Soil retention when soil detachment rate and soil redeposition rate vary with time, especially when the liquid flow velocity varies, is studied theoretically, and the following results are obtained.
(1) . When the liquid flow velocityφ (ξ) varies with time, soil retention X is
L-1X
1 (1+AK
rφ/L) / [ {1+ (K
d+AK
r/L) φ} s], where X
1=Laplace transform of input soil amount, K
dand K
r=constants, φ=
Lφ, φ (t-ξ) =φ
3 (ξ), and s=complex variable.
(2) . When the liquid flow velocity varies with time, it sometimes gives the same effect as the soil redeposition rate varies. If φ (t) is proportional to exp (-nt), where t is time, then the sum of n and the value of soil redeposition effect shows the pseudo soil redeposition effect. When n<0, it is the same as the soil redeposi-tion rate decreases.
(3) . Even if the liquid flow velocity varies with time, soil retention is determined alone by the energy given from the liquid flow, regardless of the velocity.
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