Horikawa Sen-nin Chosatai 2010 （HSC)
Summary meeting for the 26th stage

Place：
Nagoya Urban InstituteConference room (11th floor)

The secretariat of Horikawa Sen-nin Chosatai 2010
Feb.29th.2020

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 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
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 on the Japan Water
Award and Minister of Land, Infrastructure, Transport andTourism 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
Area of basin: 51.9km2
Length: 16.2km

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.

●●●

Red Tide●●●

Shonai River
Privisional raw watertransmission: 0.3m3/s

●●●

●●●

●●●

Wastewater
Treatment Plant

Tide Gate
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●●● ●●●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

29th Feb.2020

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
52,021persons

Total

165 groups
2,262 persons

2,752 groups
53,714persons

6

Number of Participants
Horikawa Sen-nin Chosatai was established to do the project to clean
Horikawa River and to check 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.

◆ Fixed Point Survey Group (FPOG) ・・・・・・・1,043
surveying on the fixed points◆ Free theme Survey Group (FSG) ・・・・・・・・・・650
surveying on free themes◆ Horikawa Support Group (HSG) ・・・・・・・52,021
supporting clarification of Horikawa
total 53,714

２９ｔｈ.Feb.2020

7

3. Survey Periods and Number of Reports
Reports
Content

Fiscal year

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

Survey Period

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

26th stage

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

Interval

Jul.1st～Sep.19th

Autumn～Early WinterSep.20th～Dec.16th

129
58
121
80
180
76
184
108
193
101
214

100
48
93
67
107
44
106
67
127
43
105

29
10
28
13
73
32
78
41
66
58
109

6,088

5,304

784

Interval

Total

To date, 6,088 reports have been reported. Of
these, the number of reports for Shin-Horikawa
River was 784.
In the 26th stage, there were 214 reports. Of
these, 105 were reported for Horikawa River and
109 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.

8

Total Number of Reports
6,088 reports at theend of 26th stage
Include 784 reportsof Shin-Horikawa River

Average of 400
reports every year

Over 50,000 people joined in Chosatai.
The total number of reports reached more than 6,000.

9

4. State of the weather(Overview)
The average temperature in Nagoya city in 2019 was thehighest 17℃( the average value 15.8℃） since start ofMeteorological Statistics.
Also the average temperature in 26th Stage was the highest
since the HSC survey started in 2007.
Precipitation and Sunshine Hours was on average. Autumn
rain front and Typhoon No. 24 brought a lot of rainfall andlittle sunshine.

in the 26th Stage(September-December)■Temperature
There was a lot of high warm day and recorded
highest average temperature(17.3℃) since survey start.
（temperature anomalies ＋1.9℃)
Especially the average temperature in Sep. and Oct. washigher than yearly by 2℃.
■Precipitation
The precipitation for term of survey was yearly , expect
less than in Sep. and Nov. although it increased about
threefold (357mm/month) due to the impact of typhoon(NO19. NO20) , and the influence of the autumn rain
front.
■Sunshine Hours
It became almost normal(168hr/month) ,expect for in
Sep. and Nov. when there was a lot of rain. In Oct. and
Dec there were less sunny days, shorter than normal.

Nagoya Local Meteorological Observatory
Rainfall
(mm)
Gross

category
Statsitical
Period
years
Apr.
May
Jun.

Average
Sep.
Oct.
Nov.
Dec.

Average

Temperature(℃)
Average
HighestLowestDaylight(hour)
Gross

1981

1981

1981

1981

1981

～2010

～2010

～2010

～2010

～2010

30
124.8
156.5
201.0
160.8
234.4
128.3
79.7
45.0
121.9

30
14.4
18.9
22.7
18.7
24.1
18.1
12.2
7.0
15.4

30
19.9
24.1
27.2
23.7
28.6
22.8
17.0
11.6
20.0

30
9.6
14.5
19.0
14.4
20.7
14.1
8.1
3.1
11.5

30
196.6
197.5
149.9
181.3
151.0
169.0
162.7
172.2
163.7

Source: Meteorological Agency _ Meteorological Statistics
http://www.jma.go.jp/jma/menu/report.html

Quite hightemperature
Higher temperature
continued even after
the early winter.

