The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila 4.4 Design Flood Discharge With examining the alternatives of flood management facility plan, optimal design flood discharge allocation and its flood management plan is proposed. Since flood control works for 1/30 years flood have been conducted in Pasig and Lower Marikina River, design flood discharge of these sections shall be set considering the previous works. Design flood water levels will be checked with the design water level of the JICA Study.
4.4.1 Evaluation of Conditions for Pasig-Marikina River Channel Improvement Project (PMRCIP) (1) Design Flood Discharge for PMRCIP PMRCIP can be divided as the following 4 phases. Phase I : Detailed Design Works for Whole Section Phase II : River Improvement Works from River Mouth to Confluence of Napindan Channel Phase III : River Improvement Works from Confluence of Napindan Channel to Diversion of Manggahan Floodway without MCGS Phase IV : River Improvement Works from Diversion of Manggahan Floodway to Marikina Bridge with MCGS
In the detailed design conducted in 2002, the design flood discharge allocation of 1/30 years flood was formulated as shown in Figure 4.29, and river improvement works and construction of MCGS was planned.
Source: Preparatory Study for Pasig-Marikina Channel Improvement Project (Phase III) Figure 4.27 H-Q Curve Formulated in JICA M/P Study
(2) Operation of NHCS The JICA Study planned that NHCS should be closed during flood to block inflow from Laguna Lake to Pasig River while the WB Study planned that NHCS should be open during flood to expect reverse flow from Pasig River to Laguna Lake. Advantages and disadvantages of operation of NHCS are summarized in Table 4.15. With the following reasons, it is judged as appropriate that NHCS shall be closed during flood to avoid uncertain phenomena in flood management plan.
Final Report 4-30 The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila Diversion through Napindan Channel to Laguna Lake is uncertain since reverse flow will happen depending on water level in Laguna Lake. If NHCS would open during flood, channel improvement of Napindan Channel is inevitable to protect surrounding dense urbanized area resulting difficulty of land acquisitions.
Table 4.15 Comparison of NHCS Operation Open during Flood Close during Flood
Inflow from Laguna Lake to Pasig River can be Advantage Gate operation is not required. prevented. In case WL of Laguna Lake is higher than Pasig River, flood risk in the center of Metro Manila increases due to inflow from Laguna Lake to Pasig River. Diversion of flood discharge to Laguna Lake through Napindan Channel is uncertain depending of water levels of Laguna Lake and Pasig River. Disadvantage If diversion to Laguna Lake through Gate operation is required. Napindan Channel is included in the discharge allocation plan, discharge of Lower Marikina becomes large resulting increase of flood risk and heightening of dyke is required. Napindan Channel also requires improvement works such as dyke heightening. Evaluation Not Favorable Favorable Source: JICA Study Team
(3) Necessity of MCGS The JICA Study planned to fully utilize Laguna Lake with sure diversion through Manggahan Floodway controlled by MCGS. On the other hand, the WB Study recommended that MCGS is not necessary and flood control is planned with diversion through Napindan Channel. Advantages and disadvantages of MCGS are summarized in Table 4.16. MCGS is necessary for sure diversion of design discharge to Laguna Lake. Besides, excess flood also can be diverted to Manggahan Floodway by MCGS resulting mitigation of flood risk at the center of Metro Manila. Without MCGS, re-improvement of channel downstream of Rosario Weir since HWL increases. Rise of HWL leads to increase of flood disaster potentials.
Table 4.16 Comparison of With/Without MCGS Without MCGS With MCGS
Sure diversion is available. Excess flood also can be diverted resulting Advantage WL of Upper Marikina decrease. mitigation of flood risk at the center of Metro Manila. Flood risk for excess flood increase. HWL in Pasig-Lower Marikina increases Gate operation is required. Disadvantage leading to increase of flood disaster WL in Upper Marikina rise. potentials Evaluation Not Favorable Favorable Source: JICA Study Team
The basic specifications and operation rule of MCGS designed in the detailed design in 2002 are summarized in Table 4.17.
Final Report 4-31 The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila Table 4.17 Comparison of With/Without MCGS Item Specifications Design Discharge 500m3/s (Lower Marikina River) Design HWL Upstream Side: EL. 17.40m Downstream Side: EL. 14.74m Design Section Riverbed Width: 43.5m Riverbed Elevation: EL.8.0ｍ Gate Dimensions: W20ｍ x H11ｍ x 2 units Type: Roller Gate Operation Rule MCGS Gate shall be operated together with Rosario Weir with monitoring of levels of Manila Bay, Laguna Lake and Sto.Nino for secure diversion of design discharge. Source: JICA Study Team
Discharge allocations to Manggahan Floodway and Lower Marikina, and influence to downstream with/without MCGS is simulated with following conditions. Diversion volumes of the both case, 1/20 years flood discharge allocation, and longitudinal flow profile of it are summarized in Table 4.18, Figure 4.30 and 4.31, respectively. Design discharge at Sto.Nino is 2,900 m3/s which equivalent to 1/20 years flood with natural retarding function is applied. NHCS is closed not to divert to Laguna Lake through Napindan Channel. Manggahan Floodway has designed capacity without illegal residents in the river course.
Without MCGS, the following disadvantage occurs. Design diversion discharge to Manggahan Floodway of 2,400 m3/s is not secured. Water levels in Pasig-Lower Marikina River rise higher than the design HWL about 1 m as maximum resulting increase of flood risk. RE-improvement such as heightening of dyke is required.
Table 4.18 Diversion Discharge With/Without MCGS Marikina Lower Marikina Manggahan Floodway (Before Diversion) (After Marikina) Without MCGS 2,900 m3/s 1,000 m3/s 1,900 m3/s With MCGS 2,900 m3/s 500 m3/s 2,400 m3/s Source: JICA Study Team
2,900 2,900 Sto.Nino Sto.Nino
MCGS San JuanRiver San San JuanRiverSan Marikina River Marikina River MarikinaRiver Pasig River 650 Pasig River (Lower) 2,900 Pasig River 650 Pasig River (Lower) RiverMarikina 2,900 1,600 1,000 1,000 1,000 1,200 600 500 500 Rosario Weir Rosario Weir Manila Bay Manila
Manila Bay Manila P P NHCS P P NHCS 0 1,900 0 2,400 Channel Channel Napindan Floodway Mangahan Mangahan Napindan Floodway Without MCGS Mangahan With MCGS
Laguna Lake Laguna Lake
Source: JICA Study Team Figure 4.28 Discharge Allocation With/Without MCGS (1/20 years, with Natural Retarding Function)
Final Report 4-32 The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila
Source: JICA Study Team Figure 4.29 Flow Profile With/Without MCGS
Final Report 4-33 The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila (4) Consideration of Urban Development along Marikina River At near Rosario Weir, urban development program is on-going by private developers as shown in Figure 4.32. Influence of this development is calculated based on the design drawings of development program. As shown in Figure 4.33, rise of water level due to the urban development is just 20 cm which can be adjusted in the Phase IV Project.
Figure 4.30 H-Q Curve Formulated in WB Study
Source: JICA Study Team Figure 4.31 Flow Profile of Influence of Urban Development Program
(5) Evaluation of Probability of Design Flood Discharge by PMRCIP Based on the review of hydrological analysis referring the observed flood in recent years, probable flood discharge of 1/30 years return period is estimated at 3,100 m3/s which is 200 m3/s larger than the design discharge of 2,900 m3/s. Table 4.19 shows the probable discharges at Sto.Nino with natural retarding function. According to Table 4.19, the design flood discharge of PMRCIP of 2,900 m3/s is reevaluated as 1/20 years flood. Table 4.19 Reviewed Probable Discharge at Sto.Nino Return Period Sto.Nino (With Inundation) Return Period Sto.Nino (With Inundation) 2 1,620 30 3,030 5 2,290 50 3,220 10 2,670 100 3,580 20 2,860 Source: JICA Study Team
Final Report 4-34 The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila 4.4.2 Flood Management Plan for 1/30 Years Flood (1) Conditions for Examination The following conditions were applied to examine the flood management plan for 1/30 years flood. Change of HWL at the section where PMRCIP has been conducted or on-going since the social infrastructures have been developed based on the designed HWL. Therefore, HWL at the section where PMRCIP has conducted including Phase III Section shall remain same. For Phase IV Section, minor change is considered acceptable. Diversion through Napindan Channel to Laguna Lake is uncertain since reverse flow will happen depending on water level in Laguna Lake. As discussed in Section 4.4.1, NHCS is closed during flood and inflow from Pasig River to Laguna Lake through Napindan Channel is not considered. MCGS is to be constructed. Flood management plan is examined for 1/30 years flood with natural retarding function as shown in Figure 4.34.
Montalban
Natural Retarding Basin Nangka River
3,100 Sto.Nino
MCGS San JuanSan River Marikina River Pasig River 700 Pasig River (Lower) MarikinaRiver 3,100 1,300 600 500 500 Rosario Weir
P P NHCS 0 2,600 Channel Napindan Floodway Mangahan
Laguna Lake Source: JICA Study Team Figure 4.32 Discharge Allocation of 1/30 Years Flood
(2) Alternatives of Flood Management Plan for 1/30 Flood Since the discharge allocation downstream of MCGS is already fixed, flood management plan can be considered upstream of MCGS such as following 2 alternatives. A: To retain flood discharge in Laguna Lake through Manggahan Floodway. B: To retain flood discharge at retarding basin upstream of Sto.Nino. Thus the following 2 alternatives for countermeasure are examined adding to the Phase IV components consisting channel improvement from MCGS to Marikina Bridge and construction of MCGS. Alternative-a: Phase IV with Dyke Heightening + Improvement of Manggahan Floodway Alternative-b: Phase IV without Dyke Heightening + Construction of Retarding Basin
Final Report 4-35 The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila (3) Alternative-a: Phase IV with Dyke Heightening + Improvement of Manggahan Floodway 1) Discharge Allocation 3,100 m3/s between Risario Weir to Sto.Nino with Channel Improvement 2,600 m3/s to Manggahan Floodway and 500 m3/s to Lower Marikina River
2) Improvement Plan In Upper Marikina River, heightening of dyke such as parapet is required since HWL rise about 50 cm of the flow sections designed in the detailed design in 2002. Since required discharge of Manggahan Floodway is 2,600 m3/s which is 200 m3/s larger than design discharge of 2,400 m3/s, improvement works is required.
Source: JICA Study Team Figure 4.33 Alternative-a: Phase IV with Dyke Heightening + Improvement of Manggahan Floodway (1/30 Years)
Final Report 4-36 The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila (4) Alternative-b: Phase IV without Dyke Heightening + Construction of Retarding Basin 1) Discharge Allocation 2,900 m3/s between Risario Weir to Sto.Nino with control of 200 m3/s at the retarding basins upstream of Sto.Nino. 2,400 m3/s to Manggahan Floodway and 500 m3/s to Lower Marikina River
2) Improvement Plan In Upper Marikina River, flow sections designed in the detailed design in 2002 can be remained. Required discharge of Manggahan Floodway is 2,400 m3/s, same as design discharge. To recover the designed flow capacity, dredging works and relocation of illegal residents are required. Increase of capacity of retarding basin up to 35 MCM is required by excavation of natural retarding basin where current capacity is 5 MCM.
