31 Jan 94
the solid ice thickness and the thickness of frazil ice
(e) Water temperature at the upstream end of the
deposited under the solid ice cover.
modeled reach of each major tributary.
(f) Air temperatures over the entire region of
f. Ice model data collection. How frequently
ice data are collected depends entirely on the rate at
which the ice conditions change. Rivers that freeze
(g) Downstream water level.
up in early winter and maintain a stable ice cover
throughout the winter season may be surveyed weekly
(2) Typical data required for forecast mode. The
or even monthly. However, rivers on which the ice
following data are required to obtain a forecast from
conditions change rapidly, and that form and break or
melt several ice covers in a given winter, may require
daily surveys of the ice conditions, with the most
(a) Forecasts of the discharge at the upstream
surveys concentrated during the times when the ice
end of the mainstem.
conditions are changing most rapidly. This ice record
should be concurrent with the record of discharges,
(b) Forecasts of the discharge at the upstream
air temperatures, and water temperatures.
end of the major tributaries.
g. Modes of operation of the river ice forecast
(c) Air temperature forecasts.
model. The river ice forecast model is operated in
two modes: a forecast mode and an update mode.
(d) Forecasts of the water temperature at the
The forecast mode starts with the existing conditions,
upstream end of the mainstem and each tributary.
and uses forecasted values of the boundary conditions
Supporting procedures are available to produce these
to produce the model output. The update mode starts
forecasts based on the air temperature forecasts, the
with the initial conditions that existed the last time
known water temperature at the time of the forecasts,
the model was run. If the model is operated daily,
and the watershed response coefficients determined
for example, the initial conditions are those that
from previous water and air temperature
existed on the previous day. The actual values of the
boundary conditions measured at the field sites are
then used to produce the model output. In this way
(e) Forecasts of the ice discharge at the upstream
the previous conditions are updated to reflect the
end of the mainstem and at the upstream end of the
present conditions. Generally, the model is run twice
on any day a forecast is made, once to update the
initial conditions and once to forecast the future ice
h. Data accuracy. The following are minimum
requirements for the accuracy and resolution of data
(1) Typical data required for update mode. The
following new data are required to update the model:
(a) Discharge at the upstream end of the
(b) Discharge at the upstream end of the modeled
reach of each major tributary and the discharge from
each lateral inflow.
0.003 m (0.01 ft)
(c) Ice discharge at the upstream end of the
mainstem and the upstream end of the modeled reach
of each major tributary.
0.03 m (0.1 ft)
0.03 m (0.1 ft)
(d) Water temperature at the upstream end of the