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Geology 100 (part 2) > Groundwater > Flashcards

Groundwater Flashcards

1
Q

Hydrology

A

the study of the movement and characteristics of water on and within land

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2
Q

water we can see vs what is harder to see

A

we can see water moving from place to place in the rivers on earths surface and we can see water stored on the surface in lakes and oceans
harder to see the massive amounts of water stored in the atmosphere and underground and the flows into and out of these storage places

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3
Q

groundwater

A

becomes groundwater when rain sinks into the ground

mass of water stored beneath earth’s surface

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4
Q

reservoir

A

a place where water is stored

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5
Q

percentage of earth that is salt water

A

95.9%

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6
Q

percentage of earth that is freshwater

A 
** total 4.04%
glaciers and polar ice 2.97%
atmosphere .001%
lakes and rivers .009%
** underground waters 1.05%
biosphere .0001%
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7
Q

infiltration

A

process by which water enters rock or soil through joints in small pore spaces between particles

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8
Q

runoff

A

sum of all rainwater that flows over surface
eventually goes to ocean
if land is more developed, there is more runoff bc less earth to sink into

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9
Q

strongest influence on hydrology

A

geology of land and climate (including temp and precip)

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10
Q

droughts

A

periods of months to years, when precip is much lower than normal

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11
Q

hydrology of runoff

A

flash floods after torrential rains
surface runoff collected and stored in natural lakes and artificial reservoirs created by the damming of rivers
**wetland areas, swamps, and marshlands also act as storage deposits for runoff

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12
Q

how water flows through soil and rock

A

we know that water moves into and through the ground
there are no large open spaces for pools or rivers of water underground
the only space available for water is the pore space between grains of sand and otehr particles that make up the soil and bedrocks
some pores, however small and few, are found in every kind of rock and soil but large amounts of pore space most often found in sandstones

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13
Q

porosity

A

the amount of pore space in sock, soil, or sediment
the ratio, usually expressed as a %, of total volume of voids of a given porous medium to the total volume of the porous medium
depends on size, shape of grains and how they are packed together
(pics on page 2 and 3)

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14
Q

permeability

A

the ability of a solid to allow fluids to pass through it
spaces connected- fluids pass throughout
(pics on page 2)

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15
Q

different types of rock and their porosity

A 
20% vesicular 
<1% basalt
25% limestone (with solution cavities)
5% shale
**30% well-sorted eolian sandstone (grains round and same size)
15% poorly sorted sandstone
**30% conglomerate unconformity
< 1% granite
(top of p 3)
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16
Q

different types of sandstone

A

** porous sandstone (the best kind)- bc rocks big and have large spaces between them
cemented sandstone- large rocks but cement in between
fine-grained sandstone
sandstone w irregular shapes- small grains fill space in between large grains
*unfractured shale (have many pores, which is good but not connected)
* fractured shale (better bc pores connected)

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17
Q

porosity and permeability of aquifer rock types

A

LOOK AT CHART ON PAGE 4 OF PACKET

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18
Q

aquifer

A

sediment or rocks that stores and transmits groundwater in sufficient quantity to supply wells

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19
Q

aquitard

A

sediment or rock that hinders water flow. A confining bed that retards but does not prevent the flow of water to or from an adjacent aquifer; a leaky confining bed

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20
Q

aquicludes

A

relatively impermeable beds. A hydrogeologic unit, which although porous and capable of storing water, does not transmit it at rates sufficient to furnish appreciable supply for a well or spring

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21
Q

confining unit

A

a hydrogeologic unit of impermeable or distinctly less permeable material bounding one or more aquifers and is a general term that replaces aquitard, aquiclude

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22
Q

unconfined aquifer

A

intersects the surface
in contact with atmosphere, easily contaminated
water travels through beds that extend with more or less uniform permeability to the surface in both discharge and recharge areas

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23
Q

level of reservoir in unconfined aquifer is

A

same height as the water table

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24
Q

unsaturated zone

A

(unconfined aquifer)
pores contain some air and are not completely filled with water
aka vadose zone

