Figure 11. Aroostook River from Tinker Dam upstream to Fort Fairfield, Maine. (After White and Acone 1995.)

Midwinter reservoir levels and ice jam flooding

Controlling timing of breakup - SR99_080023

SR99_08
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Bridge

5 km

6 km

Fort

Fairfield,

Maine

Pudd

le D

Figure 11. Aroostook River from Tinker Dam upstream to Fort Fairfield,

Maine. (After White and Acone 1995.)

Using the HEC-2 backwater model (U.S. Army

reservoir case. Also, the decreased flow area or the

presence of sediment deposits in the original head

1990), the authors found that lowering the pool

of the pool area may stop the ice run before it

during the ice-formation period would increase

reaches the intact ice cover of the lowered pool.

upstream water velocity and Froude number at

A study by White and Acone (1995) examined

some locations beyond the range of ice cover for-

mation by juxtaposition. The resulting shoved ice

the relationship between dam operation and

cover would be thicker, possibly causing the

upstream ice jamming processes on the Aroostook

River in northern Maine. The ice runs on the

breakup ice run to stop farther upstream than

Aroostook typically stop at the head of the Tinker

under the current operating scheme. During a

Dam pool, a small hydroelectric facility located 6.5

midwinter field visit, thick deposits of frazil were

km below Fort Fairfield (Fig. 11). The town has

measured 2.5 km above the dam, in the same gen-

experienced 18 damaging ice jams from 1927 to

eral area as the observed stoppages of breakup ice

1995. A bascule gate regulates pool level, and the

runs. Using the frazil transport and deposition

daily drawdown cycle is 1.2 to 1.5 m. Within the

theory developed by Shen and Wang (1995), the

typical 425- to 570-m3/s breakup flow range, the

authors predicted that maintaining a steady rather

than a peaking flow during the freezeup period

pool height difference between a fully open and

would result in frazil deposition farther upstream.

fully closed gate is only 10 to 20 cm. Under the

The upstream frazil deposits could cause the

current operating procedure, the gate is up both

breakup ice run to stop at a location closer to Fort

during the ice-formation period and breakup

events.

Fairfield, increasing the ice jam flood threat. The

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