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HYDRO SUMMER > groundwater > Flashcards

groundwater Flashcards

1
Q

• is the water in the soil mantle

A

SUBSURFACE WATER

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2
Q

TWO ZONES OF SUBSURFACE WATER

A

1) Saturated zone
2) Zone of aeration

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3
Q

1) this zone also known as groundwater zone, is the space in which all pores of the soil are filled with water. The water table forms its upper limit and marks a free surface, i.ee a surface atmosphere pressure.

A

1) Saturated zone

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4
Q

in this zone the soil pores are only partially saturated with water. The space between the land surface and the water table marks the extent of the zone

A

2) Zone of aeration

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5
Q

ZONES OF AREATION

A

• Soil water zone
• Capillary fringe
• Intermediate zone

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6
Q

this lies close to the ground surface in the major root band of the vegetation from which the water is loss to the atmosphere by evapotranspiration

A

• Soil water zone

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7
Q

in this the water is held by capillary action. The zone extends from the water table upwards to the limit of the capillary rise.

A

• Capillary fringe

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8
Q

this lies between the soil water zone and the capillary fringe

A

• Intermediate zone

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9
Q

The thickness of the zone of aeration and its constituent subzones depend upon the soil texture and moisture content and vary from region to region. The soil moisture in the zone or aeration is of importance in practice and irrigation engineering.

A

TRUE

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10
Q

• All earth materials from soil to rocks that have pore spaces. Although these pores are completely saturated with water below the water table, from the groundwater utilization aspects only such material through which water moves easily and hence can be extracted with ease are significant.

A

SATURATED FORMATION

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11
Q

CLASSIFICATIONS OF SATURATED FORMATIONS:

A

1) Aquifer
2) Aquitard
3) Aquiclude
4) Aquifuge

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12
Q

is a saturated formation of earth material which not only stores water but yields it in sufficient quantity. Thus, an aquifer transmits water relatively easily due to its high permeability.

A

1) Aquifer

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13
Q

is a formation through which only seepage is possible and thus the yield is insignificant compared to an aquifer. It is partly permeable

A

2) Aquitard

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14
Q

is a geological formation which is relatively impermeable to the flow of water. It may be considered as closed to water movement even though it may contain large amounts of water due to its high porosity.

A

3) Aquiclude

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15
Q

it is a geological formation which is neither porous nor permeable. There are interconnected openings and hence it cannot transmit water

A

4) Aquifuge

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16
Q

CLASSIFICATIONS OF AQUIFERS:

A

1) Unconfined aquifer
2) Confined aquifer

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17
Q

(also known as water table aquifer) – Is one on which a free water surface (water table exist. Only the saturated zone of this aquifer is of importance in groundwater studies. Recharge of this aquifer takes place through infiltration of precipitation from the ground surface. A well driven into an unconfined aquifer will indicate a static water level corresponding to the water table level at that location

A

1) Unconfined aquifer

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18
Q

(also known as artesian aquifer) – is an aquifer which is confined between two impervious beds such as aquiludes or aquifuges. Recharge of this aquifer takes place only in an area where it is exposed at the ground surface.

A

2) Confined aquifer

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19
Q

is a confined aquifer which is either or both of its confining beds are aquitards

A

Leaky aquifer

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20
Q

• It is the free water surface in an unconfined aquifer. The static level of a well penetrating an unconfined aquifer indicates the level of the water table at that point.

A

WATER TABLE

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21
Q

In general sense, the water table follows the topographic features of the surface. If the water table intersects the land surface, the groundwater comes out to the surface in the form of springs of seepage.

A

TRUE

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22
Q

TYPES OF WATER MOVEMENT BETWEEN STREAMS AND GROUNDWATER

A

• Effluent stream
• Influent stream

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23
Q

receives water from the ground, and therefore it expands downstream by becoming deeper and broader.

A

• Effluent stream

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24
Q

are in arid areas and lose a lot if water through evaporation and seepage into the ground.

A

• Influent stream

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25
Q

COMMON EXAMPLES OF THE FLUCTUATION OF THE WATER TABLE

A

1) Fluctuations In the water level; in a dug well during various seasons of the year.
2) Lowering of the ground water table in the region due to heavy pumping of the wells, and
3) The rise in the water table of an irrigated area with poor drainage.

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26
Q

is an accumulation of groundwater that is above the water table in the unsaturated zone.

A

PERCHED WATER TABLE

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27
Q

• The amount of pore space per unit volume of the aquifer material.
• Gives a measure of the water-storage capability of a formation.

