摘要:

The analytical theory of porous horizontal aquifers is applied to the problem of pressure response of the Tauhara geothermal field to drawdown from Wairakei. In a ‘bounded’ model the Tauhara field is regarded as a sector from an axisymmetric solution in the horizontal plane, having a permeability contrast at the curved outer boundary. The straight sides of the sector are impermeable. In a second model the only barrier to horizontal flow is a straight boundary situated to the southeast of the Tauhara field, the presence of which is suggested by a high gradient in the field resistivity. Features shared by both models include a steady horizontal outflow from Wairakei, which was present before development and probably arises from natural convection, and a superimposed downward pressure gradient, which may be a consequence of the efficient horizontal propagation of the pressure drawdown at Wairakei. Statistical tests indicate that these features are important. The best fit to the field pressure data is obtained by using the second model with impermeable upper and lower boundar

ISSN:0043-1397    

DOI:10.1029/WR017i001p00083

年代:1981

数据来源: WILEY

摘要:

Real‐time control of irrigation in areas of sparse rainfall requires probabilistic description of infiltration, soil moisture, and actual evapotranspiration. This work develops the probability density function of infiltrated water volumes as a function of climatic and soil parameters. This stochastic input is used with a physical‐conceptual model of the soil moisture depletion process to derive analytic expressions for the soil moisture transition probabilities over a given time period and the first two moments of associated actual evapotranspiration. Analytic results are corroborated with a case study example. A forthcoming paper by the authors illustrates the use of the derived expressions in an optimal decision model for deficit irrigation practi

ISSN:0043-1397    

DOI:10.1029/WR017i001p00093

年代:1981

数据来源: WILEY

摘要:

The statistical structures of the hydraulic conductivity, head gradient, specific discharge, and head fields are analyzed with the aid of a simplified model consisting of a collection of spherical (in three dimensions) and cylindrical (in two dimensions) blocks of different conductivity and diameter set at random and independently in space. Results of a previous work for the effective conductivity and unbounded formations (Dagan, 1979) are recovered and given a rational derivation. The influence of the aquifer boundary and nonuniform average flows are examined for the first time. The growth of the head variance with distance from boundary in two‐dimensional flows is compared with that of the Monte Carlo simulations of Smith and Freeze (1979

ISSN:0043-1397    

DOI:10.1029/WR017i001p00107

年代:1981

数据来源: WILEY

摘要:

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

ISSN:0043-1397    

DOI:10.1029/WR017i001p00122

年代:1981

数据来源: WILEY

摘要:

Both the measurement and computation of the bed‐material discharge of a stream involve large uncertainties because of the difficulties in determining bedload discharge. Measurements of bedload discharge are rare and frequently of unknown accuracy because no bedload sampler has been extensively tested and calibrated over a wide range of hydraulic conditions. Bed‐material discharge equations have been derived primarily from laboratory flume data where the effects of channel pattern, alluvial banks, sediment availability, sediment sorting, and unsteady flow upon the sediment discharge of a natural stream have not been simulated. Bed‐material discharge equations generally are applicable only within the range of flow conditions and sediment sizes for which the equations were derived. To compare the relative value of measuring versus computing bed‐material discharges, the bed‐material discharge of Muddy Creek, a shallow sand‐bed stream in southwestern Wyoming, was determined on 35 occasions for water discharges ranging from 0.15 to 1.57 m3/s by separately sampling the suspended‐ and bedload‐sediment discharges. Measured bed‐material discharges were statistically indistinguishable, at an 0.02 level of significance, from flume data collected under the same flow conditions. This agreement indicates that the measured bed‐material discharges are reasonable estimates of the true values. Bed‐material discharges computed by Engelund‐Hansen, Yang, Shen‐Hung, and Ackers‐White equations were compared with the measured values and found to be in good agreement. These equations predicted bed‐material discharges of between 0.5 to 2 times the observed

ISSN:0043-1397    

DOI:10.1029/WR017i001p00131

年代:1981

数据来源: WILEY

摘要:

The problem of solar radiation transfer in a body of water is complicated by several factors, which include the directional distribution of the incident radiation, reflection and refraction at the air‐water interface, absorption and multiple scattering within the water, and reflection off the bottom surface. Although theoretical methods have been developed to treat the problem, little has been done to test the accuracy of the methods through a comparison of predictions with measurements under controlled laboratory conditions. In this study, measurements of the directional and spatial distribution of the spectral radiation have been made in a diffusely irradiated aqueous medium, and the results have been compared with predictions based on the discrete ordinate and three‐flux methods. For the prescribed laboratory conditions the radiation is concentrated within a cone of half angle θ ≈ 0.85 rad, and for this region, good agreement is obtained between intensity measurements and predictions based on the discrete ordinate method. Good agreement is also obtained between radiation fluxes measured for the forward direction and predictions based on both the discrete ordinate and three‐flux methods. Discrepancies between predicted and measured results for θ ≳0.85 rad are attributed to uncertainties in the radiation intensity and phase function m

ISSN:0043-1397    

DOI:10.1029/WR017i001p00142

年代:1981

数据来源: WILEY

摘要:

