Impacts of Climate Change on Water Quality and Measures against Future Issues

Yukihisa HOSAKA, Ph.D.*

Director in charge of Water Quality, Purification Division,

Bureau of Waterworks, Tokyo Metropolitan Government

1. Introduction

We are facing a crisis that we have never experienced before. Climate change such as global

warming is thought to have large impacts on waterworks.

This paper is to explain the influence of climate change on the water quality related in waterworks,

and to consider some mitigation and adaptation measures against climate change.

2. Influence of climate change on water quality

2.1 Increase in frequency of turbid water inflow into reservoir due to an increase in the number of days

of heavy rain

Recently, we have had many days of record heavy rain nationwide. Heavy rain days with rainfall

of 100 mm or more are expected to increase over the next 100 years.

Typhoon No.9 in September 2007 brought the heaviest rain in the recorded history of Okutama

(total amount of rainfall: 699 mm in Ogochi Reservoir Maintenance Office observation). This heavy

rain caused a large amount of turbid water to flow into Ogochi Reservoir, one of the water resources of

Tokyo, leaving the reservoir with high turbidity for three months or more. The turbidity of raw water in

Ozaku Purification Plant, which takes water about 25 miles downstream of Ogochi Dam, rose to 1900

degrees just after the typhoon. The plant should modify water management and request other

purification plants to supply the deficient amount of purified water.

It is estimated that flooding and landslide will frequently occur, resulting in frequent inflow of turbid

water into reservoirs.

2.2 Stagnation of circulation in reservoir due to global warming

Due to global warming, the surface water temperature of a reservoir in winter does not lower as

much as it had before, and as a result, it does not complete circulation in the reservoir bottom.

Therefore, nutrition salts elute from sediments at the reservoir bottom, deteriorating the water quality

and resulting in phenomena such as water-bloom. Such a phenomenon is observed in Lake Biwa

already.

In Ogochi Reservoir, we are also worried that water will not be circulated in the entire reservoir,

when atmospheric temperature will not be low enough.

* 2-8-1 Nishi-shinjuku, Shinjuku-ku, Tokyo 163-8001 Japan e-mail: hosaka-yukihisa@waterworks.metro.tokyo.jp

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2.3 Increased risk of toxic chemicals in raw water due to increase in the number of vermin

It is pointed out that atmospheric temperature rise may have an impact on terrestrial ecosystems,

raising concern in terms of waterworks that it may also affect water resource forests. It is also pointed

out that a temperature rise of 2 ℃ may cause a large deviation between actual forest distribution and

optimum distribution. And wind or insect damage should be considered in a forest where distribution

deviates from the optimum and its activities are low. The amount of agricultural chemicals is expected

to rise due to an increase in the number of vermin, and therefore there is fear of an increase in the

concentration of agricultural chemicals in the water resources.

2.4 Increase in production of trihalomethane due to water temperature rise

With respect to quality of tap water, trihalomethane is considered to be largely influenced by water

temperature. The following two factors are related to this phenomenon.

(1) Trihalomethane is produced by reaction between chlorine and organic material. The reaction rate

increases with water temperature, increasing production of trihalomethane.

(2) Rise in water temperature increases consumption of residual chlorine. Therefore, more chlorine

has to be supplied in the water purification process.

2.5 Increased risk of pathogenic microorganisms in tap water due to water temperature rise

There is concern that if water temperature in distribution pipe lines and receiving tanks rises due to

increase in atmospheric temperature, larger amounts of residual chlorine will be consumed, causing a

shortage of residual chlorine at the water supply end. When water coming out of a water distribution

net is reserved in a receiving tank, water temperature will rise due to external air. Especially, elevated

water tanks influenced by the urban warming will increase the risk of pathogenic microorganisms in the

tap water. Therefore, attention for disinfection should be paid to the tanks with a higher consumption

of residual chlorine.

3. Measures in waterworks against climate change

The Bureau of Waterworks, Tokyo Metropolitan Government will continue promoting the following

current activities, and prove their effect as mitigation or adaptation measures against climate change.

3.1 Mitigation measures in waterworks

(1) Promotion of renewable energy

The Bureau of Waterworks, Tokyo Metropolitan Government is intensively promoting the use of

renewable energies such as solar power generation and small-scale hydraulic power generation.

Solar power generation facilities are installed in the upper parts of distribution reservoirs, and also

installed when lids for filtration ponds in water purification plants are introduced. Small-scale hydraulic

power generation facilities are installed, which utilize residual pressure and the amount of water when

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tap water is induced to distribution reservoirs in water supply facilities.

