1 INTRODUCTION

Mt. McKinley National Park was established on Feb.26, 1917. The Park was established to protect its largemammals (e.g. Dall sheep, grizzly bear, caribou, moose,wolves) and not because of Mount McKinley (whichwas not wholly within the original Park boundary).The original Park was designated a wilderness area in1980 and was incorporated into Denali National Parkand Preserve, which protected North America’s high-est peak at 6194 m. The Park was designated an inter-national biosphere reserve in 1976.

Only one access road leads into the Park. Icing prob-lems have occurred on the access road since at leastthe late 1950s. The term icing (i.e. Aufeis [German] ortaryn [Russian]) refers to a mass of surface ice formedduring the winter by successive freezing of sheets ofwater that seeps from the ground, from a river, or froma spring. When a large icing covers the road it creates amajor maintenance problem and a hindrance to accessinto the Park.

Over the past several decades, Park maintenancepersonnel have attempted to mitigate/eliminate the icingproblems on the access road. To date, these techniqueshave not been entirely successful. The work presentedherein describes the history of these efforts and presentsa recommendation of a strategy that may be employedin the future, respecting the fact that traditional solu-tions and their related construction activities may notbe acceptable in a designated wilderness area.

2 BACKGROUND ON ICINGS

Wrangel (1841) described icings and the obstacle theyposed to access along the northern shore of Siberia:

“Here I had the opportunity to observe a remarkablephenomenon of nature, the so-called taryns whichmade our trip very difficult, if not by the formation,then by the external appearance, which was similar toglaciers. …

“A trip across the taryns is extremely difficult anddangerous; if they are solidly frozen, then the ice sur-face is so slippery that even well-shod horses will slipat each step and are frequently lost. It is particularlydangerous to cross the taryns which lie on overhangsor on the edges of ravines. It is a misfortune for a cara-van when the strong, sudden and rather common gustsof wind in Siberia catch it on such a road. The personsand horses are thrown into the abyss.”

Icings may result from springs in an area, seepageforced to the surface by freezing down to an underly-ing impermeable strata (e.g. permafrost), or perennialseepage that exists in a shallow surficial layer. Springsmay be found in a variety of topographic situations. Inpermafrost regions, it is common for springs to befound at the base of south-facing slopes. Spring icingsusually occur early in the winter since the feed wateris continuously exposed to freezing. Spring icing for-mation often precedes the initiation of ground icing.Ground icings develop as soon as unfrozen water exitsthe ground surface and is exposed to the cold atmos-phere and freezes. This initial condition is followed byadditional seepage to the surface and the formation ofice, with the overall result being a buildup of an icelayer in successive stages, each stage being associatedwith an ice thickness that is usually less than two cen-timeters. The source of the feed water for the icing isgenerally not stationary. During the course of the icingactivity, the source(s) may shift, generally, in the upslope direction. Ground icings may be of any shape.

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Denali Park access road icing problems and mitigation options

T.S. VinsonDepartment of Civil Engineering, Oregon State University, Corvallis, Oregon, USA

D. LofgrenFederal Highway Administration, Vancouver, Washington, USA

ABSTRACT: Icing problems have occurred along the Denali Park access road since the late 1950s. The icing isformed in winter by successive freezing of sheets of water that seep to the surface from springs or ground waterin the active layer. Park maintenance personnel have attempted to control icing with canvas fencing and removalof the ice with a crawler tractor and “ripper”. Both methods respect the Park wilderness designation but they arevery costly, labor intensive and not always effective. An insulated underdrain system installed in the mid-1980s didnot perform satisfactorily. The climatological records may provide a solution to the icing problem that respects thePark wilderness designation. There is a threshold accumulation of snow early in the winter that results in no icingformation. Snow could be manufactured in late Fall/early Winter and used to insulate water sources, their drainagepaths, and reduce the risk of icing.

Permafrost, Phillips, Springman & Arenson (eds)© 2003 Swets & Zeitlinger, Lisse, ISBN 90 5809 582 7

The feed water supply associated with the ground icingis limited and may become exhausted before springarrives. Owing to the limited water supply, groundicings are generally small when compared to the sizeof spring icings.

The conditions favorable for the formation of icingsare as follows (Muller 1947):

• the presence of groundwater in the suprapermafrostzone (i.e. all of the ground above the permafrost,consisting of the active layer, talik, and perelotek),

• subfreezing air temperatures and thin snow coverduring the early part of the winter,

• the permafrost table or an impermeable layer inclose proximity to the ground surface (note: it isnow widely acknowledged that icings can occur innon-permafrost regions),

• thick snow cover during the latter part of the winter.

