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Hidrogeologi & Air Bawah
Tanah
(Hydrogeology and
Groundwater)
Star 5 Ogos 2003
Kita sudah bincang mengenai
1. Mineral
2. Batuan
3. Tanah
4. Now AIR pulak
Objectives
• Memahami perbezaan bidang hidrogeologi
dgn hidrologi
• Meninjau sumber air dan kitar air
• Memahami konsep asas: keliangan
(porosity), ketelapan (permeability), akuifer,
akuitard, akuiklud.
• Memahami konsep paras air dan faktor yg
mengawal kedudukannya
• Describe the character and behaviour of
groundwater in various settings
• Discuss environmental problems related to
groundwater.
Hydrogeology vs hydrology
• Sama saja dalam segala segi
• Kalau beza sikit sangat
Groundwater as an important
resource for
• Drinking water (life)
• Erosion (subterranean caverns)
(geological processes)
• Equalizer of stream flow (geological
processes)
• Agriculture
Water holding capabilities of
rock
• Consider properties of rock for storage &
transport of water:
– Porosity - percentage of rock's volume that is
openings
– Permeability - ability of rock to transmit a fluid
– Aquifer - Rock that is permeable, able to store
and transport water (examples)
– Aquitard - Rock that is impermeable, acts to
hinder or prevent water movement (examples)
RESERVOIR
AIR
•Infinite tapi pasti
•Luas tetapi terhad
Hydrologic cycle
Hydrologic cycle
• Powered by solar energy and gravity
• Evaporation and precipitation
• Continuous recycling of water
• Where does water go that falls on the land?
– Runoff (air larian)
– Infiltration
– Evaporation (penyejatan)
– Temporary storage as snow and ice
– Temp. storage in lakes
– Temp storage in plants (evapotranspiration) and
animals
– Chem reactions with rocks and minerals
• Source of additional water?
volcanism (steam)
–Volcanism also causes melting of
snow caps and mudflows as
meltwater mixes with ash
Distribution of water on the
Earth
• Total = 326 million cubic miles
• Percentages
– 97.2% oceans
– 2.15% ice caps and glaciers
– .65% lakes, streams, groundwater,
atmosphere
(bandingkan dgn slaid no 5)
Hydrologic Cycle (in greater
details)
• A. Division of water on Earth
• 97.2% in oceans
• 2.15% in glaciers (largest source of fresh (nonsaline) water on Earth)
• 0.62% in groundwater (underground aquifers)
• 0.017% in lakes
• 0.005% in soil moisture
• 0.001% in atmosphere
• 0.0001% in stream channels
Water budget
• Of all the water that comes out as rain on
land:
• 50% is evaporated and transpired by
plants
• 30% goes into runoff, eventually reaching
the ocean
• 20% goes into groundwater
Porosity and Permeability
• Dua ciri yg penting yg ada pada
batuan dan tanah
Porosity (keliangan) is the amount of
pore space in a rock (the spaces
between the grains)
Porosity = volume of pores/total volume
Pores (liang)
Tazkirah/peringatan
• Tahukah anda semua jenis batuan
mendak, igneus dan metamorfik?
• Tahukah anda ciri2 asas pada ketiga-tiga
jenis batuan tersebut? (struktur kimia,
sifat fizik dan kimia, proses
kejadiannya/pembentukkannya)
• Porosity is independent of grain size.
• Porosity depends on:
• Sorting of the grains (or uniformity of grain
size)
Are the grains all the same size (well sorted),
or are a variety of grain sizes present, with
finer grains filling the spaces between the
larger grains (poorly sorted)?
• Shape of the grains
• Packing and arrangement of grains.
Cubic packing. Porosity = 47.64%
Rhombohedral packing. Porosity = 25.95%
sorting
High energy environment
Low energy environment
Packing?
• What are some examples of a rock with
high porosity?
• What are some examples of a rock with
low porosity?
JAWAPAN ANDA?
