Horikawa Sen-nin Chosatai 2010 （HSC) Place：
Nagoya Urban Institute
Summary meeting for the 25th stage Conference room (11 floor)th

The secretariat of Horikawa Sen-nin Chosatai 2010
Sep.28th.2019

1

1. Horikawa Sen-nin Chosatai 2010
～Transmission of Raw Water from
Kiso Riveｒ～

The formation of HSC (April.22nd.2007)
With a viewpoint and a sence of citizens, the survey of theclarification effect of TRWKR started

1.Purpose
To verify the clarification effects of TRWKR with citizens(1)Develop to new clarifying measures(2)Asses the influence on an ecosystem(3)Sustain and enhance citizens’ activities(4)Develop citizens’ awareness in the entire
Horikawa River basin

2.Water source and Volume oftransmission of raw water(1)Water Source : Kiso River(2)Volume of transmission of raw water : Maximum 0.4 m3/s

■ The survey from a viewpoint and a sence of citizens’＊Clearness ＊Transparency ＊Color ＊Bubble ＊Smell＊Garbage ＊Creatures, etc

3.Pilot project period(1)Evaluation and Survey term : About 5 years（from Apr.2007 to Mar.2012）(Including the term of follow-up survey and evaluation after
the stop of TRWKR)(2)TRWKR period : about 3 years(from Apr.22nd.2007 to Mar.22nd.2010)■Increase of Transmisson Volume from the Shonai River(additional pilot project）
1.Water source and Volume of transmission of raw water(1)Water Source : Shonai River(2)Transmission Usual 0.4m3/sec (maxium 0.7m3/sec)

2.Period of Increase(1)Experiment Period ： Oct.1st - Dec.31st.2010(2)Period of Increased Transmision Volume : Oct.5th - Nov.2nd.2010

The first Nagoya City
Environmental Practice Prize,
Feb.2012
Branch of contribution for
Regional Environment
Development Award
for Excellence

Water Resource Contributor
Awards
Minister of Land,
infrastructure andTransportation) Aug.20162

Transmission of Raw Water from Kiso River
3 years from April.22nd.2007（Stopped on March.22nd.2010）
To verify the clarification effects of TRWKR
Surveys during TRWKR period :April.2007 ～ March.2010
Surveys after the stop of TRWKR period :April.2010 ～ March.2012

Horikawa Sen-nin Chosatai
April.2007 ～ March.2012■ Fixed Point Observation Groups
Surveying effects of TRWKR■ Free Survey Groups Researching
Horikawa River by free themes■ Horikawa Cheering Groups Cheering
clarification of Horikawa

The survey froma viewpoint and asence of citizens

Results of pilot project (Clarification effects of TRWKR)■ It was confirmed that the water quality tended to improve
during TRWKR between Sanage Bridge and Matsushige
Bridge.
■ Network of citizens who wish for clarification andrestoration of Horikawa River expanded.
■ Citizens’ awareness of cleaning of the river wasdeveloped.

■ Role of Horikawa Sen-nin Chosatai(Conclusions of Summary Meeting for the 10th Stage)① More surveys should be implemented.
・Continuity of investigation, clarification of thesituation of the river, identification of cause ofpollution in the river, are needed.
・We improve our plan and take action against
the pollution.
・After that, citizens and public administration
do what is possible to clean the river.

②There are many things that citizens
can do.
・We expand our partners who love
Horikawa River and hope TRWKR again.
・We deepen exchanges with people
living in the basin of Kiso, Nagara, and Ibi
River.
・We check the effects of pollution
removal from domestic wastewater andimplement it in each house.

3Won the21st Japan Water Award Minister of Land,
Infrastructure and Transport Award June 2019
National Museum of Emerging Science and Innovation(Ome, Koto-ku, Tokyo)

On June 25, 2019, the award
ceremony for the 21st Japan
Water Awards was held in thepresence of Crown Prince
Akishino. Horikawa Sen-nin
Chosatai Executive Committee
received the Minister of Land,
Infrastructure, Transport andTourism Award.

Horikawa Sen-nin
Chosatai Executive
Committee visited Mayor
Kawamura to report on
the Japan Water Award
and Minister of Land,
Infrastructure, Transport
and Tourism award.

4

Public-private academic
collaboration step-up partnershipＡ

Plan
Action Citizen'sＣviewpointand sense

Check

Ｐ
Do

Ｄ
5

Observation method at fixed-point
Measurement of Transparency
Transparency
Meter
100cm
Photo: Shinko Survey Group

What is yourimpression of…
Clearness?
Transparency?
Color? Bubbles?
Smell? Garbage?
Creatures?

Measurement of COD
COD: Chemical Oxygen DemandThis is an index of water contamination used
for sea, lakes, and marshes.
It is an oxygen consumption required foroxidation of organic matters dissolved inample water.
The higher COD, the more it is contaminated.

COD Pack Test

ゆりの会調査隊

6

Water Environment of Horikawa River
Area of basin: 51.9km2
Length: 16.2km(Tidal effect section 13.6km)

Change in temperature, precipitationand hours of sunshine
Cause of breedingofpphytoplankton,
nitorogen andphosphorus areincluded inwastewater fromhouses, factories
andstores.

The primary cause of water pollution is wastewater from houses, factories, and stores.

Wastewater is discharged after treatment in wastewater treatment plant.
●●●

After heavy rain, wastewater isdischarged without treatment.

It has looked like redtide or blue tide.
In Nagoya Port anddownstream ofHorikawa, it is said
that phytoplankton
does over breedingand extinction, so
water basin is polluted
Red Tide

Kiso River is our water source.

●●●●●● ●●●●●●

Shonai River
Privisional raw watertransmission: 0.3m3/s

●●●

●●●

●●●

Wastewater
Treatment Plant

Tide Gate

Sanage Bridge

Motoiri Sluiceway▼High Tide Horikawa River
Difference of water level is more than 2m between
high tide and ebb tide.
Water level, direction of current and velocity are changed, by tide.

▼Ebb Tide

Nagoya Port

Shimizu wakuwaku-sui

Groundwater, etc

RisingIse Bay
Blue Tide

Sludge rises and floats.

Floating Sludge

Raised Sludge

7

2．Number of Participants ofHorikawa Sen-nin Chosatai(Horikawa Sen-nin Chosatai started
accepting participation on 26th Mar.2007)

Investigation spots

Network of citizens who wish for clarification
and restoration of Horikawa River is growing.

More than 50 thousand citizens’ network
Horikawa, the Mother River of Nagoya, was polluted in rapid economic growth..
The citizens have rised to get the past back.
名古屋駅

Start

Now

22nd Apr.2007

28th Sep.2019

Fixed Point
Observation
Groups55 groups
497 persons

106 groups
1,024persons

Free Survey
Groups

22 groups
234 persons

40 groups
650 persons

Horikawa
Cheering
Groups

88 groups
1,531 persons

2,597 groups
51,915 persons

Total

165 groups
2,262 persons

2,743 groups
53,589 persons

8Number of Participants◆ Fixed Point Survey Group (FPOG) ・・・・・・・1,024
surveying on the fixed points◆ Free theme Survey Group (FSG) ・・・・・・・・・・650
surveying on free themes◆ Horikawa Cheering Group (HCG) ・・・・・・・51,915
supporting clarification of Horikawa
total 53,589

As of Sep. 28th, 20199

３．Survey Periods and Number of Reports
Reports
Content

Fiscal year

Survey Period

1st stage

Interval

Jul.1st～Sep.19th

Autumn～Early WinterSep.20th～Dec.16th

258
134
383
103
245
64
152
100
145
54
120
81
111
44
104
72
112
42
133
77
148
60
139
92
145
70
113
79
133
91
99
107
113
81
126
91
127
62
130

Interval

Dec.17th～Mar.31st

104

Spring～Early summer

Horikawa River Purification Social ExperimentInterval

2007

With
TRWKR
0.4
m3/s

2nd stage
3rd stage

2008

4th stage
5th stage

2009

6th stage
7th stage

2010

8th stage
9th stage

2011

10th stage
11th stage

2012

12th stage
13th syage

2013

Publicprivate
academiccollaboration
step-uppartnership

14th stage
15th stage

2014

16th stage
17th stage

2015

18th stage
19th stage

2016

20th stage

Reports

ShinHorikawa
Horikawa
River
River
Apr.22nd～Jun.30th
Jul.1st～Sep.7th

Autumn～Early WinterSep.8th～Dec.16th

Interval

Dec.17th～Mar.31st

Spring～Early summer

Apr.1st～Jun.30th

Interval

Jul.1st～Sep.27th

Autumn～Early WinterSep.28th～Dec.16th

Interval

Dec.17th～Mar.31st

Spring～Early summer

Apr.1st～Jun.30th

Interval

Jul.1st～Sep.26th

Autumn～Early WinterSep.27th～Dec.16th

Interval

Dec.17th.～Mar.31st

Spring～Early summer

Apr.1st～Jun.30th

Interval

Jul.1st～Sep.11th

Autumn～Early WinterSep.12th～Dec.17th

Interval

Dec.18th～Mar.31st

Spring～Early summer

Apr.1st～Jun.30th

Interval

Jul.1st～Sep.10th

Autumn～Early WinterSep.11th～Dec.16th

Interval

Dec.17th～Mar.31st

Spring～Early summer

Apr.1st～Jun.30th

Interval

Jul.1st～Sep.21th

Autumn～Early WinterSep.22th～Dec.16th

Interval

Dec.17th～Mar.31st

Spring～Early summer

Apr.1st～Jun.30th

Interval

Jul.1st～Sep.28th

Autumn～Early WinterSep.29th～Dec.17th

Interval

Dec.18th～Mar.31st

Spring～Early summer

Apr.1st～Jun.30th

Interval

Jul.1st～Sep.28th

Autumn～Early WinterSep.29th～Dec.16th

Interval

Dec.17th～Mar.31st

Spring～Early summer

Apr.1st～Jun.30th

Interval

Jul.1st～Sep.19th

Autumn～Early WinterSep.20th～Dec.16th

Interval

Dec.17th～Mar.31st

Spring～Early summer

Apr.1st～Jun.30th

258
134
383
103
245
64
152
100
145
54
120
81
111
44
104
72
112
42
133
77
148
59
135
78
129
55
99
68
117
78
90
89
100
69
109
79
116
54
107

