bluuebunny/crossref_metadata_2025 huggingface dataset:
A short‐term flood forecasting model based on retention hysteresis
Authors: Chowdhury M. S. K. , Bell F. C. , Learmonth J. R.
Published: February 2008

A mathematical model has been developed for the continuous prediction of streamflow from catchment rainfall and evaporation data. It realistically simulates the complex hysteretic interactions controlling the catchment moisture status during wetting and drying phases and satisfactorily allows for the effects of discontinuous and multilayered spatial distributions of soil moisture at any given time. Another important feature of this model is its ability to use the current observed discharge as a state variable, and hence it can be tuned during the operational flood forecasting for better predictions. Although relatively simple components have been adopted for channel flow and other runoff time‐distributing aspects, the predicted hydrographs generally agree well with the recorded hydrographs, particularly for moderate and large floods.
A new collocation method for the solution of the convection‐dominated transport equation
Authors: Pinder George E. , Shapiro Allen
Published: February 2008

A modified Hermitian basis function is developed as a means of enhancing numerical solutions to the convection‐dominated transport equation using orthogonal collocation. An asymmetric approximation to the first‐order spatial derivative is provided so that oscillations in the numerical solution are eliminated while introducing a minimum amount of numerical dispersion. The degree of assymetry in the basis function required to achieve a smooth solution is shown to be dependent upon the magnitude of the convective and dispersive terms.
An experimental study of hydraulic and geomorphic changes in an alluvial channel induced by failure of a dam
Authors: Chen Yung Hai , Simons Daryl B.
Published: February 2008

Dam structures may fail to cause significant changes in the downstream river hydraulics and geomorphology. In this study, basic hydraulic and geomorphic principles were utilized to analyze experimental data to assess changes in flood stage, resistance to flow, and transport of deposited sediment following failure of a dam. A relation for determining the induced maximum flood stage considering the river sinuosity is presented. It is found that the river sinuosity increases the river resistance to flow and thus increases flood stage. The presence of the sediment deposited behind the dam can significantly reduce resistance to flow and affect the river hydraulics after the dam failure. Further studies are required to improve our understanding of the interaction between the water and sediment transport and the river stability.
Analysis of water and heat flow in unsaturated‐saturated porous media
Authors: Sophocleous Marios
Published: February 2008

This work investigates the theoretical and practical aspects of modeling water and heat flow in an unsaturated‐saturated flow domain. Field experiments were designed and complementary laboratory analyses were employed to measure the relevant physical quantities that would enable the significance of non‐isothermal effects to be determined. The Philip and de Vries non‐isothermal flow model was adapted to the more general pressure (or matric) head‐based approach and a new expression for the thermal liquid water diffusivity DTl is proposed. A general and versatile computer simulation program for modeling coupled non‐isothermal transport is developed. The influence of coupling on diurnal subsurface moisture and heat transfer is evaluated by comparing the isothermal and non‐isothermal transient numerical solutions to the heat and water transport problem. The results confirmed that coupling does not noticeably influence the temperature field, but does affect the evaporation and subsurface moisture fluxes. The non‐isothermal theory is applied to calculate evaporation from dry land surfaces.
Geochemical significance of groundwater discharge and carbonate solution to the formation of Caleta Xel Ha, Quintana Roo, Mexico
Authors: Back William , Hanshaw Bruce B. , Pyle Thomas E. , Plummer L. Niel , Weidie A. E.
Published: February 2008

Xel Ha is a lagoon whose location and morphology are partly controlled by the fracture pattern in upper Pleistocene coral reef limestone. Chemical, isotopic, and hydrologic observations were made nearby where groundwater could be sampled. In addition, similar observations along vertical profiles were made at stations within the lagoon. A thin lens of rapidly moving fresh groundwater overlies a regional thick body of nearly stagnant saline groundwater that is close to ocean water in chemical composition. These two chemically distinct groundwaters are separated by a thin zone of dispersion, and both are at or slightly beyond saturation with respect to calcite. Where these two end‐member groundwaters mix to form the brackish dispersion zone, the resulting solution is undersaturated with respect to calcite. This was confirmed by mass transfer and isotopic modeling which show that the mixing of two solutions of different ionic strength, each saturated with respect to calcite, can result in an undersaturated solution. Model calculations indicate that as much as 1.23 mmol of CaCO3 may be dissolved per kilogram of water. We hypothesize that many of the cuspate beaches along the east coast of the Yucatan formed in this manner and that mixing of waters of different chemistry may be an important geomorphic process in similar geologic‐hydrologic settings.
Parsimony in modeling daily precipitation
Authors: Katz Richard W.
Published: February 2008

