Table 2. Typical ranges for ice properties and constants.
Property
Symbol
Default value
Typical ranges
Internal strength coefficient
1.2
0.81.3 (Beltaos 1983)
Lower gives
thicker jams.
Porosity of ice accumulation
e
0.5
0.40.5 at breakup
0.50.7 for slush pans
during freezeup
0 lb/ft2
Cohesion factor for ice pieces
Ci
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
Si
0.916
ρ
1.94 slugs/ft3
Density of water
32.2 ft/s2
Acceleration due to gravity
g
Maximum thickness increase per
Option 3 will require the preparation of the exter-
HEC-2/ICETHK iteration cycle
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-
Roughness multiplier
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
Ice smoothing option
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
Ice jam type
this process.
The user must indicate whether the jam is a
freezeup or breakup type. This information deter-
Ice accumulation roughness options
mines which equation (6, 7, or 8) is used. ICETHK
The user can choose between the following
calculates roughness.
four ice roughness input options:
Depth factor
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
Previous Page
