MATHEMATICAL ANALYSIS OF ARTIFICIAL RECHARGE FROM BASINS1

ABSTRACT: One of the most common methods of artificial recharge to the ground water is from basins. In this paper, seven analytical solutions that describe artificial recharge from basins are presented. Most of these solutions are derived by directly solving the general partial differential equation for ground water flow. The solutions differ in that they use different boundary conditions, basin shapes, and consider the nonlinearity of the artificial recharge problem differently. Use of each analytical solution is demonstrated in this paper by application to an example problem. A comparison of each analytical solution presented in this paper was made to give suggestions on their use, their ease of implementation, and their relative agreement. Although no attempt is made in the paper to conclude which analytical solution is best for all problems, some general conclusions can be stated on the applicability of the various analytical solutions. Of the analytical solutions presented in this paper, Glovers and Hantush's solutions for rectangular recharge basins are highly recommended. Baumanns solution for a circular basin also gave fairly reliable results and is very easy to evaluate numerically.     

Fate and movement of microorganisms in the environment

Summary This literature review indicates how little is known about the growth of introduced bacteria. The available data base is so sparse that one can only speculate on the environmental conditions and the physiological traits that are needed to permit bacterial growth. Although methods are available to label organisms so that their multiplication can be detected under natural conditions, those methods have not been used sufficiently often to provide a meaningful base of information to allow a definition of conditions that favor multiplication of particular species or the organisms that are likely to proliferate in particular environments. However, because methods exist to monitor microbial growth, and new and better methods can be developed easily, it should not be difficult—provided research funds are made available—to expand greatly the data base and provide adequate information to be used for predicting the behavior of genetically engineered organisms in nature.     

IMPACTS OF RESIDENTIAL WATER REUSE IN THE TUCSON AREA1

ABSTRACT: Groundwater pumping constitutes approximately 100 percent of the water supply in the Tucson Active Management Area (AMA), Arizona. The current annual overdraft approaches 250,000 acre-feet, but the goal of the AMA is to eliminate the overdraft by the year 2025. Urban water reuse, if implemented by only 30 percent of the area's projected population, would reduce the annual ground-water overdraft by 25,000 acre-feet.     

Biomass and nutrient removals from commercial thinning and whole-tree clearcutting of central hardwoods

The objective of this research was to evaluate the impacts of increasing product removal on biomass and nutrient content of a central hardwood forest ecosystem. Commercial thinning, currently the most common harvesting practice in southern New England, was compared with whole-tree clearcutting or maximum aboveground utilization. Using a paired-watershed approach, we studied three adjacent, first-order streams in Connecticut. During the winter of 1981–82, one was whole-tree clearcut, one was commercially thinned, and one was designated as the untreated reference. Before treatment, living and dead biomass and soil on the whole-tree clearcut site contained 578 Mg ha^–1 organic matter, 5 Mg ha^–1 nitrogen, 1 Mg ha^–1 phosphorus, 5 Mg ha^–1 potassium, 4 Mg ha^–1 calcium, and 13 Mg ha^–1 magnesium. An estimated 158 Mg ha^–1 (27% of total organic matter) were removed during the whole-tree harvest. Calcium appeared to be the nutrient most susceptible to depletion with 13% of total site Ca removed in whole-tree clearcut products. In contrast, only 4% (16 Mg ha^–1) of the total organic matter and 2% of the total nutrients were removed from the thinned site. Partial cuts appear to be a reliable management option, in general, for minimizing nutrient depletion and maximizing long-term productivity of central hardwood sites. Additional data are needed to evaluate the long-term impacts of more intensive harvests.     

ADVANCES IN THE BOUNDARY INTEGRAL EQUATION METHOD IN SUBSURFACE FLOW1

ABSTRACT: This paper explores some of the advances of the boundary element method, as applied to ground-water problems, during the last five years. Although the method is still somewhat limited compared to solution by finite elements, the range of solutions has increased considerably. Diffusion and advection-diffusion solutions are done efficiently. These include the incorporation of inhomogeneity, anisotropy, and nonlinear diffusion. The difficult problem of stream-aquifer interaction is an important application as it is much easier to follow a free surface with its multiple configurations. The application must be able to cycle between ground-water connection and disconnection with the stream and include seepage surfaces. Flow in fractured media is a natural application where the flow in fractures can usually be treated without a computational exception in spite of extremely high aspect ratios. The case of seawater intrusion forms a type of free surface problem and thus is a case for which the method has special advantages. For these and other applications the boundary element method provides an inexpensive technique for calculation where the data preparation and setup time is minimal. In most of these cases, programs can and have been written on microcomputers.     

