The assessment of the impacts of urban development on catchment response using the Winnipeg Airport extension

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Saka, Paul Kanyakatika
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Some of the problems encountered in assessing impacts of urbanization in ungauged urban watersheds are explained. The effects of urbanization on catchment response are examined under various degrees of development using design storms developed from 34 years of data provided by Atmospheric Environment Services. The effects of urbanization are presented in form of growth factors which depict the ratios of urban runoff quantities to those of rural or existing conditions. The derived flood frequencies are also compared with those that were derived using recorded data for rural and urbanized watersheds. Two approaches were considered. One consisted of using HEC-1, a general flood hydrograph model and the other approach was by utilizing the statistically derived models for assessing peak flow changes. The results show an average maximum growth of 38 percent for the 2-year flood, 26 percent growth for the 5-year flood, 21 percent for the 10-year flood, 18 percent for the 25-year flood, 16 percent for the 50-year flood, and 14 percent for the 100-year flood above the rural floods. The results of sensitivity analysis show that for drier basins where the infiltration loss rates are high, urbanization has more pronounced effects than for for wet basins where infiltration loss rates are low.