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(6) The velocity of the flowing water agaiDst the stone (7) The protection of toe and terminals of the stone blanket . The design of a dumped-stone blanket for bank protection is similar to that for s. stone-lined cbanne1 discussed in section 4.12 of reterence 8. The principal difference between stone lillil'lgs and staDe bank prot.,ction is that in linings the channel bed is also lined, and the lining is generally cODtinuous throughout the length of channel wherein erosion is imminent. Bank protection is generally limited to problem areas. The toe and termi- nals of the bank protection are particularly vulnerable to attack by the current. At some locations, wave action may present a DlOre severe form of attack tban water :flowill8 parallel to the embankment; such cases may require heavier protection. Protection frail wave action is discussed in references 1, 4, 6, and 7. . . 2.1.1 - Size ot stone The size of stone needed to protect a streubank or highway embank- ment trom erosion by a current moving parallel to the embankment is determined by the use at figures 1 and 2. Size (k) is the diameter, in feet, of a spherical stone that would have the same weight as the 50 per- cent size of stone. The size of stone is found by a trial-aDd-error procedure which consists of first estimating a stone size. The mean ve10ci ty (Vm) at the stream during the design flood must then bekconverted to velocity against the stone by use of figure 1. The . ratio (d) of the equivalent spherical diameter of the 50 percent stone size to the depth of flow during the design :flood is computed by using 0.4 of the total depth when the depth ot flow exceeds about 10 feet. The reason for this is that use of the total depth wClll1l.d result in a stone size which would be adequate at the total depth but which might be too light to provide protection near the water surface. With the velocity against the stone (Vs) enter figure 2 and read the stone size for the embankment slope. The stone size trom figure 2 is the 50 percent (median) size, by weight, of a well-graded mass of stone with a unit weight of 165 pounds per cubic foot. If the stone size from figure 2 agrees with the assumed stone size, this is the correct size. If not, the procedure is repeated until the assumed size is in reasonable agreement with the size frail figure 2. When the unit weight of the stone is other than 165 pounds per cubic foot, the size from figure 2 should be corrected by Creager's equation (discussion of in reference 4): ~ kw .. 102.~ k 2 - 2.5 where k.. stone size from figure 2 kw .. stone size for stone of w pounds 11-4 per cubic teet .