1、3535789 0056343 049 c - W-5G I US Army Corps of Engineers .- Breaking Ice Jams Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-.- .- .-. - .- L _ , . . _. . .- . . -. - . .I -. . . :. ! i I l i I . I i ! ! i i FOREWORD This booklet describes the opti
2、ons open to a community when it is plagued by ice-related flooding. Because of its exper- tise in water resource management and its nationwide local presence, the Corps is often called upon to provide technical assistance during floods. This pamphlet has been written to assist Corps personnel not fa
3、miliar with ice jam flooding and to provide background information to others responsible for local emergency management. I PAUL W. TAYLOR Colonel, Corps of Engineers Chief of Staff Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,- - .a INTRODUCTION In
4、 the cooler climates of the world where the rivers and lakes freeze during winter, spring is looked on as a time of rejuvena- tion. However, for a few people who live on the river floodplains it is also a time of trepidation, for when the ice goes out of the rivers it often jams and causes flooding
5、of fields and homes. The floating ice upstream of a jam can destroy houses, block roads and deposit itself on fields, delaying spring plowing and planting. e I Bridge endangered by ice jam 1 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-2 There are
6、 two processes that either alone or in concert are responsible for breakup. First, ice strength gradually deteriorates in the spring when higher sun angles and higher air temperatures melt snow from the ice surface, forming a water layer. This water layer absorbs more solar radiation, causing subseq
7、uent melt along the crystal boundaries. If not disturbed by other factors, the ice will melt in place. This is usually the case on lakes. In rivers, the current flow beneath the ice is a second factor. In fact, water flow is the sole cause of the midwinter breakups that can lead to the most destruct
8、ive ice jams. Any increase in water flow down the river will raise the ice level and break it loose from the shore. If the river discharge stays high because of rain or snow melt on the upper sections of the watershed, the higher flow will move the ice downstream. As it moves, the ice breaks up; the
9、 size of the pieces depends on the distance they move and the degree to which the ice strength has deterior- ated. As might be expected, the ice in those reaches with steeper slopes and higher current velocities will go out first. When the moving ice hits the fixed ice in a slow, flat reach, it may
10、break up the stationary ice and carry it along, or form a jam. Ice jams have two basic forms, the grounded jam and the conventional jam. They are essentially identical except that in a grounded jam the ice is resting on the river bottom, restricting water flow to a greater degree than does a convent
11、ional jam. The conventional jam is attached to one or both the river banks but not to the river bottom. Predicting the time or even the probability of an ice jam is still uncertain. However, there are a number of typical places where a jam will form. As mentioned earlier, any section of a river wher
12、e the slope decreases is a possible location. During freezeup, the slower moving reaches freeze first, and so will have a thicker ice cover during breakup. Another possible loca- tion might be a constriction in the channel, either natural, such as at a bend or at islands, or man-made, such as bridge
13、 abut- ments and midstream piers. A third typical location is a shallow Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,- a 1 1 m. 3515789 O056345 794 Aerial view of an. ice jam I Ice jam flooding of private home 3 Provided by IHSNot for ResaleNo repr
14、oduction or networking permitted without license from IHS-,-,-m 3535789 0056146 620 m reach where the ice can freeze to bottom bars or boulders and will not be lifted and moved by the increased water fiow. Once the ice is stopped, the jam thickens rapidly, primarily by ice blocks turning under the e
15、xisting scrface ice. The net result is a rzpid constriction of the channel and subsequent backing up of the stream flow. Flooding from an ice jam happens very qcickly. The situation is not like c1 normal open water flcod where the channel is nc;? hrge enough for the flow Instead, the channel is ofte
16、n com- Summer view of perennial trouble spot 4 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-3535789 0056147 567 m pletely blocked. Suddenly, there is a new dam in the river, albeit a leaky and temporary one, which is creating a lake and which has
