摘要:

It is shown in this paper, with two examples, that incremental dynamic programing may converge to a nonoptimal solution if the same state increment is used for every stage. Then it is shown how to adjust the increment sizes in each stage to obtain the desired results.

ISSN:0043-1397    

DOI:10.1029/WR018i006p01599

年代:1982

数据来源: WILEY

摘要:

This paper defines a tradeoff relationship between hydropower and agriculture for the monthly operations of the High Aswan Dam under current water availability conditions. A stochastic dynamic programming model is employed which incorporates the physical constraints (e.g., reservoir storage limits, turbine capacity, allowable reservoir releases, etc.) of the High Aswan Dam system. Variations of monthly reservoir releases for agricultural purposes are imposed on the system through this model, and consequent impacts on hydropower production at the high dam are studied. The results show that once operating rules are optimized for current agricultural demands an 11–20% increase in firm monthly hydropower production can be gained when summer irrigation allocations are reduced by 25%. A simple benefit/cost analysis concludes that potential benefits obtained by gains in firm monthly hydropower are nearly equal to potential losses in the agricultural sector when summer allocations are reduced by 5–10%. Operation questions raised by the introduction of a new emergency flood control spillway at Toshka are addressed. Recommendations are made for the operating guidelines of the high dam releases in light of these resu

ISSN:0043-1397    

DOI:10.1029/WR018i006p01605

年代:1982

数据来源: WILEY

摘要:

Data from 14 previous experimental studies were used to develop an empirical equation that accounts for the effects of size, density, shape, and roundness on the settling velocity of natural sediment. This analysis was done in terms of four nondimensional parameters, namely, the dimensionless nominal diameterD*, the dimensionless settling velocityW*, the Corey shape factor, and the Powers roundness index. For highD*(large or dense particles), changes in roundness and shape factor have similar magnitude effects on settling velocity. Roundness varies much less for naturally occuring grains, however, and hence is a less important control than shape. For a typical coarse sand with a Powers roundness of 3.5 and a Corey shape factor of 0.7, the settling velocity is about 0.68 that of a sphere of the sameD*, with shape and roundness effects contributing about equally to the settling velocity reduction. At lowD*the reduction in settling velocity due to either shape or roundness is much less. Moreover, at lowD*, low roundness causes a greater decrease in settling velocity at low shape factor values than at high shape factor values. This appears to be due to the increased surface drag on the flatter grains.

ISSN:0043-1397    

DOI:10.1029/WR018i006p01615

年代:1982

数据来源: WILEY

摘要:

This paper provides analytical solutions for some simple cases of subsurface stormflow. The solutions are based on kinematic approximations in both unsaturated and saturated zones. Solutions for rising, falling, and partial equilibrium hydrographs are given. The analytical model has been applied to data collected on a hillslope of the East Twin Brook catchment, Mendip, United Kingdom. Measured and predicted hillslope hydrographs were in good agreement.

ISSN:0043-1397    

DOI:10.1029/WR018i006p01627

年代:1982

数据来源: WILEY

摘要:

An exact analytical solution is developed for the problem of transient contaminant transport in discrete parallel fractures situated in a porous rock matrix. The solution takes into account advective transport in the fractures, molecular diffusion and mechanical dispersion along the fracture axes, molecular diffusion from the fracture to the porous matrix, adsorption onto the face of the matrix, adsorption within the matrix, and radioactive decay. The general transient solution is in the form of a double integral that is evaluated using Gauss‐Legendre quadrature. A transient solution is also presented for the simpler problem that assumes negligible longitudinal dispersion along the fracture. This assumption is usually reasonable when the advective flux in a fracture is large. A comparison between two steady state solutions, one with dispersion and one without, permits a criterion to be developed that is useful for assessing the significance of longitudinal dispersion in terms of the overall system response. Examples of the solutions demonstrate that penetration distances along fractures can be substantially larger through multiple, closely spaced fractures than through a single fracture because of the limited capability of the finite matrix to store solut

ISSN:0043-1397    

DOI:10.1029/WR018i006p01634

年代:1982

数据来源: WILEY

摘要:

