Data accuracy.

ETL 1110-2-363

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

interest.

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

the model:

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

measurements.

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

major tributaries.

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

conditions.

requirements for the accuracy and resolution of data

collected.

(1) Typical data required for update mode. The

following new data are required to update the model:

Resolution

Accuracy

Parameter

(a) Discharge at the upstream end of the

Water

mainstem.

temperature

0.1C (0.2F)

(b) Discharge at the upstream end of the modeled

Air

reach of each major tributary and the discharge from

temperature

0.5C (1F)

each lateral inflow.

River stage

0.003 m (0.01 ft)

0.003 m

(c) Ice discharge at the upstream end of the

(0.01 ft)

mainstem and the upstream end of the modeled reach

of each major tributary.

Ice thickness

0.03 m (0.1 ft)

(d) Water temperature at the upstream end of the

Discharge

5%

mainstem.

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