Carey (1973) notes that ground and spring icings havebeen reported to be more common on south-facingslopes than on north-facing slopes. In permafrost areas,the permafrost table is generally at greater depths onsouth-facing slopes than on slopes having a northerlyexposure. Thus, on south-facing slopes, the thickersuprapermafrost layer has a greater capacity for ground-water, and in some instances, permafrost is completelyabsent, providing a convenient route for subpermafrostwater to feed springs. Because of less insulation and theshallow permafrost table of north-facing slopes, icingson these slopes may develop earlier and last longerthan on the southerly slopes. However, due to the limitedavailability of feed water, these icings will be modestin size. On south-facing slopes, while the appearance oficings may be delayed, such icings may reach greatersize because of the greater availability of feed water.

Ground icings are not frequently encountered undernatural conditions. However, in areas where naturalconditions have been disturbed, ground icings maybecome the predominant icing type. Clearing vegetationand the construction of embankments for highways,railroads, airfields, and structures can substantiallyaffect the natural thermal regime of the ground and thehydrologic regimes of both groundwater and surfacewater. Figure 1 illustrates the formation of an icingassociated with road construction for the situation inwhich seepage occurs in an unfrozen layer that under-lies the roadway. In the warmer months, the seepage isnot impeded because the materials are unfrozen.However, with the onset of winter, the frost frontadvances through the road embankment more rapidlythan the surrounding area. Consequently, a frozen damdevelops beneath the roadway forcing the seepage tothe surface, which results in an icing.

Muller reports on two Russian studies that illustratethe effect of snow on the formation of icings. In onecase, when the snow cover reached a maximum in

March, icings in southern Siberia were noted to bemost intense and to attain their maximum spread. Thiswas believed to be the result of the snow acting as aninsulative blanket to preserve the frozen ground con-ditions that were caused by December and Januaryfrosts. In another instance, Muller notes, that one largeicing, which had been appearing regularly for manyyears in Siberia, failed to form during a winter withunusualy heavy snowfall.

3 REVIEW OF ICING PROBLEMS ON DENALI PARK ACCESS ROAD

There are four major historically significant icing areason the Denali Park access road. A location map for theareas is given in Figure 2. These areas are referred toas 1, 2, 3, and 4.

Icing Area 1 (Fig. 3) is approximately 6.7 to 7.3 kmwest of the intersection of the Denali Park access roadwith Highway 3. Icing Area 1 is considered to be thegreatest problem area. There are two major springsthat feed streams in the area. One is at the western endof the area, the other is at the eastern end of the area.

Brazo (1984) identified the mechanism shown inFigure 1 as the possible explanation for icing in area1, but noted it should be confirmed through fieldexploration. Heubner (1986) has provided an excel-lent description of the formation of icing in Area 1. Henotes that when groundwater traveling in the shallowsurface layer of organic material reaches the top of thebackslope of the ditch, it runs down the backslopevery near or at the surface of the ground.

During late fall, with near-freezing temperatures, thiswater begins to freeze on the backslope, creating anicing. Initially, the icings occur at locations wheregroundwater is obviously present. Water continues toflow over the water on the backslope, sometimes freez-ing and building up ice, sometimes reaching the ditch

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Figure 1. Formation of icing associated with road con-struction (after Carey 1973).

line. Eventually the ice builds up so that the ground-water can no longer flow over it and, consequently, itflows around the icing and begins to build ice laterallyaround the backslope. The ice builds up in this manneruntil a dam of ice is created, the crest of the ice dambeing slightly higher at the locations of the watersource. Water then starts to build up behind this dam,moving the icing upslope. Further, water that overtopsthe dam continues to build the ice below. Heubnernotes, however, that the two greatest sources of ice inArea 1 are two streams (previously noted). He indi-cates that as the stream drainages fill in with ice theybecome wider and wider and eventually cover a verygreat area of hillside with ice.

Icing Area 2 is approximately 8.0 to 8.6 km west ofthe intersection. This area is a broad, flat, low lyingarea. There is a small ditch cut approximately 30 mback from the road that apparently, in the past, wasused to drain the area and, therefore, restrict icing for-mation on the road. Very high groundwater flows areencountered in this area. It is believed that both sub-surface and surface water contribute to icing forma-tion in Area 2. There were indications during the field

investigation conducted by Lofgren (1984) that partof the site is underlain by permafrost.

