vides redundancy to reduce the likelihood of a
a disturbance of the electromagnetic field by ice.
false alarm and to monitor more width of the river
Surface water velocity or ice velocity may be esti-
against breakup. The detector unit can be set up
mated by measuring the period of time an ice piece
to handle complex situations as described in Zufelt
or other small particle takes to traverse a given
et al. (1995), or it can be as simple as a burglar alarm
length in the river.
with built-in dialer attached to a telephone. The
greatest advantages of the ice motion detector sys-
Ice movement and velocity
tem are that it is capable of monitoring around the
Ice movement is normally monitored visually
clock at a minimal cost, typically only takes a few
by USACE personnel, usually from a bridge or
hours to install, and is simple to operate. One dis-
other structure or from shore but is only moder-
advantage is that the wires must be installed in
ately important judging by survey results. Ice
movement may be monitored to determine when
the ice every year. The other disadvantage is that
and where breakup may be occurring or where
the system can only be used for the breakup pe-
moving ice may affect navigation traffic or lock
riod; a stable ice is required to form before the
operation. Often ice movement is monitored by
wires can be installed. Rachuk and Rickert (1986)
local interests or Civil Defense personnel con-
describe the use of a similar concept in Canada on
cerned about the potential of flooding, but little
the Athabasca River, using an array of sensors
automation of ice movement monitoring exists at
embedded in the ice.
the District level at this time.
Ice velocity, while not typically monitored, has
A remote means of monitoring ice movement
been measured by a variety of remote methods. It
has recently been developed by CRREL research-
can be estimated by measuring the period of time
ers and has been used in the field (Zufelt et al.
an ice piece or other small particle takes to traverse
a given length of river using a stopwatch and taped
1995). A schematic of the ice motion detector is
distance along the bank. Prowse et al. (1986) re-
shown in Figure 8. Wires imbedded in the ice are
port a similar method used by the Hungarian
connected to the detector unit, which is then con-
Water Conservation Bureau in a reference grid is
nected to a DCP, phone, or some other device ca-
pable of transmitting a signal. When the ice cover
set up at a particular location in the river through
begins to break up and move, the wires are bro-
the use of temporary markers in the water and
ken. The detector transmits one signal when the
fixed markers on land. Time-lapse photography
wires are whole, and different levels as each wire
obtained during freezeup and breakup is com-
is broken. The multiple wire configuration pro-
pared to the reference grid to estimate surface ice
Ice Cover
Data Control Platform
(DCP)
a
b
Sensor Wires
Detector Unit
c
d
River Flow
Figure 8. Schematic of ice motion detector connected to DCP (from Zufelt
1993). The detector unit returns different levels of response depending on
whether wires a,b,c,d (or various combinations) are intact, allowing the user
to determine the extent of ice cover breakup and movement.
16
Previous Page
