摘要:

The theory of percolation, originally proposed over 30 years ago to describe flow phenomena in porous media, has undergone enormous development in recent years, primarily in the field of physics. The principal advantage of percolation theory is that it provides universal laws which determine the geometrical and physical properties of the system. This survey discusses developments and results in percolation theory to date, and identifies aspects relevant to problems in groundwater hydrology. The methods of percolation theory are discussed, previous applications of the theory to hydrological problems are reviewed, and future directions for study are suggested.

ISSN:0043-1397    

DOI:10.1029/92WR02707

年代:1993

数据来源: WILEY

摘要:

Lakeshore erosion, characterized as a reduction in distance between property improvements and the lake, will eventually threaten improvements. An option price model suggests that erosion‐prone lakeshore property will be discounted and this discount may be measured by hedonic price analysis. We discuss the conditions that permit benefit estimation from the hedonic regression. Analysis of mail survey returns estimates willingness to pay for erosion protection, as measured by the number of years remaining until property improvements are endangere

ISSN:0043-1397    

DOI:10.1029/92WR02539

年代:1993

数据来源: WILEY

摘要:

This paper presents optimization models for waste load allocation from multiple point sources which include both parameter (Type II) and model (Type I) uncertainty. These optimization models employ more sophisticated water quality simulation models, for example, in the case of dissolved oxygen modeling, QUAL2E and WASP4, than is typically the norm in studies on the optimization of waste load allocation. Variability in selected input parameters to the water quality simulation models gives rise to stochastic dynamic programming approaches. Two types of reliability and feasibility attributes are highlighted, associated with the management options that are generated. Several dissolved oxygen simulation models are incorporated into the optimization procedures to explore the effects of Type I uncertainty on control decisions. Information from simultaneous consideration of multiple simulation models is aggregated in the dynamic programming framework through two regret‐based formulations. By accommodating both model and parameter uncertainty in the modeling framework, trade‐offs can be generated between the two so as to assess their influence on control decisions. The models are applied to a waste load allocation problem for the Schuylkill River in Pennsylva

ISSN:0043-1397    

DOI:10.1029/93WR00182

年代:1993

数据来源: WILEY

摘要:

Institutional economics provides an alternative framework for analyzing existing and proposed water policies. This approach differs from conventional economics in both normative and positive aspects. The normative model employs the concept of instrumental value, rather than efficiency. Water policies are judged based on whether they foster the long‐run viability of economic and ecological systems, not on whether they maximize net present value. The positive model is holistic and more inclusive than standard market models. The role of technical circumstances, nonmonetary goals, interest groups, and power are discussed. The implications of both positive and normative models for water policy are discussed. A set of questions useful in understanding or predicting the prospects for change in water policy is provided, and an institutionalist perspective is offered on water market

ISSN:0043-1397    

DOI:10.1029/92WR02645

年代:1993

数据来源: WILEY

摘要:

Differential dynamic programming with quasi‐Newton approximations (QNDDP) is combined with a finite element groundwater quality simulation model to determine optimal time‐varying pumping policies for reclamation of a contaminated aquifer. The purpose of the QNDDP model is to significantly reduce the large computational effort associated with calculation of optimal time‐varying policies. A Broyden rank‐one quasi‐Newton technique is developed to approximate the second derivatives of the groundwater quality model; these second derivatives are difficult to calculate directly. The performance of the QNDDP algorithm is compared to the successive approximation linear quadratic regulator (SALQR) technique, which sets the complicated second derivatives to 0. QNDDP converged to the optimal pumping policy in approximately half the time that the SALQR technique required. The QNDDP algorithm thus shows great promise for the management of complex, time‐vary

ISSN:0043-1397    

DOI:10.1029/92WR02480

年代:1993

数据来源: WILEY

摘要:

Results of dissolution experiments with trapped nonaqueous phase liquids (NAPLs) are modeled by a mass transfer analysis. The model represents the NAPL as isolated spheres that shrink with dissolution and uses a mass transfer coefficient correlation reported in the literature for dissolving spherical solids. The model accounts for the reduced permeability of a region of residual NAPL relative to the permeability of the surrounding clean media that causes the flowing water to partially bypass the residual NAPL. The dissolution experiments with toluene alone and a benzene‐toluene mixture were conducted in a water‐saturated column of homogeneous glass beads over a range of Darcy velocities from 0.5 to 10 m d−1. The model could represent the observed effluent concentrations as the NAPL underwent complete dissolution. The changing pressure drop across the column was predicted following an initial period of NAPL reconfiguration. The fitted NAPL sphere diameters of 0.15 to 0.40 cm are consistent with the size of NAPL ganglia observed by others and are the smallest at the largest flow vel

ISSN:0043-1397    

DOI:10.1029/92WR02581

年代:1993

数据来源: WILEY

摘要:

