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EM 1110-2-1416 15 OCt 93 Table 3-1 Hydraulic Study Objectives Type Stage Objective/Considerations Pre- Authorization Reconnaissance Feasibility Post- Authorization Re-Evaluation Report General Design Feature Design Continuing Authority Reconnaissance Report Detailed Project Report Qualitative anatvsis: one year.:l:: tims frame, primarily use existing elata, with and without project analysis to determine if economic justification is likely. establish required data collection program. Cuentitative analysis: 2-3 year time trame. with and without project H&H. economics, and plan formulation finalized, qualitative evaluation of mobile boundary problems, hydraulic design sized, continue/refine data collection program. Cuentitative enelvsis: are the feasibility report findings still appllcabie? Update economies and hydraulics to current conditions, initiate quantitative investigation of movable boundary problems (usually). Quantitative analvsis-detailed hydraulic analysis and design, detailed modeling and movable boundary enalysis. finalize all itydraullcs for simple projects. Cuentitative enalvsis-detailed hydraulic enalysis and design of one component or portion of a complex project. physical model testing, if necessary. Qualitative analysis: usually similar to reconnaissance report portion of the feasibility report. Quantitative analvsis: a combined feasibility report and design. estimate the river's response to different actions and river discharges using simple computations. Obtaining de- tailed temporal and spatial data coverage in the field, however, can be a formidable and difficult task. b. Analytic solutions. Analytic solutions are those in which answers are obtained by use of mathematical expressions. Analytical models often lump complex phenomena into coefficients that are determined emptri- cally. The usefulness of analytic solutions declines with increasing complexity of geometry and/or increasing detail of results desired. c. Physical models. Analysis of complex river hydraulic problems may require the use of physical hydraulic models. The appearance and behavior of the model will be similar 10 the appearance and behavior of the prototype, only much smaller in scale. Physical scale models have been used for many years 10 solve complex hydraulics problems. Physical models of rivers can reproduce the flows, and three-dimensional variations in currents, scour potential, and approximate sediment transport characteristics. The advantage of a physical 3-2 model is the capability to accurately reproduce complex multidimensional prolotype flow conditions. Some dis- advantages are the relatively high costs involved and the large amount of time it takes to construct a model and 10 change it to simulate project alternatives. Model calibra- tion, selection of scaling and similitude relationships, construction costs, and the need for prototype data to adjust and verify physical models are discussed by the U.S. Department of the Interior (1980), Franco (1978), Petersen (1986), and ASCE (1942). Conflicts in simili- tude requirements for the various phenomena usually force the modeler 10 violate similitode of some phe- nomena in order to more accurately reproduce the more dominant processes. d. Numerical models. Numerical models employ special computational methods such as iteration and approximation 10 solve mathematical expressions using a digital computer. In hydraulics, they are of two principal types fmite difference and fmite element They are capa- ble of simulating some processes that cannot be handled any other way. Numerical models provide much more detailed results than analytical methods and may be more . . . e l ~ e