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<br />-4- <br /> <br />consideration remains: that floodplains with recurrence intervals rele- <br /> <br /> <br />vant to hydraulic design and land use planning are not necessarily static <br /> <br /> <br />where urbanization subjects the watershed to rapid and dramatic modifi- <br /> <br /> <br />cation of its hydrologic properties. <br /> <br />Previous Research <br /> <br />Relationships between urbanization and the occurrence of floods have <br /> <br />been studied extensively during the past two decades. In 1961, Savini <br />and Kammerer reported on the lack of studies relating urban growth to <br />changes in stream regimen, and made a number of recommendations for fu- <br /> <br />ture research, stressing the importance to land use planning and engi- <br /> <br /> <br />neering activities. During the next few years, a number of publications <br /> <br /> <br />of the U.S. Geological Survey were devoted to flooding characteristics <br /> <br /> <br />in urban settings (e.g., Waananen, 1961; Mitchell, 1961; Carter, 1961; <br /> <br /> <br />Riggs, 1965; Crippen, 1965; Wilson, 1967). Although these studies ad- <br /> <br /> <br />dressed several diverse problems in different parts of the country, they <br /> <br /> <br />may be characterized by their univariate approach, their emphasis on in- <br /> <br /> <br />dividual hydrographs rather than flood frequency, and their reliance on <br /> <br /> <br />relatively short hydrologic records. Some of them also contain question- <br /> <br /> <br />able analytical procedures such as the assumption of simple linearity <br /> <br /> <br />between the magnitude of peak discharge and the percent of a watershed <br /> <br /> <br />which is impervious, and the averaging of flood frequency curves to <br /> <br /> <br />develop regional relationships. <br /> <br /> <br />More recently, Anderson (1970) analyzed information from 81 sites, <br />principally in the vicinity of Washington, D.C. He concluded that improve- <br />ments to urban drainages may reduce lag time by a factor of eight com- <br /> <br />pared to natural channels, and may increase the observed peak flow by a <br /> <br />. <br />