bluuebunny/crossref_metadata_2025 huggingface dataset:
On the detection of shallow aquifers using thermal infrared imagery
Authors: Huntley David
Published: February 2008

Patterns appearing on a thermal infrared image are primarily a function of the temperature of the earth's surface. Diurnal surface temperatures are affected by the thermal inertia and solar reflectance of the surface, by meteorologic variables, by evaporation rates, and by subsurface temperature effects such as the effect due to varying groundwater depth. Variations in surface material result in variations in both thermal inertia and solar reflectance, causing a change in both the magnitude of temperatures through the diurnal cycle and the amplitude of diurnal temperature variation. Variations in soil moisture result in similar effects and, in addition, result in a change in evaporative cooling rates. Variation in groundwater depth produces an effect on surface temperature that is discriminable from variations in solar reflectance and thermal inertia but is not discriminable from variations in evaporative cooling rates.
Elutriate–primary productivity bioassays of dredge spoil disposal in Lake Erie
Authors: Flint R. Warren , Lorefice George J.
Published: February 2008

The standard sediment elutriate procedure was combined with radioactive primary productivity methods to evaluate impacts of dredged material disposal on pelagic primary producers. Seven treatment levels suggested that dredged material disposal inhibited algal photosynthesis at higher concentrations. The procedure developed reflected the ‘bioavailability’ of dissolved constituents released during deposition. The results also implied that particle formation within the water column during disposal may promote microbial (heterotrophic) growth. The procedure described is especially valuable in evaluating pelagic effects of dredged material disposal because of its use of natural populations, minimal expense, and, most importantly, short experimental duration compared to that of standard laboratory bioassays.
An iterative method for calibrating a multicell aquifer model
Authors: Bachmat Y. , Dax A.
Published: February 2008

The inverse problem is formulated as a linear least squares problem. Lower and upper bounds on the parameters are added to ensure hydrologic plausibility. The proposed algorithm utilizes the special structure of the problem to enable efficient handling of models which are composed of a large number of cells. An example of calibrating a 241‐cell model of the coastal aquifer of Israel with the proposed algorithm is presented.
A soil‐plant‐atmosphere model for transpiration and availability of soil water
Authors: Federer C. A.
Published: February 2008

In a soil‐plant‐atmosphere model the soil was divided into several layers with different root densities and soil water potentials, but the aboveground portion was represented by single values both of diffusive resistance and of plant water potential Ψ. The model used Cowan's theory for root uptake, Monteith's combination equation for vapor flux, constant internal resistance per unit of root length, and stomatal response to light, humidity, temperature, and Ψ. For forests, unstressed transpiration Eu, defined as the transpiration that would occur if stomatal opening were not reduced by low Ψ, may be a more useful value than potential evapotranspiration. The model simulated field data from a hardwood forest in terms of both Ψ and stomatal behavior within a day and over a summer. Stomata had a threshold type of response to Ψ, with closure only occurring as Ψ approached a critical potential Ψc. Internal resistance was high enough that when Eu was high, Ψ became low enough to cause some stomatal closure and reduce transpiration even when soil was wet. As soil dried, potential gradient decreased because plant potential could not decline further than Ψc. But internal resistance remained generally larger than rhizosphere resistance, so decrease in uptake with soil drying depended more on the decreasing soil‐plant gradient than on increasing rhizosphere resistance. Simple functions, either of total soil water content or of vertical root and soil water distribution, can be used to determine the reduction of transpiration below Eu in hydrologic models.
Streamflow generation in a forested watershed, New Zealand
Authors: Mosley M. Paul
Published: February 2008

A 0.3028‐ha watershed has been instrumented to monitor streamflow and subsurface flow through the soil mantle at a variety of topographic locations. The watershed is forested, with steep (35°) slopes and shallow (average 55 cm) soils on impermeable Old Man gravels. Data for a number of storms indicate that subsurface flow via ‘macropores’ (root channels, pipes) and seepage zones in the soil is the predominant mechanism of channel stormflow generation in storms with quickflows greater than about 1 mm. Subsurface flow from all parts of the watershed appears to contribute to stormflow even in very small storms (quickflow of the order of 3% of net precipitation). The saturated hydraulic conductivity of the soil matrix is not a limiting factor on the ability of subsurface flow to generate channel stormflow, because dye tracer experiments demonstrate that water may move through macropores (particularly root channels) at rates 2 orders of magnitude greater. However, subsurface flow from lower slope areas contributes to delayed flow; cessation of subsurface flow and Streamflow after a drought period is roughly coincident in time. In the study area it appears that streamflow is at almost all times dominated by subsurface flow and that runoff from partial and variable source areas contributes significant quantities of streamflow only during the rising limb of small (less than 1 mm of quickflow) flood hydrographs.
Convective and advective circulation of Lake Powell, Utah‐Arizona, during 1972–1975
Authors: Johnson Noye M. , Merritt David H.
Published: February 2008