Two stochastic models for representing the sequence of daily precipitation amounts at a point, the Markov chain model proposed by Haan et al. [1976] and the chain‐dependent process proposed by Katz [1977a, 1977b], are contrasted. Through a further analysis of daily precipitation data, it is shown that there is a lack of evidence to support the superiority of the Markov chain model over the simpler chain‐dependent process.
Effect of periodic parameters on the autocorrelation structure of hydrologic series
Authors: Şen Zekâi
Published: February 2008

The autocorrelation structure of a seasonal hydrologic series has been analytically investigated, given a set of periodic parameters such as the means, standard deviations, and seasonal serial correlations between any two seasons. It has been observed that periodic means have the most important effect on the correlogram of the seasonal data, whereas the periodicities in the standard deviations and seasonal serial correlations have minor effects which might easily be neglected in the practical hydrological studies of any water resources system design.
The worth of hydrologic data for nonoptimal decision making
Authors: Davis Donald R. , Duckstein Lucien , Krzysztofowicz Roman
Published: February 2008

Data are of value in the design and operation of water resource projects because they provide information about uncertain states of nature. This information can in turn be used to reduce the risks inherent in the project. In this paper, risk calculations from the preposterior analysis of statistical decision theory are extended to cover nonoptimal decisions. Risk is measured in terms of the project objectives by embedding the data network into an information‐response (IR) system. The value of addition or improvement to the data base is measured by the change in the risk. Measures of the performance of the IR system are developed. From these measures, the efficiency of the information subsystem, the response subsystem, and the overall IR system are defined. These concepts are illustrated by a simple example in which the additional data sample for estimating the 6¼‐year flow is shown to have different values (negative in one case), depending on the estimation method or decision rule used. Five anomalies and paradoxes in the literature concerning the worth of data are explained.
A dynamic model of corn yield response to water
Authors: Morgan Thomas H. , Biere Arlo W. , Kanemasu Edward T.
Published: February 2008

A dynamic model of corn yield response to daily available soil moisture is presented. Using a priori information on dry matter accumulation in the plant when water is not limiting and using spline regression, we estimate the function of crop response to soil moisture from experimental test plot data. With the estimated model we simulate the corn yields for various irrigation schedules. The simulations demonstrate the sensitivity of the model to the timing of irrigations.
Traveling wave solutions of saturated‐unsaturated flow through porous media
Authors: Nakano Yoshisuke
Published: February 2008

Traveling wave solutions to the problem of saturated‐unsaturated flow of water through a uniform porous medium are derived, and the regularity properties of the solutions are studied. It is found that a singularity occurs in the higher‐order derivatives of flux with respect to the space coordinate in the solutions at water tables and that the water tables can be generally interpreted as propagating acceleration waves of the nth order, where n is a positive integer.
Longitudinal dispersion in rivers: The persistence of skewness in observed data
Authors: Nordin Carl F. , Troutman Brent M.
Published: February 2008

For some selected field studies of longitudinal dispersion the variances of observed concentration distributions increase linearly with time, as predicted by solutions to the one‐dimensional Fickian‐type diffusion equation. However, observed values of the skewness coefficient are almost constant, so deviations from the theoretical values become greater with increasing time. The usual assumption that concentration distributions converge to the Gaussian solution of the one‐dimensional diffusion equation is not supported by the empirical observations. One explanation for the persistence of the skewness is the existence of dead zones which temporarily trap portions of the dispersant. The coefficients of skewness predicted by a dead zone model fit the observed values more closely, but this model is, like the Fickian model, characterized by a decay in the skewness, which is not exhibited by the observed distributions.
Multivariate short‐term rainfall prediction
Authors: Johnson Edward R. , Bras Rafael L.
Published: February 2008

Accurate hydrologie forecasting for basins with a short response time depends on the ability to predict quantitative rainfall rates. This study develops a stochastic model for short‐term (of the order of 1 hour or less) rainfall prediction. The model simultaneously predicts rainfall rates at multiple locations and for multiple values of prediction lead. All model parameters are estimated solely from telemetered rain gage data for the event being predicted. The model includes velocity and direction of storm movement as explicit parameters. The storm arrival time at each predicted point is likewise an explicit parameter, which is estimated for each location. The mean rainfall rate is not modeled as being either homogeneous spatially or stationary (constant with time). Likewise, the variance of rainfall is nonhomogeneous and non‐stationary.
A note on changes in channel geometry at tributary junctions
Authors: Richards K. S.
Published: February 2008

