in the following sections on inputs and outputs
a single layer. A range of probable Manning's n
to ICETHK.
values is given in Table 1.
The HEC-2 ICETHK cycle repeats itself a user-
specified number of times. Several programs,
Table 1. Typical Manning's n values for
external to the main ICETHK program, such as
ice covers.
START.EXE and BIGBAT.EXE, accomplish the
multiple HEC-2 ICETHK iteration cycles by
Type of
Manning's n
writing and executing DOS batch files such as
ice cover
Description
range
MAKE.BAT and WRITE.BAT. These batch files in
Sheet ice
smooth underside
0.0080.012
turn run HEC-2 and ICETHK the desired number
rippled underside
0.010.03
of times.
fragmented
0.0150.025
Frazil ice
new--1 to 3 ft thick
0.010.03
Inputs
3 to 5 ft thick
0.030.06
ICETHK has many input options. Ice parame-
aged--
0.010.02
ters may be input through a conventional input
file, PARA.DAT, or through an interactive screen-
prompted session, driven by the INPUTS 1 and 2
Presence of ice in overbank areas
subprograms. The example PARA.DAT input file
Ice can be expected to enter the floodplain areas
in Appendix A contains typical parameters for a
if the depth is slightly greater than the ice thick-
breakup ice jam. Input options include selection
ness. The user enters a multiplier (XTo) control-
of ice parameters such as the ice pack porosity, the
ling the presence of ice in the overbank area. Once
internal strength of the ice accumulation, and the
the floodplain flow depth exceeds XTo times the
cohesion. A number of methods are available for
parent ice thickness, overbank ice thickness
calculating ice roughness, and the user may also
calculations will be made by ICETHK. If XTo
choose among methods of calculating ice thick-
times the parent ice thickness is less than the
ness in the overbank areas. These and other input
floodplain flow depth at a particular cross section
parameters are described below. The actual
it is assumed that the floodplain area is free of ice
mechanics of loading and running the program
at that location. XTo should be at least 1.0 while the
are covered later in this report.
1.5 to 2.0 range is probably more reasonable. Trees
lining the banks, or natural levees, may keep ice
Channel width smoothing
in the channel, requiring much higher values of XTo.
While natural channels can have significant
For cross sections with floodplain flow above the
variations in width, the moving ice is often con-
threshold depth, ICETHK provides five options:
fined between shore-fast shear walls during an ice
1. No ice in overbank areas.
run. The top width between these shear walls
2. User-defined overbank ice thickness.
tends to be much more uniform than the open
3. Overbank ice thickness equals channel ice
water width. It is the width between the shear
thickness.
walls that governs the thickening process during
4. Overbank ice thickness determined by
shoving events. The WDSMOOTH option can be
ICETHK.
used to account for the formation of shear walls
5. Retain overbank ice thicknesses (ZITL and
where the variation in top width between adjacent
ZITR) from the SUMPO file of the previous
cross sections is large. At a given cross section, the
HEC-2 run.
width at the bottom of the ice cover (bottom
width) is reduced to the lesser of the bottom
If option 2 is chosen (user-defined overbank ice
widths at the upstream and downstream cross
thickness), the external file OBI.DAT must be cre-
sections. A further constraint limits the width vari-
ated to store overbank ice thicknesses. (Appendix
ation between adjacent cross sections to 10 percent.
B contains a sample OBI.DAT file.) It is easiest to
use the interactive inputs method, in which case
Thickness and roughness of the initial ice cover
OBI.DAT will be created automatically.
ICETHK requires estimates of the thickness
and roughness of the parent ice cover or ice floes,
Properties of the ice accumulation and constants
ITHICK and NOLD. These values are used to rep-
Table 2 gives default values and typical ranges
resent the ice cover in river reaches where it is
for additional ice properties. Constants used by
determined that the ice does not thicken beyond
the ICETHK program are also listed.
6
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