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    Arctic and Subarctic Hydrology

    Encyclopedia Arctica Volume 1: Geology and Allied Subjects

    Arctic and Subarctic Hydrology

    Unpaginated      |      Vol_I-0552                                                                                                                  
    EA-I. (Lorenz G. Straub and L. A. Johnson)




    I. Introduction 1
    Glossary 4
    II. Precipitation 6
    III. Evaporation and Transpiration 22
    IV. Infiltration 24
    V. Runoff 28
    VI. Physiographic Changes Produced by Hydrological Phenomena 39
    Erosion 39
    Solifluction and landslides 40
    River Performance 41
    Changes Which Result upon Alteration of the

    Thermal Regime
    Changes, the Result of Soil Freezing 44
    Icings 50
    Marginal Lakes 55
    VII. Ground Water 56
    Bibliography 60

    Unpaginated      |      Vol_I-0553                                                                                                                  


    Arctic and Subarctic Hydrology

    (Straub and Johnson)



    Fig. 2 Relation of atmospheric water holding capacity and

    Fig. 3 Climatic data for three stations 10
    Fig. 4 Rainfall duration-frequency relations for Alaska 13
    Fig. 5 Rainfall intensity frequency data for Alaska 14
    Fig. 6 Supply curves for arctic and subarctic regions of

    Fig. 7 A low ceiling confines avenues of incoming moist air

    and is thereby a limiting factor of precipitation
    Fig. 8 Ground temperature s for three stations 25
    Fig. 9 Hydrological data pertaining to the Yukon River

    above Eagle, Alaska
    Fig. 10 Influence of a drainage ditch on the thermal regime

    of the ground
    Fig. 11 Ground water occurrences in polar regions 57

    Unpaginated      |      Vol_I-0554                                                                                                                  
    EA-I. Straub and Johnson: Arctic and Subarctic Hydrology



            With the manuscript of this article, and author submitted 38

    photographs and 1 colored drawing for possible use as illustrations.

    Because of the high cost of reprod u cing them as halftones in the printed

    volume, only a small proportion of the photographs submitted by con–

    tributors to Volume I, Encyclopedia Arctica , can be used, at most one

    or two with each paper; in some cases none. The number and selection

    must be determined later by the publisher and editors of Encyclopedia

    Arctica . Meantime all photographs are being held at The Stefansson


    001      |      Vol_I-0555                                                                                                                  
    EA-I. (Lorenz G. Straub and L. A. Johnson)





            Hydrology is the science that is concerned with the movement and

    distribution of water resources above, below, and on the land surface of

    the earth. Water occurs practically everywhere but varies greatly in

    quantity and form. It occurs in the atmosphere in the form of vapor, mist,

    fog, rain, sleet, hail, and snow. On land, water takes the shape of rills,

    rivulets, streams, rivers, ponds, and lakes. Below the ground surface,

    water is present in many forms and states ranging from vapor in the inter–

    stices of the soil, free liquid in large aquifers, to solid lenses and

    wedges in permafrost. Irrespective of geographic position, water is the

    fundamental natural resource. Without it, no form of animal or vegetal

    life could exist. It provides avenues of transportation in both liquid

    and solid states. It is a source of power, transmits heat, and acts as a

    solvent for chemical processes. Often water following elemental principles

    of physics can become extremely destructive. Floods can result from melting

    snow, intense rains, ice jams, and the structural failure of glaciers.

    Man-made buildings are ruined by the expansive force of freezing water.

    Land areas cave in upon degradation of permafrost. Erosion carries tons

    of irreplaceable fertile topsoil to the ocean each year.

    002      |      Vol_I-0556                                                                                                                  
    EA-I. Straub and Johnson: Hydrology

            Figure 1 schematically illustrates a sequence of events called the

    hydrologic cycle which takes place in arctic and subarctic regions in the

    same manner that it occurs in more temperate zones. Water is evaporated

    or sublimated from ocean and land areas and taken up by the atmosphere.

    The action of prevailing winds and movement of air masses carry the vapor

    to points where orographic, convective, or cyclonic processes result in

    precipitation of various forms and magnitudes. Some of the precipitation

    is evaporated or sublimated before it reaches the land. Other portions are

    intercepted by vegetation and other objects that protrude above the ground

    surface. Still another portion runs off the ground into rills, streams, and

    rivers and is returned via sinuous and serpentine routes to the sea, the

    common place of beginning. Other portions infiltrate into the ground and

    there find numerous outlets; a part is held by capillary action and is either

    evaporated or used by plants, then transpirated into the atmosphere; another

    part percolates through the soil to join the ground water and appears later

    as ground water flow; and still another part percolates to great depth through

    taliks in the permafrost, then reappears at probably a great distance in the

    form of springs.

            Although prevailing winds and topographic relief play relevant roles

    in the formation of precipitation and later distribution of water, temperature

    is probably the most important single factor in the hydrology of polar regions.

    Because of low temperatures, the atmosphere cannot hold much moisture. Con–

    sequently, the amount of precipitation is limited. Low temperatures also

    cause a change in state of water from liquid to solid, and it is in this process

    that many hydrological problems arise. Likewise, changes in volume brought

    about by thawing of saturated frozen ground result in problems not readily

    solvable. Some specific illustrations are included in later sections.

    003      |      Vol_I-0557                                                                                                                  
    EA-I. Straub and Johnson: Hydrology

            Hydrology is a comparatively new science. Basic data, such as climatic

    and stream-flow records, are available for only a hundred years or so at

    the most. In the polar regions the records are much shorter.

            Stream-gaging measurements are practically nil. Climatic data for

    a few stations date back twenty years, while studies of the thermal regime

    of the ground were initiated only a few years ago. Even with a dearth of

    scientific information to guide design and development, hydrological prin–

    ciples have been employed for a long time. The Eskimos, long before pioneering

    efforts of white men, took advantage of the insulating properties of snow

    and constructed shelters therefrom. The iglus were built dome-shaped so

    as to offer less resistance to severe arctic winds. With this type of

    structure it was also impossible to influence the thermal regime of the

    ground. Location of the building has to be made with due respect to snow–

    drifts, snowslides, water supply, and other hydrological problems. Numerous

    small villages and communities are to be found along rivers, which are avenues

    of transportation, even though sites are subject to annual springtime flooding.

    Evidently old-time settlers concluded that advantages of transportation out–

    weighed the temporary inconveniences of inundation, and they erected dwellings

    accordingly. It is of interest to note, too, that many of these sites are at

    locations where permafrost does not exist at shallow depths and that construc–

    tion on fine-textured soil has been with cognizance of the destructive effects

    of thawing permafrost.

            It is not the intention of the authors of this paper to treat analytically

    all the varied and complex phenomena that are integrated parts of arctic

    hydrology. Obviously only a slight penetration of the more general aspects

    of the subject is possible within space and word limitations. The sections

    004      |      Vol_I-0558                                                                                                                  
    EA-I. Straub and Johnson: Hydrology

    that follow were prepared largely on the basic of observations and investi–

    gations which were made by the authors in arctic and subarctic regions of

    Alaska and Canada. These subdivisions contain generalized, and in some

    cases specific, information on topics that are usually associated with

    hydrology. Precipitation is treated quite thoroughly in Section II. This

    includes an analysis of intensity, duration, and frequency relations of

    rainfall in polar areas. Although these results are specifically applicable

    to Alaska, there is reason to believe that similar conditions would be found

    in other sections of the Arctic and Subarctic. Evaporation and transpiration

    are discussed in Section III. Here there are no data to support the results

    of an analytical treatment made by the use of methods which are applicable

    in more temperate zones. Section IV contains generalized aspects of infil–

    tration. Section V deals with runoff and points out the general behavior

    of rivers and streams. Typical examples are cited. A discussion of physio–

    graphic changes produced by hydrological phenomena is contained along with

    photographic illustrations in Section VI. Section VII concludes this paper

    with a generalized discussion of ground water.



            In the preparation of this dissertation inevitably some terms were

    used which require definition; in fact, a few of the terms are not to be

    found in the unabridged dictionary. A few other words are used with a

    limited meaning, whereas the dictionary gives a broad definition. It was

    therefore deemed expedient that these several terms should be defined with

    special reference to the meaning or intent of the authors. The following

    glossary should serve this purpose.

    005      |      Vol_I-0559                                                                                                                  
    EA-I. Straub and Johnson: Hydrology

    Arctic is used to designate an area of the Northern Hemisphere that

    lies north of the 50°F. mean July isotherm. It is significant that this

    hypothetical line, connecting points of equal mean monthly temperature

    for the warmest month, corresponds approximately to the northern limit of


    Frost M m ound is a general term used to denote an up-warp of ground

    produced by various forces acting individually or in combination. These

    causative forces are usually due to freezing, ground-water pressure, and

    crystallization. (Various types of frost mounds are described in Section VI.)

    Icing designates a mass of ice of irregular shape and form which has

    been built up by successive freezing of thin layers. The oldest layer is

    always on the bottom of the mass, which has a laminated structure. Icing

    is also used to denote the process by which this mass of laminated ice


    Permafrost , as the word implies, means permanently frozen ground. It

    refers to ground, the temperature of which is permanently below the freezing

    point of water, irrespective of texture of the soil, structure, moisture

    content, or other characteristics.

    Pingo is a term which has been taken from the Eskimo and means a certain

    special type of conical hill. The authors use it to define a large frost

    mound of longer than seasonal duration.

    Polar is used herein to designate arctic and subarctic areas. It is

    also used to refer to various characteristics and aspects of this region,

    such as polar climate and polar weather.

    006      |      Vol_I-0560                                                                                                                  
    EA-I. Straub and Johnson: Hydrology

    Subarctic is a term used herein to denote an area of the Northern

    Hemisphere which is bounded on the north by a 50°F. mean July isotherm

    and on the south by the southern limit of permafrost.

    Sublimation refers to the process by which a material passes directly

    from a solid to a vapor state without going through the liquid state.

    Talik is adopted from the Russian to denote an unfrozen layer, lens,

    or seam within the permanently frozen ground.

    Thermokarst is a term, adopted from Russian scientists, to refer to

    the development of uneven and irregular topography by the melting of ground

    ice. It designates a thermal action that produces land forms which are

    similar to the sinkholes, funnels, and caverns that are produced in limestone terrain ✓ word missing

    by the solvent action of water.

