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<br />0' <br /> <br />25, <br /> <br />. <br /> <br />of flooding (Leopold, 1968, p. 2). Stripping of the naqual vegeta- <br /> <br /> <br />tion increases r'unoff, Soil compaction caused by vehicles, live- <br /> <br /> <br />stock decreases infiltration and increases runoff. Building parking <br /> <br />lots, roads, and roofs in a basin decreases the surfa~e area avail- <br /> <br />able for infiltration, and can have a spectacular effect on the <br /> <br />magnitude and frequency'of flo~dlng. Channelization tends to in- <br /> <br />crease peak flows. Culverts that are too small, and bridges that <br /> <br />,are too low pile up debris and act as dams. \men the'structures <br /> <br />fail, extremely large peak flows result. The elevation of flood <br /> <br />magnitude and frequency has not taken into consideration the possible <br /> <br />effects of land use changes in the thesis aree, <br /> <br />Comparison of calculated flows with historic flows maybe a <br /> <br />reliable method for estimating the 'frequency of the mapped floods, <br /> <br />On Lone Tree Creek the calculated discharge agrees well with a <br /> <br />historic gaged flow, The discharge calculated for the Cache la <br /> <br />,Poudre River is not an unreasonable discharge to expect. The <br /> <br />calculated discharges on the South Platte River and the Big Thompson <br /> <br />River ,are much larger than expected, Considering, however, that <br /> <br />Bij ou Creek had a flood discharge approaching half a million cubic <br />feet per second (Table 1), the'discharges calculated may be possible, <br /> <br />Although the calculations are imprecise, they support the conclusions <br /> <br />drawn earlier: the areas mapped have flooded in the past, and can be <br /> <br />expected to flood again, possibly one Or more times in a lifetime. <br /> <br />. <br /> <br />. <br />