1
4
14
16
15
14
11
16
13
9
18
13
12
17
12
11
8
23

84

20

Content

Fiscal year

21st stage

2017

Publicprivate
academiccollaboration
step-uppartnership22nd stage
23rd stage

2018

24th stgae
25th stage

2019

ShinHorikawa
Horikawa
River
River

Survey Period

Spring～Early summer

Apr.1st～Jun.30th

Interval

Jul.1st～Sep.18th

Autumn～Early WinterSep.19th～Dec.20th

Interval

Dec.21st～Mar.31st

Spring～Early summer

Apr.1st～Jun.30th

Interval

Jul.1st～Sep.19th

Autumn～Early WinterSep.20th～Dec.16th

Interval

Dec.21st～Mar.31st

Spring～Early summer

Apr.1st～Jun.30th

129
58
121
80
180
76
184
108
193

100
48
93
67
107
44
106
67
127

29
10
28
13
73
32
78
41
66

5,773

5,156

617

Interval
26th stage

Autumn～Early WinterSep.20th～Dec.16th(plan)Interval

Total

To date, 5773 reports have been reported. Of
these, the number of reports for Shin-Horikawa
River was 617.
In the 25th stage, there were 193 reports. Of
these, 127 were reported for Horikawa River and
66 were reported for Shin-Horikawa River.
On average, more than 400 surveys are
conducted every year in Horikawa River and ShinHorikawa River.
Many citizens are continuously examining theactual water environment of Horikawa River andShin-Horikawa River on a daily basis from theperspective and sense of the citizens.

10Number of Reports
6000
5500
5000

５，７７３reports
at the end of 25th stage

4500
3500
3000

More than 400 reports
every year

2500
2000
1500
1000
500

Over 50,000 people joined in Chosatai.
The number of reports will reach 6,000 more.

0

第1st.
第2st.
第3st.
第4st.
第5st.
第6st.
第7st.
第8st.
第9st.
第10st.
第11st.
第12st.
第13st.
第14st.
第15st.
第16st.
第17st.
第18st.
第19st.
第20st.
第21st.
第22st.
第23st.
第24st.
第25st.

report

4000

stage

11

4. Weather condition
In the 25th stage(Apr.-Jun.), the weather changed every few
days. And the temperature was a little high for spring or earlysummer. The rainfall was as the average. The rainy season
started on July 7th as the average.
characteristic: the weather changed every few days.
It is often fine and high temperature.
■Temperature
The rainfall was as the average.

The average temperature was 19.2℃, higher than the average(18.7℃). In the average temperature by the month, it was higher in May
than the average, as high in April and June.
■Rainfall
The rainfall was 145mm a month , as high as the average(160.8mm).
In the rainfall by the month, it was as high in April and May as theaverage, less in June.
■Time of daylight
The time of daylight a month was 222 hours, 41 hours longer than the
average. It was longer than the average in all month.

data : The statistical information by Japan Meteorological Agency
Nagoya Local Meteorological Observatory
http://www.jma.go.jp/jma/menu/report.html

The average by Nagoya Local Meteorological Observatory
Temperature
RainfallDaylight
Category(℃)(mm)(hour)
Gross
Average Highest
LowestGross
Statistical
period

1981
～2010

1981
～2010

1981
～2010

1981
～2010

1981
～2010

30
1535.3
124.8
156.5
201.0
Average 160.8
Sep.
234.4
Oct.
128.3
Nov.
79.7
Dec.
45.0
Average 121.9

30
15.8
14.4
18.9
22.7
18.7
24.1
18.1
12.2
7.0
15.4

30
20.7
19.9
24.1
27.2
23.7
28.6
22.8
17.0
11.6
20.0

30
11.9
9.6
14.5
19.0
14.4
20.7
14.1
8.1
3.1
11.5

30
2091.6
196.6
197.5
149.9
181.3
151.0
169.0
162.7
172.2
163.7

years
Annual
Apr.
May
Jun.

Average 18.7℃
Average temperature in 25th stage was 19.2℃,
it was a little higher than the average of common year.
In 25th stage, it was higher in May than the average of common
year, as high in April and June as the average of common year.

Average in April - June(1981-2010)
The average is 18.7℃.

Temperature

12

data : The statistical information by Japan Meteorological Agency
Nagoya Local Meteorological Observatory
http://www.jma.go.jp/jma/menu/report.html

State of the weather
RainfallAverage in April - June(1971-2010)
The average is 160.8mm.
Monthly average rainfall in 25th stage was 145mm,
it was as higher as the average of common year.

In 25th stage, it was as high in April asd May the average ofcommon year, a little less in June than the average of common year.

The average 160.8mm

Time of daylight
Monthly average time of daylight in 25th stage was
222 hours, it was 41hours longer than the average ofcommon year.

average 181.3 hours

Average in April - June(1971-2010)
The average is 181.3 hours.

In 25th stage, it was longer in all month than the average ofcommon year. Especially, it was more than 70 hours longer in
May.

13

( reference ) Average daily temperature and precipitation

19th stage
Ｃｈａrａｃｔｅｒｉｓｔｉｃ : high temperature,abundant rainfall

Temperature(C)Temperature ave.(C)Temperature high(C)Average temperature
0.5 C over->high temperature-0.5 C under->low temperature
Averageprecipitation(mm/month)
20mm/day over->Heavy rain
-20mm/day under->light rain

Beginning of the rainy season June 7

Normal value 18.7 C

21st stage

Precipitation (mm)Beginning of the rainy season June 4

Normal value 18.7 C

Precipitation (mm)Note) Arrangement
Characteristic ofweather in target period

Temperature high(C)Characteristic : There weremany sunny days, hightemperature

Precipitation (mm)Temperature ave.(C)Temperature(C)Precipitation (mm)14

( reference ) Average daily temperature and precipitation
Temperature ave.(C)Temperature high(C)23rd stage
Temperature(C)Note) Arrangement
Characteristic ofweather in target period

Beginning of the rainy season June 6

Ｃｈａrａｃｔｅｒｉｓｔｉｃ : Weather changes every few days.
Memorial high temperature(cap)abundant rainfall(cap)Precipitation (mm)Precipitation (mm)Average temperature
0.5 C over->high temperature-0.5 C under->low temperature
Averageprecipitation(mm/month)
20mm/day over->Heavy rain
-20mm/day under->light rain

Weather overview 25th stage

Temperature ave.(C)Temperature high(C)Temperature(C)25th stage

Ｃｈａrａｃｔｅｒｉｓｔｉｃ : Weather changes every few days.
Many sunny days and high temperature
Precipitation is normal.

Precipitation (mm)Precipitation (mm)Weather changes every few
days, and there were manysunny days.
April temperature dropped due
to cold. In May, warm air
entered and the temperature
became quite high.
The precipitation was normal in
April and May.
There were many sunny days in
June.
From May to June, thetemperature was high andsunshine hours were longer.
The rainy season was on June
7, normal June 815

■ Shaping of Rapids and Pool
kingfishers, egrets, tortoises, etc.
fish such as
carp, gibels,
hemibarbus barbus

small fish suchas pale chubs, fries of palechubs etc.
rhinogobius

shrimps, crabs, aquatic insects, etc.

stacks ofstones■ Rise of self-purification by food chain

It was identified that variousorganisms breed and growwhen rapids and pools wereshaped.
It was a place of inhabiting
and growing of creatures that
prefer the environment, suchas Oikawa, which has stones
and moss. When wintercomes, some ducks are
waiting for spring here.
Prawns and Japanesemitten crabs areorganisms that
migrate between
rivers and the sea.

dirt of water (organic substance, nitrogen, phosphorus)
Algaes and microbes stick on stones with the dirt as nutrition.

Small fish, shrimps, aquatic insects feed the algaes andthe microbes.
Big fish and birds prey the small fishes and aquatic insects.
Fufu Bridge
Kurokawa No.1 Bridge*denizen

Waterside
kingfishers,
egrets, etc.

Watermauremys
reevesii,
trachemys
scripta*carp, hemibarbus barbus
catfish, black basses*,
bluegills*, northern snakeheads*

gibels, pale chubs, goby minnows,
rhinogobius, mosquitofishes*, etc.

palaemon paucidens, prawns,
Japanese mitten crabs, aquatic insects, etc.

Ingredients in the water are
taken up by living creatures in
the food chain and consumed
for growth and reproduction.
When a waterfall is formed anda diverse and rich ecosystem isconstructed, more dirt
components are consumed in achain and the water becomesclean.
The self-cleaning action of theriver will increase.

photo by the secretariat May in 2019
Rapids and pools shaped in thepast keep a diversity withchange according to environment.

Kurokawa No.1 Bridge

photo by the secretariat May in 201916

Newly sand-cover construction Securement of a water source Measures against smells
at Shin-Horikawa River
Bet. Sakura -Habashita Bridge(Using shallow ground water)
Jan.2015-Feb.2015,Dec.2017-Jan.2018

A well at upstream of Kinjyo Bridge
started its operation in Mar 2018

Keiun Bridge(Dredging・Sand covering)
Downstream Dec.2017-May.2018

Gojo Bridge

Koshio Bridge

Habashita Bridge
School of young mullets
at the sand-covered place

Photos by the secretariat
Jan.2019
Photos : May 15, 2018

Photos by the secretariat
May 17, 201817

5. 25th stage survey report
5.1. Introduction ～Column～～Column～ For the clarification and regeneration of Horikawa River～Pilot project of the clarification of Horikawa River～;we confirmed the clarification effect of TRWKR from April.2007 to March.2012
We confirmed that water quality between Sanage Bridge and Matsushige Bridge had been improved by
TRWKR(0.4m3/sec.) in this five years. And in this period, we confirmed that garbage (artificial garbage:
plastic type garbage etc.)were reduced. It is considered that because the citizen’s awareness changed,
and cleaning activity became active.
【Five years summary】■We confirmed clarification effect of TRWKR between Sanage Bridge and Matsushige Bridge.
■Network of citizens wishing for clarification and regeneration of Horikawa River has expanded greatly.
■Citizen’s awareness changed, and the cleaning activity became active.

