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.     

HYDRO-POWER SYSTEM SIMULATION TECHNIQUE1

ABSTRACT. The non-power requirements of a large hydro-power system of multiple-purpose projects often conflict with the best power peaking operation. In order to schedule an optimum multiple-purpose operation, advanced procedures that necessitate the use of computers are required. Special techniques are used in a computer program developed in the Reservoir Control Center, North Pacific Division of the Corps of Engineers that provide the ability to define operating constraints in order of priority. These techniques are easily adapted to practical reservoir regulation problems so that the program is useful in daily reservoir regulation scheduling.     

FINANCING PRIVATE WATER RESOURCE DEVELOPMENT: ANALYSIS OF A STATE LOAN PROGRAM1

ABSTRACT. A State loan program was analyzed for its effects on groundwater development in Wyoming. The analysis focused on the effects of low-interest State financing on the economic feasibility of investments in center-pivot sprinkler irrigation systems. The feasibility analysis indicated that investments in sprinkler systems for production of cash crops are highly profitable, and would frequently be carried out whether or not the State loan program were available. Investments in sprinklers for production of forage crops are perhaps frequently made attractive by the loan program. Thus, while the program appears to have accelerated the pace of private water resource development in Wyoming, it has also subsidized some investments that would have been carried out regardless of the program's existence. Further analysis indicated that sprinkler investments carried out with State financing contribute substantially to firm growth when cast crops are grown, but have less marked, and sometimes negative, effects on growth when forage crops are produced. Some positive effects of the loan program on southeast Wyoming's regional economy were noted, though a complete empirical analysis of regional impacts was beyond the scope of the study.     

WATER RESOURCES AND SOCIAL CHOICES1

ABSTRACT The problem of water resources management can be viewed as one requiring the existence and application of some type of “collective decision” mechanism. Currently, the general water resource decision problem is solved using an “individual decision” format without explicit consideration of the dominant social decision system. This paper demonstrates the need for blending technical planning activities with organized societal processes and then proposes a specific public decision framework to satisfy this requirement. The key element in this planning framework is a generalized “bargaining arena” which serves to link technical activities with the social system. Using this bargaining device we can (1) specify policy at a local level, (2) incorporate “social decision” rules into the planning process, and (3) provide local access to the decision process. A simple case of regional water quality management is used to describe the application of this planning procedure and to offer encouragement for successful use in more complex real-world cases.