OCR Text |
Show -~- 2 2 su = ( v0 - vu ) / 2g ( ^ Jtcostu - tan + u) For su < 1, in streaming flow a damming curve can form in the upper part of the slope t0t in shooting flow a sudden change in height can occur near the region of the gradient change for which the methods of water level calculation can give more accurate information. The momentum equation for a very wide avalanche shows that for the maximum cross section of the damming cone: Force = Mass x Loss of velocity ( Y / 2) ( H' 2 - h' 2 ) = Y Vg h'vv ( Y ' = density of the flowing snow) max y2 ( 24) H' = h' [ 1 + ( 2 y , v2)/ gh, Y max ] or from Section 3 a, b: H' = ( Y1 m/' Y' max) ( v2 / 2ga + h') 2 2 as an example, for h' = 5m, v = 23 m/ sec, ps = Y m v / 2g = 10,000 kg/ m t ( with densrities according to the example accompanying Equation ( 20) and Y ' _ Y ), it is computed that H = 18 meters. The avalanche cones can reach considerable heights ( Figure 28). The height of deposition is decreased in flat deposition terrain by lateral expansion; the approximate shape of the deposition cone could be calculated by using Equations ( 2), ( 3), ( 8), and ( 22) taking into consideration continuity. If the terrain is such that the maximum cross section of the deposition cone is geometrically similar to the flow cross section of the avalanche, then pf aiwl V JilS" Fig. 28. Avalanche cone at Frasco, Verazascatal, 1951. 40 |