Icing Area 3 (Fig. 4) is approximately 8.8 to 9.0 kmwest of the intersection. The icing problem in this flatbottom draw is apparently related to a spring that isnear the west end of the draw.

Icing Area 4 is approximately 10.6 to 10.9 km westof the intersection. It is the wettest of the four icingareas. It is difficult to identify a single source for thewater. Apparently, many springs emerge from the tun-dra in this area and coalesce to form streams that flowdownslope to the roadway drainage ditch. The forma-tion of icing in this area is reported to occur over hun-dreds of meters throughout the backslope of the area.The area is apparently underlain by permafrost.

4 MITIGATION OPTIONS TO REDUCE ICINGS

Thomson (1963), Carey (1970, 1973), and Johnston(1981) have presented a number of measures that maybe employed to control or correct icings:

• removal by “ripping” with tracked equipment,• ice fences; an ice fence generally consists of lengths

of canvas or geosynthetics that are stretched betweenstakes driven into the roadway shoulder. The canvasis approximately one meter in height. A stairsteparrangement of ice fences are often more effectivethan a single fence,

• raising the road grade; this is a simple but generallycostly solution; large storage areas for the ice arerequired; the solution assumes a knowledge of thelimits of the icing,

• freezing or frost belts; at a location above the roadthe vegetation cover and snow is removed to allowrapid freezing of the surface layer; this in turn startsthe icing at a point where it is hoped that it will notreach the road; this measure is usually only tem-porarily effective,

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Figure 2. Location map for icing areas on Park access road.

Figure 3. Icing Area 1 at 6.7 to 7.3 km.

Figure 4. Icing area 3 at 8.8 to 9.0 km.

• insulated subsurface drains (interceptor and mainsubdrain installation); these drains consist of perfo-rated pipe placed in a trench backfilled with coarseaggregate with insulation placed over the trenchand pipe to prevent freezing.

The causes of icings suggest which corrective measureswill be most effective. For a freezing belt to be suc-cessful, there must be permeable layer over an imper-meable layer and it must be possible to intercept theimpermeable layer by downward freezing. For an insu-lated subdrain system to be successful, the interceptorditch(es) must capture the source of water. Generally,this can occur if the source of water is a spring and theinterceptor ditches can be configured to “sump” thespring. Also, if the source of water is through a per-meable surface layer of the order of one meter, thenflow may be intercepted through the sidewalls of aninterceptor ditch that runs parallel to the roadway. Asubdrain system will not work to prevent freezing ofsurface runoff, that is, water that exits to the surfacefrom a shallow or thin surficial drainage layer.

Livingston & Johnson (1978) reported subdraininstallations have failed owing to:

• an interceptor system that does not have enoughcapacity and, consequently, causes excess water toflow to the surface and form an icing,

• undiscovered spring(s) that form ice over portionsof the main ditch,

• water not entering the sidewall of the interceptorsubdrain and flowing over the interceptor drain sothat it did not percolate through to the subdrain system.

5 MITIGATION OPTIONS ATTEMPTED AT DENALI PARK ACCESS ROAD

Maintenance personnel at the Park have employedthree measures in an attempt to control icings. In theearly 1960s, ice fences were used to control icing inArea 1. The ice fences consisted of lengths of canvasstretched between stakes driven into the roadway sho-ulder (Fig. 5). It appears that the fences may controlicing migration very well. Unfortunately, the fencesare labor intensive to erect. Furthermore, they are not100% effective in keeping ice off the roadway (Fig. 6).Geosynthetics may provide easier erection and bettercontrol of ice compared to the canvas materials thathave previously been used.

The second method of icing control employed bymaintenance personnel is the removal of the icing on theroadway with a crawler tractor and “ripper” attach-ment. This method is also labor intensive and is notfully effective. Further, the “ripper” often scrapes andseverely damages the pavement surface layer to the

extent that additional maintenance may be required torepair the scarred areas. This method has proved suc-cessful, however, in keeping the Park access road openthrough the four icing areas noted.

