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OM SOO.I-6 January 1991 . The spillways should be kept free of obstructions so that when the basin is filled the surplus water can escape, The siphons, of course, need not be rw. if the basin fills of its own accord from normal seepage. If the spillways constructed in the setback levees do not have capacity sufficient to drain off the water to the level of the spillway crest, additional temporary spillways should be constructed. The crest of the spillways should not be raised, unless active sand boils begin to appear above the water level, The levee should be raised at once to a height sufficient to stop the active sand boil flow. d. Sand Boils. If discharging sediment, these danger spots are serious especially if within a distance of 100 feet from the toe of the levee, The common method of handling sand boils is by walling up a watertight sandbag ring dike around the boil until ':he water within the ring has attained sufficient head to counteract the effective head causing the boil, In the event that several boils of sufficient force to displace sand are observed at points where sub levees have not been provided, ar.d if any considerable number of them are within lOa feet of the levee, a sandbag sublevee should be built around the entire nest of boils rising to such a height that none of the boils will discharge with enough force to displace sand, If, after being controlled by a ring dike or sublevee, sand boils show signs of discharging with increasing force and indicate that considerable sand is beinl> displaced, preparations must be made to raise the counter water level by increasing the height of the ring dike or sublevee. e, Sloughs, There are a few reaches in the Albuquerque District where the material in the levee sections is of such a nature that prolonged high stages . of the river may cause sloughing conditions on the back slopes. Sloughing condi tions on levees and berms on Rio Grande levees near Los Lunas, NM were successfully controlled in 1973 and 1975 by spreading a minimum of 18 inches of pit run coarse gravel over the sloughing locations. The gravel halts the displacement of material and allows the free flow of seepage water. Filter cloth placed between the levee and the gravel was found to be very helpful in extreme cases of sloughing during the 1979 spring snowmelt runoff. f. Wave Wash. Section Engineers should study their areas beforehand for possibility of wave wash. All such reaches will be determined well in advance and, for use in emergency., a reserve supply of filled sandbags will be kept at convenient locations. During periods of high wind and high water, when waves attack a levee, ample labor should stand by and experienced watchmen should observe where the washouts are beginning by sounding or by actually wading along the submerged slope. Sections of burlap sacking or brush should be placed over the washed areas. As an alternative, filled sandbags should be placed in the cut in as effective a manner as possible and as soon as possible, Note that sandbags placed on Rio Grande levee banks during the 1979 spring snowmelt runoff did not survive. Dumped riprap was eventually used to control bank erosion for flows in excess of 3000 cfs. It is also considered desirable to catch heavy drift logs in some localities where, On account of recent levee work clearing, many logs are available, and to "boom" them together (sawmill style), stringing the boom along the levee slope, thoroughly anchoring it about 20 feet out from the water's edge. Some Districts have effectively used polyethylene sheeting weighted with concrete blocks to prevent wave wash, ~ 4