flooding hazards, prediction & mitigation
DESCRIPTION
Throughout the last century flooding has been one of the most costly disasters in terms of both property damage and human casualties. Major floods in China, for example, killed about 2 million people in 1887, nearly 4 million in 1931, and about 1 million in 1938. The 2007 flood was a major flood in Jakarta, affected several other areas around the city, such as West Java and Banten. The flood is considered the worst in the last three centuries, including the 1996 and 2002 Jakarta floods, which killed 10 and 25 people respectively. In less developed countries, humans are particularly sensitive to flood casualties because of high population density, absence of zoning regulations, lack of flood control, and lack of emergency response infrastructure and early warning systems. In industrialized countries the loss of life is usually lower because of flood control structures, zoning regulations that prevent the habitation of seriously vulnerable lands, and emergency preparedness. Still, property damage and disruption of life takes a great toll, and despite flood control structures and land use planning, floods still do occur.TRANSCRIPT
• Throughout the last century flooding has been one of the most costly disasters in terms of both property• Throughout the last century flooding has been one of the most costly disasters in terms of both propertydamage and human casualties. Major floods in China, for example, killed about 2 million people in 1887, nearly4 million in 1931, and about 1 million in 1938.
• The 2007 flood was a major flood in Jakarta, affected several other areas around the city, such as West Javaand Banten. The flood is considered the worst in the last three centuries, including the 1996 and 2002 Jakartafloods, which killed 10 and 25 people respectively.
f f f f• Bangladesh is one of the most susceptible countries to flood disasters. About one half of the land area inBangladesh is at an elevation of less than 8 meters above sea level. Up to 30% of the country has been coveredwith flood waters. In 1991 more 200,000 deaths resulted from flooding and associated tropical cyclones.
I l d l d i h i l l i i fl d l i b f hi h l i• In less developed countries, humans are particularly sensitive to flood casualties because of high populationdensity, absence of zoning regulations, lack of flood control, and lack of emergency response infrastructureand early warning systems.
• In industrialized countries the loss of life is usually lower because of flood control structures, zoningregulations that prevent the habitation of seriously vulnerable lands and emergency preparedness Stillregulations that prevent the habitation of seriously vulnerable lands, and emergency preparedness. Still,property damage and disruption of life takes a great toll, and despite flood control structures and land useplanning, floods still do occur.
• Flood is defined as extremely high flows or levels of rivers, lakes, ponds, reservoirs and any other waterbodies, whereby water inundates outside of the water bodies area.
• Flooding also occurs when the sea level rises extremely or above coastal lands due to tidal sea and sea• Flooding also occurs when the sea level rises extremely or above coastal lands due to tidal sea and seasurges. In many regions and countries floods are the most damaging phenomena that effect to the social andeconomic of the population (Smith et, a1.. 1998).
Causes of flooding
Many factors cause floods. In general, the reasons for increasing flooding in many parts ofth ld (S ith t l 1998)the world are (Smith et, al., 1998):
1. Climatological events2. Changes in Landuse and increasing population3. Land subsidence, Tsunami4. Dam & Levee Failures
Climatological [email protected]
Torrential rainTorrential rain
Tropical Cyclones
Monsoon rain Snow melt
Changes in Landuse and increasing [email protected]
DeforestationUrbanisation increases surface run‐off
Fl d l i lFloodplains are also subject to preferential location by industries
Land subsidence & Tsunami [email protected]
TsunamiTsunami caused by underwater earthquakecaused by underwater earthquakesubsidencesubsidence TsunamiTsunami caused by underwater earthquakecaused by underwater earthquakesubsidencesubsidence
The characteristics and related hazards
The dangers of floodwaters are associated with a number of different characteristics of the flood.A summary of the characteristics and related hazards (Kingma, 2002) is given below :
1 D th f t 2 D ti 3 V l it1. Depth of water 2. Duration 3. Velocity4. Sediment load 5. Rate of rise 6. Frequency of occurrence.
Effects of Floods
Hazards associated with flooding can be divided into primary hazards thatoccur due to contact with water, secondary effects that occur because of thefl di h di ti f i h lth i t h f i dflooding, such as disruption of services, health impacts such as famine anddisease, and tertiary effects such as changes in the position of river channels.