10

5. 26th stage survey report～Column～ For the clarification and regeneration of Horikawa River
Horikawa Sen-nin Chosatai (HSC)was established on April 22nd, 2007 for clarification and regeneration of Horikawa River, asa place for citizens’ activities (Fixed Point Observation Group, Free Survey Group and Support group).
Fixed Point Observation Group examines Horikawa River to confirm the clarification 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 clarification and regeneration of Horikawa River in various-free ways. These three groups wish forclarification and regeneration of Horikawa River, and work together in a large network.
Currently(as of 26th), there are 2,752 groups and 53,714 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 it was spread by the citizens’ activities for clarification and regeneration of Horikawa River.
（Reference. Number of participant p.7～8）
We will explain the status of activities of Fixed Point Observation Groups. The Fixed Point Observation Groups carried out
6,088 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.
Since Fixed Point Observation Groups made many observations from the perspective and sense of the citizens, We are able tograsp the average condition of the water quality of the Horikawa, and trends in that change become clear.
-Pilot project of Horikawa River clarification ”from Apr. 2007 to Mar. 2012 confirmed the effect of TRWKR”In 5 years pilot project of Horikawa River clarification, 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 clarification 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 clarification improved as cleaning activities became active

11

(１) State of the weather
The weather of the 26th Stage(2019: in September(Sep.)～ December(Dec.))was warm and the average temperature was
17.3℃, which is the highest since the HSC survey start （temperature anomalies ＋1.9℃). Especially an average of Sep. and Oct.
was higher more than 2℃ compered with the average.
The precipitation for term of survey was on average, but in Sep. and Nov. was less than yearly and it increased about threefold(357mm/month) due to the impact of typhoon (NO19. NO20), autumn rain front in Oct.
(The point of the 26th Stage ) Higher temperature and average precipitation(２) Implementation of new water quality improvement measures.
After the TRWKR was stopped ”Mar. 2010”, new measures were implemented to improve the water quality.
Specifically, in 2010, the formation of shallows and abyss “improvement of natural clarification function” began in the upstreamof Sanage Bridge, and advanced water treatment was introduced at Meijo Water Treatment Center, the Horikawa Right-bank
Stormwater Reservoir was put into service.
In 2011, the reclaimed wastewater from the Moriyama Water Treatment Center was passed to the Horikawa River. ”Max 4,000㎥/day from April to October” Currently, Horikawa Ugan Rain-water Reservior for pollution control is under construction, andexpectations are high for improving the water quality after the start of operation.
The use of shallow groundwater has been promoted as a new water resource for the Horikawa River from 2004. In 2016, the 8th
well was dug upstream of Kinjo Bridge, and this year, the 9th well has been dug upstream of the Kurokawa-daiichi Bridge(0.01㎥/sec). In 2017, based on the results of clarification experiment with sand cover in which citizens also participated, sand cover
was carried out to improve the waterfront environment between Habashita Bridge to Gojo Bridge and Naka Bridge to Sakura
Bridge.
In the Shin-Horikawa River, dredging of the river channel were implemented near the confluence as a measure against foul odors
in2017, and dredging and sand cover of the river channel were implemented at the upstream of the river in 2018. At the
Horidome Water Treatment Center, the simplified processing advanced facility was put into service in Mar. 2019.

(3) Change in water quality of Horikawa River
The water quality of the Horikawa deteriorated after the suspension of TRWKR. However, there is a general gradualimprovement trend from the upstream, except temporal deterioration due to weather conditions, etc.
At 26 stages, there was a marked improvement tendency especially in "impression of water stains", "transparency", and "smell".
For examples, “transparency” averages 76 cm between the Sanage Bridge and Oseko Bridge (the citizen's allowable value is
70 cm), and especially between Matsushige Bridge and Oseko Bridge exceeds 90 cm.
We believe this is due to changes in public awareness aimed at purifying and rehabilitating the Horikawa River and theimplementation of new water quality improvement measures including the removal of sludge from the river along with theconstruction of revetments.

12

（Note）
Impression of
Water Clearness
The ratio of “Clean”,“Slightly clean” and“Ordinary”

Improved a little from upstream(except the weather condition influences)
After the stop Of TRWKR →Worsened“Clean”, “Slightly clean” and “Ordinary” arecategorized as the acceptable range for citizens.