Source: JICA Study Team Figure 4.34 Alternative-b: Phase IV without Dyke Heightening + Construction of Retarding Basin (1/30 Years)
3) Scale of Retarding Basin a) Retarding Basin Development In case the retarding basin development scenario is taken for 1/100 years flood management measures, the necessary capacities of retarding basin to reduce discharge at Sto.Nito to 3,100m3/s and 2,900m3/s are 20MCM and 25MCM, respectively. (refer to Table 4.20 and Figure 4.35)
Final Report 4-37 The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila Table 4.20 Control Volume of Retarding Basin for 1/30 Flood
Number of Area Volume Average Excavation Natural Before Control After Control Effect Return Period FCB(Locations） （ha） (1,000m3） Depth（m） drainage (m3/s） (m3/s） (m3/s）
30 8 371 20,007 4.0 Yes 3,970 3,100 870
30 8 371 25,296 7.5 No 3,970 2,890 1,080
Source: JICA Study Team
Source: JICA Study Team Figure 4.35 Hydrograph at Sto.Nino before and after Control by Retarding Basin
b) Enhancement of Natural Retarding Basin Necessary volume of retarding basin is estimated at 5 MCM to control discharge at Sto.Nino to 2,900 m3/s from 3,100 m3/s by cutting 200 m3/s of 1/30 years flood. Total retaining volume will be 35 MCM with current natural retarding function of 30 MCM. Area and location of natural retarding basin is assumed as inundation area by 1/30 years flood by simulation as shown in Figure 4.36. The area is about 1,000ha and its capacity is about 30 MCM.
Final Report 4-38 The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila
Inundation Area ：949ha Inundation Volume ：30.3MCM
Source: JICA Study Team Figure 4.36 Location of Natural Retarding Basin (Estimated Inundation Area of 1/30 years Flood)
Final Report 4-39 The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila (5) Evaluation of Alternatives The 2 alternatives shown in Table 4.21 are compared as summarized in Table 4.22. Their discharge allocations and flow profiles are shown in Figure 4.38 to 4.40. Both alternatives is feasible, however, if land acquisition for retarding basin is difficult, Alternative-a is recommended since it can be implemented in the Phase IV Project. Table 4.21 Summary of Alternatives for 1/30 Years Flood Management
Altern Upper-Upper Pasig NHCS Lower Marikina MCGS Mangahan Floodway Upper Marikina ative Marikina River River Excavation & Existing Condition Existing Improvement a Close Improvement With Widening +Natural Retarding Condition (DD 2002) (PhaseⅢ) Q=2,600m3/s Basin With CV* River Existing Condition River Excavation(removal Existing Improvement +Natural Retarding b Close Improvement With of sedimentation) Condition (DD 2002) Basin+Additional (PhaseⅢ) Q=2,400m3/s With CV* Capacity 5MCM CV:Circulo Verde Development Plan
Upper Marikina River Improvement(DD 2002) ; Q2,900m3/s
Source: JICA Study Team
Alternative-02Alternative-a Montalban Return Period: 30-year Natural Retarding Basin: with Natural NHCS: Close Retarding MCGS: With Basin Nangka River
3,100 Sto.Nino
MCGS San Juan RiverJuan San Marikina River Pasig River 700 Pasig River (Lower) RiverMarikina 3,100 1,300 600 500 500 Rosario Weir
P P NHCS 0 2,600 Channel Napindan Floodway Mangahan Mangahan
Laguna Lake
Alternative-03Alternative-b Montalban Return Period: 30-year Natural Retarding Basin Natural +Flood Control Basin: Retarding Basin NHCS: Close +Additonal Nangka River Capacity V=5MCM
2,900 Sto.Nino
MCGS San JuanRiver San Marikina River Pasig River 700 Pasig River (Lower) RiverMarikina 2,900 1,300 600 500 500 Rosario Weir
P P NHCS 0 2,400 Channel Napindan Floodway Mangahan Mangahan
Laguna Lake
Source: JICA Study Team Figure 4.37 Alternatives of Design Flood Discharge Allocation for 1/30 Years Flood
Final Report 4-40 The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila Table 4.22 Comparison of Alternatives for 1/30 Years Flood Management Alternative-a: Alternative-b: Channel Improvement of Marikina River + Channel Improvement of Marikina River + MCGS + Improvement of Manggahan MCGS + Retarding Basin Floodway Structures Channel Improvement of Marikina River Channel Improvement of Marikina River (PhaseⅡ&Ⅲ&Ⅳ) (PhaseⅡ&Ⅲ&Ⅳ) MCGS MCGS Discharge 3,100 m3/s at Rosario Weir is diverted to Main 3,100 m3/s discharge is reduced to 2,900 m3/s Allocation River with 500 m3/s and to Manggahan at Sto.Nino by retarding basin. Floodway with 2,600 m3/s. 2,900 m3/s at Rosario Weir is diverted to Main River with 500 m3/s and to Manggahan Floodway with 2,400 m3/s. Water Less than HWL in Pasig River. Less than HWL in Pasig River. Level Less than HWL in Lower Marikina River. Less than HWL in Lower Marikina River. Excess HWL with 0.1 m to 0.5 m in Upper Excess HWL with 0.1 m to 0.5 m in Upper Marikina River. Marikina River due to Urban Development Project. Measures Excess flood can be diverted to Laguna Lake Excess flood can be diverted to Laguna Lake for Excess by MCGS. by MCGS. Flood Necessity There is no re-improvement in PhaseII and III There is no re-improvement in Phase II, III and of sections. IV sections. Additional Heightening of Phase IV section is required. Construction of retarding basin upstream of Works Improvement of Manggahan Floodway is Sto.Nino is required after Phase IV. required. Evaluation Social impact is less since there is no change of Social impact is less since there is no change of HWL in Phase II and III sections. Heightening HWL in Phase II, III and IV sections. of Phase IV section is available. Discharge of Construction of retarding basin should be after excess flood to the center of Metro Manila can Phase IV Project. Land acquisition for be controlled. retarding basin is required. Discharge of excess flood to the center of Metro Manila can be controlled.
Good Fair Source: JICA Study Team
Final Report 4-41 The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila
Source: JICA Study Team Figure 4.38 Flow Profile of Alternative-a
Final Report 4-42 The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila
Source: JICA Study Team Figure 4.39 Flow Profile of Alternative-b
Final Report 4-43 The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila (6) Scale of Manggahan Floodway Improvement 1) Current Conditions Manggahan Flood way was completed in 1988 with the design discharge of 2,400m3/s. However, flow area has been reduced mainly due to houses in river course and sedimentation. If design discharge of 2,400m3/s flows into the channel, water level rise about 1.2m higher than design HWL, which is higher than current dyke level in the section from 1.5 to 3.0 km from Rosario Weir.
Figure 4.40 Current Conditions of Manggahan Floodway
Lower End Start W.L.: Laguna Lake W.L. 13.9m River Section: Current condition (with Houses, n=0.300) After dredging condition (n=0.030) Calculation Case: Design discharge 2400m3/s
Figure 4.41 Longitudinal Flow Profile (Current and after Excavation, Q=2,400m3/s)
2) Restoration to 2,400m3/s This alternative is to restore capacity of Manggahan Floodway to the original design capacity of 2,400m3/s by resettlement of houses in river course and dredging works to the design riverbed level. Water level of the floodway with Q=2,400m3/s is confirmed by non-uniform flow calculation. Typical section and longitudinal flow profile are shown in Figure 4.44 and 4.45, respectively.
Final Report 4-44 The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila
Current Condition
After Dredging
Figure 4.42 Typical Section after Dredging Works
Lower End Start W.L.: Laguna Lake W.L. 13.9m River Section: After dredging condition (n=0.030) Calculation Case: Design discharge 2400m3/s
Figure 4.43 Longitudinal Flow Profile (After Excavation, Q=2,400m3/s)
3) Improvement to 2,600m3/s Water level increases about 30cm at Rosario Weir if discharge of 2,600m3/s flows into Manggahan Floodway. To reduce the water level to same as 2,400m3/s discharge, widening of river course is required as show in Figure 4.46. Longitudinal flow profile is shown in Figure 4.47.
Final Report 4-45 The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila
Current Condition
After Dredging After Improvement
1：2.0 1：2.0 150m
Current Condition
After Dredging
1：2.0 0.5m After Improvement
Figure 4.44 Typical Section after Widening
Lower End Start W.L.: Laguna Lake W.L. 13.9m River Section: After dredging condition (n=0.030) After improvement condition (n=0.030) Calculation Case: After dredging Q=2400m3/s After improvement Q=2600m3/s
Figure 4.45 Longitudinal Flow Profile (After Excavation Q=2,400m3/s, With Widening Q=2,600m3/s)
Final Report 4-46 The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila
(7) Lower Reach of MCGS 1) 1/30 Years Flood Allocation River channel improvement in San Juan River is planned of which design discharge at confluence is 780m3/s with 1/100 years flood while 1/30 years flood discharge is 670m3/s. Since the applied hyetograph is different, peak discharge after the confluence is becomes 1,300m3/s which is 100 m3/s larger than the design discharge in the detailed design in 2002 as shown in Figure 4.48 and 4.49.
Figure 4.46 1/30 Years Flood Allocation in Pasig River
Figure 4.47 Hydrograph of 1/30 Years Flood at Confluence of San Juan River
2) 1/30 Years Flood Measure To flow the increased design discharge of 1,300m3/s, dredging of lower Pasig Reach from 0.0k to 2.0k to the design riverbed level in 1990 Master Plan. Longitudinal Flow Profile is shown in Figure 4.50.
Final Report 4-47 The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila
Source: JICA Study Team Figure 4.48 Longitudinal Flow Profile of Pasig-Lower Marikina (Q=1,300m3/s)
Final Report 4-48 The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila
4.4.3 Flood Control Measures for 1/100 Years Flood (1) Possible Measures for 1/100 Years Flood As measures to be implemented after the Phase IV completed, flood control effects of possible 1/100 flood control facilities at upstream of Sto.Nino. Possible flood control facility is as follows. Dam Retarding Basin Dam + Retarding Basin
Source: JICA Study Team Figure 4.49 Possible Flood Control Facilities Upstream of Sto.Nino for 1/100 Years Flood
(2) Flood Control Effect of Dam For examination of effect of dam, 4 cases of reservoir capacities with 55 MCM, 65 MCM, 80 MCM and 90 MCM are examined. H-V curve is estimated based on the reservoir volumes by elevation which estimated by the WB Study since it was not examined in the JICA M/P Study. H-V curve is estimated by 1 m interval of elevation by spline interpolation. H-V relation and curve are shown in Table 4.23 and Figure 4.42, respectively. Table 4.23 H-V Relation of Proposed Dam Elevation(m) Volume(MCM) 55 0 60 2.325 80 32.325 100 89.025 120 181.53 140 320.63 Source: Master Plan for Flood Management in Metro Manila and Surrounding Areas, the World Bank Final Report 4-49 The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila
Source: JICA Study Team Figure 4.50 H-V Curve of Proposed Dam
1) Conditions for Estimation of Flood Control Effect of Dam Flood control effect of dam is estimated based on the following conditions. In the WB Study, sedimentation volume varies depending on dam height because it is estimated as 10% of total reservoir capacity. However, since sedimentation does not related to dam height, fixed dead volume is applied same as the JICA M/P Study. Considering the safety factor, flood control capacity is set as 1.2 times of calculated flood control capacity Peak outflow discharge is set considering flow capacity of downstream. Basic specifications of dams are summarized in Table 4.24.
Table 4.24 Specifications of Dams Examined
E L LWL SWL V total V effective V dead Case H (m) top Orifice (m) (m) (1,000m3) (1,000m3) (1,000m3) (m) 55MCM 68 98 67 93 63,551 54,398 9,153 5.7×5.7×3unit 65MCM 71 101 67 96 73,684 64,531 9,153 4.3×4.3×3unit 80MCM 75 105 67 100 86,342 77,189 9,153 3.1×3.1×3unit 90MCM 77 107 67 102 96,316 87,163 9,153 3.1×3.1×3unit Source: JICA Study Team
2) Estimation Results Flood control effect of dam is estimated as summarized in Table 4.25 and Figure 4.43 to 4.45. It is noted that hydrographs at Montalban and Sto.Nino does not consider inundation upstream.
