Horikawa Sen-nin Chosatai 2010 （HSC)
Summary meeting for the 29th stage

Place：
Nagoya Congress Center
Conference room 431+432

The secretariat of Horikawa Sen-nin Chosatai 2010 Photo：
Nagoya Institute of Technology
Studies of Urban Infrastructure Management
Oct. 9th. 2021
Earth Club survey group
Secretariat

11. Horikawa Sen-nin Chosatai 2010
〜Transmission of Raw Water from
Kiso Riveｒ (TRWKR)〜

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 ＊Living things, 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 (TRWKR)
3 years from April.22nd.2007（Stopped on March.22nd.2010）
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 Support Groups Supporting
clarification of Horikawa

The survey froma viewpoint andsense 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 residence.

3

Won the21st Japan Water Award Minister of Land,
Infrastructure and Transport Award June 2019
Public-private academic
collaboration step-up partnership

Ａ

Ｐ

Plan
ActionCitizen's viewpoint
and sense

Do

Ｃ

Check

Ｄ

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

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

National Museum of Emerging Science and Innovation(Ome, Koto-ku, Tokyo)

4

Water Environment of Horikawa River
Horikawa-River

Area of basin ：52.85km2
Length

：16.20km

Change in temperature, precipitationand hours of sunshine
Cause of breedingof phytoplankton,
nitrogen andPhosphorus areincluded inwastewater fromhouses, factories
and stores.

Kiso River is our water source.

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●●● ●●●●●●

Shonai River
Privisional raw watertransmission: 0.3m3/s

●●●

●●●

●●●

Wastewater
Treatment Plant

Tide Gate

Red Tide

Shin-Horikawa-River
Area of basin ：22.77km2
Length： 5.95km

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 Sludge5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, waspolluted in rapid economic growth.
The citizens have rised to get the past back.

Nagoya Station駅

Start

Now

22nd Apr.2007

9th Oct. 2021

Fixed Point
Observation
Groups55 groups
497 persons

107 groups
1,043persons

Free Survey
Groups

22 groups
234 persons

40 groups
650 persons

Horikawa
SupportGroups

88 groups
1,531 persons

2,605 groups
52,022persons

Total

165 groups
2,262 persons

2,752 groups
53,715persons

6

Number of Participants
Horikawa Sen-nin Chosatai was established to clean Horikawa River and tocheck the effective of experiment for it by city citizen s viewpoint.
This activities are not only to surveys, but also spread to the clarification,cleanup, enlightenment activities and exchanges between regions.

Activity in three categories◆ Fixed Point Observation Group (FPOG)
Investigate by city citizen’s viewpoint andsense◆ Free theme Survey Group (FSG)
Survey on free themes◆ Horikawa Support Group (HSG)
Support clarification of Horikawa