    Thermal regime designates the enduring temperature behavior of the ground.

    The thermal regime may be altered by human activity or by other means which

    change or alter the ability of surface materials to absorb and conduct heat.



            Precipitation is a term that includes all water deposited on the earth

    from the atmosphere, regardless of form. It may be rain, hail, sleet, snow,

    dew, or frost. No form of precipitation can occur unless air that contains

    moisture is cooled sufficiently to permit condensation of a part of the water

    that it holds. Air masses can be cooled in one of two different ways —

    radiation or lifting. The first of these results in dew or frost. Cooling

    by lifting results in rain, hail, sleet, or snow. This process is of utmost

    importance to the hydrologist, as precipitation brought about in this manner

    is of real quantitative significance. Lifting takes place in one or a

    007      |      Vol_I-0561                                                                                                                  
    EA-I. Straub and Johnson: Hydrology

    combination of three ways — ( a ) from convergence, ( b ) from topographic

    influences, and ( c ) from convection.

            Convergence is encountered when warm air masses moving in one direction

    meet colder air masses moving in another. The lighter, warmer air is forced

    upward over the colder mass, and cooling takes place with consequent conden–

    sation and precipitation. This is an important cause of precipitation in

    polar regions. Topographic influence s predominate in the south coast of

    Alaska. Moisture-laden air masses from the warm Pacific Ocean quickly lose

    their moisture when forced up the coastal mountain ranges. This effectively

    blocks the interior of Alaska from a warm source of precipitation supply,

    and, consequently, annual magnitudes are small north of the Alaska Range.

    Other arctic and subarctic regions are affected similarly. The relatively

    flat interior of European and Asian polar regions are blocked from a warm

    source of moisture by a system of many mountain ranges. Among these are

    Anadyr and Kolyma ranges in southeastern Siberia; Hanova Range and the

    Himalaya Mountains in central Asia; the Alps, Balkan, and Caucasus mountain

    systems in southern Europe. These mountain ranges shut off the Pacific and

    Indian oceans and the Mediterranean Sea as sources of precipitation supply.

    Consequently, as is to be expected, the arctic and subarctic regions of

    Europe and Asia are characterized also by low annual rainfall. Convection

    contributes a portion of precipitation in nearly every locality. This type

    is usually associated with the thunderstorm and is not uncommon in the

    Subarctic, although quite frequently thunderstorms exist there without

    rainfall. Lightning then often causes forest fires.

            In the foregoing paragraph, emphasis was made of the fact that arctic

    and subarctic areas do not, generally speaking, have a warm source of moisture

    008      |      Vol_I-0562                                                                                                                  
    EA-I. Straub and Johnson: Hydrology

    supply. This is significant, and particularly so when it is recognized that

    the water-holding capacity of the atmosphere increases as the temperature

    rises. The total depths of water contained in a column of saturated aqueous

    vapor is given by the following curve (Fig. 2.). Data for this figure was

    taken from the October 1918 issue of Symon’s Meteorological Magazine . In

    this it was assumed that there is a reduction in temperature of 10°F. per

    kilometer of altitude.

            Although the graph of Figure 2 is no indicator of actual rainfall, it

    does point out a limiting condition for a given place unless moisture is

    replenished from outside sources.

            Climatological records confirm the contention that polar regions have

    a low annual precipitation. Data for three stations, one typical of the

    Arctic, two representative of the Subarctic, are graphically illustrated

    in Figure 3.

            All of the area that lies to the north of an imaginary line which

    represents the 50° F. mean July isotherm is characterized by decidedly polar

    climate, with long cold winters and short cool summers. About 40 per cent

    of the precipitation falls as rain in j J uly, August, and September, while the

    remainder of an annual mean of less than 5 inches is distributed fairly

    uniformly as snow in the other 6 months. It is not uncommon for snow and

    sleet to fall in July, the warmest month, which also encounters freezing

    temperatures quite often. Drifting of snow in the winter month is very

    severe, creating large drifts which are very hard - packed. This is a very

    important item to recognize in hydrological aspects of design for the Arctic.

            Precipitation in the Subarctic can vary perceptibly, depending principally

    upon geographic position with relation to features of relief and nearness to

    009      |      Vol_I-0563                                                                                                                  

    Fig.2 Relation of Atmospheric Water Holding Capacity and Temperature

    010      |      Vol_I-0564                                                                                                                  

    Fig. 3 Climatic Data for Three Stations

    011      |      Vol_I-0565                                                                                                                  
    EA-I. Straub and Johnson: Hydrology

    a warm source of moisture supply. In Alaska the maximum amount occurs near

    the Bering Sea coast and gradually tapers off to the northeast as distances

    from the sea increase. Stations at Nome, Moses Point, and Bethel, each on

    or near the sea, report annual amounts of 18 to 22 inches; Fairbanks and Nenana,

    located about 400 miles inland, report annual precipitation of about 12 inches;

    while Fort Yukon, located 100 miles farther inland, reports only 7.06 inches

    as the mean annual magnitude. In the Subarctic most of the precipitation

    occurs as rain in June, July, August, and September. Minimum monthly amounts

    fall as snow in February, March, and April. Over most of the region approxi–

    mately 25 per cent of the annual moisture occurs in the form of snow. On

    mountain slopes and at higher altitudes, the percentage increases, and it

    seems safe to say that above an elevation of 8,000 feet all precipitation

    occurs as snow. In Alaska annual snowfall ranges between 40 and 100 inches,

    with the greatest amounts occurring in the lower Yukon Valley. Drifting here

    is not ordinarily severe because of a near absence of wind in winter in the

    interior of Alaska.

            Intensity, duration, and frequency of rainfall are important characteristics

    for the hydrologist to consider in order to form the basis for the design of

    structures such as bridges, culverts, drainage systems, dams, erosion control

    works, water supply systems, power plants, and many other works. These

    characteristics of rainfall are exceedingly difficult to evaluate because of

    insufficient climatic records. In Alaska there are only two continuous

    recording rain gages north of the Alaska Range, and these are to be discontinued.

            Hathaway (5), after a study of rainfall intensity-frequency data for a

    large number of precipitation stations in temperate zones, concluded that

    there was a fairly constant relation between the intensity of rainfall for

    012      |      Vol_I-0566                                                                                                                  
    EA-I. Straub and Johnson: Hydrology

    a period of one hour and the rainfall rates of comparable frequency for

    shorter intervals, regardless of geographic location. Conclusions of a

    study of intensity-frequency data for precipitation stations of some regions of

    Alaska are illustrated by Figure 4. It is to be noted that in this region

    there is a decided difference in the orographic rains of Ketchikan and Juneau,

    as compared to the convergent and convective rains of Nome and Fairbanks.

    At these latter two stations, rains of long duration are very small, yet the

    magnitude of short-interval rainfall exceeds those for comparable time

    periods at Ketchikan and Juneau. It is important to recognize that meteo–

    rological conditions are not similar at the two sets of stations. Figure 5

    contains isohyetals which show the magnitude of one-hour rains that are

    expected to occur once in 2 years, once in 5 years, once in 10 years, and

    once in 20 years. This is actually a design storm index for the Alaskan

    Arctic and Subarctic. It is coordinated with Figure 6, which shows the

    relation between the one-hour rate of rainfall and the rates for shorter

    and logger intervals.

            These two figures contain information that is basic to the hydrological

    design of storm water drainage facilities and other works that are affected

    by small watersheds or basins. It is believed that the intensity-duration

    relations shown on Figure 6 are applicable also to any arctic or subarctic

    region where either convergence or convection are the dominant and causative

    rain-producing factors. For design usability, frequency data such as are

    indicated in Figure 5 would have to be developed for the area in which the

    intensity relations are to be used. There is little likelihood that for

    storms of 20-year frequency the 1.2 curve of Figure 6 will ever be exceeded

    anywhere in the Subarctic. The curve designated as 0.2 is recommended for

    use anywhere in the Arctic.

    013      |      Vol_I-0567                                                                                                                  

    Fig. 4 Rainfall Duration-Frequency Relations for Alaska.

    014      |      Vol_I-0568                                                                                                                  

    Fig. 5 Rainfall Intensity Frequency Data for Alaska

    015      |      Vol_I-0569                                                                                                                  


    FIGURE 6

    016      |      Vol_I-0570                                                                                                                  
    EA-I. Straub and Johnson: Hydrology

            In earlier paragraphs two reasons have been given for low precipitation

    intensities and volumes in polar regions. It was pointed out, first, that

    there is no available warm source of moisture supply, and, secondly, that

    a cool atmosphere does not hold much water. A third limiting factor, closely

    associated with the aqueous moisture content of the atmosphere, is the height

    of a column of air that can participate in rain production. This limits the

    height to which air masses can rise and also confines the avenues in which

    moisture-laden air reaches the rain-producing cell. Figure 7 schematically

    illustrates this particular phase (10).

            The rain-producing cell illustrated in Figure 7 represents, according

    to Showalter and Solot, the most efficient precipitating mechanism. One

    obvious limiting factor is the ceiling or the upper limit of convection.

    O S haw, in Comparative Meteorology , Vol. 2, p. 138, suggests that the height

    of tropopause is determined by the upper limit of convection. This varies

    considerably with latitude and is much less for polar regions than for the

    tropics. Although this analysis does not evaluate the effect quantitatively,

    it points out a third reason why precipitation in arctic and subarctic regions

    cannot be as large or as intense as those of more temperate zones.

            Snow is of particular hydrologic importance in the polar areas. Its

    insulating properties have been used by man for a long time, and they play

    a significant role in the thermal regime of the earth’s crust. Seasonal

    variations in depth of snow cover and irregular areal distribution result in

    uneven freezing of the active layer, which, in turn, affects ground - water

    flow. Icings, frost blisters, frost mounds, and pingos (defined in intro–

    ductory Glossary) may develop as an indirect effect of uneven snow cover.

    An idea of the value of the insulating property of snow can be obtained by

    017      |      Vol_I-0571                                                                                                                  

    Fig. 7 A Low Ceiling Confines Avenues of Incoming Moist Air and Is

    Thereby A Limiting Factor of Precipitation

    018      |      Vol_I-0572                                                                                                                  
    EA-I. Straub and Johnson: Hydrology

    a study of Table I. These data indicate that freshly fallen snow (item 3)

    is a good insulator and that an increase in density or packing reduces this

    property considerably. Ice is a better conductor of heat than water. Air

    is a very poor conductor.