After the flood of December 1964, 12 gaging sections in northern California widened as much as 100% and aggraded as much as 4 m, and then degraded to stable levels during a period of 5 years or more. As channels aggraded, bed material became finer, and low to moderate flow through gaging sections in pools became shallower, faster, and steeper. Comparisons of longitudinal profiles also show the diminishment of pools as well as a decrease in bar relief accompanying the excessive sediment load. As gaging sections degraded, hydraulic geometries recovered to a limited degree; full recovery probably depends on channel narrowing and further depletion of sediment supply. The hydraulic changes with aggradation indicate an increase in the effectiveness of moderate discharges (less than 1‐ to 2‐year recurrence interval, annual flood series) to transport bed load and shape the bed. Bars become smaller, pools preferentially fill, and riffles armored with relatively small gravel tend to erode headward during falling stages and form a gentler gradient. Excess sediment can thus be more readily transported out of channels when additional contributions from watersheds are usuall sli

ISSN:0043-1397    

DOI:10.1029/WR018i006p01643

年代:1982

数据来源: WILEY

摘要:

The Lagrangian residual circulation has often been introduced as the sum of the Eulerian residual circulation and the Stokes' drift. Unfortunately, this definition of the Lagrangian residual circulation is conceptually incorrect because both the Eulerian residual circulation and the Stokes' drift are Eulerian variables. In this paper a classification of various residual variables are reviewed and properly defined. The Lagrangian residual circulation is then studied by means of a two‐stage formulation of a computer model. The tidal circulation is first computed in a conventional Eulerian way, and then the Lagrangian residual circulation is determined by a method patterned after the method of markers and cells. To demonstrate properties of the Lagrangian residual circulation, application of this approach in South San Francisco Bay, California, is considered. With the aid of the model results, properties of the Eulerian and Lagrangian residual circulation are examined. It can be concluded that estimation of the Lagrangian residual circulation from Eulerian data may lead to unacceptable error, particularly in a tidal estuary where the tidal excursion is of the same order of magnitude as the length scale of the basin. A direction calculation of the Lagrangian residual circulation must be made and has been shown to be feasibl

ISSN:0043-1397    

DOI:10.1029/WR018i006p01652

年代:1982

数据来源: WILEY

摘要:

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 nuclides238U,234Th,226Ra,222Rn,210Pb,210Po,232Th,228Ra,228Th, and224Ra. The concentration of222Rn in the waters ranged between 103and 104dpm l−1and was three to four orders of magnitude greater than that of the short‐lived alpha daughters224Ra,228Ra, and234Th, 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‐saturate

ISSN:0043-1397    

DOI:10.1029/WR018i006p01663

年代:1982

数据来源: WILEY

摘要:

The spatial variability of surface temperature has been examined on a bare soil located at the University of California at Davis. Surface temperatures were measured between 1300–1400 hours three consecutive days after a sprinkler irrigation. Measurements were made at every meter along two transects with two infrared thermometers differing only by their field of view. In addition, soil samples were collected on the third day with the same pattern to determine the gravimetric water content between the soil surface and 5 cm of depth. All data were found to be normally distributed regardless of their position along the transects. Semivariograms and autocorrelation functions were determined and the measurements were found to be correlated over space. A first‐order autoregressive process with a white noise was found to describe the spatial structure of all the sets of data. Variances of sample means were calculated by taking into account the interdependence between observations and were compared to variances obtained by assuming uncorrelated observati

ISSN:0043-1397    

DOI:10.1029/WR018i006p01677

年代:1982

数据来源: WILEY

摘要:

A multidimensional finite‐difference model for groundwater flow and contaminant transport is used to analyze the leachate migration from the Canadian Forces Base Borden landfill. Through the synthesis and interpretation of this contaminant system, the application of the model demonstrates the validation evidence that the model adequately simulates the leachate migration. The validation requires deriving parameters from independent measurements (laboratory and field) for use in the model. Review of previous hydrogeological studies leads to the use of three‐dimensional steady state flow regime of the saturated zone extending some 700 m downgradient of the landfill. Small differences between the measured and predicted piezometric surfaces are attributed to variations in potentiometric measurements, seasonal variations, and extrapolation of laboratory measurements of permeability to the field site. The contaminant migration from the landfill has been extensively monitored. Variation in observed chloride‐ion isopleths interpolated from three sampling periods over a 1‐year period are typical and indicative of significant temporal plume behavior. Three‐dimensional streamlines are used to develop a variable‐width two‐dimensional grid that allows sufficient discretization of the domain to permit the accurate simulation with small values of dispersivities. Sensitivity simulations are performed on the longitudinal and transverse dispersivity, imposed boundary condition potentials, hydraulic conductivity, landfill staging scheme, and sorption (potassium plume). Appropriate values for longitudinal and transverse dispersivities of the order of 5. m and 0.1 m, respectively, were found to b

ISSN:0043-1397    

DOI:10.1029/WR018i006p01687

年代:1982

数据来源: WILEY