diagram of probable flood runoff in the bolgoda basin (10

Runoff at Max. Water Level (m3/sec)

Max. Water Level (m)

Flow Direction at Max. Water Level

BP-4 BP-3Channel (Runoff Confined)

Channel (Present Condition)

BP-6

BP-7BP-13

BP-9

BP-15

BP-18 BP-16BP-29

BP-30

BP-28

BP-23

BP-25

130

20

(1.46)

15

50

(1.45)

101520

35(0.64)

30

15

10(0.72)

BP-14

BP-17BP-19

20

70

5

(0.66)

(0.59)

(0.67)

5

10

5

BP-8

BP-10

(0.77)

(1.12)

5

BP-26BP-27

JAPAN INTERNATIONAL COOPERATION AGENCY

The Study on Storm Water Drainage Planfor the Colombo Metropolitan Region

in the Democratic Socialist Republic of Sri Lanka

25

(1.12)

10

130

20

25

25

10

(0.63)

BP-5

30

BP-21 BP-20BP-24(0.68)(0.66)

Bolgoda Canal

Weras Ganga

Maha Oya

South Bolgoda Lake

Alut ElaKeppu Ela

Panape Ela

Kalu Ganga

Figure 8.2.4Diagram of Probable Flood Runoff in the Bolgoda Basin (10-year Return Period)

Talpitiya Ela

Panadura Ganga

Bolgoda Ganga

Legend

North Bolgoda Lake

A8 - F113






BP-6

BP-7BP-13

BP-9

BP-15

BP-18 BP-16BP-29

BP-30

BP-28

BP-23

BP-25

40

BP-21 BP-20BP-24(0.76)(0.73)

30

(1.29)

10

145

25

30

30

10

(0.69)

BP-5

5

BP-26BP-27




(0.76)

5

10

10

BP-8

BP-10

(0.89)

(1.29)

80

5

(0.72)

(0.64)

40(0.71)

35

20

10(0.82)

BP-14

BP-17BP-19

25

145

20

(1.68)

20

65

(1.65)

101520

Bolgoda Canal

Weras Ganga

Maha Oya

South Bolgoda Lake

Alut ElaKeppu Ela

Panape Ela

Kalu Ganga


Talpitiya Ela

Panadura Ganga

Bolgoda Ganga

Legend

North Bolgoda Lake

A8 - F114






BP-6

BP-7BP-13

BP-9

BP-15

BP-18 BP-16BP-29

BP-30

BP-28

BP-23

BP-25

155

20

(1.83)

25

75

(1.80)

151525

40(0.76)

40

25

15(0.90)

BP-14

BP-17BP-19

30

90

5

(0.78)

(0.69)

(0.84)

5

10

10

BP-8

BP-10

(0.99)

(1.43)

5

BP-26BP-27




40

(1.43)

15

155

30

35

40

10

(0.75)

BP-5

55

BP-21 BP-20BP-24(0.82)(0.79)

Bolgoda Canal

Weras Ganga

Maha Oya

South Bolgoda Lake

Alut ElaKeppu Ela

Panape Ela

Kalu Ganga


Talpitiya Ela

Panadura Ganga

Bolgoda Ganga

Legend

North Bolgoda Lake

A8 - F115




Figure 8.2.7Runoff Hydrograph in Panadura Ganga at Sea Outfall

Panadura Ganga at Sea Outfall

0

50

100

150

200

250

300

0 6 12 18 24 30 36 42 48 54 60Time (Hours)

Run

off (

m3 /s

ec)

Basic FloodProbable Flood

10-year Return Period

175 m3/secVolume 4.90 MCM

130 m3/sec


0

50

100

150

200

250

300

0 6 12 18 24 30 36 42 48 54 60

Time (Hours)

Run

off (

m3 /s

ec)


25-year Return Period

210 m3/sec

Volume 7.17 MCM

145 m3/sec


0

50

100

150

200

250

300

0 6 12 18 24 30 36 42 48 54 60

Time (Hours)

Run

off (

m3 /s

ec)


50-year Return Period245 m3/sec

Volume 8.72 MCM

155 m3/sec

A8 - F116




Legend

Retention Area

Expansion Area for Ratmalana Airport

Identified Location of Outstanding Land Filling

Development Plan incorporatedwith Future Land Use Projection

Location of Previous Planwith Land Filling

Garbage Dumping SitePolice AcademyCompound

N

0 400 800 1200 1600 2000 m

Scale

Location of Envisaged Development Vicinity of Retention Area

Belanwilla-Attidiya MarshRetention Area108 ha

Retention Areas in Highly Urbanized Area(Nugegoda-Rattanapitiya Sub-basin)Total 36 ha

Weras Ganga SwampRetention Area65 ha

Retention Area in Highly Urbanized Area(Ratmalana-Moratuwa Sub-basin)23 ha Retention Area in

Highly Urbanized Area(Thumbowila Sub-basin)8 ha

Maha Ela Marsh and LowlandRetention Area132 ha

Boralesgamuwa Theme Park Project Area

Figure 8.3.3Retention Areas under Future Land Use Projection

A8 - F119

diagram of probable flood runoff in the bolgoda basin (10

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