Final Report 4-50 The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila
Table 4.25 Specifications of Dams Examined Dam Case Montalban (m3/s) Sto.Nino (m3/s) Peak Inflow (m3/s) Peak Outflow (m3/s) 55MCM 1,820 2,840 3,790 65MCM 1,450 2,500 3,470 3,230 80MCM 1,050 2,140 3,100 90MCM 710 1,900 2,900 Source: JICA Study Team
Source: JICA Study Team Figure 4.51 Hydrographs at Dam Location
Source: JICA Study Team Figure 4.52 Hydrographs at Montalban
Final Report 4-51 The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila
Source: JICA Study Team Figure 4.53 Hydrographs at Sto.Nino
(3) Flood Control Effect of Retarding Basin 1) Conditons for Estimation of Flood Control Effect of Retarding Basin Specifications of retarding basins are determined with the following conditions. Candidate areas are selected based on the inundation area of 2009 Flood and un-urbanized area as of 2011. Bed elevation of retarding basin is determined as the level which allows natural drain to river. HWL of retarding basin is determined as same as HWL of Marikina River at drainage outlet position. HWL of Mrikina River is same as the design high water level. Length of overflow dyke is determined to maximize capacity of retarding basin.
Specifications and locations of candidate retarding basins are shown in Table 4.26 and Figure 4.47.
Table 4.26 Specifications of Candidate Retarding Basin NO. Area HWL Bed Elevation Depth Capacity* （ha） （EL.m） (EL.m) （m） （1,000m3） 1 85 26.254 22.254 4.0 4,870 2 114 26.142 22.142 4.0 6,195 3 82 24.877 20.877 4.0 4,267 4 8 24.749 20.749 4.0 397 5 36 23.880 19.880 4.0 1,901 6 21 21.761 17.761 4.0 1,137 7 16 21.229 17.229 4.0 835 8 8 21.637 17.637 4.0 405 Total 371 20,007 Remarks: Capacity is 1.2 times of calculated capacity considering safety factor. Source: JICA Study Team
Final Report 4-52 The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila
Source: JICA Study Team Figure 4.54 Locations of Candidate Retarding Basin
Final Report 4-53 The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila 2) Estimation Results The results of estimation of the maximum flood control effect of retarding basins against 1/100 years flood is shown in Table 4.26 and Figure 4.46. Effect is only 740 m3/s as evaluated as discharge at Sto.Nino.
Table 4.27 Flood Control Effect of Retarding Basin Average Before After Return Number of Area Volume Natural Effect Dam Size Excavation Control Control Period FCB(Locations） （ha） (1,000m3） drainage (m3/s） Depth（m） (m3/s） (m3/s） Without Dam 100 8 371 20,004 4 Yes 4,973 4,232 741 (FCB Only） Source: JICA Study Team
Source: JICA Study Team Figure 4.55 Hydrograph of Retarding Basin Effect at Sto.Nino (1/100 Flood)
(4) Flood Control Effect of Dam + Retarding Basin 1) Conditons for Estimation of Flood Control Effect of Retarding Basin The following cases are examined as the combination of dam and retarding basin.
Table 4.28 Estimation Cases of Dam + Retarding Basin Case Composition Case 1 Dam (55MCM) + Retarding Basin (Max, Natural Drain) Case 2 Dam (65MCM) + Retarding Basin (Max, Natural Drain) Source: JICA Study Team
2) Estimation Results The results of estimation of the maximum flood control effect of retarding basins against 1/100 years flood is shown in Table 4.29 and Figure 4.48.
Table 4.29 Flood Control Effect of Dam + Retarding Basin Average Before After Number of Area Volume Natural Effect Case Dam Size Excavation Control Control FCB(Locations） （ha） (1,000m3） drainage (m3/s） Depth（m） (m3/s） (m3/s） Case1 55MCM 8 371 20,004 4 Yes 3,790 3,090 700 Case2 65MCM 8 371 20,004 4 Yes 3,470 2,850 620
Final Report 4-54 The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila Source: JICA Study Team
Case 1
Case 2
Source: JICA Study Team Figure 4.56 Hydrographs of Dam + Retarding Basin Effect at Sto.Nino
(5) Lower Reach of MCGS 1) 1/100 Years Flood Allocation 1/100 years flood allocation in lower reach of MCGS is as shown in Figure 4.59 and 1/100 years flood discharge at river mouth becomes 1,400m3/s assuming channel improvement of San Juan River with design discharge of 780m3/s is completed. It is 200m3/s higher than the design discharge in the detailed design in 2002.
Final Report 4-55 The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila
Figure 4.57 1/100 Years Flood Allocation in Pasig River and Hydrograph at Confluence of San Juan River
2) 1/100 Years Flood Measure To flow the increased design discharge of 1,400m3/s, dredging of lower Pasig Reach from 0.0k to 5.6k to the design riverbed level in 1990 Master Plan. Longitudinal Flow Profile is shown in Figure 4.50.
Final Report 4-56 The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila
Source: JICA Study Team Figure 4.58 Longitudinal Flow Profile of Pasig-Lower Marikina (Q=1,400m3/s)
Final Report 4-57 The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila
4.4.4 Flood Management Plan for 1/100 Years Flood Flood management plan for 1/100 years is examined considering development scenario of flood management measures.
(1) Urgent Flood Management Measures As the urgent flood management measures until the completion of Phase IV Project, the following 3 alternatives are considerable. Alt-O: 1/30 years flood (as of 2002) measures by Phase IV component (Q=2,900m3/s at Sto.Nino) Alt-A: 1/30 years flood measures by Phase IV components with improvement of Manggahan Floodway (Q=3,100m3/s at Sto.Nino) Alt-B: 1/30 years flood measures by Phase IV components with improvement of retarding basin in upper-upper Marikina (Q=2,900m3/s at Sto.Nino)
Out of 3 alternatives, 2 alternatives to improve up to 1/30 years flood measures are recommended because additional measures can be included in Phase IV Project.
Table 4.30 Alternatives for Urgent Flood Management Measures
Source: JICA Study Team
(2) Development Scenario to 1/100 Years Flood Management Alternatives of the phased development scenario to 1/100 years flood management are shown in Figure 4.50. After the Phase IV Project completed, safety degree can be improved by construction of dam or dam + retarding basin. As for retarding basin development, the following 3 patterns shown in Figure 4.49 are possible. It shall be determined in detailed design stage.
Final Report 4-58 The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila “Natural Retarding Basin” is to maintain current natural retarding function of basin. Some urbanized area will be included in the retarding basin. “Retarding Basin Development” is to develop about 400 ha out of 1,000 ha natural retarding basin. “Enhancement of Retarding Function” is to excavate whole or parts of 400 ha to improve retarding functions. Current natural retarding basin is 1,000 ha with capacity of 30 MCM. Out of it, urbanized area is 60% with capacity of 18 MCM, and candidate retarding basin has area of 400 ha with capacity of 12 MCM.
■Natural Retarding Basin
■Enhancement of Retarding Function (as of mid-stage of development)
■Retarding Basin Development
Source: JICA Study Team Figure 4.59 Pattern of Retarding Basin Development
Final Report 4-59 The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila
Source: JICA Study Team Figure 4.60 Alternatives of Phased Development Scenario
Final Report 4-60 The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila
A-1: Dam + Natural Retarding Basin A-2-1: Dam Step1: 1/30 years Step1: 1/30 years
Step2: 1/100 years (Dam Completed) Step2: 1/100 years (Dam Completed)
A-3: Dam + Retarding Basin A-2-2: Dam + Temporary Retarding Basin
Step1: 1/30 years Step1: 1/30 years
Step2: 1/30＋α (Enhance of Retarding Function) Step2: 1/30＋α(Enhance of Retarding Function)
Step3: 1/100 years (Dam + Retarding Basin) Step3: 1/100 years (Dam Completed)
Source: JICA Study Team Source: JICA Study Team Figure 4.61 Images of Development Scenario(A-1 to A-3)
Final Report 4-61 The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila
O-1: Dam + Natural Retarding Basin O-2: Dam Step1: 1/30 yeras (as of 2002) Step1: 1/30 years (as of 2002)
Step2: 1/100 years (Dam Completed) Step2: 1/100 years (Dam Completed)
B-1: Dam + Enhancement of Retarding Function B-2-1: Dam Step1: 1/30 (Enhance of Retarding Function) Step1: 1/30 (Enhance of Retarding Function)
Step2: 1/100 years (Dam Completed) Step2: 1/100 years (Dam Completed)
B-3: Dam + Retarding Basin Development B-2-2: Dam Step1: 1/30 (Enhance of Retarding Function) Step1: 1/30 (Enhance of Retarding Function)
Step2: 1/30 + α (Enhance of Retarding Step2: 1/30＋α(Enhance of Retarding Function) Function)
Step3: 1/100 (Dam + Retarding Basin) Step3: 1/100 years (Dam Completed)
Source: JICA Study Team Figure 4.62 Images of Development Scenario(B-1 to B-4)
Final Report 4-62 The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila
(3) Alternatives of 1/100 Years Flood Management Plan with Phase IV + Manggahan Floodway as 1/30 Years Measure There are 4 alternatives can be applied if Phase IV + Manggahan Floodway is applied as 1/30 years flood management measures. Alt A-1: Dam + Natural Retarding Basin Alt A-2-1: Dam Only Alt A-3: Dam + Retarding Basin Construction Alt A-2-2: Dam + Temporary Retarding Basin (after dam completed, retarding basin will be demolished and land use changed.)
(4) Alternatives of 1/100 Years Flood Management Plan with Phase IV + Retarding Basin as 1/30 Years Measure There are 6 alternatives can be applied if Phase IV + Retarding Basin is applied as 1/30 years flood management measures. Alt O-1: Dam + Natural Retarding Basin Alt O-2: Dam Only Alt B-1: Dam + Natural Retarding Basin + Excavation of Retarding Basin Alt B-2-1: Dam + Temporary Retarding Basin (after dam completed, retarding basin will be demolished and land use changed.) Alt B-3: Dam + Retarding Basin Construction Alt B-2-2: Dam + Temporary Retarding Basin (after dam completed, retarding basin will be demolished and land use changed.)
Final Report 4-63 The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila
Table 4.31 Alternatives for Urgent Flood Management Measures (Sto.Nino: 3,100 m3/s) Flood Management Measures for 1/100 Years Alternative-A-1 Alternative-A-2-1 Alternative-A-3 Alternative-A-2-2 Flood
Dam Dam Dam Dam
1,050 3,230 1,820 3,230 1,050 3,230 1,820 3,230
V=80MCM 2,140 V=80MCM 2,840 V=55MCM 2,140 2,840 V=55MCM Montalban Montalban Montalban Montalban
Natural Flood Control Basin Nangka River Retarding Basin Nangka River Nangka River Nangka River A=1000ha A=400ha 800
800 MarikinaRiver
800 RiverMarikina 800
3,100 3,100 3,100 Discharge Allocation 3,100 Sto.Nino Sto.Nino Sto.Nino Sto.Nino
MCGS MCGS MCGS MCGS Marikina River Marikina River Marikina River Marikina River (Lower) 3,100 (Lower) 3,100 RiverMarikina (Lower) MarikinaRiver 3,100 (Lower) 3,100 500 500 500 500 500 500 500 500 Rosario Weir Rosario Weir Rosario Weir Rosario Weir NHCS NHCS NHCS NHCS 2,600 0 2,600 2,600 0 2,600 Floodway Mangahan Mangahan Floodway Mangahan Mangahan Floodway Mangahan Mangahan Floodway Mangahan Mangahan
Laguna Lake Laguna Lake Laguna Lake Laguna Lake
Dam + Natural Retarding Basin Channel Improvement + Dam + Retarding Channel Improvement + Dam (+ Channel Improvement + Dam Upper Upper Marikina River Dam: 55 MCM, Natural Retarding Basin: 30 Basin Enhancement of Retarding Function) Dam: 80MCM MCM Dam: 55MCM Retarding Basin: 20MCM Dam: 80MCM Phase IV Components + Heigthning to Phase IV Components + Heigthning to Phase IV Components + Heigthning to Phase IV Components + Heigthning to Upper Marikina River 3,100m3/s 3,100m3/s 3,100m3/s 3,100m3/s
Mangahan Dredging to 2,600m3/s Dredging to 2,600m3/s Dredging to 2,600m3/s Dredging to 2,600m3/s
Lower Marikina River Current Phase III Components Current Phase III Components Current Phase III Components Current Phase III Components
Pasig River Phase II + Dredging to 1,400m3/s Phase II + Dredging to 1,400m3/s Phase II + Dredging to 1,400m3/s Phase II + Dredging to 1,400m3/s
61,813.7 65,610.6 66,276.1 69,492.5 Project Cost(million peso) (1.000) (1.061) (1.072) (1.124)
Safety degree can be improved stepwise. Scale Scale of Dam can be minimize by utilization of of dam can be minimized by enhancement of Landuse of retarding basin after enhancement of Advantages Landuse of retarding basin is available. natural retarding basin. retarding function. function is available. Multiple use of retarding basin is available.
