psda ts air tanah-10
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Kuliah Oleh : Dr.. Eng. Sigit Sutikno, ST.,MT
PSDA
(Jurusan Teknik Sipil)
TTM-10
Groundwater Movement
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Kuliah Oleh : Dr. Eng. Sigit Sutikno, ST.,MT
GROUNDWATER MOVEMENT
1. Introduction
2. General Concept
3. Flow Net
4. Darcy’s Law
5. Hydraulic Conductivity Test
6. Distance-drawdown Analysis
7. Groundwater Overdraft
8. Groundwater Contamination
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• Movement of ground water
through pores and fractures is
relatively slow (meters/day)
compared to flow
of water in surface streams
• Flow velocity depends upon:
– Slope of the water table
– Permeability of the rock or
sediment
1. Introduction
Kuliah Oleh : Dr. Eng. Sigit Sutikno, ST.,MT
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Kuliah Oleh : Dr. Eng. Sigit Sutikno, ST.,MT
The water table is actually a sloping surface.
Slope (gradient) is determined by the difference in water table
elevation (h) over a specified distance (L).
Direction of flow is downslope.
Flow rate depends on the gradient and the properties of the aquifer.
2. General concept
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• Hydraulic gradient for an
unconfined aquifer =
approximately the slope of the
water table.
•Hydraulic conductivity = ability of material to allow water to move
through it, expressed in terms of m/day (distance/time). It is a
function of the size and shape of particles, and the size, shape, and
connectivity of pore spaces.
S. Hughes, 2003
Movement of groundwater depends on rock and sediment properties
and the groundwater’s flow potential. Porosity, permeability, specific
yield and specific retention are important components of hydraulic
conductivity.
K = length/time (m/day)
2. General concept
Kuliah Oleh : Dr. Eng. Sigit Sutikno, ST.,MT
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Water table contour lines are similar to topographic lines on a map.
They essentially represent "elevations" in the subsurface. These
elevations are the hydraulic head mentioned above.
S. Hughes, 2003
3. Flow Net
Kuliah Oleh : Dr. Eng. Sigit Sutikno, ST.,MT
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Water table contour lines can be used to
determine the direction groundwater
will flow in a given region.
S. Hughes, 2003
Water table contours (called
equipotential lines) are constructed to
join areas of equal head.
A map of groundwater contour lines
with groundwater flow lines is called a
flow net.
Remember: groundwater always
moves from an area of higher hydraulic
head to an area of lower hydraulic
head.
3. Flow Net
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Aquitard (granite)
Qal 100 50
Qal
WT
A simple flow net
Cross-profile view
well
Aquitard
Qal
3. Flow Net
Kuliah Oleh : Dr. Eng. Sigit Sutikno, ST.,MT
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4. Darcy’s Law
Kuliah Oleh : Dr. Eng. Sigit Sutikno, ST.,MT
Henry Darcy, 1856, studied water flowing through porous material.
His equation describes groundwater flow.
Darcy’s experiment:
• Water is applied under
pressure through end A, flows
through the pipe, and
discharges at end B.
• Water pressure is measured
using piezometer tubes
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4. Darcy’s Law
Kuliah Oleh : Dr. Eng. Sigit Sutikno, ST.,MT
Hydraulic head = dh (change in height between A and B)
Flow length = dL (distance between the two tubes)
Hydraulic gradient (I) = dh / dL
The velocity of groundwater is
based on
a) hydraulic conductivity (K),
b) hydraulic gradient (I).
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4. Darcy’s Law
Kuliah Oleh : Dr. Eng. Sigit Sutikno, ST.,MT
Q = Discharge = volumetric
flow rate, volume of water
flowing through an aquifer per
unit time (m3/day)
A = Area through which the
groundwater is flowing, cross-
sectional area of flow (aquifer
width x thickness, in m2)
The equation is
Q = KIA
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5. Hydraulic Conductivity Test
Kuliah Oleh : Dr. Eng. Sigit Sutikno, ST.,MT
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6. Distance-Drawdown Analysis
Kuliah Oleh : Dr. Eng. Sigit Sutikno, ST.,MT
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6. Distance-Drawdown Analysis
Kuliah Oleh : Dr. Eng. Sigit Sutikno, ST.,MT
Persamaan debit tunak
sumur nirtekan
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6. Distance-Drawdown Analysis
Kuliah Oleh : Dr. Eng. Sigit Sutikno, ST.,MT
Persamaan debit tunak
sumur tekan
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6. Distance-Drawdown Analysis (Home Work)
Sebuah Sumur A dengan diameter (49+N) cm menembus suatu
akuifer seragam nirtekan mencapai lapisan kedap air yang terletak
(39+N) meter di bawah elevasi muka air tanah. Setelah diadakan
pemompaan dengan debit konstan sebesar 1 m3/detik, ternyata
penurunan elevasi muka air tanah dalam keadaan tunak pada
sumur-sumur yang berjarak (20+N) meter dan (50+N) meter dari
sumur A masing-masing adalah 3 m dan 2 m.
Dimana, N : Digit terakhir NIM
Pertanyaan:
a) Berapa nilai konduktivitas hidraulis dari akuifer? (20%)
b) Berapa penurunan muka air yang terjadi pada sumur artesis
A (20%)
c) Jika sumur anda berjarak (150+N) m dari sumur A, berapa
penurunan muka air yang terjadi? (20%)
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7. Groundwater Overdraft
Kuliah Oleh : Dr. Eng. Sigit Sutikno, ST.,MT
•In many locations groundwater withdrawal exceeds
natural recharge rates. This is known as overdraft.
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What happens when a new well here is heavily pumped?
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Flow direction can change
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7. Groundwater Overdraft
Kuliah Oleh : Dr. Eng. Sigit Sutikno, ST.,MT
Overpumping will have two effects:
1. Changes the groundwater flow
direction.
2. Lowers the water table, making it
necessary to dig a deeper well.
• Original land users and land owners
often spend lots of money to drill new,
deeper wells.
• Streams become permanently dry.
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Dissolved contamination travels with ground water flow
Contamination can be transported to water supply aquifers down flow
Pumping will draw contamination into water supply
8. Groundwater Contamination
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8. Groundwater Contamination
Leaking Gasoline
Floats on water table
Dissolves in ground water
Transported by ground water
Contaminates shallow aquifers
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8. Groundwater Contamination
Effects of pumping
Accelerates ground water flow
toward well
Captures contamination within
cone of depression
May reverse ground water flow
Will cause saltwater intrusion
Kuliah Oleh : Dr. Eng. Sigit Sutikno, ST.,MT
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Infiltrating water may bring
contaminants down to the water table,
including (but not limited to):
– Pharmaceuticals
– Pesticides/herbicides
– Fertilizers
– Mercury and gold mining
– Landfill pollutants
– Heavy metals
– Bacteria, viruses and parasites from sewage
– Industrial chemicals (PCBs, TCE)
– Acid mine drainage
– Radioactive waste
– Oil and gasoline
8. Groundwater Contamination
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Kuliah Oleh : Dr.. Eng. Sigit Sutikno, ST.,MT
That’s all for this class today,
any questions..???