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<br /> <br />, <br />E <br />f <br />~ <br />~ <br />] <br />" <br />~ <br />o <br />~ <br />'0 <br />. <br />~ <br />a <br />~ <br /> <br />v <br />~ <br />~ <br />o <br />ij. <br />o <br />~ <br />E <br />" <br />~ <br />" <br /> <br /> <br />sion and affect soil stability on slopes. Data on water <br />velocity is available from the various floodplain technical <br />studies or can be determined by special hydrologic <br />studies. <br />Advance Warning. The amount of advance warning <br />prior to flooding is determined largely by the speed <br />with which flood waters rise, which depends on the rate <br />at which water enters the system and the topography of <br />the watershed. The topography of the watershed influ- <br />ences warning time by affecting the rate of storm water <br />runoff A watershed with flash flooding characteristics <br />will allow very little warning, while a larger and flatter <br />drainage basin will usually result in slower rise and <br />more warning time. Warning time is important in plan- <br />ning for emergency evacuation, a.<; well as in determin- <br />ing the feasibility of incorporating waterproofing tech- <br /> <br />Flood water velocity pro- <br />duces lateral forces that <br />can cause scour and result <br />in collapse of foundations <br />(ahoveleft), increase the <br />magnitude of debris impact <br />loads (below left), and dis- <br />locate buildings from their <br />foundations (below). <br /> <br /> <br />Department of Hou~in8 and Crhan Development <br /> <br />43 <br />