A

POROSITY

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28
Q

• The actual volume of the water that can be extracted by the force of gravity from a unit volume of aquifer material.

A

SPECIFIC YIELD

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29
Q

• The fraction of water held back in the aquifer.

A

SPECIFIC RETENTION

30
Q

• This is the slope of the water surface in an open channel, the slope of the water surface of the groundwater table, or the slope of the water pressure for pipes under pressure.

A

HYDRAULIC GRADIENT

31
Q

The ability of the rock or sediment to transmit a fluid

A

PERMEABILITY

32
Q

in 1856 Henry Darcy, a French hydraulic engineer, on the basis of his experimental findings proposed a law relating the velocity of flow in a porous medium

A

Darcy’s Law

33
Q

• Velocity in open pore space

A

APPARENT VELOCITY OS SEEPAGE / DISCHARGE VELOCITY

34
Q

• The ratio of inertial forces to viscous forces within a fluid that is subjected to relative internal movement due to different fluid velocities.

A

REYNOLD’S NUMBER OF UNITY

35
Q

• The velocity that is obtained by tracking a tracer added to the groundwater.

A

BULK PORE VELOCITY

36
Q

• The coefficient of permeability is related to porous media effects, whereas the hydraulic conductivity reflects the combined effects of porous medium and fluid properties.

A

HYDRAULIC CONDUCTIVITY/COEFFICIENT OF PERMEABILITY

37
Q

THE GEOLOGIC FORMATION CLASSIFICATION

A

• Unconsolidated deposits
• Consolidated/Porous Media Aquifers

38
Q

o Are mostly alluvial deposits. They can consist of river deposits, glacial tills and lake sediments and glacial outwash deposits of sand and gravel; which form the most important and productive aquifers.

A

• Unconsolidated deposits

39
Q

Coarse-grained sediments like sand and gravel have a higher porosity than small-grained sediments like clay and silt, and the pore spaces are better connected. In some cases, pore spaces can be filled by smaller-grained materials, which makes less room for water to enter and travel through the pore spaces. This decreases the porosity, and the aquifer will be less permeable.

A

TRUE

40
Q

o Porous rock layers where grains are cemented to each other are called “consolidated.”
o those with primary porosity such as sandstones are generally good aquifers.
o Normally, the yield from these aquifers is less than that of the alluvial deposits and typically may have a value of 20-50 m³/h.
o Other consolidated rocks includes limestone, shale, granite, and basalt. Water flows through these rocks through fractures, gas pores, and other openings in the rock.

A

• Consolidated/Porous Media Aquifers

41
Q

contain numerous secondary openings in the form of cavities formed by the solution action of following subsurface water. Often these form highly productive aquifers.

A

Limestones and dolomite

42
Q

also offer good potentialities as aquifers because these aquifers extend over large areas and large volumes of water can be withdrawn. Average permeability of these rocks decreases with depth. The yield is fairly low, being the order of 50-100 m³/h.

A

Igneous and metamorphic rocks

43
Q

has permeable zone in the form of vesicles, joints and fractures. Basaltic aquifers are reported to occur in confines as well as under unconfined conditions. The permeability of basaltic rocks is highly variable.

A

volcanic rock basalt

44
Q

• In confined aquifers the total pressure at any point due to overburden is born by the combined action of the pore pressure and intergranular pressure. The compressibility of the aquifer and also that of the pore water causes a readjustment of these pressures whenever there is a change in storage.
• The compressibility of an aquifer is more dominant when the aquifer is confined and completely saturated.

A

COMPRESSIBILITY OF AQUIFERS

45
Q

form the most important mode of groundwater extraction from an aquifer. A well is a hole drilled into the ground to access water contained in an aquifer. A pipe and a pump are used to pull water out of the ground, and a screen filters out unwanted particles that could clog the pipe.

A

• Wells

46
Q

WELL CONCEPT:

A

a) Static Water Level
b) Cone of Depression
c) Drawdown
d) Pumping Water Level
e) Radius of Influence
f) Specific capacity

47
Q

refers to the level of water in a well under normal, undisturbed, no-pumping conditions. Static water level is best determined when the well has not been pumped for several hours prior to measuring.

A

a) Static Water Level

48
Q

depression in the groundwater table or potentiometric surface that has the shape of an inverted cone and develops around a well from which water is being withdrawn.

A

b) Cone of Depression

49
Q

The drop in the water table elevation at any point from its previous static level is called drawdown.

A

c) Drawdown

50
Q

is the distance from the land surface (or measuring point) to the water in the well while it is pumping.

