bluuebunny/crossref_metadata_2025 huggingface dataset:
Comparison of iterative methods of solving two‐dimensional groundwater flow equations
Authors: Trescott P. C. , Larson S. P.
Published: February 2008

This paper compares the efficiency of line successive overrelaxation (LSOR) with a two‐dimensional correction procedure (2DC), the iterative, alternating direction implicit procedure (ADI), and the strongly implicit procedure (SIP) to solve finite‐difference equations used to simulate several groundwater reservoirs. Three of the reservoirs are linear, two are isotropic areal problems, and the third is an anisotropic cross‐section simulation. The fourth is a nonlinear water table aquifer with areas of thin saturation. SIP is generally the best method for the linear simulations and with the addition of another iteration parameter is the only method that gives an adequate rate of convergence for the water table problem. LSOR with 2DC is competitive with SIP on isotropic and anisotropic linear problems that are dominated by no‐flow boundaries. ADI is generally more efficient than LSOR if a good set of iteration parameters are used, but this advantage is offset by the relative ease of finding the best acceleration parameter for LSOR.
Effects of hypolimnetic aeration on nitrogen and phosphorus in a eutrophic lake
Authors: Garrell Martin H. , Confer John C. , Kirschner Dominique , Fast Arlo W.
Published: February 2008

The effects of hypolimnetic aeration on total P, NO3‐N, and NH4‐N in eutrophic Lake Waccabuc (New York) are described. This lake was aerated for two consecutive summers (1973 and 1974) by using the system previously described in a paper by past et al. (1975a). Although reductions in hypolimnetic P concentrations appeared in the first summer, they failed to reappear during the second summer. NH4‐N and NO3‐N concentrations are compared with those in an unaerated control lake, Lake Oscaleta (New York). Very slight changes in relative hypolimnetic NH4‐N concentrations and corresponding increases in hypolimnetic NO3‐N concentrations are seen. The overall results suggest that the aerated lake is subjected to substantial external loading, which may mask aeration effects on the internal nutrient cycles.
Scaling field‐measured soil hydraulic properties using a similar media concept
Authors: Warrick A. W. , Mullen G. J. , Nielsen D. R.
Published: February 2008

With a view toward developing techniques for studying water flow in spatially varying soils, field data for soil water characteristic relationships and unsaturated hydraulic conductivity are scaled by using the concept of similar media. Data observed by different investigators at three geographic areas are used. The soil water characteristic data consisted of 840, 900, and 512 observations, while those for the unsaturated hydraulic conductivity (available from only one of the three sources) consisted of 2640 observations. In the process of scaling the data a best fit for the scaled data is defined in terms of a sum of squares about an ‘average’ curve using one value for the scaling parameter for each sampling location. Comparisons made between curves fitting the data and those fitting the scaled data show that scaling reduces the sums of squares by amounts varying from 34 to over 90%. For similar media the scaling parameter determined at a given sampling location for the soil water characteristic relationship (α from h(S)) should be identical to that for the unsaturated hydraulic conductivity (αr from K(S)). Although these parameters were highly correlated (r = 0.91 ) for the only set of data available, α r from h(S) values are shown to be more effective in scaling the unsaturated hydraulic conductivity data than are αr from K(S) values in scaling soil water characteristic data.
Infiltration equations for simple soil systems
Authors: Collis‐George N.
Published: February 2008

Empirical equations and physically based equations used to describe vertical infiltration into simple soil systems are compared with experimental data. An empirical equation is proposed which satisfies the conditions that cumulative infiltration is proportional to (time)½ at short times and reaches a steady state infiltration rate at long times. This equation, i = i0 (tanh T)½ + Kt, describes the observed behavior of simple soil systems at all times, where i is the cumulative infiltration at time t, K is the infiltration rate at steady state, i0 = S(tc)½, and T = t/tc. The sorptivity S (Philip, 1957) and a time parameter tc (Collis‐George, 1974) are soil properties determinable experimentally. The Green and Ampt equation and the Horton equation do not satisfy observed behavior at all times, the former failing at long times and the latter at short times. The equation of van der Want (1976), the linearized Fokker‐Planck equation of Philip (1969), and the nonlinearized Fokker‐Planck equation of Knight and Philip (Philip, 1974) do not describe the observed behavior of simple soil systems over the whole time range as precisely as the proposed empirical equation. Since i0 is not an independent part of these equations, its numerical value is defined by the independent parameters S and K, and for the materials examined it is generally not the same as the experimental value. Procedures are outlined for treating experimental data, not necessarily complete for all times, to produce the three parameters, K, S, and tc for simple systems, and for describing infiltration into cracking clays or in cases where ultrashort time effects occur.
Network characteristics in suburbanizing streams
Authors: Graf William L.
Published: February 2008

