Japan International Cooperation
Agency (JICA)

Department of Public Works andHighways (DPWH)
Davao City Local Government Unit

Davao River Flood Control Master Plan
Structural and Non-Structural
Mitigation Measures
JERRY A. FANO

Project Manager
Flood Control Management Cluster
Department of Public Works and Highways
21 September 20221

Flood in Davao River during Nov. 9 to 10, 2021

5 year flood w/o Measures≒ 5 year flood ?

2Outline of the Project

Target Area
River BasinArea (km2)

Davao River

1,750.8

Talomo River

268.2

Matina River

71.2

Source: JICA Project Team Based on SRTM30
Calculated by GIS

Source: JICA Project Team Based on SRTM30

3Outline of the Project

Overall Project Schedule
Nov.
2018
Period of the Project
4 years
including preparation of F/RAug.
2019
Stage 1
Basic Study
10 months

We are here!

Jan2021
Stage 2Master Plan Study
17 months

July
2022
Final Reportwill beprepared in
Nov. 2022 orJan. 2023

Stage 3
Feasibility Study
18 months

TWG and Steering
Committee for DFR: October, 2022

Target of each Plan Flood control for Davao River, Matina River andTalomo River basin
 Drainage in Davao City, and Coastal flood due to Storm Surge including
coastal disaster such as coastal erosion

Expected Goals

1.Goal of the Proposed Plan
The Master Plan and the results of Feasibility Study will be approved by GOP.
2. Goal which will be attained by utilizing the Proposed Plan
Flood damage in Davao City will be mitigated.

Only Flood Controlfor Davao River

4

Approach and Contentsof the Master Plan (M/P)

Approach to Master Plan Target Year for M/P2045

 Climate Change Adaptation in Planning and Design for Flood Control Structures“Incorporating into Present Design”: the design of the structure is upgraded toaccount for climate change estimates now, is applied.
• Rainfall: the probable rainfall for annual maximum daily rainfall increases by 10%
from the climate condition in 2019.
• Mean sea level: to be 0.2m higher than the level in 2000, and 0.1m higher than thelevel in 2019.
 Target Design Level for M/PFlood Type
Flood in 3 rivers【Riverine flood】

Design Level

Davao River

100-year floodMatina River

100-year flood

Talomo River

100-year flood

Inland flood in the city【Inland flood】

for Main Drainage Channel: 25-year flood

Coastal conservation and storm surge
measures【Coastal flood】

100 year (corresponding to “Urban Areas” of DGCS)5

Proposed Structural Measures against
Riverine Flood for the Davao River
Combination ofRiver Widening

Measures

MeritDemeritRiverWidening Can minimize
flood risk bylowering Flood
Water Level
 No risk ofserious
damage bydike collapse Resettlementof theaffectedpeople along
river bank isnecessary

RetardingPonds

 Can reduce Large land
flood volume
acquisition isof downstream
necessary insection
upstream May utilize arearural area
for anotherpurpose atnormal time&Before

Retarding Ponds
Normal Time
NormalTime

After

DuringFlood
Flood
DuringOverflowing dikewhen river water level rising

Retarding
Pond
Retarding pond

RetardingPond

M/P for Davao River

Location Map of Proposed Structural Measures for the Davao
No.4
RiverMid-Long term:
No.5
Retarding Ponds
397ha

No.6
No.723km
Lacson Bridge

Short term:
Retarding Ponds
200ha

No.1
N0.2
No.3

Control Point

Waan Bridge
1,705km2
14km
River
1.5km mouth
1,751km2

By Short-teammeasures

Mid-Long term:
Widening
Short term: Riverbed Dredging

M/P for Davao RiverM/P for Davao River

River Widening (& cut-off) Works in the downstream of Davao River (1.5km-14km)
14km(L)14.0-13.2km(R)13.4-10.0km

Cut-off works(L)10.0-9.2km(R)9.2-6.6km(L)6.6-5.8km(R)6.4-4.4km(L)4.7-3.5km(L)3.5-2.3km

About 1,320 buildings
will be affected by riverwidening works asestimation at M/P stage
1.5km

River Widening/Cut-Off Area
L : Left BankR : Right Bank

(R)3.7-3.2km(R)2.6-1.3km
8Riverine Flood Control Master Planin Davao River (Structural Measures)
Implementation Period(Target Year)
Design Level
Design Discharge
Target AreaMeasures

