摘要:

The federal government has increasingly come to predominate in environmental protection. The underlying policies behind that shift are still being debated in the context of groundwater protection. Many of the reasons that led to national statutory schemes for air, surface water, toxics and other environmental media are applicable to groundwater and a greater federal role in the protection of groundwater is appropriate.

ISSN:0043-1397    

DOI:10.1029/91WR01772

年代:1991

数据来源: WILEY

摘要:

This article presents an appraisal of the developmental effects of the Tavropos Irrigation Project in central Greece. Quantitative estimates are generated on the social net present value, the ratio of discounted social benefits to discounted social costs, the social internal rates of return, the direct and indirect benefits vis‐a‐vis employment, and the redistribution of income. This paper concludes with a generalized discussion of the project's social utility, taking into account the existing structural rigidit

ISSN:0043-1397    

DOI:10.1029/91WR01636

年代:1991

数据来源: WILEY

摘要:

A 500‐m2watershed on a deposit of coal refuse was instrumented for measurements of runoff and sediment yield and monitored for 15 months. The range of 42 storm period sediment yields was greater for the watershed as a whole (16 to 3,480 g m−2) than for a 4.65‐m2portion of interfluve surface (15 to 1,596 g m−2). The ratio of sediment yield values (watershed:interfluve) was not constant. Ratios of about 7:1 occurred in late spring, when gully floors were flushed of colluvium that had accumulated during winter. The ratio remained above 2:1 in summer, when intense runoff caused gully incision. Estimates of annual sediment yield from three reaches of gully (82 to 160 kg m−2yr−1) are about an order of magnitude greater than an estimate for interfluves (12 kg m−2yr−1). A correlation analysis indicated that 78% of the observed variance in watershed sediment yield values is associated with characteristics of storm rain

ISSN:0043-1397    

DOI:10.1029/91WR01708

年代:1991

数据来源: WILEY

摘要:

Permeameter experiments were conducted to determine the permeability response of a clay‐bearing sand to changes in fluid composition. These experiments examined the effects of varying cation type and concentration using NaCl and CaCl2solutions, as well as the effects of freshwater flushing of sediments equilibrated with seawater and large versus small stepwise reductions in NaCl concentration. The major goal of the study was to correlate permeability with measured parameters of the pore microstructure. Sediment samples from the tests were analyzed using Brunauer, Emmett, Teller (BET) and ethylene glycol monoethyl ether (EGME) adsorption methods to determine specific surface area. Other samples were examined using scanning electron microscopy and digital image analysis methods. For image analysis, backscattered electron images were acquired and specific measurements of pore structure parameters (porosity, pore‐size distribution) were made. Stepwise multiple regression was used to construct an empirical model of permeability, which included terms of porosity, mean pore diameter, and specific surface area. The Kozeny‐Carman model was applied to the data and led to predicted permeabilities 2 to 3 orders of magnitude lower than measured values. This was attributed to the presence of dead‐end pores and the importance of flow through large conducting c

ISSN:0043-1397    

DOI:10.1029/91WR01570

年代:1991

数据来源: WILEY

摘要:

This study develops a methodology for deriving the spatial and temporal moments of tracer concentration in disordered geological formations and suggests a geostatistical formalism for interpolation and prediction of concentration, conditional to concentration measurements. The required spatial and temporal moments of the concentration are obtained by a biparticle tracking scheme which yields the bivariate probability distribution function of particle displacements in terms of the input log conductivity random field and the prevailing flow conditions. The structure of the moments of the concentration is discussed, and we show that (1) the concentration correlation function is anisotropic, nonstationary and nonsymmetrical; (2) there is a larger correlation between concentrations along the mean flow direction than normal to it; (3) the correlation between the concentration at any two points with fixed coordinates on a moving (Lagrangian) coordinate system increases with travel time; (4) the correlation function necessarily assumes negative values beyond a certain threshold distance; and (5) the concentration variance is finite even when neglecting pore‐scale dispersion. Application of the geostatistical prediction algorithm using the concentration spatial/temporal moments shows a good potential for reducing prediction uncertaint

ISSN:0043-1397    

DOI:10.1029/91WR01732

年代:1991

数据来源: WILEY

摘要:

Historical data for large streams in the Catskill Mountains indicate that acidic deposition has significantly influenced water quality, but that this effect is most observable in early (pre‐1945) data, and consists primarily of increased base cation (CaMg) concentrations. More recent data suggest that landscape disturbance currently exerts a stronger influence on acid/base status of large streams than does acidic deposition, resulting in increases in both CaMg and acid‐neutralizing capacity (ANC). Estimates of SO42−concentration indicate that SO42−is a conservative ion in the Catskills, and stream water concentrations have decreased since reaching maximum values around 1970, consistent with temporal trends in emissions and deposition in the northeastern United States. Nitrate concentrations, on the other hand, have increased substantially in all but one stream in the past two decades, independent of any change in nitrogen deposition in the region; changes in the capacity of watersheds to retain nitrogen are hypothesized as causes of increased stream water NO3−. In small, undisturbed streams, increases in NO3−and decreases in CaMg appear to offset the effects of reduced SO42−, and lead to decreasing

