8v dv dv] dv 



^ ^ "7" " ""^l " ^T' (2-7) 



[dt dx dy)^^ By 



where x = horizontal coordinate and y = vertical coordinate. If we assume the 

 convective acceleration across the armor layer to vary linearly vertically, then the 

 acceleration can be expressed as 



dv] dv ^ v^ 



/ max -' n 



where K^ is an empirical coefficient of order unity. The maximum inertial fluid force in 

 Equation 2.3 can thus be reduced to 



Fi = PDnC-y (2.9) 



with 



C; = K^C^ (2.10) 



Substituting Equations 2.5 and 2.9 into the stability criterion W = F^ with W = pg{S,- 

 \)D^ yields a stability relation in form similar to Shields criterion (e.g. Raudkivi 1990) 

 for the initiation of motion of sediment particles 



2 



= (C'+C' )'^ (2.11) 



24 