2022/10/9

77

３．Survey Periods and Number of Reports
内容

年度

期間
第1ステージ

平成19年
2007年

堀
川
浄
化
の
社
会
実
験

木曽川
からの
導水
0.4
m3/s

春〜初夏

中間
第2ステージ

平成20年
2008年

秋〜初冬
春〜初夏

平成21年
2009年

秋〜初冬
春〜初夏

平成22年
2010年

秋〜初冬
春〜初夏

官民学協働のステップアップ型
パートナーシップ

12月17日〜3月31日

104

4月1日〜6月30日
7月1日〜9月11日

秋〜初冬

9月12日〜12月17日
12月18日〜3月31日

中間
第9ステージ

9月27日〜12月16日
12月17日〜3月31日

中間
第8ステージ

4月1日〜6月30日
7月1日〜9月26日

中間
第7ステージ

9月28日〜12月16日
12月17日〜3月31日

中間
第6ステージ

4月1日〜6月30日
7月1日〜9月27日

中間第5ステージ

9月8日〜12月16日
12月17日〜3月31日

中間第4ステージ

9月20日〜12月16日

7月1日〜9月7日

中間
第3ステージ

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

4月22日〜6月30日

春〜初夏

4月1日〜6月30日

中間
平成23年
2011年 第10ステージ 秋〜初冬

7月1日〜9月10日
9月11日〜12月16日

中間

12月17日〜3月31日

第11ステージ 春〜初夏

4月1日〜6月30日

中間
平成24年
2012年 第12ステージ 秋〜初冬

7月1日〜9月21日
9月22日〜12月16日

中間

12月17日〜3月31日

第13ステージ 春〜初夏

4月1日〜6月30日

中間
平成25年
2013年 第14ステージ 秋〜初冬

9月29日〜12月17日

7月1日〜9月28日

中間

12月18日〜3月31日

第15ステージ 春〜初夏

4月1日〜6月30日

中間
平成26年
2014年 第16ステージ 秋〜初冬

9月29日〜12月16日

7月1日〜9月28日

中間

12月17日〜3月31日

第17ステージ 春〜初夏

4月1日〜6月30日

中間
平成27年
2015年 第18ステージ 秋〜初冬

9月20日〜12月16日

7月1日〜9月19日

中間

12月17日〜3月31日

第19ステージ 春〜初夏

4月1日〜6月30日

中間

平成28年
2016年 第20ステージ 秋〜初冬
中間

7月1日〜9月19日

報告数
堀川 新堀川
258
134
383
103
245
64
152
100
145
54
120
81
111
44
104
72
112
42
133
77
148
59
1
135
4
78
14
129
16
55
15
99
14
68
11
117
16
78
13
90
9
89
18
100
13
69
12
109
17
79
12
116
11
54
8
107
23

84

20

内容

年度

第21ステージ 春〜初夏

4月1日〜6月30日

中間
平成29年
2017年 第22ステージ 秋〜初冬

7月1日〜9月18日

中間

9月19日〜12月20日
12月21日〜3月31日

第23ステージ 春〜初夏

4月1日〜6月30日

中間
平成30年
2018年 第24ステージ 秋〜初冬

7月1日〜9月19日

中間

官民学協働の 平成31年、
ステップアップ型
パートナーシップ

報告数
堀川 新堀川

期間

令和元年

2019年

9月20日〜12月16日
12月17日〜3月31日

第25ステージ 春〜初夏

4月1日〜6月30日

中間

7月1日〜9月19日

第26ステージ 秋〜初冬

9月20日〜12月16日

中間

12月17日〜3月31日

第27ステージ 春〜初夏

4月1日〜6月30日

令和2年

中間

7月1日〜9月19日

2020年

第28ステージ 秋〜初冬

9月20日〜12月16日

中間

12月17日〜3月31日

第29ステージ 春〜初夏

4月1日〜6月30日

令和3年

中間

2021年

第30ステージ 秋〜初冬

129
58
121
80
180
76
184
108
193
101
214
123
333
32
232
131
343

100
48
93
67
107
44
106
67
127
43
105
67
168
23
161
101
190

29
10
28
13
73
32
78
41
66
58
109
56
165
9
71
30
153

9月20日〜12月16日（予定）中間

計7,282 6,014 1,268

Background about COVID-19

To date, 7,282 reports have beenreported. The number of reports for
Shin-Horikawa River was 1,268.
In the 29th stage, there were 343
reports. 190 were reported for Horikawa
River and 153 were reported for ShinHorikawa River. On average, more than
500 surveys are conducted every year.
Many citizens are continuously
examining the actual water environmentof Horikawa River and Shin-Horikawa
River on a daily basis from theperspective and sense of the citizens.
In the 29th stage, infection spread of
COVID-19 made survey groups activity
avoid 3Cs (※).

2020年
1/16 The Infected person was confirmed
in Japan.
2/27 Prime Minister requested
temporary closure of school.
4/7 The state of emergency
in 7 prefectures.
4/10 The state of emergency in Aichi.
4/16 The state of emergency in Japan.
5/31 The state of emergency was lifted.
8/6〜24 Prefectural emergency in Aichi.
2021年…about Aichi
１/14〜2/28： The state of emergency
5/12〜6/20： The state of emergency
6/20〜7/11：Pre-emergency measures
8/8〜8/26： Pre-emergency measures
8/27〜9/30： The state of emergency※ 3Cs ： Close space, Crowded places,
Close-contact8

Total Number of Reports
7,500
7,000
6,500
5,500
5,000
4,500
4,000
3,500
More than 500 reports
are issued every year

3,000
2,500
2,000
1,500
1,000
500

Over 50,000 people joined in Chosatai.
The total number of reports reached more than 7,200.

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.
第26st.
第27st.
第28st.
第29st.

調査報告数（件）6,000

7,282 reports at the end of 29th stage
Include 1,268 reports of Shin-Horikawa River

ステージ

9

４．Weather conditions

Meteorological Agency ̲ Meteorological Statistics, Nagoya Local Meteorological Observatory
http://www.jma.go.jp/jma/menu/report.html

This year's cherry blossoms in Nagoya were the fastest in the history of observation on
March 17th. During the 29st.(April-June), the temparature was about the same as thenormal, and the precipitation was higher than normal because the rainy season was on
May 16th, 21 days earlier than normal.