Dam is applicable only when geologically available. Since dam development is planned Disadvantages Landuse of retarding basin shall be regulated. Applicable only when geologically available. Land acquisition of retarding basin is required. after enhancement of retarding function, invest for temporary measure is required.
Source: JICA Study Team
Final Report 4-64 The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila
Table 4.32 Alternatives for Urgent Flood Management Measures (Sto.Nino: 2,900 m3/s)
Flood Management Measures for 1/100 Years Alternative-O-1 Alternative-O-2 Alternative-B-1 Alternative-B-2-1 Alternative-B-3 Alternative-B-2-2 Flood
Dam Dam Dam Dam Dam Dam
1,450 3,230 710 3,230 1,820 3,230 710 3,230 1,450 3,230 710 3,230
V=65MCM V=55MCM V=90 MCM 2,500 1,900 V=90 MCM 2,840 1,900 2,500 V=65MCM 1,900 V=90 MCM Montalban Montalban Montalban Montalban Montalban Montalban
Natural Natural Retarding Basin Flood Control Basin Retarding Basin +Additonal Nangka River Nangka River Nangka River Nangka River Nangka River Nangka River A=1000ha Capacity A=400ha V=5MCM 800 800 800 800 River Marikina 800 800 Marikina River Marikina River Marikina
2,900 2,900 2,900 2,900 2,900 2,900 Discharge Allocation Sto.Nino Sto.Nino Sto.Nino Sto.Nino Sto.Nino Sto.Nino Marikina River Marikina
Marikina River Marikina MCGS MCGS Marikina River MCGS River Marikina MCGS Marikina River MCGS Marikina River Marikina River Marikina River MCGS Marikina River (Lower) (Lower) 2,900 (Lower) 2,900 2,900 (Lower) 2,900 (Lower) 2,900 (Lower) 2,900 500 500 500 500 500 500 500 500 Rosario Weir 500 500 500 500 Rosario Weir Rosario Weir Rosario Weir Rosario Weir Rosario Weir NHCS NHCS NHCS NHCS NHCS NHCS 0 2,400 0 2,400 0 2,400 0 2,400 0 2,400 0 2,400 Floodway Mangahan Mangahan Floodway Floodway Floodway Mangahan Mangahan Mangahan Mangahan Mangahan Floodway Mangahan Mangahan Floodway Mangahan Mangahan
Laguna Lake Laguna Lake Laguna Lake Laguna Lake Laguna Lake Laguna Lake
Dam + Natural Retarding Basin Dam + Retarding Basin Channel Improvement + Dam Channel Improvement + Dam + Retarding Channel Improvement + Dam Channel Improvement + Dam Upper Upper Marikina River Dam: 65 MCM, Natural Retarding Basin: 30 Dam: 55MCM Natural Retarding Basin: (Enhancement of Retarding Basin) Basin (Enhancement of Retarding Basin) Dam: 90MCM MCM 30MCM＋Retarding Basin: 5MCM Dam: 90MCM Dam: 65MCM Retarding Basin 400ha, 20MCM Dam: 90MCM
Upper Marikina River Phase IV Components Phase IV Components Phase IV Components Phase IV Components Phase IV Components Phase IV Components
Mangahan Current Plan to 2,400m3/s Current Plan to 2,400m3/s Current Plan to 2,400m3/s Current Plan to 2,400m3/s Current Plan to 2,400m3/s Current Plan to 2,400m3/s
Lower Marikina River Current Phase III Components Current Phase III Components Current Phase III Components Current Phase III Components Current Phase III Components Current Phase III Components
Pasig River Phase II + Dredging to 1,400m3/s Phase II + Dredging to 1,400m3/s Phase II + Dredging to 1,400m3/s Phase II + Dredging to 1,400m3/s Phase II + Dredging to 1,400m3/s Phase II + Dredging to 1,400m3/s
61,625.3 65,257.5 63,518.5 67,683.3 66,087.7 69,139.4 Project Cost(million peso) (1.000) (1.059) (1.031) (1.098) (1.072) (1.122)
Safety degree can be improved stepwise. Scale Safety degree can be improved stepwise. Scale Scale of Dam can be minimize by utilization of Landuse of retarding basin after enhancement of Landuse of retarding basin after enhancement of Advantages Landuse of retarding basin is available. of dam can be minimized by enhancement of of dam can be minimized by enhancement of natural retarding basin. function is available. function is available. retarding function. retarding function.
Dam is applicable only when geologically Dam is applicable only when geologically available. Since dam development is planned available. Since dam development is planned Disadvantages Landuse of retarding basin shall be regulated. Applicable only when geologically available. Landuse of retarding basin shall be regulated. Land acquisition of retarding basin is required. after enhancement of retarding function, invest after enhancement of retarding function, invest for temporary measure is required. for temporary measure is required.
Source: JICA Study Team
Final Report 4-65 The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila
(5) Comparison with Proposed Measures by WB Study Feasibility, measures against excess discharge, economic efficiency and social impact are compared among Alt A-2-1, Alt B-3 and the proposed measures by WB Study as shown in Table 4.33. Table 4.33 Comparison with Proposed Measures by WB Study Alt A-2: Dam Only Alt B-3: Dam + Retarding Basin Construction WB Study Discharge Dam Dam
Allocation Alternative-A 1,050 3,230 Alternative-B 1,450 3,230 Return Period: 100-year Return Period: 100-year Dam: Large Dam: Medium Flood Control Basin: without 2,140 V=80MCM Flood Control Basin 2,500 V=65MCM NHCS: Close Montalban NHCS: Close Montalban MCGS: With MCGS: With
Flood Control Basin Nangka River A=400ha Nangka River
800 800 MarikinaRiver
3,100 2,900 Sto.Nino Sto.Nino
MCGS MCGS MarikinaRiver San JuanSan River Marikina River Marikina River JuanSan River Pasig River 780 Pasig River (Lower) 3,100 Pasig River 780 Pasig River (Lower) 2,900
1,400 600 500 500 1,400 600 500 500 Rosario Weir Rosario Weir
P P NHCS Bay Manila P P NHCS 0 2,600 0 2,400 Channel Channel Napindan Floodway Napindan Mangahan Floodway Mangahan Mangahan
Laguna Lake Laguna Lake
Scale of Dam: V=55MCM Dam: V=65MCM Dam: H=72m Facility Retarding Basin: Without Retarding Basin: 371ha(8sites) Natural Retarding Basin: 980ha Channel Improvement: Channel Improvement: Channel Improvement: Pasig : 1,400m3/s Pasig :1,400m3/s Pasig : 1,800m3/s Napindan Cannel: Without Napindan Cannel: without Napindan Cannel: 800m3/s Lower Marikina: 500m3/s Lower Marikina: 500m3/s Lower Marikina : 1,200m3/s Mangahan Floodway:2,600m3/s Mangahan Floodway:2,400m3/s Mangahan Floodway:2,000m3/s Upper Marikina : 3,100m3/s Upper Marikina: 2,900m3/s Upper Marikina : 3,000m3/s Upper-Upper Marikina: 3,100m3/s Upper-Upper Marikina: 2,900m3/s Upper-Upper Marikina: 2,900m3/s Feasibility Heightening a part of Phase IV Section is required. Additional work for Phase III and IV is not required. Inflow through Napindan is uncertain. Dredging, additional works in Phase III and IV Sections and heightening of Napindan Channel is required. Measures for Controlled by MCGS Controlled by MCGS Flood risk increase. Excess Flood Project Cost 63,075 M Pesos (100%) 65,808 M Pesos (104%) 82,763 M Pesos (131％) Social Impact Heightening a part of Phase IV Section is required. Land acquisition for retarding basin is required. Land acquisition for Napindan heightening and retarding basin is required. Source: JICA Study Team
Final Report 4-66 The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila 4.4.5 Project Cost Estimate for Alternatives Project cost is estimated based on the previous studies, “The Preparatory Study for Pasig-Mairkina River Channel Improvement (Phase III)” conducted by JICA (hereinafter referred to as the “JICA FS”) and “Master Plan for Flood Management in Metro Manila and Surrounding Areas” conducted by WB (hereinafter referred to as the “WB Study”) as shown below.
Table 4.34 Source of Cost Estimation Section/Facility Scale Source & Base Year of Estimation Reference in Original Report 3 Pasig River 1,300m /s WB Study in 2011 P5-105 1,400m3/s WB Study in 2011 P5-105 Pasig River Phase2 Phase2 JICA FS in 2010 P6-5 Lower Marikina River Phase3 JICA FS in 2010 P6-5 MCGS MCGS JICA FS in 2010 P6-5 3 Manggahan Floodway 2,400m /s WB Study in 2011 P5-105 2,600m3/s WB Study in 2011 P5-105 Upper Marikina River Phase4 JICA FS in 2010 P6-5 3,100m3/s WB Study in 2011 P6-5 NRB WB Study in 2011 P5-105 Upper Upper Marikina RB 20MCM River RB 8MCM RB 5MCM
CI 2,900m3/s WB Study in 2011 P5-105
CI 3,100m3/s WB Study in 2011 P5-105 90MCM WB Study in 2011 P5-105 Dam 80MCM WB Study in 2011 P5-105 65MCM WB Study in 2011 P5-105
55MCM WB Study in 2011 P5-105 RB: Retarding Basin, CI: Channel Improvement, NRB: Natural Retarding Basin
The following assumptions are applied to estimate the project costs.
Final Report 4-67
The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila Table 4.35 Project Cost Allocation by Component
Financial Project Cost of Phase III unit: Million Pesos
Direct Construction Consulting Services Compensation Adm. Physical Non structural Construction Physical Physical 年 Phase II Phase III Base Cost Base Cost Conting Measures Supervision Contingency Conting a b c d e f g h i 2013 0 0 0 97.7 80.6 8.9 17.4 0.9 6.5 2014 630.6 451.4 54.1 65.2 53.7 6 37.8 2015 945.3 675.4 81 65.2 53.7 6 54.6 2016 945.3 675.4 81 65.2 53.7 6 54.6 2017 313.6 220.6 26.7 32.6 26.9 3 18.7
Total 2834.8 2022.8 242.8 325.9 268.6 29.9 17.4 0.9 172.2 0.58358 0.41642
Phas Ⅱ 2834.8 141.7 190.2 156.7 17.4 10.2 0.5 100.5 Phas Ⅲ 2022.8 101.1 135.7 111.9 12.5 7.2 0.4 71.7
Direct Physical Compensation Engineering Administration construction contingency cost service cost cost cost cost a ,b g d+e i c+e+f
Phas Ⅱ 2834.8 10.2 346.9 100.5 159.6
Phas Ⅲ 2022.8 7.2 247.6 71.7 114
Financial Project Cost of Phase IV unit: Million Pesos
Direct Construction Consulting Services Compensation Adm. Physical Non structural Construction Physical Physical 年 MCGS Phase IV Base Cost Base Cost Conting Measures Supervision Contingency Conting a b c d e f g h i 2017 40.8 2 4 0.2 1.5 2018 496.2 481.6 48.9 97.7 131.2 11.5 14.1 0.7 28.6 2019 744.8 720.2 73.3 65.2 87.5 7.6 50.8 2020 744.8 720.2 73.3 65.2 87.5 7.6 50.8 2021 744.8 720.2 73.3 65.2 87.5 7.6 50.8 2022 243 235.2 23.9 32.6 43.7 3.8 17.5
Total 2973.6 2877.4 292.7 325.9 478.2 40.1 18.1 0.9 200 0.508221 0.491779
MCGS 2973.6 148.8 165.6 243.0 20.4 3.0 0.1 101.6 Phase IV 2877.4 143.9 160.3 235.2 19.7 15.1 0.8 98.4
Direct Engineerin Physical Compensat Administrat constructio g service contingenc ion cost ion cost n cost cost y cost a ,b g d+e i c+e+f
MCGS 2973.6 3 408.6 101.6 169.3
Phase IV 2877.4 15.1 395.5 98.4 164.4
Remarks for cost estimate of each section/facility is as follows.