Improved a little from upstream(except the weather condition influences)

Change ofTransparency

After the stop Of TRWKR →Worsened

春～初夏のステージ（4月～6月）：奇数ステージ
秋～初冬のステージ（9月中旬～12月中旬）：偶数ステージ

13

（Note）

Occurrence of
bubbles fromriver bottom

Improved a little from upstream(except the weather condition influences)
After the stop of TRWKR→ Worsened

春～初夏のステージ（4月～6月）：奇数ステージ
秋～初冬のステージ（9月中旬～12月中旬）：偶数ステージ

Between Sanage Brdg. – Oseko Brdg.

Occurrence of smell

1stは
調査なし

ditch

sludgeDitch & sludge

Smell less

Reduction of Ditch and Sludge
Increase of Smellness⇒Improve

Ratio of
Ditch, Sludge,
Ditch & Sludge,
Smell less14

(4) Why does garbage gather in band shapearound Shiratori Bridge ～ Oseko Bridge?
We organized the pictures Chikyu club survey group sent to us regularly(about 700 pictures) in order to find out the mechanism, “Why does garbage
gather in band shape ? ”, the question from Chikyu club survey group.
As a result, we find out the garbage gather in band shape, mainly when hightide and ebb tide exchange each other.
We are thinking that the elucidation of the mechanism of “gather in band
When high tide and ebb tide exchange, the garbage flowing
downstream on the surface of the river and the garbage flowing
shape” is beneficial information for the timing of garbage collection, for
upstream on the surface of the river bump into each other, thenexample.
the garbage gathers temporarily, we think.

The garbage gather
in band shape

Shin-Horikawa river The impression of water stains(Ref.：
p.81)

Dec.21st.2019
Photo:Chikyu club survey group(5)Change of the water quality ofShin-Horikawa river

Upstream

Downstream

Shin-Horikawa river SmellAt the end of the 26th stage, there were 784 surveys in
the Shin-Horikawa river. From the results of previous
surveys,we found that Shin-Horikawa river has a bad
impression of water stains in the upstream area, and inspecially, the area between Mukouda Bridge, Uzura
Bridge and Maizuru Bridge, where the ratio of "Terrible
smell" to "slightly smell" accounts for more than 80%, isin an environment where it smells everyday.
Downstream*Not enough data

(Ref.：
p.83)

Upstream15

(by 26th stage)

Bubble rise from
① the bottom of the river③Generation of rotten odor

The water in the
upstream section
around Uzura
Bridge is dirty④Occurrence of cloudiness

3 1②The rise of sludge（Scum）

We drew up worst rating of clearness(factor below) by spot, month andtide.
■Bubble from bottom ■Sludge ■Rotten egg ■CloudinessWe found clue of provision from now on.
e.g. Decreasing suspended substance(organic substance)
to flow in Shin-Horikawa River, Sinking water temperature,
Flushing seawater in bottom.

Tateishi Brg.

-4
-5
-6
-7
-8

Average low tide

-1.37mUzura Brg.
Kinen Brg.
Maizuru Brg.

1 1st

Mukaida Brg.
JR Chuo Line Huzimi Brg.
Shinonome Brg. Oi Brg.

Horagai Brg.
1.20m

2 1

Oi Brg.

Horagai Brg.

Average high tide

1 3

Utsugi Brg.

①By observation point
2
1
0
-1
-2
-3

1 2

1

2

JR Chuo Line

Water depth(T.P.m)

We found out that it is involved by organic pollution around Uzura Bridge,
stagnant seawater in bottom, water temperature, tide level.
①By observation point・・・Organic substance easily accumulates on theriverbed in the upstream section centering on Uzura Bridge, and waterpollution is remarkable.
②By month・・・From early spring (March) when the water temperature
日本語元スライドp91
rises, cloudiness and sludge (scum) become apparent, and foam androtten egg odor peak in July.
③By tide・・ It is especially dirty at the time of young tide, long tide andmiddle tide, the level changes larger.

3

3

Mukaida Brg.
Sinonome Brg.
Huzimi Brg.
Tateishi Brg.

One of mechanism of dirtying in Shin-Horikawa River

2

2 2nd

3 rd

Kinen Brg. Maizuru Brg. Horidome Water
Treatment Plant
Uzura Brg.
Uzuki Brg.

