AgdaPkt 2008-04-28 - Laserfiche WebLink

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6.3A Page 16 observed, a sack sub-dike may be built around the entire nest of boils to such a height that none of the boils will discharge with enough velocity to move sand or other material from the levee foundation. If the boil is close to the levee, a U-shaped chimney may be built around the boil and sealed into the levee slope. This method may also be used to control flow through a rodent hole which is discharging water from the levee slope. B. Wave Wash All levees adjacent to wide stretches of water should be watched during periods of high wind to detect the starting of wave wash. If the slope is protected by riprap revetment or is well sodded, a high wind of a limited duration should cause little damage. During periods of high wind and high water, ample labor should standby, and experienced personnel should observe where the washouts are beginning. If the current is slow and the slope not steep, the wave wash can be detected by wading along the submerged slope. During periods of high wave action, the wave wash may have to be located by sounding the dike face. A moveable type of wave wash protection consists of wood panels which can be built rapidly at any convenient place and easily installed. Another method of wave wash protection is the use of sections of cotton bagging adequately weighted and placed over the washed areas. A third method is the placement of sandbags directly in the eroded area. The bags should extend to sufficient height to give protection above the anticipated rise in water surface. C. Current Scouring A careful observation should be made of the bay-side slopes of levees to detect possible erosion due to current action. Trouble spots may occur at any location subjected to heavy wave action, road crossing ramps and locations where pipes and other structures penetrate the levees or obstruct the channel. If any indication of scour is observed, soundings should be taken to measure the amount and progress of the 'scour. An effective method to check scour on slopes or at end of levees is to construct deflection dikes using brush, tree tops, or lumber. An effective deflection dike can be constructed by driving pairs of long stakes, wiring together and filling in between the stakes with brush and filled sacks or stone. Levee scour can also be alleviated by the use of the methods employed for wave wash prevention, if care is taken to see that scour does not take place under the protection thus afforded. In general, velocities within the lagoons, Belmont Slough, and the Steinberger Slough are not expected to cause significant scouring. D. Levee Topping 9 April 2008