ISSN:0043-1397    

DOI:10.1029/91WR02009

年代:1991

数据来源: WILEY

摘要:

We explored methods for extrapolating mainstream channel lengths of first‐order drainage basins from synoptic data to characterize them for numerical watershed modeling. We analyzed four catchments in a climatologically semiarid arid geologically homogeneous region east of the Cascade Mountains in Washington state. Within each of these catchments, we identified stream channel networks manually from 1:24,000‐scale topographic maps, and from 50‐m resolution digital elevation models using commercially available drainage network extraction methods. A least squares fit of logarithms of mainstream length plotted against basin area established a regression relation to use for predicting mainstream lengths in the smallest subbasins. To test our relation, we compared predicted mainstream lengths with first‐, second‐ and third‐order channel lengths measured from low‐altitude aerial photographs of a representative fourth‐order basin. Our results indicate that relations of mainstream length to basin area derived from coarsely gridded data (e.g., 30 m) cannot be used to characterize stream and basin morphometry in the smallest basins due to the presence of hydrologic and geometric controls (i.e., thresholds) that limit the mainstream channel length and total basin length in first‐, second‐, and third‐order basins. The presence of these thresholds potentially constrains the range over which theoretically self‐similar, or fractal, relationships can be applied to

ISSN:0043-1397    

DOI:10.1029/91WR01551

年代:1991

数据来源: WILEY

摘要:

In order to obtain a good description of the exceedances in a partial duration series it is often necessary to divide the year into a number (2–4) of seasons. Hereby a stationary exceedance distribution can be maintained within each season. This type of seasonal models may, however, not be suitable for prediction purposes due to the large number of parameters required. In the particular case with exponentially distributed exceedances and Poissonian occurrence times the precision of theTyear event estimator has been thoroughly examined considering both seasonal and nonseasonal models. The two‐seasonal probability density function of theTyear event estimator has been deduced and used in the assessment of the precision of approximate moments. The nonseasonal approach covered both a total omission of seasonality by pooling data from different flood seasons and a discarding of nonsignificant season(s) before the analysis of extremes. Mean square error approximations (bias second order, variance first and second order) were employed as measures for prediction uncertainty. It was found that optimal estimates can usually be obtained with a nonseasonal appro

ISSN:0043-1397    

DOI:10.1029/91WR01731

年代:1991

数据来源: WILEY

摘要:

Response functions for drawdown, velocity, storage losses, and capture describe the spatial and temporal reaction of an aquifer to a unit pumping stress. This paper extends the use of response functions to the notion of capture for multilayered aquifer systems. Capture describes the pumping‐induced quantity of water gained by the aquifer from internal or boundary sources. Internal sources include rivers and hydraulically connected aquifers. Boundary sources include constant head and head‐dependent boundaries. Although response functions are defined only for linear systems, a methodology is demonstrated for implementing response functions in cases of nonlinear capture. The value of response functions lies in their utility as hydrologic constraints in management optimization models. An example demonstrates the use of separable programming to determine the nonlinear effects of drawdown below the bottom of a stream

ISSN:0043-1397    

DOI:10.1029/91WR01770

年代:1991

数据来源: WILEY

摘要:

Land subsidence at Ravenna is the result of aquitard and reservoir compaction caused, respectively, by extensive groundwater withdrawals from the unconsolidated Quaternary basin and gas production from a number of pre‐Quaternary pools scattered over the area. Water pumpage paralleled the postwar industrial development of Ravenna until the middle seventies when consumption was drastically curtailed owing to the economic crisis and the activation of a new aqueduct. Gas production started in 1952. The exploitation of several reservoirs is currently under way and the search for new fields is still in progress. Geodetic records indicate that the maximum cumulative subsidence over the period 1950–1986, including a natural geologic settlement of perhaps 2 mm/yr, has been 1.30 m in the industrial zone of Ravenna. In 1980 the municipality promoted a reconnaissance study with the primary aim of providing the information base needed to reconstruct the actual occurrence, understand correctly the physical behavior and produce the essential input data to a mathematical model which realistically relates the subsidence of the city to groundwater withdrawal and gas removal with an emphasis on their respective influences. The results from the three‐dimensional numerical simulations, performed with the aid of mixed finite element, finite difference and integral models, show that the primary responsibility for the regional land sinking should be placed on the subsurface water overdraft which occurred until the middle 1970s. Gas withdrawal plays a role restricted to the area overlying each reservoir with a magnitude depending on the depth of burial, thickness of mineralized rocks and overall volumetric production. A major environmental impact may be expected where the gas subsidence bowl is intersected by the Adriatic coas

ISSN:0043-1397    

DOI:10.1029/91WR01567

年代:1991

数据来源: WILEY