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EVALUATION METHODOLOGIES FOR THE FLOOD MITIGATION POTENTIAL OF INLAND WETLANDS
Recently, the recognition that wetlands are natural resources serving a variety of beneficial functions has resulted in their protection by Federal and state regulatory statutes. These laws have necessitated development of methodologies for evaluating the worth of wetlands to society. This study investigated evaluation methodologies for the flood migration function of inland wetlands and is intended to provide a tool useful in regulatory decision-making. To achieve this end, quantitative methodologies were analyzed in two phases: (1) simulation studies and (2) generalizations of the simulation results. A general simulation methodology was developed to study the effect on downstream flooding of encroachment upon an individual wetland. The methodology employed several publicly available computer models and was applied to data obtained for three eastern Massachusetts watersheds. Once calibrated, the models were simulated under three rainfall intensities (10-, 100- and 500-year recurrence intervals with 24-hour duration) and three antecedent moisture conditions (dry, moderate and wet). Combinations of these conditions produced streamflows ranging from a very dry flow to a catastrophic flood event. The wetland encroachment scheme developed in this research included five levels of encroachment: 0, 25, 50, 75 and 100 percent. The simulation procedure outlined is applicable to any watershed, and its use is generally recommended for analyses of watershed hydrology with wetland encroachment. Because detailed simulation studies are often too time-consuming for wetland regulatory decisions, the simulation results for the study watersheds were generalized using graphical plots and regression analyses. The analyses showed that the effectiveness of a wetland in reducing downstream flooding increases with increases in (1) the area of the wetland, (2) its location downstream, (3) the magnitude of flooding, and (4) the degree of encroachment on the wetland. The wetland's effectiveness decreases with increases in (1) the distance downstream from the wetland and (2) other storage areas upstream of damage locations. Regression analyses performed provided a quick and quantitative assessment of the impacts of wetland encroachment on downstream flooding. These results, however, should be used with caution since they are based on regional simulations.
OGAWA, HISASHI, "EVALUATION METHODOLOGIES FOR THE FLOOD MITIGATION POTENTIAL OF INLAND WETLANDS" (1982). Doctoral Dissertations Available from Proquest. AAI8229589.