chapter 5: flood management

Question 1

Flood management is important because many people live in flood-prone areas ………………………………………………….. and a lot of investments in towns, plants and infrastructure have been made in such areas

Answer 1

the coast or on floodplains

Question 2

Flood management can aim at

Answer 2

1. a reduced risk of floods;
2. a reduced vulnerability to floods;
3. improved preparedness;
4. streamlined emergency management once a flood damage has occurred; and
5. improved knowledge (about cause-effect relationships, driving forces and management options);

Question 3

The management can comprise activities such as

Answer 3

• forecasting services;
• education and awareness campaigns;
• flood proofing;
• land management (‘keeping people away from floods’);
• water management (storage operation);
• structural protection (dykes) (‘keeping floods away from people’); Need to protect population, agriculture, infrastructure, and environment Growing economic activity in flood-prone areas Flood management Interventions: Land use, infrastructure
• timely and appropriate response to events (such as disasters) and developments;
• studies of cause-effect relationships and of impacts of intervention; etc

Question 4

It is the poor people and the children who are most vulnerable to

Answer 4

floods

Question 5

It is the poor people and the children who are most vulnerable to floods. Therefore, a ……………………… must be extended to these parts of the population.

Answer 5

particular attention

Question 6

Good flood management would take its starting point in a suitable knowledge about

Answer 6

1. the flood risk (so that high-risk areas are delineated); and
2. the flood vulnerability (so that the most important potential consequences are identified).

Question 7

Good flood management would take its starting point in a suitable knowledge about

1. the flood risk (so that high-risk areas are delineated); and
2. the flood vulnerability (so that the most important potential consequences are identified).

If this knowledge is not adequate …………….. should be made

Answer 7

studies

Question 8

Coastal floods can be caused by

Answer 8

storm surge

Question 9

Coastal floods can be caused by storm surge, which is generated by

Answer 9

a combination of wind friction and low air pressure

Question 10

Coastal floods can be caused by storm surge, which is generated by a combination of wind friction and low air pressure. …………………………….. will add to the water level

Answer 10

Local wind waves

Question 11

Local wind waves will add to the water level, and the storm surge can be ……………………………..

Answer 11

amplified (or reduced)

Question 12

. Local wind waves will add to the water level, and the storm surge can be amplified (or reduced) by

Answer 12

interference with the strictly regular astronomical tide.

Question 13

Extreme floods can be related to

Answer 13

extreme storms - like cyclones -

Question 14

Extreme floods can be related to extreme storms - like cyclones - that attack

Answer 14

attack the open coast

Question 15

Extreme floods can be related to extreme storms - like cyclones - that attack the open coast. In areas that are otherwise more sheltered (like the…………………… )

Answer 15

Baltic Sea

Question 16

Extreme floods can be related to extreme storms - like cyclones - that attack the open coast. In areas that are otherwise more sheltered (like the Baltic Sea), extreme floods can be generated by

Answer 16

by unusual sequences of wind set-up and air pressure variations.

Question 17

Irrespective of the weather, flood waves can be generated by

Answer 17

distant, sub-sea earthquakes (such flood waves are called tsunamis), or, in arctic areas, by breaking glaciers.

Question 18

Irrespective of the weather, flood waves can be generated by distant, sub-sea earthquakes (such flood waves are called tsunamis), or, in arctic areas, by breaking glaciers.

The effect depends on the

Answer 18

coastal profile

Question 19

The effect depends on the coastal profile. A gently sloping profile causes

Answer 19

a high amplification of an approaching flood wave (and tidal wave) and a high set-up in response to local wind

Question 20

A steep profile will tend to

Answer 20

reflect the flood wave (and tidal wave), rather than amplifying it

Question 21

A steep profile will tend to reflect the flood wave (and tidal wave), rather than amplifying it, and the locally generated set-up will be small if

Answer 21

the water depth is large

Question 22

Often, a shallow coastal profile occurs in places with

Answer 22

low-lying lands

Question 23

. Often, a shallow coastal profile occurs in places with low-lying lands. If so, the flood risk will be

Answer 23

high

Question 24

It is the weakest part of the poor population - rural women, elderly, and children - who are

Answer 24

most at risk

Question 25

It is the weakest part of the poor population - rural women, elderly, and children - who are most at risk. Even those who escape unharmed in the first place may be victims to

Answer 25

to diseases in the days to follow

Question 26

. Even those who escape unharmed in the first place may be victims to diseases in the days to follow, and may in any case have

Answer 26

lost whatever they owned.