Analysis of hydrologic, geomorphic, and suburbanization data from a small instrumented drainage basin near Iowa City, Iowa, indicates that channel networks are radically altered when suburban development overtakes a drainage basin. Changes in channel networks are such that the network becomes much more efficient in collecting water quickly, so that lag time and kurtosis of storm hydrographs are altered to produce the familiar flash floods of urban areas. The data show that network changes are closely associated with lag time and kurtosis of storm hydrographs and suggest that corrective measures should be concentrated on the internal links of the network. Changes in characteristics of channel networks should be considered in addition to changes in areas of impervious surfaces when the hydrologic impact of suburbanization is assessed.
Defining reactions and mass transfer in part of the Floridan aquifer
Authors: Plummer L. N.
Published: February 2008

This paper examines the observed changes in water chemistry down a hydraulic gradient in part of the Floridan aquifer. Through the use of mass balance relationships and mass transfer calculations several reactions are derived that simulate the observed water chemistry. The calculation of σ13C and 14C activity implied by these reactions limits the number of possible reactions and leads to the following conclusions. The waters of the recharge area near Polk City have an average age of 3200 yr and have formed by congruent solution of dolomite and calcite. Although the calculated isotopic composition of CO2 entering the groundwater, σ13C = −22.5, is near that measured for soil gas CO2 in the vicinity of the recharge area (Rightmire and Hanshaw, 1973(, the mechanism)s) by which soil CO2 enters the saturated zone is not well defined. Down the hydraulic gradient from the vicinity of Polk City, isotopically light dolomites (σ13C = − 3.9 to − 1.5‰) and gypsum dissolve. All reactions south of Polk City are incongruent to a low‐magnesium calcite. The reaction path between Polk City and Fort Meade is partially open to CO2, presumably soil zone CO2. Further south between Fort Meade and Wauchula the Floridan aquifer becomes essentially closed to CO2. Beyond Wauchula to Arcadia, oxidation of lignite via sulfate reduction adds additional carbon to the water composition. 14C ages, corrected for the derived mass transfer reactions, are slightly younger than was previously recognized owing to consideration of incongruent dissolution. The age of Arcadia water (at the farthest point down the gradient) is estimated to be 36,000 yr B.P. Flow velocities derived from 14C ages are in reasonable agreement with flow velocities estimated from hydrologie considerations. The corrected 14C ages and derived mass transfer reaction coefficients allow estimation of apparent rates of reaction in central Florida from field data. The results of this study point to a complex diagenetic history in central Florida in which the position of the freshwater‐saltwater interface appears to determine whether dolomite is a reactant or product mineral.
Design of optimal water distribution systems
Authors: Alperovits E. , Shamir U.
Published: February 2008

A method called linear programing gradient (LPG) is presented, by which the optimal design of a water distribution system can be obtained. The system is a pipeline network, which delivers known demands from sources to consumers and may contain pumps, valves, and reservoirs. Operation of the system under each of a set of demand loadings is considered explicitly in the optimization. The decision variables thus include design parameters, i.e., pipe diameters, pump capacities and reservoir elevations, and operational parameters, i.e., the pumps to be operated and the valve settings for each of the loading conditions. The objective function, to be minimized, reflects the overall cost capital plus present value of operating costs. The constraints are that demands are to be met and pressures at selected nodes in the network are to be within specified limits. The solution is obtained via a hierarchial decomposition of the optimization problem. The primary variables are the flows in the network. For each flow distribution the other decision variables are optimized by linear programing. Postoptimality analysis of the linear program provides the information necessary to compute the gradient of the total cost with respect to changes in the flow distribution. The gradient is used to change the flows so that a (local) optimum is approached. The method was implemented in a computer program. Solved examples are presented.
Evaporation from the wet canopy of a pine forest
Authors: Stewart J. B.
Published: February 2008

Measurements of the energy budget of a pine forest were made on 70 days when the canopy was wet. Out of 245 20‐min periods when the canopy was wholly wet, 173 were occasions when the latent heat flux exceeded the net radiation, the additional energy being provided by a downward flux of sensible heat. Under the same level of radiation the average rate of evaporation of intercepted precipitation has been found to be three times the average rate of transpiration, so that the loss by evaporation of intercepted precipitation is only partly compensated by the suppression of transpiration. It is concluded that reliable estimates of the water resources of forested areas require a separate calculation of the interception and transpiration components of the total evaporation loss.
The sampling error of storage size
Authors: Phatarfod R. M.
Published: February 2008

The size of a reservoir for a given draft ratio and reliability is usually obtained by fitting a distribution to the historical flows. Since the parameters of the inflow model are estimates obtained from data, they are subject to sampling errors. These errors are carried on and magnified when one determines the size of the reservoir. The bias and the standard error of the reservoir size are considered. Details are worked out for the case of the gamma input.
Theory and numerical analysis of moving boundary problems in the hydrodynamics of porous media
Authors: Nakano Yoshisuke
Published: February 2008