Deposition of organic substanceon the riverbed, mainly around the Uzura Bridge.

Waters below the low tide
→Environment where water movement is low

3500

4000

5500

5000
4500
Distance from confluence(m)Bubble rise from

3

②The rise of sludge（Scum）

3

1

2

③Generation of rotten odor
④Occurrence of cloudiness
Reduces water pollution
in winter
・There is little rain and little
organic matter accumulates
on the riverbed.
・The water temperature islow, the decomposition oforganic substances on theriverbed is difficult, and theoxygen in the water is hardto decrease.
→ Accumulation of organic
matter.

White turbidity and sludge (scum)
became apparent from early spring(March)・Many organic substances
accumulated on the river bottom
gradually decomposed from early
spring when the water temperaturerises → Hypoxia

1

3

2

2

2

1

2

・Bubbles and rotten
egg odor peak in July・Accumulation oforganic matter on theriver bottom due torain during the rainyseason・The temperature
becomes high (over
25 ℃)

2

1

6

With / without rainfall
Including out-of-period data
All Shin-Horikawa River data:784(by 26th stage)

Water pollution worst ranking (by month)① the bottom of the river

6000

3

Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec.
Precipitation_Normal value(mm)②By month

Average temperature_normal value(℃)

Wastewater annual average water temperature(℃)

Wastewater annual Max. water temperature(℃)

Wastewater annual Min. water temperature(℃)

35

350

30

28℃ Max. Horidome W.T.P.

25

22℃ Average Horidome W.T.P.

26.4

27.8

300
24.1

22.7

18.9

20

250
18.1

12.2
8.7

10
4.5

5
48.4
0

200

16℃ Min. Horidome W.T.P.

14.4
15

Jan.

5.2

234.4

201.0 203.6

121.8 124.8

156.5

128.3

126.3

79.7

65.6
Feb.

Mar.

Apr.

May

June

July

Aug.

150
7.0

Sept.

Oct.

Nov.

100

Precipitation(mm)(6) Mechanism of dirtying from the worst rating ofclearness in Shin-Horikawa River

With / without rainfall
out-of-period data
Water pollution worst ranking (by observation point) Including
All Shin-Horikawa River data:784

Average temperature(℃)

日本語元スライドp88

50
45.0
Dec.

0

Data） Wastewater from Horidome Water Treatment Plant _Water Temperature：Sewer statistics Japan Sewage Works Association Average 2007fiscal year～2015fiscal year

7

Point of mechanism of dirtying in Shin-Horikawa River③By tide16

Water pollution worst ranking (by observation point)
Bubble rise from

③Generation of rotten odor

The water in the
upstream section
around Uzura
Bridge is dirty④Occurrence of cloudiness

3 1① the bottom of the river②The rise of sludge（Scum）

Mukaida Brg.
Sinonome Brg.
Huzimi Brg.

Water depth(T.P.m)

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

Average high tide

1.20m

Average low tide

-1.37m1

1 3
2 1

Uzura Brg.

Utsugi Brg.

Kinen Brg.
Maizuru Brg.

Oi Brg.

Horagai Brg.

Horagai Brg.

1 2

3

1 1st
Tateishi Brg.

3

2

JR Chuo Line

Tateishi Brg.

2

With / without rainfall
Including out-of-period data
All Shin-Horikawa River data:784(by 26th stage)

Mukaida Brg.
JR Chuo Line Huzimi Brg.
Shinonome Brg. Oi Brg.

2 2nd

3 rd

Kinen Brg. Maizuru Brg. Horidome Water
Treatment Plant
Uzura Brg.
Uzuki Brg.

Deposition of organic substanceon the riverbed, mainly around the Uzura Bridge.

Waters below the low tide
→Environment where water movement is low

3500

4000

5000
4500
Distance from confluence(m)

5500

6000

17

With / without rainfall
Including out-of-period data
All Shin-Horikawa River data:784(by 26th stage)

Water pollution worst ranking (by month)
Bubble rise from
① the bottom of the river

3②The rise of sludge（Scum）

3

1

2

③Generation of rotten odor
④Occurrence of cloudiness
Reduces water pollution
in winter2

1

3

Precipitation_Normal value(mm)Average temperature_normal value(℃)

Wastewater annual average water temperature(℃)

Wastewater annual Max. water temperature(℃)

Wastewater annual Min. water temperature(℃)

35

350

30
25

28℃ Max. Horidome W.T.P.