    (Table I. Thermal Conductivity of Water and Various other Substances (11).)
    Substance Density

    gram/cm 3

    Conductivity coefficient,

    gram-cal./sec./cm 2 .
    x 10−410 −4
    1. Water 1 30 14.4
    2. Water 1 75 15.4
    3. Snow 0.11 0 2.6
    4. Snow 0.25 0 3.8
    5. Snow Old, well-packed 0 12.0
    6. Ice 0.92 0 53.0
    7. Air 0.00129 0 0.55
    8. Concrete 1.6 0 20.0
    9. Peat (7) 0.35 4 1.58
    10. Wood (oak perp endicular

    to grain)
    0.82 15 5.0
    11. Granite 2.80 20 53.0
    12. Iron 7.8-7.9 18 1,440.0

    019      |      Vol_I-0573                                                                                                                  
    EA-I. Straub and Johnson: Hydrology

            The insulating effect of snow is further illustrated by observations

    of M. I. Sumgin at Bomnak Permafrost Station in Siberia.

    Dec. 1913 Dec. 1914 Dec. 1918
    Thickness of snow, cm. 5 24 30
    Air temperature, °C. -5.2 -4.7 -4.7
    Ground temperature at

    1.5-meter depth, °C.
    -2.33 -0.29 0.20
    Temperature difference 2.87 4.41 4.90

            Sumgin noted that soil temperatures taken in December of each year

    were highest during the years when the ground was covered with a thick

    blanket of snow and not exposed to the cold atmosphere.

            The melting of snow replenishes ground water and, if occurring at a

    rate in excess of infiltration, results in runoff. The actual physics of

    the process is very complex, as many factors, each difficult to isolate,

    are involved. The density of freshly fallen snow is very much less than

    old snow. Densities may range from 0.1 gram per cubic centimeter for new

    snow to 0.6 gram per cubic centimeter for old hard-packed snow. In the

    process of melting, the layer of snow acts somewhat like a sponge, and lower

    strata absorb large quantities of water. As the application of heat continues,

    the capacities of lower layers of snow to hold free water are exceeded and

    runoff results which is equal to the rate of melting plus the rate at which

    free stored water is released. Overland flow then begins, but paths of

    travel are dammed by snow which has not yet ripened or reached its water–

    holding capacity. Heat for melting may be transmitted from a number of

    sources. The principal cause, however, is conduction from turbulent air.

    Wilson (13) expresse d s D , the depth in inches of water from melting in 6 hours, as: ✓✓

            Formula missing. cf. original top p.20

    D = KV(T – 32°)


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    EA-I. Straub and Johnson: Hydrology

    as: where V is wind velocity in inches per hour, T is dry-bulb temperature in

    degrees Fahrenheit, and K is a constant depending upon many factors. Prelimi–

    nary analysis of experiments in Wyoming indicates a value of 0.001 for K .

    Wilson (13) also points out that the amount of meltwater derived as a result

    of condensation of moisture on the snow surface may be expressed as:

    D = K1V(e – 6.11)

    where D is inches in hours, V is wind veloscity in inches per hour, e is the

    pressure in millibars, and K 1 is a constant similar to but not the same

    as K . Wilson states that for basin elevations from 0 to 3,200 feet, and if e

    is measured at the same height above the ground as T , K 1 is about 3.2 times

    K . Rain may also be a source of heat. The amount of meltwater resulting in

    this manner can be computed by the following formula:

    D = P(T – 32)/144

    where D is inches in depth of water melted from snow, P is inches of rain,

    T is temperature of rain or wet-bulb observation in degrees Fahrenheit, and

    144 B.t.u. per pound is the heat of fusion of ice. Radiation is also a source

    of heat for melting snow, but this is usually disregarded. Analysis indicates

    that radiation gains are very difficult to evaluate and often the losses are

    nearly equal in magnitude. Heat loss or gain to the soil would be very small.

            Computation of maximum rates of snow melt on the basis of formulas

    (1), (2), and (3) would be very complex. It would be necessary first to search

    climatological records for a combination of air temperature, wind velocity,

    vapor pressure, and rainfall that would be coordinated in a manner to produce

    high rates of melt. For Fairbanks, Alaska, the following calculation is


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    EA-I. Straub and Johnson: Hydrology

            D = 0.001V(T – 32) + 0.0032V(e – 6.11) + P((T – 32)/144)

    = 0.001 x 20(60 – 32) + 0.0032 x 20(17 – 6.11) + (0.5(60 – 32)/144)

    = 0.56 + 0.70 + 0.1

    = 1.36 in. of water in 6 hours or 0.23 in. per hour average rate

            It is of interest to compare this rate of water supply with the data

    contained in Figures 5 and 6. For a rainfall that can be expected once in

    20 years, Figure 5 indicates that intensity-duration curve 0.8 of Figure 6

    is applicable to the Fairbanks area. At a duration of 5 hours, the rate of

    rainfall is about equal to the computed rate of snow melt. For shorter

    durations, the rainfall is much larger, reaching 4.3 inches per hour for

    a duration of 5 minutes. For durations longer than 5 hours, the intensity

    of rain becomes progressively less and reaches about 0.1 inch per hour at

    24 hours. This would imply that, for small water sheds in the Subarctic,

    rainfall would be the guiding runoff criterion, but, as the size of the

    basins increases, melting snow would result in the larger discharges. This

    change in the cause of flood runoff rates takes place, it is judged, somewhere

    between 75 and 150 square miles, depending upon topography and other aspects.

    This analysis confirms the statements of many local Alaskans, who reported

    that they had never seen or heard of a river flood that resulted from heavy

    rains, but that river flooding was not uncommon in the spring.

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            Evaporation and transpiration are considered, in the minds of civil

    engineers, as losses in that they subtract from rather than add to stream

    flow. To the agriculturist, evaporation is considered a loss, while transpira–

    tion is of particular significance as it represents the moisture used by

    plants. Each of the two represents an important phase of the hydrologic

    cycle. They are here treated together because there are similarities in

    the factors that influence each occurrence. There cannot be evaporation

    off land areas if there is no moisture in the soil. There cannot be trans–

    piration off land areas if the moisture content is below the hygroscopic

    coefficient. In addition to moisture supply, temperature influences the

    rate at which each will occur.

            Evaporation is the process by which a liquid is changed into a vapor.

    Sublimation is the term used to define the process by which a solid is

    changed into a vapor without first passing through the liquid state. In

    countries like Greenland, much of which is covered with ice and snow the

    entire year, this latter process furnishes a considerable portion of atmos–

    pheric moisture — in the interior of icecaps, probably all of it.

            Transpiration is the process by which a plant, through its root system,

    absorbs water from the soil, uses the water in several physiologic processes,

    then loses it largely through diffusion via the stomata into the atmosphere.

    The rate of transpiration is dependent upon many things, including availa–

    bility of moisture, climatic conditions, and variety or type of plant.

    Hydrologically speaking, plants may be segregated into three groups:

    023      |      Vol_I-0577                                                                                                                  
    EA-I. Straub and Johnson: Hydrology

            ( a ) The xerophyte, which is adapted to arid conditions and potentially

    high rates of evaporation. Sagebrush is an example of this type.

            ( b ) The mesophyte, which grows in average climatic conditions and is

    represented by grasses, cereals, and trees. This type predominates in

    subarctic regions.

            ( c ) The hydrophyte, which is a plant that lives in an abundance of

    water and either partly or wholly submerged. These plants are invading many

    lakes of the Subarctic.

            Watershed losses from an engineering point of view ordinarily include

    some items which are not mentioned here. These, however, are usually quite

    small in comparison to evaporation and transpiration. They are all closely

    related and occur in overlapping stages. Water that is intercepted and does

    not reach the ground is returned to the atmosphere by evaporation. A part

    of detention and depression storage is returned to the air in a similar

    manner. Some soil water reaches the ground by capillary action, and is

    evaporated. Some soil water is tapped by roots of plants and subject to

    transpiration . demands of vegetation. Vegetal growth shades the ground and

    thereby reduces evaporation. On the other hand, evaporation utilizes water

    that would otherwise be consumed by transpiration. The two agencies of water

    loss are closely associated and their rates of occurrence depend principally

    upon such climatic factors as humidity, temperature, and wind velocity.

            Many formulas have been advanced by scientists from which approximations

    may be made for evaporation from water surfaces. Even here, where one factor,

    the evaporation opportunity, remains constant, there is considerable difference

    of opinion as to relative merits of formula application. In many cases it

    has not been necessary to go to any further refinements than to subtract

    total stream flow from total precipitation and term the remainder water

    losses. This method, of course, would not take into account either ground-

    024      |      Vol_I-0578                                                                                                                  
    EA-I. Straub and Johnson: Hydrology

    water accretion or deletion. Hydrologists seem quite well agreed that

    temperature plays a deciding role in rates of evaporation and transpiration.

    In the southern coastal regions of the United States, 30 inches is considered

    an average annual loss from the two events. Farther north, at a latitude of

    from 45° to 50°, mean annual temperatures are lower, and the water-loss

    average is reduced to about 20 inches. Projecting these data to latitudes

    still farther north, say to 60° or 65°, the water loss would drop to approxi–

    mately 10 inches per year. Here, of course, altitude would become significant,

    as above certain elevations there is, generally speaking, no form of vegetal

    life, and transpiration would equal zero. In the Arctic, evaporation and

    transpiration aggregate to a total of less than 4 inches per year.

            Figure 8 shows the results of ground-temperature studies for three

    stations. One station, Barrow, Alaska, is located in the Arctic, while the

    other two, Fairbanks, Alaska, and Skovorodino, Siberia, are situated in the

    Subarctic. Evaporation and transpiration have been estimated for the

    Fairbanks region on the basis of prevailing average wind velocities and

    temperatures. These estimates would not be applicable in areas where the

    altitude exceeds 2,000 feet above sea level.



