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<br />FLOOD FIGHTING METHODS 2003 <br /> <br />6.3A <br />Page 37 <br /> <br />CONTROL OF BOILS (Away from Levee) <br /> <br />A boil is a condition that occurs when water is "piped" <br />through or under a levee and resurfaces on the landside. <br />These weak points are ge'nerally caused by burrowing <br />rodents or decomposed tree roots. High water pressure <br />can begin to erode the interior of the levee and weaken <br />the structure. Levee material will deposit around the exit <br />point as the water discharges on the landside. If the boil is <br />determined to be "carrying material" then corrective <br />action is required to control the situation. If left unattended <br />the material that makes up the levee can be eroded at an <br />accelerated pace, causing subsidence and overtopping of <br />the levee. This could result in a levee break. <br /> <br />The common method for controlling a boil is to create a <br />watertight sack ring around it. The sandbag structure <br />should be high enough to slow the velocity and prevent <br />further discharge of material from the boil (see Figure 8 <br />and 8A). The flow of water should never be stopped <br />completely, since this may cause the boil to "break out" in <br />an area near the existing sack ring. A spillway must be <br />constructed to direct water away from all boil sites. <br /> <br /> <br /> <br />. . :. <br /> <br />":!;"....... <br /> <br />"," ~. 'v' '. <br /> <br />Figure 8 <br />Bottom width should be at least 11/2 times the height. Do not <br />sack boils that are not carrying material, but continue to <br />monitor. Boils can begin to carry material after first located. <br /> <br />8 <br />