Ice Motion Detector System by ema19358

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									   U.S. Army Cold Regions Research and Engineering Laboratory, Hanover, New Hampshire


Ice Motion Detector System
   This issue describes the design and       jam control and flooding reduction.         imize downstream flooding. Ice runs
testing of an ice motion detector sys-       Current research is addressing ice jam      can cause damage to navigation and
tem, which was developed to give             formation and jamming location.             flood control facilities as large, fast-
downstream communities advance                   In areas where ice jamming and          moving ice pieces impact lock or con-
warning that an ice cover had broken         flooding present a recurrent threat,        trol gates. Knowing that the ice cover
up and begun moving, in an effort to         measures usually are taken to predict       upstream of a dam has broken up and
reduce damages associated with ice           the occurrence of ice jams and to mini-     is moving downstream would allow
runs and jamming.                            mize their impact. In these cases, ad-      facility managers to modify opera-
                                             vance warning that an ice run has           tions in order to minimize adverse
Why Have a Detector System?                  begun and that flooding is possible         effects both at the facility and to
   Ice jams result in more than $125         could allow downstream communities          downstream reaches.
million in damages annually (see Fig-        to evacuate flood-prone areas, close
ure 1); much of this sum represents          bridges, and mobilize flood fighting        Detecting an Ice Run
damage to personal property. A sig-          efforts in a timely manner.                    Direct observation and forecasting
nificant amount of research has con-            Advance warning of ice breakup           are the two most common methods of
centrated on the stages associated           also could provide useful information       river ice motion and ice run detection.
with ice jams and their frequency of         to Corps of Engineers flood control         Direct observation is usually done by
occurrence, as well as methods of ice        dam operators so that they could min-       one or more individuals having some
                                                                                         knowledge of river ice processes. Vis-
                                                                                         ual inspections are made of the river
                                                                                         basin, ranging from weekly visits
                                                                                         during midwinter to around-the-clock
                                                                                         watches as spring approaches.
                                                                                            Due to the inaccessibility of many
                                                                                         rivers and the length of river to be ob-
                                                                                         served, aerial surveys may be neces-
                                                                                         sary, resulting in increased costs and
                                                                                         limited coverage. River ice runs also
                                                                                         may occur very suddenly and thus
                                                                                         go undetected until the ice jams and
                                                                                         flood waters rise.
                                                                                            Forecasting river ice breakup and
                                                                                         ice runs requires a thorough knowl-
                                                                                         edge of river ice processes and the hy-
                                                                                         draulic and hydrologic characteristics
                                                                                         of the river basin. Midwinter field ob-
                                                                                         servations of the river provide esti-
                                                                                         mates of ice thickness and strength,
                                                                                         as well as the water equivalent of the
                                                                                         snowpack in the river basin.
                                                                                            By knowing the river’s response
Figure 1. Remains of Priestly Bridge on St. John River after ice jam of 11 March 1992.   to precipitation and snowmelt, rough