18

(1)Weather Condition
The weather changed every few days in April and May. But these have been many sunny. The temperature got
cold and made a big change. But it got warmer and rised quite in May. The amount of rainfall stayed as usuall in
April and May. These have been many sunny in June. Moreover, the temperature tended to be high and got more
hours of sunlight from May to June. Rainy season was started on June 6.(Usually June 8ｔｈ)
(Feature of weather in the 25th stage: Many fine weather and high temperature and average annual amount of
rainfall)(2) New Measures for Water Quality Improvement
After the stop of water conduction from the Kiso River in March 2010, new measures for water quality
improvement of Horikawa River have been implemented. Shallow and deep in upstream section of Sanage Bridge
for improvement of self-purification function has been implemented since 2010. Also, advanced water treatment
at Meijo Water Treatment Center was installed, and river rain-water reservoir for pollution control in right bank ofHorikawa River was available in 2010.
Water conduction to Horikawa River (max. 4,000 m³/day, Period: Apr.-Oct) using recycled waste water(advanced treatment/ membrane filtration method) of Moriyama Water Treatment Center) started since 2011.
Experiment of covering sand for water purification between the Naka Bridge and the Gojo Bridge started in Feb.
2015. The 8th well was dug in the upstream section of Kinjo Bridge in March 2017 and utilization of shallow
ground water (0.01m3) started as new water source. (Utilization of shallow ground water has been implemented
in 2004).
Furthermore, in reference to the results of the Horikawa River purification experiment with citizens which started
in February 2015, covering sand was carried out for waterside environment improvement of Habashita Bridge toGojo Bridge and Naka Bridge to Sakura Bridge in 2018.
Also, since deposition and exposure of sludge, air bubbles and cloudiness were confirmed in the Shin Horikawa
River junction through citizen's survey, dredging and converting sand were carried out as measures against odors.
Such a measures were also proceed in the upstream district since September 2018.
And then, new shallow and deep was formed upstream of the Kizune Bridge on the Horikawa River.

19

(3) Change of the water quality of Horikawa River
The impression of the clearness of Horikawa River worsened after stopping water conduction from the Kiso
River. However, after that, generally we can confirm the trend of improvement little by little from upstream
though water quality sometimes deteriorated due to weather conditions, etc... Espeically, it was possible toconfirm remarkable improvement trend regarding to “impression of water pollution”, “transparency” and “scent”
in the 25th stage.
The average transparency between Sanage Bridge and Oseko Bridge was more than 80 cm, and transparency
between Asahi Bridge and Oseko Bridge was around 90 cm in particular.
In addition, “bubble from bottom of river” and “percentage of ditch-smell / mud-smell” decreased, so
percentage of odorless increased to 75% between Sanage Bridge and Oseko Bridge.
As we mentioned above, some improvements were confirmed in the several clauses surveyed by citizen's
viewpoints and senses, such as the condition of the riverbed, transparency (perspective), and scent, in the mid
and downstream sections of Horikawa River in the 24th stage.
We think that reason of such a result is the change of public awareness for "purification & regeneration ofHorikawa River", implementation of new water quality improvement procedure after water conduction, andmaintenance of revetment including removal of sludge on the river channel.

20

Impression of Water Clearness（Section Average）
The ratio of “Clean”, “Slightly clean” and “Ordinary（Note）Except the data between Minatoshin Brdg. and Oseko Brdg. for not enough data

The 1st-6th stage ： With TRWKRNo rain on the day and the previous day
The 7th-25th stage： No TRWKRNo rain on the day and the previous day

New Measures for Water Quality Improvement

With TRWKR

Making shallows and deeps
Making shallows and deeps
Transmission of Raw Water from Shonai River

Covered Sand

Introduction of advanced water treatment at Meijo Water Treatment Center
In-service of Horikawa Ugan Rain-water Reservoir for pollution control
Utilization of reclaimed wastewater at Moriyama Water Treatment Center(Ｅｖａｌｕａｔｉｏｎ)（ upstream ）Btwn. SakaeBrdg.
and SanageBrdg.
（Not enough data)

39

Btwn. Sanage Brdg.
and Johoku Brdg.

16

Btwn. Johoku Brdg.
and Asahi Brdg.
(Not enough data)
Btwn.Asahi Brdg.
and Matsushige Brdg.

Influence of transmission of raw water from Shonai River

％
93

87

50

87

100

60

100 100 100 100 100

75

100

100 100 100 100 100 67

60

100 50100 (55)
No Data
Average
21・23st

57

43

73

53

36

29

62

40

39

23

20

50

30

56

73

58

70

60

69

46

77

63

56

57

Improved a little from upstream(Sometimes, the weather condition influences)
8

38

36

50

23

50

With TRWKR→Improved from upstream
11

39

23

57

21

25

0

20

12

42

21

25

14

27

40

67

50

62

0

20

34

50

75

67

0

37

28

21

12

20

24

31

24

53

27

48

17

10

5

55

39

After the stop
Of TRWKR→Worsened
028

5

Btwn. Matsushige Brdg.
53
14 55
6
72 43
84
50
16 54
3
34
61
56
18
27 45
22
20
12
56
62 100 57
20
and Oseko Brdg
1st. 2st. 3st. 4st. 5st. 6st. 7st. 8st. 9st. 10st. 11st. 12st. 13st. 14st. 15st. 16st. 17st. 18st. 19st. 20st.21st. 22st. 23st. 24st. 25st.
（downstream ）Hot Hot Cold Hot Hot
Hot
Hot＊“Clean”, “Slightly clean” and “Ordinary” are categorized
as the acceptable range for citizens.

Heavy Heavy Little Heavy Heavyrain rain rain rain
rain％（Dirty）％（Clean）

Impression of water clearness could see the tendency of the improvement from upstream with TRWKR. But it worsened after the stopof TRWKR. After that, overall it improved a little from upstream. (sometimes it deteriorated by the weather condition.) It is thought that
this is the effect by change in citizen consciousness and new measures for water quality improvement after the stop of TRWKR.

22The 1st-6th stage ： With TRWKR

Occurrence of bubbles from river bottom(Section Average) No rain on the day and the previous day
The 7th-25th stage： No TRWKRNo rain on the day and the previous dayNote）Except the data between Minatoshin Brdg. and Oseko Brdg. for not enough data

New Measures for Water Quality Improvement

With TRWKR

Making shallows and deeps
Use of shallow ground waterTransmission of Raw Water from Shonai River
Covered Sand
Introduction of advanced water treatment at Meijo Water Treatment Center

In-service of Horikawa Ugan Rain-water Reservoir for pollution control
Utilization of reclaimed wastewater at Moriyama Water Treatment Center(Evaluation)（upstream）
Btwn.Sakae Brdg.
And Sanage Brdg.

25

3

33

50

13

0

0

0

0

0

Btwn. Johoku Brdg.
and Asahi Brdg.

0

0

0

0

0

0

0

0

0

0

20

0

0

0

(10)

Though the bubbles condition got worse
depending on water conditions,
It had a tendecy to improve from upstream area

（Not enough data）

Btwn. Sanage Brdg.
and Johoku Brdg.

No Data
Average
21・23st

％

21

6

19

0

11

With TRWKR→Improved

6

32

13

20

After the stop
Of TRWKR→Worsened

13

36

25

31

6

13

17

22

13

27

23

8

0

0

7

20

8

5

0

0

8

0

0

0

10

0

21

17

0

0

20

0

40

17

0

0

0

0

0

0

0

58

23

56

30

42

0

38

13

58

12

18

35

40

0

31

7

24

19

18

9

21

11

62

8

24

7

3

3

0

0

0

14

0

13

3

8

0

7

0

5

0

0

5

13

5

0

5

0

0

0

（Not enough data）

Btwn.Asahi Brdg.
and Matsushige Brdg.

Btwn. Matsushige Brdg.
and Oseko Brdg.

1st. 2st. 3st. 4st. 5st. 6st. 7st. 8st. 9st. 10st. 11st. 12st. 13st. 14st. 15st. 16st. 17st. 18st. 19st.20st. 21st. 22st. 23st. 24st. 25st.
In
Hot
Hot
Hot
In
Hot
Hot
Little Year Year
LittleAverageRain
Rain Average（downstream）%

Hot
Hot Hot
Hot Hot
Hot
Cold
Hot
Hot
Hot
Hot Hot
Hot
Cold
Heavy Heavy Little Heavy Heavy
Heavy Heavy Little Heavy Heavy
Rain
rain rain
Rain
Rain
Rain
rain rain
Rain
Rain

%

It is observed that bubbles from river bottom condition was improved with TRWKR and after TRWKR stopped, it got worse. After that, it had a tendency to improve while
bubbles condition has fluctuated repeatedly although weather conditions sometimes made it worse. It is assumed that the change of public awareness and new measures for
Water Quality Improvement after stop of TRWKR have effects on this. It seems that the condition of river bottom is gradually improved.

