bluuebunny/crossref_metadata_2025 huggingface dataset:
Stochastic models of subsurface flow: infinite versus finite domains and stationarity
Authors: Gutjahr Allan L. , Gelhar Lynn W.
Published: February 2008

Stochastic solutions of the differential equation describing one‐dimensional flow through a porous medium with spatially variable hydraulic conductivity which is represented by a stationary (statistically homogeneous) random process are developed using several techniques. The analytical approximations using first‐order analysis (propagation of error), covariance differential equations, and variogram analysis all yield consistent results which demonstrate the important effects of boundary conditions and conditioning. Using the theory of intrinsic random functions, stochastic solutions are developed for the case when the logarithm of the hydraulic conductivity is a three‐dimensional stationary random field. In contrast to the one‐dimensional case, it is found that the resulting three‐dimensional head perturbation will be locally stationary under very general conditions. Results from the one‐dimensional analytical solutions are found to be in agreement with previous Monte Carlo simulations for a flow system of finite length. The solution based on linearization in the logarithm of hydraulic conductivity proved to be very robust, showing reasonable agreement with Monte Carlo results even for the largest input standard deviation of σlnK = 4.6.
Optimal short‐term hydro scheduling from the principle of progressive optimality
Authors: Turgeon André
Published: February 2008

This paper presents an algorithm based on the principle of progressive optimality for determining the optimal short‐term scheduling of multireservoir power systems; the method takes into account water head variations, spilling, and time delays between upstream and downstream reservoirs. The method is computationally efficient and has minimal storage requirements. The convergence is monotonic and a global solution is reached. Contrary to dynamic programing, the state variables do not have to be discretized with this method. An example consisting of four hydroplants in series is solved, and the results are presented.
Contaminant transport in fractured porous media: Analytical solution for a single fracture
Authors: Tang D. H. , Frind E. O. , Sudicky E. A.
Published: February 2008

A general analytical solution is developed for the problem of contaminant transport along a discrete fracture in a porous rock matrix. The solution takes into account advective transport in the fracture, longitudinal mechanical dispersion in the fracture, molecular diffusion in the fracture fluid along the fracture axis, molecular diffusion from the fracture into the matrix, adsorption onto the face of the matrix, adsorption within the matrix, and radioactive decay. Certain assumptions are made which allow the problem to be formulated as two coupled, one‐dimensional partial differential equations: one for the fracture and one for the porous matrix in a direction perpendicular to the fracture. The solution takes the form of an integral which is evaluated by Gaussian quadrature for each point in space and time. The general solution is compared to a simpler solution which assumes negligible longitudinal dispersion in the fracture. The comparison shows that in the lower ranges of groundwater velocities this assumption may lead to considerable error. Another comparison between the general solution and a numerical solution shows excellent agreement under conditions of large diffusive loss. Since these are also the conditions under which the formulation of the general solution in two orthogonal directions is most subject to question, the results are strongly supportive of the validity of the formulation.
Aquifer parameter identification with optimum dimension in parameterization
Authors: Yeh William W‐G. , Yoon Young S.
Published: February 2008

This paper presents a systematic procedure whereby the functional coefficients imbedded in a two‐dimensional partial differential equation which governs unsteady groundwater flow are optimally identified. The coefficients to be identified are transmissivities which vary spatially. Finite elements are used to represent the unknown transmissivity function parametrically in terms of nodal values over a suitable discretization of a flow region. A modified Gauss‐Newton algorithm is used for parameter optimization. Covariance analysis is used to estimate the reliability of the estimated parameters. As the dimension of the unknown parameter increases, the modeling error represented by a least squares criterion will generally decrease, but errors in data would be propagated to a greater degree into the estimated parameters, thus reducing the reliability of estimation. The reliability of the estimated parameters is characterized by a norm of the covariance matrix. This information is used for the determination of the optimum dimension in parameterization.
Long‐memory flow models in reservoir analysis: What is their practical value?
Authors: Klemeš V. , Srikanthan R. , McMahon T. A.
Published: February 2008

The theoretical value of long‐memory stochastic models lies in their ability to generate time series that resemble long historic records of some geophysical processes better than do short‐memory models. Since the use of short‐memory streamflow models has become standard practice in reservoir design, it is worth asking whether the suspected theoretical superiority of long‐memory models justifies a change in this practice; in other words, whether their theoretical appeal can be translated into better design of storage reservoirs. This paper analyzes the problem from the point of view of the differences in reservoir performance reliability obtained on the basis of long‐ and short‐memory models fitted to the same historic streamflow record of a length typically encountered in reservoir design. It appears that the differences in reliability resulting from the replacement of one model by the other (shorter memory yields higher reliability) are small compared both to (1) the accuracy of measurement of the socioeconomic impact of reliability changes and (2) the accuracy of estimating the reliability itself on the basis of available streamflow records and for economically relevant lengths of reservoir operation periods. Thus it is argued that given the socioeconomic and hydrologic data typically available for reservoir planning and design, the replacement of short‐memory models with long‐memory models in reservoir analyses cannot be objectively justified. It is suggested that for a long time to come the use of long‐memory models will, in principle, remain equivalent to the use of a small safety factor in the intrinsically inaccurate estimate of reservoir performance reliability.
Supply‐demand coordination in water resources management
Authors: Guariso G. , Maidment D. , Rinaldi S. , Soncini‐Sessa R.
Published: February 2008