Question 27

A major problem in this connection is that it is

Answer 27

is not possible to predict the route of a moving extreme depression like a cyclone

Question 28

Cyclone shelters Built to be used only

Answer 28

once in a lifetime

Question 29

Cyclone shelters Built to be used only once in a lifetime, cyclone shelters are

Answer 29

an expensive means of protection against the flood peril

Question 30

Cyclone shelters Built to be used only once in a lifetime, cyclone shelters are an expensive means of protection against the flood peril. On the low islands in the Meghna Estuary, however, they are the only refuge within reach. After the 1991 cyclone, different donor organisations have funded the construction of some ……………. cyclone shelter in the …… area

Answer 30

1,200

Banglandesh

Question 31

. After the 1991 cyclone, different donor organisations have funded the construction of some 1,200 cyclone shelters in the coastal areas of Bangladesh. They are impressive reinforced ………….. structures

Answer 31

concrete

Question 32

After the 1991 cyclone, different donor organisations have funded the construction of some 1,200 cyclone shelters in the coastal areas of Bangladesh. They are impressive reinforced concrete structures, often built in places accessible by ……………………………….

Answer 32

narrow footpaths only

Question 33

They are impressive reinforced concrete structures, often built in places accessible by narrow footpaths only. Apart from their primary objective, the cyclone shelters serve as

Answer 33

schools, mosques, storage, or clinics.

Question 34

Cyclones are frequent in the Bay of Bengal. In Bangladesh, where around 2 mio. people live in the coastal areas and the islands of Meghna Estuary, a severe cyclone is expected to hit the coast (at one place or another) once in

Answer 34

5 years on the average

Question 35

. During a severe cyclone, wind speeds range from

Answer 35

90 km/hour and upwards

Question 36

During a severe cyclone, wind speeds range from 90 km/hour and upwards. In the northern Bay of Bengal, the associated storm surge can reach

Answer 36

5-10 m

Question 37

In the northern Bay of Bengal, the associated storm surge can reach 5-10 m. This is well above

Answer 37

the land level of the coastal areas

Question 38

In the northern Bay of Bengal, the associated storm surge can reach 5-10 m. This is well above the land level of the coastal areas, which is typically

Answer 38

only slightly above sea level

Question 39

The cyclone that hit the coast of Bangladesh on April 1991 was among the most severe in recent times. It was forecast in due time, but the warnings were not heeded until the very last moment, or, in many cases, until it was too late. Furthermore, the protective coastal embankments were in

Answer 39

a poor state of maintenance

Question 40

The cyclone that hit the coast of Bangladesh on April 1991 was among the most severe in recent times. It was forecast in due time, but the warnings were not heeded until the very last moment, or, in many cases, until it was too late. Furthermore, the protective coastal embankments were in a poor state of maintenance. As it turned out, in some places, the damaged embankments amplified the ………… rather than …………………….

Answer 40

impact

controlling it

Question 41

The cyclone that hit the coast of Bangladesh on April 1991 was among the most severe in recent times. It was forecast in due time, but the warnings were not heeded until the very last moment, or, in many cases, until it was too late. Furthermore, the protective coastal embankments were in a poor state of maintenance. As it turned out, in some places, the damaged embankments amplified the impact, rather than controlling it. It is estimated that over

Answer 41

100, 000 people died

Question 42

As it turned out, in some places, the damaged embankments amplified the impact, rather than controlling it. It is estimated that over 100,000 people died. Most of the livestock and all the poultry of the affected area was lost. ……………………………………… were gravely damagned

Answer 42

buildings, structures and crops

Question 43

Inland, seasonal floods in the ………………. of a river ………………..

