摘要:

The role of agricultural sediment in water quality is well documented. While numerous policies have been advocated and initiated, it still appears to be a significant problem. The present analysis concentrates on the outcome of several policy alternatives in terms of sediment delivery and project costs. These results are obtained by combining social science investigation of probable farmer behavior under a variety of scenarios with a hydrologic simulation model which predicts the sediment delivery with different land uses. This integration of social science behavioral research with the hydrologic response simulation model provides a framework to assess the environmental effectiveness of alternative policies aimed at reducing sedimentation. While the results presented here are preliminary, this approach seems to offer great promise as a tool for federal, state and local conservation agencies in their efforts to efficiently and effectively use their limited resources to reduce soil loss.

ISSN:0043-1397    

DOI:10.1029/WR021i008p01065

年代:1985

数据来源: WILEY

摘要:

Analytical and approximate solutions are developed for radial dispersion in aquifers with simultaneous diffusion into adjacent strata. Contaminants from the injection well are transported within the main aquifer by advection and mechanical dispersion, assuming a steady state and radially diverging ground‐water flow field. The leakage of contaminants from the main aquifer to the aquitards is accounted for by molecular diffusion. A mathematical model consisting of two coupled differential equations is proposed to investigate concentration distributions in the main aquifer as well as in the adjacent aquitards. By making use of Laplace transforms, analytical solutions valid for small time periods are obtained without difficulty. To complement these analytical solutions, concentration distributions for intermediate and large time intervals are determined approximately by numerically inverting the appropriate transformed solution in the Laplace domain with the Stehfest algorithm. Excellent agreement exists between analytical solutions and approximate solutions for small time intervals, supporting the validity of approximate solutions for intermediate and large time periods. It is shown that the diffusive leakage may significantly delay contaminant movement within the main aquifer at relatively large time periods. The solutions can be applied to study radial dispersion in granular aquifers bounded by relatively low permeability aquitards, or in planar fractures contained in porous formation

ISSN:0043-1397    

DOI:10.1029/WR021i008p01069

年代:1985

数据来源: WILEY

摘要:

This paper presents the results of a study utilizing time domain reflectometry and the neturon moderation technique to monitor changes in total water content and unfrozen water content during fall, winter, and spring on a sandy loam site which was maintained snow free to maximize seasonal frost penetration. Soil temperatures were recorded continuously, and meteorological conditions were observed at a nearby climatological station. The procedure of combining the neutron probe and time domain reflectometry employed here showed good potential for augmenting the limited data on soil moisture redistribution in freezing soils under natural conditions. The data indicated the importance of obtaining a representative spatial average of water content measured with time domain reflectometry in order to obtain a good correspondence with neutron probe observations.

ISSN:0043-1397    

DOI:10.1029/WR021i008p01077

年代:1985

数据来源: WILEY

摘要:

The effect of commercial navigation (barge tows) on the mixing and the reestablishment of a stratified river has been measured in the upper Mississippi River downstream from a major wastewater effluent site. Observations have also been made in a laboratory flume. Mixing effectiveness increases from single towboats to unloaded barges to loaded barge tows. Energy expenditure by barge tows per foot of river length traveled is much larger than work done by gravity forces of the free‐flowing river to overcome bottom shear. The displacement of water by loaded barge tows appears to be more significant than the jet effect of the towboat propellers. One passage usually produces complete vertical mixing in the path of the tow; an entire cross section (700 feet × 11 feet (213.4 m × 3.4 m)) will be fully mixed by two or three passages. Surface waves and internal waves generated by a towboat passage cause surging of the effluent for up to 30 min after passage. Reestablishment of a stratified river is controlled by mean river velocity and the frontal velocity of the density current (underflow or overflow) resulting from the discharge. Calculated and observed reestablishment times depend on distance from the outlet and strength of the stratification. Order of magnitude comparisons of calculated and observed reestablishment times were in good agreement. Reestablishment of stratification may take from 15 to 45 min at a distance of only 1000 feet (304.8 m) from an outfall. Water quality models and field studies in impounded rivers with high navigation frequency must account for mixing and transport effects of towboats, particularly under low flow conditi

ISSN:0043-1397    

DOI:10.1029/WR021i008p01085

年代:1985

数据来源: WILEY

摘要:

A mass transport model, TRANQL, for a multicomponent solution system has been developed. The equilibrium interaction chemistry is posed independently of the mass transport equations which leads to a set of algebraic equations for the chemistry coupled to a set of differential equations for the mass transport. Significant equilibrium chemical reactions such as complexation, ion exchange, competitive adsorption, and dissociation of water may be included in TRANQL. Here, a finite element solution is presented first for cadmium, chloride, and bromide transport in a one‐dimensional column where complexation and sorption are considered. Second, binary and ternary ion exchange are modeled and compared to the results of other investigators. Results show TRANQL to be a versatile multicomponent transport model, with potential for extension to a wide range of equilibrium reaction

ISSN:0043-1397    

DOI:10.1029/WR021i008p01095

年代:1985

数据来源: WILEY

摘要:

A model for steady fluid flow in three‐dimensional, random networks of fractures has been developed. In this model the fractures are disc shaped discontinuities in an impermeable matrix. The fracture discs can be arbitrarily located within the rock volume and can have any desired distribution of aperture, radius orientation, and density. Thus where the disc model is appropriate it is possible to calculate flow through fracture networks which are statistically similar to those that occur in nature. After the boundary conditions and the desired fractures are specified, the intersections (nodes) between these discs (elements) are identified. Then steady flow through the network is calculated using a mixed analytical‐numerical technique. In each fracture, analytic equations for flow into or out of each node as a function of the average head at each node are developed. The equations are based on image theory and the assumption that each node is a source (or sink) of uniform strength. A set of mass balance equations is constructed which equate flow into a node from one of its associated fractures to flow out of the node into the other associated fracture. These equations are solved for the average head at each node, and flux between fractures can then be calculated by substituting the average head values back into the analytical equations. The model has been successfully checked against analytical results for several cases of two and three intersecting fractures. We plan to use these techniques to measure the permeability of fracture netwo

ISSN:0043-1397    

DOI:10.1029/WR021i008p01105

年代:1985

数据来源: WILEY

摘要:

Macroscopic balance equations for mass and linear momentum in soils and aquifers are derived in the relativist concept under the condition that all physical variables are associated with a single instrumental weighting function that depends on both position and time. The resulting balance equations differ in concept from expressions obtained recently in the representative elementary volume (REV) approach by exhibiting additional terms that depend on the time and space derivatives of the instrumental weighting function. These terms indicate that mass and linear momentum balance at the macroscopic scale are not preserved unless the weighting function has space‐time invariance properties over the period and spatial domain of measuremen

ISSN:0043-1397    

DOI:10.1029/WR021i008p01116

年代:1985

数据来源: WILEY

摘要:

The Hantush theory of leaky aquifers with storge in the semiconfining layers is combined with large‐diameter well theory to produce equations that can be used in the analysis of pumped‐well and observation well data for stratified formations. Included in the equations are storage in the pumped well and a linear resistance to flow at the sand face or well bore skin. Three cases proposed by Hantush are considered. These depend upon whether the upper boundary of the overlying semiconfining layer or the lower boundary of the underlying semiconfining layer are constant head or no‐flow boundaries. Laplace transform solutions, valid for the complete time domain, are given for each of the three cases for the hydraulic head in the pumped well, the aquifer, and each of the semiconfining layers. Type cures obtained by numerical inversion are selected to illustrate the effects of well bore storage, well bore skin, and leakage. Although several dimensionless parameters are involved, these parameters tend to influence the character of different portions of the type curves, suggesting that unique matches are possible. The type curves show that well bore storage in a large‐diameter well may completely obliterate effects of leakage derived from compressible storage in semiconfining layers. For the purposes of aquifer testing, it may be possible to reduce the magnitude of well bore storage in a large‐diameter well and thus reveal the presence of leaky semiconfining layers. This may help to prevent erroneous interpretation of the well test data and incorrect evaluation of the aquifer p

ISSN:0043-1397    

DOI:10.1029/WR021i008p01121

年代:1985

数据来源: WILEY

摘要:

A solution to the kinematic wave equations for overland flow routing where the lateral inflow term is determined from a constant rainfall rate and the infiltration model of Philip is presented. The solution utilizes the method of characteristics, and while it is not completely analytical, it is reduced to a simple numerical procedure which does not require the use of finite differences. The analysis presented deals with both the rising and falling stages. Example calculations, water surface profiles, and hydrographs are shown.

ISSN:0043-1397    

DOI:10.1029/WR021i008p01132

年代:1985

数据来源: WILEY

摘要:

The transport and transformation of three C species (insoluble, soluble, and gaseous) in soil were mathematically described as functions of depth and time, subject to intervals of 0

ISSN:0043-1397    

DOI:10.1029/WR021i008p01141

年代:1985

数据来源: WILEY