A simple procedure is proposed for the determination of the water supplies and demands which maximize the total net benefit from water use in a region. The technique is in some ways a standard iterative market method, and, in fact, the convergence to the optimal solution is achieved when the marginal benefit at each demand point is equal to the marginal cost of delivering water to that point. The possibility of applying this technique to a given problem can immediately be ascertained from the pattern of the links between supply and demand units. An example is presented in which the method is applied to analyze the possible interbasin water transfer in the Northwest Water Plan in Mexico.
Optimal risk‐based design of flood levee systems
Authors: Tung Yeou‐Koung , Mays Larry W.
Published: February 2008

Methods for risk analysis of flood levee systems that account for hydraulic and hydrologic uncertainties are incorporated into optimal design procedures. The uncertainties are considered in the expected damage functions so that the objective is to determine the optimal flood levee system design that minimizes the total expected cost. Dynamic programing (DP) and discrete differential dynamic programing (DDDP) models are developed for the optimization. The DDDP approach tremendously reduces the computation effort and provides more accurate results when compared to the DP. Through the use of an example, different design philosophies (level of risk consideration) are examined.
Intraseasonal water allocation in deficit irrigation
Authors: Bras Rafael L. , Cordova Jose R.
Published: February 2008

This paper is concerned with the optimal temporal allocation of irrigation water, taking into consideration the intraseasonal stochastic variation of the crop water requirements and the dynamics of the soil moisture depletion process. Expressions for the soil moisture transition probabilities over a given time period and the first two moments of associated actual evapotranspiration are derived analytically. The conditional probabilities of soil moisture and associated actual evapotranspiration are used within a stochastic dynamic programing (DP) algorithm with rewards being a function of cost and crop yield. The DP algorithm is used to determine optimal control policies at each irrigation decision point, conditional on the state of the system (soil moisture content). Both mean and variance of net benefits are computed. Analytic results are corroborated with a case study example.
Effect of cold water entry into a liquid‐dominated two‐phase geothermal reservoir
Authors: Grant Malcolm A.
Published: February 2008

The effect of fluid withdrawal and injection into a two‐phase geothermal reservoir is considered. The geothermal reservoir matrix is modeled as a homogeneous porous medium, except that fracturing ensures that injected fluid mixes fully into two‐phase fluid. Withdrawal of fluid causes a pressure drop. Injection of fluid causes a pressure change dependent on the fluid enthalpy and rate of injection, nearly always a pressure drop for cold fluid injection. In addition to the pressure disturbance traveling away from the point of injection, there is a change in saturation near the injection point that travels away vertically. Natural perturbations might introduce cold water into a reservoir by lateral flow. To stabilize the twophase fluid by minimising the advance of such intrusions, a stability criterion is derived. This is shown to be approximately satisfied by observed pressures in several fields.
Canopy temperature as a crop water stress indicator
Authors: Jackson R. D. , Idso S. B. , Reginato R. J. , Pinter P. J.
Published: February 2008

Canopy temperatures, obtained by infrared thermometry, along with wet‐ and dry‐bulb air temperatures and an estimate of net radiation were used in equations derived from energy balance considerations to calculate a crop water stress index (CWSI). Theoretical limits were developed for the canopy air temperature difference as related to the air vapor pressure deficit. The CWSI was shown to be equal to 1 ‐ E/Ep, the ratio of actual to potential evapotranspiration obtained from the Penman‐Monteith equation. Four experimental plots, planted to wheat, received postemergence irrigations at different times to create different degrees of water stress. Pertinent variables were measured between 1340 and 1400 each day (except some weekends). The CWSI, plotted as a function of time, closely paralleled a plot of the extractable soil water in the 0‐ to 1.1‐m zone. The usefulness and limitations of the index are discussed.
Determination of the confidence intervals of the Wakeby Distribution using order statistics
Authors: Bobée B. , Boucher P.
Published: February 2008