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 optimiz

ISSN:0043-1397    

DOI:10.1029/92WR02801

年代:1993

数据来源: WILEY

摘要:

Changes over time in the species composition of fish communities in Adirondack lakes were assessed to determine (1) the approximate numbers offish populations that have been lost and (2) the degree to which fish population losses may have resulted from surface water acidification and acidic deposition. Information on the present‐day status offish communities was obtained by the Adirondack Lakes Survey Corporation, which surveyed 1469 Adirondack lakes in 1984–1987 (53% of the total ponded waters in the Adirondack ecological zone). Two hundred and ninety‐five of these lakes had been surveyed in 1929–1934 during the first statewide biological survey; 720 had been surveyed in one or more years prior to 1970. Sixteen to 19% of the lakes with adequate historical data appeared to have lost one or more fish populations as a result of acidification. Brook trout and acid‐sensitive minnow species had experienced the most widespread effects. Populations of brook trout and acid‐sensitive minnows had been lost apparently as a result of acidification from 11% and 19%, respectively, of the lakes with confirmed historical occurrence of these taxa. By contrast, fish species that tend to occur primarily in lower elevation and larger lakes, such as largemouth and smallmouth bass and brown trout, have experienced little to no documented adverse effects. Lakes that were judged to have lost fish populations as a result of acidification had significantly lower;pH and, in most cases, also had higher estimated concentrations of inorganic aluminum and occurred at higher elevations than did lakes with the fish species still present. No other lake characteristics were consistently associated with fish population losses attributed to acidification. The exact numbers and proportions of fish populations affected could not be determined because of limitations on the quantity and quality of historical data. Lakes for which we had adequate historical data to assess long‐term trends in fish communities were significantly larger and deeper and have higherpH than do Adirondack lakes in general; thus, fish communities adversely affected by acidification and acidic deposition may be underrepresented

ISSN:0043-1397    

DOI:10.1029/92WR02329

年代:1993

数据来源: WILEY

摘要:

The relationships between habitat characteristics and reproductive status of Adirondack brook trout populations were examined utilizing the Adirondack Lake Survey Corporation data base, which includes physical, chemical, and biological data for 1469 lakes. The only variables strongly related to brook trout natural reproduction were indices of groundwater influence on surface water chemistry, specifically silica and sodium concentrations. This finding supports the hypothesis that lake spawning populations of brook trout are strongly dependent on groundwater seepage for successful reproduction. Spawning habitat in small headwater lakes impounded by beaver activity may be degraded as a result of siltation of nearshore zones and diminished groundwater seepage. Adirondack lakes situated in thick‐till basins receive proportionally greater groundwater input than thin‐till lake types and thick‐till lakes also had the highest proportion of self‐sustaining brook trout populations. Acidification is most pronounced in thin‐till basins, which also exhibited a low frequency of self‐sustaining brook trout populations. Although brook trout fisheries may be maintained in acidic lakes by liming and stocking, the establishment of self‐sustaining brook trout populations is not a likely outcome of these management practices. Additionally, there appears to be limited potential for restoration of lake spawning brook trout populations in currently acidic, fishless lakes should acidic inputs decline as a result of reductions in acid‐fo

ISSN:0043-1397    

DOI:10.1029/92WR02336

年代:1993

数据来源: WILEY

摘要:

Mineral acids and bases influencepH largely through their effects on acid‐neutralizing capacity (ANC). This influence becomes particularly significant as ANC approaches zero. Analysis of data collected by the Adirondack Lakes Survey Corporation (ALSC) from 1469 lakes throughout the Adirondack region indicates that variations in ANC in these lakes correlate well with base cation concentrations (CB), but not with the sum of mineral acid anion concentrations (CA). This is because (CA) is relatively constant across the Adirondacks, whereasCBvaries widely. Processes that supply base cations to solution are ion‐specific. Sodium and silica concentrations are well correlated, indicating a common source, mineral weathering. Calcium and magnesium also covary but do not correlate well with silica. This indicates that ion exchange is a significant source of these cations in the absence of carbonate minerals. Iron and manganese concentrations are elevated in the lower waters of some lakes due to reducing conditions. This leads to an ephemeral increase inCBand ANC. When the lakes mix and oxic conditions are restored, these ions largely precipitate from solution. Sulfate is the dominant mineral acid anion in ALSC lakes. Sulfate concentrations are lowest in seepage lakes, commonly about 40 μeq/L less than in drainage lakes. This is due in part to the longer hydraulic detention time in seepage lakes, which allows slow sulfate reduction reactions more time to decrease lake sulfate concentration. Nitrate typically influences ANC during events such as snowmelt. Chloride concentrations are generally low, except in lakes impacted by road

ISSN:0043-1397    

DOI:10.1029/92WR02327

年代:1993

数据来源: WILEY