摘要:

An Eulerian‐Lagrangian localized adjoint method (ELLAM) numerical solution is developed for the multiphase contaminant transport equations in two dimensions. The ELLAM uses finite volume test functions in the space‐time domain defined by the characteristics of the hyperbolic part of the governing equation. The use of the characteristics results in an approximation that allows large time steps while still maintaining accurate solutions. This greatly reduces the computational effort required to find solutions to the advection‐dispersion equation. Combination of the finite volume test functions with the conservative form of the governing equation results in a local conservation of mass property. For problems with a constant saturation such as that of contaminant transport in the saturated zone this property is highly advantageous as the resulting numerical approximation conserves mass both globally and locally. For problems with a variable saturation the requirement of local conservation of mass is too stringent, particularly around first‐type boundaries where oscillations can occur because of errors inherent in the numerical determination of fluid velocities and in the backtracking routine. A combined conservative/nonconservative ELLAM is developed with an ELLAM formulation based on the nonconservative form of the governing equation being applied to subdomains intersecting first‐type boundaries and a conservative ELLAM being used for all other subdomains. The combined conservative/nonconservative ELLAM is compared to a Galerkin finite element scheme and is found to have greatly superior performance, requiring far fewer time steps to obtain a solution of equivalent

ISSN:0043-1397    

DOI:10.1029/95WR02763

年代:1996

数据来源: WILEY

摘要:

A fully automated method uses Landsat Thematic Mapper data to map snow cover in the Sierra Nevada and make quantitative estimates of the fractional snow‐covered area within each pixel. We model winter and spring reference scenes as linear mixtures of image end member spectra to produce the response variables for tree‐based regression and classification models. Decision trees identify cloud cover and fractional snow‐covered area. We test the algorithm on a different Thematic Mapper scene and verify with high‐resolution, large‐format, color aerial photography. The accuracy of the automated classification of Thematic Mapper data equals that obtainable from the aerial photographs but is faster, cheaper, and covers a vastly larger area. The mapping method is insensitive to the choice of lithologic or vegetation end members, the water equivalent of the snow pack, snow grain size, or local illuminat

ISSN:0043-1397    

DOI:10.1029/95WR02718

年代:1996

数据来源: WILEY

摘要:

Natural variability in the annual flow of the Nile River has been the subject of great interest to the civilizations that have historically occupied the banks of that river. Here we report results from analysis on two extensive data sets describing sea surface temperature of the Pacific Ocean, and the flow of water in the Nile River. The analysis suggests that 25% of the natural variability in the annual flow of the Nile is associated with El Niño oscillations. A procedure is developed for using this observed correlation to improve the predictability of the Nile flood. A simple hypothesis is presented to explain physically the occurrence of the Hurst phenomenon in the Nile flow

ISSN:0043-1397    

DOI:10.1029/95WR02968

年代:1996

数据来源: WILEY

摘要:

The ability of passive microwave remote sensing (PMRS) to assess soil moisture has been amply demonstrated. Building on the expertise, this research is a first attempt at obtaining near‐surface soil hydraulic characteristics from PMRS. We show that relative change in surface soil moisture can be determined accurately from PMRS measurements of brightness temperature, given the commonly observed linear relationship between the two variables. Relative, rather than absolute, change within a series of PMRS images, obtained during a period of drying, is also a very useful statistic for filtering out the drydown heterogeneity caused by spatial variability in initial wetness rather than soil heterogeneity. We develop a test of soil heterogeneity based on the detection of deviations of relative change from the average rate in a series of images by more than the instrument error. With the test, the existence of soil heterogeneity for a pair of images showing a drydown during the 1992 Hydrologic Atmospheric Pilot Experiment (HAPEX‐Sahel) experiment can be proven. Areas of relatively fast or slow drying can be mapped. These areas coincide with geomorphological features and soil‐type patterns that are expected to show the observed moisture dynamics. The variogram of relative change in the HAPEX images differs from those of brightness temperature, corroborating the rejection of the soil homogeneity hypothesis. Furthermore, the variogram indicates the existence of an effective correlation length much larger than that commonly observed in ground‐based soil surveys. These findings encourage the use of PMRS for assessing soil hydraulic characteristics that are valid at a scale appropriate for hydrometeorological

ISSN:0043-1397    

DOI:10.1029/95WR02916

年代:1996

数据来源: WILEY

摘要:

