To absorb – всасывать, впитывать

porous rocks – пористые породы

water table – водное зеркало

to intersect – пересечь, разделить

 

2. Read and translate the following international words:

infiltrate [¢infiltreit]; cycle [¢saikl]; channel [¢tòænl]; system [¢sistim]; zero [¢ziərəu]; agriculture [¢ægrikÙltòə]; transit [¢trænzit]; structure[¢strÙktòə].

 

3. Translate the following word combinations:

rate of precipitation; may infiltrate into the soil; this part of the precipitation; the surface depressions; over the surface of the ground; the beginning of a definite stream channel system; to be discharged ultimately into the ocean; some inland water body; some loss in transit; because of evaporation to the atmosphere; infiltration to the bottom and sides of the channel; to lie within the zone of saturation; major importance in connection with agriculture; to return to the atmosphere without penetrating; a portion of the precipitation; to percolate into the ground; to be absorbed by soil deficient in moisture; by porous rocks; to reach a level; may intersect a stream bed; will be returned to a body of surface water; to flow through porous strata; may be confined by tighter soils; may be artesian; the same pressure zone; may contact the ocean bed; various lengths.

 

Text (A)

Read the text «Surface Runoff and Ground Water»:

When the rate of precipitation exceeds the rate at which water may infiltrate into the soil (infiltration capacity), surface runoff usually occurs. This part of the precipitation after filling the surface depressions finds its way over the surface of the ground until it reaches the beginning of a definite stream channel system, through which it passes and is discharged ultimately into the ocean or some inland water body. There is some loss in transit because of evaporation to the atmosphere and infiltration to the bottom and sides of a definite stream channel. The latter may vary from practically zero to nearly 100 %.

Ground water as defined by geologists and engineers, comprises only that portion of the water which lies within the zone of saturation or below the water table. It does not include the suspended water which is held in the ground above that zone but does include the water which lies below a perched water table. Water above the zone of saturation and near the ground surface is of major importance in connection with agriculture because of its relation to plant growth. Much of this water, of course is utilized and transpired by vegetation and is thus returned to the atmosphere without penetrating deeply below the surface or becoming a part of the body of ground water.

A portion of the precipitation penetrating the ground surface as infiltration will percolate into the ground. If not absorbed by soil deficient in moisture, or by porous rocks, this water eventually reaches a level which is completely saturated — the «ground water table». The slope and confining structure surrounding the ground water body may be such as to prevent its immediate release; or the ground water body may intersect a stream bed where part of it will be returned to a body of surface water. Ground water may also flow through porous strata and reach a level where it may be confined by tighter soils and thus subjected to pressure. If a well penetrates to this level, it may be artesian and the water discharged will like wise become part of the surface water. The same pressure zone may contact the ocean bed and discharge water into the sea.

Thus, the atmospheric moisture with which this description of the cycle started may follow paths of various lengths and complexity before it can complete the circuit.

Exercises (B)

1. Establish compliance between parts of sentences:

1. when the rate of precipitation exceeds 1. as infiltration will percolate

the rate at which water may infiltrate into the ground

into the soil

2. this part of the precipitation after 2. a level which is completely

filling the surface depressions saturated

3. there is some loss in transit because of 3. surface runoff usually

evaporation to the atmosphere occurs

4. a portion of the precipitation 4. where it may be confined by

penetrating the ground surface tighter soils and thus subjected

5. if not absorbed by soil deficient to pressure

in moisture, this water eventually reaches 5. finds its way over the surface

6. ground water may also flow through of the ground

porous strata and reach a level 6. and infiltration to the bottom

and sides of a definite

stream channel

 

Text (B

Read the text « Evaporation and Transpiration, using a dictionary:

Moisture exists in all three states of matter in the atmosphere, as vapour, liquid, or solid; changes from one to the other are known as phase changes, and significant amounts of energy are involved in accomplishing these changes. In the process of evaporation, 600 calories of latent heat are required to change one gram of water from a liquid to a vapour state. Normally such a heat loss would be quickly compensated by conduction and radiation. In the reverse process of condensation, latent heat is released into the atmosphere, causing a slight rise in temperature.