The water circulation in Lake Powell has been documented and analysed for the period 1972–1975 on a monthly, synoptic basis. From its inception Lake Powell has convectively mixed only during the winter cooling period. At no time, however, during 1972–1975 did this vertical mixing extend to the lake bottom. During the winter dissolved salt becomes important in stabilizing the lake. The yearly heat budget of the lake averages 40 kcal/cm2. A dominant feature of the summer circulation of the lake is an overflow density current from the upstream Colorado River. The overflow current mechanically sets the depth and extent of the thermocline. During maximum stratification (July–September) a pervasive and intense oxygen‐depletion layer develops immediately below the epilimnion‐thermocline interface. Cold, dense upstream waters intrude the lake during the winter as an underflow density current, which annually replenishes the oxygen supply of the bottom waters. An integral component of the lake's circulation throughout the year is a withdrawal current at mid‐depth within the lake. The configuration and extent of the withdrawal current is a function of dam operation and seasonal density stratification.
Dispersion in stratified porous media: Analytical solutions
Authors: Al‐Niami A. N. S. , Rushton K. R.
Published: February 2008

Analytical solutions are presented for dispersion in stratified porous media. Two different situations are considered, namely, flow parallel to the stratifications and flow perpendicular to the stratifications. Numerical examples are selected to illustrate certain of the trends.
Probability weighted moments compared with some traditional techniques in estimating Gumbel Parameters and quantiles
Authors: Landwehr J. Maciunas , Matalas N. C. , Wallis J. R.
Published: February 2008

Estimates of the parameters and quantiles of the Gumbel distribution by the methods of probability weighted moments, (conventional) moments, and maximum likelihood were compared. Results were derived from Monte Carlo experiments by using both independent and serially correlated Gumbel numbers. The method of probability weighted moments was seen to compare favorably with the other two techniques.
Observations of a potential size effect in experimental determination of the hydraulic properties of fractures
Authors: Witherspoon P. A. , Amick C. H. , Gale J. E. , Iwai K.
Published: February 2008

In several recent investigations, experimental studies on the effect of normal stress on the hydraulic conductivity of a single fracture were made by using three rock specimens ranging in cross‐sectional area from 0.02 m2 to over 1.0 m2. At the maximum stress levels that could be attained (10–20 MPa), minimum values of the fracture hydraulic conductivity were not the same for each rock specimen. These minimum values increased with specimen size, an indication that the determination of fracture conductivity may be significantly influenced by a size effect. The implications of these results are important. Cores collected in the field are normally not larger than 0.15 m in diameter. However, the results of this work suggest that when a core of this size is used for laboratory investigations, the results may be nonconservative in that fracture permeabilities will be significantly lower than those that will be found in the field. If the results with an ultralarge Core (0.95 m in diameter) are more indicative of field conductivities for a fracture under stress, then further work is needed to determine optimum specimen size so that reliable results on flow in fractures under stress will be available.
Recycling of water in the Amazon Basin: An isotopic study
Authors: Salati Eneas , Dall'Olio Attilio , Matsui Eiichi , Gat Joel R.
Published: February 2008

The oxygen‐18 content of precipitation in the Amazon basin is characterized by a very small inland gradient, 0.75 × 10−3 ‰ km−1. This is a consequence of the large contribution of reevaporated moisture to the basin's water balance. A distinct seasonal and regional pattern of stable isotope composition has been recognized and shows the basin to be inhomogeneous from the hydrometeorological point of view. The occasional appearance of very low δ values is believed to be related to the position of the ITCZ rather than to interbasin processes.
The geomorphologic structure of hydrologic response
Authors: Rodríguez‐Iturbe Ignacio , Valdés Juan B.
Published: February 2008

A unifying synthesis of the hydrologic response of a catchment to surface runoff is attempted by linking the instantaneous unit hydrograph (IUH) with the geomorphologic parameters of a basin. Equations of general character are derived which express the IUH as a function of Horton's numbers RA, RB, and RL; an internal scale parameter LΩ and a mean velocity of streamflow v. The IUH is time varying in character both throughout the storm and for different storms. This variability is accounted for by the variability in the mean streamflow velocity. The underlying unity in the nature of the geomorphologic structure is thus carried over to the great variety of hydrologic responses that occur in nature. An approach is initiated to the problem of hydrologic similarity.
A stochastic model for particle sorting and related phenomena
Authors: Troutman Brent M.
Published: February 2008