We study the possibility that variations in the volume of the Great Salt Lake (GSL), a large, closed basin lake, may be described as a low‐dimensional nonlinear dynamical system. There is growing evidence for structure in the recurrence patterns of climatic fluctuations that drive western United States hydrology. Moreover, the time behavior of such lakes is generally more regular than that of the climatic forcing. This suggests the possibility that an analysis of the 144‐year, biweekly time series of the GSL volume may shed some light on the underlying dynamics of lake variations. Three methods (correlation dimension, nearest neighbor dimension, and false neighbor dimension) of estimating attractor dimension are applied and compared. The analysis suggests that the GSL dynamics may be described by a dimension of about four. Implications of such analyses relative to low‐frequency variations and colored noise and limitations of such analyses are disc

ISSN:0043-1397    

DOI:10.1029/95WR02872

年代:1996

数据来源: WILEY

摘要:

An analytical expression is derived for the Priestley‐Taylor coefficient, α. This coefficient is generally interpreted as the ratio between the actual evaporation rate and the equilibrium evaporation rate. The derived expression is shown to be equal to the accepted value of 1.26 for typically observed atmospheric conditions and to be relatively insensitive to small changes in atmospheric parameters. A comparison is made between the new expression and data taken over an irrigated field in California. The concept of equilibrium evaporation is called into question and it is suggested that the Priestley‐Taylor expression with α equal to 1.26 is a more accurate representation of evaporation under “equilibrium” wet surface c

ISSN:0043-1397    

DOI:10.1029/95WR02920

年代:1996

数据来源: WILEY

摘要:

We investigated observation‐error‐induced parameter bias using least squares and Stein‐corrected least squares estimators in a model for predicting lake phosphorus. The Stein‐corrected estimator performed better than the uncorrected estimator from bias and “closeness” perspectives, though the corrected estimator was still biased. Examination of the model structure revealed that parameter bias is strongly related to both the parameter space and sample space. Additionally, the model is robust to parameter bias over a large portion of the sample and parameter space, indicating that this model may be particularly useful for estimation and prediction. Analogous structure in other models could be an important consideration for mode

ISSN:0043-1397    

DOI:10.1029/95WR03109

年代:1996

数据来源: WILEY

摘要:

One of the most recurrent questions in eutrophication control is the extent that nutrients from wastewater discharges are transported and transformed in a receiving water system. For example, phosphorus from point and nonpoint sources could be incorporated into the biomass of phytoplankton in the water column, deposited into the sediments, or transported downstream. Perhaps a more meaningful question is, How much phosphorus in the algal biomass at a certain location in the receiving water is from a given source? A modeling technique has been developed to track the fate and transport of phosphorus from various sources using a numerical tracer. Model results from an application to the upper Mississippi River provide insight into the impact on the receiving water of phosphorus loads from various sources.

ISSN:0043-1397    

DOI:10.1029/95WR02918

年代:1996

数据来源: WILEY

摘要:

This paper presents a nonlinear multivariable fitting model to decompose the optimal policies obtained by dynamic programming of a unique aggregated reservoir. The nonlinear functions are generated using radial basis functions (RBF) neural networks. In this method the potential energy of all the reservoirs in the hydropower system is added to form one equivalent reservoir. The operating policy of the equivalent reservoir is determined by stochastic dynamic programming, and finally the operating rules of each reservoir are determined using RBF neural networks. To improve the multivariable representation of the data, a series of piecewise RBF neural networks is determined using clustering analysis. A fuzzy clustering approach is used to determine the RBF's parameters. This approach has the advantages of being fast and simple to implement with well‐established convergence properties. It also has a good representation of the covariance matrix, since all the data belong to all the classes at the same time with different membership grades. A comparison with the back propagation learning and principal components techniques is also reported for Québec's La Grande River installations. As a result, the proposed approach gives satisfactory operating rules compared with principal component analysis, and the CPU time is reduced by a factor of 15 to 20 compared with the back propagation techniq

ISSN:0043-1397    

DOI:10.1029/95WR02971

年代:1996

数据来源: WILEY

摘要:

An optimal control model for improving the design of in situ bioremediation of groundwater has been developed. The model uses a finite element biodegradation simulation model called Bio2D to find optimal pumping strategies. Analytical derivatives of the bioremediation finite element model are derived; these derivatives must be computed for the optimal control algorithm. The derivatives are complex and nonlinear; the bulk of the computational effort in solving the optimal control problem is required to calculate the derivatives. An overview of the optimal control and simulation model formulations is also given.

ISSN:0043-1397    

DOI:10.1029/95WR02969

年代:1996

数据来源: WILEY