Groundwater

National University of Malaysia

1

Groundwater (Our Hidden Asset)

Class: Special lecture II for Regular Course 5th grade students

Oct. 9th (WED) 15:35-16:20

28-Jan-14

Wan Zuhairi Wan Yaacob (Assoc. Prof, PhD) Faculty of Science and Technology

National University of Malaysia 43600 Bangi, Selangor, MALAYSIA.


• What is Groundwater

• Groundwater as a resource

• Groundwater and Geotechnical Problems

• Groundwater movement in soil

• Conclusion

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Content:


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What is Groundwater?


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Two Types of Water

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Hydrogeology (Groundwater) Subsurface water

Hydrology (Surface water)

Unsaturated

Saturated

Water table

National University of Malaysia Groundwater

• Groundwater is a water that is found underground and is stored in the pore spaces (between grains) of porous geologic formation called an “aquifer”.

• The importance of groundwater is easily overlooked.

• Groundwater is a hidden asset, out-of-sight and out-of-mind.

Water Cycle

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Groundwater

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Piezometric surface

• Aquifer (permeable) • Aquitard (Impermeable) • Artesian well • Water table • Piezometric surface


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Groundwater as a Resource


Groundwater and the world’s freshwater supply

"...Altogether, (groundwater) aquifers store 97% of the planet's (available) freshwater."

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Water Usage in Large Cities in the World

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Water Usage in Malaysia

35

5

60

Groundwater utilization by sector

Industrial

Agricultural

Domestic

3

97

Water use by source

Groundwater

Surface water

10

Surface water

Ground water

• Japan (13%) • South Korea (32%)

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• Kelantan : 70% of its water source is from groundwater.

Groundwater

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“Air Kelantan”

Production well

Crystal clear groundwater

Privately owned tube well

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My hometown


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Surface water vs Groundwater

Slide from Dr. Saim Suratman (NAHRIM, Malaysia)


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Source: Dr Saim Suratman, NAHRIM

Sg. Langat, Selangor

Sg. Jeli, Kelantan

SW GW

SW GW

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Bank Infiltration

Fresh Water

River Water

Type of filtration that works by passing water to be purified for use as drinking water through the banks of a river or lake.


Source: Dr Azuhan Mohamed, Groundwater Expert.

Groundwater !!

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This is what people normally see This is what people should be able to see


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Source: Dr Azuhan Mohamed, Groundwater Expert.

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Groundwater and Geotechnical Problems


1. Groundwater & Mining

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Groundwater to mining engineer (eg. Penjom Gold Mine)

PENJOM GOLD MINE, MALAYSIA

How to manage the influx of groundwater into the open pit mine?


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Vaiont Dam, Italy

2. Groundwater & Stability of Dam

Before After


Trigger factor: the fluctuation of groundwater level

Vaiont Dam, Italy

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Slip surface

Water level before

Water level after


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Trigger factor: the fluctuation of groundwater level

Ancient Slip surface

Water level before Water level after

Before

After

Dam Reservoir Old landslide area


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Groundwater & Foundation

Expensive house

Crack developed under the house and surrounding area Problem: The foundation of the house failed,

Resulting cracks and unstable foundation.


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Reason for failure - Fill material = silt + gravel + boulder material - High K values - Channeling (old river) - Higher new water level/high water pressure

After development

Fill material

Retaining Wall

Before development

Original WT

Old river (diverted)


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Groundwater & Foundation Groundwater Modeling using Visual MODFLOW Pro


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Groundwater Contamination

Groundwater Remediation at Taman Beringin Landfill site Malaysia

Drilling (boreholes)


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Groundwater Contamination



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Groundwater Modeling using Visual MODFLOW Pro


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Groundwater Movement


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A measure of how easily a fluid (e.g., water) can pass through a porous medium (e.g., soils)

Loose soil

- easy to flow

- high permeability

Dense soil

- difficult to flow

- low permeability

water

Hydraulic conductivity

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Darcy’s Law

• Darcy’s experiment

• Henry Darcy

• French engineer

• 1856

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Darcy’s Law

Z = 0 (Datum) Z1, Z2 Elevation of manometer h1, h2 Elevation of fluid ∆𝒍 Distance of manometer

V (specific discharge) of cylinder

𝒗 =𝑸

𝑨

𝒗 𝜶 ∆𝒉

𝒗 𝜶 𝟏/∆𝒍

E1

𝒗 𝜶 (𝒉𝟏 − 𝒉𝟐)

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Darcy’s Law

𝑸 = V.A = (−𝒌 𝝏𝒉/𝝏𝒍) . 𝑨

𝒗 𝜶 − ∆𝒉 𝒗 𝜶 𝟏/∆𝒍

𝒗 𝜶 − ∆𝒉/∆𝒍

𝒗 = −𝒌 ∆𝒉/∆𝒍

𝒗 = −𝒌 𝝏𝒉/𝝏𝒍

If 𝝏𝒉/𝝏𝒍 (constant); 𝒗 𝜶 𝑲 ; 𝑲 = 𝒉𝒚𝒅𝒓𝒂𝒖𝒍𝒊𝒄 𝒄𝒐𝒏𝒅𝒖𝒄𝒕𝒊𝒗𝒊𝒕𝒚

E2

E2 E1

𝑸 = −𝒌 . 𝒊 . 𝑨

-ve sign: the direction of flow is towards the

decreasing hydraulic head

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Laboratory Field

- Manometer - piezometer

Borehole / Well

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• A confined aquifer has a source of recharge.

• The discharge, Q = 37500 m3/day

• The piezometric head in two wells 1000 m apart is 55 m and 50

m respectively, from a common datum.

• The average thickness of the aquifer is 30 m, and the average

width is 5 km.

Example of Darcy’s Law

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National University of Malaysia Calculate:

(a) Calculate the hydraulic conductivity (K) ?

5 km

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Solution

Cross-Sectional area (A) = 30(5)(1000) = 15 x 104

m2

Hydraulic gradient (i) = (55-50)/1000 = 5 x 10-3 (No unit / unit less)

Q = 37,500 m3/day Darcy’s Law, Q = k.i.A k = Q / i.A = (37500) / (5 x 10-3)(15 x 10

4 )

= 50 m/day (0.000578703704 m/sec) = 5.79 x 10-4 m/sec


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50


int xn dx = xn + 1/(n + 1)

logex = 2.303 log10 x

𝑘 = 2.3

𝑄𝑡 . 𝑙𝑜𝑔10

𝑟2

𝑟1

𝜋 (𝑧2 2 − 𝑧1

2 )

Determination of permeability in the field


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Example:

Pumping well Rate = Q

Observation well

Z1, Z2

r1,r2

𝑘 = 2.3

𝑄𝑡 . 𝑙𝑜𝑔10

𝑟2

𝑟1

𝜋 (𝑧2 2 − 𝑧1

2 )


Groundwater is precious as a clean water resource

Groundwater has implication on engineering structures and stabilities

Groundwater can pollute – need for better understanding about the groundwater safety

Movement of groundwater is govern by Darcy’s Law.

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Conclusions


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Thank you どうもありがとうございました

Education

Groundwater