Evidence is presented to justify the assumption that channel width varies stochastically about an approximately constant mean width within a stream link of an alluvial channel. Adjustments of channel width occur predominantly at junctions, but Miller's (1958) simple model describing such changes is misleading, and an alternative is proposed whose implication is that channel width (and probably other channel dimensions) is a power function of link magnitude. It is suggested that an alternative to conventional hydraulic geometry is provided by the combination of a step function describing changes at junctions and a stochastic model of variation within individual links.
Optimal operation of multireservoir power systems with stochastic inflows
Authors: Turgeon Andre
Published: February 2008

The optimization of the weekly operating policy of multireservoir hydroelectric power systems is a stochastic nonlinear programing problem. For small systems this problem can be solved by dynamic programing, but for large systems there is yet no method of solving this problem directly, so that one must resort to mathematical manipulations in order to solve it. This paper presents and compares two possible manipulation methods for solving this problem. The first, called the one‐at‐a‐time method, consists in breaking up the original multivariable problem into a series of one‐state variable subproblems that are solved by dynamic programing. The final result is an optimal local feedback operating policy for each reservoir. The second method, called the aggregation/decomposition method, consists in breaking up the original n‐state variable stochastic optimization problem into n stochastic optimization subproblems of two‐state variables that are also solved by dynamic programing. The final result is a suboptimal global feedback operating policy for the system of n reservoirs. The two methods are then applied to a network of six reservoir‐hydroplant complexes, and the results obtained are reported. It is shown that the suboptimal global feedback operating policy gives better results than the optimal local feedback operating policy.
Flow net for unsaturated infiltration from periodic strip sources
Authors: Batu Vedat
Published: February 2008

Using unsaturated flow theory, general equations have been obtained of the stream functions for a variable infiltration rate over periodic strip sources located on the soil surface. Solutions are obtained for the water table located at infinite and finite depths. The steady state unsaturated flow equation, linearized using the KirchhofF transformation based on the exponential relationship between the unsaturated hydraulic conductivity and soil water pressure, is solved with the Fourier analysis technique. Then the solutions for equally spaced strip sources are obtained with the constant infiltration rate as a special case. Also, as another special case, an approximate result for infinite water table depth is obtained for an array of equally spaced line sources which was first obtained by Raats [1970]. Using the matric flux potential distribution for the infinite water table depth [Batu, 1978], flow nets are presented for equally spaced strip sources. The stream functions corresponding to the saturated flow cases are also obtained. Comparisons between the saturated and unsaturated streamlines are made, and it is concluded that the discrepancies between the two are larger with decreasing matric flux potential in the flow field. These solutions are of interest in connection with sprinkler and furrow irrigation. Other than these, the results may be used for different purposes in civil and agricultural engineering applications.
Numerical analysis of infiltration into a sand profile bounded by a capillary fringe
Authors: Curtis Alan A. , Watson Keith K.
Published: February 2008

The rapid response sometimes observed in a tile drain system following surface ponding of water is discussed in terms of the air compressibility effect. An earlier numerical study describing water movement into a bounded profile with a lower boundary impermeable to the passage of both air and water is reviewed with particular reference to the validity of the time‐dependent boundary condition transformation used in simulating the inhibiting effects of the air pressure increase on infiltration. The extension of the transformation approach to a profile bounded by a capillary fringe is then considered in detail, and the results of numerical analyses are presented for infiltration into two columns of a fine sand initially in hydraulic equilibrium from a prior gravity drainage regime. The shorter column develops a steady state flow condition at short times which is consistent with earlier experimental findings. In contrast, the pressure of the entrapped air in the longer column gradually increases as infiltration proceeds until the analysis is terminated when air escape through the lower boundary is imminent.
A stochastic‐conceptual analysis of rainfall‐runoff processes on a hillslope
Authors: Freeze R. Allan
Published: February 2008

A stochastic‐conceptual mathematical model of hydrologie processes on a hillslope is utilized to investigate the influence of the spatial stochastic properties of the hillslope parameters on the statistical properties of the resulting runoff events. The model utilizes a stochastic rainfall generator and allows the generation of overland flow by both the Horton mechanism and the Dunne mechanism. Streamflow statistics are determined on the basis of an event‐based Monte Carlo simulation. The simulated hillslope runoff events are individually and statistically representative of actual runoff events reported in the literature from experimental watersheds. Results indicate that each of the parameters representing the spatial stochastic properties of the hydraulic conductivity distribution on a hillslope exerts an important influence on the statistical properties of runoff events arising from a hillslope under a given climatic regime. The mean value is the most important parameter; the standard deviation is quite important; the autocorrelation function is the least important. If one tries to represent a heterogeneous hillslope by an ‘equivalent’ homogeneous hillslope, the statistical properties of the predicted runoff generated from a given stochastic sequence of storm events may be greatly in error. Results of the simulations reported in this paper suggest that the distribution of hydraulic conductivities over a watershed should be included in parametric representations of the unit hydrograph, in conceptual predictions of flood exceedance probabilities, and in physically based assessments of the autocorrelation structure of the Streamflow sequences. Results of this study also infer a close relationship between climate, hydraulic conductivity, and geomorphic landform development.
Field heterogeneity: Some basic issues
Authors: Philip J. R.
Published: February 2008