Primary EffectsThe primary effects of floods are those due to direct contact with the flood waters
(Water velocities tend to be high in floods).
• With higher velocities streams are able to transport larger particles/ sediment as suspended load• With higher velocities, streams are able to transport larger particles/ sediment as suspended load.• Massive amounts of erosion can be accomplished by flood waters.• Water entering human built structures cause water damage.• Flooding of farmland usually results in crop loss. Livestock, pets, and other animals are often carried away
and drownand drown.• Humans that get caught in the high velocity flood waters are often drowned by the water.• Floodwaters can concentrate garbage, debris, and toxic pollutants that can cause the secondary effects of
health hazards.
Secondary Effects(Secondary effects are those that occur because of the primary effects)
(Secondary effects are those that occur because of the primary effects)
Disruption of services• Drinking water supplies may become polluted, especially if
sewerage treatment plants are flooded. This may result indisease and other health effects, especially in underdeveloped countries.
• Electrical and gas service may be disrupted.
• Transportation systems may be disrupted, resulting inshortages of food and clean-up supplies. In underdeveloped countries food shortages often lead tostarvation.
Tertiary Effects(Tertiary effects are the long term changes that take place)
(Tertiary effects are the long term changes that take place)
Long - term effects• Location of river channels may change as the result of flooding, new channels develop, leaving the old
channels dry.• Jobs may be lost due to the disruption of services, destruction of business, etc. (although jobs may be
gained in the construction industry to help rebuild or repair flood damage).• Insurance rates may increase.• Corruption may result from misuse of relief funds.• Destruction of wildlife habitat.
IV. Theory(Here we discuss the main cause of flooding, that is heavy rainfall over a short period of time.)
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The Water Cycle
When rain falls on the surface of the Earth, some of the water is evaporated and returns toh h f i i fil h il d d d i h dthe atmosphere, some of it infiltrates the soil and moves downward into the groundwatersystem, and some is intercepted by depressions and vegetation. What remains on thesurface of the Earth and eventually flows into streams is called Runoff.
A flood results when a stream runs out of its confines and submerges surrounding areas.
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Runoff = Precipitation – Infiltration – Interception – Evaporation
Water Surplus = Precipitation – EvapotraspDRO = WS – InfiltrationDRO WS Infiltration
Runoff = DRO + Base Flow
Rainfall [email protected]
If i f ll i h i th l i ti l d i filt ti i t ti d• If rainfall is heavier than normal in a particular area and infiltration, interception, andevaporation are low then runoff can be high and the likelihood of flooding will increase.
• Heavy rainfall can be depicted on maps that show curves of equal rainfall. Such curvesare called isohyets and the resulting maps are called isohyetal mapsare called isohyets, and the resulting maps are called isohyetal maps.
• The time difference between when heavyprecipitation occurs and when peak dischargeoccurs in the streams draining an area is calledlag time.
• Lag time depends on such factors as theLag time depends on such factors as theamount of time over which the rain falls and theamount of infiltration and interception that takesplace along the path to a stream.o If the amount of rain is high over a short time
period, lag time is short.o If the amount of rain is high over a longer time
period lag time is longerperiod, lag time is longer.o Lack of infiltration and interception reduce lag
time.
• Upstream flooding and flash floodsIn areas where large amounts of rain fall over a short period of time within a smallarea, streams in the local area may flood, with little or no effect on areas, y ,downstream. Such floods are referred to as upstream floods. In such floods, waterrises quickly and flows away quickly after the storm has passed. Lag times aremeasured in days.
Flash floods occur when the rate of infiltration is low and heavy rains occur over ashort period of time. They are upstream floods with very little lag time (lag times maybe only a few hours) Because they come with little warning flash floods are the mostbe only a few hours). Because they come with little warning, flash floods are the mostdangerous to human lives.
• Downstream floodingIf large amounts of rain fall over an extended period of time over a large region,downstream floods may occur Lag times are usually longer as tributary streamsdownstream floods may occur. Lag times are usually longer as tributary streamscontinually increase the discharge into larger streams. Such floods extend over longperiods of time and affect the larger streams as well as tributary streams. The 1993flood on the upper Mississippi River is considered a downstream flood. Water levelspp pprise slowly and dissipate slowly.