The exact mathematical descriptions of a boundary between unsaturated flow and saturated flow as well as a wetting front are obtained. A new concept for numerical analysis of flow in a partly unsaturated and partly saturated porous medium is introduced. A boundary of infinitesimal width intersecting the unsaturated and saturated parts is substituted by an artificial transitional zone of finite width for computational simplicity. The concept is proved to be theoretically justifiable. The feasibility of the concept is demonstrated as it is applied to a two‐dimensional finite difference solution of a special problem of column drainage, for which an analytical solution is obtained.
Analysis of dynamic aquifers with stochastic forcing function
Authors: Sagar Budhi
Published: February 2008

The existence of different types of uncertainties in deterministic aquifer models and the need of quantitatively accounting for them are discussed. The case of one‐dimensional saturated flow represented by a linear parabolic partial differential equation with a stochastic forcing function is analyzed. The dependence of the autocovariance function of the hydraulic head on properties of the forcing function and nature of the aquifer is brought out.
Estimating recharge from ephemeral streams in arid regions: A case study at Kairouan, Tunisia
Authors: Besbes M. , Delhomme J. P. , De Marsily G.
Published: February 2008

On the assumption that the behavior of an aquifer is linear, it is shown that recharge from an ephemeral stream can be computed by deconvolution of the fluctuations of the piezometers in the vicinity of the stream. First, the ‘impulse response’ of the piezometer has to be determined, either from an exceptional flood event or with the help of a digital model of the aquifer. Application of this method to the plain of Kairouan (Tunisia) proved to give estimates of recharge during a 5‐year period within the same order of magnitude as direct volume estimates obtained by an automatic contouring technique of the recovery of the aquifer after infiltration (kriging). An empirical runoff‐recharge relationship was then determined to extend the estimation of recharge to a 23‐year period.
On thermal stratification in reservoirs during the winter season
Authors: Rahman M.
Published: February 2008

A one‐dimensional mathematical model describing the thermal structure in stratified reservoirs during the winter season is considered. With the help of this model an attempt is made to clarify some of the physical factors which strongly influence the temperature profiles in reservoirs. It has been observed that there are many factors which influence the shape of the vertical temperature distribution, namely, the profile at the time of ice formation, the heat exchange by diffusion in the water mass, the heat exchange due to inflow and outflow of water in reservoirs, etc. This model accounts for a qualitative assessment of the possible effects of diffusivity and the initial shape of the temperature profiles on the variation of the vertical temperature distribution.
A finite element study of steady state flow in an unconfined aquifer resting on a sloping bed
Authors: Choi E. C. C.
Published: February 2008

A two‐dimensional finite element method is used to study the problem of seepage over a sloping impermeable bed. Flow profile and seepage rates obtained from the analysis are compared with those solved from Pavlovsky's and Childs' equations. The latter equation is found to be more favorable, especially for large slopes. The effects on the flow profile due to (1) a change in the upstream and downstream conditions and (2) a sudden change in the magnitude of the slope of the impermeable bed are also investigated.
Unsteady flow to a pumped well in a fissured aquifer with a free surface level maintained constant
Authors: Boulton N. S. , Streltsova T. D.
Published: February 2008

New equations are derived for the drawdown in an aquifer consisting of two horizontal layers referred to as the block and the fissure, which have different hydraulic properties. The free water surface forming the upper aquifer boundary is located in the block. The water level is assumed to remain constant during pumping. The block and the fissure are compressible. The depth of the fissure is small in comparison with that of the block. The abstraction well, lined along the block, is pumped at a constant rate. The discharge per unit length of the unlined part in the fissure is constant, and the radius of the well is vanishingly small. Type curves for the drawdown in the fissure and the block are computed and plotted for some selected parameters involved. The effect of the block compressibility on the drawdown in the fissure is shown by comparing the type curves with the type A drawdown curves of Boulton (1963). The influence of the free surface compared with that of an impervious top layer on the drawdown in the fissure and the block is estimated by comparing the type curves with those of Boulton and Streltsova (1977a) found from the equations for a two‐layered formation, the top and bottom surfaces of which are impermeable.
Holocene stratigraphy in flood frequency analysis
Authors: Costa John E.
Published: February 2008

The risk of rare catastrophic flood events is extremely difficult to evaluate by using conventional flood frequency analyses. The true return period may be so long compared to gaging station or historical records that the stratigraphic record of the Holocene (0–10,000 years B.P.) may be the best method for assessing the risk of outstanding floods. Several geologic methods applicable to flood frequency analysis are (1) tree ring analysis of floodplain trees destroyed or scarred by floodwaters, (2) radiocarbon dating of organics in deposits (landforms) eroded by recent floods, (3) radiocarbon dating of organic materials in older flood deposits, (4) pollen analysis and radiocarbon dating of organic materials in lenses of fine‐grained alluvium buried by coarse flood deposits, (5) radiocarbon dating of soil horizons or organic material in slack‐water deposits, (6) radiocarbon or archaeological dating of soils developed in older flood deposits, and (7) dating of landforms eroded or buried by floods based on changes in quantitative soil properties versus time. Using one or more of the above geologic techniques, return periods of some recent catastrophic floods in the United States are: 1976 Big Thompson River, Colorado, 5000 years (?); 1964 Klamath River, California, 100 years (?); 1972 Western Run, Maryland, 2100 years (?); and 1972 Elm Creek, Texas, 400 years (?).
Seasonal variation in PCO2 and 13C content of soil atmosphere
Authors: Rightmire Craig T.
Published: February 2008