            Infiltration is the process by which water is absorbed by the earth’s

    crust. It entails the movement of water from the ground surface into the

    soil. To the agriculturist it represents a gain of water supply, and to

    the d c ivil engineer it represents a loss of surface runoff. Water entering

    the soil in this manner may relieve a soil-water deficiency, add to ground-

    water content with a corresponding rise in the water table, or percolate to

    025      |      Vol_I-0579                                                                                                                  

    Fig. 8 Ground Temperatures for Three Stations

    026      |      Vol_I-0580                                                                                                                  
    EA-I./ Straub and Johnson: Hydrology

    greater depths through taliks in the permafrost. The infiltrated water

    that replenishes a deficit in soil moisture is later taken up by roots of

    plants and returned to the atmosphere by transpiration. Some of this water

    may move by capillary action to the ground surface and there evaporate. The

    part that is added to ground water may be used by plants, provided the water

    table is sufficiently close to the surface. If the water table is too close

    to the ground surface, it deters plant growth as it then inundates and shuts

    off oxygen from small root fibers. The mesophyte and the xerophytes types of

    plants cannot endure this condition. Other portions of ground water result

    in ground-water flow above the permafrost and reappear at some lower eleva–

    tion in the watershed to augment stream flow. Infiltrated water that goes

    into deep seepage furnishes the supply for deep aquifers. These aquifers

    or underground reservoirs, which may be in the form of lenses, veins, or beds

    of pervious material, are usually located below the permafrost, but can be

    situated entirely within the permanently frozen layer.

            The rate at which water infiltrates into the soil is called infiltration

    capacity and is dependent upon many factors. At the beginning of supply, either

    in the form of rain or melting snow, infiltration rates are high. As the

    supply continues, the rate at which the ground absorbs water diminishes and

    approaches an ultimate minimum but constant value. There are three logical

    explanations for this behavior:

            ( a ) Initial rates are high as they are associated with a soil-water

    deficiency, and capillary action supplements the motivating force until the

    defici e t is replenished.

    027      |      Vol_I-0581                                                                                                                  
    EA-I. Straub and Johnson: Hydrology

            ( b ) The impact of falling raindrops has a tamping effect that diminishes

    the size of surface pores and interstices through which subsequent infil–

    trated water has to pass.

            ( c ) Upon wetting, colloidal soil material swells and in that manner

    partially fills the voids.

            In the polar regions of Alaska, this third item is of little signifi–

    cance as the colloidal content of most soils is commonly quite small. Factors

    which influence both the initial infiltration rate ( f o ) and the ultimate

    minimum but constant rate ( f o ) are in order of significance: ( a ) thermal

    condition of the surface and active layer, ( b ) type of vegetal surface cover,

    ( c ) soil texture, ( d ) nature of supply (melting snow or rain), and ( e ) soil


            For polar regions, the most important influencing factor of infiltration

    is the thermal condition of the ground surface and of the entire active layer.

    The permeability of any frozen saturated soil is quite small. The depth to

    the impervious permafrost varies a great deal and influences the amount of

    water that can be infiltrated. The rate at which water can pass through

    small interstice h c hannels of soil depends to a great extent upon viscosity,

    which, in turn, is influenced by temperature. A 50°F. increase in soil and

    water temperatures should approximately double the infiltration rate. Cooling,

    however, increases surface tension and capillary forces are strengthened.

    Freezing of soil is accompanied by a movement of water from warmer to colder

    areas. A nonuniformity in homogeneity of surface soil layers will result

    in a nonuniformity of moisture content, and continued freezing results in

    numerous cracks. This tends to increase infiltration rates in the spring.

    A frozen ground surface may also influence the infiltration rates of lower

    layers (3).

    027a      |      Vol_I-0582                                                                                                                  
    EA-I. Straub and Johnson: [?] H ydrology

            Closely associated with the thermal condition is the type of vegetal

    surface cover. After only slight disturbances in the natural cover in arctic

    and subarctic areas, the thermal regime of the ground might be expected to

    change tremendously. Removal of the surface cover destroys natural insula–

    tion, with a consequent result of degradation or melting of permafrost. The

    thickness of the active layer increases. At first there is an abundance of

    moisture from the melting permafrost; as the action continues and the

    active layer becomes thicker, internal drainage improves. Ability to

    infiltrate water becomes greater and the possibility of transmitting water

    by ground-water flow is improved. Local farmers have noted a progressive

    decline in yield of crops as years of operation increases. They are inclined

    to believe that the cause is a depletion of soil fertility. Although this

    is no doubt a contributing factor, the authors believe that a diminishing

    supply of water for plant growth aggravates the situation. During the first

    few years of crop production, the permafrost table is relatively close to

    the surface and melt waters from the degrading process are within reach of

    plant roots. In this manner the moisture supply, by reason of rainfall, is

    augmented and excellent yields result. A few years later the degrading

    process has lowered the permafrost to depths that cannot readily be reached

    by plants. In addition, the thickness of the active layer has increased

    by a corresponding amount and internal drainage has improved. The infil–

    trated water in excess of soil moisture deficiencies would have avenues

    of escape without being available to plants.

            Most of the factors that affect infiltration (all except ( c )) vary

    with the season of the year. Surface cover increases in density in the

    summer. The moisture content of the soil is high in the spring and low in

    028      |      Vol_I-0583                                                                                                                  
    EA-I. Straub and Johnson: Hydrology

    the fall. The thermal condition changes from very cold in the fall, winter,

    and spring to warm in the summer. Soil texture remains constant throughout

    the season, but soil structure may very due to burrowing of animals. The

    nature of moisture supply is self-explanatory.

            Analysis of the recession side of several multipeak hydrographs during

    periods following excessive rains indicates a unique behavior. Apparently

    a considerable residual of the rain does not reach stream channels via

    surface flow, as the area contained beneath the peak of the hydrograph and

    bounded on the sides by the steep ascension and declension amounts to only

    a small part of the rain. The area contained beneath the “concave upward”

    part of the receding side appears abnormally long and represents a large

    part of the supply. The first impression is that the drainage basin must

    contain large areas of lakes and swamps, but this is not the case. Infil–

    tration into a surface layer of high absorptive capacity seems a plausible




            Runoff is the residual part of precipitation that escaped the action

    of interception, evaporation, transpiration, and deep seepage. It is

    represented by the water that flows from the earth’s crust, and consists

    of a part that has never been below the surface, called surface runoff,

    and a part, subsurface runoff, that has previously passed into the soil

    by infiltration but subsequently reappeared at the surface. Stream and

    river discharges are usually made up of a combination of both surface and

    subsurface water which vary widely in proportion. Of the two, the water

    that reaches natural drainage channels via overland flow is by far the

    029      |      Vol_I-0584                                                                                                                  
    EA-I. Straub and Johnson: Hydrology

    more unstable and fluctuates widely with climatic conditions. Subsurface

    flow is quite steady but may range from a magnitude of zero for some drain–

    age basins to relatively large values for others. Fluctuations in short–

    time periods are usually small, with large variations confined to longer

    durations such as weeks, months, or seasons of the year. In general it is

    difficult to separate surface from subsurface runoff by analysis of records

    of river discharge. Stream flow after an extended drouth drought may be made up from

    underground sources or the result of a change in stage of areas of surface

    storage such as lakes and marshes. Flow from a combination of these two

    sources is not uncommon.

            When snow melts or rain begins to fall at intensities which are in excess

    of infiltration capacity, a thin layer of water is formed at the surface, and

    overland flow begins down slope. As the supply of water continues, surface

    depressions of variable size are filled and start to overflow. The thin

    layers of water enter small channels which join to form rills; the rills

    combine to form rivulets that eventually merge with natural drainage channels.

    The whole process is accompanied by lateral flow from the land surface along

    the length of each collecting rill or channel. This entire hydrological

    process is further complicated, not only by evaporation which is taking

    place at the same time, but also by erosive action of flowing water which

    exposes new ground-surface areas with attendant variations in the rate of

    infiltration. Depression storage may sudden t ly be released by the displace–

    ment of a small clod of earth. The capacity of a layer of snow to hold

    water may suddenly be exceeded by overland flow from an adjacent area, thus

    abruptly releasing larger volumes of runoff. Obviously, evaluation of rates

    of runoff is extremely complex.

    030      |      Vol_I-0585                                                                                                                  
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            On the basis of information contained in preceding sections of this

    article, it seems reasonable to expect that, for corresponding rates of

    supply, the runoff in arctic and subarctic regions would be higher than in

    more temperate zones. Because of cool temperatures, evaporation and trans–

    piration are quite low. Permanently frozen ground close to the surface

    is widespread and deters infiltration. Interception is of a relatively

    small magnitude because the density of vegetation is not high. The residual,

    then, of precipitation must be large.

            Stream-flow data for polar areas are meager. The records of discharge

    of rivers in Alaska are confined to specific areas where knowledge of mini–

    mum flows would be of importance to mining operations. No record is con–

    tinuous for more than six years. There is a great demand for resumption

    of stream-flow measurements. Most of the work that has been accomplished

    along this line was carried out in the period from 1906 to 1915. The data

    are contained in Water - Supply Papers 314, 342, 345, and 372 of the United

    States Geological Survey.

            Of special interest is the record of discharge of the Yukon River at

    Eagle, Alaska. At this point the watershed is 122,000 square miles and

    embraces large areas of the Canadian Subarctic. Table 2II (4) shows the mean

    monthly flow in cubic feet per second and also in inches of runoff from the

    watershed. The monthly precipitation at Eagle is indicated for purposes

    of comparison. It is to be noted that the precipitation at Eagle, although

    indicating the general trend of runoff, does not necessarily denote moisture

    supply for the entire watershed. Eagle is located at a comparatively low

    elevation and therefore does not receive as much precipitation as do the

    areas of higher altitude.

    031      |      Vol_I-0586                                                                                                                  
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            Figure 9 contains hydrological information with respect to the Yukon

    River watershed at and above Eagle, Alaska. The mass diagrams point out a

    close association between precipitation and runoff. During the period of

    record, 10,900 cubic feet per second was the minimum flow. All surface

    runoff ceases after November first of each year, and river discharge

    diminishes at a progressively decreasing rate until melting of snow begins

    in the following spring. It is believed that the larger part of this winter

    flow results from a decrease in lake and river storage and not from ground–

    water flow, as is often suspected. This would mean a 2-foot reduction in

    stage of a storage area of approximately 5,000 square miles, and does not

    sound unreasonable. Earlier it was pointed out that, in arctic and subarctic

    regions, a large precipitation residual or runoff was to be expected. The

    mass curves of Figure 9 corroborate this point of view. In the three-year

    period, water losses equaled about 10 inches, and there were nearly 25 inches

    runoff out of approximately 35 inches of supply. It is estimated, however,

    that the climatological station of Eagle is not representative of the whole

    Yukon watershed above this point and that the average available moisture and

    losses would be higher. The runoff figures are considered to be quite

    accura g t e.

