floods in sri lanka

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Dr. Kingsley GurugeRetired Senior Lecturer in GeographySri Lanka

♥ The disaster event profile of Sri Lanka is based on the Sri Lanka

Historical Disaster Information System,designed by the Disaster

Management Centre (DMC), Ministry of Disaster Management, in line

with DesInventar system developed by the LA RED in Latin America.

♥ The relevance is based on the number of events and different effect

variables, such as

(a) Number of people affected,

(b) Loss of life,

(c) Number of destroyed or damaged houses/buildings,

(d)Loss of agricultural crops.

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Sri Lanka National Report on Disaster Risk, Poverty and Human Development Relationship

♥ The disaster event profile of Sri Lanka presents how disaster events of different categories have been distributed chronologically, seasonally and spatially.

♥ Distribution wise, the overall disaster typology in Sri Lanka is not distributed evenly. In terms of annual time series distribution, animal attacks seem to have increased.

♥ However, disasters like floods seem to take place every year.

♥ The seasonal distribution of disasters shows two peaks; one from April to June and the other from October to December, representing the two monsoon seasons.

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Profile of Different Disaster Categories: 1974-2008

There are many types of disaster events in the country but the most common are :

♦ Animal attacks (7,203 events),

♦ Fire (2,704 events urban and forest fire),

♦ Floods (1,397 events- riverine flood, urban flood,

flash flood, rain), ♦ Extreme wind events (1,263 events- cyclone, strong wind,

surge, gale),

♦ Drought (285 events),

♦ Landslides (1,156 events) and

♦ Lightning (295 events).

6 Source : Sri Lanka National Report on Disaster Risk, Poverty and Human Development Relationship

Profile of Different Disaster Categories: 1974-2008

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Chronological Trend of Disaster Events

Source: desinventar.lk

♥ The sudden increase in animal attacks after 1998 is mainly due to the commencement of systematic recording of events, rather than a sudden outbreak of animal attacks.

♥ There are two main trends First, from 1974 to 1997, there is gradual increase in the number of disaster events fluctuating from 0 to 200 events with several peaks.

Secondly, disaster events during the period 1997- 2006 show a clear trend of very rapid increase of number of disaster events

from about 200 records in 1997 to more than 1,800 records in 2006, with the only break in the trend

observed in 2001. ♥ There is a sharp break in this trend beginning 2007, but it is too early to predict whether this is a start of a declining trend or not.

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Droughts have been mostly responsible for agricultural loss,

followed by floods and wind events.

Extreme wind events have caused the most number of deaths (926).

Geological disasters like earthquakes, tsunami, volcanoes and

landslides can cause massive destruction to lives and property

In Sri Lanka, landslide is the most common geological hazard.

Earthquakes of low to moderate magnitude have been recorded over

the past 400 years in Sri Lanka with very limited damage. No accurate

data is available

Spatial distribution of disaster records is uneven. District

level ranging from 96 to 1887

DS level from 9 to 74

It can be observed that while taking the number of people

affected by disasters into consideration, the share of climate

related disasters is 96%, showing the dominating

importance of these disasters over the others.

Most of the damage and destruction to houses has been

due to floods (232,236) and wind events (201,793).

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Source : Sri Lanka National Report on Disaster Risk, Poverty and Human Development Relationship

Floods General Trend of Occurrence 1974-2007

Source: Towards a Safer Sri Lanka: A Roadmap for Disaster Risk Management

People Affected by Different Disasters in Sri Lanka1974-2004

Source: Towards a Safer Sri Lanka: A Roadmap for Disaster Risk Management

Floods: Number of People Affected by Region- 1974- 2004

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Profile of People Affected due to Different Disaster Categories

without Tsunami : 1974 - 2008

Profile of People Affected due to Different Disaster Categories

without Tsunami : 1974 - 2008

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Profile of Loss of Life due to Different Disaster CategoriesWithout Tsunami : 1974-2008

Profile of Loss of Life due to Different Disaster Categories

With Tsunami : 1974-2008

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Source : Sri Lanka National Report on Disaster Risk, Poverty and Human Development

Relationship

Profile of houses Destroyed and Damaged due to Disasters Without Tsunami : 1974-2008

Profile of houses Destroyed and Damaged due to Disasters

With Tsunami : 1974-2008

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Source : Sri Lanka National Report on Disaster Risk, Poverty and Human Development

Relationship

Profile of Agricultural Losses Due to Disasters (in Hectares)Without Tsunami :1974 - 2008

Profile of Agricultural Losses Due to Disasters (in Hectares)Without Tsunami :1974 - 2008

♥ Mainly drought (52.2%), flood (38.9%) and Extreme wind events (4.2%) cause damage to agricultural crops.