Present‐day soil‐water physics enables useful quantitative predictions in the laboratory and in simple field situations. Difficulties, however, frequently arise for areas of appreciable size in the field. Known and unknown heterogeneities, on many scales, may vitiate predictions based on theory for homogeneous, or very simple heterogeneous, systems. Two types of heterogeneity are distinguished, deterministic and stochastic. The first often demands an extension of established analyses and may involve important phenomena absent from the analogous homogeneous problem. Stochastic heterogeneity may involve many scales and is imperfectly known. The statistical properties may be stationary, but in more complicated cases, randomness may be embedded in (either known or unknown) systematic trends. Some aspects of unsaturated and generally unsteady flow in heterogeneous systems are reviewed: the mathematical nature of the flow equation; the concept of scale‐heterogeneity; analytical and quasi‐analytical solutions. The enormity of the total problem of unsaturated unsteady flows in stochastic heterogeneous systems is illustrated through a dialectic of eight successive stages of simplification. The concept of the autocorrelation function governing λ, the internal characteristic length, is introduced; and the problem posed in terms involving the distribution and autocorrelation functions of λ, the reduced potential and conductivity functions, and the initial and boundary conditions as the data, from which it is required to establish distribution functions of various descriptors of the flow. The solution to a grossly simplified example of horizontal absorption is presented. Mean apparent sorptivity decreases rapidly to about one fifth of the mean (and about half the minimum) sorptivity of the component soils. Variation about the mean is very great but decreases as absorption proceeds. The example epitomizes the failure of additivity of properties in stochastic heterogeneous media, which arises because spatial textural changes in either sense tend to reduce unsaturated flow rates.
A derivation of the macroscopic solute transport equation for homogeneous, saturated, porous media
Authors: Chu Shu‐Yuan , Sposito Garrison
Published: February 2008

The macroscopic transport equation for a conservative solute in a homogeneous, water‐saturated porous medium is derived on the basis of a rigorous cumulant expansion applied to the equation of mass balance. The essential physical concept underlying the derivation is that of a local volume‐averaged solute velocity which fluctuates on a time scale that is orders of magnitude smaller than its autocorrelation time scale, which, in turn, is much smaller than the time scale of interest in a typical solute transport experiment. This clear separation of time scales is illustrated with representative data on solute transport in homogeneous, water‐saturated soils and is employed to justify the truncation of an exact cumulant expansion of the divergence of the volume‐averaged solute mass flux density. With the cumulant expansion terminated at first order in the ratio of the solute velocity autocorrelation time to the macroscopic solute transport time interval, an expression for the macroscopic solute mass flux density is produced which is the same as Fick's Law extended to porous media.
Nonlinear effects in two‐phase flow to wells in geothermal reservoirs
Authors: Sorey Michael L. , Grant Malcolm A. , Bradford Elizabeth
Published: February 2008

Numerical and quasi‐analytical solutions for nonlinear two‐phase flow of steam and water to a geothermal well discharging at constant mass flow are presented. Simulated variations in pressure, saturation, and the enthalpy of the flowing fluid mixture are compared for various initial reservoir conditions and relative permeability functions. Nonlinear effects associated with variations in the relative permeabilities and viscosities with saturation and pressure cause curvature in the semilog pressure response during drawdown and overrecovery in liquid saturation following shut‐in. The flowing enthalpy is shown to increase as liquid saturation decreases during drawdown but to reach a stable value near the well face at times small enough to be useful in well test analysis.
A model to forecast short‐term snowmelt runoff using synoptic observations of streamflow, temperature, and precipitation
Authors: Tangborn Wendell V.
Published: February 2008