            Table 3 III (graphical) contains runoff data for five watersheds on the

    Chatanika River. It is of interest to note that runoff i s n altitudes of

    from 2,000 to 5,000 feet exceeds the runoff from lands of lower elevation.

    It is fairly certain also that precipitation at the higher altitudes exceeds

    the amounts indicated by the station at Fairbanks, which is at an elevation

    of about 500 feet. It would hardly be possible otherwise to have the runoff

    indicated for the Faith Creek watershed. Even though July is one of the

    032      |      Vol_I-0587                                                                                                                  

    TABLE 2

    Runoff and Percipitation Data for Yukon River above Eagle, Alaska
    Month 1911 1912 1913
    Runoff * Runoff * Runoff *
    Jan 21000 0.20 .27 21000 .20 .10 21000 .20 .62
    Feb 15000 .13 .10 15000 .13 .29 15000 .29 .41
    Mar 11000 .10 .39 11000 .10 .11 11000 .10 .65
    Apr 12000 .11 .97 12000 .11 Tr 12000 .11 .64
    May 156000 1.48 2.87 125000 1.18 .43 117000 1.10 .39
    June 184000 1.72 1.26 160000 1.47 2.09 199000 1.88 .37
    July 178000 1.68 2.16 147000 1.38 2.92 164000 1.50 1.06
    Aug 139000 1.31 2.65 127000 1.20 2.48 133000 1.26 2.74
    Sept 106010 .97 1.21 73600 .67 .76 90000 .81 .56
    Oct 60000 .57 .13 51000 .48 1.66 55000 .51 .78
    Nov 37000 .34 .29 37000 .34 .24 37000 .34 .26
    Dec 28000 .27 .80 28000 .27 1.10 28000 .27 .46

    * Denotes precipitation in inches at Eagle, Alaska.

    033      |      Vol_I-0588                                                                                                                  

    Figure: Table 3

    Runoff data for five watersheds in Alaska

    034      |      Vol_I-0589                                                                                                                  

    Fig. 9 Hydrological Data Pertaining to the

    Yukon River Above Eagle, Alaska

    035      |      Vol_I-0590                                                                                                                  
    EA-I. Straub and Johnson: Hydrology

    wetter months, little runoff occurs. During this month all vegetation is

    at an advanced stage of growth and utilizes soil water at a high rate;

    this holds true for August as well. There was no runoff in the smaller

    watersheds in October, which indicates nearly a total absence of ground–

    water flow in the basin. The variations in runoff from five watersheds,

    all located adjacent to each other and within the Chatanika River basin,

    emphasizes the role topography plays in hydrological phenomena.

           The three plates (1, 2, and 3) of photographs that follow demonstrate

    four river patterns that are common to the Arctic and Subarctic. The Yukon

    River at Eagle flows through a broad, flat valley. It is made up of a

    meandering pattern of many sinuous streams, each of which carries varying

    proportions of the total discharge depending on ever-changing short-term

    conditions. One or several of the individual serpentine channels may become

    blocked by floating ice, causing an increase in stage and a greater flow in

    the open routes. The increased erosive power of the greater flow cuts the

    occupied channels deeper and wider, or it is often the case that new avenues

    for water passage are developed and others abandoned. Deposition of sediment

    takes place in the sections of decreased flow. Abandoned serpentine channels

    often contain still water and take on the appearance of lakes to be invaded

    by emergent vegetation and attendant formation of peat. The entire process

    continues from year to year. The braided stream pattern of the Sagavanirkto l k

    River (see Plate 1) differs considerably from the Yukon. Transverse limits

    are relatively narrow and the profile declivity is steeper. Shifting of the

    channels within the river bed occurs quite frequently and is probably a

    function of changes in sediment load. Bed materials are coarse. Streams

    with small watersheds, exemplified by Plate 2 which shows Crooked Creek near

    036      |      Vol_I-0591                                                                                                                  
    EA-I. Straub and Johnson: Hydrology

    Central , Alaska, have not yet reached any form of equilibrium. The channel

    bed is aggrading in down-valley reache d s and degrading in the up-valley.

    Many of these small streams flow intermittently and freeze solid in the

    winter. The beadlike streams on gently sloping land near Umiat, Alaska,

    are the result of a thermal process. The small circular ponds vary in size

    with little or no regularity of spacing. Each pond represents an area of

    high heat-conductivity capacity in comparison to its immediate surroundings.

    Permafrost in within a few inches of the ground surface. This type of river

    channel is illustrated by Plate 3.

           Floods of the Arctic and Subarctic occur frequently and are the result

    of three causative factors. It is of interest to note that there are no

    river floods due to heavy rains in the polar areas of Alaska. Ice is no

    doubt the largest single causative factor of high river stages. During

    spring break-up, large masses of floating ice become blocked at bends or in

    narrow reaches of channel where floating material is apt to lodge. As flow

    continues, more ice is added until eventually the entire channel is clogged.

    It is not uncommon for these jams to build up to heights of 25 feet or more,

    with a consequent and corresponding increase in river stage. These ice dams

    usually occupy a considerable length of channel and possess surprising struct–

    tural stability. When failure eventually does occur, another flood down-valley

    from the site of the jam is generated. This, of course, is created by the

    sudden release of large volumes of store s d water when the ice jam fails. Floods

    in varying degrees of severity, produced in this manner, are yearly occurrences

    on many rivers in Alaska. Rivers that flow north or toward areas of cooler

    climate are particularly susceptible. The Yukon and Kuskokwin rivers, although

    flowing in a westerly direction, break up progressively downstream. Lands close

    037      |      Vol_I-0592                                                                                                                  
    EA-I. Straub and Johnson: Hydrology

    to Bering Sea are subjected to a cooling effect from the sea and do not

    warm up as fast as lands of the interior regions near the source of the


           In Alaska preventive measures entail the bombing of the ice dam as

    soon as possible after formation commences. Experience thus far indicates

    that a 500-pound bomb, equipped with a delayed-action fuse, is quite

    effective. Bombing technique calls for placement of the missiles in a

    progressive pattern, with the first ones dropped near the downstream a e nd

    of the ice jam. Often it is essential to rescue residents of flooded villages

    by landing with helicopters on the roofs of buildings.

           Melting of snow often results in floods, particularly on large watersheds.

    The second highest flood in history occurre e d on the Chena River at Fairbanks

    and on the Tanana River at Nenana in May 1948, as a result of melting snow

    in areas of higher altitude. The highest known flood at Fairbanks occurred

    in May 1937 and resulted from an ice jam.

           The third cause of a river flood is the structural failure of glaciers.

    Floods produced in this manner are usually late summer or early fall occur–

    rences. An interesting example is Knik River in Alaska. This river drains

    an area of about a thousand Square miles and rises in Knik Glacier of the

    Chugach Mountains. During the warm climate of the spring and summer months,

    George Lake rises in stage as snow and ice melt, forming runoff which runs

    into the lake. While the lake is filling, a melting process degrades an arm

    of Knik Glacier which dams the lake’s outlet. This action continues until

    the increased pressure of the rising lake stage exceeds the structural strength

    of the ice dam. Sudden collapse results in flood discharges and a recession

    of the stage of George Lake. When high flow subsides and colder weather sets

    038      |      Vol_I-0593                                                                                                                  
    EA-I. Straub and Johnson: Hydrology

    in, Knik Glacier extends another arm of ice to block the outlet channel.

    This flooding procedure takes place every year and produces discharges

    that occupy about 30,000 square feet of river section.

           Glacier-fed streams are usually not in any form of equilibrium in

    either slope or form of channel. The stream bed is braided ordinarily and

    the individual channels may shift transversely from season to season or

    during a period of high runoff. Detritus, produced by a melting glacier,

    varies in quantity with the seasons of the year, the larger amounts occurring

    in the summer. There is no uniform pattern of production or composition of

    the product. Often loads of sediment reach upper sections of the channel in

    excess of stream , competence, and the discharge is unable to carry it away.

    A building up of the stream bed is then inevitable. At other times the capa–

    city of the flowing water to carry detritus is in excess of the influx of

    sediment. The consequent result then is a process of degrading or lowering of

    the channel bed. These two actions take place in an alternate fashion, depend–

    ing on the amount and composition of solid material that is produced by the

    melting and sometimes flowing glacier. Thus far, the up-building forces

    seem to predominate as it has been noted that many of the streams of glacial

    origin flow over deep deposits of debris. During periods of low flow, glacier–

    fed streams can be identified by the milky appearance of the water. This

    condition is brought about by the sediment that is transported in suspension.

    039      |      Vol_I-0594                                                                                                                  
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            most without exception, the physical difficulties that are encountered

    in northern settlement and construction, originate by reason of changes that

    are produced hydrologically. Some of the physiographic changes are discussed

    in the following paragraphs and are illustrated with photographs.

            Erosion . In arctic and subarctic regions there are two definite types of

    erosion in addition to the sheet and gully types which are encountered in

    more temperate zones. Both of these types, peculiar to polar conditions, are

    associated with the thawing of frozen soil. Both occurrences are influenced

    by movement of water, not only in an abrasive action, but also as a conductor

    and transmitter of heat that accelerates the rate of thaw.

           Bank erosion is illustrated by the photographs on Pla z t e 4. The soil a

    short distance beneath the ground surface is permanently frozen. Wave and

    tide action subject a l ayer of permafrost at the water line to the movement

    of water that is considerably warmer than the frozen ground. Thawing is

    accelerated and large sections of bank are undercut. Eventually the weight

    of the undermined portions becomes too great to be offset by the resistance

    to shear of the material above the water line, and huge chunks break off.

    This characteristic process of erosion is continuous and the consequent effect

    damaging. At Bethel, Alaska, several hundred feet of bank and an entire

    peninsula have washed away. It has been necessary several times to move

    village buildings back, away from the ever-receding shore line. The last

    such move was in 1939, and since that time the bank has cut back about 200 feet.

    The top photograph of Plate 5 shows the shore-line condition of Bethel in 1913.

    Note the contrast with conditions indicated in 1948 by the lower picture on

    the same plate.