17、no convenient spillway. The best time to try to move a jam is while the water pressure behind it is still high and the flow ntes are adequzite to carry the ice downstream. If the jam occurs in midwinter and a cdd spell reduces the flow before the jam moves on, it can settle ofi the bottom and remain
18、 for the rest of the winter, creating a potential hazard. Durinc; the balance of the winter a new ice cover can Luckily, no cars were in ths lot when the jm broke IQOSE 5 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,- - m 3515789 0056148 4T3 m z =
19、.b form upstream, and when the spring break-up comes the new ice cover will be stopped at the old jam-flooding is almost a certainty. The need to free or remove some ice jams is thus obvious, both in cases when flooding is actually present and in cases when the potential for subsequent flooding exis
20、ts. There are three methods for removing ice jams, each with its advantages and drawbacks. These are mechanical removal, blasting and the use of icebreaking ships. The ice can also be weakened so that it will break into small enough pieces to flow freely. 6 Provided by IHSNot for ResaleNo reproducti
21、on or networking permitted without license from IHS-,-,-I Rivers often produce thicker ice than lakes - this 6-foot-thick ice was floated ashore by an ice jam flood I P f I t i s J i ICE JAM REMOVAL n I i I It is important to remember that ice loosened in a sli-eam may jam elsewhere. A decision must
22、 be made. Is it best to remove the jam and take the possible financial responsibility for down- stream damage, or to accept the potential damages caused by the jam as is? Once the decision has been made to try to remove the jam, the most effective approach must be established. I i ! I 7 7 z. Provide
23、d by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-_. Mechanical removal Removing the jam mechanically, for lack of a better term, means simply taking the ice out of the stream bed and placing it elsewhere. This, of course, eliminates any downstream prob- lems
24、 but it is neigher inexpensive nor fast. For example, in Gorham, New Hampshire, it cost $1 7,800 in 1982 to make a 2500-foot channel about 75 feet wide and 1 O to 15 feet deep. A Caterpillar D6 bulldozer and I-% yard P however, experience has shown that ANFO works well. ANFO is a mix- ture of ammoni
25、um nitrate fertilizer and fuel oil. The best ratio is 6 percent by weight oil with prilled (in pellet form) nitrate. This ratio works out as 1 gallon of oil per 100 pounds of fertilizer. The mixture must be detonated with a strong booster such as a stick of dynamite, TNT, or the special booster char
26、ges sold by the powder companies. Like many other explosives ANFO must be kept relatively dry, so placing the mixture in a plastic bag that can also hold the weight (for example, a brick or sand) neces- sary to sink the charge is recommended. ANFO is relatively inexpensive and it will dissolve with
27、time if a misfire takes place; this will avoid leaving large, live charges on the river bottom. As 14 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-= 3535789 0056357 406 . . -. . ._ . -. I 1 O00 51 2 21 6 64 n U O 1 O0 Crater Hole Diameter (feet) 1
28、5 200 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-: . - a guide, it is preferable to use Primaccrd for all downhde and taped to the Primacord at the last moment when the Slasting party is off the ice. Blasting is not a quick, easy solution. It re
29、quires sGme plan- ning to locate and acquire the explosive, the equipment to make holes to place the charges and the personnel. At all times when the crew is working on the jam, a lookout should be on duty some thousand feet upstream to sound the alarm if the jam lets go by itself. At least two peop
30、le are required to drill holes ami, depending on the roughness of the surface, Zt least four more are needed to carry the charges to the holes. Add a blaster, a hookup lines. This is then set off with one electric cap that is Preparing charges on shore 16 Provided by IHSNot for ResaleNo reproduction
31、 or networking permitted without license from IHS-,-,-m 3515789 0056157 289 Loading a charge into a drilled hole 17 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-3535789 0056360 TTO supervisor, and two people to load the charges and you have a crew
32、 of 11. With good luck this crew can blast two rows of charges along about a half mile of river per day, possibly more when a routine has been established. Clearing the scene before a blast 18 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-3515789 0
33、056363 937 - -. A formal safety plan covering all operations is necessary. It should comply with both local and Federal regulations. Such matters as person in charge, communication, transportation, warning personnel, etc., should be fully covered. 19 Provided by IHSNot for ResaleNo reproduction or n