23

The change of occurrence of smell（The ratio of “Terrible smell”&”smell”：Section Average）

The 1st-6th stage ： With TRWKRNo rain on the day and the previous day
The 7th-25th stage： No TRWKRNo rain on the day and the previous dayNote）Except the data between Minatoshin Brdg. and Oseko Brdg. for not enough data

New Measures for Water Quality Improvement

With TRWKR

Making shallows and deeps
Use of shallow ground waterTransmission of Raw Water from Shonai River
Covered Sand

Introduction of advanced water treatment of Meijo Water Treatment Center
In-service of Horikawa Ugan Rain-water Reservoir for pollution control
Utilization of reclaimed wastewater at Moriyama Water Treatment Center(Evaluation)（upstream）
Btwn.Sakae Brdg.
And Sanage Brdg.

(％)
9

3

7

50

0

0

0

Btwn. Johoku Brdg.
and Asahi Brdg.

0

0

0

0

0

0

0

0

0

0

0

0

0

0

(0)

2

15

9

10

6

29

6

10

17

16

25

6

0

0

0

22

7

25

0

8

0

14

7

0

50

15

0

50

16

0

60

40

33

0

7

41

14

36

20

0

0

0

27

13

0

5

0

0

0

After the stop
Of TRWKR→WorsenedWith TRWKR→Improved
39

23

Btwn. Matsushige Brdg. 7 12
and Oseko Brdg.
1st. 2st.
（downstream）

027（Not enough data）

Btwn.Asahi Brdg.
and Matsushige Brdg.

0

Although weather conditions sometimes made it worse,
It had a tendecy to improve from upstream area

（Not enough data）

Btwn. Sanage Brdg.
and Johoku Brdg.

13

37

4

43

19

44

12

32

9

19

26

35

8

39

10

17

15

42

8

30

3

38

8

24

39

11

31

4

46

15

38

29

4

38

54

13

15

0

20

14

0

0

12

0

0

3

0

3st. 4st. 5st. 6st. 7st. 8st. 9st. 10st. 11st. 12st. 13st. 14st. 15st. 16st. 17st. 18st.19st.20st. 21st. 22st. 23st. 24st. 25st.
Hot
In
Hot
Little Year
Rain Average

The ratio of “Terrible Smell”&”Smell”%

Hot

Hot Hot
Hot
Heavy Heavy Little
rain rain
Rain

Hot
Cold
Heavy Heavy
Rain
Rain

Hot

Hot

%

It is observed that the smell condition was improved with TRWKR and after TRWKR stopped, it got worse. After that, it had a tendency toimprove while the smell has fluctuated repeatedly although weather conditions sometimes made it worse. It is assumed that the change of
public awareness and new measures for Water Quality Improvement after stop of TRWKR have effects on this.

23

The change of ratio about “Ditch・Sludge・Smell less”
With TRWKR•New Measures for Water Quality Improvement

Making shallows and deeps

Use of shallow ground waterTransmission of Raw Water from Shonai River
Covered Sand
Introduction of advanced water treatment of Meijo Water Treatment Center
In-service of Horikawa Ugan Rain-water Reservoir for pollution control

The 1st-6th stage ： With
TRWKR
No rain on the day and theprevious day
The 7th-25th stage： No
TRWKR
No rain on the day and theprevious day

Utilization of reclaimed wastewater at Moriyama Water Treatment Center

猿投橋～大瀬子橋間

どぶの臭い

ヘドロの臭い100

どぶの臭い+ヘドロの臭い

Reduction of Ditch and Sludge
Increase of Smellness⇒Improve90においの種類の構成比率(％)

80
70

68

1stは
調査なし

63

62
57

56

55 55

57

50

41

44

38

44

31
26

30

35 36

33

37

35

30

21

9

10

6

24

19

33

18

19

22

22

15

22
26

10 18

16
13

12

29

22

21

19

10

37
32

24

25

23
18

43

40

35

32

32

31

20
21

48

50

43
38

36

20

調査数

52

63
59

58

57

44

38

19

0

61

49

48

75

65

63
59

■How the ratio of“Ditch・Sludge・Smellless” change?

74

73

60

40

無臭

12
12

19 22

29
23
21 14

11
15
10

15
8

6

5

After stop of TRWKR,
the ratio of “Ditch・
Sludge” decrease,
the ratio of “smell
less” increase(improvement)
between Sanage
Bridge and Oseko
Bridge.
Considered theresult of change of
public awareness andthe new water quality
improvement measure.

2
7

1st. 2st. 3st. 4st. 5st. 6st. 7st. 8st. 9st. 10st.11st.12st.13st.14st.15st.16st.17st.18st.19st.20st.21st.22st.23st.24st.25st.
106 210 170

50

109

62

84

67

75

113 108

98

93

82

87

62

74

82

52

65

81

61

46

85

106

24

(4) Factors that worsen water quality between Asahi Bridge to Matsushige Bridge
We organized large amounts of data based on the section and tide in order to consider the factors influencing
water quality, especially in the section between Asahi Brdg. to Matsushige Brdg. that runs through Nagoya's
downtown.
We divide the section upper stream(Asahi Brdg.-Naya Brdg) and lower stream(Tennozaki Brdg-MatsushigeBrdg)and tide higher and lower than average level.
According to the result ‘Impression of water clearness' and 'COD' are worse, the score of 'Bubbles' and 'Smell'
are higher and 'the color of sludge' was seen more often in the section between Asahi Brdg. to Naya Brdg. when
it is low tide.(dimension D in the figure below)
We consider that low tide stirs sludge on the riverbed and release bubbles.(H2S etc.)
The following measures are required for cleaner Horikawa River.
● removing sludge after bank protection works between Asahi Brdg. to Naya Brdg.
● preventing sludge accumulating riverbed again(developing new water sources, measures against combined sewer overflow and regular ship operation etc.)
lower stream

Organized data based on the section and tide level
Asahi Bridge to Matsushige Bridge

7th stage-25th stage(spring - early summer)
number of report : 343

no rain on the day and the previous day

lower stream upper stream
Tennozaki Brdg
- Matsushige Brdg

tide Level
higherA58
reports

Asahi Brdg. - Naya Brdg.

C

84
reports

averagelower

B 60
reports141
D reports

Tennozaki B.- Matsushige B.

higher than average
impression ofwater clearness

transparency
COD
bubblessmellcolor of sludge
milky color

upper stream

Asahi B.- Naya B.

evaluation

evaluation

good

good

good
a few
a little
a little
●much

good
a little
●much

A

C

average tide level
lower than average
impression ofwater clearness

evaluation

evaluation

●bad

●bad

transparency
COD
bubblessmellcolor of sludge
milky color●bad
a little

●bad
●bad
●bad
●bad
-

B

D

higherlower

We need to pay attention to the sludge on the riverbed again
for cleaner Horikawa River.

25

(5) Movement and accumulation mechanizm of floating materials of Shiratori and Miyanowatashi.
According to civil survey, Floating materials at Shiratori and Miyanowatshi in Horikawa river moved andaccumulated with the tide. People continue surveying to investigate that movement and accumulation
mechanism. Floating materials at Shiratori are reaves, reed, algae, plastic bags, PET bottles and paper. We
expect that analyzing that mechanism can help cleaning floating materials more effective.
Chikyu club chosatai(Ref：p.88)(REF：p.91～93) 調査実施日の潮位

潮位差
小さ い

潮位差
大き い

潮位差
小さ い

潮位差
大き い

潮位差
小さ い

潮位差
大き い

潮位差
大き い

2019年7月31日～1日(大潮)地球倶楽部調査隊
2019年8月2日(大潮)2019年7月31日 7時頃 熱田記念橋上流向き
事務局
撮影:地球倶楽部調査隊

旗屋橋

浮遊物が広がっ て流下
図2の状態から図1の状態に移行

26

(Results)
Naturally occurring
garbage at Shiratori・leaves・withered reed・algaeFloating materials
from upstream

Artificial garbage
・From walking path or road・Inflow with rainwater.

Floating materials at Shiratori・leaves, withered reed, algae
season and wheater・ Artificial garbage (plastic bags, PET bottles and paper)
condition affects
Move and accumulate with the tidewithered in summer

Floating
materials from
Shinhorikawa
river.

Low tide•High tide

• Flowing down along the waterside. • Rising water level and strong water flow to
upstream push up floating materials at a
• Flowing and accumulating into a
depression, a revetment and a waterside to
depression of a dock,kyuchobokujou-watergate, pumping upstream.
station and junction point with
• Floating materials pushed up accumulated around
Atsutakinen Bridge and Heiya Bridge where the• Shinhorikawa(Miyanowatashi)surface of waters stagnate.
• Drifting to a revetment.

We continue surveying to investigate that movement and accumulation mechanism.

We expect that analyzing that mechanism can help cleaning
floating materials more effectively.

27

(Hypothesis) Movement and accumulation of suspended substance28

(6)After removal of sludge in Shin-Horikawa River
The survey held in Shin-Horikawa River between Maizuru Bridge
and Mukaida in the 23rd stage (Apr.-Jun. 2018, before removal
of sludge)and the 25th stage (Apr.-Jun. 2019, after removal of
sludge)shows that sludge was seen more frequently in the 25thstage (after removing sludge). Although more successive
observation is needed to find the cause, it is being clear little
by little field by survey of HSC. （ref：6.13、6.14_p.99～116）
Survey by citizens confirmed that “impression of water
clearness” is significantly affected by sludge (scum)generated
from organic matters and impurities along with rainwater flowed
into the river from combined sewer during rainfall in upstream
area of Shin-Horikawa River, of which water source is limited.

Before removal of sludge(参照：p.99)*Impurities: small wastes including wastewater including naturally originatedwastes, cooking wastes, and toilet papers, etc.

After removal of sludge (field survey)

Suimonken survey group, ecodoco survey group,
Taiyu Const. survey group, Kokawasemi survey group

小さな泡が密集29

Before removal of sludge①

A large lump of sludge(scum)
floats up to the river surface

In winter
・Law water temperature
・Little Rainfall
Surface of piled bottom sedimentbecomes a little lumps
2017 May 12

Before removal of sludge②

photo by secretariat

Before removal of sludge③
sludge(scum)floats

In spring・Warming water temperature・Rainfall
Rainwater fromcombined sewer(including organic
matter etc.)