Number 4                                                        1                                           September 1993
                                                                                       4.95 VDC. The signal was 2.58 VDC
                                                                                       if wire “a” was broken, and 1.86 VDC
                                                                                       if wire “b” was broken. If both sensor
                                                                                       wires were broken, the signal was
                                                                                       1.40 VDC. The detector unit also con-
                                                                                       tains four normally closed switches
                                                                                       that can be used to test the system
                                                                                       (simulate sensor wire breakage) once
                                                                                       the sensor wires have been installed
                                                                                       in the ice cover.
                                                                                          Each sensor wire is a fused loop of
                                                                                       18-gauge, plastic-jacketed, stranded
                                                                                       wire or equivalent. Each sensor wire
                                                                                       is placed into a slot cut in the ice
                                                                                       cover. The slot is then filled with
                                                                                       snow or ice chips and water and al-
                                                                                       lowed to refreeze. When the ice cover
                                                                                       begins to break up, the sensor wires
                                                                                       will be broken, opening that leg of
                                                                                       the circuit.
                  Figure 2. Schematic of ice motion detector system.                      Each sensor wire is fused so that
                                                                                       breakage will occur at a predefined lo-
estimates of the probability of river ice    A schematic of the River Ice Motion       cation in the loop, reducing the chance
breakup can be made. This method re-         Detector is shown in Figure 2.            that the two broken ends will recon-
quires good air temperature and pre-            The system consists of the detector    tact each other. There is a pair of sen-
cipitation forecasts, and therefore can      unit, fused sensor wires placed into      sor wires for each analog input to the
advise only that conditions are suit-        the ice cover, and a voltage source/      DCP, providing for redundancy in the
able for river ice breakup. Forecasting      reader. For the prototype system, the     system and reducing the likelihood of
often is used to determine when to           voltage source and reading were pro-      false indications of ice breakup.
send river observers into the field          vided by a satellite data collection         Because it can be difficult to predict
prior to breakup, and can result in          platform (DCP). The DCP provides a        exactly where the ice cover will break
false alarms or undetected ice runs.         switched 5-VDC power source that          up first, two pairs of sensors are used,
   Recording water stage gauges also         passes through the detector unit and      which allows for sensing the ice cover
can be monitored on a near-real time         the fused sensor wires, providing two     movement at two locations across the
basis with rapid stage rises signaling       analog inputs (DC voltages) back to       river section. Typically, one pair of
a possible ice breakup. While stages         the DCP. The DCP relays the signal to     sensors would be placed mid-channel,
help to assess ice conditions, they pro-     a satellite and downlink on a near-real   with the other pair of sensors placed
vide no positive information on ice          time basis.                               halfway between the shoreline and
movement. Depending on the river                The detector unit is the interface     the first pair. This technique allows
characteristics and ice strength, rapid      between the DCP and two pairs of          one to determine if the entire cover is
stage rises may or may not induce ice        sensor wires. Each pair of wires pro-     in the process of breakup or merely
breakup or movement, and thus may            vides one analog signal back to the       undergoing some minor movement in
result in false alarms. A gradual stage      DCP. The level of the analog signal is    one area.
rise also may induce movement in a           determined by the integrity of the           By monitoring the signal from the
sufficiently rotted ice cover, resulting     electrical circuit through each pair of   River Ice Motion Detector through a
in undetected ice runs.                      sensor wires. The 5-VDC input is          DCP or similar device, one can deter-
                                             passed through a series of resistors,     mine in near-real time when the ice
The Ice Motion Detector                      and a voltage drop occurs depending       cover begins to break up at a location.
   In order to provide more time to act      on whether one, the other, or both sen-   Dissemination of this information
once an ice run had begun, a low-            sor wires in each pair breaks, indicat-   through existing communication net-
cost, around-the-clock monitoring            ing ice movement.                         works provides time for downstream
system that reliably could determine            For the prototype unit shown in        communities to initiate evacuation,
when an ice cover was breaking up            Figure 2, if both sensor wires “a” and    flood preparation, or ice breaking
and beginning to run was developed.          “b” were intact, the signal would be      operations. This advance warning


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should reduce property damage and          record exactly when ice cover break-         ey is about 10 to 12 hours, which im-
improve the effectiveness of flood-        up occurred. The sensor pair that was        plies that the Ninemile ice jammed
fighting efforts.                          installed at the mid-channel location        and released along the way. Other
                                           shows a signal drop before the shore         field observations indicated that the
Prototype Testing                          sensor pair. The level of the signal in-     Ninemile ice did indeed jam about
    The prototype was installed in the     dicates that one of the mid-channel          nine miles downstream of the gauge,
St. John River in northern Maine at the    sensors broke about six hours before         and then released approximately 12
location of the USGS Ninemile gauge.       the other mid-channel sensor or the          hours later.
This was done to take advantage of         shore ice sensors.                              The above description of events in-
the USGS satellite DCP station at the         At the same time that the other           dicates that the town of Dickey could
gauge site. This gauge is approximate-     three sensor wires broke, a peak on          receive advanced warning that an ice
ly 65 river miles upstream of the com-     the stage record was observed, which         breakup is occurring at the Ninemile
munity of Dickey, Maine, the first         signifies storage and release of water       gauge and that an ice run is imminent
community downstream of the gauge.         associated with the cover breakup. It        within 12 to 24 hours. Field observa-
Dickey suffered more than $12 mil-         also can be seen that several ice runs       tions near the town of Dickey, how-
lion in damages from an ice jam and        passed the Ninemile gauge site fol-          ever, indicated that much of the ice
run during April 1991. Several resi-       lowing the breakup, evidenced by the         from Dickey upstream to Priestly
dents were stranded as ice and water       steep blips on the generally rising          Bridge (40 river miles) broke up and
surrounded their homes and destroyed       hydrograph. These are due to the             ran prior to the ice at Ninemile. This
the only bridge across the St. John        breakup of covers or jams upstream,          indicates the need for an additional
River within sixty miles.                  which then pass the Ninemile gauge.          sensor in the reach between Dickey
    The prototype system was installed        Observations at Dickey indicated          and Priestly Bridge.
as described above, with two pairs of      that the ice from the Ninemile gauge
sensors to provide redundancy. One         breakup passed through the town ap-          Advantages and Alternatives
pair of sensors was placed 125 feet        proximately 24 hours after the sensor          The River Ice Motion Detector as
from the right bank and the other 250      wires broke. The open water travel           described has several advantages
feet from the right bank (about mid-       time from the Ninemile gauge to Dick-        over currently utilized methods:
channel). The snow was shoveled
from the ice and a slot was cut into                                                      • It provides a definite indication
the cover with a chain saw. The wires                                                       of ice cover breakage and move-
were placed in the slot and covered                                                         ment, and doesn’t rely on exten-
with ice chips and water to freeze                                                          sive scientific knowledge of the
them back into the cover and then                                                           river basin and ice processes.
were subsequently buried with snow.                                                       • It provides around-the-clock
The sensor wires were fed into the                                                          monitoring of the ice cover at
gaugehouse and connected to the in-                                                         minimal operating or mainte-
terface box, and from the interface                                                         nance costs.
box to the DCP.                                                                           • Installation of the unit is accom-
    Figure 3 shows the gaugehouse                                                           plished during midwinter when
from the ice cover after the sensor                                                         the ice cover is typically stable
wires had been placed in the slot in                                                        and safe to work on.
the ice cover. The wires were placed                                                      • Installation is quick and easy,
loosely up the riverbank prior to be-                                                       taking only two to three hours
ing buried with snow. The DCP was                                                           with manually powered equip-
programmed to read the ice motion                                                           ment, e.g., an ice chisel or axe.
detection circuits every half hour, and                                                   • The system can be tested after
transmitted the previous six hours of                                                       sensor wire installation by using
data on a three-hour cycle.                                                                 the switches on the detector unit.
    Figure 4 presents both the 15-                                                        • Redundancy in the system re-
minute stage readings and the 30-                                                           duces the chance of false alarms.
minute ice motion detector readings                                                       • The system provides near-real
during ice cover breakup on the St.        Figure 3. Ice motion detector sensor wires       time indication of ice-cover
John River. As can be seen from the        placed in slot in ice cover leading into         movement, thus allowing maxi-
figure, it is not evident from the stage   gaugehouse.                                      mum notification time.