(Characteristic)・The average temperature was the same as normal.
・The rainy season was on May 16th, 21 days earlier than normal.
・The precipitation was higher than normal, it rained about
80 mm/month.
・The daylight hours was he same as normal.
■Temparature
The average temparature was 19.4℃, which was about the same as normal(19.0℃). It
was higher than normal value in April. It was about the same as normal in May and June.
■Precipitation
The rainy season was on May 16th, 21 days earlier than normal.The average of monthly
Precipitation was 194 mm, which was higher than normal(154.8 mm).It was higher thannormal in April and May. It was less than normal in June. It rained about 80 mm/month.
■Daylight hours
The average of monthly daylight hours was 175 hours, which was about the same asnormal(185.8 hours). It was less than normal in May.It was about the same as normal in
April and June.

■1991-2020 Normal
Nagoya Local Meteorological ObservatoryNormal value(Monthly)
Precipitation
Temperature
Daylight(mm)(℃ )(hour)
Category
Highest/day
Lowest/day
Total
total
Ave.
Record period

Record year
Year
Apr.
May
Jun

Ave.

Sep.
Oct.
Nov.
Dec.

Ave.

1991
〜2020

1991
〜2020

1991
〜2020

1991
〜2020

1991
〜2020

30
1535.3
127.5
150.3
186.5
154.8
231.6
164.7
79.1
56.6
133.0

30
15.8
14.6
19.4
23.0
19.0
24.5
18.6
12.6
7.2
15.7

30
20.7
20.1
24.6
27.6
24.1
29.1
23.3
17.3
11.7
20.4

30
11.9
9.7
14.9
19.4
14.7
21.0
14.8
8.6
3.4
12.0

30
2091.6
200.2
205.5
151.8
185.8
159.6
168.9
167.1
170.3
166.5

Temparature

Average 19.0℃
During the 29st., the average temparature was
19.4 ℃.It was about the same as normal.
During the 29st., it was higher than normal value in April.
It was about the same as normal in May and June.

April-June normal value(1991-2020) Average 19.0℃

10Weather conditions

Meteorological Agency ̲ Meteorological Statistics, Nagoya Local Meteorological Observatory
http://www.jma.go.jp/jma/menu/report.html

Precipitation

April-June normal(1991〜2020) Average 154.8mm
During the 29st., it was less than normal in June.
It was higher than normal in April and May.

During the 29st., the average of monthly precipitation was
194 mm. It was higher than normal.
Average 154.8mm

Daylight hours
During the 29st., the average of monthly daylight hours
was 175 hours. It was about the same as normal.

Average 185.8 hours

April-June normal(1991-2020) Average 185.8 hours

During the 29st., it was less than normal in May.It was about
the same as normal in April and June.

11

(Reference) Daily temperature and precipitation

23th stage

25th stage
12

(Reference) Daily temperature and precipitation

27th stage

There are a lot of hot
weather days from the
beginning of the year,
Bloom of a
Someiyoshino cherry
tree was March 17 of
the record fastest.
Beginning of the rainyseason was May16 for21 days early morethan a common year.
It found how toadvance a season to beearly.
Therefore thetemperature becamehigh until April in 29
stages.
Low air pressure andhigh air pressure
passed alternately at
the first ten days ofApril and May,and the weatherchanged periodically.
Much rain often fell by
influence of low airpressure and seasonalrain front.
About 80 mm of mucha lot of rain fell as thistime.

29th stage
13

５．Main Water Quality Improvement Measures
Measures

2007

2008

2009

2010

2011

2012

2013

2014

1st.

3st.

5st.

7st.

9st.

11st.

13st.

15st.

2st.

4st.

6st.

8st.

10st.

14st.

12st.

16st.

New Water Quality Improvement Measures

TRWKR(0.4m3/s)

upstream
Kurokawa No.2 Bridge

downstream
Kurokawa No.2 Bridge

Making shallow and deep(Improvement of self-

Kurokawa No.1 Bridge〜Meoto Bridge

purification function and water enviroment)

Increase of Raw Water transmission from Shounai
3River (＋0.4m /s)
New water resource(from shallow ground water)
3(0.0805m /s)*provisional raw water transmission from Shonai River 2001.Jul〜

Max0.3m3/s

upstream Tsujie Bridge 0.01m3/s(2004)
upstream Kizune Bridge 0.01m3/s(2005)

upstream
Seko Bridge

upstream
Sanage Bridge

0.01m3/s

0.01 m3/s

Shimizu wakuwaku water 0.0005m3/s(2008)

Experiment of sand covering for water purification
Habashita Bridge〜Sakura Bridge(water's edge along both banks)

Gojo Bridge〜Naka Bridge

Remove bad smell at Shin-Horikawa River（dredging,sand cover）
Reclaimed wastewaterat the Moriyama Waste Water Treatment
Center(0.046m3/s)
Advanced waste water treatment
at the Meijo Waste Water Treatment Center
Horikawa Ugan

Rain-water Reservoir for pollution control
Advanced primary treatment facility
Measures(after 2015)

2015

2016

2017

2018

2019

2020

2020

17st.