Snowmelt runoff is forecast with a statistical model that utilizes daily values of stream discharge, gaged precipitation, and maximum and minimum observations of air temperature. Synoptic observations of these variables are made at existing low‐ and medium‐altitude weather stations, thus eliminating the difficulties and expense of new, high‐altitude installations. Four model development steps are used to demonstrate the influence on prediction accuracy of basin storage, a preforecast test season, air temperature (to estimate ablation), and a prediction based on storage. Daily ablation is determined by a technique that employs both mean temperature and a radiative index. Radiation (both long‐ and short‐wave components) is approximated by using the range in daily temperature, which is shown to be closely related to mean cloud cover. A technique based on the relationship between prediction error and prediction season weather utilizes short‐term forecasts of precipitation and temperature to improve the final prediction. Verification of the model is accomplished by a split sampling technique for the 1960–1977 period. Short‐ term (5–15 days) predictions of runoff throughout the main snowmelt season are demonstrated for mountain drainages in western Washington, south‐central Arizona, western Montana, and central California. The coefficient of prediction (Cp) based on actual, short‐term predictions for 18 years is for Thunder Creek (Washington), 0.69; for South Fork Flathead River (Montana), 0.45; for the Black River (Arizona), 0.80; and for the Kings River (California), 0.80.
A model for the prediction of ice lensing and frost heave in soils
Authors: Gilpin R. R.
Published: February 2008

A model of the frost heave phenomenon in soil was developed. This model predicts ice lensing and heave rates as a function of the basic soil properties (thermal conductivities and particle size) and the externally applied boundary conditions (surface temperatures and overburden pressure). The results are in general agreement with experimental observations as to the effects of the various parameters. The predicted heave rates are also of the right order of magnitude. An examination of the model equations reveals that at least four different processes may limit the heave rate of a soil. The specific process which controls the heave rate will depend on the soil properties and the applied boundary conditions. From the model it has also been possible to identify the properties of a soil that must be known in order to make an accurate prediction of heave rate in that soil.
The Linear Decision Rule (LDR) reservoir problem with correlated inflows: 1. model development
Authors: Joeres Erhard F. , Seus Günther , Engelmann Herbert M.
Published: February 2008

A generalized chance‐constrained linear decision rule (LDR) reservoir model is presented which incorporates explicit consideration of the correlation structure of the inflow process. A decision rule which includes predicted flow as a state variable (termed the predictive rule) is contrasted with the rule assuming uncorrelated monthly flows (the independent rule) and a rule which takes knowledge of the upcoming period inflow as given (the Utopian or perfect hindsight rule). Changed feasibility conditions defining minimum and maximum reliable release goals are developed and analyzed. Earlier judgements that LDR models are conservative are examined and contrasted with the improved ability to make reliable release commitments with the predictive rule. Comparison with a target hitting model over a wide range of performance reliabilities shows the new rule to provide consistently more total scheduled release.
Analysis of longitudinal dispersion in unsaturated flow: 1. The analytical method
Authors: Wilson John L. , Gelhar Lynn W.
Published: February 2008

An analytical technique is developed for the analysis of solute displacement in unsaturated soils involving one‐, two‐, or three‐dimensional flow with fixed streamlines. The transport processes are separated into two parts: convection with the mean flow and dispersive mixing. The convective process is solved exactly using the method of characteristics; the effects of dispersion are incorporated in the analysis by using singular perturbation techniques. The analytical technique is illustrated by application to solute transport during steady and transient infiltration. It is observed that nonuniform moisture content in space results in stretching or contracting of a solute pulse as it travels through the soil, with or without the presence of dispersive mixing. For transient infiltration into initially moist unsaturated systems the rate of solute displacement is usually much smaller than the rate of movement of moisture change.
Calculation of vertical profiles of lake‐averaged temperature and diffusivity in Lakes Ontario and Washington
Authors: McCormick Michael J. , Scavia Donald
Published: February 2008

By using statistical analysis of temperature observations and model calculations, the common parameterization of vertical eddy diffusivity (k) in terms of the gradient Richardson number (Ri) is simplified. The simpler formulation accurately reproduces seasonal variations in temperature profiles from Lakes Ontario and Washington. Energy arguments support use of the simplified parameterization and suggest use of a modified Ri in calculating k. The new expression for k resulted in more realistic estimates of thermocline k. The modeling of free convective mixing in Lake Ontario by heat conservation resulted in excessive temperatures in the hypolimnion during fall overturn.
Design discharge as a random variable: A risk study
Authors: Ashkar Fahim , Rousselle Jean
Published: February 2008

We consider two partial duration series models for flood analysis. In one, flood exceedances are treated as mutually independent and identically distributed, while in the other they are taken as identically distributed only on a seasonal basis (but mutually independent both within and between seasons). The maximum likelihood estimates of the parameters appearing in each of the two models are obtained, and the probability density functions of these estimates are determined. The distribution functions of (1) the design exceedance XT,n, corresponding to a given return period T and to n years of record, and (2) the return period T, corresponding to a given discharge X and n years of record, are then deduced. Finally, the risk encountered in the construction of a hydraulic project based on a certain design discharge is studied. Our results are applied to the partial duration series of the St. Paul station, in Minnesota on the Mississippi River. Some of these results are compared with those obtained by a previous study in which a Bayesian approach was followed.
Thermal energy storage in a confined aquifer: Second cycle
Authors: Molz F. J. , Parr A. D. , Andersen P. F.
Published: February 2008

