Arctic and Subarctic Hydrology

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EA-I. (Lorenz G. Straub and L. A. Johnson)

ARCTIC AND SUBARCTIC HYDROLOGY

       

CONTENTS

		Page
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	43
	Changes, the Result of Soil Freezing	44
	Icings	50
	Marginal Lakes	55
VII.	Ground Water	56
	Bibliography	60

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Arctic and Subarctic Hydrology

(Straub and Johnson)

       

LIST OF FIGURES

		Page
Fig. 2	Relation of atmospheric water holding capacity and temperature	9
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 Alaska	15
Fig. 7	A low ceiling confines avenues of incoming moist air and is thereby a limiting factor of precipitation	17
Fig. 8	Ground temperature s for three stations	25
Fig. 9	Hydrological data pertaining to the Yukon River above Eagle, Alaska	34
Fig. 10	Influence of a drainage ditch on the thermal regime of the ground	47
Fig. 11	Ground water occurrences in polar regions	57

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EA-I. Straub and Johnson: Arctic and Subarctic Hydrology

       

PHOTOGRAPHIC ILLUSTRATIONS

        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

Library.

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EA-I. (Lorenz G. Straub and L. A. Johnson)

       

ARCTIC AND SUBARCTIC HYDROLOGY

       

I. INTRODUCTION

        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.

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        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.

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        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

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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.

       

Glossary

        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.

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II. PRECIPITATION

        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

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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

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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

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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

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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.

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        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

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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	Temperature, °C.	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

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        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°)

(1)

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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

appropriate:

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        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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III. EVAPORATION AND TRANSPIRATION

        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:

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        ( 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-



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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.

       

IV. INFILTRATION

        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

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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. ✓

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        ( 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

structure.

        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).

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        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

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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

explanation.

       

V. RUNOFF

        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

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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.

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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.

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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

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TABLE 2

Runoff and Percipitation Data for Yukon River above Eagle, Alaska

Month	1911			1912			1913
	Runoff		*	Runoff		*	Runoff		*
	CFS	INS	INS	CFS	INS	INS	CFS	INS	INS
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.

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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

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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

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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

rivers.

       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

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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.

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VI. PHYSIOGRAPHIC CHANGES PRODUCED BY HYDROLOGICAL PHENOMENA

        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.

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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

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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

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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 —

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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

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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

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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.

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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

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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.

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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

thick.

       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

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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

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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.

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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

level.

       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

level.

       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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VII. GROUND WATER

        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

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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.

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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.

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---

BIBLIOGRAPHY

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 .

342.

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