EVAPOTRANSPIRATION FROM FLORIDA PONDCYPRESS SWAMPS1

ABSTRACT: We measured diurnal changes in water levels in three swamps dominated by pondcypress trees (Taxodium distichum var. nuans) in central Florida for four years in order to obtain additional documentation of relatively low evapotranspiration (ET) rates. Two of these swamps were monitored for another three years after one of them was clearcut. Estimated annual ET from undisturbed cypress swamps varied from 38 cm/yr to 86 cm/yr, averaging 60 cm (not including interception). Faster ET rates may have been related to faster pondcypress growth rates, a greater proportion of hardwoods in the canopy, and clearcutting in the surrounding pine plantation. The average ET rate was considerably lower than ET rates that have been estimated for north Florida pine plantations. However, incorporating estimates of interception indicates that overall ET rates in pondcypress swamps may be only slightly lower than ET from pine plantations. ET decreased only 5 percent in one swamp after it was clearcut, indicating that this management practice is not likely to affect regional water balances.     

On the relationship between objective increases in pay and employees' subjective reactions

This study explored whether two principles describe the relationship between the size of a pay increase (a bonus expressed as a percentage of current salary) and the attractiveness of that increase. Based on a sample of sales personnel (N = 639) and consistent with the constant proportion principle of the psychophysical law, pay increase attractiveness was unrelated to current salary level after controlling for the size of the percentage increase. In addition, at any given salary level, the relationship between the size of the increase and its attractiveness was curvilinear. The attractiveness of larger and larger bonus percentages continues to increase, but at a decreasing rate supporting the principle of diminishing returns.     

Channelization and levee construction in Illinois: Review and implications for management

The environmental impact of loss of natural stream and riparian habitat is of concern throughout the United States and Europe. Environmental impacts related to such activities as channelization of and levee construction along streams and rivers are particularly apparent in the Midwestern United States. The objective of the research presented here was to delineate the extent, relative degree of impact, and implications for management of channelization and levee construction along watercourses located in the state of Illinois. According to records maintained through the Illinois Streams Information System data base (Illinois Department of Conservation), nearly 25% of surface water resources in the state have been modified directly by channelization and/or levee construction. Reviews of agency records, elaboration of case histories, interviews with agency personnel, and inspections of impacted sites indicated that these alterations have occurred without the benefit of effective mitigation. Although permit records may provide suggestions for mitigation to be incorporated in the design of a particular project, permits issued generally do not require even minimal instream habitat and bank stabilization efforts in conjunction with channel alteration. Information derived from policy and case study analyses suggests that institutional constraints, rather than lack of particular understanding about mitigation, provide major barriers to protecting the state's surface water resources in terms of regulatory review, policy interpretation and implementation, and project evaluation. Recommendations for environmental management efforts regarding these and similar channel alterations are elaborated from these findings.     

Studies on enhanced degradable plastics: 1. The geographic variability in outdoor lifetimes of enhanced photodegradable polyethylenes

Studies on three types of enhanced photodegradable polyethylenes showed tensile elongation at break to be a suitable parameter for assessing disintegration due to outdoor weathering. Disintegration rates varied greatly with exposure location, with Arizona the harshest environment and Washington and New Jersey the mildest. The rate of breakdown of the enhanced degradable polyethylenes relative to unmodified plastic was termed an enhancement factor. For the materials studied, average enhancement factors generally ranged from five to fifteen. The location-dependent variability in rate parameters can be mostly explained in terms of different average radiation levels and temperatures at these locations. A duplicate exposure protocol was developed to determine if the test data were complicated by short-term fluctuations in sunlight or temperature during exposure.     

PARALLEL DRAINS FROM THE LAPLACE STANDPOINT1

Where natural drainage is inadequate for keeping the water table below the root zone of the crops being grown, drains are often employed to control water table levels. Such drains are commonly installed in parallel lines at depths and spacings adapted to the needs of the area. Formulas used for determining drain spacings are generally based upon Dupuit-Forchheimer concepts. These developments postulate a saturated, permeable aquifer underlying the irrigated area and an impermeable barrier underlying the aquifer. The basic differential equation expresses the requirement that the flow out through the sides of a vertical column of infinitesmal cross sectional area must be supplied by a corresponding drop of the water table at the top of the column. If variations of transmissivity due to variations of water table level are taken into account the second order differential equation obtained is nonlinear. To avoid the mathematical difficulties posed by this nonlinearity it is customary to neglect the effects of changes of transmissivity due to changes of water table levels. This imposes a restriction that the formulas derived from these linearized differential equations suffer a loss of accuracy if the change of water table levels becomes a considerable portion of the initial saturated depth. Offsetting these difficulties is the tactical advantage that the linearized differential equations are of types long studied in older developments concerned with conduction of heat in solids. The advantages conferred by the possibilities for exploiting the results of investigations in the older discipline are many. An alternative approach is based upon a requirement that there can be no accumulation of water in any elementary cubical volume located in the zone of complete saturation below the water table. The differential equation obtained on this basis, if the aquifer is homogeneous and isotropic, is the one which bears the name of Laplace. It will be the purpose of this paper to explore the possibilities afforded by this approach for evaluating the flow to parallel drains and to compare the results with those obtainable by the Dupuit-Forchheimer method.     

FLOOD PEAKS AS MODIFIED BY DAM SIZE AND LOCATION1

ABSTRACT. The ability to replicate storms on a rainfall simulator over an iconic watershed model permits the study of the effectiveness of dams of different sizes and locations in reducing flood peaks. This study empirically confirms that, when storms uniformly and completely cover the watershed, large dams are nearly twice as effective as a network of small and medium dams in reducing the flood.     

IMPROVED RIVER BASIN UTILIZATION THROUGH SYSTEMS ANALYSIS1

ABSTRACT. Theoretical and practical results are summarized for a study to determine optimal water resource allocation in a proposed water conservancy district. The area of this district, which covers several river basins, contains a large number of existing and proposed facilities such as reservoirs and diversions. The operation of all of these facilities was to be determined along with the sizing of the proposed facilities in order to optimize given objective functions. Related efforts in optimal river basin utilization were surveyed, and linear programming was selected as an expedient optimization technique. The problem is formulated by identifying time stages which together constitute a repetitive cycle such as a year. With these stages, it is possible to associate operational and capacity variables with network components, which are branches and nodes. Objective functions are assembled for the component variables. Constraint equations are written in terms of the variables to reflect network nodal continuity, capacity restrictions, and adjudications such as water rights. A numerical example is considered in which the existing and proposed facilities are aggregated to produce a small, tractable number of facilities. This paper examines the example results and suggests future improvements for models of this type.     

THE WATERSHED IN PRINCIPLE1

Three fundamental concepts linking drainage basin characteristics, stream behavior, and management of watersheds are deduced from field data and observations. An electrical analogy of a watershed clarifies definitions and broadens understanding of this complex natural resource. The three basic principles deal with (1) the interrelationships of watershed morphology, constitution, and appearance; (2) the nature of the control man can exert over runoff-influencing forces, and (3) the efficiency of watershed management efforts. Recognition of these principles can assist educators, managers, planners and researchers to more fully inform students and to more effectively guide and evaluate management decisions.