Form generates

Large lump ofsludge arepeeled off frombottom of riverand float bybuoyancy of alarge amount offorms

Rainwater fromcombined sewer(including organic
matter etc.)

Form generates

30

After removal of sludge①
In winter
・Law water temperature
・Little Rainfall

Small lumps of sludge (scum)
floats up to surface of the river from April

Sludge removed by dredging
Surface of bottom sediment is softand loosened by sludge removing work

After removal of sludge②

April 19 2019

photo by secretariat

After removal of sludge③
sludge(scum)floats

In spring・Warming water temperature・Rainfall
Rainwater fromcombined sewer(including organic
matter etc.)

Form generates

Soft and small
lumps of sludge
float by buoyancy
of small amount offorms

Rainwater fromcombined sewer(including organic
matter etc.)

Form generates 31

We think that securing new water source, reduce of (soluble) organic matter and impurities flowing into the riverduring rainfall, and countermeasures to reduce sludge (ex. control of combined sewer overflow) are necessary
to realize water quality improvement of Shin-Horikawa Riveｒ。

32

(7) 10th Horikawa-river general survey (changes point of
Horikawa-river vessel liner)
As the result from general survey, we found the trend that
sediment on the riverbed was agitated and the impression ofwater stains will worsen temporarily, according to nonperiodically operation of vessel.
Furthermore, if number of vessel operations increases, wehypothesized that impression of water stains might improve,
because water of the Horikawa-river and riverbed
sediments are agitated periodically, and oxygen continues tobe supplied to the riverbed, improving the riverbed
environment, and reducing bubbles, odors and cloudiness.
As the result from this survey, after passing of vessel
between Naya-Bridge and Gojyo-Bridge (upstream
section), we confirmed that rolling up of sludge, andbubbles from the riverbed. Especially, this trend wasparticularly noticeable in the ebb tide period of springtide.(Depth is shallow)
On other hand, there was no remarkable change signal
between the Matsushige Lock Gate and Tennozaki-Bridge(downstream section) such as that rolling up of sludge after
passing of vessel. Estimated reason why we confirmed sucha trend might be “sludge dredging” with revetment
maintenance, and houseboats (but not periodically)
operation etc. We compared the conditions of May 11 andMay 25 at Gojyo-Bridge (at the time of neap tide). On May
11, sludge was rolled up and rotten-egg smell was
confirmed, but it didn't on the May 25. The condition of theriverbed on May 25 may have improved due to twice vessel
operation on the May 11 and May 18. During this generalsurvey, we recorded a video that could prove part of the
hypothesis which we mentioned above.
We, citizens, expect the effect of purifying and maintaining
for water area by mud re-depositing on the bottom aftersludge removal (during revetment maintenance etc.) andreducing sludge according to start periodical vessel
operations.

Due to non-periodical operation of vessel,

the sediment on the riverbed are agitated and the impression of water
stains is aggravation temporarily■ Momentary,・Sludge rolls up
・Bubbles are generated
・Odor occurs (unpleasant smell of rotten eggs, sludge)

If the vessel operate periodically,
the sediment on the riverbed is agitated periodically,

and impression of water stains is improved.
■Periodically,
・Oxygen will be supplied to the water area
・Sediment at the riverbed (mud etc.) will be decreased
・Hydrogen sulfide etc. in the sediment will be released

Rolling up of sludge around Gojyo-Bridge
May 11 Neap tide
Gojyo-Bridge
・Too much sludge rolls up
・Bubbles are generated

Neap tide

tide level

Spring tide

Neap tide

tide levelMay 25 Neap tide
Gojyo-Bridge
・No-sludge rolls up
・Bubbles are generated
on the wakeSpring tide
tide leveltide levelMay 18 Spring tide
Gojyo-Bridge
・Sludge rolls up
・Too much bubbles
are generated

May 18 Spring tide
Gojyo-Bridge
・Sludge rolls up
・Too much bubbles
are generated

33

(Survey results)① Naya Bridge～Gojyo Bridge (Upstream Section)
After passing of vessel, sludge rolling up andbubbles from the riverbed were confirmed.
→Especially, this trend in the spring tide is remarkable(the water depth is shallow)② Matsushige Lock Gate～Tennouzaki(Down Stream)
Even when the vessel passed, significant
changes such as rolling-up of sludge were notobserved.
→Estimated reason why we confirmed such a trend
might be “sludge dredging” during revetment
maintenance, and houseboats (but not periodically)
operation etc.
③ Comparison of the conditions of Gojyo bridge on
May 11 and 25 (neap tide)
Sludge was rolled up, and rotten-egg smell was
confirmed on May 11, but these problem were
not confirmed on May 25.
→ Since vessel was operated on May 11 andMay 18, condition of riverbed might be temporarily
improved as of May 25th.
④ Bubbles occur in the wake
→ Same as 9th Survey (24th stage)

According to non-periodically operation of vessel,
the sediment on the riverbed was agitated
and the impression of water stains will worsen temporarily■ Momentary,・Sludge rolls up
・Bubbles are generated
・Odor occurs (unpleasant rotten-egg smell, sludge)

If the vessel operate periodically,
the sediment on the riverbed is agitated periodically,

and impression of water stains is improved.
■Periodically,•Oxygen will be supplied to the water area
•Sediment at the riverbed (mud etc.) will be decreased•Hydrogen sulfide etc. in the sediment will be released(Summary)
If periodical vessel operation is available, it
reduce the re-accumulate of mud on the riverbed
and sludge, after removing the sludge (at therevetment maintenance).

We can expect the effect of
purification and keeping theenvironment of water area.
34

Rolling up sludge around Gojyo Bridge
May 11 Neap tide
Gojyo Bridge
・Too much sludge rolls up
・Bubbles are generated

Neap tide

tide level

Spring tide

Neap tide

tide levelMay 25 Neap tide
Gojyo Bridge
・No-sludge rolls up
・Bubbles are generated
on the wakeSpring tide

tide leveltide levelMay 18 Spring tide
Gojyo Bridge
・Sludge rolls up
・Too much bubbles
are generated

May 18 Spring tide
Gojyo Bridge
・Sludge rolls up
・Too much bubbles
are generated

35

(Hypothesis) Image of water quality improvement
according to periodical vessel operation(The riverbed environment improves, if frequency
of vessel operations increases.)Naya Bridge Gojyo Bridge

Current Status
Promotion of sedimentation

Motoiri Sluiceway
Sanage Bridge
Asahi Bridge
The edge end thatseawater reachFreshwater

Seawater

The condition of riverbedof Horikawa-river

floating mud layer

Sumiyoshi Bridge

Subsidence of fine flotage
in the water is promoted
at the boundary between
seawater and fresh water.
Near the edge end thatseawater reach of the
Horikawa-river, its trend
is shown prominently, andfloating mud layer iscreated on riverbed.

Naya Bridge

Stirring of sludge+ Oxygen supply

Environment that fine flotage
does not sink easily

If frequency of vessel operations increases,
environment of riverbed is improved.

Reported by :Video Team, 3rd Survey Group Meeting

潮の先端部でFloating mud layer like graydust is confirmed on the
ヘドロのもとになる
riverbed, and black sludge
浮泥がつくられます
accumulates under it. Bubbles
come from riverbed.

Floating mud layer

Gojyo Bridge

Asahi Bridge

Stirring of sludge+ Oxygen supply

潮の先端部でImprovement
ヘドロのもとになる

FreshwaterIf frequency of vessel operation increases,
water and sludge of the Horikawa-river areagitated periodically and oxygen is continuously
supplied to the riverbed. And then, bubble, badodor and muddiness will decrease, environment ofriverbed will be improved. So, we believe that
impression of water stains will improve.

浮泥がつくられます36

5.2. Consider of factor of water quority bitwen Asahi Matsusige
Asahi Brdg ～Matsusige Brdg
Comparison of the differne by section and tide
Asahi Brdg
level.
Keiun Brdg
Habashita Brdg
To prepare a document about studying the reson
KoshioBrdg
Sakura Brdg
五Gojo Brdg
of water quality change between Naya
AsahiBrdg
bridge
and
Naka
Brdg
Temma Brdg
NishikiBrdgogf
Matsusige bridge Shinsuzai
which arelocatedthecenterTennozaki
Brdg
Brdg
Nagoya city.
(Upstream・High)
Iwai BrdgSuzaki Brdg

C

A

Hioki Brdg
Matsusige Brdg

High
Chage oftide level

Low

Sea Level 1.20m
Mean sea level of spring tide

Sea level 0m

Sea level -1.37m
Mean sea level of spring tide

(Downstream・High)

D(Upstream・Low)

B

Upstream(Downsteam・Low)

Downstream
7th stage～25th stage(Spring～Early summr) Survey number:343

Naya Brdg～Asahi Brdg

Matsusige Brdg～Tennozaki Brdg
April～June

No rain on the day& the day before

Downstream Upstream
Matsusige Brdg～Tennozaki Brdg
Naya Brdg～Asahi Brdg

In our field survey,wehave organized themechanism of water
quality change, but we
got more data
because of thecontinued field survey
by citzen. That is why
we have compared thedifferene bysectionand tide level.

Tide levelHigh

Not less thansea level 0m

A Survey number:58
B Survey number:60
ComparisonLess thanLowsealevel 0m

Comparison

Comparison

C Survey number:84
DSurvey number:141
Comparison

Sea level 0m
37

松重橋～朝日橋

Asahi Bridge

(Map)

Ｎ

SubwaySengen-cho St.

SubwayShiyakusyo St.

Habashita Bridge

南押切小

なごや小

菊井中

Nagoya Castle
Koshio Bridge
丸の内中SubwayKamegima St.

景雲橋

City hall

名城小Gojo Bridge

Hisaya-odori St.Takaoka St.