19st.

21st.

23st.

25st.

27st.

29st.

18st.
TRWKR(0.4m3/s)
Making shallow and deep(Improvement of self-

20st.

22st.

24st.

26st.

28st.

New Water Quality Improvement Measures
downstream
downstream
upstream
upstream
Rurikou Bridge
Meoto Bridge
新たな水質改善施策の実施
Shinbori Bridge Kizune Bridge

30st.

downstream
Shinbori Bridge

purification function and water enviroment)(donated by Johoku Lions Club)

Increase of Raw Water transmission from Shounai
River (＋0.4m3/s)
New water resource(from shallow ground water)(0.0805m3/s)
Experiment of sand covering for water purification
Habashita Bridge〜Sakura Bridge(water's edge along both banks)
Remove bad smell at Shin-Horikawa River（dredging,sand cover）
Reclaimed wastewaterat the Moriyama Waste Water Treatment
Center(0.046m3/s)
Advanced water treatment
at the Meijo Water Treatment Center
Rain-water Reservoir for pollution control
Advanced primary treatment facility

upstream
Shiga Bridge
0.01m3/s

upstream
Nakatsuchido Bridge
0.01 m3/s

Gojo Bridge〜Naka Bridge

upstream
Kinjo Bridge
0.01m3/s

upstream
Kurokawa No.1 Bridge
0.01m3/s

Habashita Bridge〜Gojo Bridge Naka bridge〜Sakura Bridge

downstream area

upstream area

※Advanced waste water treatment
at the Tsuyuhashi Waste Water Treatment Center(Oct. 2017)

Horikawa Sagan
Meijo Waste Water Treatment Center
Horidome Waste Water Treatment Center

14

■ Shaping of Rapids and Pool
It was identified that variousorganisms breed and grow when
rapids and pools were shaped.
This place has been a habitat oforganisms that like cobble stones.
In winter, there are some ducks
waiting for spring here.
Let s also pay attention to thedifference in the stones
used(round stones, angularstones)and observe them.

Kingfishers, egrets, tortoises, etc.
Fishes such as
Small fishes such
Fries of paleas pale chubs,
carp, gibels,
chubs etc.
hemibarbus barbus rhinogobius

Stacks ofstonesShrimps, crabs, aquatic insects, etc.

■ Rise of self-purification by food chain

Waterside
Kingfishers,
egrets, etc.

Prawns andJapanese mitten
crabs are organismsthat migrate between
rivers and the sea.

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

*denizen
*外来種

Water

Mauremys
reevesii,
trachemys
scripta*Carp, hemibarbus barbus
catfishes, black basses*,
bluegills*, northern snakeheads*

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

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

Angular stone

Small fishes, shrimps, aquatic insects feed the algaes and the microbes.
Big fishes and birds prey the small fishes and aquatic insects.

The components of dirt in water are
taken up by living things in the foodchain and consumed for growth andreproduction.
As the riffles and pools is formed and adiverse and affluent ecosystem is built,
more dirt components are consumed ina chain and removed from the water,
cleaning the water. The purifying effectof the river will increase.（＝Increased
self-cleaning effect）

Round stone

The riffles and pools, which wasformed in the past, maintains its
diversity while transitioning
according to the environment.
Photo：Secretariat Apr,2021
Meoto Bridge downstream

Completed in 2020
Photo：Secretariat Apr,2021
Shin-Hori Bridge downstream

15

Coverd sand construction
Sludge removal
Btwn.SakuraBrdg. and HabashitaBrdg. Btwn FuruwatariBrdg and SanoBrdg.
Photo : Secretariat June.2021
Jan.-Feb.2015,Dec.2017-Jan.2018

Securing a water source(Use of shallow groundwater)
Upstream well of Kurokawa no.1 Brdg.
March.2020 operated

KeiunnBrdg.

Clean well water
0.01m3/s

ＧｏｊｏBrdg.
Koshio Brdg.

Ｈａｂａｓｈｉｔａ Brdg.

State of the middle stream
Where the revetment work is proceeding.
( Includeing sludge removal)

Near Shinsuzaki Brdg.
Photo : Secretariat May.2021

Near Matsue Brdg.

Near Habashita Brdg.

Near Hioki Brdg.