(2) Promotion of measures for water leakage prevention

The Bureau of Waterworks, Tokyo Metropolitan Government has been intensively promoting

water leakage prevention as one of its major activities. We have successfully reduced leakage rate

that was 20%, 50 years ago to 3.3% in 2007, enabling the use of water resources of 340 million m3

annually. As a result, discharge of about 68 thousand tons of carbon dioxide could be reduced.

3.2 Adaptation measures in waterworks

(1) Measures to mitigate water-bloom in reservoir

In Ogochi Reservoir, there has been water-bloom in the summer season for the past 15 years.

There has been growth of algae covered on all surface of the reservoir in 2003. Therefore, we

equipped the fences to stop the flow of algae toward the direction of the dam and the pump systems to

transport algae to the reservoir bottom. In the last few years, the effect of this equipment has been

very successful.

The Bureau of Waterworks, Tokyo Metropolitan Government requests annually to make measures

in the other upper reservoirs, where Ministry of Land, Infrastructure, Transport and Tourism manage.

(2) Introduction of advanced water purification treatment

The Bureau of Waterworks, Tokyo Metropolitan Government is trying to reduce musty odor

materials and other organic materials by combining the normal, rapid filtration method with ozone or

biological activated carbon treatment as an advanced water purification treatment. We plan to

structure the advanced water treatment facilities at all of the 5 main purification plants receiving raw

water from Tone/Ara River by 2013.

Introduction of the advanced water treatment causes lower consumption of residual chlorine due

to lower concentration of organic materials in purified water.

(3) Proliferation/promotion of direct connection water supply

The Bureau of Waterworks, Tokyo Metropolitan Government is promoting proliferation/promotion

of direct connection water supply. Changing to direct connection water supply causes not only

reduction of carbon dioxide emission due to decreasing power consumption of pumps used for lifting

water from receiving tanks, but also decreasing consumption of residual chlorine.

Currently, direct connection water supply systems have been introduced to 90% or more of new

construction.

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Impacts of Climate Change on Water Quality and Measures against Future Issues

Yukihisa Hosaka, Ph.D.Director in charge of Water Quality

Bureau of Waterworks,Tokyo Metropolitan Government

Contents:

Influence of climate change on water qualityMeasures in waterworks against climate change

Mitigation measuresAdaptation measures

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Influence of Climate Change on Water Quality

1. Increase in frequency of turbid water inflow due to increase in heavy rain

2. Stagnation of circulation in reservoir due to global warming

3. Increased risk of toxic chemicals in raw water due to increase in vermin

4. Increase in production of trihalomethane due to water temperature rise

5. Increased risk in pathogenic microorganisms in tap water due to water temperature rise

Heaviest Rain by Typhoon No.9 in September 2007

Course of Typhoon No.9 in September 2007

Reference from Japan Meteorological Agency

Weather map at 9 a.m. on September 6th

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Water Resources for Water Supply in Tokyo

Dam (completed)Dam (under construction)

Tone River

Ara RiverMusashi Channel

Tama River

Sagami River

Tone RiverEdo River

Ogochi Reservoir

Ogochi Reservoir and Ozaku Purification Plant

Ogochi Reservoir

Ozaku Purification Plant

Okutama-machi

Hinohara-mura

Ohme-shi

Hinode-machi

Akiruno-shi

Hamura-shi

Hachioji-shi

Fussa-shi

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Rainfall Status of Typhoon No.9 in September 2007

4950

0

10

20

30

40

50

60

2007/9/5 1

:00

2007/9/5 7

:00

2007/9/5 1

3:0

0

2007/9/5 1

9:0

0

2007/9/6 1

:00

2007/9/6 7

:00

2007/9/6 1

3:0

0

2007/9/6 1

9:0

0

2007/9/7 1

:00

2007/9/7 7

:00

Hourly

rain

fall

dept

h (

mm

/hr) Total amount of rainfall: 699 mm

in Ogochi Reservoir Maintenance Office observation

Contour Map of Turbidity in Ogochi Reservoir on September 18, 2007

Alti

tude

(m)

Example of turbidity data in front of the Dam

300 deg.200

5010

3.550

60

effluent

In fr

ont o

f the

Da

m

Atam

i

Yuba

Kouc

hi

Mug

iyam

a

Miya

ma-

bash

i

Tozu

ra

Toko

roha

ta

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Change in Turbidity of Raw Water in Ozaku Purification Plant after Typhoon No.9

0

100

200

300

400

9/1 9/16 10/1 10/16 10/31 11/15

Turb

idity

of

raw

wat

er

(de

g.)