Soil carbon dioxide is the dominant source of dissolved inorganic carbon in recharging waters. Samples of soil CO2 were collected to determine if seasonal variations in 13C content parallel those previously observed for PCO2. Significant seasonal variations in both PCO2 and 13C content were observed. Studies of groundwater carbonate chemistry require knowledge of the season during which major recharge occurs.
Climate, soil, and vegetation: 5. A derived distribution of storm surface runoff
Authors: Eagleson Peter S.
Published: February 2008

The Philip infiltration equation is integrated over the duration of a rainstorm of uniform intensity to give the depth of point surface runoff from such an event on a natural surface in terms of random variables defining the initial soil moisture, the rainfall intensity, and the storm duration. In a zeroth‐order approximation the initial soil moisture is fixed at its climatic space and time average, whereupon by using exponential probability density functions for storm intensity and duration, the probability density function of point storm rainfall excess is derived. This distribution is used to define the annual average depth of point surface runoff and to derive the flood volume frequency relation, both in terms of a set of physically meaningful climate‐soil parameters.
Climate, soil, and vegetation: 6. Dynamics of the annual water balance
Authors: Eagleson Peter S.
Published: February 2008

Mass conservation is employed to express the natural water balance of climate‐soil‐vegetation systems in terms of the average annual values of precipitation, evapotranspiration, surface runoff, and groundwater runoff as derived from the probability distributions of storm properties and from the physics of the appropriate storm and interstorm soil moisture fluxes. The resulting conservation equation is used to define the dimensionless parameters governing the dynamic similarity of the annual water balance. An asymptotic analysis of this water balance equation yields a set of rational criteria for the classification of climate‐soil‐vegetation systems. Sensitivity with respect to the primary climate, soil, and vegetal parameters demonstrates that qualitative changes in water balance behavior are primarily dependent upon the exfiltration effectiveness of the soil. A natural selection hypothesis is presented which specifies the stable vegetation density and the plant coefficient for a given climate‐soil system in which water and not nutrition or light is limiting.
A storage‐routing model relating drainage basin hydrology and geomorphology
Authors: Boyd Michael J.
Published: February 2008

A study of four nested drainage basins has been used to measure relations between lag time, stream order, and network magnitude for basins within a larger watershed. Solution of the stream order laws produced a relation between lag time and drainage area which had the same form as the relations developed between different watersheds. A relation between lag time and drainage area was used to allocate storage parameters to the elements of a storage‐routing model based on the stream channel network. When it was applied to the most probable stream networks for a given channel magnitude, the model was shown to reproduce relations between lag time and stream order, channel magnitude, and drainage area, having the same form as was observed for the actual drainage basins used in the study.
Carbonate chemistry of groundwater from Tropical Tower Karst in South Thailand
Authors: Pitman John I.
Published: February 2008

Waters from tropical tower karst in an area with no seasonal variations in temperature show marked variations in their dissolved carbonate chemistry. Saturation indices for calcite and dolomite indicate that most samples are saturated to supersaturated with these solids. Calculated log PCO2 values for the waters give a mean of −2.12 ± 0.41. Measured PCO2 values for the soil atmosphere and soil leachates give a mean log PCO2 of −1.43 ± 0.07. The wide variation of springwater PCO2 is best explained by a predominantly closed system evolution from the initial PCO2 of the soil.
Isotope and ion geochemistry of groundwaters in the Milk River Aquifer, Alberta
Authors: Schwartz Franklin W. , Muehlenbachs Karlis
Published: February 2008