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                                                                                          This edition of Ice Engineering was
                                                                                       written by Mr. Jon Zufelt, Research Hy-
                                                                                       draulic Engineer, of the Ice Engineering
                                                                                       Research Branch (IERB) of the U.S. Army
                                                                                       Cold Regions Research and Engineering
                                                                                       Laboratory, and was edited and laid out
                                                                                       by Ms. Gioia Cattabriga of CRREL’s
                                                                                       Technical Communication Branch.
Figure 4. Stage and motion detector readings for 1992 St. John River breakup at
Ninemile Bridge.



   Several alternatives are possible in   downstream either actively (data log-
the system configuration described        ger auto-dials the community) or by
above. The voltage source could be        inquiry (community calls the data
any readable constant DC voltage          logger). Where telephone lines do not
supply, and any combination of resis-     exist, radio transmission or cellular                                 Ice Engineering
                                                                                           CRREL
tors could be used to give distinct       telephone systems could be used in-                               Information Exchange
outputs to detect whether and when        stead of the satellite system described                                   Bulletin
any sensor wire has been broken. The      above.
instru-ment used for reading the ana-                                                       The Ice Engineering Information Exchange Bulletin
                                                                                        is published in accordance with AR 25-30 as one of
log signal typically would have a                                                       the information exchange functions of the Corps of
switchable DC voltage supply that                                                       Engineers. It is primarily intended to be a forum
                                                                                        whereby information on ice engineering work done
could be used conveniently. As an al-                                                   or managed by Corps field offices can be dissemi-
ternative, the resistance of the sensor                                                 nated to other Corps offices, other U.S. Govern-
                                                                                        ment agencies, and the engineering community in
pair circuit, rather than the voltage,
                                                                                        general. The purpose of the Ice Engineering Infor-
could be read.                                                                          mation Exchange Bulletin is information exchange
   The number of sensor pairs is lim-                                                   and not the promulgation of Corps policy; thus,
                                                                                        guidance on recommended practice in any given
ited only by the number of analog in-                                                   area should be sought through appropriate chan-
put channels available on the reader.                                                   nels or in other documents. This bulletin’s contents
                                                                                        are not to be used for advertising, publication, or
A minimum of one pair could be used,                                                    promotional purposes. Citation of trade names
with each sensor placed at a different    The ice motion detector was designed by       does not constitute an official endorsement or
                                                                                        approval of the use of such commercial products.
location across the river, thus elimi-    Mr. Jon Zufelt, Research Hydraulic En-            Communications are welcomed. Write to: U.S.
nating the redundancy of sensor pairs     gineer, and Mr. Charles Clark, Electron-      Army Cold Regions Research and Engineering
                                                                                        Laboratory, ATTN: J.-C. Tatinclaux (CECRL-EI),
described above.                          ics Technician, of the Ice Engineering Re-
                                                                                        72 Lyme Road, Hanover, NH 03755-1290, or call
   There also are many configurations     search Branch (IERB) of the U.S. Army         603-646-4361.
of signal reader and transmitter. A       Cold Regions Research and Engineering
data logging instrument could read        Laboratory.
the data and then relay the informa-          For more information, please contact
tion by telephone to the communities      Mr. Zufelt at 603-646-4275.


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