In part 1 of this paper, first and second order analysis of uncertainty is applied to numerical models of groundwater flow. The models are cast in state‐space form, with boundary conditions and inputs that are functionally dependent, but statistically independent, of time. Using a compact matrix calculus notation, first and second order Taylor series expansions of the model equations are derived and used to estimate the mean and variance‐covariance properties of piezometric head predictions, given corresponding statistics for aquifer parameters: material properties, initial conditions, boundary conditions, and inputs. The mathematical results demonstrate that the prediction uncertainty is a function of the magnitude of the parameter uncertainty, and sensitivity of the predictions to the parameters. Furthermore, the first order estimate of the piezometric head is identical to the deterministic result. Part 2 of this paper, to be presented later, will illustrate these and other results through numerous applications of the methodol

ISSN:0043-1397    

DOI:10.1029/WR017i001p00149

年代:1981

数据来源: WILEY

摘要:

A numerical technique for modeling a multiaquifer system is developed on the basis of a quasi three‐dimensional flow model. The model consists of many horizontal aquifers interconnected by leakage flux from aquitards. The direct flow across aquitards and yield from aquitard storage are taken into account in leakage flux terms in the form of convolution integrals. Mathematical formulation results in flow functions which diminish with time and can be approximated by few exponential terms. They have been proved to be very convenient in a numerical solution scheme involving the convolution integrals. The approach reduces the dimensionality of the problem and uncouples the equations corresponding to each of the aquifers. The technique is flexible and can be used for any basin geometry with an arbitrary pumping scheme. The validity of the technique is demonstrated by comparing the model results with available analytical solutions. In general, it appears that this technique is more economical than the full three‐dimensional model or even the quasi three‐dimensional models that use one‐dimensional elements to represent the aq

ISSN:0043-1397    

DOI:10.1029/WR017i001p00162

年代:1981

数据来源: WILEY

摘要:

Bulk precipitation samples were taken weekly on the shore of Lake Valencia, Venezuela, over a period of 2 years. All samples were analyzed for total participates, particulate carbon, hydrogen, nitrogen, and phosphorus, major soluble cations and anions, and soluble nitrogen, phosphorus, and carbon compounds. Total insoluble particulate material reaching the watershed averages 139 kg/ha/yr, of which about 25% is organic and 75% inorganic. The total loading rate of insoluble particulates is dramatically higher during the 100‐day dry season than during the remaining portion of the year. The dry season increase in total insoluble particulates is entirely attributable to the inorganic fraction, however, as the particulate carbon and nitrogen loading actually decreases during the dry season. Total loading rates for soluble constituents are generally within the upper range of values reported in the literature for the temperate zone. In terms of equivalents the order of total annual loading rates for soluble cations is Na+>Mg++>Ca++>H+>NH4+>K+. For soluble anions the order of loading is HCO3−>Cl−>SO4−−>NO3−>PO43−. Organic nitrogen and organic phosphorus account for major portions of the total nitrogen and phosphorus loading. Soluble silicon loading is quite low. The loading rates of all soluble components on a weekly basis are much higher during the wet season than during the dry season except for soluble inorganic phosphorus, which shows evidence of association with the inorganic particulate fraction that begins to peak during the dry season. There are striking seasonal peaks in the loading rates for almost all precipitation components. Except for soluble inorganic phosphorus and insoluble particulates, which begin to peak well before rains start, the peaks occur very abruptly with the first rains. At this time, as much as 15% of the total annual loading may occur in a flush lasting 1 or 2 weeks. Removal of nitrogen oxides is particularly dramatic and can lead to the development of very acid rainfall at this time (pH<4.0). Considerable combustion of vegetation occurs toward the end of the dry season and appears to contribute significantly to the buildup of large atmospheric burdens of materials that are removed during the first few rains. A components of variance analysis shows that within the wet season the total amount of rainfall in a given week is the most important variable explaining week‐to‐week variation in loading rates. After the first week or two of flushing there is some continued seasonal decline in loading of some components, but the trend is weak. The amount of insoluble particulate material in a given week during the rainy season accounts for negligible amounts of variance in loading of solubles except for calcium and phosphate, which show suggestive associations with particulates. The radical seasonal changes in loading rates, the flushing effect just at the beginning of the wet season, and the role of combustion in seasonally augmenting loading rates are all factors of possible general importance in the tropics wherever extended

ISSN:0043-1397    

DOI:10.1029/WR017i001p00169

年代:1981

数据来源: WILEY

摘要:

Long samples of weather data are frequently needed to evaluate the long‐term effects of proposed hydrologic changes. The evaluations are often undertaken using deterministic mathematical models that require daily weather data as input. Stochastic generation of the required weather data offers an attractive alternative to the use of observed weather records. This paper presents an approach that may be used to generate long samples of daily precipitation, maximum temperature, minimum temperature, and solar radiation. Precipitation is generated independently of the other variables by using a Markov chain‐exponential model. The other three variables are generated by using a multivariate model with the means and standard deviations of the variables conditioned on the wet or dry status of the day as determined by the precipitation model. Daily weather samples that are generated with this approach preserve the seasonal and statistical characteristics of each variable and the interrelations among the four variables that exist in the observed d

ISSN:0043-1397    

DOI:10.1029/WR017i001p00182

年代:1981

数据来源: WILEY