A number of factors contribute to the variability in particle size distribution with position, or sorting, that is often observed in natural channels. Several of these factors are readily examined by using stochastic models of particle movement along a streambed. If particle position and particle size are treated as jointly distributed random variables, then sorting is reflected in the fact that the conditional distribution of size given position depends on the value of position. This conditional distribution is most easily derived by first postulating the form of the conditional distribution of position given size and of the marginal size distribution. Further, the effect of mixing particles from two or more distinct sources can be considered by examining the joint distribution of three random variables: size, position, and source. This is useful in predicting size distribution downstream from the point where a tributary enters a channel. Longitudinally varying transport conditions, which also contribute significantly to sorting, are conveniently modeled with a nonhomogeneous Poisson process. Here it is assumed that the particle motion consists of a sequence of steps of random length, each step followed by a rest period of random duration. It is the number of particle rest positions as a function of distance from the initial position that obeys a Poisson process, so the proposed model allows for systematic change of the step length and rest duration distributions with position downstream.
A statistical approach to the inverse problem of aquifer hydrology: 3. Improved solution method and added perspective
Authors: Neuman Shlomo P.
Published: February 2008

Paper 1 of this sequence presented a new statistically based approach to the problem of estimating spatially varying aquifer transmissivities on the basis of steady water level and flux data. Paper 2 described a case study in which the new method had been applied to actual field data from the Cortaro Basin in Southern Arizona. The purpose of paper 3 is to introduce a new efficient method of solution which works under a much wider range of conditions than the method employed in papers 1 and 2. The new method is based on a variational theory developed by Chavent (1971), which is extended here to the case of generalized nonlinear least squares. The method is implemented numerically be a finite element scheme. The inverse problem is posed in terms of log transmissivities instead of transmissivities and is solved by a Fletcher‐Reeves conjugate gradient algorithm in conjunction with Newton's method for determining the step size to be taken at each iteration. The method does not require computing sensitivity coefficients, and one may therefore expect it to result in considerable savings of both computer storage and computer time. Posing the problem in terms of log transmissivities is shown to have important advantages over the traditional approach, not the least of which is guaranteeing that the computed transmissivities will always be positive. The paper includes a theoretical analysis of the effect that various errors corrupting the data and the model may have on the final log transmissivity estimates. This analysis shows that small errors in the model and in the flow rate and sink/source data have only a minor influence on the log transmissivity estimates and therefore can often be disregarded. On the other hand, low‐amplitude noise in the water level data may cause these estimates to become unstable and therefore must always be filtered out during the solution of the inverse problem. Two theoretical examples are included to demonstrate the ability of the new method to deal with artificial noise of a relatively large amplitude, derived from a given stochastic model. The results demonstrate that the inverse method may be capable of computing log transmissivity estimates with an error variance which is significantly smaller than that of the original (or prior) log transmissivity data. The variance reduction achieved in this manner is shown to depend on the quantity and quality of data describing the flow regime. Finally, it is shown that undercalibration (when the variance of the computed residuals exceeds the error variance of the ‘Observed’ water levels) and/or overcalibration (when the variance of the residuals is less than the error variance of the ‘Observed’ water levels) may lead to relatively poor results, whose error variance can be so large as to render the inverse solution useless.
Dynamic models of residential water demand
Authors: Agthe Donald E. , Billings R. Bruce
Published: February 2008

Static, Fisher‐Kaysen, Koyck, flow adjustment (Bergstrom), and stock adjustment econometric models of the demand for residential water are tested for their ability to explain the monthly residential demand for water in Tucson. Marginal price and a second price‐related variable are used in the estimating equations to account for block rates and fixed charges in the water rate schedule. The other independent vari ables are household income and evapotranspiration minus rainfall. The Fisher‐Kaysen model produced very poor statistical results. The estimated long‐run marginal price elasticities of demand varied from −0.266 to −0.705. The short‐run marginal price elasticity estimates varied from −0.179 to −0.358 except for the linear flow adjustment model with a value of −2.226. This unexpected result casts some doubt on the applicability of the flow adjustment model to estimating the price elasticity of demand with monthly data.
Determination of soil water content from terrestrial gamma radiation measurements
Authors: Loijens H. S.
Published: February 2008

Natural gamma radiation emitted by the soil and measured at the surface with a gamma ray spectrometer is a function of the radioactive activity of the soil and the linear attenuation coefficient. The dependence of the linear attenuation coefficient on soil water content is explored for selected soil water profiles by numerical integration. These soil water profiles were generalized distributions based on gravimetric measurements over a sandy soil at the Central Experimental Farm in Ottawa. A comprehensive analysis of the measurements showed that inhomogeneous water distribution accounted for a 1.8% error in the count rate compared to a 2.6% error associated with random count rate fluctuation and instrument error. The depth of the soil layer contributing to natural gamma radiation at the surface depends also on the water content; 90% of the total radiation is contributed by a dry soil of depth 0.18 m, compared to 0.14 m for a soil with a fractional water content of 0.2. The total expected error in the measurement over the range of soil water encountered (0.03–0.24) is shown to be 0.033 for the 0.10‐m layer and 0.025 for the 0.25‐m layer.
Short‐ and long‐run effects of price on municipal water use
Authors: Carver Philip H. , Boland John J.
Published: February 2008