34、etworking permitted without license from IHS-,-,-m 3535787 0056362 873 m Icebreakers The third method of removing jams is only usable in a few rivers. When the channel depth is sufficient and the vessels available, icebreakers are certainly the easiest, safest and least expensive way to break up a j
35、am. This operation is carried out by the vessels captains, who are responsible for the safety of their vessels so little more needs to be said regarding safe operations. If two vessels are available, they work best in echelon (staggered, one behind and to the side of the other), starting from the do
36、wnstream end of the jam. The following vessel has to be careful to ensure an equal channel width. If it crosses the path of the leader, the resulting narrow section will 20 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-1 inevitably cause a jam and
37、the downstream channel will no longer keep itself clear. Occasionally, if circumstances permit, an icebreaker can work in conjunction with blasting. The propeller wash and wave action of the vessel will clear the ice loosened by the blasting faster, and the vessel will offer a factor of safety for t
38、he people on the ice. A combined operation like this will require extra cooperation as well as good communication. When the jam is very thick, two towboats of essentially equal power have been used together. They mate-up bow to bow, and while the pro- peller wash of one boat loosens and erodes the i
39、ce, the second boat holds the first in position. This operation takes a great deal of skill and coordination between pilots. I Towboats working in echelon to clear ice jam i 21 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-. .- = 3535789 00563b4 64
40、6 H ICE WEAKENING Preventing ice jams is better than removing them after they happen. It is possible to weaken the ice in a river reach that has often caused problems so that when breakup comes, upstream ice will be able to carry the weakened ice with it instead of stop- ping and jamming. Dusting A
41、method for weakening ice is the use of dust. Dust is defined here as any dark substance that can be spread on the ice in a thin layer to absorb solar radiation and thereby hasten the deter- ioration process. For example, a reach of the Yukon River downstream of Galena, Alaska, which has regularly ca
42、used ice jams, is dusted each spring two to three weeks before breakup. This weakens the ice sufficiently so that there have been no jams there since the practice started. Ideally, the dust should be applied as early as possible but after the last snowfall. In general, any reach with an ice cover th
43、at regularly stops the ice run and causes a jam could be weakened in this manner. Dusting involves spreading-as evenly as possible-a dust or sand layer and letting the sun provide the energy. Thus, time is involved as well as the higher sun angles in the late spring and good luck in avoiding snow st
44、orms that would cover the dust. Agricultural aircraft generally apply the dust which keeps costs fairly low; 34.9 cents (1 970 dollars) per lineal foot (1 O0 feet wide) in a remote section of Alaska is a typical cost. The particle size can vary, depending on what is available-0.50 pounds per square
45、yard for sand and 0.35 pounds per square yard for fly ash are used in Alaska. For 0.04-inch-diameter dust, 0.18 pounds per square yard and for 0.2-inch-diameter dust, 0.92 pounds per square yard cover the range of normally acceptable material. 22 Provided by IHSNot for ResaleNo reproduction or netwo
46、rking permitted without license from IHS-,-,-4 t 4 = 3535789 005b365 582 E I . t A logical offshoot of dusting is to pump water and bottom materials onto the ice surface. This is limited to streams with silt or sand bottoms and is more expensive than aerial dusting. However, the approach does have a
47、pplication where the stream is too narrow or sinuous for aerial work, or where environmental considerations preclude adding material to the stream. i+ . I - ! Cropdusters are ideal for ice dusting 23 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-m
48、3535789 O056366 419 m -* - Air cushion vehicles Air Cushion Vehicles (ACVs) can be used for breaking up large areas of sheet ice before the ice run. They are used in those areas where the sheet ice may stop the run and cause a jam. The advantages of an ACV are its speed and its ability to operate in shallow water. A disadvantage is that it simply breaks the ice and does not move it. This technique has been per- fected by the Canadian Coast Guard, primarily on t