Infiltration(Infiltration is controlled by how readily the water can seep into the soil, be absorbed by the soil, and work its way down to the water table)
Several factors determine the rate of infiltration :
( y y p , y , y )
• Vegetation cover
Several factors determine the rate of infiltration :
• Human construction
V. Prediction
• Statistical studiesFl d H d M i• Flood Hazard Mapping
• Monitoring the Progress of StormsMonitoring the Progress of Storms
Statistical studies(St ti ti l t di b d t k t tt t t d t i th b bilit d f f hi h
(Statistical studies can be undertaken to attempt to determine the probability and frequency of highdischarges of streams that cause flooding)
........................Weibull equationR = (n+1)/m
Frequency of Flooding
qR (n 1)/m• In order to determine the recurrence interval,
the yearly discharge values are first ranked.Each discharge is associated with a rankEach discharge is associated with a rank(m), with m = 1 given to the maximumdischarge over the years of record, m = 2given to the second highest discharge, m = 3given to the third highest discharge, etc.
• The smallest discharge will receive a rankequal to the number of years over whichequal to the number of years over whichthere is a record (n). Thus, the dischargewith the smallest value will have m = n.
• The number of years of record (n), and therank for each peak discharge (m) are thenused to calculate recurrence interval (R)
The probability
Pe = m/(n+1)
• The value, Pe is called the annual exceedence probability.
For example, a discharge equal to that of a 10-year flood would have anannual exceedence probability of 1/10 = 0.1 or 10%.
This would say that in any given year, the probability that a flood with adischarge equal to or greater than that of a 10 year flood would be 0.1 or10%. Similarly, the probability of a flood with discharge exceeding the 100y, p y g gyear flood in any given year would be 1/100 = 0.01, or 1%.
Flood Hazard [email protected]
• Flood hazard mapping is used to determine the areas susceptible toFlood hazard mapping is used to determine the areas susceptible toflooding when discharge of a stream exceeds the bank-full stage.
• Using historical data on river stages and discharge of previousfloods, along with topographic data, maps can be constructed toshow areas expected to be covered with floodwaters for variousdischarges or stages.
The illustration above shows a possible hazard map based on estimated discharges or riverstages for a hypothetical 10-year flood, 50-year flood, and 100-year flood.
Monitoring the Progress of [email protected]
If f t h t f i f ll d f d t ti d f• If factors such as amount of rainfall, degree of ground saturation, degree ofpermeable soil, and amount of vegetation can be determined, then thesecan be correlated to give short-term prediction, in this case called aforecast of possible floodsforecast, of possible floods.
• If a forecast is issued, then a flood warning can be communicated to warnthe public about the possible extent of the flood, and to give people time tomove out of the area. Such forecasts are very useful for flooding that has along lag time between the storm and the peak discharge.
• Flash floods, which characteristically have short lag times, are moreproblematical. Thus, in some areas known to be susceptible to flash floods,a flash flood warning is often issued any time heavy rainfall is expectedbecause there is always the chance of a flash food accompanying heavyrainfall.
VI Flood [email protected]
VI. Flood Mitigation
Response to flood hazards can be attempted intwo main ways:
• An engineering approach to control flooding• An engineering approach, to control flooding(Structural Flood Mitigation measures).
• a regulatory approach designed to decreasevulnerability to floodingy g
(Non‐structural Flood Mitigation Measures).
Structural Flood Mitigation [email protected]
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l h l l1. Control the water level
2. Build barriers
3. Alter the river’s channel(Channel modifications)
4. Floodways
1.a. [email protected]
International standards define large dams as higher than 15 meters and major dams as over 150 meters in height.
River Nile, Egypt
The Aswan High Dam
Gordon dam, Tasmania
Gravity dam
A h d i hi ( d f l) d• An arch dam is a thin, (made of masonry & steel) curvedconcrete or masonry dam structure with the curve to curveupstream so that the force of the water against the canyon wallwhere the dam is constructed squeezes the arch, compressing
d h i i d hi i i h d [
Arch dam
and strengthening its structure and pushing it into the ground.[• The gravity dam is massive, made of masonry and cement with
earth and rock fill, uses its own weight to resist opposing forces.
