REPUBLIC OF THE PHILIPPINESDEPARTMENT OF PUBLIC WORKS AND HIGHWAYS

Manila

FLOOD MITIGATION PLAN

FOR

METRO MANILA AND SUBURBAN AREAS

(PASIG-MARIKINA-LAGUNA LAKE BASIN)

– FROM EXPERIENCES OF FLOOD BY TYPHOON ONDOY –

January 2010

8am Sep. 268 pm Sep. 26

TYPHOON ONDOY

Flood Condition byTyphoon Ondoy inPasig-MarikinaRiver Area

FLOOD, FLOOD, FLOOD - Pasig-Marikina River

Angono, Rizal

Tanay, Rizal

Cainta, Rizal

Cainta, Rizal

FLOOD, FLOOD, FLOOD - Pasig-Marikina River

Marikina City

1450

m3/s

Flood Flow Distribution due to Typhoon Ondoy

500

4,150

3,000

3,500

650

1,900 1,100

800

500

FLOOD DISCHARGE IN TYPHOON ONDOYUnit: m3/s

TaytayTaguig

Cainta

Pasig

1,500

2,400

4001,200 500

Flow

Capacity

Marikina River water level rapidly rose 4.6 m in 6hours at Marikina Bridge on September 26, 2009 dueto approximately 400mm rainfall in 6 hours.

Also, Laguna Lake water level rose from Elev. 12.9mat 9:00 AM on September 26, 2009 to Elev. 13.84 min 24 hours.

5,000

4,150

3,500

3,000

500

1,200

Inflow: 7,000m3/s

Sierra Madre Mountains

Flood in Pasig-Marikina-Laguna Lake Basin by Typhoon Ondoy (Unit: m3/s)

Marikina Dam

Laguna Lakeshore Ring

Road Dike

Inflow: 7,000m3/s

5,000

Sierra Madre Mountains

L A G U N A L A K E

Flood in Pasig-Marikina-Laguna Lake Basin With Marikina Dam and Laguna Lakeshore Ring Road Dike(Unit: m3/s)

PROPOSED FLOOD MITIGATION PLAN

Pasig-Marikina River Basin

• Construction of the Marikina Dam for flood controlpurpose

• Land Use Zoning and Upper Marikina FloodplainManagement

• Construction of Stages II and III of the PMRCIP

Laguna Lakeshore Ring Road Dike

• Construction of the lakeshore ring road dikeincluding pumping stations, floodgates and drainagefacilities

MARIKINA DAM - at Montalban Gorge

Marikina Dam

• Height : 70 m (No control gate)• Reservoir Area : 200 ha.• Reservoir Capacity : 100 million m3

• Cost : P 4.00 Billion (Approx.)• Construction Period : 4 years• EIRR : 26.4% (incl. cost & benefits of river improvements of Pasig-

Marikina, and construction of MCGS)

Montalban Fault Line (300m away from dam site) has made no deviation of strata at damfoundation rock. Further, Safety of dam against earthquake could be assured with theseismic design, which will bring a minimal increase in construction cost.

Concrete Gravity Type Dam (Yokoyama Dam in Japan)

Dam Body Dam and Reservoir

MARIKINA DAM

Typical Cross-Section of Marikina Dam

Yokoyama Dam, Japan (Same type of Marikina Dam)

PASIG-MARIKINA RIVER CHANNEL IMPROVEMENT PROJECT (STAGE II & III)

Phase III: Construction of Stage II, (for funding)

- Construction of MCGS & Improvement of

Lower Marikina River

Phase IV: Construction of Stage III, (for funding)

- Improvement of Upper Marikina River (up to

Marikina Bridge only)

Laguna Lake Area = 900 km2Laguna Lake Shoreland Area = 18,000 ha(Below EL. 12.5m)

Inundation Area by Typhoon Ondoy = 24,000 haLake Water Level = EL. 13.84 m

LAKESHORE RING ROAD DIKE

● Total Length : 99.10 km

● Pumping Station : 10 sites● Dike Road : 4 lanes● Bridges : 11 bridges

(1.1 km in total)● Const. Cost. : P 23.58 B● Const. Period : 10 years● EIRR : 17.6 % (incl.

the benefits from the use

of lakeside dike road)

Total volume to be stored in Laguna Lake by the Road Dike is 1.17 B m3 (El 12.5m-13.8m)

Typical Cross-Section of Dike

Laguna Lake Water Level – Inundation Area

FLOOD YEARS AND FLOODED AREAS

FLOODED YEARS

YEAR ELEVATION (meters) @ LAGUNA LAKE

1919 14.62

1943 14.35

1972 14.03

2009 13.84

EVALUATION OF FLOODED AREAS OF LAND SURROUNDING LAGUNA DE BAY (Based

on the 1972 Flood)

ELEVATION (meter) INUNDATED/FLOODED AREAS (Hectares)

10.50 to 12.00 11,025 has

12.00 to 13.00 7,240 has

13.00 to 14.03 5,710 has

14.60 2,631 has

TOTAL (10.50 to 14.60) 26,606 has

FLOODED YEARS

YEAR ELEVATION (meters) @ LAGUNA LAKE

1919 14.62

1943 14.35

1972 14.03

2009 13.84

EVALUATION OF FLOODED AREAS OF LAND SURROUNDING LAGUNA DE BAY (Based

on the 1972 Flood)

ELEVATION (meter) INUNDATED/FLOODED AREAS (Hectares)

10.50 to 12.00 11,025 has

12.00 to 13.00 7,240 has

13.00 to 14.03 5,710 has

14.60 2,631 has

TOTAL (10.50 to 14.60) 26,606 has

BENEFITS OF THE PROPOSED LAGUNA LAKESHORE RING ROAD

DIKEDIRECT BENEFITS

• FLOOD CONTROL - Dike with Pumping Station will mitigate the flooding problems in thetwenty-five (25) towns around the lakeshore area, totaling 25,000 ha around the lakeshore area..