During the first 6‐month injection‐storage‐recovery cycle of the Auburn University Aquifer Thermal Energy Storage Project, water pumped from an upper supply aquifer was heated to an average temperature of 55°C with an oil‐fired boiler and then injected into a lower storage aquifer. Injection and recovery temperatures, flow rates, and temperatures at six depths in 10 observation wells and hydraulic heads in seven wells were recorded twice daily. The second‐cycle injection, which was performed in a manner similar to the first, began on September 23, 1978, and continued until November 25, 1978, when 58,010 m3 of water had been pumped into the storage aquifer. The major problem experienced during the first cycle, a clogging injection well, was reduced by regular backwashing. This was done 8 times during injection and resulted in a 24% average injection rate increase compared to the first cycle. A 63‐day storage period ended on January 27, 1979, and production of hot water began with an initial temperature of 54°C. By March 23 this temperature had dropped to 33°C, with 66,400 m3 of water and 76% of the injected thermal energy recovered. This compares to 66% recovery during the first cycle over the same drop in production temperature. Production of hot water continued until April 20, at which time 100,100 m3 of water and 89% of the injected thermal energy was recovered at a final production temperature of 27.5°C. During the second cycle, measurements were made of relative land subsidence and rebound to a precision approaching 0.1 mm. The surface elevation near the injection well rose 4 mm during injection, fell during storage, and fell more rapidly toward its original elevation during production. This movement was due to thermal expansion and contraction rather than to effects caused by head changes in the storage aquifer.
Study of a complex water resources system with screening and simulation models
Authors: Chaturvedi M. C. , Srivastava D. K.
Published: February 2008

A sequential iterative modeling process for a complex water resources system is described. Two types of analytical models are used to find a reasonably small set of possible systems optimal design alternatives for a complex river basin. These models are a linear programing deterministic continuous (LPDC) model and a linear programing deterministic discontinuous (LPDD) model. Linear programing has been used with linear approximation of the nonlinear functions. A simulation program has been developed which continues screening on the basis of the information obtained from the linear programing model. The models are developed in the context of analysis of the Narmada River, a large river basin in India, for which in the first instance alternative combinations and capacities of six major dams have to be decided.
Drainage network structure and the diameter‐magnitude relation
Authors: Jarvis Richard S. , Sham Chi H.
Published: February 2008

Drainage network structure can be described in terms of elongation or compaction by using the network diameter and magnitude. The relation between network diameter and magnitude is the topologic equivalent of the well‐known relationship between mainstream length and drainage basin area. Diameter increases with magnitude but at a decreasing rate as networks are sampled over a greater size range. Downstream variations in river network structure reflect regional geomorphic environment, erosional history, and space‐filling by tributaries of different sizes. The sequence of tributary magnitudes down a mainstream is not random. Large tributaries preempt drainage area and tend to be followed downstream by a number of small tributaries. In fluvial landscapes free from geological constraints, river networks tend to become relatively more elongate in structure with increasing size downstream.
Carbon 14 dating of groundwater in confined aquifers: Implications of aquitard diffusion
Authors: Sudicky E. A. , Frind E. O.
Published: February 2008

The influence of diffusive losses into fine‐grained aquitards on the 14C age interpretation of groundwater in long, thin confined aquifers is examined. An analytical model is developed by coupling two one‐dimensional steady state differential equations, one representing advective‐dispersive transport in the aquifer and the other representing diffusion into the aquitards. The results indicate that aquitard diffusion is a mechanism that can cause a significant reduction in 14C concentrations in a confined aquifer. Groundwater velocities derived from 14C measurements that are unadjusted for diffusion would therefore be underestimated. The error that ensues is highly sensitive to the aquifer thickness and the magnitude of the diffusion coefficient. In contrast, the steady‐state distribution of 14C is shown to be relatively insensitive to the magnitude of the longitudinal dispersivity value of the aquifer. Dispersivities representative of the upper range of values that have been reported in the literature produced a negligible difference in steady state 14C concentration compared to results obtained using small dispersivities. An equation is presented which permits the adjustment of 14C data to account for diffusion, providing that the aquifer‐aquitard system is not stratigraphically complex and heterogeneous. The analysis can be extended to include age‐dating isotopes that have half‐lives different from that of 14C. The results of this study also apply to age dating in fractured porous media.
Variance estimates for a dynamic eutrophication model of Saginaw Bay, Lake Huron
Authors: Scavia Donald , Canale Raymond P. , Powers William F. , Moody Jennie L.
Published: February 2008