The Milk River artesian aquifer underlines an area of approximately 6300 km2 in southern Alberta. This aquifer fits almost exactly Chamberlain's (1885) concept of a classic artesian system. It crops out or is covered by a thin veneer of glacial drift in southern Alberta and northern Montana. It is believed that major recharge occurs in these areas (Meyboom, 1960). Structurally, the aquifer appears fan‐like in form, dipping gently to the east, north and west from its areas of outcrop. It is overlain by the Pakowki Formation which is a grey shale that acts as a confining bed. Analysis of stable isotope and major ion data for water samples collected from the aquifer reveals a variety of striking patterns. Oxygen‐18 and deuterium concentrations for groundwater from the recharging portion of the aquifer fall very close to the meteoric water line (Craig, 1961a) indicating that they are isotopically unaltered meteoric waters. Proceeding down‐dip in the aquifer groundwaters become enriched isotopically to a maximum of 70 and 12‰ with respect to deuterium and oxygen‐18 in the recharging waters. In addition, a systematic deviation (slope of 6.1 instead of 8) from the meteoric water line is also apparent. The most plausible explanation of these isotopic patterns is based on a process of dispersion or mixing on a regional scale. Waters probably enriched with respect to the isotopic composition of the aquifer recharge may be present and simply are being displaced by meteoric water, or leakage may have entered the aquifer from below progressively comprising an increased proportion of the aquifer water. This same type of mixing process appears to exert a major control on the major ion chemistry of the aquifer. In addition, chemical processes such as mineral dissolution and cation exchange play a role.
A Monte Carlo Analysis of the hydrologic effects of spatial variability of infiltration
Authors: Smith R. E. , Hebbert R. H. B.
Published: February 2008

Monte Carlo simulation is employed to analyze the effects of random distribution of soil infiltration properties on the hydrologic performance of catchment areas. Soil hydraulic parameters are distributed with log normal distribution as reported from previous field measurements. Although independent sampling units are assumed, a discussion is presented on the nature and effect of spatial dependence. The composite infiltration rate of an area is simply the average, at an instant in time, of the infiltration rate of all points within that area. Rigorous treatment of the topic is a forbidding problem in stochastic differential equations. Monte Carlo simulation is used here to study the effects of random distribution of soil properties on distribution of ponding time, composite areal rate, and bias due to variability in space. More accurate treatment for watershed studies must also consider interaction of various points on the surface by way of overland flow paths. A distributed watershed simulation model is used for this purpose to demonstrate hydrograph bias due to deterministic spatial variability, and from random variation, plus the relation of bias to rainfall rate. An analysis is also made of the partial area contribution in early parts of storm runoff caused solely by random variation in surface soil properties.
An analysis of residential demand for water using micro time‐series data
Authors: Danielson Leon E.
Published: February 2008

Residential water demand is estimated as a function of temperature, rainfall, house value, water price, and household size using monthly cross‐section and time‐series meter readings from 261 residential households in Raleigh, North Carolina, between May 1969 and December 1974. Tests for validity of assumptions are made, and a methodological approach is used that provides unbiased estimates of parameters and standard errors with data that exhibit serially correlated residuals. Demand relations are estimated for total residential, winter, and sprinkling demands. Sprinkling use per period per customer for each year is estimated by subtracting winter (November–April) from summer (May–October) use. Household size explained the largest proportion of the variation in the data. Estimated sprinkling demand was found to be highly responsive to changes in water price and the level of the climatic variables, while total residential demand and winter demand were less responsive to price changes.
Mathematical derivation of linear and nonlinear runoff kernels
Authors: Hino Mikio , Nadaoka Kazuo
Published: February 2008

From a viewpoint of overall grasp of response characteristics of a basin to rainfall, an integral form of expression such as the unit hydrograph, the Volterra series, and the Wiener series is superior to differential equation type expressions. However, hitherto, response or runoff kernels have been derived from empirical data or at the most from numerical simulation data. In this paper the runoff is represented by the Wiener‐Hermite orthogonal functional expansion. By application of the Galerkin technique a set of ordinary nonlinear differential equations for the expansion coefficients of kernel functions are derived from the basic equation of motion. The differential equations are solved by the Runge‐Kutta‐Gill scheme to obtain the runoff kernels. Various features of the theoretical linear and nonlinear runoff kernels thus derived compare well with the empirical ones.
A new numerical method for solving the solute transport equation
Authors: Ross Benjamin , Koplik Charles M.
Published: February 2008

The solute transport equation can be solved numerically by approximating the water flow field by a network of stream tubes and using a Green's function solution within each stream tube. Compared to previous methods, this approach permits greater computational efficiency and easier representation of small discontinuities, and the results are easier to interpret physically. The method has been used to study hypothetical sites for disposal of high‐level radioactive waste.
Relationship between precipitation and tornado activity
Authors: Galway Joseph G.
Published: February 2008

Precipitation and tornado statistics for three different geographic areas are compared. Weak correlations exist between yearly and seasonal precipitation totals and tornadic activity. Also, a slight trend for wet years to have more tornadoes than dry ones is present. However, tornadic activity does not appear to be related to the existence of drought.
Soil water hysteresis as a cause of delayed yield from unconfined aquifers
Authors: Bouwer Herman
Published: February 2008

Hysteresis in the relation between soil water content and (negative) pressure head of the soil water produces a lag in the release of pore water from a rewetted soil when the pressure heads are lowered (made more negative). For an unconfined aquifer this means that the water table must drop some distance in response to pumping a well before pore water is fully released, if the water table prior to pumping had been rising. Since water tables around active wells usually have been rising before a pumping test is performed (to establish equilibrium), soil water hysteresis may well be a common cause of delayed yield from unconfined aquifers.
An effluent charge schedule: Cost, financial burden, and punitive effects
Authors: Brill E. Downey , Revelle Charles S. , Liebman Jon C.
Published: February 2008