Photo : Secretariat June.2021

Photo : Secretariat June.2021

Photo : Secretariat June.2021

16

■ Measure against foul odors The removed sludge
in the Shin-Horikawa ｒiver was in this situation.
(Dredging・Sludge dredged)
Section : Btwn Upstream of
Tateishi Brdg. and Upstream end.
Period:Sep.2018ーFeb.2019

Newly launched facilities after the stop of TRWKR■Improvement of Treatedwater Quality
Meijo Water Treatment Plant installed filtration devices andimproved quality of treated water．

Meijo Water
Treatment Plant
・Processing method: Conventional activatedsludge process+ Rapid filtration
・Operated since: May 2010

■Preventing the outflow of debris into rivers

BeforeDebris Guide Device

Upatream of Memorial Brdg. 5th ,Oct.2018
overflow into rivers

Water treatment center

参考資料：第18回 堀川１０００人調査隊会議

Securing a new water source.
■Utilization of Reclaimed wastewater(Except winter)Moriyama Water
Conducting reclaimed wastewater treated byTreatment Center
Membrane filtration at the Moriyama Water
Treatment Center (up to 4000m3/day)is discharged.
Start to conduct in Aug.2011

Shonai
Irrigation

Reclaimed wastewater is conductedduring irrigation season(Apr ‒ Oct)
(Excluding the period Nov.-Mar. whenwater is passed throught the Shonai
irrigation canal.)

Debris in sewage overflow
into rivers when heavy rain.

overflow into rivers
Rainwater without debris
overflows into rivers.

Water treatment center
Debris in sewage are led totreatment plants and removed.

■Installation of
Narrower Slit ScreensStart to conduct inAug. 2011
Conductiong point into
Horikawa River.

After

Horikawa
River・Shiratoribashi Pump Station
・Nakajima Pump Station
・Chitose Water
Treatment Plant◆Interval of Slits
40mm → 25mm

17

Facilities which started operation after the stop of TRWKR■Control of combined sewer overflow
Reduce volume and frequency of overflow from sewer outlets inrainy weather condition by temporarily store first flush of which
pollution load is highHorikawa-River right bank Rainwater Reservoir
for pollution control
3
Volume 13,000m
Started operation in Sep. 2010

Horikawa-River right bankRainwater Reservoir
for pollution control
Horikawa-River left bankRainwater Reservoir
for pollution control

Subject area of Rainwater Reservoir
for pollution control

Horikawa-River left bank Rainwater Reservoir
for pollution control
Volume 14,000m3
Started operation in Nov. 2019

Horikawa-River right bank reservoir
Horikawa-River left bank reservoir

18

Combined sewer system
Overflow level from the CSO outfall in rainy weather
July 2nd 2021

Sanage Bridge

5 am photo : secretariat

Daiko River
Continuous rainfall

Continuous rainfall

Hourly rainfall

Hourly rainfall

Tide level of Nagoya Ｐort
T.P.-18cm

Times of day

Sewer outlet （right bank）

Kizune Bridge

Kizune Bridge
Sewer outlet （left bank）

Sewer outlet （right bank）

Sewer outlet （left bank）

19

August 15th 2021 photo : secretariat

Downstream of Kizune Bridge
Sewer outlet （right bank）

Sewer outlet （right bank）

Kizune Bridge
Kizune Bridge
Sewer outlet （left bank）
Around 5:30 am

Sewer outlet （left bank）

Downstream of Sanage Bridge

When it was raining

around 6:30 am

Daiko River

Daiko River

When it was raining

Around 5:30 am

Upstream of Shiga Bridge
Sewer outlet （right bank）

Around 5:30 am

around 6:30 am

Sewer outlet （right bank）

When it was raining

around 6:30 am

20Advanced Facility for simple treatment in Horidome Water Treatment Center

Examination of using ground waterfor Shin-Horikawa River

Started in Mar. 2019

Combined Sewer System in rainy day■Summarize information ofgroundwater capable to use forShin-Horikawa■Review model cases of using groundwater for river clarification

Less than certain amount of rainwater istreated with wastewater in water treatment
center, but more amount is directly
discharged into the river.

Rain-water Reservoir for pollution
control is the facility temporally storing
the initial rainwater (= first flush whichis particularly dirty).
Accumulated rainwater in the reservoir isdelivered to the water treatment centerfor treatment after rain stops.
Raw water

Filtered
water
Upper
screenFiltrationmaterial

Waste cleaningwater tank

There are many water springs in basement floor of
Tsuruma Library. One of springs is abundant (more than
100 litters/min. (fluctuated) ) and water quality is good.

Source:25th HSC Conference(Report by Nagoya City)
Advanced Facility of simple
treatment * can remove morecontaminants from rainwater(excess of normal treatment).

treatment flow
Garbage removal device
set in sewer outlet
Sewer outlet(reference)Well Water of Tsuruma Library

Water Treatment Center

Rain-water Reservoir forpollution control

Advanced Facility ofsimple treatment

Shrinkage of rainwater
screen slit in pumping station
Pumping Station(Source)Website of Nagoya City Waterworks and Sewerage Bureau
https://www.water.city.nagoya.jp/category/mizukankyoukoujou/2096.html*By replacing
sedimentation tank tofiltration facility, water
quality improves
substantially comparedwith conventional simple
treatment.

