a. Unlimited ice supply.
b. Ice supply limited by Caribou
dam (hi = 28 in.).
Figure 16. Effects of ICSs at both sta-
tion 423 and Haley Island (Q =
1200 x 10 2
and at the confluence of the Big Black River. It is
servations of ice formation and breakup in the
estimated that the former system would give an
St. John River basin provided an initial under-
advanced warning of up to 24 hours to the town
standing of the ice processes particular to the St.
of Dickey and 24 to 48 hours to Fort Kent, while
John River and its main tributaries.
the latter system would give up to 12- to 36-
From these observations, complemented with
hours of advanced warning respectively.
available information on the extremely severe
2. Ice control structures downstream of the
ice events of spring 1991, we propose alternative
Priestly bridge. Either a 6- to 8-ft high weir simi-
ice-control methods in several general areas
lar to the Oil Creek or Cazenovia Creek ICS, or a
along the St. John River and the Aroostook River
series of rock-filled cribs connected by modified
to alleviate ice jam flooding. These methods
ice booms could be built. It is estimated that
need to be further analyzed to determine wheth-
such an ICS would alleviate all ice damage from
er they can be economically and environmental-
the 500-year event at all locations downstream
ly justified by NED and the state of Maine. Such
from the structure.
analysis must consider that the implementation
3. Ice control structure downstream of Big
of any ice-control technique will benefit all
Black River confluence.
downstream sites and not only the area in the
4. St. Clair Island area excavation upstream
immediate site of the project.
from Dickey. The anticipated benefits are similar
On the basis of the limited information gath-
to an ICS at the Priestly bridge.
only recommend that, at a minimum, the follow-
1. An ice control structure located approxi-
Road bridge. Such an ICS, especially when com-
Upper St. John River
plemented by another one in the vicinity of
1. Ice motion detection systems at Nine Mile