    040      |      Vol_I-0595                                                                                                                  
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    Runoff water, flowing in rills over a frozen active layer in the spring,

    accelerates thawing of the soil on the bottom of the small channel. Newly

    thawed soil, of medium texture and single-grain structure, which is typical

    of much of the soil in polar areas, takes the form of a plastic fluid and erodes

    readily. The active layer is usually not homogeneous in composition, and the

    frozen crust is not uniform in thickness. The thawing and erosive action of

    the rill may then penetrate the frozen lamina, and a part or all of the flow

    will percolate into unfrozen material. This permeable material is bounded

    below by impervious permafrost and above by the still unthawed active layer.

    As runoff continues, the unfrozen material becomes saturated and nydrostatic

    pressure builds up. Eventually the head created in this manner becomes

    sufficiently great to erupt another weak point in the active layer at some

    distance down slope. Underground flow then takes place between the upper

    penetration and the lower erupted outlet. The saturated subsoil erodes easily

    and a cavern, which later collapses, is excavated. This process of erosion

    is very common in the Subarctic, but rare in the Arctic. In the latter, the

    top of the permafrost coincides with the bottom of seasonal freezing; conse–

    quently, there could be no ground-water flow between the two. This hydrologi–

    cal condition must be taken into account in the design of drainage facilities.

    The photographs on Plates 6 and 7 illustrate this type of erosion.

            Solifluction and landslides are very common in polar regions and are

    closely associated with erosion. When ground of fine texture thaws, it becomes

    plastic, so to speak, and frequently forms a mudlike paste which if located

    on a relatively steep incline will slowly flow down slope. This is called

    solifluction and differs from erosion in that outside water is not essential

    for transportation, as the mass itself acts as a fluid. A common cause of

    041      |      Vol_I-0596                                                                                                                  
    EA-I. Straub and Johnson: Hydrology

    landslides is the concentration of moisture immediately above the impervious

    permafrost. If this occurs on a slope in proximity of a river where the

    inclination of the permafrost table is quite steep toward the river, sliding

    of unfrozen ground along the permafrost surface will take place. Actions of

    this kind have been known to shear well casings and cause destructive damage

    to highway and railroad grades. Not much can be said with regard to preventive

    measures except that it is essential to be cognizant of the hydrological

    phenomena during preliminary investigations, and sites should be selected

    accordingly. Human activity may also disturb the thermal and hydrologic

    regimes sufficiently to aggravate the situation.

            River Performance . Earlier in this discourse, explanations were made

    of hydrological phenomena that affect the behavior of streams and rivers. It

    was pointed out that ice jams caused high river stages. This alters consider–

    ably the stage-discharge relation, as great depths of water may occur without

    an appreciable discharge. Consequently, a rating curve for streams in the

    northern latitudes does not have the same significance that it implies in

    more temperate zones. It was noted also that the individual streams that

    make up a braided channel shift in transverse direction from year to year,

    season to season, and sometimes within one high flow period. This influences

    the stage-discharge relation. A third factor affecting the behavior of rivers

    is the phenomena of high discharges that result subsequent to the structural

    failure of a glacier. In this instance it is axiomatic that rainfall is not

    associated with either a high stage or discharge.

           The ultimate conclusion with regard to the behavior of streams and rivers

    in polar regions is that analysis cannot be made with the tools the hydrologist

    ordinarily employs. The unit hydrograph gives no indication of flood heights

    or discharges, as intense rain is not an important cause of floods. For the

    042      |      Vol_I-0597                                                                                                                  
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    same reason, intensity-duration-frequency relations of rain cannot be

    associated with the frequency of high river discharges. There is a relation

    for very small watersheds and of course, the ultimate yield of yearly runoff

    must depend on precipitation. Melting of snow is closely associated with

    river floods, but here a combination of snow-melt and ice jams complicates

    river performance. Even though melting of snow is susceptible to analytical

    treatment, insofar as rate of melt is concerned, the rate of runoff produced

    thereby is another matter which is more complex and not thoroughly understood.

    In one section of a watershed, runoff may be perceptibly lower than the rate

    of melt because of storage as capillary water in the snow, while at other

    locations, an increase in runoff results from a sudden release of stored water as

    the snow ripens. Projection of this process and its relation to ice jams and

    river performance is a lucrative and necessary field for future research.

           The depth to the permafrost table below rivers is commonly much greater

    than the corresponding distance below the ground surface in general. Consider–

    able ground-water flow occurs along the route and below the bed of most rivers.

    The surfaces of rivers freeze after cold weather sets in and simultaneously,

    if not slightly previously, overland flow ceases. Ground-water flow into

    streams becomes progressively less as the depth of freeze penetrates the

    active layer. If the active layer freezes entirely, all ground-water flow

    into natural channels stops. Then the source of river supply is artesian,

    through taliks in the permafrost and ground-water flow beneath the channel

    bed which reduced sub-bed storage in upper reaches. As the winter season

    advances, river ice becomes progressively thicker and often freezes to the bed.

    Ground-water flow in the sub-bed continues and, if there are no artesian

    sources of supply, this flow becomes progressively less as upriver sub-bed

    storage is gradually depleted.

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    It is often the case that the sub-bed flow capacity of a river section

    is less than that of adjacent and successive upriver sections. In this case

    hydrostatic pressure is built up, and water is forced to the surface through

    weak points and cracks in the river ice. Here, exposed to the cold atmos–

    phere, it freezes in consecutive laminar layers and may cover larger areas.

    The thickness of each layer is dependent on the rate of flow and intensity

    of cold. It is not uncommon to find river ice built up, in this manner, to

    thicknesses as high as 20 feet. It may submerge highway bridges and culverts

    as well as form obstructions at other locations to impede river performance in

    the following spring. Hydrological aspects of design must reckon also with the

    force of large and thick layers of floating ice. Illustrations of river ice

    are shown by the photographs on Plates 8 and 9.

           In summary, it must be admitted that the performance or behavior of

    streams and rivers in polar regions is much unlike that which takes place in

    more temperate areas. So far very little has been accomplished in the way of

    river regulatory works, and there are insufficient data to form the basis o for

    the hydrological design of as ordinary a structure as a river bridge.

            Changes Which Result upon Alteration of the Thermal Regime . After an

    elapse of time, ground temperatures become oriented in a manner of equilibrium

    so that heat taken up by the soil in warm seasons is equal to that given off

    during colder parts of the year. This regime is affected by many things, yet

    the type and density of vegetal growth is very prominent. This seems to act

    as a protective insulating layer, and, if disturbed, a number of odd physical

    changes occur. Each of several of these are discussed in the following

    paragr a phs : .

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    ( a ) Agricultural. Several fields in the subarctic area of Alaska

    had to be abandoned for agricultural purposes because of uneven settlement

    due to the thawing of ground ice. Apparently the removal of the natural

    vegetation accelerated thawing of the ground sufficiently to melt lenses and

    wedges of ice which are commonly found in fine-textured subarctic soils.

    Soil above the location of the ice then caves in, creating irregular and

    sometimes deep depressions at the surface. Some of these depressions are

    sufficiently deep and large to stop the use of ordinary farm machinery.

    Plate 10 shows the location of two fields which were altered in this manner.

    Pictures on Plate 11 are close-up on-the-ground views of field 2. It is of

    interest to note that field 1 is located on a slope which faces south, while

    field 2 is situated on a slope that faces north. Even though the illustra–

    tions indicate a greater change in topography in the form of sinks, ravines,

    and humps on north-facing slopes, it is inconclusive that directional aspects

    have more than minor contributory influences. The essential requirement for

    this formation is a subsoil in which there is an abundance of ground ice in

    the form of lenses and wedges. As long as the natural insulating cover in

    the form of moss and other vegetation remains undisturbed, the thermal

    condition maintains the ground moisture in a solid state. In agricultural

    operations, this surface covering is removed and the land plowed. Heat

    absorption is increased, permafrost degrades, ice lenses and wedges melt, and

    surface soil caves in to occupy the space which was formerly filled with ice.

    Russians use the term thermokarst to designate topography that is formed in

    this manner. In some respects the sink holes, ravines, and depressions resemble

    those that develop in limestone terrains due to the solvent action of water.

    It is obviously essential to make careful exploration of ground - water and

    045      |      Vol_I-0600                                                                                                                  
    EA-I. Straub and Johnson: Hydrology

    ice conditions before going into the expense of clearing and preparing an

    area for agricultural purposes. Scientists believe that research would

    disclose some surface feature characteristic that would be peculier to this

    type of subsoil condition.

           Another cause of surface deformation is the melting of permafrost, the

    soil of which was saturated before freezing initially. This, however, is

    quite uniform and does not give much trouble to the farmer, although percep–

    tible settlement takes place. It is important to avoid both conditions as

    sites for engineering construction.

           ( b ) Cave-In Lakes. Closely associated with ( a ) are natural cave-in

    lakes. These occur on land, the subsoil of which is saturated and frozen,

    or contains a large number of lenses and wedges of ice. The melting begins

    when the natural surface vegetal cover is removed by fire or windstorm.

    Settling occurs to replace the space occupied by the frozen material. The

    surface depression becomes filled with water and, as this is a good conductor,

    thawing is accelerated in lateral directions. The circular pond area becomes

    larger and larger in diameter and often joins other adjacent areas to form a

    larger, irregular-shaped cave-in lake.

           A lake formed by this thermal process can be detected rea d ily by the shape

    of trees located near the shore line. The rate at which the pond is enlarging

    and the shore line receding can be estimated by the length of vertical growth

    of the tree that is above the top of the inclined trunk. The difference in

    age of trees which are entirely surrounded by water and those which are still

    on higher ground is also an important criterion.

            D C ave-in lakes are usually quite shallow and have no outlet for surface

    outflow. These depressed areas would not contain water if the permafrost table

    046      |      Vol_I-0601                                                                                                                  
    EA-I. Straub and Johnson: Hydrology

    were at great depths below the ground surface, as then there would be an

    avenue of escape via percclation into subsurface material. Two views of a

    typical cave-in lake are shown on Plate 12. Two other classes of lakes

    typical of polar regions are shown on Plate 13. The top picture of this

    plate exemplifies lakes that are numerous in glaciated regions. The lower

    photo illustrates the many elongated bodies of water peculiar to arctic

    coastlands of Alaska. In addition to the cave-in, morainic, and elongated

    types, the authors have noted two other classes. One class, called marginal

    lakes, is described on page 55 ; the other is the serpentine body of water

    that occupies an abandoned river channel.

