11/30/2018

FLOOD- CAPTION THIS:

DAMAGE
MITIGATION

FLOOD DAMAGE
FLOOD DAMAGES: MITIGATION
taking steps to eliminate or reduce the long-term
impacts of flooding
Methods for combatting the effects of excess
water in streams
Flood control

Objective: Reduce flood damage to a minimum consistency with

bearable cost.
"Responding to climate change involves two possible approaches: reducing and
stabilizing the levels of heat‐trapping greenhouse gases in the
atmosphere (“mitigation”) and/or adapting to the climate change already in the
pipeline (“adaptation”).
‐NASA

ACCEPTED MEASURES FOR

WHAT IS FLOOD? REDUCING FLOOD DAMAGE
1. Reduction of Peak Flow by reservoirs
◼ Result of runoff from  2. Confinement of flow within a predetermined
rainfall in high quantities  channel by levees, flood walls, or conduit

to be confined in the  3. Reduction of peak stage by increased velocities

resulting from channel improvement
low‐water channels of 
4. Diversion of Flood waters through bypasses or
streams. floodways
5. Temporary evacuation of the flood plain
Major Floods are impossible to prevent, but the damage it cause to crops
and properties with-in the flood plain can be minimized. 6. Flood proofing of specific properties
7. Reduction of flood runoff by Land Management
8. Flood insurance

1
 11/30/2018

FLOOD MITIGATION JURISDICTION: PRESIDENTIAL DECREE NO. 1152

FLOOD PLAIN
PHILIPPINE ENVIRONMENTAL CODE MANAGEMENT
Flood Plain – formed by sediment deposition or removal,
accompanying intermittent overflows of the stream above its
low-water channel.

FLOOD PLAIN TOOLS OF FLOODPLAIN

MANAGEMENT MANAGEMENT
OBJECTIVE: 1. Flood Hazard Survey

To minimize the cost of flood-plain • Indicates the extent of flooding at various

probability levels
utilization • Provide the basic information for defining
1. Initial cost of Development flood risk

2. Cost of Flood Protection
3. Residual Flood Damage
4. Cost of Relief and Rehabilitation

2
 11/30/2018

TOOLS OF FLOODPLAIN
MANAGEMENT

2. Flood Plain Zoning

• Legal device
through which local
jurisdictions can
restrict occupancy
of the flood plain to
uses which will
suffer little or no
damage during
floods

ACCEPTED MEASURES FOR

TOOLS OF FLOODPLAIN REDUCING FLOOD DAMAGE:
MANAGEMENT 1. FLOOD MITIGATING
3. Flood Proofing
RESERVOIR
• Can be used by individual property owners to Purpose: To Store a portion of flood flow in such a way to
minimize the flood peak at the point to be protected.
protect their property
Usually located upstream from the protected area

Economic factor control the size of reservoir

ACCEPTED MEASURES FOR

REDUCING FLOOD DAMAGE:
1. FLOOD MITIGATING
RESERVOIR
Types of Reservoir (based on outlet works)

1. Storage Reservoir
• Regulated by gates and valves operated on
the basis of the judgment of the project
engineer
2. Retarding Basin
• Have Fixed, ungated outlets which
automatically regulate the outflow in
accordance with the volume of water in the
storage

3
 11/30/2018

ACCEPTED MEASURES FOR ACCEPTED MEASURES FOR

REDUCING FLOOD DAMAGE: REDUCING FLOOD DAMAGE:
2. LEVEES AND FLOOD 2. LEVEES AND FLOOD
WALLS WALLS
Longitudinal dams erected roughly parallel to a river rather than Levees are most frequently used because of low cost of
across material
Levee = Earth dike
Flood wall = Masonry Con: prolonged high water may raise the line of saturation to
the point where seepage through the levee may cause
extensive shallow flooding of the protected land

ACCEPTED MEASURES FOR REDUCING FLOOD ACCEPTED MEASURES FOR REDUCING FLOOD
DAMAGE: DAMAGE:
2. LEVEES AND FLOOD WALLS 2. LEVEES AND FLOOD WALLS
LEVEE CROSS SECTION FAILURE MODES OF
LEVEES