Alternative effluent charge programs are examined with regard to cost, charge payments, financial burden, and punitive effects. These efficiency and equity issues are evaluated for constant unit charge programs and for effluent charge schedule programs; the latter are found to reduce the charge payments and the financial burden significantly. Example charge schedule solutions are also shown to compare favorably to the corresponding direct regulation solutions.
Generating multiobjective trade‐offs: An algorithm for bicriterion problems
Authors: Cohon Jared L. , Church Richard L. , Sheer Daniel P.
Published: February 2008

A technique for generating an approximate or an exact representation of the noninferior set for problems with two objectives is presented. The approach proceeds by using the slope of the line segment between adjacent, previously generated noninferior extreme points to find new noninferior solutions to improve the approximation or to establish the noninferiority of the line segment when the entire noninferior set is to be generated. The proposed technique compares favorably with other generating techniques when the analytical goal is to approximate the noninferior set. A major innovation is the computation of the maximum possible error, which the analyst may control, to obtain an approximation of a desired degree of accuracy. A small example and a river basin planning problem of moderate size are used to demonstrate the use of the algorithm. Further research is required to extend the algorithm to problems with more than two objectives.
Constrained differential dynamic programming and its application to multireservoir control
Authors: Murray Daniel M. , Yakowitz Sidney J.
Published: February 2008

This paper describes a modification of differential dynamic programming (DDP) which makes that technique applicable to certain constrained sequential decision problems such as multireservoir control problems discussed in the hydrology literature. The authors contend that the method proffered here is superior to available alternatives. This belief is supported by analysis (wherein it transpires that constrained DDP does not suffer the ‘curse of dimensionality’ and requires no discretization) and computational experimentation (wherein DDP is found to quickly locate solutions of 4‐reservoir problems introduced by other investigations as well as the solution of a 10‐reservoir problem thought to be beyond the capability of alternative methods).
Use of hypolimnetic oxygen depletion rate as a trophic state index for lakes
Authors: Walker William W.
Published: February 2008

The feasibility of lake water quality management planning has been greatly increased over the past 10 years with the development of relatively simple, empirical methods for assessing eutrophication problems. These relate phosphorus loading, hydrology, and morphometry to such traditional trophic state indices as phosphorus concentration, chlorophyll‐a concentration, and transparency. One of the difficulties associated with use of these methods is that water quality criteria, as related to beneficial use, do not generally correspond to subjective definitions of ‘trophic state.’ This paper attempts to improve upon existing methods by relating measures of phosphorus, chlorophyll‐a, and/or transparency to hypolimnetic dissolved oxygen, which is of direct relevance to existing water quality standards, particularly for fisheries management. A modified version of Carlson's (1977) trophic state index summarizes relationships among summer, epilimnetic measurements of total phosphorus, chlorophyll‐a, and transparency. On the basis of data from 30 lakes this index is shown to be highly correlated with areal hypolimnetic oxygen depletion rate when the apparent effects of mean depth are also taken into account (R2 = 0.91). Tests of the empirical model on a separate data base of 86 lakes indicate that the approach can be used to predict oxygen status based upon lake morphometry and trophic index. The methodology provides a link between phosphorus mass balance models and existing water quality criteria for dissolved oxygen.
Impact of road networks on southeastern Michigan lakeshore drainage
Authors: Bannister Everette N.
Published: February 2008

The postglacial drainage of till plains and lake beds by perennial and intermittent streams in southeastern Michigan reveals local adjustments caused by human activity. The present drainage pattern reflects the construction and subsequent maintenance of the local road network. The impact of the road grid on the linear coastal drainage off the Port Huron Moraine's eastern flank was studied from Lexington Heights to Forester, Michigan. Borrow pits supplied the aggregate used to construct bridges and culverts. These facilities restrict flow and reduce transportation of sediment‐laden runoff. This results in increased but localized sedimentation. The extension, maintenance, and use of road networks has artificially increased the drainage density of the region by creating additional avenues for surface flow. Road networks also truncate natural drainage channels, forcing the coalescence of the smaller order basins, thereby increasing downcutting and runoff in channels whose natural erosional development would have been much less. Channel reaches whose upland drainage has been pirated experience decreased runoff and exhibit less erosion. Such modern changes in drainage topology pose problems to the reconstruction of historical postglacial drainage patterns, since they result in greater stream drainage density.
Extension and application of feature prediction model for synthesis of hydrologic records
Authors: Panu Umed Singh , Unny T. E.
Published: February 2008