           ( c ) Drainage Channels. Flowing water has a marked influence on the

    thermal regime of the ground. The permafrost table below rivers is at much

    greater depths than below the general ground surface. An artificial drain–

    age channel, then, will destroy the natural thermal equilibrium, and the

    permafrost will degrade, depending on the volume and temperature of the

    flowing water. Figure 10 illustrates the effect on permafrost of a small

    road ditch near Fairbanks, Alaska. Before construction in 1946, the perma–

    frost table was about 2 feet below the surface. In 1948, the top of the

    permanently frozen ground had lowered about 9 feet. One can readily imagine

    the consequent results should an artificial drainage channel traverse areas

    where ground ice is present in the subsoil. Maintenance requirements of

    mining company diversion canals are very high, and maintenance personnel

    have noted considerable difficulty due to settlement of various reaches.

            Changes , the Result of Soil Freezing . The mechanics of soil freezing

    are very complex and not fully understood, and there are some differences of

    opinion among scientists as to various phases of the freezing process. Rather

    047      |      Vol_I-0602                                                                                                                  

    Fig. 10 Influence of a Drainage Ditch on the

    Thermal Regime of the Ground

    048      |      Vol_I-0603                                                                                                                  
    EA-I. Straub and Johnson: Hydrology

    than cover the topic from a technical point of view, it is the intention here

    to point out gener a lized aspects, in terms of present-day thinking, together

    with an enumeration of some well-known manifestations.

           Until quite recently, volumetric increases which accompany the freezing

    of some soils were attributed to the difference in volume of water between

    its sol d i d and liquid states. Now it is generally conceded that this property

    of water has b v ery little to do with frost heaving and the expansion of some

    soils upon freezing. Taber (12) has shown that expansion of water due to

    freezing is not at all the fundamental cause of heaving for experiments in ✓ 1 word missing cf. original p. 50

    which water has been replaced by other liquids which decrease in volume when

    frozen have shown strong heaving d ru ur ing freezing. The principal reason for

    volumetric increases is that, in the freezing process, water moves from warm

    to colder areas and thereby supplements the moisture content of the frozen

    zone. It has been observed also that water freezes readily in the large

    capillary voids, but in the very fine interstices water may remain in the

    liquid state to temperatures as low as −78°C. The water supply to the

    freezing layers in frost-heaving ground comes almost entirely from capillary

    flow of the water below (1).

           From the preceding brief statements relative to the freezing process,

    it is quite apparent that frost heaving is dependent on the distribution of

    water within the earth’s crust and is therefore a hydrological phenomenon.

    If there is no water supply available within reach of capillary forces, very

    little if any volumetric changes occur. Likewise, if soil texture is coarse

    and possesses low capillary capacity, there is very little swelling irrespec–

    tive of moisture supply.

    049      |      Vol_I-0604                                                                                                                  
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    Frost heaving is obviously not confined to polar regions, as it may occur

    any place where below-freezing temperatures prevail for some time. In the

    colder regions, however, there are many manifestations of it that are not en–

    countered elsewhere. In the Arctic, particularly along the coast, there is

    little likelihood of frost heaving because the layer of seasonal tha t w is very

    thin; consequently, there is no space for moisture supply. In the southern

    portions of the Subarctic, the relatively thick layer of unfrozen material

    between the top of the permafrost and the bottom of seasonal frost tends to

    minimize the swelling action. It is between these two extremes in location

    that frost-heaving forces predominate.

           Soil freezing when associated with ground-water flow provides a combina–

    tion of forces that causes the formation of conspicuous frost mounds. These

    may vary widely in height, shape, and horizontal extent. Their duration may

    be seasonal or continuous. Although very little is known with respect to

    morphology of frost mounds, the following terms are generally accepted : .

            ( a ) Frost blister is an up-warp of ground produced by pressure of

    ground water. It is ordinarily confined to a small area along sloping ground

    and is quite small in size. These mounds usually break or crack near the

    dome, providing in that manner an avenue for re p lease of ground-water flow.

    Russian observers have reported sudden eruption of frost blisters.

           ( b ) Peat - mounds are small mounds located in swampy and tundra terrain.

    Their duration is not seasonal but extends many years. It is believed that

    they are associated with ice polygons and wedges , and the mechanics of the

    creation of one phenomenon develops the other as well. The mounds and polygons

    are usually found where the permafrost is close to the ground surface; conse–

    quently, ground-water flow is not present. It is thought that, by a redistri–

    bution of soil water during freezing, causing a movement from well-insulated

    050      |      Vol_I-0605                                                                                                                  
    EA-I. Straub and Johnson: Hydrology

    to comparatively bare zones, ice lenses or wedges are created in the bare

    zones. These wedges occupy more space than the liquid from which they were

    formed, and the well-insulated peat areas from which the water came is con–

    fined to less lateral space and thereby forced to assume an increase in

    height. Small hummocks surrounded by ice wedges are the eventual formation.

    These are readily identified in serial photography.

            ( c ) Pingo is an Eskimo term meaning a conical hill. The word is used

    here to denote a frost moun t d of large size and of long duration. Pingos

    are known to occur near rivers in flat, poorly drained areas of the Arctic.

    South of the tree line, the surface of a pingo is usually covered with a

    growth of brush and scraggly trees. The summit of the dome-shaped formation

    is usually cracked and fissured. Very little is known concerning the actual

    process of formation of its life cycle, once it is created. The pingo shown

    on Plate 14 is thought to be the largest in the arctic Alaska. It is located

    in the Ikpikpuk River valley in the lake-studded arctic coast region.

            Icings . The term icing refers to a mass of ice which forms during the

    winter by consecutive freezing of films or sheets of water. The source of

    water supply may be from springs, ground-water flow, river seepage, or from

    a combination of these sources. Icings are usually of irregular shape and

    may be in the form of fields, mounds which attain large dimensions, or

    incru s tations along slopes. The probability of occurrence is greater on a

    slope which faces south than on one which faces north. The surface of an

    icing is commonly very uneven and very difficult to traverse with any kind

    of mobile equipment. Most icings melt during the summer and reappear the

    following winter.

    051      |      Vol_I-0606                                                                                                                  
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    Ground-water flow is an essential requisite for the formation of ground

    icings. Other favorable factors of growth are:

           ( 1 ) Low temperatures of the air and only a thin cover of snow during

    the early part of winter.

            ( 2 ) Thick snow cover during the latter part of winter.

           ( 3 ) A low capacity for ground-water flow above the permafrost so that

    reduction of section by seasonal freezing builds up hydrostatic pressure

    which causes a flow to the surface.

           It is not essential for freezing of the active layer to penetrate to

    the permafrost table and thereby block all ground-water flow. It is entirely

    possible for water to reach the surface with just a partial damming of the

    ground-water section. Ordinarily, ground icings occupy quite small areas and

    have the general shape of a mound. Incrustations form when water seeps to the

    surface at many points of about equal elevation. Over-all size of icings

    vary perceptibly, depending on hydrological conditions and the water supply.

    Observations in Alaska noted heights of from a few inches to several feet,

    and areas of from 0.1 acre to 5 or 6 acres. In practically every case these

    icings were found along highways where human activity had disturbed the

    thermal regime of the ground.

           Icing mounds form near springs. These mounds are usually quite large,

    depending on the discharge. One icing located in the Mom y a River valley in ✓ (checked with Be

    Siberia is more than 12 miles long, 4 miles wide, and averages nearly 12 feet


           River icings were discussed in a previous section.

            All types of icings may cause extensive damage to roads, bridges, buildings,

    and other engineering installations. Icings may completely cover highways and

    052      |      Vol_I-0607                                                                                                                  
    EA-I. Straub and Johnson: Hydrology

    stop traffic. River icings are especially destructive to bridges and may

    at times completely engulf them and overflow the road. Explosion of icing mounds whole line missing cf. original p. 53 bottom

    cause great road damage. Icings in tunnels may attain a size sufficient

    to interfere with traffic. Buildings erected on permafrost may cause the

    underlying active layer to thaw out and thereby form a space up which ground–

    water flow may come to the surface. In some cases buildings have become

    completely filled with ice. Photographs on Plates 15, 16, 17, 18, and 19

    illustrate various forms of icing.

           Many innovations and methods have been employed to eliminate or

    ameliorate the destructive action of icings. Four measures to eliminate the

    cause of formation have met with success in varying degrees and are enumerated

    as follows: ( 1 ) Draining the site of icing or diverting the flow of water

    which feeds the icing. ( 2 ) Construction of frost belts, fences, and barriers.

    These cause the fields of icing to form upstream and away from the area that

    is to be protected. ( 3 ) Deepening and straightening of river channels. This,

    to be effective, must provide sufficient channel cross section below the depth

    of winter freeze to carry the stream discharge in winter. ( 4 ) Insulating

    stream channels.

           Although drainage is a basic active measure against the formation of icings,

    it is difficult, except in the case of springs, to maintain adequate facilities.

    If the ground is composed of fine silt, drainage channels will erode badly.

    Ground-water flow except from springs is usually of such a small magnitude that

    it freezes rapidly, necessitating insulation of conduits. Drainage measures

    should be carried out considerably in advance of construction, as there is

    always the possibility of some unexpected unfavorable effect on the ground.

           Frost belts, fences, and barriers are important measures against icings.

    Frost belts or dams consist of a specially constructed ditch, the object of

    053      |      Vol_I-0608                                                                                                                  
    EA-I. Straub and Johnson: Hydrology

    which is not to drain the water but to cause an early freezing of the active

    layer at a point which is sufficiently removed so that the induced icing will

    not damage the protected area. Vegetation is removed and a ditch is dug at

    some distance upstream from the area which is to be protected. Freezing along

    this ditch is more intense than elsewhere, as it has no insulating in the way

    of moss or other vegetation. [?] frozen wedge will be created, thereby damming

    ground-water flow. An icing will be induced above the frost dam. To be effect–

    tive, a frost belt should be constructed early in the winter before the first

    snowfall, preferably before the beginning of freezing weather. The snow should

    be kept off the frost belt until frost has penetrated the entire active layer.

