eq 153 would no longer be in balance and would represent a condition of greater
jam stability. In this case, the a/c ratio decreases because the a term remains con-
stant. As water discharge increases, the jam should remain stable for a longer
period prior to shoving and thickening, thus resulting in lower ice velocities and
less of an effect of ice momentum on the jam thickness. Also, for a given initial jam
thickness (whether at the limit of stability or not), a smaller discharge rise has less
effect on jam thickness than does a larger one. Finally, a larger relative discharge
increase has more effect than does a smaller one. For instance, ice momentum would
be expected to influence the final jam thickness more for an increase from 100 to
200 m3/s than an increase from 200 to 300 m3/s.
To express these trends, a dimensionless parameter was developed that includes
initial jam conditions (indicating how close the jam is to the limit of stability), as
well as the relative increase in discharge expected. This number is
∆Q
a ∆Q
fiu2B
Ω =
=
c Qin 8gsi (1 - p)(1 - si )k0λKpη2 Qin
(155)
where Qin is initial water discharge and ∆Q is the expected change in discharge.
This dimensionless parameter is the product of the initial state of stability of the
jam and the relative discharge increase applied to cause an instability.
Several runs were made with the fully coupled model using an inflow hydrograph
that rose at the same rate as the baseline inflow hydrograph, but with ten different