ISSN:0043-1397    

DOI:10.1029/91WR01973

年代:1991

数据来源: WILEY

摘要:

Simulated annealing is introduced and applied to the optimization of groundwater management problems cast in combinatorial form. This heuristic, probabilistic optimization method seeks minima in analogy with the annealing of solids and is effective on large‐scale problems. No continuity requirements are imposed on objective (cost) functions. Constraints may be added to the cost function via penalties, imposed by designation of the solution domain, or imbedded in submodels (e.g., mass balance in aquifer flow simulators) used to evaluate costs. The location of global optima may be theoretically guaranteed, but computational limitations lead to searches for nearly optimal solutions in practice. Like other optimization methods, most of the computational effort is expended in flow and transport simulators. Practical algorithmic guidance that leads to enormous computational savings and sometimes makes simulated annealing competitive with gradient‐type optimization methods is provided. The method is illustrated by example applications to idealized problems of groundwater flow and selection of remediation strategy, including optimization with multiple groundwater control technologies. They demonstrate the flexibility of the method and indicate its potential for solving groundwater management problems. The application of simulated annealing to water resources problems is new and its development is immature, so further performance improvements can be expec

ISSN:0043-1397    

DOI:10.1029/91WR01468

年代:1991

数据来源: WILEY

摘要:

Use of mathematical models in water resource management has been plagued in the past by the lack of communication, understanding, and involvement of managers in the model development. Interactive modeling methods give managers an appropriate role in model use, calibration, and verification. This paper extends the idea of interactive reservoir modeling using the intelligent decision support system approach. An advisory tool developed using this approach integrates formal reservoir models with reservoir expertise for making both numerical and logical inferences. This integration required special treatment, programming skills, and representations. This tool is intended to help a user to select and use the proper formal model(s) for single multipurpose reservoir analysis. The use of the tool may improve the accuracy and effectiveness of information available to managers, decision makers, and researchers. A practical example of the Gruza reservoir study demonstrates the benefits of implementing the approach.

ISSN:0043-1397    

DOI:10.1029/91WR01621

年代:1991

数据来源: WILEY

摘要:

A model of contingent market behavior is developed which emphasizes the role of household information about wetlands and related environmental goods. Information is acquired through previous experience with wetlands and through the contingent market. Households which are unaware of substitute or complement environmental goods when participating in contingent markets may overstate or understate willingness to pay values. This paper estimates willingness to pay for preservation of the Clear Creek wetland in western Kentucky when faced with surface coal mining. We test for the effects of explicit information about related environmental goods on contingent values by measuring the difference in stated willingness to pay. Willingness to pay for preservation of the Clear Creek wetland decreases with information about surface coal mine lake reclamation and, in the initial, independent format increases with information about a nearby publicly owned, wetland area. These findings suggest that the lack of explicit information about related environmental goods in contingent markets can contribute to a misstatement of willingness to pay.

ISSN:0043-1397    

DOI:10.1029/91WR01769

年代:1991

数据来源: WILEY

摘要:

A chloride tracer was applied to the surface of a vegetable field and then leached downward by rainfall and irrigation. Tracer concentrations in a vertical two‐dimensional region down to a depth of 2.4 m were monitored with suction cups that, were installed horizontally from a tunnel. The uniformly applied tracer pulse split into a slowly moving main pulse and a series of fast pulses. The first of the fast pulses reached a depth of 2.2 m after an infiltration of just 31 mm of natural rainfall, whereas the peak of the main pulse was still at a depth of 0.84 m by the end of the experiment after an infiltration of 0.853 m. The movement of the main pulse can be described by a convection‐dispersion process in a homogeneous medium, provided that time is replaced by cumulative infiltration. However, the values of the parameters that produce a maximum agreement between the model and the observed main pulse have no physical basis, and consequently prediction of solute movement, based on measurements of soil properties, is not possi

ISSN:0043-1397    

DOI:10.1029/91WR01771

年代:1991

数据来源: WILEY

摘要:

The spatial variability of hydrogeochemical processes was studied within an 18‐m‐thick unit of clayey till beneath a flat prairie landscape. Models of major element mass transfer, constrained by chemical, mineralogical, and isotopic measurements on waters and solids, were developed for two end‐member water quality types occurring within the unit. The observed pattern of chemical variation, which is predominantly lateral on a scale of tens of meters, is caused by microtopographically controlled differences in the ratio of vertical water flux to oxidation rate associated with depression‐focused recharge. Such variation is to be expected where dynamic flow regimes develop in thin surficial tills containing chemically reduced constituents. Observed depletions of major elements from oxidized zones of the till support the mass transfer models and demonstrate that the time scales of persistence of hydrogeochemical variability in the till and of water quality evolution in the aquifer beneath range from 104to 105year. Na and S concentrations in such aquifers will depend primarily on ratios of influxes of end‐member water quality types from the till above, while Ca, Mg, and inorganic C concentrations will remain high as long as partial pressures of CO2in the till remain high. CO2generation in the till is discussed in the companion paper (Keller, th