It is possible to determine in an explicit fashion the distribution of the order statistics for the Wakeby distribution. The confidence intervals of an event of return period T can be calculated at any given level. Since the determination of the variance of an event of a given return period has not yet been computed for the proposed methods of estimation of the parameters of the Wakeby distribution, the general procedure presented in this report makes possible an approximate determination of the confidence intervals when the distribution is fitted to a sample of size N. This procedure is particularly easy to apply to distributions such as the Wakeby distribution, which may be expressed in inverse form.
The mathematical structure of rainfall representations: 3. Some applications of the point process theory to rainfall processes
Authors: Waymire Ed , Gupta Vijay K.
Published: February 2008

Part 3 constitutes the final part of three parts devoted to the mathematical structure of rainfall. The objective is to illustrate the scope of the tools developed in part 2 in the mathematical description of rainfall and rainfall‐driven processes. A general overview of the three‐part series is given in part 1.
Multiperiod design of regional wastewater systems: Generating and evaluating alternative plans
Authors: Nakamura Masahisa , Brill E. Downey , Liebman Jon C.
Published: February 2008

A simplified method is proposed for analyzing multiperiod design of regional wastewater systems and other systems possessing a similar network flow structure. The primary objective of the method is generation of multiperiod locations and facility expansion timings. The method is based on several simplifying assumptions. The solution procedure involves a branch and bound algorithm specifically developed for integrating a set of solutions obtained using the initial design flow with a set of solutions obtained using the terminal design flow. A method for comparing the generated multiperiod alternatives is also proposed. The usefulness of the method is demonstrated, using as an example a hypothetical regional waste water system. A Fortran program was written to implement the method. The program is not in a form that would permit its transfer, but interested readers may contact the first author.
Stochastic state variable dynamic programing for reservoir systems analysis
Authors: Maidment David R. , Chow Ven Te
Published: February 2008

The concept of state as used in state space modeling, dynamic programing, and Markov chain analysis is used to link these methods together. The random nature of inflows to the system is treated by incorporating a stochastic inflow model directly within the dynamic programing procedure. Transition probabilities found from the resulting stochastic dynamic programing are employed to determine the steady state probability distribution of the state and decision variables. As an example, the methodology is applied to determine operating policies for the proposed Watasheamu Dam in Nevada. Policies developed considering monthly flows as independently distributed or as serially correlated are similar over the normal range of flows but differ for very high and low inflows. Chance constraints applied at each stage of the dynamic programing are shown to limit the steady state probability of the storage being outside its desirable range but reduce the average annual benefits of operation by up to 15%. Computer time requirements compare favorably with those of an equivalent deterministic analysis of the same system.
Two‐dimensional soil moisture flow in a sloping rectangular region: Experimental and numerical studies
Authors: Nieber John L. , Walter Michael F.
Published: February 2008

Results from experiments with a 3.66 by 0.58 by 0.108 m flume filled with sand are used to study the two‐dimensional flow of soil moisture under the condition of rainfall infiltration. The experimental results are compared to results obtained by a numerical solution (via a finite element‐finite difference transformation) of the two‐dimensional Richards equation. The results are presented in the form of flow field conditions (hydraulic head distribution and position of the phreatic surface) and the rising limb of the runoff hydrograph. The experimental and the numerical results are in satisfactory agreement when the effect of capillary hysteresis is incorporated into the numerical solution. When capillary hysteresis is ignored, the numerically simulated hydrograph lags far behind the experimentally derived hydrograph.
Reliability, resiliency, and vulnerability criteria for water resource system performance evaluation
Authors: Hashimoto Tsuyoshi , Stedinger Jery R. , Loucks Daniel P.
Published: February 2008

Three criteria for evaluating the possible performance of water resource systems are discussed. These measures describe how likely a system is to fail (reliability), how quickly it recovers from failure (resiliency), and how severe the consequences of failure may be (vulnerability). These criteria can be used to assist in the evaluation and selection of alternative design and operating policies for a wide variety of water resource projects. The performance of a water supply reservoir with a variety of operating policies illustrates their use.
‘Second best’ effluent fees in water quality management: Problems of achieving efficiency
Authors: Revesz Richard L. , Marks David H.
Published: February 2008

‘Second best’ effluent charges, based on minimizing the cost of meeting a predetermined level of water quality, have been advocated as a policy alternative for water quality management without giving serious consideration to the physical characteristics of river basins. In this paper the detailed efficiency characteristics of such charge schemes are derived by coupling an economic and a physical model. These conditions reveal the need to make efficient charge schemes dependent upon the location of the downstream polluter and the physical parameters of the river. The informational requirements and administrative burden of imposing efficient fees is very great; in a practical setting, nonefficient adjustments need to be made.
On why gravel bed streams are paved
Authors: Parker Gary , Klingeman Peter C.
Published: February 2008