Conservation and management of the American crocodile

The American crocodile is a rare and endangered species, the range of which has contracted to disjunct locations such as Hispaniola, Jamaica, Cuba, Panama, and southern Florida. In an attempt to determine what factors might be limiting population growth, an extensive collaborative research program was conducted in 1978–82 in southern Florida. Limiting factors explicitly studied included climate, hurricanes, population dispersion, nesting habitat, fertility, predation, nest chamber environment, juvenile survivorship, artificial mortality, disturbance, and environmental contamination. No single natural factor limits the population, although in concert various factors result in low adult recruitment rates. Such natural limitations explain the natural rarity of this tropical species at the temperate limits of its range. Two artificial sources of mortality are death of adults on roads and the flooding of nests by high groundwater tables. These sources of mortality are potentially controllable by the appropriate management agencies. Active management, by such means as protection of individuals, habitat preservation and enhancement, nest site protection, and captive breeding, is also appropriate for assuring the survival of a rare species. The American crocodile has survived in southern Florida in face of extensive human occupancy of parts of its former nesting habitat, demonstrating the resilience of a threatened species. This case history illustrates the efficacy of conducting research aimed at testing specific management hypotheses, the importance of considering biographical constraints limiting population status in peripheral populations, the need for active management of rare species, and the role of multiple reserves in a conservation and management strategy.     

INTERBASIN WATER TRANSFERS IN RIPARIAN STATES: A CASE STUDY OF GEORGIA1

ABSTRACT: Under the riparian doctrine of eastern states, transfers of water to nonriparian lands and, thus, to different river basins, are only possible if the natural flow theory has been modified to allow for reasonable use. Even this adaptation is too nebulous to provide water managers and water users with certainty regarding water transfers. To provide a more precise mechanism for allocating water, 14 eastern states have adopted some form of administrative permitting process. Of these, five states statutorily allow for interbasin transfers of water. Thus far, no states have successfully issued permits for interbasin water transfers but Georgia and South Carolina are positioned to do so. Whether the permitting process will deter court action may rest on the ability of affected parties to negotiate an equitable agreement.     

RESISTANCE TO FLOW OVER RIPRAP IN STEEP CHANNELS1

ABSTRACT: A series of flume tests were conducted to determine the flow resistance of angular shaped riprap in steep channels. Flow resistance was expressed in terms of the Darcy-Weisbach friction factor and the Manning's roughness coefficient. Prototype channels of 4 ft. (1.2 m) and 12 ft. (3.7 m) in width were constructed at slopes ranging from 0.01 to 0.20. The channel beds were comprised of angular riprap of median diameters of 1, 2, 4, 5, and 6 inches (2.59, 5.59, 10.41, 12.95, and 15.75 cms). The Darcy-Weisbach and Manning's coefficients were determined for each test condition prior to bed failure. The resulting Darcy-Weisbach coefficients were related to the channel energy gradient and the bed relative submergence for highly turbulent flow. Also, Manning's roughness coefficients were related to the product of the median stone diameter and energy gradient. Because of the angular shape of the riprap and the wedging and/or packing of the bed materials, the resistance to flow was found to exceed the flow resistance values predicted by previous studies. Expressions were presented for estimating the resistance to flow for angular riprap in steep channels.     

Groundwater monitoring plans at small-scale sites--an innovative spatial and temporal methodology

An innovative methodology for improving existing groundwater monitoring plans at small-scale sites is presented. The methodology consists of three stand-alone methods: a spatial redundancy reduction method, a well-siting method for adding new sampling locations, and a sampling frequency determination method. The spatial redundancy reduction method eliminates redundant wells through an optimization process that minimizes the errors in plume delineation and the average plume concentration estimation. The well-siting method locates possible new sampling points for an inadequately delineated plume via regression analysis of plume centerline concentrations and estimation of plume dispersivity values. The sampling frequency determination method recommends the future frequency of sampling for each sampling location based on the direction, magnitude, and uncertainty of the concentration trend derived from representative historical concentration data. Although the methodology is designed for small-scale sites, it can be easily adopted for large-scale site applications. The proposed methodology is applied to a small petroleum hydrocarbon-contaminated site with a network of 12 monitoring wells to demonstrate its effectiveness and validity.