Answer 43

floodplains of river basins

Question 44

Inland, seasonal floods in the floodplains of river basins are generated by the

Answer 44

seasonal melting of snow and ice, and/or seasonal rainfall variations

Question 45

Inland, seasonal floods in the floodplains of river basins are generated by the seasonal melting of snow and ice, and/or seasonal rainfall variations, for example determined by

Answer 45

the monsoon weather system

Question 46

The variation can be strong and regular in case of

Answer 46

large rivers that origin in mountainous areas with snow and glaciers

Question 47

The variation can be strong and regular in case of large rivers that origin in mountainous areas with snow and glaciers (like the ……………………….)

Answer 47

Himalaya plateau

Question 48

The variation can be strong and regular in case of large rivers that origin in mountainous areas with snow and glaciers (like the Himalaya Plateau) and proceed through areas with …………………….. (like …………………………… )

Answer 48

a monsoon climate (like South and Southeast Asia)

Question 49

In such areas, in the course of time, the environment and the economy have adapted to the

Answer 49

occurrence of floods

Question 50

In such areas, in the course of time, the environment and the economy have adapted to the occurrence of floods, to an extent that some livelihoods (and ecosystems)

Answer 50

depend on it

Question 51

In such areas, in the course of time, the environment and the economy have adapted to the occurrence of floods, to an extent that some livelihoods (and ecosystems) depend on it, while others are

Answer 51

strongly supported by it

Question 52

In such areas, in the course of time, the environment and the economy have adapted to the occurrence of floods, to an extent that some livelihoods (and ecosystems) depend on it, while others are strongly supported by it.

Problems occur in case of

Answer 52

deviations from the normal pattern, with floods being higher than usual, or if they take place at an unusual time of the year

Question 53

Problems occur in case of deviations from the normal pattern, with floods being higher than usual, or if they take place at an unusual time of the year. This can be for

Answer 53

natural reasons, or due to human intervention, or both

Question 54

Also, problems can occur when the development takes a course that does not conform well with

Answer 54

the occurrence of floods

Question 55

Also, problems can occur when the development takes a course that does not conform well with the occurrence of floods. This can relate to

Answer 55

land use, investment in physical infrastructure, or new ways of natural resources utilisation.

Question 56

The flood risk is influenced by

Answer 56

• the climate (which can fluctuate over small, medium and long periods of time);
• morphological changes of the river system, whether of natural or human origin; and
• any human intervention in the river system that changes the runoff, the flow resistance, or the wet season flow itself.

Question 57

Comprehensive deforestation can occur due to

Answer 57

forest fires and human intervention

Question 58

Deforestation can increase

Answer 58

the flood risk

Question 59

Deforestation can increase the flood risk, both by changing the

Answer 59

runoff pattern and by increasing the sediment yield

Question 60

Deforestation can increase the flood risk, both by changing the runoff pattern and by increasing the sediment yield and hereby increase the

Answer 60

flow resistance in the main river channels

Question 61

………………………………………………………………………. can at the same time increase and reduce the flood risk at different places

Answer 61

Dredging of navigation channels and regulation of bends

Question 62

Likewise, a flood protection scheme can

Answer 62

reduce the flood risk at one place while increasing it at other places

Question 63

Likewise, a flood protection scheme can reduce the flood risk at one place while increasing it at other places. Earthquakes can change the ……………… by

Answer 63

flood risk by changing the planform of the river, and by releasing large pulses of sediments

Question 64

Apart from the climate, the flood risk depends on

Answer 64

• the runoff
• the flow resistance
• the storage capacity
• structural protection

Question 65

Damage caused by floods can comprise

Answer 65

• loss of life, property, crops and livestock;
• diseases related to interrupted water supply and sanitation;
• damage to buildings and different types of infrastructure;
• pollution caused by flooding of waste deposits, storage facilities, and waste disposal facilities; and
• disruption of livelihoods and education. As it is the case with coastal floods, it is the poorest part of the population that is most vulnerable.