26.4

27.8
24.1

22.7

22℃ Average Horidome W.T.P.

300

18.9

20

250
18.1

12.2

15
8.7

10
4.5

5.2

48.4

65.6

5
0

200

16℃ Min. Horidome W.T.P.

14.4

Jan.

Feb.

234.4

201.0 203.6

121.8 124.8

156.5

7.0
128.3

126.3

79.7
Mar.

Apr.

May

June

July

Aug.

150

Sept.

Oct.

Nov.

Data） Wastewater from Horidome Water Treatment Plant _Water Temperature：Sewer statistics Japan Sewage Works Association Average 2007fiscal year～2015fiscal year

100

Precipitation(mm)White turbidity and sludge (scum)
became apparent from early spring(March)・Many organic substances
accumulated on the river bottom
gradually decomposed from early
spring when the water temperaturerises → Hypoxia

22Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec.

Average temperature(℃)

・There is little rain and little
organic matter accumulates
on the riverbed.
・The water temperature islow, the decomposition oforganic substances on theriverbed is difficult, and theoxygen in the water is hardto decrease.
→ Accumulation of organic
matter.

1

3
2

・Bubbles and rotten
egg odor peak in July・Accumulation oforganic matter on theriver bottom due torain during the rainyseason・The temperature
becomes high (over
25 ℃)

2

1

50
45.0
Dec.

0

18

Worst rating of clearness（by tide）①Bubble from bottom

It is especially dirty at middle tide, thelevel changes larger in the day.

the altitude ②Floating of sludge
above 0m ③Rotten egg

1
1④Cloudiness①Bubble from bottom
the altitude ②Floating of sludge
below 0m ③Rotten egg

3

2

2

2

④Cloudinessneap tide
Tidal level falls little=Difference oftidal level is little.

Sulfide, because of dirty is made up on bottom atneap tide. At middle tide, the level starts to fall,sulfide is release into water at the altitude below
0m, water pressure falls.

the altitude 0m
1
3

1

2

3

3

3

middle tide

spring tide

July in 20190m

tidal level

Effects at the altitude
above or below 0m
rerates to mixing waterand changing waterpressure by tide.

including rainfall andoff period data
All data(Shin-Horikawa):784(until 26th stage)

Tidal level changes larger in the day.

neap tide

middle tide

spring tide19

(6)Shin-Horikawa River got better after dredging sludge
We found 'color', 'smell' and 'environment for lives' were improved after dredging sludge through the upstream of Shin-Horiwa
The group of Flathead mullets
River.

① 'clean'-'ordinary' got up 20% more.
② 'milky‘ and 'gray' got down 20% less.
③ ‘not smell’ and 'slightly smell' got up 20% more.
④ The group of fish were witnessed in the upstreamof Shin-Horikawa River.

(7)The color of the water and its feature ofShin-Horikawa River are checked.
■Comparison before and after sludge dredging
Based on a picture of the fixed-point observationof ECO DO-CO Cheering Groups(Shin-Horikawa
River: Mukkaida Bridge),it was compared before
and After sludge dredging conducted in an upperclass area on Shin-Horikawa river.
As the result, it was confirmed that the color of
the cloudy system decreases by dreading ofsludge.

We are thinking decrease with thecolor of cloudy system means that asulfide in the water decreased.
Organic matter decreases by sludge
removal in a riverbed and using in
simplicity treatment advance facilities
in Horidome water treatment
center(control of combined sewer
overflow),and the oxygen conditionlessness in a water area may be
improved.

