Arctic and Subarctic Hydrology: Encyclopedia Arctica Volume 1: Geology and Allied Subjects
Hydrology
Arctic and Subarctic Hydrology
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 |
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 |
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.
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.
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.
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
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.
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.
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 trees.
- 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 developed.
- 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.
- 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.
EA-I. Straub and Johnson: Hydrology
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
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
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
Fig.2 Relation of Atmospheric Water Holding Capacity and Temperature
Fig. 3 Climatic Data for Three Stations
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
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.
Fig. 4 Rainfall Duration-Frequency Relations for Alaska.
Fig. 5 Rainfall Intensity Frequency Data for Alaska
SUPPLY CURVES FOR ARCTIC AND SUBARCTIC REGIONS OF ALASKAFIGURE 6
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
Fig. 7 A Low Ceiling Confines Avenues of Incoming Moist Air and Is Thereby A Limiting Factor of Precipitation
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 | 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 |
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
<formula>D = KV(T – 32°)</formula>
(1)
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: <formula>D = K1V(e – 6.11)</formula> where D is inches in hours, V is wind velos^c^ity 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: <formula>D = P(T – 32)/144</formula> 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:
EA-I. Straub and Johnson: Hydrology
<formula>D = 0.001V(T – 32) + 0.0032V(e – 6.11) + P((T – 32)/144)
</formula>
<formula> = 0.001 x 20(60 – 32) + 0.0032 x 20(17 – 6.11) + (0.5(60 – 32)/144) </formula>
<formula> = 0.56 + 0.70 + 0.1 </formula>
<formula> = 1.36 in. of water in 6 hours or 0.23 in. per hour average rate</formula>
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.
EA-I. Straub and Johnson: Hydrology
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:
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^-^
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.
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
Fig. 8 Ground Temperatures for Three Stations
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.
^
✓^
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
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).
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
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
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
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.
EA-I. Straub and Johnson: Hydrology
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 2^II^
(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.
EA-I. Straub and Johnson: Hydrology
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
4
Figure: Table 3 Runoff data for five watersheds in Alaska
Fig. 9 Hydrological Data Pertaining to the Yukon River Above Eagle, Alaska
| TABLE 2 Runoff and Percipitation Data for Yukon River above Eagle, Alaska | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Month | 1911 | 1912 | 1913 | ||||||
| Runoff | 1 2 3 | Runoff | 1 2 3 | Runoff | 1 2 3 | ||||
| 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 |
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
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
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 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
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.
EA-I. Straub and Johnson: Hydrology
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.
EA-I. Straub and Johnson: Hydrology
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
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
EA-I. Straub and Johnson: Hydrology
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.
EA-I. Straub and Johnson: Hydrology
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
:
^
.^
^—^ ^
✓^
EA-I. Straub and Johnson: Hydrology
( 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 ^—^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
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
Fig. 10 Influence of a Drainage Ditch on theThermal Regime of the Ground
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.
EA-I. Straub and Johnson: Hydrology
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
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.
EA-I. Straub and Johnson: Hydrology
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
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
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.
EA-I. Straub and Johnson: Hydrology
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.
EA-I. Straub and Johnson: Hydrology
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.
EA-I. Straub and Johnson: Hydrology
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
Fig. 11 Ground Water Occurrences in Polar Regions
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.
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.EA-I. Straub: Hydrology
BIBLIOGRAPHY1. 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
Loading...