(Source)Website of Nagoya City Environment Bureau
http://www.city.nagoya.jp/kankyo/page/0000089008.html

21

6. 29th stage survey report〜Column〜 For the clean-up and regeneration of Horikawa River
Horikawa Sen-nin Chosatai (HSC)was established on April 22nd, 2007 for clean-up and regeneration of Horikawa River, as aplace for citizens activities (Fixed Point Observation Group, Free Survey Group and Support group).
Fixed Point Observation Group examines Horikawa River to confirm the clean-up effect by the water quality improvement
measure and to make clear the condition of water quality and cause of pollution, from a viewpoint and a sense of citizen.
Free Survey Group studies Horikawa River from various view points.
Support Group supports clean-up and regeneration of Horikawa River in various-free ways. These three groups wish for cleanup and regeneration of Horikawa River, and work together in a large network.
Currently(as of Oct.9.2021), there are 2,752 groups and 53,715 people in HSC.
(107 groups in Fixed Point Observation Groups, 40 groups in Free Survey Group and 2,605 groups in Support Group) At thetime of launch of HSC, there were 165 groups and 2,262 people.
We can see that the network of citizens who wish to purify and regenerate Horikawa-River has expanded significantly.
（Reference. Survey group registration status p.7〜8）
We will explain the status of activities of Fixed Point Observation Groups. The Fixed Point Observation Groups carried out
7,282 observations. It has become clear from the surveys so far that the state of the water area changes from moment tomoment due to the ebb and flow of the tide at the downstream section ( tidal section )from the Sanage Bridge in Horikawa
River. Since Fixed Point Observation Groups made many observations from the perspective and sense of thecitizens(Observation in various places, tide conditions, and time zones), we are able to grasp the average condition of thewater quality of the Horikawa, and trends in that change become clear. (Reference: 3. Survey period / number of reports ofsurvey results̲p.9-10)-Pilot project of Horikawa River clean-up from Apr. 2007 to Mar. 2012 confirmed the effect of TRWKR In 5 years pilot project of Horikawa River clean-up, it was confirmed that the range of improved water quality due to TRWKR
0.4 /sec was about between Sanage Bridge and Matsushige Bridge. And in this period, it was confirmed that the amount ofwaste artificial waste : plastic waste was reduced. This is probably because the public awareness has changed due toincreased cleaning activities.
【Summary of 5 years pilot project】■Confirmed the effect of clean-up between Sanage Bridge and Matsushige Bridge due to TRWKR■The network of citizens who wish to clean and revives the Horikawa River has been expanded■Citizens awareness of clean-up improved as cleaning activities became active

22

The weather of the 29th Stage(2021: Spring〜Early Summer(April〜June) ⇒ Emergency declaration was issued between May
12th and June 20th to prevent the spread of COVID-19. The activities of the HSC team were forced to stopped, or carried out
with prevention of confined space, dense state, close contact. So its activities were limited.
In addition, we think that evaluation of survey is not enough at this time, for example such as study of impact for decline in socialand economic activities due to COVID-19. We think that it is necessary to reorganize, according to further investigations.

(１) State of the weather
The flowering of Yoshino cherry blossom (Nagoya) in this year was March 17. This was earliest in the history of observation.
The temperature in the 29th stage (April-June) was normal. And also rainfall was higher than normal because rainy season
started on May 16, which was 21 days earlier than normal.
(Feature of the 29th stage weather, etc.) ・ Average temperature was normal
・ Rainy season started on May 16, which was 21 days earlier than normal
・ Precipitation was higher than normal, and it rained about 80 mm / day.
・ Sunshine hours were almost same as normal(2) Implementation of new water quality improvement measures
After the TRWKR was stopped Mar. 2010 , new measures were implemented to improve the water quality. New riffles and pools
was formed downstream of Shinhori Bridge in Horikawa in the last year (2020 (Reiwa 2)).

(３) Change in water quality of Horikawa River
Although water quality of Horikawa River got worse after TRWKR there has been a general tendency for improvement. But
Impression of water clearness , Odor and Bubbles from the riverbed deteriorated in the 29th stage compared to the 27th.
Impression worsened between Asahi Brdg to Ooseko Brdg. Especially ratio of clean - ordinary decreased to 17％, bubbles
were more witnessed and odor got worse between Asahi Brdg to Matushige Brdg. Moreover ratio of ditch and sludge smell
increased between Sanage Brdg to Ooseko Brdg.
We believe that the bad condition of the river bed deteriorated the impression of water clearness between Asahi Brdg to
Matsushige Brdg. Water agitation may have decreased due to reduced ship operations caused by covid19.
Continuous observation and verification are required to investigate the effect of water quality improvement by ship operations.

