Measures to make Horikawa River
Limpid.
Implementation by Nagoya City.

Feb.15th.2014
Nagoya City Greenification & PublicWorks Bureau River Dep.
River Plannning Div.

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■Reservation of additional water source (FY2013)◆Downstream of Chigonomiya Bridgetransmitted into Horikawa River(０．０１ｍ３/ｓ)

Downstream of
Chigonomiya Bridge
SanageBridge

2■Removal and inflow reduction of pollutants.
◆Garbage Catcher(near Johoku Bridge) from FY2006
pick up the collectedgarbage regularity
for the disposal
Drain the rain waterin case of heavy rain

garbage collection basket

Suspended garbage

catching fence
catch floating garbage by
the fence using tidal river
flow toward up anddownstream

collect the garbage
in the basket

gate

inflow gate

watertreatment centre

SanageBridge

Horikawa

sewagecollect floating garbage when thegate gets open automatically
based on the water level

FY 2010 collected

２．４t

FY 2011 collected
FY 2012 collected

２．３t
１．１t

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BOD

Result of water quality survey
by Greenification & public warks Bureau

6.0
導水前（H18）
Before TRWKR(2006)
During TRWKR(2nd4th6thstage)
導水中（第2,4,6ステージ）
After TRWKR(8th10th12thstage))
導水後（第8,10,12ステージ）th14 Stage
第14ステージ

4.0

4.0

3.6

BOD(mg/L)

3.4

3.2

2.9

2.8
2.1
2.0

紀左ヱ門
橋

Koushin

尾頭橋

Kizaemon

新洲崎橋

Oto

納屋橋

Shinsuzaki

小塩橋

Nayabashi

北清水橋

KoshioKitasihmizu

0.0

港新橋

BOD level was high on 14th stage at all points(without Nayabashi Bridge)

Result of water quality survey
by Greenification & public warks Bureau

DO
10.0

導水前（H18）
導水中（第2,4,6ステージ）

7.5

8.0

導水後（第8,10,12ステージ）

DO(mg/L)

第14ステージ

6.0

5.7

6.0

5.1

4.6

4.3
3.6

4.0

2.0紀左ヱ
門橋

Koushin

尾頭橋

Kizaemon

新洲崎橋

Oto

納屋橋

Shinsuzaki

小塩橋

Nayabashi

北清水橋

KoshioKitasihmizu

0.0

港新橋

DO level was higher on 14th stage than during TRWKR at all points without
Kitashimizu Bridge near Sanage Bridge.

Ｏｕｔｌｉｎｅ ｏｆ Ｓｕｒｖｅｙｓ
・We implemented Several surveys to consider
clarification measures focused on the sludge
appeared on the ebb tide.
(from Tenozaki Bridge to Sujikai Bridge)

6Ｏｕｔｌｉｎｅ ｏｆ Ｓｕｒｖｅｙｓ【items】
・Sludge accumulation→ check the situation by measuring.
・Deterioration of existing revetment→ check the effect of removing sludge
on the existing revetment
・Water quality→ check during the ebb tide at Nayabashi and Koshio Bridge
items items：BOD,COD,SS,T-N,T-P etc.

・Odor
→

focused on the difference between the smell at

the time of Sludge appeared and that of sludge submerged.
Items: Ammonia, H2S, Methyl mercaptan, Trimethylamine

・Experts hearing

7■Interim report（Naka Bridge～Gojo Bridge）○ Survey of Sludge accumulation
Appearance of sludge
３ｍ fromthe edge
Height ofsludge
accumulation

Sludge thickness
average;３０ｃｍSludge on surface
Low watr level

Height ofBed rock

Results

Stones of the lower layer●Sludge layer is about 30cm thick on average(min 4㎝, max 66㎝)
●there are many stones on the lower layer
at the almost all points8

■Interim report（Naka Bridge～Gojo Bridge）○ Survey of deterioration of existing revetment

Measuring of Sheet pile thickness

八幡AⅡ型
Ｌ＝4.5ｍ

Structural Drawing（Ｓ７～８ established）

Results

Becoming hollow at sheet pile damaged●We found the standard of the sheet pile. The sheet pile has not been repaired andembedment depth is shallow.
●We found erosion of an exposed part and deteriorated part.
●As the result of this survey and the stability analysis, we found it hard to remove
sediment on the sheet pile.
●Revetment become more instable when the water level is low.

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■Interim report（Naka Bridge～Gojo Bridge）○ Odor survey
We survey○the accumulating odor when the sludge appeared○the accumulating odor when the sludge is submerged○the odor emitted by the sludge collected
Results●We found H2S when the sludge appeared at the ebb tide.
（that level exceeds regulation level of the offensive odor control low.）●We found coliform group exceeds regulation level of the waterpollution prevention act.
*River is not itself subject of the offensive odor control low and thewater pollution prevention act.

We have an exparts’hearing after these surveys

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■Exparts’hearing
Opinions◎About clarification measures.
・Overlaying sand is one of the suited way.
・It’s better to improve clarification measures as mixing clarification
goods with overlaying sand.
・We had better try to improve Horikawa River bottom sediment with acolumnar improvement.
・We oppose the vegetation for water clarification because its
maintenance require much effort and it remain as an organic matter if
we don’t collect.
・Measure to H2S is important when we take in account an odor or anorganism living.
◎About damming
・It’s impractical to dam because of a flood control, an inflow water andan ebb and flow of the tide.
・ There is a possibility the deteriorated revetment crumbled due toreleasing a water pressure by damming.
・There are some problems of odor or sanitation in public participation.

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