Three reasons why reclamation of nearshore Manila Bay is a VERY BAD IDEA:

1. Rapid subsidence of coastal lands is enhancing the risk of flooding and high tides.

2. Storm surges are an ever-worsening threat, due in part to subsidence, but also from climate change because typhoons are increasing in strength and frequency.

3. Reclaimed coastal areas are the most susceptible to liquefaction during earthquakes.

1. Land subsidence

At Manila’s South Harbor, mean sea level rose at about 2 millimeters per year from 1902 to the early 1960’s. . .

. . . then started rising ten times as fast. WHY?

Groundwater withdrawal!

<20 million liters per day (MLD)

250 MLD

778 MLD

1770 MLD in 2004 (CEST 2004)

989 MLD in 1990 (JICA 1992)

Metro Manila`s

groundwater demand

is still increasing.

Consequently, subsidence

will continue and may even

accelerate!

(Global warming)

January 25, 1999 April 14, 2012

(Pinkish areas are house roofs)

Growth of Metro Manila

More areas below

sealevel

1900 1920 1940 1960 1980 2000 Year

12

10

8

6

4

2

0

Metr

o M

an

ila P

op

ula

tion

, m

illio

ns

GW

Extr

act

ion

, M

illio

n L

iters

per

Day

1800

1600

1400

1200

1000

800

600

400

200

0<20

250

778

989

Metro Manila Ground Water Usage

As population increases, groundwater use increases !!!

Average recharge for Metro Manila = 564

MLD (JICA 1992)

1770

If we use more water than nature

can put back (“recharge”), the land must sink!

Growth of Metro Manila Population

Pumping water too rapidly out of the aquifer reduces the pressure pore spaces between grains of sand and gravel. Water in the clay layers is sucked into the aquifer.

This causes the clay layers to shrink . . .

. . . and the ground surface to sink.

Pipe may appear to rise out of the ground

Pumps extract water from “aquifers” –layers of sand and gravel soaked with water.

How groundwater withdrawal causes land to subside

Loosely packed sand

When water is removed, grains crowd together a little more closely.

Volume is somewhat reduced, so land sinks a little. But sand cannot

compact very much.Clay deposits contains much more water . . .

and can shrink much more.

Our delta sediments are very clayey!

Subsidence from water withdrawal

Benchmarks used for re-leveling (1978 vs 2000) survey (Jacob 2004)

0.95

1.40

1.46

0.76

0.790.1

60.77 0.9

6

0.96

0.88

0.57

0.67

0.95

0.73

0.61

0.59

0.51

0.57

0.43

0.46

0.46

0.46 0.4

7

0.64

Maximum magnitude of subsidence – 1.46 meters or 6.4 centimeters/year (about 2½ inches/year) .

More recently, Lagmay et al. of National Institute of Geological Sciences have measured subsidence using satellite-borne Permanent Scatterer Interferometric Synthetic Aperture Radar

Subsidence in Greater Metro

Manila and vicinity from 2003-2006 from PSInSAR

(precision satellite data)

+ 19.2 mm/y

-43.8 mm/y

0 mm/y

MalolosGuiguinto

Valenzuela

Marilao

Kalookan

Obando

Taguig-Pateros

NavotasMalabon

Manila

Las PiñasMuntinglup

a

Cavite City

KawitRosario

Dasmariñas

San Pedro-Biñan

Mga Ibang Lungsod na Tabing-dagat sa Silangang Asia na Lumulubog Dahil sa Sobrang

Paggamit ng Tubig-poso SUBSIDENCE

LOCATION PERIOD Meters cm/year

Tokyo, 1918-87 4.5 6.5 Japan

Tokyo

Osaka, 1934-68 2.8 8.2 Japan

Osaka Shanghai, 1921-65 2.63 6 China

Shanghai

Yun-Lin, 1989-97 0.66 8.25 Taiwan (Fishpond area!)

Yun-Lin

Hanoi, 1988-93 0.1-0.3 2-6 Vietnam

Hanoi

KAMANAVA 1991-2002 0.3-1 2.7– 9.1

Manila

Bangkok, 1980-90 0.5-1 5-10 Thailand

Bangkok

Jakarta, 1991-99 0.3-0.8 4-10 Indonesia Jakarta

Dahil halos pantay ang lupain sa paligid ng Manila Bay, kahit maliit na pagtaas ng dagat

ay mahalaga.

Ang ibig sabihin nito ay kung tataas ang dagat ng isang metro

lamang, susulong ang tubig-dagat ng 10 o 20 kilometro.

. . . Ang lupa ay nakaangat ng 1 metro lamang mula sa taas ng

dagat.

10 o 20 kilometros mula sa dalampasigan…

Lowering of coasts (land subsidence) makes them increasingly vulnerable to the attack of waves and storm surges.

2. Storm surge

Storm Surge--Typhoon Pedring in Philippines(1).mov

23 September 2011 Super Typhoon Pedring

Roxas Boulevard

[stop the slide show and click the video icon below

before resuming the presentation]

Roxas Boulevard