Bedload transport in poorly sorted gravel bed streams is considered. Bedload and typical bed material (subpavement) size distributions are observed to be similar; it follows that the coarse half of the subpavement moves through a reach at a rate near that of the fine half. Since coarser grains are intrinsically less mobile than fine grains, it follows that some mechanism must act to nearly equalize mobility. It is hypothesized that the pavement seen in gravel bed streams at low flow is in fact in place during typical transport events capable of moving all available sizes. This pavement can provide the equalizing mechanism by exposing proportionally more coarse grains to the flow. Field data are used to quantify this concept and to develop a predictive relation for river pavement. The model indicates that pavement should be absent in most sand bed streams, in agreement with observation.
Radium, thorium and radioactive lead isotopes in groundwaters: Application to the in situ determination of adsorption‐desorption rate constants and retardation factors
Authors: Krishnaswami S. , Graustein William C. , Turekian Karl K. , Dowd John F.
Published: February 2008

Five groundwater samples taken from different Hydrogeologie settings in Connecticut were analyzed for major cation chemistry and the concentration of U and Th decay series nuclides 238U, 234Th, 226Ra, 222Rn, 210Pb, 210Po, 232Th, 228Ra, 228Th, and 224Ra. The concentration of 222Rn in the waters ranged between 103 and 104 dpm l−1 and was three to four orders of magnitude greater than that of the short‐lived alpha daughters 224Ra, 228Ra, and 234Th, even though the rates of supply of these four nuclides to solution are expected to be similar. We infer that sorption removes radium and thorium from these groundwaters on a time scale of 3 minutes or less. The (224Ra/228Ra) and (234Th/228Th) activity ratios in these waters indicate that desorption of these nuclides occurs on a time scale of a week or less and that equilibrium between solution and surface phases is established. In situ retardation factors for radium, thorium, and lead may therefore be calculated directly from the isotopic data; values range from 4,500 to 200,000. Neither sorption time scales nor retardation factors are strongly dependent on the nuclide or on hydrogeology of the aquifer. Since our study includes nuclides with diverse chemical properties, we suggest that other uncomplexed heavy metals and transuranic elements will also behave in a manner similar to those measured here. The approach presented here should therefore find application in developing site‐specific models of the transport of radioactive or stable elemental waste through water‐saturated media.
Seasonal patterns in extreme 1‐hour rainfalls
Authors: Revfeim K. J. A.
Published: February 2008

The information content of monthly rainfall extremes is used to estimate simple harmonic coefficients of a rainfall model. Extreme rainfalls are assumed to occur as a periodic Poisson process, with time‐varying rate, and independent exponentially distributed amounts where the mean of the exponential distribution also varies with a period of 1 year. Amplitudes of both recurrence and intensity were found to be significantly different from zero for a 31‐year by 12‐month record of 1‐hour rainfall extremes. The phases of recurrence and intensity differ by approximately 6 months so that the lowest recurrence rate is associated with the highest rainfall intensity. More precise predictors of extreme events within a given time period are obtained using the monthly data base rather than the series of annual extremes.
A linear programing economic analysis of lake quality improvements using phosphorus buffer curves
Authors: Ogg Clayton W. , Pionke Harry B. , Heimlich Ralph E.
Published: February 2008

A linear programing model is used to evaluate the economic feasibility of reducing phosphorus loads from cropland to levels that are expected to alter adequately the trophic conditions of a water supply reservoir. The model employs phosphorus buffer curves for distributing phosphorus losses between runoff and eroded soil. Phosphorus pollution reductions are estimated for conservation activities according to the amount of erosion control and phosphorus fertility status. The planning model is intended to provide the best available estimates of pollution control attainable with given budget outlays, as well as to allocate pollution control funds efficiently among watersheds. It also contains sufficient detail to suggest practices for each local soil that are consistent with water quality plans.
Mechanisms leading to enrichment of the atmospheric fluorocarbons CCl3F and CCl2F2 in groundwater
Authors: Russell Ann D. , Thompson Glenn M.
Published: February 2008

Field measurements of CCl3F and CCl2F2 in groundwater have shown that concentrations in recharge areas are often higher than those in water at equilibrium with the atmosphere. Sorption and desorption of these fluorocarbons from soil surfaces in response to changes in soil moisture may be responsible for this enrichment. Soil slurry experiments were performed to determine whether concentrations of aqueous fluorocarbons increased when water came into contact with dry soils. The aqueous concentrations of CCl3F increased by a factor of 83–981% after mixing water with soils. Concentrations of CCl2F2 in water increased over a range of 34.6–144% for six slurries and decreased in two slurries.
Aquifer thermal energy storage : A well doublet experiment at increased temperatures
Authors: Molz F. J. , Melville J. G. , Parr A. D. , King D. A. , Hopf M. T.
Published: February 2008