Empirical studies of the response of municipal water use to price have frequently failed to distinguish between long‐ and short‐run aspects of adjustments in water use. Pooled time series and cross‐sectional data for the Washington, D. C., metropolitan area are used to estimate both the long‐ and short‐run response of aggregate water use to price. The data are fitted to a flow adjustment model of the Nerlove (1958) type. Short‐run elasticity for aggregate annual water use is shown to be less than 0.1 in absolute value, while long‐run elasticities are evidently within the range of results reported by previous investigators. When water use is separated into seasonal and nonseasonal components, however, the elasticities estimated for the seasonal component are substantially smaller (more inelastic) than previously reported, both in the short run and in the long run.
A reevaluation of price elasticities for irrigation water
Authors: Howitt Richard E. , Watson William D. , Adams Richard M.
Published: February 2008

The effectiveness of pricing systems in the allocation of irrigation water is linked with the price elasticity of demand of farmers for water. Using microeconomic theory, it is shown that omission of the elasticity of demand for the crop produced leads to an inelastic bias in the demand for irrigated water. Linear programing approaches omit the product elasticity of demand and are consequently biased, whereas quadratic programing approaches to estimating derived demands for irrigation water include product demand functions. The difference between the resulting estimates are empirically demonstrated for regional derived demand functions estimated from a model of California's agricultural industry.
Runoff responses to soil heterogeneity: Experimental and simulation comparisons for two contrasting watersheds
Authors: Luxmoore R. J. , Sharma M. L.
Published: February 2008

Simulated annual water budgets and daily streamflows for a well‐managed (R5) and an overgrazed grassland (R7) watershed at Chickasha, Oklahoma, were computed with the one‐dimensional terrestrial ecosystem hydrology model (TEHM, Huff et al. (1977a)) in which the soil hydraulic properties were scaled according to similar media criteria. The scaling factors and the area contributions for seven scaled soils were represented by a log normal frequency distribution based on measurements from an earlier study. Drainage and runoff were greatly influenced by change in scaled soil properties, and there were increases in evapotranspiration at smaller scaling values (finer soils). More runoff was generated from the overgrazed watershed which had lower evapotranspiration and lower hydraulic conductivity. Despite consideration of spatial variability in soil hydraulic properties, surface runoff generated from the scaled soil frequency distributions proportionally accounted for only 29 and 55% of simulated streamflows from the R5 and R7 watersheds, respectively. An algorithm that represented lateral subsurface flow to the streambed as a function of soil drainage rate was used in the one‐dimensional model to derive agreement between the observed and measured streamflows. For both watersheds the simulated runoff from the log normal distribution of soils was closer to the measured value than the runoff from the mode, median, or mean soils. The comparisons between measured and simulated soil water contents showed significant differences even though the streamflows showed agreement.
Solute transport through fractured media: 1. The effect of matrix diffusion
Authors: Grisak G. E. , Pickens J. F.
Published: February 2008

Solute transport through fractured media is described by numerically combining advective‐dispersive transport, which is dominant in the fractures, and diffusive transport, which is usually dominant in the unfractured matrix. Transport is considered in a manner conceptually similar to ‘double‐porosity’ or ‘intra‐aggregate’ transport models. A finite element model is developed for simulating nonreactive and reactive solute transport by advection, mechanical dispersion, and diffusion in a unidirectional flow field. The effect of the value of the solute diffusion coefficient in the matrix (termed the matrix diffusion coefficient) is illustrated by solute breakthrough curves and concentration profiles in the fracture as well as in the matrix. The illustrated conditions are similar to the laboratory tracer study on fractured till described in the accompanying paper (Grisak et al.). The effects on solute transport of fracture aperture size, water velocity in the fracture, matrix porosity, matrix distribution coefficient, and dispersivity in the fracture are illustrated with breakthrough curves and concentration profiles. The net effect of large matrix diffusion coefficients and/or large distribution coefficients in the matrix is to reduce significantly the effective solute velocity in the fracture. Reduction in the effective solute velocity can also be seen to be possible in materials with low matrix porosities such as crystalline rocks. The aperture size, matrix porosity, matrix diffusion coefficient, and distribution coefficient, all are important in determining the relative amounts of solute transported in the fracture and stored in the matrix. Implications with regard to aquifer recharge, groundwater chemistry, contaminant transport, tracer tests, and groundwater age dating in fractured media are discussed. The numerical model and the laboratory tracer test data provide considerable insight into the processes controlling solute transport in fractured media.
Analysis of surface moisture variations within large‐field sites
Authors: Bell K. R. , Blanchard B. J. , Schmugge T. J. , Witczak M. W.
Published: February 2008