An insulated underdrain system was constructed inicing Area 1 during late Fall 1985. The insulated under-drain system followed the recommendations given byLivingston & Johnson (1978) very closely. The typi-cal section for the insulated interceptor underdrainrunning parallel to the roadway consists of a 1.2 by1.2 m trench with a 0.3 m perforated CMP placed oncenterline at the bottom of the trench. The trench isbackfilled with coarse rock (80% @8 to 30 cm, maxi-mum 5% under 1 cm), a 2.4 m wide-15 cm sand bed-ding layer is placed over the trench and a 2.4 m wide10 cm layer of polystyrene board insulation is placedover the sand. The insulation is covered with materialexcavated from the trench. The perforated pipe is usedto concentrate flow and provide a structure that can bethawed if the trench becomes frozen. An insulated cross-drain trench with features similar to the interceptortrench is constructed through the embankment to collect water from the interceptor trench and dischargeit downslope of the embankment. A geosynthetic fil-ter fabric should be placed between the coarse rock

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Figure 5. Stairstep ice fencing constructed with canvas.

Figure 6. Ice overtopping canvas fencing.

backfill in the interceptor trench and the adjacentnative materials and the sand bedding that overlies thetrench. The geosynthetic would prevent “fines” con-tamination of the coarse rock backfill material.

The design of the insulated underdrain system foricing Area 1 was predicated on the source of waterbeing in a layer of permeable material at the surface ofthe backslope that could be intercepted by the side-wall of the underdrain system. Unfortunately, as indi-cated by Heubner (1986), during the construction ofthe insulated underdrains it was noted that virtually allof the groundwater in icing Area 1 travels in a shallowlayer of organic material that is just beneath the tun-dra. This layer is underlain by an impermeable soilthat varies in thickness, but could be as much as twometers thick. The material at the side of the trench wasreported as primarily clay with some rock from about0.3 m below the surface to pipe grade. Heubner notesthat very little subsurface water was encountered atdepths greater than about 0.3 m. Consequently theinsulated underdrain system has not controlled/miti-gated the icing in Area 1.

6 AN ICING MITIGATION STRATEGY BASED ON CLIMATE RECORDS

Muller (1947) states:

“In areas of heavy snowfall during the early part ofthe winter, river and ground icings usually appear latein the winter or early spring, or may not appear at all.On the other hand in areas with less than 1/2 meter orno snow at all, icings are likely to appear as early asDecember.”

A similar statement is made by Carey (1973):

“… it is clear that heavy snow during the first twoor three months of the winter can have the effect thaticings during the rest of the winter are minor in extentor nonexistent. Correspondingly, light snow accumu-lations or the absence of snow cover during this periodcontribute to extensive and severe icings.”

Climate records dating back to 1922 are available forthe Park. The daily data includes: maximum and min-imum temperature, precipitation, new snowfall, anddepth of snow accumulation. Furthermore, a qualita-tive record of maintenance activity dating back to1973 is also available for the Park. By combiningthese two databases it is possible to validate the fieldobservations reported by Muller and Carey. Table 1presents information from the combined databases.The climate database includes the late Fall/earlyWinter records for the months of October, November,and December (for the year preceding the year notedin column 1). The maintenance data-base represents

29 years, however, there were 5 years with no indica-tion of maintenance activity, hence, 24 years are rep-resented. Column 2 indicates whether icing did or didnot occur for each year represented in the populationconsidered.

Table 2 presents the results of a sort of the databaseby maximum depth of snow accumulation. It is obvi-ous that when the maximum snow accumulationreached approximately 50 cm icing did not occur. This

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Table 1. Climate and maintenance history for October,November, and December – 1973–2001.

(3) (4) (5)(1) (2) Maximum Average FI Year Icing Snow (cm) Snow (cm) °C-days

1973 yes 51 14 10031974 yes 28 12 11421975 no 51 30 12261978 yes 43 24 14051979 yes 36 11 8361980 no? 30 14 9131982 no? 33 16 10081983 no 58 31 11181984 yes 25 10 9061985 no 117 28 10181986 yes 33 11 9431987 yes 20 7 7791988 yes 31 12 8791989 no 53 41 11491990 no 58 24 10611991 no 114 36 13021992 no 53 33 11361993 no 140 74 11321994 no 56 27 7281995 no 64 30 11541996 yes 18 7 10561999 yes 33 9 9952000 no 76 25 13272001 yes 25 16 655

Table 2. Results of sorting climate and maintenance database.