Question 66

In broad general, floods tend to affect the …………….. population to a higher extent than the ……………….. population

Answer 66

rural

urban

Question 67

In broad general, floods tend to affect the rural population to a higher extent than the urban population, and the ………………………….. population to a higher extent than …………………………………… groups

Answer 67

poor part of the

middle- and high-income

Question 68

In broad general, floods tend to affect the rural population to a higher extent than the urban population, and the poor part of the population to a higher extent than middle- and high-income groups. This can be due to

Answer 68

inadequate information, knowledge and awareness, but also due to a lack of capacity to sustain one or two failed crops, or to sustain a disruption of paid employment

Question 69

Benefits of floods comprise

Answer 69

• water being retained for (paddy) cultivation;
• improved soil fertility;
• maintenance of primary production on the flood plains;
• maintenance of the fish yields; and
• preservation of wetlands ecosystems.

Question 70

Flash floods are caused by

Answer 70

local rainfall in mountainous catchments

Question 71

Flash floods are caused by local rainfall in mountainous catchments. They got their name because they occur

Answer 71

unexpectedly and develop rapidly

Question 72

Flash floods are caused by local rainfall in mountainous catchments. They got their name because they occur unexpectedly and develop rapidly. They can cause

Answer 72

loss of human lives and comprehensive damage to buildings, infrastructure and crops

Question 73

Flash floods are caused by local rainfall in mountainous catchments. They got their name because they occur unexpectedly and develop rapidly. They can cause loss of human lives and comprehensive damage to buildings, infrastructure and crops. A related type of disaster is

Answer 73

dam breaks

Question 74

They can cause loss of human lives and comprehensive damage to buildings, infrastructure and crops. A related type of disaster is dam breaks. In …………………. Asia, there are indications that flash floods have become

Answer 74

Southeast

more frequent and/or more serious in recent years

Question 75

A related type of disaster is dam breaks. In Southeast Asia, there are indications that flash floods have become more frequent and/or more serious in recent years. In some cases it may be speculated that deforestation

Answer 75

plays a role

Question 76

In Southeast Asia, there are indications that flash floods have become more frequent and/or more serious in recent years. In some cases it may be speculated that deforestation plays a role. In other cases, the observation may be due to

Answer 76

new settlements in areas that have hitherto been undeveloped

Question 77

In Southeast Asia, there are indications that flash floods have become more frequent and/or more serious in recent years. In some cases it may be speculated that deforestation plays a role. In other cases, the observation may be due to new settlements in areas that have hitherto been undeveloped. Another development is that today, due to effective ………………………, any serious flash flood will become a spectacular ……………….. item.

Answer 77

communication

news

Question 78

In Southeast Asia, there are indications that flash floods have become more frequent and/or more serious in recent years. In some cases it may be speculated that deforestation plays a role. In other cases, the observation may be due to new settlements in areas that have hitherto been undeveloped. Another development is that today, due to effective communication, any serious flash flood will become a spectacular news item. Flash floods cannot be predicted with any …………………………

Answer 78

reasonable lead time.

Question 79

In Southeast Asia, there are indications that flash floods have become more frequent and/or more serious in recent years. In some cases it may be speculated that deforestation plays a role. In other cases, the observation may be due to new settlements in areas that have hitherto been undeveloped. Another development is that today, due to effective communication, any serious flash flood will become a spectacular news item. Flash floods cannot be predicted with any reasonable lead time. Only, a warning can be issued once a flash flood is

Answer 79

imminent or in progress

Question 80

Flash floods cannot be predicted with any reasonable lead time. Only, a warning can be issued once a flash flood is imminent or in progress. A simple and inexpensive warning system based on dissemination by mobile telephone has been developed in

