３） Issues in Tsurumi River basin

Flood Concentration Time: 10 hours → 2 hours

Doubled peak discharge and Greatly reduced flood concentration time

　　　　　　　　　　　　　

Flood Concentration Time

Peak Discharge: Doubled

　　　　　　　　　　　　　

1,300m3/ｓ

770m3/ｓ

Comparison by the simulation of the same rainfall

As of 1990(Urbanization ration: 78%）

As of 1958(Urbanization ration: 10%）

Flood discharge

10 155(Hour)0

開発による流出土砂が堆積し、流下能力減少

600,000

400,000

200,000

Sedim

ent D

ischarge

１９６０ １９６５ １９７０ １９７５

The amount of annual Sediment Discharge

From River-mouth to 16km

Height of a river floor rose about 150mm/year.

Accumulation of the discharged sediment due to the development decreased the river channel discharge capacity

３） Issues in Tsurumi River basin

Frequent Flood damageSeptember 1976

　 Kohoku Ward

３） Issues in Tsurumi River basin

３） Issues in Tsurumi River basin

Frequent Flood damageSeptember 1982

　 Tsurumi Ward

Increased damage of the Torrential Rain

Increased rainfall of over 100mm per hour in the urban areas

1994 Shinyokohama

神戸の地下鉄浸水写真Increasing threats of underground complex in the urban areas 1999 Fukuoka city

３） Issues in Tsurumi River basin

Increased anxiety of the Torrential Rain

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

10.0

30日0時 30日12時 31日0時 31日12時 1日0時日時

水位(m)

0

20

40

60

80

100

120

140

160

180

200

30日0時 30日12時 31日0時 31日12時

日時

雨量(㎜)

流域平均雨量

計画高水位

危険水位

警戒水位

指定水位

亀の子橋

Water level

Rainfall

Hourly-max.55mm

More than 5m during

1hour

July 1998 Flood（16km point）

３） Issues in Tsurumi River basin

Basin average rainfall

Design high water level

Bankful water level

Warning water level

Advisory water level

Kamenoko Bridge

Wat

er le

vel(

m)

Rain Precipitation (m

m)

30 0:00 30 12:00 31 0:00 31 12:00 1 0:00

Increased damage of the Torrential Rain and landside water

３） Issues in Tsurumi River basin

Ratio of sewage System installation

(%)

Populationin the basin（Ten thousand）

Changes in population, sewage system installation ratio and river water quality of Tsurumi River basin

Otsuna Bridge environmentalstandard value

Under BOC10mg/ℓ

Ratio of sewage system

installation

Population in the basin

BOD Average of theOtsuna bridge

N‐BOD Measure

Water quality measure for the rainy day

New water quality issue

＝　Endocrine Disrupter

Issues in water quality improvement

３） Issues in Tsurumi River basin

３）Issues in Tsurumi River basin

Bypass by the Sewage System Improvement

concrete block revetment

　（Shutoff of groundwater inflow)

→Decreased water volume in upper reach

Yagami River (Tributary)

Shinpukuji River（Tribunary）

Normal Discharge Issue

Normal Discharge Issue

Abundant water volumein the downstream due to sewer discharge

Flow of water supply etc.

Tokyo Bay

Tama River

Ara RiverEdo River

Tone River

Sagami River

Sakai River

Tsurumi River basin

Water resource for municipal water:98% from other basin

３）Issues in Tsurumi River basin

Decreased rainfall infiltration

Decreased river dischargeDecreased clean water

３）Issues in Tsurumi River basin

Issue in river improvement emphasizing flood control

Inappropriate for utilization in times of earthquake/fire

Revetment-Difficult access to the water-Unsuitable for inhabitation and

growth of creatures

Crowded urban areaSteep revetment

３）Issues in Tsurumi River basin