In the past several years, 1974–1977, NASA has conducted several research studies to develop an extensive collection of ground truth soil moisture data. As a result of these experiments, moisture data were available from 58 ‘large‐field sites,’ each being 400 × 400 m (40 acre). The field locations were 1 field in Phoenix, Arizona (sampled four times), 28 fields in Jefferson County, Kansas, 23 fields in Finney County, Kansas, and 5 fields in Hand County, South Dakota. At the first three locations, samples were taken in specific vertical increments or horizons (i.e., 0–1; 1–2, 2–5, 5–9, and 9–15 cm). In the South Dakota study, moisture samples were taken in increments from the surface ( i.e., 0–2.5, 0–5, and 0–10 cm). A detailed statistical analysis was made to define the general relationship and ranges of values of the field moisture relative to both the variance (standard deviation) and coefficient of variation (CV) for a given test site and depth increment. On the basis of the results of the variability study it was concluded that (1) moisture variations within any given‘large‐field’ area are inherent and are normally distributed about the mean, (2) neither a single (constant) value of the standard deviation nor coefficient of variation uniquely define the variability over the complete range of mean field moisture contents examined, and (3) using an upper bound standard deviation parameter clearly defines the maximum range of anticipated moisture variability. It was found that 87% of all large‐ moisture content standard deviations were less than 3%, while about 96% of all the computed values had an upper bound of s = 4% for these intensively sampled fields. Using these upper bound magnitudes as an estimate of the population standard deviation and a preselected confidence level, limit of error curves of mean soil moisture measurements for large‐field sites relative to the required number of samples were determined.
A numerical method for the calculation of the average drawdown in a fully penetrating observation well in an unconfined aquifer
Authors: Rolfes Laurette
Published: February 2008

A numerical method which is numerically stable and makes use of a convergence acceleration algorithm is proposed for the calculation of Neuman's formula for the average drawdown in an observation well completely penetrating an unconfmed aquifer.
A theoretical analysis of interflow of water through surface soil horizons with implications for movement of chemicals in field runoff
Authors: Ahuja L. R. , Ross J. D. , Lehman O. R.
Published: February 2008

Steady interflow of water in the near‐surface saturated soil horizons, which are the important nonpoint sources of applied agricultural chemicals appearing in field runoff, is investigated theoretically. Analytical solutions are obtained for some relevant cases of interflow in a sloping layered soil having a subsoil of lower permeability. Analysis is made for the effect of the relative permeability of the subsoil and of the depth of the subsoil above an impermeable base varying from zero to infinity, in relation to different ratios of slope length to soil profile depth. Solutions and analyses are also extended to a case where flow through the topsoil is saturated and steady, but where the subsoil is still accepting a constant downward flux of water uniformly over all its area. The solutions are for a rectangularly bounded, tilted flow medium; but for long slopes the details of the flow medium boundaries at the top and bottom ends should have negligible effects on overall flow. The results show that the interflow through each horizon of a layered soil profile can be approximated by a one‐dimensional Darcian flow parallel to the slope, if the ratio of slope length to soil profile depth is greater than about 6 to 10. This extends the finding reported earlier in the literature for a uniform soil. For an extreme case of a sloping soil with a semi‐infinitely deep subsoil on an impermeable base, the interflow through the topsoil, if it is highly conductive compared to the subsoil, can still be treated as a one‐dimensional flow. For such cases, the movement of soil chemicals with interflow can be described as a one‐dimensional miscible displacement process. A uniformly constant downward flux of water into the subsoil decreases interflow through the topsoil. The extent of the decrease depends upon the land slope and the relative conductivity of the subsoil. Of even greater significance for chemical transport is the finding that the cross section of the topsoil through which the interflow traverses and picks up its chemical load is drastically reduced by downward leakage, even when the subsoil conductivity is two orders of magnitude smaller than that of the topsoil. A simplified prediction of this region of interflow is deduced from the results. By representing this wedge‐shaped area by an equivalent rectangle, the chemical movement, for a first‐order estimation in field application, may still be approximated as a one‐dimensional displacement.
Stochastic simulation of daily precipitation, temperature, and solar radiation
Authors: Richardson C. W.
Published: February 2008