Answer 80

Thailand

Question 81

the floods are ranked according to

Answer 81

magnitude

Question 82

the floods are ranked according to magnitude, the largest flood is assigned a rank

Answer 82

1

Question 83

The flood statistics are estimated graphically by

Answer 83

plotting the logarithm of discharge for each flood in the annual series against the fraction of floods greater than or equal to that flood

Question 84

• The flood statistics are estimated graphically by plotting the logarithm of discharge for each flood in the annual series against the fraction of floods greater than or equal to that flood; this fraction is given by

Answer 84

r/(n+1)

Question 85

• The flood statistics are estimated graphically by plotting the logarithm of discharge for each flood in the annual series against the fraction of floods greater than or equal to that flood; this fraction is given by

r/(n+1),

where r is …………………………………. and n is ………………………………………

Answer 85

r is the rank of the particular flood and n is the number of observations (years)

Question 86

The return period:

Answer 86

the average span of time between any flood and one equaling or exceeding it

Question 87

• The return period, the average span of time between any flood and one equaling or exceeding it, is calculated as

Answer 87

T_return = 1/(exceedance probability)

Question 88

The 100 years flood can then be estimated from

Answer 88

the graph

Question 89

Normal distribution works often well with

Answer 89

precipitation data and peak discharge

Question 90

Problems: not deterministic, based usually on

Answer 90

non-adequate data, climate and terrestrial environment is variable

Question 91

One of the things we want to know most about rivers is “what’s the probability that a flood of size x will happen this year? In 100 years?”

There are two ways to do this

Answer 91

empirically, and parametrically

Question 92

There are two ways to do this—empirically, and parametrically. First, empiricism

Answer 92

Let’s take a bunch of data. For now, we’ll take flood data—the maximum flood for each year for some number of years

Question 93

To plot this data empirically, we need

Answer 93

to order these according to rank. That is, the highest flow comes first, and then the next highest, on down

Question 94

Incidentally, you can get Excel to do this for you. Select the data, then go to Data|Sort, and it will order all the data! From here, use the formula

Answer 94

Question 95

Incidentally, you can get Excel to do this for you. Select the data, then go to Data|Sort, and it will order all the data! From here, use the formula:

where T, n , m represent

Answer 95

Where T is the recurrence interval, n is the number of years in the record, and m is the rank

Question 96

All that’s left is to plot …………………. on the horizontal axis and ……………………….on the vertical

Answer 96

T

Flow

Question 97

What is actually meant by “100-year flood,” by the way, is that it has a 1% chance of happening

Answer 97

every year

Question 98

. Here’s a nifty formula for determining frequency or probability rather than recurrence

Answer 98

Question 99

PMP stands for

Answer 99

Probable Maximum Precipitation

Question 100

PMP is defined as

Answer 100

the theoretically greatest depth of precipitation for a given duration that is physically possible over a particular drainage area at a certain time of year

Question 101

PMP is defined as “the theoretically greatest depth of precipitation for a given duration that is physically possible over a particular drainage area at a certain time of year,”

In consideration of our

Answer 101

limited knowledge of the complicated processes and interrelationships in storms

Question 102

In consideration of our limited knowledge of the complicated processes and interrelationships in storms, PMP values are identified as

Answer 102

estimates

Question 103

Another definition of PMP more operational in concept is

Answer 103

the steps followed by hydrometeorologists in arriving at the answers supplied to engineers for hydrological design purposes

Question 104

Another definition of PMP more operational in concept is “the steps followed by hydrometeorologists in arriving at the answers supplied to engineers for hydrological design purposes”. This definition leads to answers deemed adequate by

Answer 104

competent meteorologists and engineers and judged as meeting the requirements of a design criterion

Question 105

PMP is the estimated limiting value of

Answer 105

precipitation

Question 106

PMP is defined as the estimated

Answer 106

greatest depth of the precipitation for a given duration that is possible physically and reasonably characteristic over a particular geographic region at a certain time of year.