(1) Pasig River Based on the direct construction cost of riverbed excavation to increase flow capacity up to 1,700m3/s which estimated by the WB Study, direct construction cost for channel improvement work is estimated with following manner. It is noted that compensation is not included.
Final Report 4-68
The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila c) Direct Construction Cost Direct Construction Cost: 4,825mil.peso（1,700m3/s） Increase of Flow Capacity: 1,700-1,200＝500m3/s Unit Cost for Flow Capacity Increase: 9.65 mil.peso/1m3/s
Flow Capacity Improvement up to 1,300m3/s: (1,300-1,200)×9.65＝965 mil.peso Flow Capacity Improvement up to 1,400m3/s: (1,400-1,200)×9.65＝1,930 mil.peso d) Compensation Cost Since the work component is riverbed excavation, compensation is not estimated.
(2) Pasig River Phase2 Price contingency is added to the cost which estimated in the JICA FS.
(3) Lower Marikina Phase3 Price contingency is added to the cost which estimated in the JICA FS.
(4) MGCS Price contingency is added to the cost which estimated in the JICA FS.
(5) Upper Marikina 1) Phase4 Price contingency is added to the cost which estimated in the JICA FS.
2) 3,100m3/s Direct construction cost and compensation cost are estimated by target flow capacity ratio based on Phase 4 cost of which target capacity is 2,900m3/s.
(6) Manggahan Floodway 1) 2,400m3/s The following cost estimate is applied based on the WB Study.
Direct Construction Cost: 3,252mil.peso Compensation Cost: 89mil.peso
2) 2,600m3/s Direct construction cost and compensation cost are estimated by target flow capacity ratio based on the WB Study. a) Direct Construction Cost 2,400m3/s: 3,252 mil.peso 2,600m3/s: (2,600/2,400)×3,252＝3,523.0 mil.peso b) Compensation Cost 2,400m3/s: 89mil.peso 2,600m3/s: (2,600/2,400)×89＝96.4 mil.peso
(7) Upper-upper Marikina River 1) Natural Retarding Basin (NRB) Only compensation cost is estimated based on the WB Study. The unit compensation cost by the WB Final Report 4-69
The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila Study is expensive, 32 mil. Peso/ha since it includes compensation for houses/building. Thus, 5 mil. peso/ha is applied for compensation of bare land based on the hearing results to DPWH.
2) Retarding Basin (RB) Major works for retarding basin construction with capacity of 8 MCM and 5 MCM is excavation. The direct construction cost is estimated applying unit cost of 300 peso/m3 for excavation, hauling and other works. For the improvement works to 20 MCM capacity, unit price of 200 peso/m3 for embankment is applied.
Table 4.36 Cost Estimate of Retarding Basin Unit Cost Cost Price Case Cost Item Work Item Unit Q'ty Remarks (peso) (mil.peso) Year Excavation ｍ3 - 300 - Including Hauling & Finishing 2011 Direct Construction Embankment ｍ3 - 200 - 2011 Cost Total - NRB Urban Area ha 600 32,000,000 19,200 Land + House 2011 Compensation Bare Land ha 400 5,000,000 2,000 Land only 2012 Total 21,200 Excavation ｍ3 - 300 - Including Hauling & Finishing 2011 Direct Construction Embankment ｍ3 1,960,000 200 392 2011 Cost Total 392 20 MCM Urban Area ha - 32,000,000 - Land + House 2011 Compensation Bare Land ha 400 5,000,000 2,000 Land only 2012 Total 2,000 Excavation ｍ3 8,000,000 300 2,400 Including Hauling & Finishing 2011 Direct Construction Embankment ｍ3 - 200 - 2011 Cost Total 2,400 8 MCM Urban Area ha - 32,000,000 - Land + House 2011 Compensation Bare Land ha 400 5,000,000 2,000 Land only 2012 Total 2,000 Excavation ｍ3 5,000,000 300 1,500 Including Hauling & Finishing 2011 Direct Construction Embankment ｍ3 - 200 - 2011 Cost Total 1,500 5MCM Urban Area ha - 32,000,000 - Land + House 2011 Compensation Bare Land ha 250 5,000,000 1,250 Land only 2012 Total 1,250
3) Channel Improvement Works (CI) The direct construction cost for channel improvement to the capacity of 2,900 m3/s is estimated based on the WB Study of which major works is embankment. The direct construction cost for channel improvement to the capacity of 3,100 m3/s is estimated applying capacity ratio. The compensation cost is estimated based on Phase 4 unit cost by the JICA FS applying channel length. a) Direct Construction Cost 2,900m3/s: 1,341 mil.peso (WB Study) 3,100m3/s: (3,100/2,900)×1,341＝1,433.5 mil.peso b) Compensation Cost Phase IV Section (Upper Marikina, 6.8km Length) 2,900m3/s: 15.1 mil.peso 3,100m3/s: 16.1 mil.peso
Upper Upper Marikina Section (14.2km Length) 2,900m3/s: (14.2/6.8) x 15.1 = 31.5 mil.peso 3,100m3/s: (14.2/6.8) x 16.1 = 33.6 mil.peso
Final Report 4-70
The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila (8) Dam The unit construction cost per 1m dam height is estimated based on the direct construction cost estimated by the WB Study. The necessary dam height for storage capacity is estimated based on H-V curve formulated by the Study, and the direct construction cost is estimated as follows.
Table 4.37 Cost Estimate of Dam Direct Construction Cost Case Dam Height (m) (mil.peso) 55 MCM 68 8,160 60 MCM 69 8,280 65 MCM 71 8,520 80 MCM 75 9,000 90 MCM 78 9,360
(9) Cost for Each Section and Estimation of Current Price Since base years of cost estimation is different between the JICA FS (2010) and the WB Study (2011), the current price as of year 2012 is estimated applying the price escalations based on CPI of Metro Manila as shown in Table 10. The prices before and after conversion is shown in Table 12 and Table 13, respectively. Applied price escalations are as follows.
2010 2012: 1.070 2011 2012: 1.029
Table 4.38 CPI of Metro Manila Year 2010 2011 2012 CPI 116.3 120.9 124.4
(10) Project Costs of Proposed Alternatives The summary of project cost estimate of proposed alternatives is shown in Table 4.39 while the breakdown of each alternative is shown in Table 4.42.
Table 4.39 Summary of Project Cost of Proposed Alternatives (2012 Price) Alterna Project Cost Scale Components tives （million peso） 1/30 O PhaseIV Component＋NRB:30MCM 20,131.9 A PhaseIV Component+NRB:30MCM 22,170.8 + Manggahan Floodway Improvement B PhaseIV Component +RB:35MCM 25,034.1 1/100 A-1 Dam:55MCM+NRB:30MCM 59,866.0 A-2-1 Dam:80MCM 63,074.9 A-3 Dam:55MCM+RB:20MCM 66,110.7 A-2-2 Dam:80MCM* 66,742.1 O-1 Dam:65MCM+NRB:30MCM 59,694.5 O-2 Dam:90MCM 62,772.4 B-1 Dam:55MCM+RB:35MCM 61,479.3 B-2-1 Dam:90MCM* 65,064.5 B-3 Dam:65MCM+RB:20MCM 65,808.3 B-2-2 Dam:90MCM* 66,439.6 Note) NRB: Natural Retarding Basin, RB: Retarding Basin, *After Dam, RB will be demolished.
Final Report 4-71
The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila
Table 4.40 Project Cost before Conversion unit: million peso Direct Physical Price Compensatio Engineering Administratio construction contingency contingency Total Section Contents n cost service cost n cost Remarks cost cost cost
a b c=a*16% d=(a+b)*3.5% e=a*5% f=Σ(a～e)*10% g=Σ(a～f) 1,300m3/s 965.0 0.0 154.4 33.8 48.3 120.2 1,321.7 2011 Pasig River 1,400m3/s 1,930.0 0.0 308.8 67.6 96.5 240.3 2,643.2 2011 Pasig River Phase2 Phase2 2,834.8 10.2 346.9 100.5 159.6 345.2 3,797.2 2010 Lower Marikina River Phase3 2,022.8 7.2 247.6 71.7 114.0 246.3 2,709.6 2010 MCGS MCGS 2,973.6 3.0 408.6 101.6 169.3 365.6 4,021.7 2011 2,400m3/s 3,252.0 89.0 520.3 116.9 162.6 414.1 4,554.9 2011 Manggahan Floodway 2,600m3/s 3,523.0 96.4 563.7 126.7 176.2 448.6 4,934.6 2011 Phase4 2,877.4 15.1 395.5 98.4 164.4 355.1 3,905.9 2010 Upper Marikina River 3,100m3/s 3,075.8 16.1 422.8 105.2 175.7 379.6 4,175.2 2010 NRB 0.0 21,200.0 0.0 742.0 0.0 2,194.2 24,136.2 2011 RB 20MCM 2,792.0 2,000.0 446.7 167.7 139.6 554.6 6,100.6 2011 Upper Upper Marikina RB 8MCM 2,400.0 2,000.0 384.0 154.0 120.0 505.8 5,563.8 2011 River RB 5MCM 1,500.0 1,250.0 240.0 96.3 75.0 316.1 3,477.4 2011 CI 2,900m3/s 1,341.0 31.5 214.6 48.0 67.1 170.2 1,872.4 2011 CI 3,100m3/s 1,433.5 33.6 229.4 51.3 71.7 182.0 2,001.5 2011 90MCM 9,360.0 0.0 1,497.6 327.6 468.0 1,165.3 12,818.5 2011 80MCM 9,000.0 0.0 1,440.0 315.0 450.0 1,120.5 12,325.5 2011 Dam 65MCM 8,520.0 0.0 1,363.2 298.2 426.0 1,060.7 11,668.1 2011 55MCM 8,160.0 0.0 1,305.6 285.6 408.0 1,015.9 11,175.1 2011 Note) NRB: Natural Retarding Basin, RB: Retarding Basin, CI: Channel Improvement Source of item a, b, c, d and e: JICA SF Report, Cost for CI 3,100 m3/s is estimated based on cost for CI 2,900m3/s.
