions is constructed. Moderate increases in drainage emissions fees can result in large reductions in drain water emissions with relatively small impacts on income. Management response and income effects from increased water salinity are estimated. The model is also extended to consider drain water reuse. Typical optimal management with reuse is low‐volume, low‐quality water on first‐year cotton, improved quality and quantity on second‐year cotton, and the highest quality water on salt‐sensitive tomatoes. An approach to maximization of multifield farm‐level returns is proposed using decentralized pricing and the field‐level o

ISSN:0043-1397    

DOI:10.1029/92WR01745

年代:1992

数据来源: WILEY

摘要:

This paper is concerned with the distributive consequences of alternative methods of allocating transferable water licenses in Queensland, Australia. The equilibrium of a number of different cooperative games will be used to judge which method of initial allocation of water entitlements potentially produces the most equitable distribution of the income derived from regulated water.

ISSN:0043-1397    

DOI:10.1029/92WR01795

年代:1992

数据来源: WILEY

摘要:

Mercury, which is transported globally by atmospheric pathways to remote aquatic environments, is a ubiquitous contaminant at very low (nanograms Hg per liter) aqueous concentrations. Until recently, however, analytical and sampling techniques were not available for freshwater systems to quantify the actual levels of mercury concentrations without introducing significant contamination artifacts. Four different sampling strategies were used to evaluate ground water flow as a mercury source and transport mechanism within aquatic systems. The sampling strategies employ ultraclean techniques to determine mercury concentrations in groundwater and pore water near Pallette Lake, Wisconsin. Ambient groundwater concentrations are about 2–4 ng Hg L−1, whereas pore waters near the sediment/water interface average about 12 ng Hg L−1, emphasizing the importance of biogeochemical processes near the interface. Overall, the groundwater system removes about twice as much mercury (1.5 g yr−1) as it contributes (0.7 g yr−1) to Pallette Lake. About three fourths of the groundwater mercury load is recycled, thought to be derived from the wat

ISSN:0043-1397    

DOI:10.1029/92WR01766

年代:1992

数据来源: WILEY

摘要:

Radiosonde measurements above the heterogeneous forest of the Landes region in southwestern France provided vertical profiles of potential temperature and specific humidity in the atmospheric boundary layer. For all of the 62 profiles analyzed under unstable atmospheric conditions a surface sublayer could be identified within which the Monin‐Obukhov similarity was consistent with the regional surface fluxes of sensible heat and latent heat (evaporation). For the potential temperature the vertical extent of this sublayer was found to be 41 (±30) ≤ (z−d0)/Z0≤ 130 (±49), whereZ0= 1.2 m is the roughness height andd0= 6.0 m is the displacement height; for the specific humidity it was 48 (±36) ≤ (z−d0)/z0≤ 153 (±63). These results show that irregular forest surfaces are not anomalous, as regards the lower limit of the surface layer in comparison with surfaces with smaller roughness. The surface fluxes derived from the profile measurements were compared with flux measurements obtained by means of an eddy correlation system atop a 29 m mast, some 9 m above a mature section of forest some 4.5 km away from the launching site of the radiosondes; these independent measurements were made by a team from the Institute of Hydrology (Wallingford, England). On average, these two types of estimates were in good agreement. For the sensible heat flux the correlation coefficient wasr= 0.75. For the evaporation rate it wasr= 0.66. For the evaporation obtained by means of the energy budget from the sensible heat flux it improved tor= 0.82. The profile‐derived fluxes did not compare as favorably with corresponding flux values measured above agricultural crops in clearings. This confirms that the forest was the dominant surface at

ISSN:0043-1397    

DOI:10.1029/92WR01860

年代:1992

数据来源: WILEY

摘要:

The feasibility of integrating multicomponent mass transport equations over geologic time spans is demonstrated for the case of pure advection in a homogeneous porous medium. The mathematical formulation of the problem is based on the quasi‐stationary state approximation, or multiple reaction path description, in which the time evolution of a geochemical system is represented by a sequence of stationary states or reaction paths. The method is implemented in the computer code MPATH which solves the transport equations in a single spatial dimension taking into account irreversible mineral precipitation/dissolution reactions and local equilibrium of aqueous complexing reactions. An adaptive grid enables the positions of reaction zones, with widths which vary over many orders of magnitude and which move with greatly differing velocities, to be tracked simultaneously over geologic time spans. There appears to be virtually no limitation to the number of chemical species that can be included in the code without rendering the computational effort beyond the bounds of a high‐performance workstation. The numerical accuracy of the solution can be verified through global mass conservation equations and by comparing the asymptotic kinetic solution with the corresponding solution to algebraic equations representing local equilibrium conditions for pure advective transport, if such solutions exist. The code MPATH is applied to several examples including migration of redox fronts, weathering and hydrothermal alteration in a spatially varying temperature field. These examples demonstrate the absolute necessity of solving the governing transport equations for sufficiently long time spans in order to fully characterize the behavior of the sys

ISSN:0043-1397    

DOI:10.1029/92WR01765

年代:1992

数据来源: WILEY

摘要:

A numerically efficient procedure is presented for computing optimal time‐varying pumping rates for remediation of contaminated groundwater described by two‐dimensional numerical models. The management model combines a pollutant transport model with a constrained optimal control algorithm. The transport model simulates the unsteady fluid flow and transient contaminant dispersion‐advection in a two‐dimensional confined aquifer. A Galerkin's finite element method coupled with a fully implicit time difference scheme is applied to solve the groundwater flow and contaminant transport equations. The constrained optimal control algorithm employs a hyperbolic penalty function. Several sample problems covering 5–15 years of remediation are given to illustrate the capability of the management model to solve a groundwater quality control problem with time‐varying pumping policy and water quality constraints. In our example, the optimal constant pumping rates are 75% more expensive than the optimal time‐varying pumping rates, a result that supports the need to develop numerically efficient optimal control‐finite element algorithms for groundwa

ISSN:0043-1397    

DOI:10.1029/92WR01685

年代:1992

数据来源: WILEY

摘要:

A multivariate dynamic disaggregation model is developed as a stepwise approach to stochastic disaggregation problems, oriented toward hydrologic applications. The general idea of the approach is the conversion of a sequential stochastic simulation model, such as a seasonal AR(1), into a disaggregation model. Its structure includes two separate parts, a linear step‐by‐step moments determination procedure, based on the associated sequential model, and an independent nonlinear bivariate generation procedure (partition procedure). The model assures the preservation of the additive property of the actual (not transformed) variables. Its modular structure allows for various model configurations. Two different configurations (PAR(1) and PARX(1)), both associated with the sequential Markov model, are studied. Like the sequential Markov model, both configurations utilize the minimum set of second‐order statistics and the marginal means and third moments of the lower‐level variables. All these statistics are approximated by the model with the use of explicit relations. Both configurations perform well with regard to the correlation of consecutive lower‐level variables each located in consecutive higher‐level time steps. The PARX(1) configuration exhibits better behavior with regard to the correlation properties of lower‐level variables with lagged higher‐

ISSN:0043-1397    

DOI:10.1029/92WR01299

年代:1992

数据来源: WILEY