The method described in this paper for the synthesis of streamflows differs from the traditional approaches in synthetic hydrology in the sense that it utilizes the information contained in or among the groups of data in a streamflow record. The existense of such groups in geophysical records, including hydrologic records, is well emphasized by Hurst (1951). Further, in the proposed method, based on concepts of pattern recognition, neither a basic structure nor any preconceived model is imposed on the data; rather the data are allowed to speak for themselves in a most ‘democratic’ way. The preliminary details of the method were provided in an earlier paper by Panu et al. (1978). The intent of this paper is to describe a procedure whereby it is possible to specify explicitly multivariate probability distribution for the intrapattern structure and first‐order Markovian dependence for the interpattern structure in the feature prediction model (Panu et al., 1978). The various steps involved in the construction and operation of the model for streamflow synthesis are presented. The application of the model for synthesizing monthly streamflow records of three Canadian rivers exhibiting biannual cycles is explained. Statistical and hydrological tests show that these synthetic realizations possess relevant properties that are comparable with the corresponding properties contained in the historical record. This article should be read in conjunction with the previous publication by Panu et al. (1978).
Percolation theory and models of unsaturated porous media
Authors: Golden J. M.
Published: February 2008

Concepts from percolation theory (Broadbent and Hammersley, 1957) are applied to a model of unsaturated flow through porous media. This approach in principle allows one to build into the model aspects of the topological structure of pore space. At a very general level the input of results from percolation theory gives a relationship between minimum and maximum saturation values for a medium which should be experimentally checkable, though probably not without sophisticated techniques. Also, it gives some qualitative insight into known properties of unsaturated flow. Furthermore, there emerges a way of looking at the phenomenon of hysteresis that is quite different from the standard approach. This aspect is explored in some detail, and two possible new models are presented. A subsidiary result obtained from the detailed model used is that in a simple pore model the inclusion of a pore length parameter, statistically correlated with pore radius, is equivalent, at least in a restricted sense, to incorporating into the model the concept of tortuosity.
A method for determining the hydraulic properties of tight formations
Authors: Bredehoeft John D. , Papadopulos Stavros S.
Published: February 2008

A method for testing formations of very low permeability is presented. The method is based on an analytical solution that describes the decay of a head change caused by pressurizing the volume of water stored in a shut‐in well. Type curves prepared from this solution are matched with observed data to determine the hydraulic properties of the formation tested. The test is similar to the conventional slug test; however, its much shorter duration makes the testing of extremely tight formations feasible.
Development of a self‐sealing sampler for ephemeral Wadi Floods
Authors: Levin M. , Adar E. , Barzilai A.
Published: February 2008

The sampling of random floods for the analysis of environmental isotopes in flood water is handicapped by the fact that this water may partially evaporate between the time of the flood and the actual collection of the sample. Conventional methods of sampling are frequently ineffective, as floods occur at random both in time and space. With these considerations in mind, we designed and built an instrument that enables automatic sampling of flood water. The sample is hermetically sealed, and secondary effects that could change the original sample in any way are thus avoided.
Unsteady one‐dimensional flow over a plane: Partial equilibrium and recession hydrographs
Authors: Morris E. M. , Woolhiser D. A.
Published: February 2008

This paper presents a comparison of solutions of the shallow water (Saint Venant) equations for unsteady one‐dimensional flow over a plane and solutions of the diffusion and kinematic wave equations, which are approximate forms of the Saint Venant equations. In the cases studied, the lateral inflow is constant and positive but may cease before a steady state flow is reached. It is shown that for highly subcritical flow, the criterion proposed by Woolhiser and Liggett is necessary but not sufficient to enable a choice between the shallow water equations and the kinematic approximation. An additional criterion is proposed for these cases.
Application of the Green‐Ampt Model to infiltration under time‐dependent surface water depths
Authors: Freyberg David L. , Reeder John W. , Franzini Joseph B. , Remson Irwin
Published: February 2008

The performance of the Green‐Ampt model for infiltration problems where the depth of water above the ground surface is varying with time is investigated. In order to yield infiltration rates that agree with those predicted by the Richards equation for flow in a homogeneous, nondeforming, and nonhysteretic soil the effective suction head parameter in the Green‐Ampt model must be considered a function of time, surface water depth, initial moisture content, and soil type. However, when a constant value of the effective suction head is assumed, the response of the Green‐Ampt model to variations in surface water depth is qualitatively equivalent to the response of the Richards model. The effectiveness of a number of definitions of the suction head parameter that have been proposed in the literature is investigated. While the differences in predicted infiltration rates and cumulative infiltration obtained by using the different definitions are, in general, of marginal significance, the best choice of the value of the effective suction head depends upon the particular problem to which the model is being applied.
Development of a self‐sealing rain sampler for arid zones
Authors: Adar E. , Levin M. , Barzilai A.
Published: February 2008