A

d) Pumping Water Level

51
Q

means the radial distance from the center of a pumped well to the point where there is no lowering of the water table or potentiometric surface (the edge of the cone of depression).

A

e) Radius of Influence

52
Q

is the discharge per unit draw down at the well and is a measure of the performance of the well.

A

f) Specific capacity

53
Q

TYPES OF WELLS

A

• Bored wells
• Driven wells
• Drilled wells

54
Q

are holes dug in the ground using a shovel or backhoe. To prevent collapse, they are lined (cased) with stones, brick, tile, or other material. Dug wells have a big diameter, are shallow (between 10 and 30 feet deep) and are not continuously cased.

A

• Bored wells

55
Q

are built by inserting pipe into the ground. Driven wells are shallow (about 30 to 50 feet deep) and continuously cased. Despite the fact that driven wells are cased, they are easily contaminated because they take water from aquifers near the surface.

A

• Driven wells

56
Q

are constructed by percussion or rotary-drilling machines. Casing is required for drilled wells that are thousands of feet deep. Because of their depth and use of continuous casing, drilled wells are less likely to be contaminated.

A

• Drilled wells

57
Q

(also known as dug wells) is a cylindrical shaft made out of masonry in the ground with an uncovered opening. They are best suited for shallow and low yielding aquifers.

A

OPEN WELLS

58
Q
  • or “deep drainage” or “deep percolation” is a hydrologic process, where water moves downward from surface water to groundwater.
A

GROUNDWATER RECHARGE

59
Q

TWO CLASSIFICATIONS OF RECHARGE

A

Natural recharge
Artificial recharge

60
Q

taking place naturally as a part of hydrologic cycle. Water is recharged naturally by rain and snow melt and to a smaller extent by surface water (rivers and lakes).

A

Natural recharge

61
Q

the process of increasing infiltration of surface water to groundwater system by altering natural conditions. It is the practice of increasing the amount of water that enters an aquifer through human-controlled means

A

Artificial recharge

62
Q

VARIOUS RECHARGING METHODS COMMONLY ADOPTED FOR ARTIFICIAL RECHARGE:

A
  1. Spreading (flooding, basin, ditch, pit and channel)
  2. Through injection wells
  3. Induced recharge from surface water bodies
  4. Subsurface dykes
  5. Percolation tanks and check
63
Q

DATA REQUIREMENTS FOR A GROUNDWATER BALANCE STUDY

A

• Rainfall data
• Land-use data and cropping patterns
• River data
• Canal data
• Tank data
• Water table data
• Groundwater draft
• Aquifer parameters

64
Q
  • is the maximum rate at which the withdrawal of groundwater in a basin can be carried without producing undesirable results.
A

SAFE YIELD

65
Q

UNDESIRABLE RESULTS OF GROUNDWATER STORAGE YIELD:

A
  1. Permanent lowering of the groundwater table or piezometric head
  2. Maximum drawdown exceeding a present limit leading to inefficient operations of wells, and
  3. Saltwater encroachment in a coastal aquifer
66
Q

– is the permanent withdrawal of groundwater from storage and it connotes a depletion of a resource in a manner similar to the exploitation of mineral resource.

A

Mining

67
Q

TWO COMPONENTS OF GROUND WATER RESOURCE:

A
  1. Dynamic resource
  2. Static resource
68
Q

represents the safe yield, which is essentially the annual recharge less the un-avoidable natural discharge.

A
  1. Dynamic resource
69
Q

is the groundwater storage available in the pores of the aquifer and its exploitation by mining leads to the permanent depletion.

A
  1. Static resource
70
Q

THE TOTAL ANNUAL RECHARGE IS MADE UP OF:

A

• Rainfall recharge
• Seepage from canals
• Deep percolation from irrigated area
• Inflow from influent stream etc.
• Recharge from tanks, lakes, submerged lands, and
• Artificial recharge schemes, if any

71
Q

THE GROUNDWATER LOSSES FROM AQUIFER DUE TO:

A

• Outflow to rivers
• Transpiration by trees and other vegetation
• Evaporation from the water table

72
Q

THE NATIONAL WATER POLICY (1987) STIPULATES:

A
  1. Exploitation of the groundwater resources should be so regulated as not to exceed the recharging possibilities, as also to ensure social equity. Groundwater recharge projects should be developed and implemented for augmenting the available supplies.
  2. There should be periodical reassessment on a scientific basis of the groundwater resources taking into consideration the quality of the water available and economic viability.

HYDRO SUMMER (8 decks)

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