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3-3 <br />6. The usual means to protect local residents is to install a fence <br />around the facility. These fences are often unsightly and prone <br />to vandalism and many times are as much of a hazard to local children <br />as the detention basin. <br />7. Safety is a problem where the banks are steep and the temporary pond <br />is designed to detain water to great depths. <br />The flood control effectiveness of detention basins is questionable. The <br />effects of detention may be identifiable only immediately downstream of a basin. <br />In some cases the effect is increased flooding from the more frequent storms. <br />1. The result in many cases is to change the runoff pattern from several <br />separate pathways of runoff as sheet flow and small channels to one <br />distinct pathway. While the peak runoff from the watershed may not <br />have increased, it may now be concentrated in only one channel, a <br />i <br />channel which heretofore was carrying a much lesser rate of flow. <br />2. By installing several detention basins in a single watershed, the <br />timing of flood discharges will be changed. This change in timing can <br />result in combining flows downstream from different subwatersheds that <br />bypassed each other under uncontrolled or natural conditions. The com- <br />bined flow can create higher peak flows downstream than would have <br />occurred without the basins. <br />3. Many of the detention basins installed in the Atlanta area are no <br />larger than small swimming pools because small on -site basins have <br />been encouraged. Their effectiveness on downstream flooding is questionable. <br />4. Because detention basins concentrate runoff into a single flow path and <br />the runoff downstream extends over a longer period of time, two major <br />;' erosion problems result. The increased flow in a single channel causes <br />