Muthurajawela BP-6 25 Conservation Zone

Outer Circular Highway

Muthurajawela BP-7 40 BP-1 50 Buffer Zone Kalu Oya

115 95 75 (4.83) (5.43) (6.01) BP-5 BP-4 BP-3

25 BP-2

Kandy Old Canal Road 160 BP-9 (4.40)

20

BP-10 Isolation Bund (Crossing Culvert) BP-145 180 BP-11

BP-13 185 (3.81)

BP-15180 10 BP-12 (3.29) Legend

75 Runoff at Max. Water Level (m3/sec) (6.01) Max. Water Level (m) Flow Direction at Max. Water Level

Channel (Runoff Confined) BP-17100 85 BP-16

Channel (Present Condition)

Kelani Ganga

Colombo Negombo Road Expressway The Study on Storm Water Drainage Plan Figure 4.16 for the Metropolitan Region Diagram of Basic Flood Runoff Distribution in the Democratic Socialist Republic of JAPAN INTERNATIONAL COOPERATION AGENCY in the Kalu Oya Basin (50-year Return

F - 56 Muthurajawela BP-6 10 Conservation Zone

Outer Circular Highway

Muthurajawela BP-7 10 BP-1 25 Buffer Zone Kalu Oya

30 30 30 (2.14) (2.66) (3.45) BP-5 BP-4 BP-3

5 BP-2

Kandy Old Negombo Canal Road 30 BP-9 (1.97)

10

BP-10 Isolation Bund (Crossing Culvert) BP-145 35 BP-11

BP-13 35 (1.83)

BP-1530 5 BP-12 (1.74) Legend

30 Runoff at Max. Water Level (m3/sec) (3.45) Max. Water Level (m) Flow Direction at Max. Water Level

Channel (Runoff Confined) BP-1730 5 BP-16

Channel (Present Condition)

Kelani Ganga

Colombo Negombo Katunayake Road Expressway The Study on Storm Water Drainage Plan Figure 4.17 for the Colombo Metropolitan Region Diagram of Probable Flood Runoff Distribution in in the Democratic Socialist Republic of Sri Lanka the Kalu Oya Basin (50-year Return Period) JAPAN INTERNATIONAL COOPERATION AGENCY

F - 57 Kalu Oya at Negombo Road

200 10-year Return Period

Basic Flood 150 Probable Flood 3

/sec) 110 m /sec 3 100

Runoff (m Volume 2.52 MCM 50 20 m3/sec

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

Kalu Oya at Negombo Road

200 25-year Return Period

150 m3/sec Basic Flood 150 Probable Flood /sec) 3 100 Volume 3.18 MCM Runoff (m 50 30 m3/sec

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

Kalu Oya at Negombo Road

200 185 m3/sec 50-year Return Period

Basic Flood 150 Probable Flood /sec) 3 100 Volume 3.65 MCM Runoff (m 50 35 m3/sec

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

The Study on Storm Water Drainage Plan Figure 4.18 for the Colombo Metropolitan Region Runoff Hydrograph in Kalu Oya at in the Democratic Socialist Republic of Sri Lanka Negombo Road JAPAN INTERNATIONAL COOPERATION AGENCY

F - 58 0

Katunayake

Mapalam Oya Negombo Lagoon Colombo-Katunayake Expressway

Conservation Zone of Muthurajawela Marsh (Retention Area) Attanagalu Oya

Ja Ela Old Negombo Canal Improvement Uruwal Oya

Diversion Channel to Muthurajawlera Marsh

Storm Water Retention Area

Buffer Zone

Old Negombo Canal

Hamilton Canal P Kalu Oya Construction Storm Water Retention Facilities in Urban Area ( )

Outer Circular Wattala Pumping Station Highway and Gate Kelani Ganga

Scale Colombo Kalu Oya Channel Improvement

The Study on Storm Water Drainage Plan Figure 4.19 for the Colombo Metropolitan Region in the Democratic Socialist Republic of Sri Lanka Conceivable Structural Measures for Kalu Oya Basin JAPAN INTERNATIONAL COOPERATION AGENCY