23

1-6 stage ： during TRWKR
7-29 stage： after TRWKR
no rain on the day & previous day

Impression of Water Clearness● Ratio of Clean - ordinary

decreased in the
29th stage
compared to 27th

Sanage Brdg-Ooseko Brdg

improved
Impression of cleanessless than 50％
means bad
impression● Ratio of Clean - ordinary
worsened in the
29th stage

TRWKR
less than 50％
means bad
impression

improved

worsened in the
29th stage

TRWKR
less than 50％
means bad
impression

improved

24

Bubbles1-6 stage ： during TRWKR
7-29 stage： after TRWKR
no rain on the day & previous day● Bubbles from the riverbed (spring - early summer)
TRWKR

Sludge and record hightemperature affected

TRWKR
worsened in
the 29thstage

improved
improved● Change in the composition ratio on Odor
sludge

TRWKR
1stは
調査なし

"No Smell" was increasing

sludgedecreased in
the 29th stage
compared to
27th

25

(4)Is Horikawa becoming clean?

＊period of years

We analyzed for period of years* or months. As a result, from change of transparency, COD, ■2010〜2011⇒right after
bubble and smell, we found state of water and bottom improved little by little and impression
stopping TRWKR■2012〜2014of clearness improved by new water quality improvement measure. But tardy improvement■2015〜2017from Asahi Bridge to Matsushige Bridge and that dirt sticked out in hot and the rainy season ■2018〜2020⇒present
were found out. It is desirable that organic pollution is decreased and scarcely sink andaccumulate to bottom.
Change of impression of clearness by month■ Is Horikawa becoming clean in rainless season?
（Legend） ■：tendency to improvement 〇：content rating □：slow improvement
Contents

Sanage Brdg.
〜Oseko Brdg.
TRWKR
stop

The

→ present

30 → 51■Impression of clearness(%)
〇
percentage of clean-medium
67 → 75■Transparency(cm)〇
10 → 8■ＣＯＤ(mg/L)〇■Bubble(%)
13 → 12percentage of rising■Smell(%)
45 → 71
percentage of no smell〇

Sanage〜Asahi
TRWKR
stop

Asahi
〜MatsushigeThe→ present

33 → 55〇
62 → 6412 →

8〇13 → 5〇45 → 77
〇

TRWKR
stop

The

→ present

19 → 3667 → 75〇
12 → 1022 → 1938 → 59〇

Matsushige〜OsekoNote→ present

The(ref.)Rating

40 → 73〇
71 → 80
〇
〇
7 → 7
〇
〇
5 → 2
〇
〇
52 → 84〇〇

half of citizens⇒50％ and more

TRWKR
stop

permissible range ofcitizens⇒70cm andmorestandards on the sea
preserved⇒8mg/L and less

10% and lesshalf of citizens⇒50％ and more

Correlation between impression of clearness and weather■ Is Horikawa becoming clean after rain?
Contents

Sanage Brdg.
〜Oseko Brdg.
TRWKR
stop

The

→ present

Sanage〜Asahi
TRWKR
stop

The

→ present

Asahi〜Matsushige
TRWKR
stop

→ present

The

→ 11

■Impression of clearness(%)
30 → 33
percentage of clean-medium
54 → 61■Transparency(cm)38 → 358

56 → 46

43 → 60

10 → 10

8 → 7
〇
〇
7 → 9
〇
〇
63 → 82〇〇

12 → 11■ＣＯＤ(mg/L)■Bubble(%)
percentage of rising■Smell(%)
percentage of no smell

13 → 2039 → 62〇

17 → 34
23 → 48

Matsushige〜Oseko
TRWKR
stop

The

→ present

Note(ref.)Rating

43 → 56 half of citizens〇 ⇒50％ and more
permissible range of
61 → 66
citizens⇒70cm andmore

8 → 10 standards on the sea
preserved⇒8mg/L and less〇
14 → 3
10% and less〇
40 → 71 half of citizens〇 ⇒50％ and more

(5)14th Simultaneous Survey on Horikawa River「The nearest full moon become the totality.」 With citizen s view and sense, we examined Horikawa when change of water level was large.

