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. . . OM ',00,1. (, ..JllllWll.-Y ll)91 reinforced. The stakes should be driven at least three feet in the ground, leaving at least three feet out, thus providing, in extreme cases, a three-foot topping if properly braced behind with bags and earth. (3) A Standard (Double Bulkhead) Mud Box. Conditions under which a standard mud box will function, available materials and methods of placing the dirt, and the time element will control the selection of the size box to be constructed. The method of constructing a mud box is illustrated in Appendix B, Plate B-3. (4) Raising Crown. When time and other conditions permit, the crown height of the levee may be raised by reconstruction in a manner similar to the original construction by borrowing material from the adjacent riverside borrow pits or from other available sources. This may be accomplished, where the width of the crown permits, by small dragline machines. Tractors and wheeled scrapers may be used if seepage has not developed on the back slopes of the levee. The latter expedient should not be undertaken without specific authorization from the District Engineer, and great care should be used in traveling up and down the landslide slopes. In an extreme emergency, when filled sandbags or lumber cannot be obtained and other sources of borrow cannot be reached, cut crown topping, consisting of borrowing the landslide of the crown for raising the riverside, may be constructed, Where possible, all newly constructed fill should be reinforced on the front slope with filled sandbags, lumber, or polyethylene sheeting. 8. Dams. Flood fight activities by the Corps are authorized to prevent the failure of flood control dams and other dams where the failure would create a serious flood threat. Draining of the Reservoir or controlled breaching of the dam may be the only practical protective measure. Draining or breaching the dam may be suggested to local and state officials if warranted but should be directly accomplished by the Corps only when requested in writing with suitable assurances by the owner of the dam. Most State agencies with responsibility for the safety of dams have the authority to order the draining of an unsafe reservoir. 9. Channels. a. Natural Channels Without Significant Improvement. Natural channels should be cleared by local interests prior to a flood emergency. Emergency flood control work by the Corps is authorized only to remove debris or other channel obstructions, during a flood fight, which is damaging or endangering flood control works, improved property, or human life. Also Corps authority for post flood repair of damaged flood control works does not include removal of sediment from natural channels, 7