The two main objectives of this communication are to present a study of potential advantages and disadvantages of the doublet supply‐injection well configuration in an aquifer thermal energy storage (ATES) system and to report on aquifer storage problems with injection temperatures in the 80°C range. A 3‐month injection‐storage‐recovery cycle followed by a 7.3‐month cycle constituted the main experiment. The injection volumes were 25,402 m3 and 58,063 m3 at average temperatures of 58.5°C and 81°C respectively. Unlikely previous experiments at the Mobile site, no clogging of the injection well due to clay particle swelling, dispersion, and migration was observed. This is attributed to the fact that the supply water used for injection contained a cation concentration equal to or slightly greater than that in the native groundwater. For cycles I and II, the fraction of injected energy recovered in a volume of water equal to the injection volume was 0.56 and 0.45 respectively. Both groundwater temperature and tracer data support the conclusion that this relatively low recovery was due to the detrimental effects of free thermal convection, possibly augmented by longitudinal zones of high permeability. Construction of a partially penetrating recovery well improved recovery efficiency but is not thought to be an adequate solution to thermal stratification. A maximum increase of 1.24 cm in relative land surface elevation was recorded near the end of second cycle injection. The engineering implications of such an elevation change would have to be considered, especially if an ATES system were being designed in an urban environment. A third cycle was started at the Mobile site on April 7, 1982. This final experiment contains a partially penetrating, dual‐recovery well system which is expected to maximize energy recovery from a thermally stratified storage aquifer.
Crop yield as affected by spatial variations of soil and irrigation
Authors: Warrick A. W. , Gardner W. R.
Published: February 2008

Crop yield is calculated for varying uniformities of seasonal available water. The variation is a consequence of both irrigation and soil heterogeneity. Analytical expressions and Monte Carlo simulations are used to calculate yields for an assumed linear response function. A comprehensive table from the Monte Carlo simulations includes results for 50, 100, and 200% of the water necessary for maximum yield. These are collated with five uniformities and three levels of effective available water. Uniformities of water are expressed as coefficients of variation ranging from 0 to 2. Variation in either irrigation or soil uniformity changes the results, but irrigation uniformity is likely more important, especially for surface systems. The effect of taking the two distributions—for irrigation and soil—to be correlated does not affect results greatly. When only cost of water is considered, the marginal rate of return is verified to be a maximum for smaller applications.
Automatic calibration of conceptual rainfall‐runoff models: The question of parameter observability and uniqueness
Authors: Sorooshian Soroosh , Gupta Vijai Kumar
Published: February 2008

Reasons for the inability to obtain unique and conceptually realistic parameter sets for conceptual rainfall‐runoff models are examined in this paper. The problem is first posed in a framework that allows a more consistent and logical analysis of the related aspects. Response surface studies demonstrate that choice of an objective function that better explains some of the stochastic properties of the errors in the output results in a smoother, better shaped response surface; hence the chances of obtaining unique and realistic parameter estimates are improved. However, our analysis indicates that part of the problem is also due to inadequacies in the model structure. The arguments are illustrated using results obtained with the soil moisture accounting model of the National Weather Service's river forecast system.
Land use, floods, and channel changes: Upper Middle Fork Willamette River, Oregon (1936–1980)
Authors: Lyons Joseph K. , Beschta Robert L.
Published: February 2008

Flow trends and channel characteristics from 1936 to 1980 were evaluated for the Middle Fork Willamette River, which drains a 668‐km2 forested watershed in the Cascade Mountains of western Oregon. An inventory of aerial photographs from 1959 to 1972 shows that landslides associated with roads and in clearcuts were 27 and 23 times more frequent, respectively, than in forested areas. Numerous landslides unloaded sediments directly into the drainage system; most landslides appear to have been initiated during a large flood (return period greater than or equal to 100 years) of December 22, 1964. Analysis of precipitation and peak flows (greater than 100m3 s−1) from 1958 to 1980 by means of power function models suggests a trend of increasing flows as timber harvesting and road building expanded in the basin. Changes in channel pattern, documented from aerial photographs, show major increases in channel width from 1959 to 1967 and a trend of decreasing width from 1967 to 1980. During summer low flows in 1979 and 1980, 65 cross sections of the channel were surveyed to provide detailed measurements of existing channel conditions. Channel widths of 62% of the aggraded reaches were significantly greater (α=0.05) than those for nonaggraded reaches.
An analysis of the effect of surface heat exchange on the thermal behavior of an idealized aquifer thermal energy storage system
Authors: Güven O. , Melville J. G. , Molz F. J.
Published: February 2008