Long samples of weather data are frequently needed to evaluate the long‐term effects of proposed hydrologic changes. The evaluations are often undertaken using deterministic mathematical models that require daily weather data as input. Stochastic generation of the required weather data offers an attractive alternative to the use of observed weather records. This paper presents an approach that may be used to generate long samples of daily precipitation, maximum temperature, minimum temperature, and solar radiation. Precipitation is generated independently of the other variables by using a Markov chain‐exponential model. The other three variables are generated by using a multivariate model with the means and standard deviations of the variables conditioned on the wet or dry status of the day as determined by the precipitation model. Daily weather samples that are generated with this approach preserve the seasonal and statistical characteristics of each variable and the interrelations among the four variables that exist in the observed data.
The effect of snowmelt on the water quality of Filson Creek and Omaday Lake, northeastern Minnesota
Authors: Siegel D. I.
Published: February 2008

Sulfate concentration and pH were determined in surface water, groundwater, and precipitation samples collected in the Filson Creek watershed to evaluate the sources of sulfate in Filson Creek. During and immediately after snowmelt, sulfate concentrations in Filson Creek increased from about 2 to 14 mg/l. Concurrently, H+ ion activity increased from an average of 10−6.6 to 10−5.5. These changes suggest that sulfate acidity is concentrated in the snowpack at snowmelt, which is similar to changes reported in Scandinavia in areas subject to acid precipitation. Mass balance calculations indicate that the sulfate contribution from groundwater during snowmelt was minimal in comparison to that from snow. During base flow, sulfate did not appreciably increase from the headwaters of Filson Creek to the mouth, even though sulfate was as high as 58 mg/l in groundwater discharging to the creek from surficial materials overlying a sulfide‐bearing mineralized zone in the lower third of the watershed. Approximately 10.6 kg of sulfate per hectare per year was retained in 1977.
Sulfate budget and a model for sulfate concentrations in stream water at Birkenes, a Small forested catchment in southernmost Norway
Authors: Christophersen Nils , Wright Richard F.
Published: February 2008

As part of the Norwegian SNSF project, the volume and chemical composition of precipitation and stream water have been measured for 6 years at Birkenes, a small (0.41 km2), gaged, coniferous‐forested catchment on granitic bedrock in southernmost Norway. Daily measurements of SO2 gas and SO4 aerosol have also been collected and provide the basis for estimation of dry deposition. The sulfate budget for the period November 1972 to October 1978 indicates that about 15% more sulfate left the catchment in runoff (7880 mg SO4 m−2 yr−1) than entered in dry (1870 mg SO4 m−2 yr−1) and wet (4970 mg SO4 m−2 yr−1) deposition. This difference is probably not significantly different from zero, given the difficulties inherent in the measurements. The input‐output budget reveals a marked seasonal pattern (accumulation during summer and winter; washout during spring and autumn). The annual sulfate flux is perhaps 5–10 times larger than natural. The result is an acidification of stream water and an increased leaching of base cations from the soil. The concentration of sulfate in stream water at Birkenes shows a characteristic pattern of high levels (10–13 mg l−1) in the first stormflow following a dry summer period and low levels (∼ 5 mg l−1) in baseflow. For the summer half‐year we have simulated sulfate concentrations using a simple two‐compartment model. Sulfate is assumed to accumulate in the uppermost soil layers because of dry deposition and evapotranspiration of rainwater. Mineralization of other sulfur compounds is included indirectly. In the lower mineral soil layers, adsorption/desorption of sulfate is assumed to occur. The ability of this simple model to simulate sulfate concentrations in stream water suggests that the model quantitively accounts for these processes.
Laboratory measurements of the strontium distribution coefficient KdSr for Sediments From a Shallow Sand Aquifer
Authors: Patterson R. J. , Spoel T.
Published: February 2008

A batch method has been modified and improved for measuring strontium distribution coefficients KdSr for sediments from the shallow aquifer at Chalk River. An average measured KdSr value of 10 ml/g for whole aquifer sediments compares favorably both with a field value of 7 ml/g determined using the retardation equation and with an average KdSr of 10 ml/g based on analytical results for aquifer sediments and coexisting groundwaters from a portion of the flow system that is contaminated with 90Sr. Measurements of KdSr for mineralogically pure segregates indicate that vermiculite, an alteration product of biotite, is the most effective adsorbent phase. KdSr results for grain size fractions suggest that the distribution of minerals with respect to grain size may strongly influence the KdSr of the whole sediment. Relationships between KdSr and exchangeable calcium on the sediments and competing cation concentration in the test solution indicate that electrostatic forces primarily control the sorption of strontium.
Simulation of a complex groundwater system and an application
Authors: Premchitt Jerasak , Das Gupta Ashim
Published: February 2008