Final Report 4-72
The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila
Table 4.41 Project Cost after Conversion (2012 Price) unit: million peso Direct Physical Price Compensatio Engineering Administratio Section Contents construction contingency contingency Total Remarks n cost service cost n cost cost cost cost 1,300m3/s 993.0 0.0 158.9 34.8 49.7 123.7 1,360.1 Pasig River 1,400m3/s 1,986.0 0.0 317.8 69.6 99.3 247.3 2,720.0 Pasig River Phase2 Phase2 3,033.2 10.9 371.2 107.5 170.8 369.4 4,063.0 Lower Marikina River Phase3 2,164.4 7.7 264.9 76.7 122.0 263.5 2,899.2 MCGS MCGS 3,181.8 3.2 437.2 108.7 181.2 391.2 4,303.3 2,400m3/s 3,346.3 91.6 535.4 120.3 167.3 426.1 4,687.0 Mangahan Floodway 2,600m3/s 3,625.2 99.2 580.0 130.4 181.3 461.6 5,077.7 Phase4 3,078.8 16.2 423.2 105.3 175.9 380.0 4,179.4 Upper Marikina River 3,100m3/s 3,291.1 17.2 452.4 112.6 188.0 406.2 4,467.5 NRB 0.0 21,814.8 0.0 763.5 0.0 2,257.8 24,836.1 RB 20MCM 2,873.0 2,000.0 459.7 172.6 143.6 570.7 6,219.6 Upper Upper Marikina RB 8MCM 2,469.6 2,000.0 395.1 158.5 123.5 520.5 5,667.2 River RB 5MCM 1,543.5 1,250.0 247.0 99.1 77.2 325.3 3,542.1 CI 2,900m3/s 1,379.9 32.4 220.8 49.4 69.0 175.1 1,926.6 CI 3,100m3/s 1,475.1 34.6 236.1 52.8 73.8 187.3 2,059.7 90MCM 9,631.4 0.0 1,541.0 337.1 481.6 1,199.1 13,190.2 80MCM 9,261.0 0.0 1,481.8 324.1 463.1 1,153.0 12,683.0 Dam 65MCM 8,767.1 0.0 1,402.7 306.8 438.4 1,091.5 12,006.5 55MCM 8,396.6 0.0 1,343.5 293.9 419.8 1,045.4 11,499.2 Note) NRB: Natural Retarding Basin, RB: Retarding Basin, CI: Channel Improvement
Final Report 4-73
The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila (11) Project Cost of WB Proposal The project cost of proposed measures by the WB (Alternative-02) is estimated adding engineering service cost, administration cost, physical contingency and Price contingency cost to the direct construction cost and compensation cost estimated by the WB Study. For comparison purpose, the cost for San Juan River improvement is excluded since it was not estimated in the JICA FS. On the other hand, the project costs for Phase II and Phase III project based on the JICA FS are added. The breakdown of project cost in 2011 price and 2012 price are shown in Table 4.43.
Table 4.42(1) Project Cost of WB Proposed Measures (2011 Price) unit: million peso
Direct Physical Price Compensati Engineering Administrati Section Contents construction contingency contingency Total on cost service cost on cost cost cost cost Dredging 4,825.0 - 772.0 168.9 241.3 600.7 6,607.9 Pasig River Phase 2※ 2,948.2 10.6 360.8 104.5 166.0 359.0 3,949.1 Napindan Chanel Heightening of Parapet 98.0 - 15.7 3.4 4.9 12.2 134.2 Lower Marikina Dredging and Heightening 186.0 - 29.8 6.5 9.3 23.2 254.8 River Phase 3※ 2,103.7 7.5 257.5 74.6 118.6 256.2 2,818.1 MCGS ------Mangahan Dredging 3,252.0 89.0 520.3 116.9 162.6 414.1 4,554.9 Floodway Upper Marikina Dyke and Excavation 5,601.0 4,309.0 896.2 346.9 280.1 1,143.3 12,576.5 River Upper Upper Dyke and Excavation 1,341.0 31,521.0 214.6 1,150.2 67.1 3,429.4 37,723.3 Marikina River Dam H=72m 8,626.0 - 1,380.2 301.9 431.3 1,073.9 11,813.3
Total 28,980.9 35,937.1 4,447.1 2,273.8 1,481.2 7,312.0 80,432.1 ※JICA FS Cost converted to 2011 Price
Table 4.43(2) Project Cost of WB Proposed Measures (2012 Price) 2012 価格 unit:million peso
Direct Engineeri Physical Price Compens Administr Section Contents constructi ng service contingen contingen Total ation cost ation cost on cost cost cy cost cy cost Dredging 4,964.9 - 794.4 173.8 248.2 618.1 6,799.4 Pasig River Phase 2※ 3,033.2 10.9 371.2 107.5 170.8 369.4 4,063.0 Napindan Chanel Heightening of Parapet 100.8 - 16.1 3.5 5.0 12.5 137.9 Lower Marikina Dredging and Heightening 191.4 - 30.6 6.7 9.6 23.8 262.1 River Phase 3※ 2,164.4 7.7 264.9 76.7 122.0 263.5 2,899.2 MCGS ------Mangahan Dredging 3,346.3 91.6 535.4 120.3 167.3 426.1 4,687.0 Floodway Upper Marikina Dyke and Excavation 5,763.4 4,434.0 922.1 356.9 288.2 1,176.5 12,941.1 River Upper Upper Dyke and Excavation 1,379.9 32,435.1 220.8 1,183.5 69.0 3,528.8 38,817.1 Marikina River Dam H=72m 8,876.2 - 1,420.2 310.7 443.8 1,105.1 12,156.0
Total 29,820.5 36,979.3 4,575.7 2,339.6 1,523.9 7,523.8 82,762.8 Price in 2012, ※JICA FS
(12) Comparison of Project Costs Comparison of proposed project costs between the JICA Study and the WB Study is summarized in Table 4.44.
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The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila Table 4.43 Comparison of Project Cost between JICA Study and WB Study
JICA Study JICA Study Section Contents A-2-1: B-3: WB Study CI + Dam CI + Dam + RB 1,400m3/s 2,720.0 2,720.0 - Pasig River Dredging 1,800m3/s - - 6,799.4 Pasig River Phase2 Phase2 4,063.0 4,063.0 4,063.0 Napindan Chanel Heightening of Parapet - - 137.9 Phase3 2,899.2 2,899.2 2,899.2 Lower Marikina River Dredging and Heightening - - 262.1 MCGS MCGS 4,303.3 4,303.3 - 2,400m3/s - 4,687.0 4,687.0 Mangahan Floodway 2,600m3/s 5,077.7 - - Phase4 - 4,179.4 - Upper Marikina River 3,100m3/s 対応 4,467.5 - - Dyke and Excavation - - 12,941.1
NRB with Future Dyke Heightening 24,801.5 - (3,100m3/s in Channel) NRB with Future RB Development - 22,803.7 (2,900m3/s in Channel + 20MCM in RB) Upper Upper Marikina RB 20MCM - 6,219.6 - River CI 2,900m3/s - 1,926.6 - CI 3,100m3/s 2,059.7 - - Dyke and Excavation - - 38,817.1 Dam 80MCM H=75m 12,683.0 - - Dam Dam 65MCM H=71m - 12,006.5 - Dam H=72m - - 12,156.0
Total 63,074.9 65,808.3 82,762.8
4.5 Investigation of Appropriateness of Measures to Floods The appropriateness of measures to floods is investigated by Economic Evaluation taking into consideration this project forms a part of the public investment in order to reduce floods damage in the Metro Manila.
4.5.1 Economic Cost The market prices of Pasig River Dredging, Pasig River Phase 2, Lower Marikina River, MCGS, Manggahan Floodway, Upper Marikina River, Dam are converted to the economic prices by multiplying the conversion factor shown below. Table 4.45 shows the economic cost for the Target Case. The economic cost descriptions for all cases are shown in Appendix.
The conversion factors of the past investigation (Preparatory Study for Pasig-Marikina River Channel Improvement Project (Phase III), hereinafter, referred to as “Preparatory Study”) are used in this study.
Table 4.44 Conversion Factors Item Conversion Factors 1 Direct Construction Cost 0.79 2 Compensation 0.57 3 Engineering Service 1.19 4 Government Administration 0.97 5 Physical Contingency 0.93
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The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila Table 4.45 Economic Cost of the Target Case (million pesos) Direct Physical Compensation Engineering Administration Alternatives construction cost service cost cost contingency Total cost cost Ｏ 11,695.6 73.9 2,418.0 502.9 760.0 15,450.3 Ａ 12,868.1 78.8 2,694.9 553.6 830.5 17,025.8 Ｂ 13,699.4 807.1 2,901.0 632.8 878.0 18,918.3 Ａ－１ 20,285.9 12,513.2 4,482.7 1,613.0 1,267.0 40,161.8 Ａ－２－１ 22,134.1 12,513.2 4,928.3 1,693.5 1,375.9 42,645.0 Ａ－３ 23,720.9 12,513.2 5,310.7 1,831.7 1,469.2 44,845.7 Ａ－２－２ 24,085.0 12,513.2 5,398.4 1,847.3 1,490.8 45,334.7 Ｏ－１ 20,190.5 12,508.3 4,465.4 1,608.6 1,260.1 40,032.9 Ｏ－２ 21,963.4 12,508.3 4,892.7 1,686.0 1,364.4 42,414.8 Ｂ－１ 21,117.2 12,508.3 4,688.8 1,692.3 1,314.6 41,321.1 Ｂ－２―１ 23,182.8 12,508.3 5,186.6 1,782.1 1,436.2 44,096.0 Ｂ－３ 23,550.3 12,508.3 5,275.2 1,824.0 1,457.8 44,615.5 Ｂ－２－２ 23,914.4 12,508.3 5,362.9 1,839.7 1,479.3 45,104.5
4.5.2 Economic Benefit The benefit in a Flood Prevention Project is the expected amounts of average annual damage reduction prevented by the project based on the difference of damage reduction amount between With Project Case and Without Project Case. To put it concretely, details are given below. (1) Arrangement of the assets in the probable flood area (2) Calculation of the flood damage amounts by each occurrence probability through the flood simulation in Without Project Case (3) Calculation of the expected amounts of average annual damage reduction based on the flood damage amounts both in With Project Case and Without Project Case
Table 4.47 shows the detail of Flood Damage.
Table 4.46 Detail of Flood Damage Division Detail Damage to Residential Buildings Damage to Household Effects Direct Damage Damage to Depreciable Assets of Business Establishments Damage to Inventories of Business Establishments Damage to Agricultural Crops Damage to Infrastructure Loss of Interruption of Business Activities Indirect Damage Emergency Cleaning Cost for Household Emergency Measure for Business Establishments
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The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila (1) Assets in the probable flood area Table 4.47 Assets in the probable flood area Item Quantity Assets（Pesos） Number of Residential Buildings 2,703,072 511,421,308,169 Residential Area (m2) 132,450,550 - Number of Household 2,703,072 - Number of a Household 11,623,212 - Household Effects - 257,873,112,047 Number of Business Establishments 12,480 - (Manufacturing) Depreciable Assets - 74,218,756,576 Stock Inventories - 62,659,009,122 Number of Business Establishments 311,581 - (Retailing) Depreciable Assets - 90,371,391,749 Stock Inventories - 765,461,898,115 Cultivated Land Area (m2) 6,911,629 - Crops - 27,646,515 Note; Each unit value is estimated below by multiplying CPI based on the past investigation (Detailed Engineering Design of Pasig-Marikina River Channel Improvement Project, (hereinafter, referred to as ”Detailed Investigation”). ・Residential Building ：189,200 Pesos/Building ・Household Effects：95,400 Pesos/Household ・Depreciable Assets of Business Establishments (Manufacturing)：5,947,100 Pesos ・Stock Inventories of Business Establishments (Manufacturing)：7,241,400 Pesos ・Depreciable Assets of Business Establishments (Retailing)：201,100 Pesos ・Stock Inventories of Business Establishments (Retailing)：2,456,700 Pesos ・Crops：40,000 Pesos/ha
(2) Flood Damage 1) Direct Damage a) Damage to Residential Buildings The damage to residential buildings in the probable flood area is estimated as follows.
Damage to Residential Building = Assets Amount of Residential Buildings in a unit area x Damage Rate of Residential Buildings in inundation depth
Damage Rate of Residential Buildings in inundation depth is shown below.
Table 4.48 Damage Rate of Residential Buildings in inundation depth Inundation Depth Less than 0.5m 0.5 m～0.99 m 1.0 m～1.99 m 2.0 m～2.99 m 3.0 m and over Damage Rate 0.092 0.119 0.266 0.580 0.834 Source: The Manual of Economical Investigation of Flood Disaster (the Ministry of Land, Infrastructure and Transportation, Japan 2005 April) b) Damage to Household Effects The damage to household effects in the probable flood area is estimated as follows.
Damage to Household Effects = Amounts of Household Effects in a unit area x Damage Rate of Household Assets in inundation depth
Damage Rate of Household Effects in inundation depth is shown below.