Analytical expressions are derived for the temperature distribution and the mean temperature of an idealized aquifer thermal energy storage (ATES) system, taking into account the heat exchange at the ground surface and the finite thickness of the overlying layer above the storage aquifer. The analytical expressions for the mean temperature may be used to obtain rough estimates of first‐cycle recovery factors for preliminary evaluations of shallow confined or unconfined ATES systems. The results, which are presented in nondimensional plots, indicate that surface heat exchange may have a significant influence on the thermal behavior of shallow ATES systems. Thus it is suggested that the effects of surface heat exchange should be considered carefully and included in the detailed analyses of such ATES systems.
Laboratory investigations of steam flow in a porous medium
Authors: Herkelrath W. N. , Moench A. F. , O'Neal C. F.
Published: February 2008

Experiments were carried out in the laboratory to test a theory of transient flow of pure steam in a uniform porous medium. This theory is used in modeling pressure transient behavior in vapor dominated geothermal systems. Transient, superheated steam flow experiments were run by bringing a cylinder of porous material to a uniform initial pressure and then making a step increase in pressure at one end of the sample while monitoring the pressure transient breakthrough at the other end. It was found in experiments run at 100°, 125°, and 146°C that the time required for steam pressure transients to propagate through an unconsolidated material containing sand, silt, and clay was 10–25 times longer than predicted by conventional superheated steam flow theory. It is hypothesized that the delay in the steam pressure transient was caused by adsorption of steam in the porous sample. In order to account for steam adsorption, a sink term was included in the conservation of mass equation. In addition, energy transfer in the system has to be considered because latent heat is released when steam adsorption occurs, increasing the sample temperature by as much as 10°C. Finally, it was recognized that the steam pressure was a function of both the temperature and the amount of adsorption in the sample. This function was assumed to be an equilibrium adsorption isotherm, which was determined by experiment. By solving the modified mass and energy equations numerically, subject to the empirical adsorption isotherm relationship, excellent theoretical simulation of the experiments was achieved.
Causes of river bed degradation
Authors: Galay V. J.
Published: February 2008

River bed degradation can proceed downstream as well as upstream depending upon the cause of degradation. The causes of downstream progressing degradation are primarily related to changes in independent river channel variables, such as increase in water discharge, decrease in size of bed material, and decrease in bed material discharge. The causes of upstream progressing degradation are all related to an imposed increase in river slope which can occur as a result of natural river behavior or by man‐made changes. Study of various case histories indicates that river slopes are increased by lowering a base level, by decreasing the length of a river, or by removal of a control point. Case histories also show that downstream and upstream progressing degradation can act in combination along a river system: downstream progressing degradation along the main stream of a river system can initiate upstream progressing degradation on a tributary.
Optimal groundwater depletion with interdependent nonrenewable and renewable resources
Authors: Mueller Michael J.
Published: February 2008

An economic model of the optimal use of a nonrenewable resource, groundwater from a nonrecharging aquifer, which is used as an input in the production of a nonrenewable and a renewable resource, petroleum and agriculture crops, is explained and analyzed. The model is developed in a regional context. The problem is analyzed using a linear allocation parameter, nonlinear cost functions, and optimal control techniques. Results are discussed and interpreted with emphasis on policy applications.
Erosion from low slopes
Authors: Mutchler Calvin K. , McGregor K. C.
Published: February 2008

Simulated rainfall was used to generate erosion of plots on 0.1% slopes with different surface water depths. Maximum erosion rates occurred under an average surface runoff depth of about 2 mm. Little change in erosion rates occurred for depths greater than about 20 mm. These results help explain the mechanics of erosion on low slopes and suggest that manipulation of surface water depths might be used for erosion control.
Analyzing alternative flood damage reduction measures on small rural watersheds using multiple return period floods
Authors: Goulter I. C. , Morgan D. R.
Published: February 2008

In many areas of rural Manitoba, conventional flood control measures such as diking and channel clearing are proving to be ineffective, both in their cost and in their ability to reduce flood damages. A heuristic technique has been developed to assess the economic feasibility of a number of unconventional measures for flood damage reduction. Two measures considered are: (1) substitution of crops with a low susceptibility to flood damage for crops with a high susceptibility to flood damage and (2) storage of floodwaters on poor crop land to prevent flood damage on better crop land downstream. The probability of occurrence of various flood events is incorporated into the technique. The method is based upon the dynamic programming optimization technique and has been developed with particular emphasis on the Wilson Creek Watershed on the eastern boundary of Riding Mountain National Park, Manitoba, Canada.
A model of human response to flood warnings for system evaluation
Authors: Ferrell William R. , Krzysztofowicz Roman
Published: February 2008

A behavioral model of human response to flood warnings is developed as a component of a methodology for evaluation of the performance of flood forecast‐response systems. A floodplain dweller responds to a sequence of flood warnings by taking protective action (such as evacuation, flood proofing, shutdown of a facility) in order to reduce his loss. The model is meant to mimic the actual response behavior of the floodplain dweller or to predict such behavior under future system conditions. It is built of mathematical representations of four interconnected cognitive elements of response: (1) uncertainty about flooding and loss prior to a flood, (2) sequential inference based on warnings during a flood, (3) response strategy, and (4) learning after a flood. Results of an application and qualitative verification of the model are discussed.
A Binary State DP Algorithm for Operation Problems of Multireservoir Systems
Authors: Ozden Mufit
Published: February 2008

