摘要:

This paper presents an algorithm for the estimation of parameters in state‐space models that represent hydrologic processes in which the state variables are observed with error. The algorithm is based on the maximization of the conditional expectation of the likelihood function of the state equation. The estimation algorithm is numerically stable and guarantees local convergence under mild conditions. It is also shown that the estimation algorithm can be coupled with an optimal control method to yield a combined control estimation technique that can be easily implemented. An application of the theory and methods developed herein is given for flood routing via reservoir operatio

ISSN:0043-1397    

DOI:10.1029/WR021i011p01575

年代:1985

数据来源: WILEY

摘要:

A currently used approach to flood frequency analysis is based on the concept of parametric statistical inference. In this analysis the assumption is made that the distribution function describing flood data is known, for example, a log‐Pearson type III distribution. However, such an assumption is not always justified and often leads to other difficulties; it could also result in considerable variability in the estimation of design floods. A new method is developed in this article based on the nonparametric procedure for estimating probability distribution function. The results indicate that design floods computed from the different assumed distribution and from the nonparametric method provide comparable results. However, the nonparametric method is a viable alternative with the advantage of not requiring a distributional assumption, and has the ability of estimating multimodal distribution

ISSN:0043-1397    

DOI:10.1029/WR021i011p01585

年代:1985

数据来源: WILEY

摘要:

Research in recent years has led to conceptualizations of the long‐term responses of catchment surface water quality to acidic deposition. That research has focused attention on certain soil processes as likely keys to catchment responses (anion retention, cation exchange, primary mineral weathering, aluminum dissolution, and CO2solubility). We present a mathematical model which uses quantitative descriptions of these soil chemical processes to estimate the long‐term chemical changes that occur in the soil, soil water, and surface waters of catchments in response to changes in atmospheric deposition. The model is applied to a small forested catchment in the Shenandoah National Park, Virginia. Historical changes in surface water quality are reconstructed for the catchment for the last 140 years. The model indicates that alkalinity of surface waters in the catchment may have been reduced by as much as 50%. Water quality is forecast for the catchment under three different scenarios of future changes in atmospheric deposition. The model indicates that all but very large reductions in deposition will result in further deterioration of the catchment water quality. The process‐oriented, lumped‐parameter approach used is consistent with all currently available observations of water quality in the catchment. Due to the lack of long‐term records of catchment water quality, strict verification of the model estimates and an assessment of the model validity is problematic. This is the case for all models of long‐terrn catchment chemical responses to acid deposition. Nonetheless, the model provides a means of integrating the results of individual process level laboratory and field studies. Used this way, the model becomes a vehicle for examining the interactions and long‐term implications of our conceptualization of the acidific

ISSN:0043-1397    

DOI:10.1029/WR021i011p01591

年代:1985

数据来源: WILEY

摘要:

The application of adjoint sensitivity theory to steady state ground water flow is illustrated with three one‐dimensional flow problems. Adjoint states are analytically derived for four performance measures of these test problems: hydraulic head at a point, spatially average hydraulic head, Darcy velocity at a point, and flux from a prescribed head boundary. Sensitivity coefficients are analytically calculated for average head. The adjoint states are interpreted and their usefulness is discussed. The implementation of a numerical adjoint sensitivity flow code to solve for these adjoint states is described, and the computed adjoint states are used in the code to evaluate the sensitivities of model results to model input parameters. The one‐dimensional flow problems provide a set of verification tests for the numerical code. The numerical code successfully reproduces both the analytically derived adjoint states, including those involving jump conditions, and the sensitivity coefficients for model output values that are nonlinear with respect to model paramet

ISSN:0043-1397    

DOI:10.1029/WR021i011p01602

年代:1985

数据来源: WILEY

摘要:

Changes in salinity in groundwater and surface water in the Arkansas River valley of southeastern Colorado are primarily related to irrigation practices. A solute transport model was applied to an 11‐mile reach of the valley to compute salinity changes in response to spatially and temporally varying stresses. The model was calibrated in 1973 using detailed field measurements made during 1971 and 1972. In 1973 the calibrated model was used to predict that a gradual long‐term increase in groundwater salinity of about 2–3% per year would occur if the observed irrigation practices continued. The study area was resampled during the winter of 1982 to help evaluate if any long‐term changes in salinity are actually occurring. Nonparametric and parametric statistical tests were used to help assess the significance of observed changes in groundwater salinity. These tests indicate that a statistically significant increase in salinity occurred between the winters of 1971 and 1972 (the model calibration period). However, a comparison of the winter 1972 and winter 1982 data indicates that no significant net change in salinity has occurred during this 10‐year period. An analysis of the few available historical data (1895, 1923, 1959–1961, and 1964) supports the hypothesis that groundwater salinity in this irrigated area has reached a long‐term dynamic equilibrium in response to irrigation practices. The model predictions of long‐term salinity increases were invalid probably because the calibration period occurred during a short‐term annual trend of increasing salinity in the river (and hence in leaky irrigation canals and in applied irrigation water), which was not representative of th