First‐order variance propagation is used to estimate variance of model output originating from variances of uncertain initial conditions, parameter values, and external load estimates for a nutrient‐phytoplankton‐zooplankton dynamic eutrophication model of one segment of Saginaw Bay, Lake Huron. Coefficients of variation of model output during summer are not unlike those estimated from measurements. The major source of variance is parameter value variances. The most important parameters, in terms of model sensitivity and variance propagation, are identified by analysis of the predicted correlation matrix. Methods for reducing model output variance are suggested.
Aluminum in precipitation, streams, and shallow groundwater in the New Jersey pine barrens
Authors: Budd W. W. , Johnson A. H. , Huss J. B. , Turner R. S.
Published: February 2008

Total (acid reactive) aluminum deposited in bulk precipitation in the McDonalds Branch (New Jersey) basin was 140 mg m−2 yr−1 for the period May 1978–May 1980. Stream and groundwater outputs for the same period were 149 and 110 mg m−2 yr−1, respectively. Aluminum inputs and outputs were highest during summer months because of elevated concentrations coupled with increased precipitation and streamflow. Median acid reactive Al concentrations in precipitation, stream water, and groundwater were 100, 350, and 230 μg 1−1, respectively. In streams, acid reactive Al concentration is correlated with dissolved organic matter concentration, suggesting that Al is transported as an organometallic complex. Shallow groundwater Al concentration is apparently controlled by gibbsite solubility in mineral soils and thus is pH dependent. The relatively high Al concentrations are attributable to acid conditions and mobile organic matter.
Models of water transport in the soil‐plant system: A review
Authors: Molz Fred J.
Published: February 2008

Although the study of plants (botany) is one of the oldest sciences, relatively detailed quantitative theories of water transport in plant tissue have lagged behind those describing water transport in soils and other geologic materials which constitute the saturated and unsaturated zones. Many existing texts deal with various aspects of water transport in these earth materials, but little or nothing is devoted to the analogous transport of water in plant roots and tissue at a similar quantitative level. Yet the soil‐root‐stem water pathway is a major component of the subsurface hydrologic system. Evidently there is a need for both engineering and agricultural hydrologists to further develop their quantitative understanding of water movement in plant and soil‐plant systems. Modern quantitative theories of water transport in plants can be traced to concepts developed and disseminated effectively in landmark papers by Gradmann and van den Honert in 1928 and 1948 respectively. The material reviewed in this paper, while more advanced, is based on these concepts. Emphasis is placed on water movement in soil containing roots and on a general approach to water transport in living plant tissue. Detailed quantitative studies of water extraction by plant roots date back to studies by Gardner published in 1960. Many contemporary models are built around extraction functions in the Darcy‐Richards equation. Several such functions are listed in a table, and their applications, relative advantages, and limitations are discussed in the text. In a series of papers published in 1958, Philip developed the first detailed quantitative description of water transport in plant tissue. His approach resulted in a diffusion equation which could be written with water potential as the dependent variable. Philip's derivation assumed that water movement was primarily from vacuole to vacuole. Subsequent workers have refined and extended Philip's development to include water movement in cell walls and plasmodesmata. The development, interpretation, and application of these models over the past decade is presented in some detail. It can be argued that contemporary models of water transport in plant tissue are oversimplified. However, they have been subjected to some successful testing and they provide a framework within which to devise experiments. Moreover, the recent development of sophisticated experimental techniques should result in more detailed model testing during the 1980's.
Methods of discharge compensation as an aid to the evaluation of water quality trends
Authors: Harned D. A. , Daniel C. C. , Crawford J. K.
Published: February 2008

Two new methods are described for compensating for discharge when evaluating trends in water quality data. One method, discharge normalization, adjusts daily discharges using a central value calculated for the period of record and recalculates daily specific conductance from the adjusted discharges and discharge versus specific conductance regressions. Normalized concentrations for many constituents can then be calculated from linear relationships between specific conductance and constituent concentrations. The second method, discharge‐frequency weighting, weights each observed concentration by a fraction of the total area underneath the discharge‐frequency distribution of the period of record. This fraction is determined using the stream discharge at the time of sampling and the discharge‐frequency distribution for the period of record. The weighted concentrations are summed for each year. Both normalized values and weighted values can be plotted against time to produce trends essentially independent from discharge effects. Results from the methods are statistically similar to each other and to results from other trend detection techniques.
Nitrogen and carbon solution chemistry of an old growth coniferous forest watershed before and after cutting
Authors: Sollins P. , McCorison F. M.
Published: February 2008