Highest value: 1900 deg.

Lower supply capacity in Ozaku if turbidity is 200 degrees or more.

Annual average of turbidity of Ozaku raw water

Stagnation of Circulation in Reservoir due to Global Warming

Winter

Cold

Warm Warm

Cold Cold

From spring to autumn

Normal water circulation

Cold

Global warming

Winter

If global warming advancesFrom spring to autumn

Warm Warm

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Nutrition salts eluting from sediments at the reservoir bottom may cause phenomena such as water-bloom even in winter.

Stagnation of Circulation in Reservoir due to Global Warming

Winter

Global warming PO43-, NO3

-

Increased Risk of Toxic Chemicals in Raw Water due to Increase in Vermin

Atmospheric temperature rise may have an impact on terrestrial ecosystem.The amount of agricultural chemicals is expected to rise due to an increase in the number of vermin.

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Increase in Production of Trihalomethane due to Water Temperature Rise

The reaction rate of production of trihalomethane increases with water temperature.More consumption of residual chlorine due to water temperature rise requires more supply of chlorine in the water purification plant.

Organic material + Chlorine → Trihalomethane

Increased Risk of Pathogenic Microorganisms in Tap Water due to Water Temperature Rise

Elevated water tanks affected by urban warming will increase the risk of pathogenic microorganisms in the tap water.

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Measures in Waterworks against Climate Change

Mitigation measures in waterworks1. Promotion of renewable energy2. Promotion of measures for water leakage

preventionAdaptation measures in waterworks

1. Measures to mitigate water-bloom in reservoir

2. Introduction of advanced purification3. Proliferation/promotion of direct

connection water supply

Promotion of Renewable Energy in Waterworks

0

2,000

4,000

6,000

8,000

10,000

12,000

At the end of FY2006 (Record)

At the end of FY2016(Target)

Pow

er g

ener

atio

n sc

ale

(kW

)

6,803kW

10,000kW

Solar power generation

(Asaka Purification Plant)

Target of power generation scale of renewable energy in Tokyo

Waterworks

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Promotion of Measures for Water Leakage Prevention

0

10

20

30

40

50

60

70

80

90

100

1945

1946

1947

1948

1949

1950

1955

1960

1965

1970

1975

1978

1979

1980

1981

1982

1983

1984

1985

1986

1987

1988

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

(%)

Leakage rate （％）

Systematic detection Emergency repair

20% in 19553.3% in 2007

Effect of Water Leakage Prevention

Saving of approx. 340 million m3/year of water (equivalent to water distribution in a city with 2.5 million residents)Saving of approx. 70 billion yen/year of costApprox. 68 thousand tons/year reduction of CO2 emissions

20% in 1955

Leakage rate

3.3% in 2007

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Measures to mitigate water-bloom in reservoir against global warming

Fences stop the flow of algae toward the direction of the dam in Ogochi Reservoir.

Water flow

Influent

Algae

10m

Gate for ship Float

2m

Fence Fence

Measures to mitigate water-bloom in reservoir against global warming

Algae between the fences is transferred to the reservoir bottom with the pump system.

35m from full water level

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0

50

100

150

200

250

300

19

90

19

91

19

92

19

93

19

94

19

95

19

96

19

97

19

98

19

99

20

00

20

01

20

02

20

03

20

04

20

05

20

06

20

07

Blue-green algae Others

Effect of measures to mitigate water-bloom in Ogochi Reservoir

Fences

Pumps

Day

of

wat

er-b

loom

app

eara

nce

(day

s)

Installation of equipment

Introduction of Advanced Water Purification Treatment to Reduce Odors and Chlorine Supply

Coagulation and sedimentation

Ozonetreatment

Biological activated carbon absorbing

advanced water purification

Rapid sand filtering

Purifiedwater

Raw water

Ozone treating basinBiological activated carbon absorbing basin

Ozone generator

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Proliferation/promotion of Direct Connection Water Supply

Water pressure in distribution

pipe released at receiving tank

Effective use of the water

pressure in distribution pipe

Water supply system with receiving tank

Pressure water service system

Elevated tank

Receiving tank

PumpBooster pump unit

Waterworks in the Future: Preparing for Risks Caused by Climate Change

Analysis/research of risks associated with climate change and provision of appropriate information

Studies of approaches that are not bound to conventional ideas or frameworks

Unprecedented Unprecedented changes in the changes in the environment environment

due to climate due to climate change change

Waterworks: Operations based on past climate conditions(patterns of rainfall and snowfall)

Temperature rise after 100 years

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