A hydrologic model of an extensive groundwater basin was developed for the study of land subsidence due to deep well pumping in Bangkok, Thailand. It is a quasi‐three‐dimensional flow model with relevant modifications to suit the hydrogeologic situations in the problem area. The troublesome effect of yield from aquitard is discarded, while the field information on subsurface strata is fully utilized to establish a realistic model. The subsurface is considered to be a single hydraulically connected body stratified into model layers for convenience in the simulation. Pumping can be imposed at any depth, and discharge rates can be arbitrary. Any number of model layers can be incorporated, with coupling being provided through the leakage flux. The power and flexibility of the model is demonstrated in the simulation of groundwater flow regime in the Lower Central Plain of Thailand for a time period of 45 years. At first the model is calibrated with available field measurements in the past, and it is then extended for the prediction of future situations. The model represents the actual field situation. The mathematical process is simple, and it would require less computing effort than the equivalent full three‐dimensional model or the quasi‐three‐dimensional model with one‐dimensional elements to represent aquitards.
Preconsolidation stress of aquifer systems in areas of induced land subsidence
Authors: Holzer Thomas L.
Published: February 2008

Aquifer systems in the Eloy‐Picacho area, Arizona, the Houston‐Galveston area, Texas, and the Tulare‐Wasco area and Santa Clara Valley, California, appear to have been overconsolidated by an amount that ranged approximately from 1.6 to 6.2 bars (16 to 63 m of water) before man began to withdraw groundwater from them. The relation between land subsidence and water level decline in these areas, consists of two linear segments. In these areas, subsidence per unit water level decline was approximately constant until water levels had declined an amount that ranged from 16 to 63 m. When water levels declined past these values, subsidence per unit water level decline increased to larger constant values. Although slow drainage from aquitards may have contributed to this response, it is interpreted here to be caused primarily by natural overconsolidation of the compacting part of the aquifer system. The water level decline at which the ratio of subsidence to unit water level decline changed indicates approximately the amount by which the preconsolidation stress exceeded the overburden stress on the aquifer system that existed before groundwater withdrawals began.
Analysis of national water pollution control policies: 2. Agricultural sediment control
Authors: Gianessi Leonard P. , Peskin Henry M.
Published: February 2008

Application of a national water network model permits an analysis of the likely affects of agricultural sediment control policies on the quality of the nation's waters. This analysis is believed superior to previous assessments based mainly on erosion estimates without accounting for the characteristics of the receiving water or the contribution of pollutants from nonagricultural activities. Specifically, while the earlier assessments concluded that agriculture‐related pollution problems are widespread and ubiquitous, this analysis concludes that it is probably more efficient to focus sediment‐related pollution control policies on about one third of the nation's agricultural regions.
The depth of rainfall‐runoff‐soil interaction as determined by 32P
Authors: Ahuja L. R. , Sharpley A. N. , Yamamoto M. , Menzel R. G.
Published: February 2008

This study dealt with the extent and dynamics of a thin zone of soil that interacts with rainfall and overland flow in releasing soil chemicals to runoff. A relatively immobile tracer, 32P, was applied at 0.0 (soil surface), 0.5, 1.0, 1.5, or 2.0 cm depths in duplicate soil boxes of three different soils. Simulated rainfall of 6.5 cm/h was applied to each soil box for two separate 30‐min periods. The degree of interaction decreased very rapidly, more or less exponentially, with depth below the surface. An effective average depth or zone of interaction, within which the degree of interaction equals that of the soil surface, was assumed to exist. The effective average depth calculated from the data ranged between 0.2 and 0.3 cm, depending more upon the period of rainfall than upon the type of soil. These average depths were used, along with values of total desorbable P and the fractions of the 32P applied on the soil surface that appeared in runoff, to predict the P concentrations in runoff, which agreed rather well with the measured values. The assumption of an effective average depth was thus valid for P. Transient changes in the effective average depth of interaction during a rainfall period were calculated by using simultaneous P and 32P concentrations in runoff, where the 32P was applied at the soil surface. The effective average depth increased somewhat with time during a rainfall period, especially during the first 30‐min rain. The 30‐min mean effective average depth of interaction calculated by this method agreed well with that obtained by the first method described above.
Scaling of infiltration behavior in dissimilar porous materials
Authors: Youngs E. G. , Price R. I.
Published: February 2008

Microscopic characteristic lengths, as used in the theory of similar porous media, were obtained from measurements of hydraulic conductivity at saturation, of soil‐water pressure at half saturation, and of the integral of hydraulic conductivity with soil‐water pressure, for dissimilar materials with a wide range of particle sizes and shapes. The ratio of the microscopic characteristic lengths obtained in these three ways showed little variation between materials. Dimensionless variables defined in terms of them were used to scale experimental results with packed columns of the materials for vertical downward infiltration, for horizontal infiltration, and for vertical upward capillary rise. The scaled results for all materials were in agreement and fitted theoretically derived relationships for the three situations.
Mass transport of solutes in dual‐porosity media
Authors: Bibby Robert
Published: February 2008