(1) (2) (3)Sort Criteria Icing – Yes Icing – No

Max. snow accumulation 1 1150 cm

Max. snow accumulation 10 2�50 cm

Ave. snow accumulation 0 1025 cm

Ave. snow accumulation 11 3�25 m

Freezing Index 3 91050°C-days

Freezing Index 8 4�1050°C-days

conclusion is in agreement with the quantitativeobservation reported by Muller. Table 2 also presentsthe results of a sort by average depth of snow accu-mulation. When the average snow accumulation wasgreater than approximately 25 cm for the months ofOctober, November, and December (for the year pre-ceding the year noted in Table 1, column 1) icing didnot occur. Finally, Table 2 presents the results of a sortby freezing index FI for the months considered. It isnot possible to identify a threshold for freezing index forwhich icing would always occur. In fact, icing occurredin some years when the freezing index was very lowand icing did not occur in some years when the freezingindex was very high.

The strong correlation between snow cover and icingsuggests a solution to the icing problem that respectsthe wilderness designation for the Park. Snow couldbe manufactured in late Fall/early Winter and used toinsulate water sources, their drainage paths, and elim-inate icing. It would appear that a 25 cm layer main-tained over October, November, and December wouldprevent icing. Snow making systems are commerciallyavailable. There are two basic snow manufacturingsystems: airless and air/water. Airless “snowguns” aregenerally mounted on permanent towers or sleds thatare towed behind a snow cat. These guns spray waterout of small nozzles; the nozzles ring a large, electri-cally powered fan in the center of the “barrel.” The fandisrupts the jets of water into small droplets, and pro-pels them into the air. In an air/water system water isforced through a nozzle under high pressure by com-pressed air. The tiny water droplets freeze into crystalsbefore falling to the ground as snow. The exact mix ofwater and compressed air determines how wet or dry theresultant snow will be. The proper mix of air and wateris dependent upon temperature and humidity. Snowcan be manufactured when the wet bulb temperature is�2°C or colder. With commercially available equip-ment, a 25 cm snow layer can be placed on a two-hectare area in approximately one hour (Guido 1999).

7 SUMMARY AND CONCLUSIONS

Icing problems in Denali National Park have beenaddressed by maintenance personnel for 50 years. Icefences, removal of ice with a crawler tractor and “rip-per”, and an insulated underdrain system have beenemployed. These techniques have either not been suc-cessful in controlling icing or, when successful, havebeen labor intensive. A solution to the icing problemthat respects the wilderness designation for the Parkmay be found in the climatological and road mainte-nance history for the Park. When the average snow

accumulation for the months of October, November,and December is greater than approximately 25 cm,icing does not occur. Considering this fact it would befeasible to identify the accumulation of snow as part ofan icing control strategy. Snow could be manufacturedin late Fall/early Winter and used to insulate watersources, their drainage paths, and eliminate icing.

ACKNOWLEDGEMENTS

The authors gratefully acknowledge the kindness andassistance of Brad Ebel and Pam Sousanes, DenaliNational Park and Preserve, for providing the mainte-nance and climate records used in this research project.

REFERENCES

Brazo, G. 1984. Aufeis at Denali National Park AccessRoad. Memorandum to Paul Misterek, SupervisingMaterials Engineer, Northern Region.

Carey, K.L. 1970. Icing Occurrence, Control andPrevention – Annotated Bibliography. Special Report151. U.S. Army CRREL, Hanover, NH.

Carey, K.L. 1973. Icings Developed from Surface Waterand Ground Water. Monograph III-0. U.S. ArmyCRREL, Hanover, NH.

Guido, M. 1999. The Art and Science of Making Snow.First Tracks (Online Ski Magazine). www.firsttrack-sonline.com.

Heubner, B. 1986. Aufeis Update. Memorandum to MonteSymons, FHWA, February.

Johnston, G.H. (Editor) 1981. Permafrost –- EngineeringDesign and Construction. Toronto: John Wiley andSons.

Livingston, H. & Johnson, E. 1978. Insulated RoadwaySubdrains in the Subarctic for the Prevention of SpringIcings. Proceedings, ASCE Conference on AppliedTechniques for Cold Environments, Anchorage, AK:513–521.

Lofgren, D. 1984. Investigation of Aufeis on DenaliNational Park Highway, Denali National Park andPreserve, Alaska. Geotechnical Report No. 28-84,FHWA, WDFD.

Muller, S.M. 1947. Permafrost or Permanently FrozenGround and Related Engineering Problems. AnnArbor, MI: J.W. Edwards, Inc.

Thomson, S. 1963. Icings on the Alaska Highway.Proceedings, First International Conference onPermafrost, Purdue University. USA: 526– 529.

Wrangel, F.P. 1841. A Journey to the Northern Shores ofSiberia and along the Arctic Ocean made in 1820–1824. Text in Russian. St. Petersburg.

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