20

(8) Is it true that the water gets dirty when it rains？
We used Horikawa river ・ Between Asahi Brdg. and Matsushige Brdg. （7stage～26stage：number of surveys 1171）,
Shin-Horikawa River（All data for all sections： number of surveys 784） to organize and compare “without rain” and “with rain”
As a result, it was found that when it rained, “the impression of water clearness” and transparency worsened in both Horikawa
river and Shin-Horikawa river, and the smell and cloudiness worsened in Shinhorikawa river.
when it rains the water gets dirty■Impression of Water Clearness and Transparency… Both Horikawa river and Shin-Horikawa river worsened■Smell ・ white cloudy … Shin-Horikawa river worsened

Division

Horikawa
river

Dirtying of water are more noticeable Shin-Horikawa riverthan Horikawa river

Impression of
Water Clearness Transparency
ratio of "dirty toslightly dirty"

acceptable value
for citizens
over 70cm

Without rain

73%

68cm

With rain80%
worsened

50cm
worsened

74%

72cm

90%
worsened

43cm
worsened

Related to the mechanism of dirtying on the Shin-Horikawa river

Without rain

Since it is difficult for water to be replaced, it is easy to become anenvironment where sulfides are generated and dirtying are likely to last
for a long time

ShinHorikawa
river With rain

Without rain： No rain on the day and the previous day
With rain ： rain on the day and the previous day(9)The 11th Horikawa-River simultaneous survey

4-Why?

(Changes in Horikawa-River according to
1.Between Miyano Watashi and Asahi
Bridge(Operation segment)
periodical operation of vessel service)
Rolling up sludge and bubble from theIf frequency of operation increases, water andbottom of the river.・・Why？
sludge in Horikawa-River are periodically agitated,
2. Between Koshio Bridge and Nishiki Bridge,
and oxygen is continuously supplied to the river
Near Atsuta Memorial Bridge.
Light color(⑧light gray yellow green)andbottom. So, we think that river bottom environment
turbidity were seen. ・・Why？
improve, reduce “bubbles, odors and cloudiness"
3. Habashita-Bridge (downstream)and impression of water quality is improved.
・ We confirmed soil and sand disturbance at theIn the previous simultaneous survey, temporary
waterside after passing the vessel.
sludge hoisting and bubbles were confirmed at the ・ It did not turn black at the edge of water-side(visual inspection: no sludge at the edge of waterstart of vessel operation, but in this survey, sludge side)・・Why？
hoisting and bubbles from the river bottom were
4. Between Miyano Watari and Asahi Bridge (operation
not confirmed after passing the vessel.
section)Same as 9th and 10th Horikawa－River simultaneous
As a result of our study for "4-why" which was
surveysobtained in this simultaneous survey, we thought
・ Bubble occurred on the wake・ We confirmed that the it takes long times tothat the river bottom environment was indisappear the bubbles・ ・ Why?
transitional situation when it was improving.

Color

Smell

ＣＯＤ

11mg/Lratio of “badsmell～smell”

ratio of “whitecloudy”

ratio of“sludge”

21%

25%

21%

11mg/L

23%

25%

25%

No difference

No noticeable
difference

No difference

No noticeable
difference

16mg/L

37%

34%

16%

16mg/LNo difference

54%
52%
worsened worsened

7%-

Expected effective for cleaning andmaintaining around water area
If vessel operate periodically, sediments of waterarea and riverbed are regularly agitated.

Periodically,
・ Oxygen is supplied to the water area
・ Sediment (mud etc.) on the river bottom is reduced
・ Hydrogen sulfide, etc... in the deposit is released regularly

Direct improvement measures
・ Removal of sludge (at the time of revetment maintenance)
・ Improvement of combined sewer system (storage pipe), etc.

＋
If vessel operate periodically,
・ Re-deposition of bottom mud and suppression of sludge
formation
・ Improve natural purification capacity of Horikawa-Riveris expected

Impression of water pollution is improved

21

(Summary of the survey)
１. Rolling up sludge and bubble from the bottom of the river.
1.Between Miyano Watashi and Asahi
Bridge(Operation segment)
Rolling up sludge and bubble from thebottom of the river.

Why？
Part.1
Effect of ship operation
By stirring in water area and supplying oxygen,
Reduced sludge formation and redeposition.
Before operation

Temporary strring
Transitional
State

Regular strring
Body of water
stirring

bubblebottomsedimentbottomsedimentbottomsediment

Part.3Rain is less than May and the temperature(water temperature)is lower.
There is little organic substance that flows into the riverwith rain, and decomposition is slow.
For this reason, the water area accumulated on theriverbed without sludge formation.
(floating mud is accumulated)
・The tide level at daytime doesn’t drop below inspring.
The tide level is lower at night than at daytime, and thewater depth doesn’t easily become shallow during
tyrants.
For this reason, it’s difficult to watch rolling up sludge
and large amount of bubbles by stirring.