Reservoir operation problems are complicated by the nonlinearities in the objective functions. The dynamic programing (DP) procedure is often used to solve this problem because of the sequential nature of the decisions involved, but for simultaneous operations of multireservoir systems, other DP‐based techniques are frequently found to be more efficient in overcoming the curse of dimensionality problem caused by the interdependencies of the decisions. In this paper, another DP‐based procedure is proposed which performs better than the other well‐known techniques. The applications of this technique are presented in two different formulations for four‐reservoir operation problems. The convergence properties of the algorithm are investigated as revealed from the systematic solutions of a control problem with various dimensions.
A Method for Comparing Scalar Irradiance Measurements With Upward and Downward Irradiance in Lakes
Authors: Spigel Robert H. , Howard‐Williams Clive
Published: February 2008

A method is outlined for comparing measurements of scalar irradiance, as measured with a 4π scalar irradiance meter, with downward and upward irradiance, as measured with a cosine‐corrected flat plate irradiance meter. The method is based upon an empirical formulation of the aśymptotic radiance distribution given by Jerlov (1976). Results are compared with measurements in several New Zealand lakes with generally good agreement.
Risk‐Reliability Programming for Optimal Water Quality Control
Authors: Simonovic Slobodan P. , Orlob Gerald T.
Published: February 2008

A risk‐reliability programming approach is developed for optimal allocation of releases for control of water quality downstream of a multipurpose reservoir. Additionally, the approach allows the evaluation of optimal risk/reliability values. Risk is defined as a probability of not satisfying constraints given in probabilistic form, e.g., encroachment of water quality reservation on that for flood control. The objective function includes agricultural production losses that are functions of water quality, and risk‐losses associated with encroachment of the water quality control functions on reservations for flood control, fisheries, and irrigation. The approach is demonstrated using data from New Melones Reservoir on the Stanislaus River in California. Results indicate that an optimum water quality reservation exists for a given set of quality targets and loss functions. Additional analysis is presented to determine the sensitivity of optimization results to agricultural production loss functions and the influence of statistically different river flows on the optimal reservoir storage for water quality control. Results indicate the dependence of an optimum water quality reservation on agricultural production losses and hydrologic conditions.
An Integer Programming Analysis of the Regionalization of Large Wastewater Treatment and Collection Systems
Authors: Leighton Jeffrey P. , Shoemaker Christine A.
Published: February 2008

An optimization procedure is described that can serve to identify attractive regionalization plans for large wastewater treatment and collection systems. Potential expansion of facilities in Western Suffolk County, Long Island, New York is considered. A mixed integer programming approach is utilized. Each system element cost, taken as a function of wastewater flow, is represented by a linear variable cost plus a fixed cost. The objective is to minimize total cost while ensuring that all wastewater flow generated is treated. Political and administrative feasibility and the location of effluent discharge constrain the model. The Long Island problem is too large to be solved with a standard formulation of wastewater network as a mixed integer programming problem. To improve computational efficiency, additional constraints are introduced on the minimum flow in each pipe and on the number of pipes leaving each node. Network configurations obtained for Western Suffolk County show that limiting development plans to 201 regions is not cost effective. Regional solutions indicate a general trade‐off between lower costs for coastal discharge and increased groundwater recharge.
An Assessment of the Spatial Variation in the Chemical Composition of Bulk Precipitation Within an Upland Catchment
Authors: Reynolds B.
Published: February 2008

Bulk precipitation was collected weekly for chemical analysis over a period of 64 weeks at six sites within the headwater catchments of the Upper Wye in mid‐Wales, United Kingdom. Results indicate that for these catchments, which are remote and uninhabited, the aspect and elevation of the collectors have no detectable effect on solute concentrations measured in the bulk precipitation. Differences in rainfall catch within the watersheds contributed to the variation in solute load to the sites.
Irrigated Agricultural Expansion Planning in Developing Countries: Investment Scheduling Incorporating Drainage Water Reuse
Authors: Allam Mohamed N. , Marks David H.
Published: February 2008