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The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila Table 4.49 Damage Rate of Household Assets in inundation depth Inundation Depth Less than 0.5m 0.5 m ～0.99 m 1.0 m ～1.99 m 2.0 m ～2.99 m 3.0 m and over Damage Rate 0.145 0.326 0.508 0.928 0.991 Source: The Manual of Economical Investigation of Flood Disaster (the Ministry of Land, Infrastructure and Transportation, Japan 2005 April) c) Damage to Business Establishments The damage to business establishments in the probable flood area is estimated as follows.
Damage to Depreciable Assets = Amounts of Depreciable Assets in a unit area x Damage Rate of Depreciable Assets in inundation depth Damage to Stock Inventories = Amounts of Stock Inventories in a unit area x Damage Rate of Stock Inventories in inundation depth
Damage Rate of Business Establishments in inundation depth is shown below.
Table 4.50 Damage Rate of Depreciable Assets and Stock Inventories in inundation depth Inundation Depth Less than 0.5 m 0.5 m～0.99 m 1.0 m～1.99 m 2.0 m～2.99 m 3.0 m and over Damage Rate 0.232 0.453 0.789 0.966 0.995 (Depreciable Assets) Damage Rate 0.128 0.267 0.586 0.897 0.982 (Stock Inventories) Source: The Manual of Economical Investigation of Flood Disaster (the Ministry of Land, Infrastructure and Transportation, Japan 2005 April) d) Damage to Agricultural Crops The damage to agricultural crops is estimated as follows.
Damage to Agricultural Crops = Amount of Agricultural Crops in a unit area x Damage Rate of Agricultural Crops in inundation depth Damage Rate of Agricultural Crops in inundation depth is shown below
Table 4.51 Damage Rate of Agricultural Crops in inundation depth Inundation Depth Less than 0.5 m 0.5 m～0.99 m 1.0 m～1.99 m 2.0 m～2.99 m 3.0 m and over Damage Rate 0.67 0.74 0.91 0.91 0.91 (7 days and over) Source: The Manual of Economical Investigation of Flood Disaster (the Ministry of Land, Infrastructure and Transportation, Japan 2005 April), Average Value of Cultivated Field e) Damage to Infrastructure Damage to Infrastructure is 35% of Total Assets Amount in the same way as “Preparatory investigation”.
2) Indirect Damage Indirect Damage is 10% of Total Direct Damage in the same way as “Preparatory Investigation”.
(3) Damage Amount Table 4.53 shows the damage amount, 112,312 million Pesos for 30- probability year flow amount and 182,916 million Pesos for 100-probability year flow amount.
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The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila Table 4.52 Damage Amount by Probability year ITEM Damage Amount （Pesos） 2-probability year 5-probability year 10-probability year 20-probability year 30-probability year 50-probability year 100-probability year Number of Residential Buildings 2,231,905,354 6,553,171,480 8,701,915,032 10,718,881,437 12,338,687,289 15,008,257,030 19,793,054,564 Household Effects 2,231,905,354 6,553,171,480 8,701,915,032 10,718,881,437 12,338,687,289 15,008,257,030 19,793,054,564 Number of Business Establishments (Manufacturing) Depreciable Assets 836,532,676 2,573,997,642 3,371,030,413 4,063,096,629 4,619,283,775 5,690,163,598 7,578,291,351 Stock Inventories 1,018,591,871 3,134,190,871 4,104,686,256 4,947,370,639 5,624,603,845 6,928,545,119 9,227,596,473 Number of Business Establishments (Retailing) Depreciable Assets 557,744,554 1,716,171,057 2,247,579,691 2,709,003,583 3,079,832,315 3,507,274,298 5,052,702,482 Stock Inventories 6,813,580,532 20,965,278,148 27,457,130,920 33,094,028,355 37,624,187,210 46,346,531,390 61,725,381,341 Crops 2,008,619 3,832,554 4,709,093 5,181,819 5,397,013 5,570,595 5,810,989 Sub Total 13,692,268,958 41,499,813,231 54,588,966,438 66,256,443,899 75,630,678,734 92,494,599,059 123,175,891,764 Infrastructure 4,792,294,135 14,524,934,631 19,106,138,253 23,189,755,365 26,470,737,557 32,373,109,671 43,111,562,117 Indirect Damage 1,848,456,309 5,602,474,786 7,369,510,469 8,944,619,926 10,210,141,629 12,486,770,873 16,628,745,388 Total 20,333,019,403 61,627,222,649 81,064,615,160 98,390,819,190 112,311,557,920 137,354,479,602 182,916,199,270
(4) (4) Expected Amount of Average Annual Damage Reduction Consequently the expected amount of average annual damage reduction can be estimated about 25,671 thousand Pesos for 30-probability year flow amount and 28,937 thousand Pesos for 100-probability year flow amount as shown below, which is calculated by multiplying the amount of average annual damage corresponding to probable flood with occurrence probability and by accumulating the annual damage of each probable flood.
Table 4.53 Expected Amount of Average Annual Damage Reduction (30-probability year flow amount) 1,000 Pesos Damage Amount Expected Average Annual Sectional Amount of Amount of Size of Flow ③ Sectional Exceedance ① ② Damage Average Average Average Annual (m3/s) probability Probability Without Project With Project Reduction (① Damage Annual Damage Damage -②） Reduction 1,620 1/2 20,333,019 0 20,333,019 40,980,121 0.300 12,294,036 12,294,036 2,290 1/5 61,627,223 0 61,627,223 71,345,919 0.100 7,134,592 19,428,628 2,670 1/10 81,064,615 0 81,064,615
2,860 1/20 98,390,819 0 98,390,819 89,727,717 0.050 4,486,386 23,915,014
3,030 1/30 112,311,558 0 112,311,558 105,351,189 0.017 1,755,853 25,670,867
Table 4.54 Expected Amount of Average Annual Damage Reduction (100-probability year flow amount) 1000 Pesos Damage Amount Expected Average Annual Sectional Amount of Amount of Size of Flow ③ Sectional 3 Exceedance ① ② Damage Average Average Average Annual (m /s) probability Probability Without Project With Project Reduction (① Damage Annual Damage Damage -②） Reduction 1/2 20,333,019 0 20,333,019 40,980,121 0.300 12,294,036 12,294,036
1/5 61,627,223 0 61,627,223
71,345,919 0.100 7,134,592 19,428,628 1/10 81,064,615 0 81,064,615
1/20 98,390,819 0 98,390,819 89,727,717 0.050 4,486,386 23,915,014
1/30 112,311,558 0 112,311,558 105,351,189 0.017 1,755,853 25,670,867
1/50 137,354,480 0 137,354,480 124,833,019 0.013 1,664,440 27,335,307
1/100 182,916,199 0 182,916,199 160,135,339 0.010 1,601,353 28,936,661
The map of areas likely to be inundated by probability year are shown in Figures below.
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The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila
Figure 4.63 Map of areas likely to be inundated by probability year（1/2、1/5）
Figure 4.64 Map of areas likely to be inundated by probability year（1/10、1/20）
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The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila
Figure 4.65 Map of areas likely to be inundated by probability year（1/30、1/50）
Figure 4.66 Map of areas likely to be inundated by probability year（1/100）
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The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila 4.5.3 Economic Evaluation The economic evaluation for 13 cases (3-case under 30-year return period and 10-case of 100-year return period) shown in Table 4.56 is carried out by utilizing both the abovementioned economic cost and benefit. 13 cases are confirmed to be expected on a economic benefits as a result of high cost-effectiveness as organized into the Table4.57. Economic Internal Rate of Return (EIRR) Although there is a discrepancy between cases that 3-case under 30-year return period shows over 25% of EIRR and 10-case of 100-year return period shows 17% of EIRR range, all cases have a high cost-effectiveness because of the value far above 15% of EIRR. Net Present Value (NPV) All cases have a high cost effect judging from that the benefit exceeds the economic cost greatly, yet there is a discrepancy between 3-case under 30-year return period with over 40,000 Million Pesos of NPV and 10-case of 100-year return period with the range between 8,000 Million Pesos and 11,000 Million Pesos of NPV in a manner similar to EIRR. Benefit Cost Ratio (B/C Ratio) A similar relation holds for B/C Ratio. Although there is a discrepancy 3-case under 30-year return period showing over 3 of the B/C Ratio and 10-case of 100-year return period showing the B/C Ration raging between 1.3 and 1.5, all cases have a high cost-effectiveness because of the value far above 1 of B/C Ratio.
The case showing highest value for EIRR and B/C among 13 cases is the case ① (Phase IV Component Buildup Plan). As concerns NPV, the case ② (Alternative Plan A)) comes first. From this, meanwhile 3-case under 30-year return period indicates high evaluation, there is no big difference between 10-case of 100-year return period.
The cash flows for all cases are shown in Appendix.
Table 4.55 Investigation Cases Economic Internal Benefit Cost Return Net Present Value Case Alternative Rate of Return Ratio Period (NPV) (EIRR) (B/C Ratio) 1/30 ① Alternative Plan O* 63.50% 91,769 Million Pesos 8.1 ② Alternative Plan A 62.60% 98,136 Million Pesos 7.9 ③ Alternative Plan B 28.00% 40,868 Million Pesos 3.7 1/100 ④ Alternative Plan (A-1) 17.60% 10,973 Million Pesos 1.4 ⑤ Alternative Plan (A-2-1) 17.30% 9,854 Million Pesos 1.4 ⑥ Alternative Plan (A-3) 17.00% 8,689 Million Pesos 1.3 ⑦ Alternative Plan (A-2-2) 17.00% 8,542 Million Pesos 1.3 ⑧ Alternative Plan (O-1) 17.70% 11,259 Million Pesos 1.5 ⑨ Alternative Plan (O-2) 17.40% 10,189 Million Pesos 1.4 ⑩ Alternative Plan (B-1) 17.50% 10,591 Million Pesos 1.4 ⑪ Alternative Plan (B-2-1) 17.20% 9,369 Million Pesos 1.4 ⑫ Alternative Plan (B-3) 17.10% 9,024 Million Pesos 1.3 ⑬ Alternative Plan (B-2-2) 17.10% 8,877 Million Pesos 1.3 * : Design Flood Discharge of 2,900m3/s is reevaluated as 1/20 years flood as previously mentioned.
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The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila
4.6 Comparison of Study Contents and Results with Previous Studies The contents and results are compared with the previous studies as summarized in Table 4.60. Table 4.60 Comparison of JICA Preparatory Study, WB Study and Data Collection Survey (This Study) Item JICA Preparatory Study WB Study Data Collection Survey (THIS STUDY) Design Objective Important item for estimation of peak discharge and scale of storage facility (capacity) Hyetograph Applied Middle-peak Fictional Hyetograph Type 1: Typhoon Ondoy Type Observed 7 Hyetographs + Middle-peak Fictional Hyetograph Hyetograph based on probable rainfall intensities by Observed Hyetograph Hyetograph rainfall durations of Port Area Type 2: Middle-peak Fictional Hyetograph Hyetograph based on probable rainfall intensities by rainfall durations of Port Area
Evaluation JICA Preparatory Study applied same method as JICA Master Plan in1990. WB Study analyzed Typhoon Ondoy Type and Middle-peak Fictional Type and applied Typhoon Ondoy Type. It is necessary to analyze various hyetographs since it is uncertain that which hyetograph with enlargement to probable rainfall causes the largest peak discharge. In this Study, another 6 hyetographs beside Typhoon Ondoy Type and Middle-peak Fictional Type is analyzed and concluded that peak discharge and necessary capacity of storage facility becomes maximum when Typhoon Onody Type is applied.
Estimation of Objective Important Item to estimate probable rainfall, peak discharge and scale of storage facility (capacity) consequently Basin Average Rainfall Estimation Rainfall at Port Area x Rainfall Adjustment Coefficient Type 1: Typhoon Ondoy Type Adjusted by Thiessen Method and IDW Method based on Method of Estimated as uniform rainfall in whole area Thiessen Method and Adjustment by IDW Method observed rainfall Basin Estimated each 34 Thiessen Polygon Average Type 2: Middle-peak Fictional Hyetograph Rainfall IDW Method Estimated for 3 Sub-basins
Evaluation JICA Preparatory Study applied same method as JICA Master Plan in1990. 1990 Master Plan did not consider spatial variation due to lack of data. In WB Study, methods to analyze spatial and time variation were applied based on recent data. Spatial variation shall be considered to estimate basin average rainfall accurately. Thus, in this Study, methods to analyze spatial and time variation are applied based on data after 1994.