Part.2
Effect of improvement of combined sewer system.
Started operation in 2010.
・Hoｒikawa Ugan Rain-water Reservior for pollution control.
(storage pipe)
・Advanced treatment at Meijo water treatment center.
Due to the decrease of organic substance. Flowing into the river,Reduced sludge formation and redeposition.
The condition of riverbed gradually improved.

22

２. About water color and turbidity

About the situation of color and turbidity immediately after passing ships.

Between Koshio Bridge and Nishiki Bridge,
Near Atsuta Memorial Bridge.
Light color(⑧light gray yellow green)andturbidity were seen.

Part.411th Horikawa simultaneous survey
November 2019Why？

The bottom water of Horikawa river and theenvironment of the riverbed transitional
state of improvement.
Hoisting of sludge by ship operation wasn’t
confirmed, but bottom water and riverbed
sulphides and sludge that existed in it is thoughtthat it was done.

■Between Koshio Bridge and Nishiki Bridge
With the stirring of water and sludge and the supplyof oxygen by the operation of ships, I think that the
Tide level: the tide level of the port of Nagoya at the latest hour of the survey time.
following factors caused light colored water andturbidity.
I think that this is a transitional situation in which
the environment of the bottom water and river
The water is stirred andNovember 9 2019the muddy water appears to float up
bottom is improving.
7:50（Cause）
Earth Club Research TeamIt was reported sulfur colloid or①Sulfide in water changes sulfur colloid
bottom layer water containing(blue turbidity)
sulfides mixed with surface water②Black sludge reduced, but there was grayby stirring water generated at the
dusty mud and it rolled up.

■Atsuta Memorial Bridge

abutment of Goryo Bridge.

By the supply of oxygen by stirring by theoperation of ships. The sulfide in the bottom waterchanged to a sulfur colloid. (blue turbidity)
It’s considered that It because a factor of lightcolor water and turbidity.

Photo:
Earth Club Research Team23

3. Disturbance of soil and sand at the water edge

4. About bubbles on the wake

■Habashita Bridge (Downstream)・ We confirmed soil and sand disturbance at wateredge after passing of vessel
・ It did not turn black at edge
(Visual Inspection: No-sludge at water edge)■Between Miyano Watashi and Asahi-Bridge (vessel
operation section)
Same as the 9th and 10th Horikawa-River
simultaneous survey (24th and 25th stage)
・ Bubble on the wake is confirmed
・ It takes long times to disappear the bubbles

Part５

Why？

Environment of sand cover section(implemented in 2017) is kept.
We think that continuous disturbance at water edge
due to vessel operation has the effect ofmaintaining good environment at water edge. And
also it create and maintain a diverse ecosystem
and improve natural purification function ofHorikawa-River.

Part６

Why？

(Assumed factors)Quote: The 24th Survey team meeting p.116① About surfactant- Surfactant from detergent contained in the water source ofHorikawa-River causes bubbles.
② About mucus of plankton etc..
If plankton or seaweed grows, these mucus causes bubbles.

Continuous disturbance at wateredge due to vessel operation(Visual Inspection: No-sludge
at water edge)

Koshio-Bridge (upstream)Dec.21 2017

Habashita-Bridge (downstream)
Apr.19 2018

Habashita-Bridge (downstream)
Nov.8 201924

Expected effective for cleaning and maintaining around water area
Temporary vessel operation
If vessel operate periodically,
sediments of water area and riverbed are regularly agitated.

In this simultaneous survey,
transitional situation of
improvement of bottom waterand river bottom wereconfirmed through vessel
operation.

Periodically,
・ Oxygen is supplied to the water area
・ Sediment (mud etc.) on the river bottom is reduced
・ Hydrogen sulfide, etc... in the deposit is released regularly

Direct improvement measures
・ Removal of sludge (at the time of revetment maintenance)
・ Improvement of combined sewer system (storage pipe), etc.

＋
If vessel operate periodically,
・ Re-deposition of bottom mud and suppression of sludge formation
・ Improve natural purification capacity of Horikawa-River is expected

Impression of water pollution is improved25

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.

26