Water in the liquid state, when sufficiently subjected to heating by solar energy or otherwise, passes into the gaseous state. This phenomenon is called «evaporation».

Of the total precipitation, a very large proportion falls directly upon the oceans, large inland lakes, and other water surfaces such as rivers and ponds. That falling on the ocean, together with the water returned as runoff, maintains the equilibrium evidenced by the substantially constant sea elevation. Parts of this precipitation on water surfaces are ultimately evaporated into the atmosphere and become part of the atmospheric moisture. In the Arctic and in the northern areas of the temperate zones, evaporation from water and snow surfaces is frequently less than the precipitation, but the surplus in ultimately discharged to the oceans from which it is evaporated. Elsewhere, evaporation from water surfaces is generally equal to or greater than the precipitation falling on them.

One of the basic functions in the life processes of vegetation involves the process of taking water from the soil through the roots, utilizing it in producing growth and maintaining life, and discharging it from pores into the atmosphere as water vapour. This process of returning soil moisture to the atmosphere is called «transpiration». The amount of precipitation thus returned varies greatly with the character of vegetation and the moisture available to the root system of the plants.

 

1. Read about factors that affect the rates of transpiration. Make a topic, using data of tables:

Table 2

The factors that affect the rates of transpiration

Feature	How this affects transpiration
Number of leaves	More leaves (or spines, or other photosynthesizing organs) means a bigger surface area and more stomata for gaseous exchange. This will result in greater water loss.
Number of stomata	More stomata will provide more pores for transpiration.
Size of the leaf	A leaf with a bigger surface area will transpire faster than a leaf with a smaller surface area.
Presence of plant cuticle	A waxy cuticle is relatively impermeable to water and water vapour and reduces evaporation from the plant surface except via the stomata. A reflective cuticle will reduce solar heating and temperature rise of the leaf,[citation neededhelping to reduce the rate of evaporation. Tiny hair-like structures called trichomes on the surface of leaves also can inhibit water loss by creating a high humidity environment at the surface of leaves.[citation needed] These are some examples of the adaptations of plants for conservation of water that may be found on many xerophytes.
Light supply	The rate of transpiration is controlled by stomatal aperture, and these small pores open especially for photosynthesis. While there are exceptions to this (such as night or "CAM photosynthesis"), in general a light supply will encourage open stomata.
Temperature	Temperature affects the rate in two ways: 1) An increased rate of evaporation due to a temperature rise will hasten the loss of water. 2) Decreased relative humidity outside the leaf will increase the water potential gradient.
Relative humidity	Drier surroundings gives a steeper water potential gradient, and so increases the rate of transpiration.
Wind	In still air, water lost due to transpiration can accumulate in the form of vapor close to the leaf surface. This will reduce the rate of water loss, as the water potential gradient from inside to outside of the leaf is then slightly less. Wind blows away much of this water vapor near the leaf surface, making the potential gradient steeper and speeding up the diffusion of water molecules into the surrounding air. Even in wind, though, there may be some accumulation of water vapor in a thin boundary layer of slower moving air next to the leaf surface. The stronger the wind, the thinner this layer will tend to be, and the steeper the water potential gradient.
Water supply	Water stress caused by restricted water supply from the soil may result in stomatal closure and reduce the rates of transpiration.

Unit 3. Rivers

1. Translate the following word combinations:

a flow of water in a natural channel; main trunks of a drainage system; to carry water part of the time; from a fluctuating groundwater table; at the level of the river bottom; below the bed of the channel; to be lost by infiltration; a stream or river; in a defined channel; to distinct from surface run-off on slopes; both types of water movement; together with groundwater flow; important components of the basin hydrological system; can be recorded in the form of a hydrograph; to show the variation of discharge with time; to distinguish the level of base flow; from ground water supply; to produce sharp peaks in the hydrograph; the peak of discharge; the most intense rainfall; a great deal of information; to be gained about flbod magnitude and frequency; to the water engineer and geomorphologist; the variation in hydrograph shape from river to river; on the geological and morphological characteristics of the catchment area; a hydrograph with a very sharp peak; from high immediate surface run-off; with little absorption and storage of water in the basin.