In many aquifers, solute mass transport is controlled by molecular diffusion between mobile and static water. This is especially the case in fissured aquifers in which the rock matrix has a high porosity but low permeability. In order to model mass transport in such a dual‐porosity medium, an analytical solution for diffusion from a constant concentration boundary has been incorporated into a two‐dimensional mass transport model. The model uses Galerkin's method of weighted residuals and isoparametric finite elements to solve the flow and transport equations. The method has been successfully applied to a largescale pollution event. Historical data on the event were available over a long period of time and permitted calibration of the model. In situations in which such historical data are not available, calibration is very difficult, particularly the determination of dispersivities. This is because the molecular diffusion between mobile and static water so greatly retards the transport of solutes that field tests at the appropriate scale are essentially preempted.
Highly efficient, oscillation free solution of the transport equation over long times and large spaces
Authors: O'Neill K.
Published: February 2008

Transport problems with sharp transitions or high convection often stress even the most advanced computational methods beyond feasibility limits. One promising line of attack involves transforming problems to a moving, deforming coordinate system (MDCS). Using MDCS as recently developed, one may concentrate computational attention when and where it is most appropriate, also possibly greatly reducing the effective magnitude of terms which cause trouble. In principle, MDCS may be used with finite difference, finite element, or other numerical methods, according to preference. In the particular finite element system advanced here, mesh movement may be variable in time and space, so that physically fixed boundaries may remain fixed in the transformed coordinate system. A simple finite difference system is used in time. When the method is applied to the standard transport equation test case, great efficiency and accuracy are obtained in early time. Even very steep fronts may be represented well, with no oscillations, using space and time step sizes well beyond conventional (Peclet, Courant number) constraints. More important problems are solved, involving transport over much longer times and larger spaces, when diffusion has some chance to operate and hence a parabolic model is more warranted. The same accuracy and stability are achieved as during early time, using no more nodes and time steps overall than during early time runs. This constitutes orders of magnitude savings in effort over what the application of conventional constraints would require. Relative efficiency from application of MDCS to other problems would depend on the particulars of each case.
Optimal dynamic management of groundwater pollutant sources
Authors: Gorelick Steven M. , Remson Irwin
Published: February 2008

The linear programing‐superposition method is presented for managing multiple sources of groundwater pollution over time. The method uses any linear solute transport simulation model to generate a unit source‐concentration response matrix that is incorporated into a management model. This series of constraints indicates local solute concentration histories that will result from any series of waste injection schedules. The linear program operates on the matrix to arrive at optimal disposal schedules. An example demonstrates application of the method to maximizing groundwater waste disposal while maintaining water quality of local water supplies within desired limits. Flow field variations associated with waste injection are ignored as an approximation. Parametric programing is shown to be an important tool in evaluating waste disposal trade‐offs at various injection sites over time. Mixed‐integer programing permits restrictions to be placed upon the number of injection wells which may operate during given management periods.
Multiobjective river basin planning with qualitative criteria
Authors: Gershon Mark , Duckstein Lucien , McAniff Richard
Published: February 2008

The impact of alternative river basin development strategies is examined from a multicriterion viewpoint using the ELECTRE I and II techniques. The main stem of the Santa Cruz River in the vicinity of Tucson, Arizona is taken as a case study. A systematic formulation of the problem is provided leading to an array of 25 alternative systems versus 13 criteria, only 5 of which are quantified. A procedure for ranking these alternatives is presented which uses ELECTRE I to obtain preference graphs as input into ELECTRE II, which is then used to obtain the ordering. Sensitivity analysis shows that changing the weights assigned to each criterion has a greater effect on the results than does changing the scales. However, neither effect is very significant. It is recommended that ELECTRE I be used for screening purposes to narrow the set of alternatives under consideration. ELECTRE II can then be applied to this reduced set to obtain a complete ordering. For the case study the preferred systems include reservoirs and channelization and the least preferred systems include new groundwater development.
Objective analyses and mapping techniques for rainfall fields: An objective comparison
Authors: Creutin J. D. , Obled C.
Published: February 2008

Many methods have been proposed and applied individually to rainfall fields in order to estimate point or average values at ungauged sites. This paper reviews some of the usual as well as some of the more recent techniques. They are classified according to their fundamental principles, optimality criteria, and practical aspects. Some theoretical developments, mostly for the statistically based techniques, are offered, and the practical aspects are mainly directed to the particular case of rainfall fields. A case study is presented for a region with particularly high rainfall variability, providing a good sample of events for testing the sensitivity of the estimation to the different methods used. The identification of statistical structure functions, required by certain methods using regionalized variable concepts, is discussed in detail for the case considered. Method evaluation is based on a classical validation technique that divides the available stations into two separate networks, i.e., a base network is used to perform estimations at the stations of a test network for a set of independent storm events. Careful attention is paid to result interpretation and visualisation. Finally, conclusions are drawn as to which method should be implemented, taking into account cost‐efficiency considerations.