Internal strength coefficient

1.2

0.81.3 (Beltaos 1983)

Lower gives

thicker jams.

Porosity of ice accumulation

0.5

0.40.5 at breakup

0.50.7 for slush pans

during freezeup

0 lb/ft2

Cohesion factor for ice pieces

0 for breakup jams

025 lb/ft2 for freeze-

up accumulations

Maximum non-eroding

VEROS

4.0 ft/s

35 ft/s for freezeup

water velocity: Hydraulic

48 ft/s for breakup

limit on jam thickness.

Specific gravity of ice

0.916

ρ

1.94 slugs/ft3

Density of water

32.2 ft/s2

Option 3 will require the preparation of the exter-

nal ice roughness input file, RUF.DAT. Using the

In certain instances, limiting the allowable

interactive inputs method, this file is created auto-

thickness increase in a single HEC-2/ICETHK

matically. An example of RUF.DAT is included in

iteration cycle will improve the stability of the

Appendix C.

solution or reduce the number of iterations nec-

essary to arrive at a stable solution. This is accom-

plished by adjusting the input variable Del *T*. The

A roughness multiplier (RMULT) is used to

default value for Del *T *is 1.0 ft.

calibrate ICETHK to observed field data. If

RMULT is non-zero and positive, all ICETHK

calculated roughnesses are multiplied by a single

The smoothing option employs a three-point

RMULT. In some cases, however, calibration to

moving average to smooth ice thickness, if the

field-observed water levels requires different

thickness difference between adjacent sections

multipliers at different cross-section locations.

exceeds a threshold value (ISDEL). Abrupt

In this case a zero (0) value is entered for RMULT

changes in thickness are unlikely to occur in the

and the file RUFMULT.DAT must be prepared

natural ice jam case. Ice is likely to be eroded from

by the user. Appendix D gives an example

thicker parts of the accumulation to be redepos-

RUFMULT.DAT file.

ited at downstream locations where the jam is

thinner. The smoothing option attempts to model

this process.

The user must indicate whether the jam is a

freezeup or breakup type. This information deter-

mines which equation (6, 7, or 8) is used. ICETHK

The user can choose between the following

calculates roughness.

four ice roughness input options:

1. Let ICETHK calculate *n *of ice (NICE), no

The depth factor (DFACT) limits the maximum

user input.

possible thickness due to shoving to DFACT times

2. Let ICETHK calculate NICE, user estimates

water depth. The depth option can be used to

fragment size.

prevent the modeled ice accumulation from

3. User estimates NICE directly.

approaching a grounded condition.

4. Retain NICE values from SUMPO file of pre-

vious HEC-2 run.

7