    In some cases it is advantageous to add insulation in the form of snow to the

    adjacent area immediately uphill from the frost belt to encourage percolation

    at this point. Frost belts are used extensively to protect roads and bridges

    against the destructive effects of icings. In cases of large discharge, it

    may be necessary to add to the height of a frost dam by building fences or

    barriers on top of it. These do not have to be any more elaborate than the

    ordinary wood stave type of snow fence, as their function is merely to deter

    the flow of water sufficiently to cause freezing. Frost belts cannot be looked

    upon as a permanent protective measure, as in summer accelerated thaw in this

    area can be expected. In a few years the permafrost table will degrade below

    the depth [?] to which frost will penetrate in the winter and thereby leave

    sufficient space below the frost dam in which ground water can percolate.

           River icings often attain large dimensions and become destructive to

    roads and bridges. About the only protective measure that has thus far bden

    developed is the protection provided by deepening and straightening. This is

    not a permanent solution, as channels of a braided stream shift often in

    transverse position. Protection by means of channel improvement would be a

    continuous and very expensive maintenance problem.

    054      |      Vol_I-0609                                                                                                                  
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    Inadequate snow cover causes stream beds beneath bridges to freeze earlier

    and more intensely than adjacent river sections. This commonly results in

    severs icings at the bridge site. In many cases the most rational and economical

    protective measure is to insulate the river channel near the under the bridge.

    Insulation can be provided in a number of ways. Some of these are briefly

    discussed : .

            ( 1 ) Insulation Cover. The insulating cover consists of two layers, the

    lower composed of logs, branches, and brush. The upper layer is untamped snow

    about 1.5 feet thick. Peat or moss may be substituted for the insulating

    material. The cover should be installed in the fall of the year and extend

    across the entire width and length of the bridge, as well as considerable

    distances both upstream and downstream from the bridge site. It is quite an

    expensive maintenance undertaking, and the installation is not permanent. To

    be effective, the cover must be close to the area which it is supposed to

    insulate. It is therefore located below springtime flood heights.

           ( 2 ) Ice Crust Method. Small streams and ditches can be insulated by a

    layer of air formed under an ice crust. The channel is temporarily dammed

    and the water allowed to freeze at a predetermined level. After this process

    is complete, the dam is removed and the water level lowered. An intervening

    air layer from 10 to 15 inches thick is sufficient to prevent freezing of

    flowing water.

            ( 3 ) Snow Fence Method. In some regions it is possible to create suffi–

    cient insulation by the use of snow fences. These are erected along the length

    of the channel in such a way that the snow is deposited over the stream ice.

    Obviously this is not effective unless the section of channel is normal to

    the direction of prevailing wind.

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    Marginal Lakes (8). The five Berg lakes, situated on the margin of

    Bering Glacier, present some interesting features. These lakes are bordered

    on their landward sides by steep banks which are, in general, barren of

    vegetation and which are covered chiefly with glacial debris. The banks

    extend to an elevation of about 1,000 feet above tide, or about 200 feet

    above the level of the lakes. They are cut and built into well-developed

    terraces, which mark former stages of lake elevation. The lower terraces

    are entirely barren of vegetation, but the upper ones have a scant f g rowth of

    grass, herbs , and small bushes, which are only a few years old.

           The surface of the four western lakes is known to be at the same altitude

    (about 810 feet in 1905), and the fifth lake is probably at the same


           These lakes are certainly connected by water channels through the crevasses

    of the glacier, and possibly by open spaces under the ice. The surface of the

    ice is level, except where it rests against the land on the points between the

    lakes. The identity in the altitude of the lakes, the level surface of the

    ice between the lakes, and the way in which bergs break off on the margin of

    First Lake show that this arm of the glacier is floating in one large lake,

    of which the five Berg Lakes are only open areas. The surface of the glacier,

    after a gentle slope, descends in a low, crevassed ice fall to its floating


           The level of the lake is oscillating. The absence of vegetation on the

    lower terraces shows that it has fallen in recent years. In June 1905, it

    was rising several inches per day. The outlet of the lake, which is beneath

    the ice at the end of the long point south of First Lake, becomes choked with

    debris at irregular intervals. The water then rises until the pressure clears

    the outlet or until the water can flow on the surface around the end of the point,

    when the lake is emptied, causing floods in the valley of Bering River.

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            This section deals with some phases of ground-water hydrology with special

    reference to polar regions. A complete discussion, which would include quan–

    titative aspects of ground water, is beyond the scope of this paper. Occur–

    rences of ground water in the permafrost region are pointed out along with

    their relation to the hydrological cycle.

           Geology is a science that is closely associated with ground-water hydrology.

    The earth’s crust, which is composed of varied hard rocks and unconsolidated

    overburden, is a vast reservoir for the storage and conveyance of water that

    infiltrates through the surface material. The surface material of the earth

    is seldom solid rock. It contains many openings that vary in size and are

    often interconnected, permitting the percolation of water. In some cases the

    interstices may be of cavernous size and completely isolated. In polar areas

    an abundance of ground water remains in the solid state either as large lenses

    and wedges or contained in the small voids of the soil. The permanently frozen

    layer acts as an aquiclude through which movement of water does not occur

    readily. The permafrost contains many vertical and horizontal seams which

    remain unfrozen and through which ground water percolates in either an upward

    or downward directions. Figure 11 diagrammatically illustrates various forms

    of ground-water occurrence in arctic and subarctic regions.

           In the natural state there must be a form of equilibrium between supply

    and exhaustion of ground water. The amount of water that goes into ground

    water via infiltration must equal the quantities that escape as transpiration,

    discharge to lakes, streams, and springs. The most favorable period for recharge

    from precipitation is in the nongrowing season, when demands of vegetation are

    nearly negligible and soil evaporation is considerably reduced. Topography is

    057      |      Vol_I-0612                                                                                                                  

    Fig. 11 Ground Water Occurrences in Polar Regions

    058      |      Vol_I-0613                                                                                                                  
    EA-I. Straub and Johnson: Hydrology

    also an important factor. Steep slopes accelerate the rate of overland flow,

    leaving little time for water to infiltrate into the soil, while on flat

    slopes there is considerable ponding and thus a greater opportunity for

    ground-water recharge.

           Ground water in arctic and subarctic regions may be classified according

    to its occurrence with respect to the layer of permanently frozen material.

    The portion that is found above the permafrost is called suprapermafrost

    water. This is not abundant and would not serve as a source of water supply

    when w s easonal frost penetrates to the permafrost table. Along rivers and lakes,

    however, the top of the permafrost is usually depressed considerably, leaving

    a considerable area that does not freeze in winter. On low-lying islands

    and peninsulas it is not uncommon to find the permafrost table higher near

    the shore line than it is in the interior. This forms a large saucer, the

    bottom of which is impervious permafrost. Ground water is usually present under

    these circumstances. Ground-water flow takes place in the active layer by

    percolation down the slopes of the uneven top surface of permafrost. In winter

    when the active layer freezes from the top, this section for ground-water flow

    becomes progressively constricted. Ground water then finds its way to the

    surface and there freezes to form icings.

           Ground water that is within the permafrost layer is called intrapermafrost

    water. Much of this water exists in the frozen state, although it is not

    uncommon to find considerable liquid quantities as well. Unfrozen aquifers

    within the permafrost are called taliks and are most prevalent near the southern

    part of the Subarctic.

    059      |      Vol_I-0614                                                                                                                  
    EA-I. Straub and Johnson: Hydrology

    Subpermafrost water is ground water that lies below the permafrost layer.

    The supply of this form of water is usually abundant and exists in formations

    of many types. The water may be found in fissures, sandstone layers, and

    alluvial deposits. Penetration of the permafrost in the Far North in quest

    for water supply is a relatively expensive operation.

    060      |      Vol_I-0615                                                                                                                  
    EA-I. Straub: Hydrology


    1. Beskow, Gunner. “Soil freezing and frost heaving with special appl a i cation

    to roads and railroads,” Swedish Geological Society, 26th Yearbook No.3,

    1935. Tr. By J.O. Osterberg, Technological Institute of Northwestern

    University, November, 1947.

    2. Chekotillo, A.M. Naledi i borba s nimi . (Ice mounds and the struggle against

    them.) Moscow, Dorozhnoe Izdatelstvo Gushosdor, NKVD, 1940. Akademia

    Nauk SSSR. Institut Merzlotovedeniia Im. V.A. Obrucheva i Gushosdor.

    3. Dreibelbis, F.R. “Some influences of frost penetration on the hydrology of

    small watersheds,” Amer.Geophys.Un. Trans . [ ?] vol.30, no.2, pp.274-282.

    April, 1949.

    4. Ellsworth, C.E., and Davenport, R.W. Surface Water Supply of the Yukon-Tanana [ ?]

    Region, Alaska . Wash.,D.C., G.P.O., 1915. U.S.Geol.Surv. Wat.Supp.Pap .


    5. Bathaway, G.A. “Design of drainage facilities for military airfields,” Amer.

    Soc.Civ.Engrs. Trans . Vol.110, pp.697-730, 1945.

    6. Johnson, L.A. Investigation of Airfield Drainage, Arctic and Sub-Arctic

    Regions . Minneapolis, Minn., University of Minnesota, 1949. The

    University, St. Anthony Falls Hydraulic Laboratory Project, Rep . no.16, pt.1.

    7. Kersten, M.S. Thermal Properties of Soils . Minneapolis, Minn., University of

    Minnesota, 1949. Minn.Univ.Engng.Exp.Sta. Bull . no.28.

    8. Martin, G.S. “Geology and mineral resources of the Controller Bay region,

    Alaska,” U.S.Geol.Surv. Bull . 335. Wash.,D.C., G.P.O., 1908, pp,47-48.

    9. Muller, S.W. Permafrost and Related Engineering Problems . Ann Arbor, Mich.,

    Edwards, 1947.

    10. Showalter, A.K., and Solot, S.B. “Computation of maximum possible precipita–

    tion,” Amer.Geophys.Un. Trans . [ ?] pt.2, pp.258-274, 1942.

    11. Smithsonian Institution. Smithsonian Physical Tables . Prepared by Frederick

    Fowle. 8th rev. ed. Wash.,D.C., 1933. Tables 253, 254, 260. Smithson.

    Misc.Coll. vol.88; Publ .3171.

    12. Taber, S.M. “Frost heaving,” J.Geol . vol.37, pp.428-461, July, 1929.

    13. Wilson, W.T. “An outline of thermodynamics of snow melt,” Amer.Geophys.Un.

    Trans . [ ?] pt.1, pp.182-194, 1941.


    Lorenz G. Straub and Loyal A. Johnson

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