SubwaySakura Bridge

Denba Bridge

Upstream

御園小

笹島小中

Nagoya St.

Aonami Line

Komeno St.

Sasashima-raibu St.

Subway地Subway

Yaba-cho St.

Subway Tsurumai Line

Iwai Bridge
大須小

千早小
Horidome Water Treatment Center

前津中

老松小
Maizuru Bridge
Uzura Bridge

Horikawa River

Hioki Bridge

広見小

SubwayTsuyuhashi Water Treatment Center
愛知小
名鉄

松重閘門

Kamimaezu St.

Matsushige Bridge
松原小

Kinen Bridge
Utsugi Bridge

橘小

Shin-Horikawa River

Sannou Bridge

山王駅

Huzimi Bridge

Nakagawa Canal

山王中
露橋小

ＪＲ

Oi Bridge
Subway正木小Higashibetsuin St. Mukaida Bridge
ＪＲ Chuo Line
Huruwatari Bridge
Shinonome Bridge
平和小

LegendMain road
Railway line

地下鉄

Elementary
荒畑駅and junior high schools
Public facility

伊勢山中

白金小

尾頭橋駅
JR Tokaido Shinkansen

Horagai bridge

Kanayama St.
八熊小

八幡小

新栄小

白山中

Sakae St.

Shinsuzaki Bridge
Suzaki Bridge Subway Meijo Line

Matsushige Bridge～Tennouzaki Bridge

SubwayShinsake- Machi St.

Tennouzaiki Bridge

Kintetsu

葵小Subway Subway Higashiyama
Meitetsu
Fushimi St.
Line
Sakaemachi St.

Naya Bridge

Downstream

Subway Sakuradori Line

冨士中
東桜小

Nishiki Bridge

栄小

SubwaySubwayNaya Bridge～Asahi Bridge Kokusai center St.Naka BridgeMarunouchi St.
Subway山吹小

Oto Bridge0m

Sumiyoshi Bridge

ＪＲ Tokaido Line
Meitetsu Nagoya Line Tateishi Bridge
200m

400m

600m

800m

1000m

村雲小

円上中

40

Mainly Point at Sea level 0ｍ
Naka Brdg
Habashita Brdg

Asahi Brdg 12:37
September.13th. 2019

Gojo Brdg 12:18
September.13th. 2019

Sea level -0.73m
at shooting

Sea level -0.76m
at shooting

Sea level 0m

Sea level 0m

Sakura Brdg
Temma Brdg

Nishiki Brdg

Nishiki Brdg 12:12
September.13th. 2019
Sea level -0.78m
at shooting

Sea level 0m

Naya Brdg 12:06
September.13th. 2019
Sea level -0.79m
at shooting

Sea level 0m
39

Mainly Point at Sealevel 0ｍ
Iwai Brdg

Tenno Brdg

Shin-Suzaki Brdg 11:52
September.13th. 2019

Shin-Suzaki Brdg 11:44
September.13th. 2019

Sea level -0.83m
at shooting

Sea level -0.82m
at shooting

Sea level 0m
JR lineMeitetsu line

Sea level 0m

Nagoya International
Convention Hall

Hataya Brdg
Atsuta Baseball Stadium

Asahi Brdg 12:37
September.13th.
2019
Oto Brdg 11:18
September.13th. 2019

Atsyuta-Kinen
Brdg 11:05
Sealevel -0.73m
September.13th. 2019at shooting

Sea level -0.77m
at shooting

Sea level -0.74m
at shooting

Sea level 0m

Sea level 0m
40

(Survey Result)
If the tide level will be the low environment (the environment that the water depth is shallow),We
have found out that “Dirty impression of water”and”COD”goes worse, “the bubble andsmell”becomes a lot , and the color of the sludge course becomes a lot compared with other ones
between Naya Bridge and Asahi Bridge.
(Comparative Arrangement)

Downstream

Matsushige Bridge～Tennouzaki Bridge
More than 0m of thelevel

Evaluationtide level

Dirty impression of water

good
good
good

color the sludge system

good
good
littlelittlelittlethe cloudy system

●lot

●lot

High
Low
Less than 0m of theComparison

viscous visibility
COD
Bubble from a riverbed

smell

littlelitte

section-sectioncolor the sludge system

●bad
●bad
-

●bad
●bad
●bad
●lot
●lot
●lot

the cloudy system

littlelittleviscous visibility
COD
Bubble from a riverbedsmell

Naya Bridge～Asahi Bridge
section-tide level

Evaluation

good
good
good
littlelittlelittlegood
goodlittle●lot●lot

0m of the leveltide level

level

C

Comparison ●bad
good
good
●bad
little●lot
little●lot-

Evaluation

Dirty impression of waterA

Upstream

B D

If the tide level will be the low
environment (the environmentthat the water depth isshallow), ・・・(Comparative Arrangement)“Dirty impression of water”and”COD”
goes worse, “the bubble andsmell”becomes a lot , and the color of
the sludge course becomes a lot.

Comparison
sectiontide level

Evaluation●bad
Comparison
goodlittlelittlelittle

good
●bad
●lot
●lot
●lot

●bad
●bad
●bad
●lot
●lot
●lot

●bad
●bad
●lot
●lot
●lot

little●lot

little-■ Sludge in a riverbed is related.
I’m thinking that it may be thesludge in a riverbed in curling and theenvironment that a generated bubble
from the sludge(ex.Hydrogen
Sulfide)tends to be released.

To achieve Horikawa’s water quality improvement, we’re thinking it’s necessary to aim
at existence of sludge in a riverbed once more between Naya Bridge and Asahi Bridge.

We’re thinking specifically, the measure to remove the sludge with bank protection maintenanceand to reduce re-accumulation between Naya Bridge and Asahi Bridge is needed. ※Examples ofmeasures①Securement in the new water source②Promotion of improvement of conbined sewer
system(ex.Horikawa left bank stormwater reservoir)③Realization of regular service of the ship 41

(Reference materials)Vertical section-like shape of Horikawa River(Diagrammatical view)
Atutakinen Bridge

Furuwatari Bridge

Gojyo Bridge

Shiratori Bridge Ksmeya Bridge JR,Meitestu Bridge
Ohseko Bridge
Confluence with
Shin-Horikawa River

Horikawa tidewater gate

Water lver(T.P.m)

2
1
0
-1
-2
-3
-4
-5
-6
Sea water-7-8 0

Nakatsuchito Bridge

Sanage Bridge.

Naka Bridge Habashita Bridge

Jyohoku Bridge
Otou Bridge Hioki Bridge Naya Bridge
Koshio Bridge Meijo water treatment center
Hataya Bridge
Matsushige Bridge
Sumiyoshi Bridge
Tennouzaki Bridge Asahi Bridge

1.20m
Mean high water level

Change in water level by tide
2.57m

-1.37m0m of the level
Mean law water level

Horikawa River
1

2

3

4

5

6

7

8

9

10

11

12

13

14

Distance from river mouth (km)Reference materials: Class A Shonai River water system

Horikawa area River maintenance plan
p.43 Cross section of Horikawa River

The height above the sea level …It is the height on the basis of sea level of Tokyo Bay.(T.P)
There are measuring the height, in Japanese land (elevation)based on average sea level in theTokyoBay.
Tokyo peil is abbreviated to T.P. Peil is the meaning of reference plane in Dutch.

42

Downstream Upstream
There is noremarkabletendency.

Ratio of “Clean”～“Neither”

Ratio of “Clean”～“Neither”

The impression in thearea of 0 meter over
above sea level is better
than that of below 0 level.

A

Numbers
Of survey

Above
Below

C

Numbers
Of survey

good

0 m Sea level goodbad

Impression bad

Ratio of “Clean”～“Neither”

D

B

Ratio of “Clean”～“Neither”

There is noremarkabletendency.

Numbers
Of survey

Numbers
Of survey＊short of data

43

Downstream Upstream

Bad

海抜0m以上の透視度は0m未満の値よりも良い

Above
Below

Transparency between
Naya Bridge and Asahi
Bridge is better than thatof between Matsushige
Bridge and Tenozaki
Bridge.

A

Numbers
Of survey

The Transparency in the areaof 0 meter over above sea levelis better than that of below 0
level

C

海抜0m以上の透視度は0m未満の値よりも良い

Numbers
Of survey

Good 0 m Sea level Good
BadTransparency Bad
Bad

松重橋～天王崎橋間の0m未満が悪い理由は何?

Good

B

The Transparency in the areaof 0 meter over above sea levelis better than that of below 0
level

Good

D

The Transparency inthe area of 0 meter over
above sea level is better
than that of below 0 level
Why is the transparencyof the area below 0
meter sea level bad ?

Numbers
Of survey

Numbers
Of survey＊Short of data

44

Matsushige Brdg.～Tennozaki Brdg.
Spring to early summer

More than 0m above sea level

COD above zero meters above
sea level is generally better
than COD below zero meters.

High
Low

More than 0m above sea level

As a result of organizing
the section between Naya
Brdg. and Asahi Brdg. andbetween Matsushige Brdg.
and Tennozaki Brdg., it was
found that the COD at tidelevel of 0m or higher isbetter than the COD of lessthan 0m.

COD above zero meters above
sea level is generally better
than COD below zero meters.

Good Poor

A

Number ofsurveysNaya Brdg.～Asahi Brdg.
Spring to early summer

Downstream Upstream

C

Number ofsurveysGood 0m above sea level

Good

Poor

Poor

Matsushige Brdg.～Tennozaki Brdg.
Spring to early summer

Less than 0m above sea level

ＣＯＤ
Good Poor

B

Naya Brdg.～Asahi Brdg.
Spring to early summer

Less than 0m above sea levelD

We found that the
COD below 0m above
sea level between
Nayabashi Brdg. andAsahi Brdg. is high.

Number ofsurveysNumber ofsurveys※Small number of surveys

47

When the sea level between
Matsushige Brdg. and Tennozaki
Brdg. is over 0m above sea level,no bubbles from the riverbed havebeen confirmed.