Owing to evaporation from standard rain gauges in arid zones the natural isotopic abundance of deuterium and oxygen 18 in rainwater may not have been correctly determined in the past. A single‐stage rain sampler has been developed involving the use of a hermetic seal to help eliminate the evaporation problem. This gauge provides a suitable sample for isotopic analysis. A multiple‐stage rain sampler has been developed to enable the collection of successive rainfall fractions within a particular storm. Instruments of both types were distributed throughout the Negev Desert in Israel. Results from 2 years of observations involving 20 storms indicate the efficiency and reliability of the instruments developed.
Boundary integral solutions to three‐dimensional unconfined Darcy's Flow
Authors: Lennon Gerard P. , Liu Philip L.‐F. , Liggett James A.
Published: February 2008

The boundary integral equation method (BIEM) is used to solve three‐dimensional potential flow problems in porous media. The problems considered here are time dependent and have a nonlinear boundary condition on the free surface. The entire boundary, including the moving free surface, discretized into linear finite elements for the purpose of evaluating the boundary integrals. The technique allows transient, three‐dimensional problems to be solved with reasonable computational costs. Numerical examples include recharge through rectangular and circular areas and seepage flow from a surface pond. The examples are used to illustrate the method and show the nonlinear effects.
Solute transport through fractured media: 2. Column study of fractured till
Authors: Grisak G. E. , Pickens J. F. , Cherry J. A.
Published: February 2008

A tracer solution containing Cl and Ca was passed through a large intact cylindrical sample of fractured clayey glacial till obtained from a depth of 5 m in a fresh excavation. The sample was intersected by two orthogonal sets of fractures oriented parallel to the long axis of the column. Breakthrough curves for Cl and Ca show that these species were significantly retarded in relation to the average fracture flow water velocity as they passed through the column. The retardation is attributed to the effect of diffusion of the solutes from the fractures into the porous matrix of the till. The relative positions of the Ca and Cl breakthrough curves are attributed to the combined influence of a smaller effective diffusion coefficient for Ca than for Cl and adsorption of Ca in the matrix during the diffusion process. Relatively good agreement with the experimental data was achieved in mathematical simulation using the finite element solute transport model described by Grisak and Pickens (1980). Effective diffusion coefficients for Cl and Ca in the till matrix were found to be 5.0 × 10−7 and 1.9 × 10−7 cm2/s, respectively. The lack of total continuity between fracture sets was accounted for in the model by using an effective fracture spacing and effective aperture width based on the concepts of flow in planar fractures in sets of simple geometry.
The estimation of small‐watershed peak flows in China
Authors: Liu Changming , Wang Guangte
Published: February 2008

A small‐watershed model based on the analysis of data measured from a number of small experimental watersheds and various physical geographic factors in our country is formulated for predicting the flood peak discharge resulting from storm rainfall. As the relevant factors and field measurements cover a wide range of conditions, this method is now being widely used for railway design works in the northwest and for hydraulic engineering design in certain other regions in China with fairly good results.
Stochastic estimation of bed load yield in pool‐and‐riffle mountain streams
Authors: Griffiths George A.
Published: February 2008

In many mountain streams the supply of gravel, transported as bed load, is predominantly influenced by the stability of a restricted area of riparian land. During storms this zone contributes sediment to the stream through random mass movements and stream bank collapses with the result that floods, having similar hydrographs, produce different bed load yields. A stochastic model is developed which predicts total expected bed load yield from a given basin, in a prescribed interval, through the convolution of a Poisson number of events with an exponential probability of bed load yield. The exponential distribution is defined from regional flood frequency relations, an empirical bed load transport formula, and flow records from a nearby basin within the same hydrologic regime as the one under consideration; the expected number of events in an interval is also determined from these flow records. The model may be applied to small mountain watersheds, ungauged for either water or sediment outflows.
A simplified functions approach for determining soil hydraulic conductivities and water characteristics in situ
Authors: Ahuja L. R. , Green R. E. , Chong S.‐K. , Nielsen D. R.
Published: February 2008

The unsaturated hydraulic conductivity and the soil water content are assumed to be piecemeal power form and linear logarithmic functions of the soil water suction, respectively. The parameters of these functions are determined by an analysis of the drainage phase tensiometric data, combined with the field measured value of near saturated conductivity and one soil moisture sampling during the drainage. The unsaturated hydraulic conductivity and diffusivity are determined without the prior knowledge of the soil water characteristic, which is required for the more rigorous Darcian analysis. The method was tested on field data of four Hawaii soils and one California soil. The results, generally, were encouraging. However, in some cases there was discrepancy in the conductivity values for very small suctions, less than 20 cm, between the rigorous and the simplified methods, due probably to an error in measuring the field‐saturated conductivity or the errors of analysis and using soil core water characteristics for the very wet region in the rigorous Darcian method. The slope parameter of the water characteristic function was somewhat more sensitive to the scatter in the input data, but large errors in this function can be independently detected. Overall, the simplified method looked promising for further testing as such and in large‐area applications of the calculated soil parameters.