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<br />5. THE fLOOD PLAIN MANAGEM~NT PROCESS <br /> <br />5.1 The Nee~ for M<<ster PlanninQ <br /> <br />The hydraulic behavior and associated hazards of fan <br /> <br /> <br />flooding. as discussed in Section q. are considerably more <br /> <br /> <br />complex than typical riverine conditions. This increased <br /> <br /> <br />complexity is due to: <br /> <br />. very high velocities and associated momentum <br /> <br /> <br />forces, <br /> <br /> <br />. large sediment transport capacities. <br /> <br /> <br />. potential for extreme scour and sediment <br /> <br /> <br />deposition in different parts of the same fan. <br /> <br /> <br />. erratic. unpredictable flow paths. and <br /> <br />. rapidly changing channel geometries as scour <br /> <br /> <br />and deposition take place. <br /> <br /> <br />As a result. approaches to alluvial fan flood protection and <br /> <br /> <br />management must be more flexible as well as more careful <br /> <br /> <br />than has been the norm on rivers. <br /> <br />The results of field and model studies reveal that any <br />management action or new development on a fan is likely to <br />substantially change. and sometimes exacerbate. flood <br />problems down-fan. Due to the unstable nature of most fan <br />floods and the conical shape of fans. a small change in <br />channel direction or geometry near the apex can radically <br />shift flood impacts downstream from one area to another <br />previously unaffected location. <br /> <br />A whole-fan approach to flood management which considers the <br />flood process from apex to toe will provide maximum <br />information about the effects of development on flood <br /> <br />57 <br />