Design Rainfall Objective Item which affect peak discharge and scale of storage facility (capacity), depending on basin characteristics such as basin area, slope, landuse and so on. Duration Applied 2 days rainfall is applied to cover observed rainfall 2 days rainfall is applied to cover observed rainfall Relation between rainfall and water level is analyzed. Design duration of past floods. duration of past floods. Due to its high correlation, 1 day rainfall is applied. Rainfall Duration
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The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila
Item JICA Preparatory Study WB Study Data Collection Survey (THIS STUDY) Evaluation Both JICA Study and WB Study applied 2 days rainfall to cover the observed rainfall durations. However, precipitation until flood concentration time is the most important in runoff analysis. Thus, correlations of 1 day rainfall and 2 days rainfall with water level are examined and it is found that correlation of 1 day rainfall is much higher than 2 days rainfall. Since it does not effect to runoff analysis that 1 day rainfall does not cover observed rainfall, it is appropriate to apply 1 day rainfall.
Basin Average Objective Important to estimate runoff discharge for each probable year. Probable Applied Whole Basin (2 days) Type 1: Typhoon Ondoy Type Whole Basin (1 day) Rainfall Basin ・30 years 392.3mm Observed 2 days rainfall x Enlargement Ratio ・30 years 232.4mm Average ・100 years 445.8mm Estimated each 34 Thiessen Polygon ・100 years 285.5mm Probable 3 Sub-basin Average Rainfall (Trial by WB Study) Rainfall Return Probable 2 days Rainfall Period SB-01 SB-02 SB-31 30 368 369 390 100 439 444 468 Type 2: Middle-peak Fictional Hyetograph Estimated for 3 Sub-basins Return Probable 2 days Rainfall Period SB-01 SB-02 SB-31 30 368 366 382 100 438 441 458 Evaluation 2 days basin average probable rainfall was estimated both by JICA and WB Studies. In this Study, 1 day basin probable rainfall is estimated. In this Study, typhoon type rainfall and monsoon type rainfall are analyzed separately, because these typhoon and monsoon are different phenomena and it is uncertain which phenomena causes larger floods. As a result of analysis, typhoon type rainfall causes larger probable rainfall. It is said that accuracy of probable analysis is improved by analyzing rainfall with causes. Flood Discharge Objective Discharge at Sto.Nino is important to calibrate model constants which is the key of accuracy of runoff model. at St.Nino Since it is difficult of continuous observation of discharge directory, H-Q equation to convert from water level to discharge is applied. Applied Annual highest water level in 1958-77, 1986, and Annual highest water level in 1958-77, 1986, and Annual highest water level in 1958-77, 1986, and 1994-2009 Estimation 1994-2009 were converted to discharge. 1994-2009 were converted to discharge. were converted to discharge. of Flood H-Q Equation: H-Q Equation: H-Q Equation: Discharge ・Q = 32.03 ×( H-10.80)2 H < 17.0 ・Q = 31.44 ×( H-10.96)2 H > 13.0 ・Q = 32.03 ×( H-10.80)2 H < 14.0 ・Q = 17.49 × (H-8.61)2 H > 17.0 ・Q = 25.65 × (H-10.46)2 H > 14.0 H-Q equation was made based on observed discharge H-Q equation was made based on observed discharge and H-Q equation was made based on observed discharge and and water level data in 1958-77 and 1986. water level data in 1958-77 and 1986, and estimated water level data in 1958-77 and 1986, and estimated discharge by uniform flow and observed water level in discharge by non-uniform flow and observed water level in 1994-2009. 1994-2009.
Max. discharge of Typhoon Ondoy (2009) Max. discharge of Typhoon Ondoy (2009) Max. discharge of Typhoon Ondoy (2009) ・3,211m3/sec ・3,950m3/sec ・3,480m3/sec Evaluation H-Q equation by JICA Study was based on observed data, however, observed data during flood was sparse and accuracy in high water level is uncertain. H-Q equation by WB Study was based on observed and estimated data, however, accuracy of estimated discharge is low since energy gradient and roughness coefficient applied for
Final Report 4-84
The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila
Item JICA Preparatory Study WB Study Data Collection Survey (THIS STUDY) estimation is not proper. In this Study, non-uniform flow calculation is applied to estimate H-Q equation in high water level so that accuracy in high water level is improved. Applying the H-Q equation estimated in this Study, peak discharge at Sto.Nino of Ondoy Typhoon is estimated as 3,500m3/s. Since accuracy of H-Q equation is improved, accuracy of estimated discharge is also improved. Runoff Analysis Objective It is the analysis to convert rainfall to discharge, and accuracy of analysis effect peak discharge and scale of storage facility. Runoff Rainfall-Runoff Model Integrated Analysis Model of Basin, River and Flood Integrated Analysis model of basin, river course and flood Analysis Storage Function Method: Mountainous Area Plains plain. Method Quasilinier Storage Type: Urbanized Area Basin: Rainfall-Runoff Model (SCS Unit Basin: Rainfall-Runoff Model (WEB-DHM Model) Hydrograph Method) River Course: One-dimensional Non-uniform Flow River: One-dimensional Unsteady Flow Model Model Flood Plain: Two-dimensional Unsteady Flow Model Flood Plain: Two-dimensional Unsteady Flow Analysis Model
Calibration and Verification of Model Parameters Calibration and Verification of Model Parameters Calibration and Verification of Model Parameters 2 floods in 2004 was reproduced. Flood by Ondoy Typhoon was reproduced. Flood by Ondoy Typhoon was reproduced. Model parameters were calibrated to conform Model parameters were calibrated to conform Model parameters were calibrated to conform calculated hydrograph to observed discharge. calculated hydrograph to observed peak discharge calculated hydrograph to observed hydrograph as well Parameters for Storage Function Method (delay and water level. as peak discharge and water level. factors) were determined based on previous Model was verified by reproducing 2004 flood and Model was verified by reproducing 2004 flood and model. 1998 flood. 2012 flood.
Evaluation JICA Study applied lumped system model so that spatial variation of rainfall could not reproduced well. WB Study also applied lumped system model. To reproduce spatial variation, river basin was segmentalized into small sub-basins, however, it could not reproduce well. This Study applies distributed system model which can reproduce spatial variation of rainfall. This model can also analyze long term runoff so that it can reproduce soil and river course conditions before flood. In WB Study, peak discharge and water level were conformed in the calibration of model. On the other hand, calibration of model in this Study is conducted to conform calculated hydrograph to observed hydrograph as well as peak discharge and water level. Considering model characteristics and calibration method, flood analysis model in this Study is appropriate comparing previous studies. Water Level in Objective Water level in Laguna Lake effect discharge of Manggahan Floodway and water level of Marikina River upstream of Manggahan Floodway. Laguna Lake Applied Average Water Level during Flood: 12.2m Observed Water Level during Ondoy Typhoon: Past Highest Water Level after Manggahan Floodway Water Level 12.78-13.85m Constructed: 13.90m in Laguna Lake Evaluation JICA Study applied average water level during flood which is less than observed water level during Ondoy Typhoon. WB Study applied observed water level during Typhoon Ondoy, however, water level in Laguna Lake at the moment of peak water level of Marikina River is less than peak water level. In this Study, past maximum water level is applied since there is a case that peak water level in Laguna Lake occur prior to peak water level in the river, and water level in Laguna Lake does not decline in short time once rise.
Final Report 4-85
The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila
Item JICA Preparatory Study WB Study Data Collection Survey (THIS STUDY) Water level in Laguna Lake effect discharge of Manggahan Floodway and it is necessary that planned diversion discharge is maintained after peak water level in Laguna Lake. Diversion volume to Manggahan Floodway is quite important to flood control plan of Pasig-Marikina River. Considering safety of flood control plan, the applied water level in this Study is appropriate.
Inundation Objective It is important for evaluation of planned flood control facilities. Analysis Applied Inundation Analysis Model Integrated Analysis Model of Basin, River and Flood Integrated Analysis model of basin, river course and flood Inundation River: One-dimensional Unsteady Flow Model Plains plain. Analysis Flood Plain: Two-dimensional Unsteady Flow Flood by Typhoon Ondoy was reproduced. Flood by Typhoon Ondoy was reproduced. Model Simulation results were well conformed with Simulation results were well conformed with inundation Flood by Typhoon Ondoy was reproduced. inundation map based on flood damage survey. map based on flood damage survey. Simulation results were well conformed with interview survey results.
Evaluation Not so much difference among the studies. Basic Design Without Probable Discharge at Sto.Nino (Not analyzed) Probable Discharge at Sto.Nino Discharge Inundation ・30 years 2,740 m3/sec ・30 years 3,990 m3/sec ・100 years 3,210 m3/sec ・100 years 4,980 m3/sec
With (Not analyzed) Probable Discharge at Sto.Nino ・30 years 3,030 m3/sec Inundation ・30 years 3,600 m3/sec ・100 years 3,580 m3/sec ・100 years 4,100 m3/sec
Large scale inundation at left side between confluence of Nangka River and Rosario Weir by dyke break
Flood Discharge 30 years Previous discharge allocation is applied. (None) The following counter measure are recommended. AllocationDesig Countermeasures against 30 year probable flood: Countermeasures against 30 year probable flood: n ・River Improvement Alternative-A; ・MCGS (Not implemented in Phase III) ・River Improvement ・MCGS ・Improvement of Manggahan Floodway Alternative-B; ・River Improvement ・MCGS ・Construction of Retarding Basin 30 years probable discharge (with MCGS) 30 years probable discharge (with MCGS) unit: Q(m3/s) Section Q(m3/s) Section Alt-A Alt-B Wawa 1,590 Wawa 2,720 2,720
Final Report 4-86
The Republic of the Philippines Data Collection Survey on Flood Management in Metro Manila
Item JICA Preparatory Study WB Study Data Collection Survey (THIS STUDY) Rodoriges Bridge 2,110 Montalban Bridge 3,560 3,560 Before Nangka River 2,420 (Retarding Basin) St. Nino 2,900 St. Nino 3,100 2,900 Mangahan Floodway 2,400 Mangahan Floodway 2,600 2,400 Lower Marikina River 500 Lower Marikina River 500 500 Napindan Channel 0 Napindan Channel 0 0 Pasig River 605 Pasig River 600 600 SanJuan River 700 SanJuan River 700 700
Pasig River – Manila Bay 1,200 Pasig River – Manila Bay 1,300 1,300
100 years (None) Alternative 2 including the following measures is Alternative A-2-1 and B-3 are shown in below. recommended. Countermeasures against 100 year probable flood: Countermeasures against 100 year probable flood: Alernative-A-2-1; ・River Improvement ・River Improvement ・Marikina Dam ・MCGS ・Retarding Basin ・Improvement of Manggahan Floodway ・Non-structural Measures ・Marikina Dam Alernative-B-3; ・River Improvement ・MCGS ・Marikina Dam ・Retarding Basin 100 years probable discharge (without MCGS) 100 years probable discharge (with MCGS) unit:(m3/s) Section Q(m3/s) Section A-2-1 B-3 Wawa 3,600 Wawa 3,230 3,230 Marikina Dam 900 Marikina Dam 1.260 1.260 Montalban Bridge 2,400 Montalban Bridge 2,140 2,500 (Retarding Basin) (Retarding Basin) St. Nino 2,900 St. Nino 3,100 2,900 Mangahan Floodway 2,000 Mangahan Floodway 2,400 2,400 Lower Marikina River 1,000 Lower Marikina River 500 500
Napindan Channel 600 Napindan Channel 0 0
Pasig River 850 Pasig River 600 600
SanJuan River 1,000 SanJuan River 780 780
Pasig River – Manila Bay 1,800 Pasig River – Manila Bay 1,400 1,400
Final Report 4-87