• TRANSPORTATION/DISTRIBUTION - Dike will also serve as an alternate road to helpdecongest highways leading to Metro Manila as well as the corridor connecting cities/municipalities around Laguna Lake.

INDIRECT BENEFITS

• POLLUTION CONTROL - Drainage channel of Lakeshore dike will be used as an interceptor forwastewater collection as well as a catchment for siltation. With the construction/improvement ofwastewater treatment facilities, the pollution of Lake water level will be controlled, and siltation inthe lake could be limited.

• TOURISM AND RECREATION – Ring road dike will facilitate an easy access to tourist spotsand promote more tourism development.

• LAND RECLAMATION - No chronic inundation in the lakeshore area will encourage moreeconomic development. (Land value of area close to Laguna Lakeshore became triple after thecompletion of the West of Mangahan Floodway Area Lakeshore Dike).

ENHANCING REGIONAL DEVELOPMENT AND ENVIRONMENTAL CONSERVATION

AND

Effects of PARAŇAQUE SPILLWAY

● Total Length : 8.3 km, partly arched tunnel (200 m) under the expressway

● Related Structures : Control Gate● Bridge : 2 nos.● Total Cost : P 17.60 Billion (incl. ROW) ● Construction Period : 7 years● The flood prevention benefits of the Spillway are measured by the reduction in

the flood damages by shortening the flooding duration, while the flooding in thelakeshore area will not becontrolled by the Spillway.

Paranaque River

PARANAQUE SPILLWAY

Profile of Paranaque Spillway

Effects of PARAŇAQUE SPILLWAY– Lowering Water Level of Laguna Lake -

Flow discharges from Laguna Lake are estimated at the maximum.

EFFECTIVENESS OF PARANAQUE SPILLWAY- Flow capacity: 350m3/s- Average flow: 50 to 100m3/s

OTHER OUTLETS (Max. Flow)- Napindan Channel: 550m3/s- Mangahan Floodway: 150m3/s

DURATION TO LOWER THE WATER LEVEL from 13.5m to 10.5m:

Average Flow Discharge = 1/3 of Max. With Paranaque Spillway:108 daysWithout Paranaque Spillway:130 days

CONCLUSION

1. For the Pasig-Marikina River Basin, the floodcontrol plan of 1990 is concluded to be viablewith the recent experience of Typhoon Ondoy.The implementation of Marikina Dam shouldbe given priority.

2. Laguna Lakeshore Ring Road Dike is themost feasible structural intervention tomitigate the flooding problem around theLaguna Lake. (Since it has less social andenvironmental impacts)

RECOMMENDATIONS

1. The Study of both Marikina Dam and LagunaLakeshore Ring Road Dike shall be carried outas soon as possible in order to mitigate theflood damages in the Pasig-Marikina-LagunaLake Area.

2. Proper Information, Education Campaign (IEC)should be undertaken during the updating ofFeasibility Study for both projects.

End of Presentation Thank You!!!!!

Additional Slides for Reference

FLOOD MITIGATION PLAN FOR PASIG-MARIKINA- LAGUNA LAKE BASIN

OBJECTIVE

• To mitigate flood damages in the PASIG-MARIKINA-LAGUNALAKE BASIN (Metro Manila and Suburban Areas) against theFlood brought by Typhoon Ondoy

SCOPES

• River Flood is mitigated against the flood of a 100-year returnperiod.

• Drainage System is improved against the storm rain of a 10-year return period.

• Laguna Lakeshore Area is protected against the lake waterlevel of a 40-year return.

FLOODING IN UPPER MARIKINA FLOODPLAIN

Floodplain has been further developed in 2007 Floodplain was developed in 2001

Flooding Area by Typhoon Ondoy

Administration:Establishing policy guidelines to define the river area and creating its responsible administrativebody/organization in the national government to properly control the land use plan of flood plain area.Local Ordinance:Ordinances should be issued for the jurisdictional areas of concerned LGUs.

Pasig-Marikina River Basin• Marikina Dam Construction and Upper Marikina Floodplain Management

100-Year Flood Discharges without Marikina Dam & Floodplain Management

100-Year Flood Discharges with Marikina Dam & Floodplain Management

Flood Area byTyphoon Ondoyalong LagunaLakeshore atWater Level ofEl.13.84m=24,000ha.

Proposed Implementation Schedule

Typhoon Ondoy (454 mm/24hrs.)

Hurricane Katrina (414 mm/24hrs.)

Typhoon Frank (354 mm/24hrs.)

COMPARISON OF RAINFALL INTENSITY

Maximum Flood Level

354 mm

414 mm

454 mm

60 mm increase

40 mm increase