AnAn archarch‐‐gravitygravity damdam isis aa damdam withwith thethe characteristicscharacteristicsofof bothboth anan archarch damdam andand aa gravitygravity damdam AA gravitygravity damdamofof bothboth anan archarch damdam andand aa gravitygravity damdam.. AA gravitygravity damdamrequiresrequires aa largelarge volumevolume ofof internalinternal fillfill.. AnAn archarch‐‐gravitygravitydamdam cancan bebe thinnerthinner thanthan thethe purepure gravitygravity damdam andandrequiresrequires lessless internalinternal fillfill..
1.a3. Timber [email protected]
The locations where timber dams are most economical to build are those wheretimber is plentiful, cement is costly or difficult to transport, and either a low headdiversion dam is required or longevity is not an issue.
1.a3. Steel [email protected]
A steel dam is a type of dam briefly experimented with in around the turn of the 19th‐20th Century which uses steel plating (at an angle) and load bearing beams as thestructure to determine if a construction technique could be devised that was cheaperstructure to determine if a construction technique could be devised that was cheaperthan masonry, concrete or earthworks, but sturdier than timber crib dams.
1.b. [email protected]
The huge spillway for the Robert-Bourassa Reservoir, Quebec, Canada, fittingly called the "Giant's Staircase".
A spillway is a structure used to provide for the controlledrelease of flood flows from a dam or levee into a downstreamarea typically being the river that was dammed Spillwaysarea, typically being the river that was dammed. Spillwaysrelease floods so that the water does not overtop anddamage or even destroy the dam. Spillway of Spillway of Llyn BrianneLlyn Brianne dam in dam in WalesWales
1.c. Pumping [email protected]
2 a Embankments
2.a. Embankments
San Luis Embankment damSan Luis Embankment dam
Pothundi Embankment, India
An Embankment dam is a massive semi-plastic mound ofearth and/or rock with a dense, waterproof core.Embankment dams come in two types: the earth filled damyp(or earthen dam) made of compacted earth, can also becalled a terrain dam and the rock filled dam.
2.b. [email protected]
A levee is artificial slope or wall, often parallels thecourse of a river
The Mississippi River levee system represents one of the largest such systems foundanywhere in the world. They comprise over 3,500 miles (5,600 km) of levees extendingsome 1,000 miles (1,600 km) along the Mississippi. They average 24 feet (7 m) inheight; some Mississippi levees are as much as 50 feet (15 m) high.
Note the school bus for scale and the seepage along the side of the levee (Mississippi).
2.c. [email protected]
A dike (or dyke) is an artificial earthen wall,constructed as a defense or as a boundary.Dikes can be mainly found along the sea, where dunesare not strong enough, along rivers for protectionagainst high‐floods, along lakes or along polders.Furthermore, dikes have been built for the purpose ofempoldering or as a boundary for an inundation areaempoldering, or as a boundary for an inundation area.
The Ringvaart dyke in North Holland
2.d. Flood [email protected]
Seawall in Sicily Seawall‐large(USGS)y g
Seawall in Ventnor, Seawall in Poland
Types of Floodwalls
A range of Floodwall (seawall) types can be envisaged in relation to wave energy,resembling cliff and beach profiles.• Vertical seawalls are built in particularly exposed situations. These reflect wave
energy and under storm conditions standing waves (clapotis) will develop. In somecases piles are placed in front of the wall to lessen wave energy slightly.
• Curved or stepped seawalls are designed to enable waves to break and to• Curved or stepped seawalls are designed to enable waves to break and todissipate wave energy. The curve can also prevent the wave overtopping the wall,and provide additional protection for the toe of the wall.
3. Alter the river’s [email protected]
Widen and deepen it Straighten itWiden and deepen it Straighten it
4. FloodWaysLake Poncetrain
Lake Poncetrain
Floodways are areas where no construction is allowed, and where the land is used foragricultural or recreational purposes when there is no threat of a flood, but which provide anoutlet for flood waters during periods of high discharge.