Agricultural expansion planning in developing countries where there is extensive government involvement in the planning process can be defined in a two‐level hierarchy. At the first level, the role of the agricultural expansion investment in achieving the strategic goals of the sector is to be determined. At the second level, analysis of the agricultural expansion is to be carried out in such a way that the strategic decisions from the first level can be implemented. The focus of this paper is on the analysis of investment scheduling, the major issue of the second level. A mathematical optimization model is built to aid in analyzing the scheduling problems of land development, crop selection, drainage water reuse, and capacity expansion of the irrigation and drainage networks. A minimum cost criterion is used, where costs of land development, farming, irrigation and drainage infrastructures, maintenance and operations, and pump stations are considered. The model has a nonlinear objective function to account for economies of scale and linear and nonlinear constraints. A fixed charge approximation is used for the nonconvex cost functions, and a mixed integer programming algorithm along with an enumeration procedure is used for solving the model. The solution procedure guarantees global optimality for the approximated problem. A hypothetical expansion of 70,000 acres (28,350 ha) based on data from the Nile Delta in Egypt is used as a case study to illustrate the procedure under different conditions of irrigation water quality.
Groundwater Response Under an Electronuclear Plant to a River Flood Wave Analyzed by a Nonlinear Finite Element Model
Authors: Gambolati Giuseppe , Toffolo Fabio , Uliana Fiore
Published: February 2008

In the foundation design of electronuclear plants, conservative stability criteria with respect to earthquakes are usually assumed, where the maximum water table level beneath the nuclear reactor in response to possible flood waves occurring in the nearby river is taken to coincide with the ground surface elevation. This approach may dictate heavier structural constraints; hence additional costs that could be minimized if a realistic prediction of the aquifer behavior and of the actual largest pressure head below the plant is provided by appropriate mathematical tools. A nonlinear finite element model based on the Dupuit‐Boussinesq equation of flow in an unconfined aquifer has been developed and applied to simulate the water table fluctuation under the electronuclear plant of the test site of Trino Vercellese (northwestern Italy) in response to the flood event that occurred in the Po River from March 30 to April 4, 1981. The nonlinearity has been overcome by the aid of an efficient iterative linearization technique wherein the model equations are solved by symbolic factorization, numerical factorization, and backward‐forward substitution after an optimal preliminary reordering. The model was run for uniform values of aquifer permeability and specific yield within the typical range evidenced for the Trino sands by the early data in our possession. The results show that the maximum water level elevation below the reactor is almost 3 m lower than the corresponding river flood peak even in the most unfavorable conditions, i.e., with the hydraulic conductivity in the upper range, and is rather insensitive to the specific yield values within the plausible interval. The model allowed for an easy evaluation of the effectiveness of the impermeable protection walls and of a possible secondary aquifer recharge from a minor channel. The modeling approach for the analysis of the water table behavior appears to be a very promising tool to help in the structural design of future electronuclear plants.
A Probabilistic Approach to the Spatial Assessment of River Channel Instability
Authors: Graf William L.
Published: February 2008

The deterministic approach to the analysis of river channel instability has not proved to be a completely useful basis for geographic predictions of channel behavior. Economic estimates for benefits of structural channel control projects commonly account for flood inundation, but in arid and semiarid regions these estimates are incomplete because they fail to take into account destructive channel migration and erosion. As a solution, a method whereby historical records of channel locations are reduced to spatially defined probabilistic functions allows calculation of the probability that given parcels of near‐channel terrain will be destroyed by erosion. The probability of erosion for any given parcel over a given period of time is directly proportional to the sizes of the annual floods during the period and inversely proportional to two distance measures: distance upstream and distance laterally to the channel. In a test of the probabilistic geographic method using data on the locations of Rillito Creek, Arizona, from 1871 to 1978, erosion probability maps accurately characterized the locations of observed changes. In a 50‐year simulated period, erosion ultimately produced economic losses that were 5 times greater than potential inundation losses.
Techniques for Making Finite Elements Competitve in Modeling Flow in Variably Saturated Porous Media
Authors: Huyakorn P. S. , Thomas S. D. , Thompson B. M.
Published: February 2008

A Galerkin finite element formulation is developed for the numerical simulation of water flow in variably saturated soil systems. Included in this formulation is a solution strategy based on Picard and Newton‐Raphson algorithms. Both algorithms are designed especially to cope with severely nonlinear field problems. The two algorithms are formulated for both rectangular and triangular elements. The element matrices are evaluated in a simple and efficient manner using a technique referred to as the “influence coefficient” technique. This technique avoids numerical integration and leads to a substantial saving of computational cost. Four examples are presented to demonstrate the effectiveness of the present finite element approach. These examples show that the nonlinear solution schemes are capable of accomodating cases involving large variations in the saturated hydraulic conductivity, as well as highly nonlinear soil moisture characteristics. A comparative study of the Picard and the Newton‐Raphson algorithms is also provided. The study indicates that despite the higher cost per iteration of the Newton‐Raphson scheme, it usually requires a substantially smaller number of iterations than the Picard scheme. In some instances where convergence difficulties are experienced with the latter scheme, it is desirable to use the Newton‐Raphson scheme in order to obtain a cost‐effective solution to the problem.