Question 107

PMP cannot be exactly estimated as its probability of occurrence is

Answer 107

not known

Question 108

PMP is useful in

Answer 108

operational applications (e.g., design of large dams)

Question 109

Any allowance should not be made in the estimation of PMP for

Answer 109

long term climate change

Question 110

Any allowance should not be made in the estimation of PMP for long term climate change. ……………….Probable Maximum Precipitation (PMP)

Answer 110

43%

Question 111

PMS involves

Answer 111

temporal distribution of rainfall

Question 112

……………………………………….. is required to develop hyetograph of a PMS

Answer 112

Spacial and temporal distribution of rainfall

Question 113

PMS values are given as

Answer 113

maximum accumulated depths for any specified duration

Question 114

PMS values are given as maximum accumulated depths for any specified duration. For example, given depths for 4h, 8h,…24h represent the

Answer 114

total depth for each duration & not the time sequence in which precipitation occurs

Question 115

PMS values are given as maximum accumulated depths for any specified duration. For example, given depths for 4h, 8h,…24h represent the total depth for each duration & not the time sequence in which precipitation occurs. ……………. Probable Maximum Storm (PMS)

Answer 115

45%

Question 116

PMS stands for

Answer 116

probable maximum storm

Question 117

PMF stands for

Answer 117

probable maximum flood

Question 118

The PMF is the

Answer 118

largest flood that could conceivably occur at a particular location, usually estimated from probable maximum precipitation, and where applicable, snow melt, coupled with the worst flood producing catchment conditions

Question 119

The PMF is the largest flood that could conceivably occur at a particular location, usually estimated from probable maximum precipitation, and where applicable, snow melt, coupled with the worst flood producing catchment conditions. Generally, it is not physically or economically possible to provide complete

Answer 119

protection against this event

Question 120

The PMF defines the extent of

Answer 120

flood prone land, that is, the floodplain

Question 121

The PMF defines the extent of flood prone land, that is, the floodplain. The extent, nature and potential consequences of flooding associated with

Answer 121

a range of events rarer than the flood used for designing mitigation works and controlling development, up to and including the PMF event should be addressed in a floodplain risk management study

Question 122

PMF is the greatest flood expected considering

Answer 122

complete coincidence of all factors that produce the heaviest rainfall and maximum runoff.

Question 123

PMF is derived from

Answer 123

PMP

Question 124

PMF is used only for

Answer 124

selected designs in view of economy

Question 125

PMF is used only for selected designs in view of economy For example,

Answer 125

large spillways whose failure could lead to excessive damage and loss of life

Question 126

A realistic approach is to scale downwards by certain percentage depending on ………………………………………… .

………..% Probable Maximum Flood (PMF)

Answer 126

type of structure and the hazard if it fails

46%

Question 127

PMF is also termed as

Answer 127

Standard Project Flood (SPF)

Question 128

SPF is estimated from

Answer 128

Standard project storm (rainfall-runoff modeling).

Question 129

SPF is estimated from Standard project storm (rainfall-runoff modeling). ……………….. % Probable Maximum Flood (PMF)

Answer 129

47%

Question 130

Water quality refers to

Answer 130

the chemical, physical, biological, and radiological characteristics of water

Question 131

Water quality refers to the chemical, physical, biological, and radiological characteristics of water. It is a measure of

Answer 131

the condition of water relative to the requirements of one or more biotic species and or to any human need or purpose

Question 132

Water quality refers to the chemical, physical, biological, and radiological characteristics of water. It is a measure of the condition of water relative to the requirements of one or more biotic species and or to any human need or purpose. It is most frequently used by reference to a set of

Answer 132

standards against which compliance can be assessed

Question 133

Water quality refers to the chemical, physical, biological, and radiological characteristics of water. It is a measure of the condition of water relative to the requirements of one or more biotic species and or to any human need or purpose. It is most frequently used by reference to a set of standards against which compliance can be assessed. The most common standards used to assess water quality relate to

Answer 133

to health of ecosystems, safety of human contact, and drinking water.