Dissolved Kjeldahl N and nitrate concentrations were monitored for 1 to 2 years before and for 3 years after clearcutting of a 10.2‐ha, Douglas‐fir dominated watershed in the Oregon Cascade Mountains. Dissolved organic C (DOC) and ammonium concentrations were monitored after cutting. We sampled throughfall, litter leachate, and soil solution (at four depths in and below the rooting zone) at four locations along a transect up and down the slope. We also sampled precipitation, streamwater, and seepage water. A site just off of the watershed served as the control for all positions in the water profile except for streamwater, for which a similar, nearby watershed was the control. Objectives were (1) to document effects of clearcutting on solution chemistry and (2) to provide data from which to calculate ecosystem nutrient cycling budgets before and after cutting. Beginning 7–18 months after clearcutting, nitrate concentrations increased 3–100 times on the cut watershed but remained nearly unchanged on an adjacent, uncut, control area. Increases were greater at 2.0‐m depth than at other positions along the water profile and least in seepage and streamwater. Greatest nitrate levels were detected near the bottom of the slope. At the uppermost site, about 50 m below the ridgetop, nitrate values remained the same as at the control site. Concentrations of Kjeldahl N (organic N plus ammonium) increased much less than those of nitrate (only 50–100% over precut levels) but were greater than nitrate concentrations at most profile positions both before and after cutting. Even after cutting, nitrate dominated only at 2.0‐m depth and in seepage water. DOC concentrations were slightly greater on the cutover area than on the control. However, they increased as much as 3 times from year 2 to year 3 after cutting at both treated and control sites, whereas nitrate decreased from year 2 to 3, and Kjeldahl N increased little or remained the same. DOC concentrations decreased consistently with depth in the soil profile. The study showed (1) that dissolved organic N must be measured if total N transfers are to be calculated at most sites, (2) that patterns of nitrate appearance can be explained in part on the basis of decreased availability of oxidizable C, (3) that patterns of nitrate appearance after devegetation vary greatly with depth in the soil and with slope position, and (4) that loss of dissolved N after cutting was small (<2.0 kg ha−1 yr−1) compared with nearly 400 kg N ha−1 removed in tree boles.
BIEM solutions to combinations of leaky, layered, confined, unconfined, nonisotropic aquifers
Authors: Lafe O. E. , Liggett J. A. , Liu P. L‐F.
Published: February 2008

The boundary integral equation method (BIEM) has usually been limited to problems governed by Laplace's equations or at least, linear homogeneous equations with constant coefficients. In complex aquifers it is necessary to solve nonlinear equations and equations with nonconstant coefficients. In this paper the BIEM is expanded to treat such cases. The nonhomogeneous equations are solved by use of efficient and automatic area integrations. Matrix substructuring is used to decrease computer requirements for large, complex problems and also to maintain efficiency. Solutions in leaky, layered aquifers are found by iteration. Thus the advantages of the BIEM are available for the solution of complex systems. In the calculations presented herein the effective dimension of an aquifer system is reduced to two by use of the Dupuit assumption. The BIEM further reduces the computational dimension by one. Therefore a three‐dimensional problem is solved by a line integration.
Areal distribution of snow water equivalent evaluated by snow cover monitoring
Authors: Martinec J. , Rango A.
Published: February 2008

A method is proposed to determine the areal distribution of the maximum seasonal water equivalent of snow in mountain basins. Because a sufficient density of direct measurements is not available in remote, inaccessible areas, the accumulation of snow at the start of the melting season is reconstituted. The disappearance of snow in grid units is monitored using Landsat data, the number of degree days necessary to melt the snow is totalized, and the water equivalent of the snow melted is calculated. The reconstituted water equivalent values can be used to correct precipitation measurements in winter. Together with limited point measurements these new areal data can improve the evaluation of snow reserves for seasonal discharge forecasts.
A decomposition method for the long‐term scheduling of reservoirs in series
Authors: Turgeon André
Published: February 2008

This paper presents a method for determining the weekly operating policy of a power system of n reservoirs in series; the method takes into account the stochasticity of the river flows. The method consists of rewriting the stochastic nonlinear optimization problem of n state variables as n −1 problems of two state variables which are solved by dynamic programing. The release policy obtained with this method for reservoir i is a function of the water content of that reservoir and of the total amount of potential energy stored in the downstream reservoirs. The method is applied to a power system of four reservoirs, and the results obtained are compared to the true optimum.