The number of bubbles
from the riverbed
between Matsushige
Brdg. and Tennozaki
Brdg. is less than thatbetween Naya Brdg. andAsahi Brdg.

Few

A

Number ofsurveys

Percentage of bubbles from the riverbed

High
Low

Number ofsurveys

Bubbles from the bottom of theriver above 0m above sea
level are less than bubbles
from the bottom of the river
below 0m above sea level.

Few

Many

C

0m above sea level

Few

B

Many

D

When the sea level
was less than 0m,
there were many
bubbles from thebottom of the river
between Naya Brdg.
and Asahi Brdg.

Naya Brdg.～Asahi Brdg.
Spring to early summer

More than 0m above sea level

Number ofsurveys

Few

Many Bubbles Many

Matsushige Brdg.～Tennozaki Brdg.
Spring to early summer

Less than 0m above sea level

Percentage of bubbles from the riverbed

More than 0m above sea level

Downstream Upstream

Percentage of bubbles from the riverbed

Percentage of bubbles from the riverbed

Matsushige Brdg.～Tennozaki Brdg.
Spring to early summer

Number ofsurveys

When the sea level is
0m or higher, bubbles
from the bottom of theriver cannot be
confirmed.
Naya Brdg.～Asahi Brdg.
Spring to early summer

Less than 0m above sea level

48※Small number of surveys

More than 0m above sea level
At points above 0m above
sea level, there is less"Smell badly～Smell" than atpoints below 0m above sea level.

There is less“Smells badly～
Smells” between
Matsushige Brdg. andTennozaki Brdg. thanbetween Naya Brdg.
and Asahi Brdg.

Few

A

Many

C

At points above 0m above
sea level, there is less"Smell badly～Smell" than atpoints below 0m above sea level.

Few 0m above sea level Few
Many
Matsushige Brdg.～Tennozaki Brdg.
Spring to early summer

Less than 0m above sea level
There is less “Smells
badly～Smells” between
Matsushige Brdg. andTennozaki Brdg. thanbetween Naya Brdg. andAsahi Brdg.

Smell

Few

B

Many

D

When it is less than 0m
above sea level between
Naya Brdg. and Asahi Brdg.,
there is a lot of “Smells
badly～Smells”.

Many
Percentage of “Smells badly～Smells”

High
Low
Percentage of “Smells badly～Smells”

More than 0m above sea level

Number ofsurveysNumber ofsurveysNumber ofsurveysNaya Brdg.～Asahi Brdg.
Spring to early summer

Downstream Upstream
Percentage of “Smells badly～Smells”

Percentage of “Smells badly～Smells”

Matsushige Brdg.～Tennozaki Brdg.
Spring to early summer

Number ofsurveysNaya Brdg.～Asahi Brdg.
Spring to early summer

Less than 0m above sea level
When it is less than 0m above
sea level between Naya Brdg.
and Asahi Brdg., there is a lot of“Smells badly～Smells”.

49※Small number of surveys

Matsushige Brdg.～Tennozaki Brdg.
Spring to early summer More than 0m above sea level

Downstream Upstream

Naya Brdg.～Asahi Brdg.
Spring to early summer More than 0m
above sea level
海抜0m以上Color composition ratio（％）

Color composition ratio（％）

海抜0m以上No noticeable trend

A

C

Number ofsurveysNumber ofsurveys

Little color of
Many color ofriver like sludge 0m above sea level river like cloudy

Many color ofriver like sludge
Matsushige Brdg.～Tennozaki Brdg.
Spring to early summer Less than 0m above sea level

Color composition ratio（％）

海抜0m未満Number ofsurveysColor

B

Little color ofriver like cloudy

D

Naya Brdg.～Asahi Brdg.
Spring to early summer Less than 0m above sea level

海抜0m未満

Little color ofriver like sludge

Many color ofriver like sludge

Little color ofriver like cloudy

Many color ofriver like cloudy

Color composition ratio（％）

High
Low

Number ofsurveys50※Small number of surveys

5.3. Movement and accumulation mechanism of suspended substance around Shiratori and Miyano-Watashi
July 31 to August 2, 2019 (research organization) Earth Club Survey Group・・・Under investigation

The state of suspended substance around Shiratori and Miyano-Watashi
where the actual state of movement and accumulation of suspended substancehas not been investigated has been gradually revealed by public surveys.

Around Shiratori and Miyano-Watashi
Please take a pictureof suspended substancemoving and accumulatingwith mobile phone, andsend the date and placeof photography to thesecretariat.

乗船場

旧貯木場水門白鳥庭園

49

(Hypothesis) When the tide level difference is small
・・・ There is little movement and accumulation of suspended substance
Binya Bridge

Binya Bridge

Hataya Brigde

Hataya Brigde

Boarding place

Boarding place

Atsuta Memorial Bridge
Old water
reservoir gate
Goryo Bridge
Shiratori Bridge
pumping station

Atsuta Memorial Bridge
Flow down inthe state of
spreading over
the water
surface

Shiratori Bridge

Oseko Bridge

Old water
reservoir gate
Goryo Bridge

Shiratori Bridge
pumping station
Shiratori Bridge

Suspended substance
moved upstream to risingtide accumulate at theplace where the surface
flow is stagnant at hightide time.
The accumulation ofsuspended substancedoes not appear to besignificant compared towhen the tide level
difference is large.
The rise of the waterlevel and the flow of
upstream water pushsuspended substance inthe dents, castaway, andsuspended substance on
the edge of the river
upstream.

Nakashimapumping station

Nakashimapumping station

Uchida Bridge
Oseko Bridge
Miyano-Watashi

Uchida Bridge
Miyano-Watashi

Drifting on riverdike stacking
stones, etc
Legendsuspended substanceFig.1 Ebb tide～low tide timeFig.2 Rising tide～high tide timesuspended substancemoving direction
river dike stacking stones

50

(Hypothesis) When the tide level difference is large ・・・ Suspended substance easily move and accumulate

Binya Bridge
Hataya Brigde
Boarding place

Binya Bridge

Movement andaccumulationin the dent of
the boarding
place and oldwaterreservoir gate

Hataya Brigde
Boarding place

Atsuta Memorial Bridge

Atsuta Memorial Bridge

Old water
reservoir gate
Goryo Bridge

Old water
reservoir gate
Goryo Bridge

Shiratori Bridge
pumping station

Downstream
along the edgeof the river

Shiratori Bridge

Oseko Bridge

Shiratori Bridge
pumping station
Shiratori Bridge

Suspended
substance moved
upstream to risingtide accumulate at
the place where thesurface flow isstagnant at high tidetime(near Atsuta
Memorial Bridge toKamiya Bridge).
The rise of the waterlevel and the flow of
upstream water pushsuspended
substance in thedents, castaway, andsuspended
substance on theedge of the river
upstream.

Nakashimapumping station

Nakashimapumping station

Uchida Bridge
Oseko Bridge
Miyano-Watashi

Uchida Bridge
Miyano-Watashi

Drifting on riverdike stacking
stones, etc
Movement and accumulation in
the dent at the junction of
Shin-Horikawa (near MiyanoWatashi)

Fig.3 Ebb tide～low tide time

Fig.4 Rising tide～high tide time

Legendsuspended substancesuspended substancemoving direction
river dike stacking stones

515.4. Shin-Horikawa after dredging of sludge■Area
Shin-Horikawa between Maiduru bridge and Mukoda bridge■Data
Before dredging：23th Stage(April～June,2018) 65 Data
After dredging：25th Stage（April～June,2019) 63 Data

Frequency of discovering sludge①Number of survey ②Number of survey which sludge was discovered

ヘドロ(スカム)確認頻度
Frequencyof discovering sludge 期間:4月～6月（April ～ June）
確認頻度②/①*100(%)

100
14%UP

80
60

54%UP

19%UP

75

67

64

63

50

49

48

40
20
0
4月
April

23ステージ23th Stage ヘドロ浚渫前■The reason of increase on April
Dredging soften mud in the bottom of river.
Therefore, the mud became easy to rise up.

■ The reason of increase on June21

April期間～ June(hypothesis)
The reason of increase of frequency of
discovering sludge

June
5月
6月
May
25th Stage ヘドロ浚渫後
25ステージ

It become clear due to civil survey that at upstream of river whichwater resourse is limited and substitution of water is few, organic
substance and contaminant ** flow out during rainfall and sludge basedon these things have great effect on impact of water stain.
Further investigation is necessary because survey at 25th stage is thesurvey immediately after dredging.

The mud rolled up due to dreadging piled up and thealgae breeded on the mud. Then, it is discoveredthat the algae was separated and floating.
Also, the floating sludge from the bottom of river was
discovered. A lot of these sludge was staying in thewater long time. This phenomenon is considered due
to tide and weather condition.
It is considered that these factors caused increaseof frequency of discovering sludge**Contaminant :Small trush in sewage52

of clearness in Shin-Horikawa River is not good all year round. Because
Why is the impression of clearness not Impression
river bottom of Shin-Horikawa River is low to upstream from downstream, it is thoughtthat the bottom water in the lower layer is always stagnant, and it is difficult for thewater to be replaced. For this reason, the upstream area where effluent water from
Good all year round?
water treatment center and suspended substance associated from rain water by（hypothesis）
Mechanism of contamination in the
upstream area of Shin-Horirawa River
Bad smell occurrence（smell of the rotten egg）

Hydrogen sulfide(H2S)

combined sewer system is an environment that tends to settle and accumulate on
bottom river. And it is thought that poor oxygenation of water and mud of bottom isadvanced. In the area, it is considered that a large amount of sulfide is generated,causing milky and bad smell, and it is a factor that deteriorates impression of clearness.

