Lecture 6 - Flood Control

Question 1

is the result of runoff from rainfall in quantities to great to be conveyed or confined in the low-water channels of streams.

Answer 1

flood

Question 2

Disaster risk is a complex interplay of several factors…

Answer 2

Hazard (strength, frequency)

Population (exposed population density)

Vulnerability (structural, physical, socio-economic profile)

Question 3

Commonly Accepted Methods for Reducing Floods

Answer 3

Reduction of peak flow by reservoirs

Confinement of the flow within a predetermined channel by levees, flood walls, or a closed conduit

Reduction of peak stage by increased velocities resulting from channel improvement

Diversion of floodwaters through a flood bypass, which may return the water to the same channel at a point downstream or deliver it to another channel or different watershed

Floodproofing of specific properties

Reduction of flood runoff by land management

Temporary evacuation of flood threatened areas on the basis of flood warnings

Flood plain management

Question 4

is the normally dry land area adjoining rivers, streams, lakes, bays, or oceans that is inundated during flood events.

Answer 4

floodplain

Question 5

can be defined as natural geologic features or from a regulatory perspective.

Answer 5

Floodplains

Question 6

Hydrologic and hydraulic analyses of floods are:

Answer 6

a. Floodplain information studies
b. Evaluation of future land-use alternatives
c. Evaluation of flood-loss reduction measures
d. Design studies
e. Operation studies

Question 7

Hydrologic analysis entails:

Answer 7

rainfall-runoff analysis or a flood-flow frequency analysis

Question 8

Hydraulic analysis involves the determination of water-surface elevations using

Answer 8

steady or non-steady state

Question 9

Effective Flood Control Operating System (EFCOS)

Answer 9

Aims to achieve an effective flood control operation for Pasig-Marikina- Laguna Lake Complex through Real time rainfall and water level data collection at the Rosario Master Control Station via telemetry system; The effective use of the warning system along Mangahan Floodway; and The multiplex communication system among Rosario MCS, Napindan HCS, DPWH Central Office and PAGASA Data Information Center.
Water

Question 10

The flood-prone area in Metro Manila

Answer 10

a) Coastal lowlands alongside Manila Bay
b) Marikina flood plain
c) Laguna Lake plain
d) Valley plains cutting through the central plateau

Question 11

Pressing Flood Hazard Issues in Metro Manila

Answer 11

1. Watershed Deforestation
2. Watershed Land-use change
3. Improper and unregulated land-use and urban planning
4. Inefficient flood control infrastructure system
5. Lack of flood early warning system
6. Lack of maintenance of rivers and drains
7. Impact of global environmental change
8. Fragmented institutional flood management arrangements

Question 12

is the operation of an overall program of corrective and preventive measures for reducing flood damage

Answer 12

Floodplain management

Question 13

Flood Protection in Urban Flooding

Answer 13

a. Increase bankfull capacity
• Modification of channels and banks 
• Artificial channel linings 
• Flood relief channels 
b. Decrease flood peaks and increase flood flow duration 
• Upstream water flow regulation 
• Upstream sediment flow regulation 
• Spreading ground through floodways 
c. Increase channel gradient 
• Straightening of sinuous rivers

Question 14

Flood abatement in Urban Flooding

Answer 14

a. Upstream afforestation or reforestation
b. Flood control effective farming practices
c. Comprehensive forest and vegetation protection programs

Question 15

Countermeasures to flooding

Answer 15

Behavioral Adaptation

a. Monitoring and prediction
b. Floodplain zoning
c. Flood proofing
d. Public relief funds
e. Flood insurance

Question 16

Two types of floodplain inundation maps

Answer 16

flood-prone area and flood-hazard maps.

Question 17

One aspect of floodplain management

Answer 17

balancing the economic gain from floodplain development against the resulting increase in flood hazard.

Question 18

The 100-year flood area can be divided into

Answer 18

floodway and a floodway fringe

Question 19

The objective of flood control

Answer 19

to reduce or alleviate the negative consequences of flooding.

Question 20

Alternative measures that modify the flood runoff are referred to

Answer 20

structural measures

Question 21

modify the damage susceptibility of floodplains are referred to

Answer 21

non-structural measures

Question 22

The basic functional relationships required to assess the value of flood damage reduction alternatives are

Answer 22

stage-damage, stage-discharge, and flood-flow frequency relationships

Question 23

Two types of flood mitigation infrastructures

Answer 23

storage reservoirs and retarding basins

Question 24

Main function of flood mitigation infrastructures

Answer 24

is to store a portion of the flood flow so as to minimize the flood peak at the point to be protected.

Question 25

One criterion for evaluating FMR is the

Answer 25

percentage of the drainage area controlled by total the reservoirs.

Question 26

Site selection should be based on the yield of

Answer 26

highest economic return.

Question 27

A second criterion for evaluating flood-mitigation reservoirs is

Answer 27

storage capacity

Question 28

are necessary in planning reservoir operations for flood mitigation.

Answer 28

Streamflow forecasts

Question 29

The outlet of retarding basins consists of

Answer 29

large spillway or one ungated or more sluiceways

Question 30

The discharge capacity works should the

Answer 30

maximum

of outlet equal flow the D/S ca pacity of channel.

Question 31

The planning of a system of retarding basins must prevent the

Answer 31

synchronization of flows.

Question 32

One of the oldest and widely used methods of protecting land from floodwater is to

Answer 32

erect a barrier preventing overflow.

Question 33

Most levees are

Answer 33

homogenous embankments.

Question 34

Floodwalls are constructed to

Answer 34

withstand hydrostatic pressures

Question 35

The cost of a levee system consists of the

Answer 35

cost of the land for levees and channel plus the cost of levee construction.

Question 36

Two options for levees crossing tributary channels.

Answer 36

a) Carry the levee U/S along the tributaries;

b) Block the channel and create an interior drainage problem

Question 37

The best solution for the problem depends on the

Answer 37

local the topography and stream/coast characteristics.

Question 38

in effect, an artesian spring in the aquifer under the levee, with velocity sufficient to move the foundation material.

Answer 38

sand boil

Question 39

If the possibility of failure is imminent, a ________may be constructed.

Answer 39

setback levee

Question 40

is created by diversion works and topography that permits excess water in a river to be diverted.

Answer 40

flood bypass

Question 41

is considerably more complicated than a simple determination of the amount of flow to be diverted.

Answer 41

hydraulic design of the diversion works for a bypass

Question 42

Admission of water can be through a gap in

Answer 42

levee line, fuseplug levee, spillway section or use of weirs.