ISSN:0043-1397    

DOI:10.1029/91WR01586

年代:1991

数据来源: WILEY

摘要:

The spatial distributions of inorganic and organic carbon in gas, aqueous, and solid phases were studied in an 18‐m‐thick surficial deposit of fractured clayey calcareous till. Large PCO2increases were observed with increasing depth at the bottoms of vadose zones from which solid organic carbon had been depleted. Hydrochemical reaction simulations indentified a reaction path consistent with PCO2, O2, major element chemistry,13C, and14C isotope observations; this path is “open” to a biogenic CO2reservoir with PCO2higher than, and14C composition considerably different from, that of the soil zone. Such CO2reservoirs, occurring in deep‐vadose/shallow saturated zones and thus isolated by overlying sediments from temperature fluctuations which limit soil‐zone respiration, may be common in the Western Glaciated Plains as evidenced by prevalence of hard, high‐PCO2waters in the region's intertill aquifers. Carbon 14 data suggest that in the till, both dissolved organic C and dissolved inorganic C have two sources: soil organic matter and kerogen in the till matrix. Regardless of source(s), initial14C activities of both aqueous C pools at the water table are “diluted” substantially relative to the actual residence time of the water; unappreciated, this could cause large relative errors in the calculation of radiocarbon‐based gr

ISSN:0043-1397    

DOI:10.1029/91WR01587

年代:1991

数据来源: WILEY

摘要:

A periodic analytical theory previously tested only against diurnal variations is applied to a 66‐day springtime period at Agassiz, British Columbia. Comparison is made with daily average values of the surface energy balance components, soil temperatures, and near‐surface atmospheric potential temperatures and water vapor densities measured throughout this period. It is shown that the inability of the periodic theory to predict the measured warming trend at the 0.5 m depth in the soil can be overcome by applying the theory to the whole of 1978, i.e., by imbedding the period of interest in a longer period. A new analytical theory that accounts for aperiodic transient effects is also described and compared with measured soil temperatures. This theory can also account for the observed soil wanning trend but is sensitive to small errors in the prescribed soil surface heat flux density. Additional analytical calculations show that advection of heat within the soil associated with evaporation and rainfall could have significantly influenced the long‐term temperature trends observed at Agassiz. The poorer success with the analytical approach when applied to long‐term rather than diurnal variations suggests that to predict the former accurately a numerical model is r

ISSN:0043-1397    

DOI:10.1029/91WR01637

年代:1991

数据来源: WILEY

摘要:

The effects of investigator‐dependent configuration and calibration procedures on model predictions are difficult to evaluate when sufficient data for model testing are not available. We derived a set of rules and algorithms (referred to as input mapping) to provide consistent inputs for the Integrated Lake Watershed Acidification Study (ILWAS), Model of Acidification of Groundwater in Catchments (MAGIC), and Enhanced Trickle Down (ETD) watershed acidification models without calibration. Model predictions of lake chemistry based on input mapping were similar for two dissimilar northeast U.S. watersheds, and were within the variability obtained with independent calibration of the three models and the interannual variability observed in two studies of natural watersheds. In a companion paper (Rose et al., this issue), Monte Carlo analysis is used, in conjunction with input mapping, to compare model predictions under varying input

ISSN:0043-1397    

DOI:10.1029/91WR01718

年代:1991

数据来源: WILEY

摘要:

A combination of input mapping (Rose et al., this issue) and Monte Carlo simulation was used to quantitatively compare the predictions of the Integrated Lake Watershed Acidification Study (ILWAS), Model of Acidification of Groundwater in Catchments (MAGIC), and Enhanced Trickle Down (ETD) watershed acidification models. Monte Carlo simulation was used to impose regional variability on selected model inputs of two dissimilar watersheds resembling those found in the northeastern United States for four different SO42−deposition scenarios. Model predictions were viewed in aggregate (distributions, medians) corresponding to population‐level predictions, and on an iteration‐by‐iteration basis corresponding to watershed‐specific predictions. For each of these, predicted values of acid‐neutralizing capacity (ANC) were treated as relative scale (changes in ANC in response to changes in deposition) and absolute scale (ANC concentrations, number of acidic lakes) predictions. Aggregate and iteration‐specific predictions viewed on a relative scale were similar for three models under small to moderate changes in SO42−deposition. Aggregate and iteration‐specific predictions differed among models when viewed on an absolute scale. Absolute scale predictions were most similar under conditions of high variability in deposition. Proper interpretation of multiple model forecasts requires objective quantification of the effects of model differenc

ISSN:0043-1397    

DOI:10.1029/91WR01717

年代:1991

数据来源: WILEY