Non‐structural Flood Mitigation [email protected]
1 Fl d l i i
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1. Floodplain zoning
2. Floodplain building codes
3. Floodplain buyout programs
4. Mortgage limitationsg g
1. Floodplain [email protected]
Laws can be passed that restrict construction and habitation of floodplains. Instead floodplainsp p pcan be zoned for agricultural use, recreation, or other uses wherein lives and property are notendangered flood waters re-occupy the floodplain.
2. Floodplain building [email protected]
Structures that are allowed within the floodplain could be restrictedthose that can withstand the high velocity of flood waters and are highthose that can withstand the high velocity of flood waters and are highenough off the ground to reduce risk of contact with water.
3. Floodplain buyout programs [email protected]
In areas that have been recently flooded, it may be morecost effective for the government, which usually pays forflood damage either through subsidized flood insurance orflood damage either through subsidized flood insurance ordirect disaster relief, to buy the rights to the land ratherthan pay the cost of reconstruction and then have to payp y p yagain the next time the river floods.
4. Mortgage [email protected]
Lending institutions could refuse to give loans tobuy or construct dwellings or businesses in floodbuy or construct dwellings or businesses in floodprone areas.
Floods in JakartaFloods in Jakarta
Type• Floods triggered by heavy seasonal rainFloods, triggered by heavy seasonal rain.Background• 40 % of Jakarta is located under the sea level.• Jakarta is prone to flood due to poor drainageJakarta is prone to flood due to poor drainage.• Jakarta experienced yearly.• The 2007 flood was the greatest flood to fit Jakarta in the last three centuries.
The history of floods in [email protected]
yNo Year Affect
1 1699 Ciliwung river floods “Oud (old) Batavia” after Mount Salak erupts
2 1714 Ciliwung river overflows after clearing forest areas in Puncak.
3 1854 “Niew (new) Batavia” is a meter underwater, caused by the raging Ciliwung.
4 1918 Extensive flooding The Dutch colonial government begins work n the 4 1918 Extensive flooding. The Dutch colonial government begins work n the Western Flood Canal.
5 1942 The Canal is completed, but Jakarta still floods.
6 1996 A flood sweeps through the capital. Approximately 10 people die.
7 2002 The Dartmouth Flood Observatory notes it as the largest flood in J k ’ hi 25 l di dJakarta’s history, 25 people died.
8 2007 The greatest flood to fit Jakarta in the last three centuries.
Collapsing Land;As a result of skyscrapers and Takingwell water, about 250 million cubicmeters of land in Jakarta collapseseach year.
Diagrammatic map showing the geographic location of Jakarta
SUN; From Jan-March, the sun evaporatesseawater. Then westerly winds drive thiscondensation to Jakarta These are the
BOGOR-PUNCAK-CIANJUR (±850km2)40% of this region is covered by buildings.5,000 mm/year of rainwater runs straightinto the rivers .(Jakarta ± 650km2 )
condensation to Jakarta. These are themonths with the heaviest levels ofprecipitation.
WATERSHED Continoues toshrink. At the head Ciliwung
PRECIPITATION; Jakarta can beflooded by its own. In the recent
Here is the reason why the recent flood is more severe than that in 2002; therain level is more than 50 mm. In addition, rivers in Jakarta whose upperreaches are located in Bogor are deteriorating
River in 1996 absorbent landarea was 6,650 km2. In 2006only 5,412 km2 remained.
disaster, there was a massivedownpoor, as much as 401.5 mm in asingle day. Jakarta can flood even at alevel of 50-100 mm/day
BODIES OF WATER; The numberof lakes has decreased from 218 in the1990s to about 100 in 2006
WATER LEVELS; As a result of damage towatershed areas, the water level of Ciliwung Riverrises 200 m3/s from its normal 28 m3/s.
OPEN GREEN AREAS 9 12%
River Currents.It takes about 4-6 hours to beach Jakarta.
OPEN GREEN AREAS 9.12%(60km2). The ideal area is 180 km2.
ELEVATION40% of the land in Jakartais 1-1.5 m below sea levelat high tide.
NARROW...The Ciliwung Riverused to be 65 m, now itis only 15-20 m wide.