ISSN:0043-1397    

DOI:10.1029/WR021i011p01611

年代:1985

数据来源: WILEY

摘要:

This study provides an analysis of the water table configuration and hydraulic‐head distribution in layered hillsides. A finite‐element model was used to simulate two‐dimensional, saturated‐unsaturated, steady state flow through layered slopes. A laboratory sand tank experiment was used to verify the physical foundation of the mathematical model. It is shown that layered slopes feature multiple seepage faces, perched water tables, and wedge‐shaped unsaturated zones. The hydraulic‐head distribution and water table configuration are strongly dependent on the position of the impending layers and the ratio of the hydraulic conductivity between adjacent layers. This work has geotechnical implications with regard to slope stability and the control of groundwater inflows into excavations. It has hydrogeological implications with regard to flow path analysis in contamination studies. It has geomorphological implications with respect to landform development by mass movements and surface water erosions, and to drainage network development thr

ISSN:0043-1397    

DOI:10.1029/WR021i011p01625

年代:1985

数据来源: WILEY

摘要:

Solutions are calculated for both steady and unsteady flow to a well in a multiaquifer system withN‐horizontal aquifers. Aquifer and aquitard properties may vary from one layer to the next but are assumed constant in the horizontal direction. The solutions, which are expressed in closed form, require the solution of generalized eigenvalue problems for their numerical evaluation. It is shown that the matrices appearing in these eigenvalue problems are symmetric and positive definite, which means that the eigenvalues are real and positive and that the solution always exists. Finally, a solution is calculated for a numerical exampl

ISSN:0043-1397    

DOI:10.1029/WR021i011p01637

年代:1985

数据来源: WILEY

摘要:

This note illustrates that certain shifting level processes possess long‐term dependence and preserve the Hurst effect for the rescaled adjusted range. Although such processes belong to a stable domain of attraction, and not that of fractional Brownian motion, they do have asymptotic behavior of the rescaled adjusted range identical to that of fractional Brownian noise; further, they are easily simulated. Other shifting level processes belonging to the same stable domain of attraction preserve the Hurst effect for the raw and adjusted ranges but not for the rescaled adjusted rang

ISSN:0043-1397    

DOI:10.1029/WR021i011p01642

年代:1985

数据来源: WILEY

摘要:

The radiation balances of melting snowpacks for three seasons at an open site at the Central Sierra Snow Laboratory near Soda Springs, California were examined. The snow covers were examples of below‐normal, near‐normal and much‐above‐normal water equivalents. Two of the snow covers melted under generally clear skies in late spring while the other melted under cloudier conditions and at a time when less extraterrestrial radiation was available. Moreover, the snow covers were of very different densities, thereby allowing examination of a possible relationship between that characteristic and albedo. No such relationship was observed. Despite the dissimilarities in the conditions under which melt occurred, the disposition of solar radiation was similar for the three melt seasons. Albedos and their rates of decline through the melt season were similar for the three seasons. Absorbed solar radiation and a cloudiness index were useful predictors for daily net radiation, accounting for 71% of the total v

ISSN:0043-1397    

DOI:10.1029/WR021i011p01649

年代:1985

数据来源: WILEY

摘要:

A field method is proposed for determining the three‐dimensional hydraulic conductivity tensor and specific storage of an anisotropic porous or fractured medium. The method, known as cross‐hole testing (to distinguish it from conventional single‐hole packer tests), consists of injecting fluid into (or withdrawing fluid from) packed‐off intervals in a number of boreholes and monitoring the transient head response in similar intervals in neighboring boreholes. The directions of the principal hydraulic conductivities need not be known prior to the test, and the boreholes may have arbitrary orientations (e.g., they can all be vertical). An important aspect of the proposed method is that it provides direct field information on whether it is proper to regard the medium as being uniform and anisotropic on the scale of the test. The first paper presents theoretical expressions describing transient and steady state head response in monitoring intervals of arbitrary lengths and orientations, to constant‐rate injection into (or withdrawal from) intervals having similar or different lengths and orientations. The conditions under which these intervals can be treated mathematically as points are investigated by an asymptotic analysis. The effect of planar no‐flow and constant‐head boundaries on the response is analyzed by the theory of images. The second paper describes the field methodology and shows how the proposed approach works in the case of fractured g

ISSN:0043-1397    

DOI:10.1029/WR021i011p01655

年代:1985

数据来源: WILEY