 

Text (A)

Read the text « Rivers Defined»:

River is a flow of water in a natural channel. The term generally refers to the large, main trunks of a drainage system; smaller channels may be called streams, creeks, brooks, or rills, in descending order of size. Rivers may carry water all the time, and are then called perennial streams or rivers, or they may carry water part of the time, in which case they are called intermittent streams. If the base flow is from a fluctuating groundwater table, a river will carry water only when the table is above or at the level of the river bottom, and will be dry when the groundwater table lies below the bed of the channel. If the stream has a bed which is always above the water table, water will be lost by infiltration as it moves downstream; it will then be called an ephemeral stream.

Thus, a stream or river is a body of water flowing in a defined channel as distinct from surface run-off on slopes. Both types of water movement, together with groundwater flow, are important components of the basin hydrological system. Channel flow can be recorded in the form of a hydrograph, which shows the variation of discharge with time. It is usually possible to distinguish the level of base flow, resulting largely from ground water supply, from that of quick flow (flood flow), which produces sharp peaks in the hydrograph. The peak of discharge characteristically occurs sometime after the most intense rainfall has ceased. This time lapse is referred to as basin lag.

From such hydrographs a great deal of information can be gained about flbod magnitude and frequency, data which is vital to the water engineer and geomorphologist. The variation in hydrograph shape from river to river shows the dependence of the discharge on the geological and morphological characteristics of the catchment area. A hydrograph with a very sharp peak, for instance, results from high immediate surface run-off, with little absorption and storage of water in the basin.

1. Establish compliance between parts of sentences:

1. the term "river" generally refers to 1. flbod magnitude and

2. rivers may carry water all the time data which is vital to the water

and are then called engineer

3. a stream or river is a body 2. on the geological and

of water flowing in a defined channel morphological сharacteristics

4. channel flow can be recorded of the catchment area.

in the form of a hydrograph, which 3. as distinct from surface run-off

5. from hydrographs a great deal on slopes

of information can be gained about 4. the large, main trunks of a

6. the variation in hydrograph shape drainage system

from river to river shows the 5. shows the variation of discharge

dependence of the discharge with time

6. perennial streams or rivers

 

Text (B)

Read the text «Water flows», using a dictionary:

When water flows in a stream it is subject to two basic forces. Gravity exerts an impelling force and is opposed by the frictional resistance between the water and the bed of the channel. A stream’s ability to work, that is, to erode and transport material, is related to these two forces. Potential energy is provided by the weight and elevation of the water. This is converted by gravity into downflow and hence into kinetic energy. However, something like 95 % of this energy is lost because of the frictional forces, and the precise shape and nature of the channel bed can have a significant effect on this figure.

In all but the most sluggish streams, water flow is not steady and uniform but is affected by turbulence, which takes the. Form of chaotic movements and eddies. Turbulence is an important flow characteristic because it creates upward water motion, which lifts and supports the finer sediments. The effect of friction ensiirei that water closest to the banks normally moves more slowly than that near the stream centre. The highest velocity is usually located in mid-stream about one third of the distance down from the surface to the bed, but in an asymmetrical channel the zone of maximum velocity shifts to the deeper side, and may cause - significant erosion. The discharge (velocity X cross-sectional area) of a stream is affected by the characteristics of the channel itself, particularly width, depth, and channel roughness.

The effeciency of the channel shape can be expressed by its hydraulic radius, a quantity defined as the ratio of the cross-sectional area (a) to the length of the wetted perimeter (p). The higher the ration the more efficient the stream and the smaller the loss due to the friction. Channel roughness can also have a marked effect. A rough channel creates considerable eddying and loss of energy, whereas a smooth channel minimizes the frictional loss. Channels in silt and clay tend to be deeper and narrower than those in sand and gravel, because the finer materials are cohesive and promote bank stability.