Project Cost (Financial /Economic Cost)
Economic Evaluation(EIRR)
Economic Evaluation(ENPV) (Discount rate: 10%)
Economic Evaluation(B/C) (Discount rate: 10%)

Short-Term Measures2023-2032(2032)

M/P for Davao River

Mid-Long Term Measures2033-2045(2045)

5-10 year scale flood
100 year scale flood
1,500m3/s
3,400m3/s
From river mouth to 23km
ditto
・Dredging from river mouth to 23km ・River widening (from Bolton
・Cut-off works (a part of river
bridge to 14km)
・Installation of four retardingwidening works)
・Installation of three retarding pondsponds$ 1.017 B/ $ 945 M$ 334 M/ $ 310 M(including short-term measures)
16.50%
16.10%(including short-term measures)$ 197 M$ 244 M
(including short-term measures)
2.128
1.833
9
(including short-term measures)Target Structural Measures in F/S Stage

23km

Retarding Pond
RP 08 (ANAB: 0 (IFB: 0%))-700m3/s（Excavation
RP 09 (ANAB: 0 (IFB: 0%))volume 12.2 MCM）
RP 11 (ANAB: 1 (IFB: 0%))
(ANAB: 1 (IFB: 0%)) 200ha

Priority Projects for F/Sand Actitity in F/S

ANAB: Assumed Number of Affected Buildings
IFB: InFormal BuildingControl Point

Waan Bridge
1,705km2
14km4kmRiver
1.5km mouth
1,751km2

Widening+900m3/s

Cut Off Works(ANAB: 40-90 (IFB: --%))

Riverbed Dredging +200m3/s（Exca.Vol. 1.3MCM）（→ Minimum Flood Capacity 800m3/s）(ANAB: 0)

Impacts by Priority
Projects for F/S

Impacts by Target Priority Projects for F/S

11

Impact against floods by F/S Target Structural Measures 5yr Scale
Inundation Maps with/without Target Measures for F/S“Reference”
Q (m3/s) *FloodScale

Design Q (m3/s)
With Climate
Change Condition

3 yr

1,100852

5 yr

1,4001,118

10 yr

1,850

1,492

25 yr

2,500

2,020

50 yr

3,000

2,418

100 yr

3,400

2,817

Impacts by Priority
Projects for F/SFloodWithoutClimate
ChangeCondition

5 year without Measures

125 year with All Measures

Comparison of Impact against floods
by Combination of Target Structural Measures of F/SInundation Maps with/without Target Measures

All Three measure of1) Dredging
2) Cut-off Works
3) Retarding Ponds

Name ofBarangay

Waan
TigattoMaa
19
8Bucana
OtherTotal

In Present Condition

With Projects

5yr Scale
Flood

Inundation
Inundation Reduced
Area in
Area withArea ofPresentProjects
Inundation
Condition(B)(C =A-B)
(A)
(ha)
(ha)
(ha)
63.6
1.6
61.9
171.0
1.7
169.4
91.8
1.2
90.6
48.4
0.6
47.8
46.6
0.9
45.7
53.1
22.5
30.6
6.2
1.7
4.5
480.6
30.2
450.4

- Inundation area is simulated inundationarea
13with more than 0.1m inundation depth.

Comparison of Impact against floods
by Combination of Target Structural Measures of F/SInundation Maps with/without Target Measures

5yr ScaleFloodAll Three measure of1) Dredging
2) Cut-off Works
3) Retarding Ponds
Estimated Number Estimated Number
Reduced Number ofName ofof Affectedof Affected
Affected Buildings /Barangay Buildings / People Buildings / People
Peoplein Present Condition
with Projects

In Present Condition(without Measures)With Projects(with Target Measures)

Waan
TigattoMaa
19
8
Bucana
Other
Total

146 /
1,771 /
2,804 /
445 /
1,874 /
3,131 /
672 /
10,843 /584
7,084
11,216
1,780
7,496
12,524
2,688
43,372

2 /
1 /
24 /
2 /
26 /
1,198 /
140 /
1,393 /

8496
8
104
4,792
560
5,572

144 /
1,770 /
2,780 /
443 /
1,848 /
1,933 /
532 /
9,450 /

576
7,080
11,120
1,772
7,392
7,732
2,128
37,800- Affected buildings were identified based on building data (GISdata) and simulated inundation area with more than 0.1m
inundation depth.
- Number of affected people is estimated using the assumption
14
of 4 persons in 1 building.

15