ACCEPTED MEASURES FOR

ACCEPTED MEASURES FOR REDUCING FLOOD REDUCING FLOOD DAMAGE:
DAMAGE:
2. LEVEES AND FLOOD WALLS 2. LEVEES AND FLOOD
FAILURE MODES OF WALLS
LEVEES
Flood Wall

4
 11/30/2018

ACCEPTED MEASURES FOR ACCEPTED MEASURES FOR REDUCING FLOOD DAMAGE:

REDUCING FLOOD DAMAGE: 2. LEVEES AND FLOOD WALLS
2. LEVEES AND FLOOD MANILA BAY FLOOD WALL

WALLS
Flood Wall

ACCEPTED MEASURES FOR

ACCEPTED MEASURES FOR REDUCING FLOOD
REDUCING FLOOD DAMAGE:
DAMAGE:
3. CHANNEL
3. CHANNEL IMPROVEMENT
IMPROVEMENT Various Methods of channel improvement:

1. Increase in size of cross-section

• Caters for a high designed flood without
spilling over the bank is practical for small
streams
• Very expensive for large rivers
• Disposal of excavated material is a problem

2. Realignment of channel along a shorter route

• Practical for small streams with low discharge
3. Increasing velocity of flow in channel
4. Increasing waterway at crossing

ACCEPTED MEASURES FOR ACCEPTED MEASURES FOR REDUCING FLOOD

REDUCING FLOOD DAMAGE: DAMAGE:
4. BYPASSES OR 4. BYPASSES OR FLOODWAYS
FLOODWAYS

provides for the passage of a

specified flood

Between existing levees

5
 11/30/2018

ACCEPTED MEASURES FOR REDUCING FLOOD

DAMAGE:
4. BYPASSES OR FLOODWAYS

ACCEPTED MEASURES FOR REDUCING

FLOOD DAMAGE: FLOOD EVACUATION -
5. EVACUATION AND
PHILIPPINES
FLOOD PROOFING
Emergency Evacuation = one of the most effective means of
flood-damage reduction under certain circumstances. (with
reliable flood forecast)

ACCEPTED MEASURES FOR REDUCING

FLOOD DAMAGE: ACCEPTED MEASURES FOR REDUCING FLOOD DAMAGE:
5. EVACUATION AND 5. EVACUATION AND FLOOD
FLOOD PROOFING PROOFING

6
 11/30/2018

ACCEPTED MEASURES FOR ACCEPTED MEASURES FOR

REDUCING FLOOD DAMAGE: REDUCING FLOOD DAMAGE:
6. LAND MANAGEMENT 6. LAND MANAGEMENT

ACCEPTED MEASURES FOR ACCEPTED MEASURES FOR

REDUCING FLOOD DAMAGE: REDUCING FLOOD DAMAGE:
6. FLOOD INSURANCE 6. FLOOD INSURANCE

ESTIMATING BENEFITS OF
FLOOD MITIGATION PRIMARY BENEFITS
Tangible Benefits 1. Cost of replacing or repairing damaged property
2. Cost of evacuation, relief, and rehabilitation of victims
1. Those arising from prevention of flood and emergency flood-protection measures
damage
3. Losses as a result of disruption of business
2. Land enhancement from more intensive use 4. Loss of crops, or cost of replanting crops
of protected land

Intangible Benefit

1. Prevention of loss of life

2. Reduction of disease resulting from flood

7
 11/30/2018

STEPS IN THE DESIGN STEPS IN THE DESIGN

OF A FLOOD OF A FLOOD
MITIGATION PROJECT MITIGATION PROJECT
1. Determine the project design flood and 4. Design the necessary facilities for each method of
the flood characteristics of the area mitigation in sufficient detail to permit cost estimates
and an analysis of their effect on flood flows
2. Define the areas to be protected, and, on 5. Select the facilities or combination of facilities that offer
the basis of a field survey, determine the the desired protection at minimum cost
flood damages which can be expected at 6. Compare the cost and benefit of the project to
various stages determine whether the project is economically justified
3. Determine the possible methods of flood
protection. If Reservoirs or floodways are
considered feasible, select possible sites
and determine the physical
characteristics of these sites

STEPS IN THE DESIGN

OF A FLOOD
MITIGATION PROJECT
7. Prepare a detailed report setting forth the possibilities
explored, the protection recommended, and the degree
of protection which will be provided