■Matsushige〜Oseko Brdg.・・・Hypoxia tended to improve.
■Asahi 〜Matsushige Brdg.・・・ Improvement of bottom is subject. Compare with time of partial solar eclipse(2009.7),marked
As past simultaneous surveys, Between Asahi and Matsushige milky water wasn t found. Then, it was found that ries ofBridge it is found out that sludge and bubble from bottom rose. mullets swam up. We think it prove that hypoxia of the basin
Improvement of bottom is subject.
26
tend to improve.

(6)Floating garbage moving and accumulated around Sanage Bridge

We confirmed that clouded water was going upstream with tidal front and also floating matter was moving and accumulatedaround Sanage Bridge on July 26th(spring tide and high tide). Secretariat made a hypothesis and carried out
field survey at Sanage Bridge to prove the hypothesis.
(Hypothesis)When high tide on spring tide and decreasing raw water transmission
from upstream happen at the same time, floating matter can move to upstream andbe accumulated around Sanage Bridge.

(Result of field survey)We confirmed that when both high tide on spring tide anddecreasing of water transmission from upstream area happen at the same time, floating
matter sometimes moves to upstream and is accumulated around Sanage Bridge.
At wide section of Horikawa such as between Shiga Bridge and Tabata Bridge flow
speed becomes so slow that floating matter is tend to stay. We think that s why
sedimentation of organic matter to the bottom and occurrence offloating matter increases at the section.
Horikawa
We re-confirmed that water transmission fromRiver
Shonai River, use of shallow underground water,
utilization of reclaimed wastewater is important
to improve impression of water clearness.

(7)Situation by section of Shin Horikawa River
impression of water clearness is bad in the upstream
Impression of water clearness of Shin Horikawa
section and junction with Horikawa RiverIn Shin Horikawa River impression of water clearness is
tend to be bad at the upstream section(between
Horidome and Tateishi Bridge) and downstream section
including near junction with Horikawa River.
Especially impression of water clearness is worse at thesection between Horidome and Utsugi Bridge, which is themost upstream section. Because bubble from the bottom,
rotten-eggs smell and clouded water are reported aroundthe section, we think water and sludge of river bottom
become the environment which easily generate sulfide.

27

(8) Flood control and change of water quality in Shin-Horikawa River
Rapid urbanization in Shin-Horikawa region increased rainwater runoff and caused flood damage in wider
area. To prevent and mitigate flood damage, river improvement measures (mainly shore protection andriverbed excavation)had been implemented since 1977. Due to these measures, a large amount ofrainwater is flowed inｔo the Shin-Horikawa River and washed out into Nagoya Port, and flood damage has
been decreased.
On the other hand, riverbed excavation increased water area where water doesn t move during no rainfall,and sea water came to flow into deep riverbed. As a result, odor of rotten egg and cloudiness of river occurs more likely.
（ref : p.119〜120 ）Before riverbed excavation

After riverbed excavation
大雨時の水の流れ■ In case of■heavy
rain

Cross section area of water flow
increasedRiverbed
excavation

Distance from the confluence(m)Confluence of Horikawa Riverand Shin-Horikawa River

Shore protection and riverbed
excavation increased cross section offlowing water and decreased flood
damage.

■ No■rainfall
雨が降っていない時の水の流れ

Water level changes
according to sea levelof Nagoya Port

Stagnant water area increased
Riverbed
excavation

Stagnant water area during no rainfall
increased.
→ odor of rotten egg and cloudinessof river occurs more likely.

28

(9) Impression of water clearness in uppermost area of Shin-Horikawa River■Data
Sep. 2012（Start of this survey） 〜 Mar. 2021
Horidome〜Utusgi Bridge
No rain on the day and the previous day

In the uppermost area (Horidome 〜 Utsugi Bridge), many bubbles rise from riverbed in month of hightemperature and heavy rainfall, then impression of water clearness tends to be worse.

60

50

56

42
40
20

28

27
19 17

15
5

4

9

0
Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar
39

58

46 31

22

29

56

50 51

35 23

18

90
y = -2.1546x + 64.006
R² = 0.6362

80
70

Impression tends tobe worse in monthof high temperature

60
50
40
30
20
10

ratio of "clean" 〜"ordinary"(%)

80

100

100

ratio of "clean" 〜"ordinary"(%)

ratio of "clean" 〜"ordinary"(%)

100

Impression of water clearness Horidome〜Utsugi
BridgeNo rain on the day and the previous day
7790

y = -0.306x + 69.352
R² = 0.6673

80
70

Impression tends tobe worse in monthof heavy rainfall

60
50
40
30
20
10
0

0
0

5

10 15 20 25 30
average temp.(℃)

0

50 100 150 200 250 300
rainfall(mm)29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 photos taken in Taisho and Showa era to know forgotten past
Horikawa. Do you keep photos which Horikawa was photographed in in your album?
For example, photo of your family with Horikawa in the background of the picture 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.

30