Fresh water(Warm all year round)

Milky＝Blue white

Diffusion

Sulfied（mostly H2S,HS-）
reacts with Ｏ２ &ＣＯ２ tocolloid formation sulfide(including organic
substance)

Suspended
substance(including organic
substance)

2Ｈ2Ｓ+O2→2S+2H2O
2Ｈ2Ｓ+CO2+Sun→CH2O+2S+2H2O

Sea water

Floating mud with manyorganic substances

Sinking

A flow occurs that lifts the bottom
layer sea water to the face
→Sea water and fresh water mix
・Flocculation…suspending
・Oxidation of sulfide…milky

Sea water→Sludge generation
Deposited in the mud and water
Sulfied（Ｈ２Ｓ，ＨＳ－etc）

ＳＯ42(Including
Sulfate ion)・Effluent water fromwater treatment center・Rain water by combined
sewer system

Dissolved
substance

Consumption of oxygen accompanying decomposition of organic
substance, etc. and colloid formation of sulfide.

Poor oxygenation of water and mud of bottom

Sulfate reducing bacteria（mostly in mud）
＊bacteria that like environment without oxygen

Sulfate reducing bacterium produce hydrogensulfide (Ｈ2Ｓ) etc. ,with organic substance(Properties of hydrogen sulfide)
decomposed and sulfate ion(ＳＯ42- ) reduced. ・Heaviar than air ・Specific gravity 1.1905
ＳＯ42-＋Organic Substance→Ｓ2-＋Ｈ2Ｏ＋ＣＯ2
・Colorless, water soluble ・mild acidity
Ｓ2-＋Ｈ+→ＨＳＨＳ-＋Ｈ+→Ｈ2Ｓ

55

Shin-Horikawa River Upｓtream area After taking away Sludge Citizens Survey(some part)
Survey Group：Water Research Institute survey group、eco doko cheer group
Taiyu Kensetsu survey group、Kokawasemi srvey group

April 19ｔｈ ,2019

Nagoya Port Tide Level Spring Tide
20190419

Floating sludge with small bubbles
0a.m 36

912p.m 3

6

9

0a.m

2019April19th 10:24am
Uzura bridge view upstream

Photo by secretariat

landsidebanquettelandsidebanquette

Scale Up

There are a lot of small sludge

54

May 10ｔｈ ,2019
May 10th ,2019 10:03am
Kinen bridge view upstream

Phot by Kokawasemi survey group

River flow speed was getting fast. Near
the bridge, 1/3 of the left bank was milk
white without flowing. Also 1/3 of theright bank had no flow too. Only middle
part could flow. It looked like shape V.
2/3 of the right bank had a darker color
than left and smell is not good.
Report by Kokawasemi survey group

Nagoya Port Tide Level Middle Tide

20190510

May 10th ,2019 10:00am
Kinen bridge view upstream

0a.m 36

912p.m 3

6

9

0a.m

Phot by Kokawasemi survey group55

May 16th ,2019
Nagoya Port Tide Level Middle Tide

landsidebanquette

20190516

landsidebanquette

Big and small bubbles were morethan usual so we could see them
whole of the river. We felt not good
because sludgs wrer big and whole.
Report by Kokawasemi survey group0a.m 3

6

9

12p.m

3

6

9

0a.m

Landsidebanquette

May 16th ,2019 10:17am
Kinen bridge view upstream

Phot by Kokawasemi survey group

May 16th ,2019 10:17am
Kinen bridge view upstream

Phot by Kokawasemi survey group56

June 12th,2019

June12th ,2019 Around2:00pm
Maitsuru Bridge view upstream

Photo by Water Research Institute survey group

Nagoya Port Tide Level Long Tide
20190612

Small bubbles came out in a 1meter diameter circle.
After that small black scums were floating with thesmell of hydrogen sulfide.
It was happening one after another.
0a.m 36

912p.m 36

9

Report by Water Research Institute survey group0a.m

June 19th,2019

June19th ,2019 11:00am
Photo by secretariat

Nagoya Port Tide Level Spring Tide
20190619

Landsidebanquette

Landsidebanquette

June 19th ,2019 10:38am
Uzura Bridge View upstream

Photo by secretariat

Scale Up
0a.m 36

912p.m 3

6

9

0a.m

Green algaes in a mat shape were
floating. We thought they grew at
the landside banquette and peeled
off.

57

June 26th, 2019tidal level at Nagoya Port June 26th,2019

13:45, June 26th, 2019
at Maizuru Bridge

July 8th, 2019tidal level at Nagoya Port July 8th,2019↑
upstream

There were scum both which came to the surface
from the bottom and which came off from berg ofphoto :
revetment.
Water depth was 4.9m and Do was measured from Water issue research institutesurvey groupthe surface to 2m deep.
report : Water issue research institute survey group

Scum was on the left side of the bank on July
5th, then moved to the center of the river on July
8th. It might be affected by the flow and wind.
report : Water issue research institute survey
group

Do was measured from thesurface to 2m deep.
→Environment of the areaof the river and the bottom
sediment is improved.

↑
upstream

berg

berg

13:53 July 8th, 2019at Uzura Bridge

photo : Water issue research institute survey group

photo : Water issue research institutesurvey group58

10:09, July 13th, 2019at Mukaida Bridge

July 13th , 2019

photo : eco doco cheering grouptidal level at Nagoya Port July 13th,201910:09, July 13th, 2019at Mukaida Bridge

photo : eco doco cheering group
10:09, July 13th, 2019at Mukaida Bridge

photo : eco doco cheering groupberg

A lot of scum make us depressed.
We want to find out a difference
between place scum occurs andplace scum never occur. We also
want to know relation between
occurrence of scum and watercolor.
report : eco doco cheering group

13:40, July 13th, 2019at Shinonome Bridge

13:49, July 13th, 2019at Shinonome Bridge

photo : eco doco cheering group

photo : eco doco cheering group59

10:15, July 24th, 2019at Horagai Bridge

July 24th, 2019berg

photo : Taiyu Kensetsu survey grouptidal level at Nagoya Port July 24th,2019

scum
Photo : secretariat
10:00, July 26th, 2019

July 26th, 2019tidal level at Nagoya Port July 26th,2019algae which grew on the berg
and came off
berg

berg

10:50, July 26th, 2019at Fujimi Bridge

photo : secretariat

60

Bubbles are produced by sailing ship
After a ship passed, the produced bubbles are easy to be left
on the surface of the water
11th May

Neap tide

Tide level

11th, neap tide
Nishiki Bridge- No raised sludge- No mass bubbles fromthe bottom of the river- Bubbles on the ship trail
11th May

Neap tide「第24ステージ と同様」を訳しましたが何について同様なのか（同じデータを再掲起きている現象が同じなのかデータの再掲
Tide level

same condition などと補記が必要かと思- No raised sludge- No mass bubbles fromthe bottom of the river- Bubbles on the ship trail

11th, neap tide
Matsushige
Bridge*9th investigation(same as 24th stage)

61

When a ship is sailed temporary・ ・ ・・Sludge is rolled up
・Bubbles are generated
・Bad smells are generated (the rotten egg smell, mud smell)
As time passes, the bubble on the surface of the water
disappears, and rolled up sludge settle.

When there are gases
such as methane andhydrogen sulfide inbottom sludge
Bottom sludge
Methane andhydrogen sulfide gas
come to the surface

Bottom sludge
Methane andhydrogen sulfide gas
come to the surface

As water area is stirred, bottom
sludge is rolled up and Methane andhydrogen sulfide gas come to thesurface.
Bottom sludge

Bottom sludge
Methane and hydrogensulfide gas come to thesurface

Methane and hydrogensulfide gas come to thesurfaceAs water area is stirred, bottom
sludge is rolled up and Methane andhydrogen sulfide gas come to thesurface.
Bottom sludge

As water area is stirred, bottom
sludge is rolled up and Methane andhydrogen sulfide gas come to thesurface.
Bottom sludge62

When long-term regular ship’s sailing isrealized ・・・・

When a ship is sailed regularly
Gases such as methane gas andhydrogen sulfide gas are released
from bottom with rolling up of sludge,
and decreased.
When there are gases such as
methane and hydrogen sulfide inbottom sludge

As water area is stirred regularly. oxygen continues
being supplied to the bottom of the river. In this way,
the state of the bottom of the river is improved little
by little (control accumulation of sludge) , and we
think that water quality will be improved more.

As time passes, the bubble on the surface of the water
disappears, and rolled up sludge settle.

Bottom sludge

Bottom sludge
Methane and hydrogensulfide gas come to thesurface

Methane andhydrogen sulfide gas
come to the surface

As water area is stirred, bottom sludge isrolled up and Methane and hydrogensulfide gas come to the surface.

Bottom sludge
Methane and hydrogensulfide gas come to thesurface

Bottom sludge
Methane and hydrogensulfide gas come to thesurfaceAs water area is stirred, bottom
sludge is rolled up and Methane andhydrogen sulfide gas come to thesurface.
Bottom sludge

As water area is stirred, bottom
sludge is rolled up and Methane andhydrogen sulfide gas come to thesurface.
Bottom sludge

63

from secretariat■ Every data you offer to us is valuable
Information about subtle change you find when you survey Horikawa river can bevaluable data to understand the present situation of the river. We’re looking forward
to your data from now on.
■ Let us introduce your activity
Your activity, such as survey, think and cheer up Horikawa, is the motivation toincrease the number of those who love Horikawa, Nagoya City and the Earth.
■ Let’s hand down the past appearance of Horikawa as record
To know about the past Horikawa is very important to design the future Horikawa.
We refer Horikawa’s pictyures taken in Taisho and Showa era to know forgotten
past Horikawa. Do you keep photos which Horikawa was photographed in in youralbum? For example, photo of your family with Horikawa in the background of thepicture is Okay.
(contact)secretariat
e-mail:2010@horikawa1000nin.jp
Please send comments and pictures (with date and place) from mobile phone orPC.
＊We think image quality of picture taken by mobile phone camera is enough.

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