F - 59 Kalu Oya at Inland Retention Area (Return Period 50-year) 2.60

2.50

2.40

2.30

2.20

2.10

K15 2.00 K0

K13 1.90 K14

1.80 Allowable Water Level + 1.67 m K11 1.70 Average Water Level in Retention Area (m)

K16 1.60

K18 1.50

1.40

K19 1.30

1.20 0 50 100 150 200 250 300 350 400 450 500 Retention Area (ha)

The Study on Storm Water Drainage Plan Figure 4.20 for the Colombo Metropolitan Region Relationship between Retention Area and in the Democratic Socialist Republic of Sri Lanka Water Level in the Kalu Oya Basin JAPAN INTERNATIONAL COOPERATION AGENCY

F - 60 Outer Circular Highway 0 Upper Retention Area (89 ha)

ga an G i n a el K

a y

a O

l

E alu

a K

J

Ragama Bridge KO-5 L=50m B=10m Lower Retention Area (360 ha)

L = C 1 h B ,2 an = 0 n 2 0 e 5m m l Im p t L r emen = o prov 3 v al Im ,8 em Can 0 mbo 0 en ego 40m n, B t Old N m, B= ,500 = L= 4 Bridge KO-4 5 L=50m B=20m 0m

Ja Ela Bridge KO-8 L=40m B=10m Wattala ke aya Bridge KO-3 tun Bridge KO-7 -Ka L=50m B=10m bo y L=40m B=10m Bridge KO-2 Legend olom wa Bridge KO-6 C ress l L=50m B=10m Exp ana L=40m B=10m bo C River/Canal gom d Ne Bufferzone Bridge KO-1 Channel Improvement Ol L=45m B=10m River Basin Boundary Conservation Zone of Wattala Gate Town Muthurajawela Marsh Storm Water (Retention Area) Retention Area Conservation Zone of Marsh Conservation Zone of Canal Proposed Bridge Marsh amilton Muthurajawela H Gate (Retention Area) Expressway/Highway

Scale The Study on Storm Water Drainage Plan Figure 4.21 0 1 2 3 km for the Colombo Metropolitan Region Proposed Storm Water Drainage Plan in the Democratic Socialist Republic of Sri Lanka for Kalu Oya Basin JAPAN INTERNATIONAL COOPERATION AGENCY

F - 61 Muthurajawela BP-6 10 Conservation Zone Outer Circular Highway

Kalu Oya Muthurajawela BP-7 15 BP-1 25 Buffer Zone

30 30 30 (1.79) (2.54) (3.44) BP-5 BP-4 BP-3

5 BP-2

Kandy Old Negombo Canal Road 40 BP-9 (1.60)

10

BP-10 Isolation Bund (Crossing Culvert) BP-1435 50 BP-11

BP-13 50 (1.52)

BP-1525 0 BP-12 (1.48) Legend

30 Runoff at Max. Water Level (m3/sec) (3.44) Max. Water Level (m) Flow Direction at Max. Water Level

Channel to be Improved BP-1725 0 BP-16

Retention Area

Kelani Ganga

Negombo Colombo Road Katunayake Expressway The Study on Storm Water Drainage Plan Figure 4.22 for the Colombo Metropolitan Region Diagram of Probable Flood Runoff in the in the Democratic Socialist Republic of Sri Lanka JAPAN INTERNATIONAL COOPERATION AGENCY Kalu Oya Basin (50-year Return Period)

F - 62 0

, 0 m m ,20 25 = 1 .T= L O.C W.

t en em ov pr Im l m ne 0 n 5 ha .= C .T ya .C O .O lu a , W K m ed 0 os 0 p ,8 ro 3 P = L

Scale 0 500 m 1 km Note) W.O.C.T. means width of channel top The Study on Storm Water Drainage Plan Figure 4.23 for the Colombo Metropolitan Region General Plan of Proposed Kalu Oya and in the Democratic Socialist Republic of Sri Lanka Old Negombo Canal Improvement JAPAN INTERNATIONAL COOPERATION AGENCY

F - 63