25
saturated sone
(unconfined aquifer) | pores of the rock or soil are completely filled with water
26
groundwater table (aka water table)
boundary between unsaturated and saturated zones | unconfined aquifer
27
recharge
water enters saturated zone | unconfined aquifer
28
discharge
water leaves the saturated zone | unconfined aquifer
29
shape of water table usually takes shape of
topography
30
perched water tables
discontinuous confining lenses may exist in the subsurface these arrest downward infiltration to the water table these lenses form perched water tables - overlie unsaturated material, represent a "false" water table, more easily dewatered
31
water tabletopography
water table takes shape of topography not flat, is sloping surface water flows from higher elevations to lower topography is useful for estimating groundwater flow
32
typcical rate of groundwater flow
.00002 km/hr
33
effluent stream
when a stream channel intersects the water table, water discharges from the groundwater to the stream
34
influent streams
when a stream channel lies at an elevation above the water table
35
confined aquifer
aquifer bounded above and below by aquiludes | isolated from surface, less susceptible to pollution
36
water pressure in confined aquifer
water is contained under pressure at any point in the aquifer, the pressure is equivalent to weight of all the water above pressure of water usually higher than atmospheric pressure, which is why when a well is bored into the aquifer the water rises up the well tube, to a level higher than the aquifer
37
artesian wells
drilled into a confined aquifer at a point where the elevation of the ground surface is lower than that of the potentiometic surface, the water will flow out of the well spontaneously
38
most common aquifers
unconsolidated sands and gravels, permeable sedimentary rocks such as sandstones and fractured limestones and heavily fractured volcanic and crystalline rocks
39
most common confining beds
clays, shales, and dense crystalline rocks
40
geologic conditions can lead to confined aquifers
alternating beds of dipping sandstones and shales fault zones in crystalline igneous rocks folded beds with alternating layers, recharged along joing fractures horizontal sedimentary rocks involving unconformable relationships glacial deposits consisting of til and outwash stabilized sand dunes displaying impervious deposits in the interdune area (tldr: tilted beds, high and low area, recharge area @ high elevation, water table determined by height of source aka potentiometric surface)
41
potentiometric surface
imaginary surface that defines the level to which water in confined aquifer wold rise were it completely bored with wells aka water table for unconfined aquifer
42
artisian flow
caused because water is under very high pressure and can't move up, down, or sideways. If the confined aquifer is drilled into, the water will rise to the surface
43
artisian wells
wells that tap confined, tilted aquifers
44
groundwater in the desert
oases in the Sahara develop from spring flow Water from recharge areas (mountains 1000s of miles away and above) flows to oasis discharge points These locations have been culturally important for millenia
45
Ogallala Aquifer
best reservoir in the US part of High Plains Aquifer System shallow underground water table located beneath great plains 174,000 sq miles in portions of SD, NE, WY, KS, CO, OK, TX, NM can feed the whole US
46
lowering the water table due to excessive pumping
when we extract water from wells at a rate faster than is can be resupplied the water table drops first, cone of depression forms around well, then water table gradually becomes lower
47
cone of depression
the downward-pointing, cone-shaped surface of the water table in a location where the water table is experiencing drawdown because of excessive pumping
48
water table drops when people divert surface water from the recharge area
this problem has develped in the everglades, a huge swamp, where before the expansion of Miami and development of agriculture, the water table lay at ground surface. division of water from the everglades recharge area into canals has significantly lowered the water table, causing parts of the everglades to dry up Water used to flow south from Lake Okeechobee but now it has to go around the cities etc Some of swamp has dried up and saltwater intrusion
49
reversing the flow direction of groundwater
the cone of depression that develops around a well creates a local slope to the water table. The resulting hydraulic gradient may be large enough to reverse the flow direction of nearby groundwater. Such reversals can lead to the contamination of wells (septic effluent can be carried)
50
saline intrusion
in coastal areas, fresh water lies in a layer above saltwater that entered the aquifer from the adjacent ocean. Normally, the pressure of fresh water keeps the saltwater margin offshore
51
pore collapse and land subsidence
as water in some sediments is removed, the sediments undergo compaction; the loss of volume is manifested in the lowering of the surface about 1 m every 3 years. Leaning tower of Pisa's foundation was destabilized by groundwater removal ex: San Joaquin Valley, CA, Mexico City, Venice, Italy
52
erosion by groundwater
dissolution of limestones, -or rarely other soluble rocks such as evaporites- by groundwater dissolution of limestone is enhanced by the atmospheric CO2 contained in rainwater. waters that infiltrate soils may pick up even more of the gas from the Co2 given off by plants, roots, bacteria, and other soil dwelling organisms. As this Co2-rich water moves down the water table, through the unsaturated zone to the saturated zone, it creates openings as it dissolves carbonate minerals Dissolution mostly in the saturated zone
53
stalactite
suspended from ceiling
54
stalagmite
inverted icicle-like deposit on the floor below the stalactite
55
joined stalactite and stalagmite form a
column
56
sinkhole
small, steep depression in the land surface above the cavernous limestone formation. In some places, dissolution may thing the roof of f limestone cave so much that is collapses suddenly contribute to a distinctive form of topography known as Karst topography Arecibo Radio telescope in Puerto Rico was built in a sinkhole
57
tower Karst landscape in teh guilin region of China
ridges or walls between adjacent sinkholes tend to be steep-sided, for they were originally joint controlled. Over time, the walls erode, leaving only jagged, isolated spires- a karst landscape dominated by such spires is called a tower karst
58
karst topography most strongly advanced in regions with
1. high rainfall climate, with abundant vetgetation 2. extensively jointed limestone formations 3. appreciable hydraulic gradient
59
karst topography charaterized by
sinkholes- surface depressions formed by the collapse of caves or other underground void spaces springs- places where water flows naturally from the ground (from spaces in the bedrock) disappearing streams- streams that terminate abruptly by seeping into the ground

Geology 100 (part 2) (5 decks)

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