Other assumptions include:

Cross sections are uniform and prismatic in shape, ensuring that streamline

curvature remains small. For this analysis, a rectangular channel shape is as-

sumed.

All flow is subcritical. Though there may be considerable changes in depth

and ice thickness between two cross sections (notably at the locations of shov-

ing or thickening fronts), it is assumed that through methods (i.e., with no

explicit representation of fronts) suitably describe these fronts.

Ice-piece properties remain constant (i.e., no heat transfer, phase change, or

Jams are particulate continua, such that forces and stresses are describable

using Mohr-Coulomb stress theory and an average value across the cross sec-

tion.

Jams float with a constant bulk specific gravity, do not ground on the channel

bed, and are not subject to significant motion or accelerations in the vertical

direction.

The integral form of the equations for water and ice flow are developed using a

control volume approach. The Cartesian coordinate system used is depicted in Fig-

ure 24, in which *x *denotes horizontal distance along the longitudinal river axis, *y*

denotes vertical distance, and *z *denotes transverse distance normal to the longitu-

dinal axis.

Conservation of water mass requires the net inflow of water entering a control

volume (bounded by *x*1, *x*2, the bed, and the bottom of the jam in Fig. 24) during a

given period be equal to the change in water storage within the control volume for

the period, that is

[

]

]

∫ [(ρ*uA*)x2 - (ρ*uA*)x1

(34)

2

1

For practical purposes, water is incompressible, such that ρ is constant and eq 34

reduces to

[

]

[(A)

]

∫ (uA)x2 - (uA)x1 dt + ∫

- (A)t dx = 0.

(35)

t2

1

Further simplifications are made subsequently, such as expressing area *A *in terms

of flow depth *d(x,t)*.

The net inflow of ice and pore water (between the ice pieces) into the control

volume, bounded by *x*1, *x*2, and the bottom and top of the jam in Figure 24, is the

time integral of the difference between the mass flow rates entering the control

volume at *x*1 and leaving the control volume at *x*2, i.e.

)x

)x

- (ρυ*A*i si p)x *dt*

∫ (ρi υ*A*i [1 - *p*]

+ (ρυ*A*i si p)x - (ρi υ*A*i [1 - *p*]

2

(36)

1

1

2

30