Wentworth scale
Particle name
- grain size scale
Particle diameter
• Boulders
> 256 m
• Cobbles
64 - 256 mm
• Pebbles
2 - 64 mm
• Sand
1/16 – 2 mm
• Silt
1/256 - 1/16 mm
(or 0.004 - 0.0625 mm)
• Clay
< 1/256 mm
(or < 0.004 mm) <2 mikron
Pengelasan batuan mendak
1 Terrigenous (detrital or clastic) – bumi/benua
Conglomerate or Breccia
Sandstone
Siltstone
POROSITY?
Shale
Ada/tak ada
claystone
2 Chemical/biochemical
Rendah/tinggi
Evaporites
Carbonate sedimentary rocks (limestones and dolostone)
Siliceous sedimentary rocks
3 Organic (coals)
Other – ironstones
Permeability (ketelapan) is the
ease with which fluids flow
through a rock or sediment
• A rock is permeable if fluids pass through
it, and impermeable if fluid flow through
the rock is negligible
Definition of permeability
Rujukan: Rock Slope Engineering
by Hoek and Bray (1979)
Permeability depends on:
• Grain size
Coarser-grained sediments are more
permeable than fine-grained sediments
because the pores between the grains are
larger.
• Sorting
• Grain shape
• Packing (controls pore size)
• What are some examples of a rock with
high permeability?
• What are some examples of a rock with
low permeability?
JAWAPAN ANDA?
Classification of igneous rocks
REGIONAL
Mineral yg terdapat pada zon
metamorfik
Rumus
Changes that occur in the transformation to
become metamorphic rocks
FACIES GRADE
Hubungan antara porosity-permeability
• AQUIFER, AQUICLUDES, WATER
TABLE, UNCONFINED, CONFINED
AND PERCHED WATERS
Aquifers and aquicludes
• An aquifer is a water-bearing rock.
Aquifers have high porosity and high
permeability.
• Examples of rock types that could be aquifers?
• Aquicludes are water-excluding rocks.
They have little or no porosity or permeability.
• Examples of rock types that could be
aquicludes?
• Note that some impermeable
rock types may serve as
aquifers if they are highly
jointed. Water may be in the
joints or cracks in the rock
Water table/Paras air
•Bergantung kpd topografi
Water table
The Water Table (Paras air)
• When it rains, some of the water
percolates or soaks into the ground. We
call this infiltration. Some of the water is
held in the soil because it clings to the
soil particles because of molecular
attraction. It may evaporate from the
soil or be used by plants (zone of
aeration, also called the vadose
zone). Both air and water occupy the
pores spaces.
• Excess water penetrates
downward until it reaches the
water table. Below this point, all
of the pore spaces are filled with
water (zone of saturation (ZON
TEPU), also called the phreatic
zone).
• The water table is the top of
the zone of saturation.
• The water table is not flat. It
mimics the topography, but is
more subdued. It stands
somewhat higher under hills,
and lower under valleys.
• Where the water table intersects
(or lies above) the ground surface,
springs, lakes, swamps, or rivers
are present. In humid areas,
groundwater movement supplies a
flow of water to a stream or river.
• If a well is drilled, the waterlevel in
the well is at the water table.
• The position of the water table may
fluctuate with droughts.
• If water is withdrawn from a well, the water
table is lowered in the immediate vicinity of
the well. The lowered surface of the water
table around a well forms a conical
depression in the water table. It is called
the cone of depression.
• If significant quantities of water are
withdrawn from a well, the cone of
depression may be so large that it affects
the water level of other wells nearby.
Water table & groundwater flow
Processes
• Recharge-precipitation and infiltration
• Discharge-rivers, runoff, pumping
• Relation to topography
• Relation to seasonality
Water table & groundwater flow
groundwater
Artesian Wells
Perched water
Groundwater as resource
• Seasonal changes
• Effects of pumping
• Pollution of groundwater
• Ogallala aquifer
Problems associated with
groundwater withdrawal
• Ground water depletion
• Subsidence
• Sinkhole formation
• Groundwater pollution or contamination
• Saltwater encroachment
Seawater before and after
pumping
groundwater
groundwater
•Ogallala Aquifer
PUMPING TEST
DRAWDOWN
Sensor untuk mengesan
paras air (piezometer)