...AND SHALLOW
GLOBAL WARMINGhas caused melting of iceat the poles, raising sea
28%28%Garbage Dumps
30%30%Rivers
42%Unofficial garbage d
High tide level of 1.9 m
0.5-1.5 m Presedential palace3m
National Monument4 m
Jl. Sudirman7m
...AND SHALLOWin the past 5 m, nowonly 1.2 m, due togarbage build up.
levels. It is estimated thatin 2050 the sea level willrise by 45 cm
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Flood Hazard MapJakarta
Inundation risk of Suter River
Inundation risk of Pesanggrahan River
Inundation risk of Angke River
Inundation risk of Ciliwung RiverInundation risk of Ciliwung River
Inundation risk of Cipinang River
Inundation risk of Krukut River
Station
Degradation < 10 cmDegradation 10 - 30 cmD d i 30 0 Degradation 30 - 50 cmDegradation 50 - 70 cmDegradation > 70 cm
6 16.19.212.4
Infiltration rate = 54.03 mmAtika lubis. 2007. Banjir jakarta 2007: Disaster atau konsekwensi lingkungan?. ITB. Bandung.
Direct Runoff [email protected]
Atika lubis. 2007. Banjir jakarta 2007: Disaster atau konsekwensi lingkungan?. ITB. Bandung.Rate of DRO = 314,7 mm
Direct Runoff Simulation [email protected]
Green Area
Rate of DRO = 303,23 mmAtika lubis. 2007. Banjir jakarta 2007: Disaster atau konsekwensi lingkungan?. ITB. Bandung.
Water debit [email protected]
in Ciliwung river
YearYear Debit (mDebit (m33/s)/s)1990 1911990 1911996 3832002 4822002 4822012 578
Hidro‐[email protected]
Jakarta
• Precipitation : 219-238 mm/day.Jakarta can be flooded by its own. In the recent disaster, there was a massiveydownpoor, as much as 401.5 mm in a single day. Jakarta can flood even at a level of50-100 mm/day
• Infiltration : 0 – 30 mm/month• Water Levels; As a result of damage to watershed areas, the water level of Ciliwung
River rises 200 m3/s from its normal 28 m3/s.• Flood waters Debit : 1.600 m3/s
3• West Jakarta Flood Control System Capacity (Banjir kanal barat) : 300 m3/s• Bodies Of Water : The number of lakes has decreased from 218 in the 1990s to
about 100 in 2006W t h d C ti t h i k At th h d Cili Ri i 1996 b b t l d• Watershed Continoues to shrink. At the head Ciliwung River in 1996 absorbent landarea was 6,650 km2. In 2006 only 5,412 km2 remained.
• Open Green Areas : 9.12% (60km2). The ideal area is 180 km2.• Elevation : 40% of the land in Jakarta is 1 1 5 m below sea level at high tide• Elevation : 40% of the land in Jakarta is 1-1.5 m below sea level at high tide.
References• Papers/journals:
- Atika lubis. (2007). “Banjir jakarta 2007: Disaster atau konsekwensia ub s ( 00 ) a j ja a a 00 sas e a au o se e slingkungan?”. ITB. Bandung.
- Nelson. S. A. (2006). “Natural Disasters; Lecturer Notes”. Tulane( )University.
- Smith. K and Ward. R. (1998). “Floods: Physical Processes andHuman Impacts”. John Willey and Sons. Chichester. USA.
• Taken from many sources, such as:--
www.wikipedia.orghttp://cybermap.cbn.net.id/h // j k id/-
• Comments & corrections to:http://www.jakarta.go.id/
Precipitation is any
Surface runoff is a term used to
p yproduct of the
condensation of atmospheric water vapor that is deposited on the
earth's surface Surface runoff is a term used to describe the flow of water, from rain, snowmelt, or other sources, over the land and is a major component of the
water cycle.
earth s surface.
A land area which produces runoff draining to common point is called a watershed.
Interception, or canopy interception, refers to precipitation that does not
reach the soil, but is instead intercepted by the leaves and
branches of plants..
Subsurface flow is the flow of water beneath ground surface in beneath ground surface in
hydrology.