♥ 1987, 2001 and 2004 and damage appears to be mainly caused by drought and flood.

♥ The seasonal distribution of loss to agricultural crop shows a cyclical distribution with two peaks. One peak takes place in the months of November, December, January and February due to both drought and flood.

♥ During this period, most damage is caused by floods which can be attributed to the monsoon rains. The other peak can be seen in August and September mainly due to drought.

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Spatial Distributionof Events by Districts

and DS Divisions :1974-2008


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Agricultural Loss Due toDisasters (in Hectares) -

Spatial Distribution:1974 - 2008

♥ The spatial distribution shows that the districts of Kurunegala and Ampara appear to have the highest loss of crop. In districts such as Colombo, Kandy and Kalutara the loss is somewhat low. This is because the agricultural sector is not as significant in these districts as in other districts.

♥ Further, the most affected DS divisions are located in the Southern and Western parts of the island, while certain DS divisions in the Northern and Eastern parts of the island are less affected.

♥ Mainly drought (52.2%), flood (38.9%) and Extreme wind events (4.2%) cause damage to agricultural crops. In 1987, 2001 and 2004 and damage appears to be mainly caused by drought and flood.

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♥ Flood was identified as the most common and hazardous

natural event in Sri Lanka.

♥ Floods in Sri Lanka are mainly due to excessive rainfall

received during monsoons and received as a result of

development of low-pressure systems in the Bay of

Bengal. (Cyclonic Floods)

♥ Floods are directly related to the amount of rainfall and

therefore a proper understanding about the distribution of

rainfall becomes important.

Floods in Sri Lanka

♥ Major floods are associated with the two monsoon seasons. During south-west monsoon (May – Sept.) The western, Southern and Sabaragamuwa provinces are vulnerable for floods during this period.

♥ During north-east monsoon (Dec. – Feb.) the Eastern, Northern and North-Central provinces are at risk of flooding.

♥ Since the beginning of the 20th century major floods that affected extensive areas of the country, appear to have occurred about 9 times. (1902, 1913, 1925, 1931, 1940,1947, 1957, 1963, 1978)

Monsoons and Floods

♥ Bank-full discharge – most important in terms of incidence and impact.This type of flood occurs when surface run-off entering the river exceeds the discharge capacity of the river channel.

♥ Flash Floods: Sudden accumulation of water on low-lying areas leads to flash floods. ( common occurance in urban areas)

♥ Breaching of reservoirs and channel bunds: mostly seen in the dry zone

♥ Tsunami: along coastal areas

Types of Floods in Sri Lanka

♥ The most destructive flood in the wet zone during the past 100 years, occurred in August 1947.

♥ Unusual heavy rainfall within the upper catchment areas of the Mahaveli and Kelani rivers was the main cause for this flood

♥ Daily rainfall figures for, Blackwater Estate 485 mm, Watawala 478 mm, Oonagaloya 475 m.m., Maskeliya 462m.m., Lucombe Estate 457m.m., Nawalapitiya 447 m.m., ( Highest ever recorded)

♥ In several areas along the windward side of the central highlands, the total rainfall in August 1947, was also the highest ever on record.

Floods in Sri Lanka– Historical Perspective- 1947 flood

Station Total Rainfall in August

1947 (m.m.)

Previous Highest August Total (m.m.)

Kandy 722 434

Peradeniya 813 363

Madulkelle 1280 365

Dickoya 1263 788

Hatton 1359 1047

Maskeliya 1493 1259

Norton Bridge

1556 n.a

Watawala 1584 n.a.

Blackwater 1612 n.a.

Source: Report of the Colombo Observatory 1947

Rainfall in August 1947

♥ High runoff rate ( as high as 60%, according to Maddumabandara)♥ The narrowness of the river valleys,♥ Excessive sedimentation along the river channels♥ Presence of sand bars, that obstruct the river outlets to sea.

♥ Flood levels: Nagalagam Gauge (Colombo) 12’.6” (Previous highest level was 11’.4”)

♥ Extensive areas along Mahaveli , Kelani and Kalu Ganga have been submerged to a depth of 30 feet.

Flood Damage♥ Floods destroyed at least about 40,000. private dwellings.♥ Rendered more than 400,000, people homeless.♥ Extensive damages to roads, bridges and railways.♥ Deaths, loss of Personnel possessions, not comprehensively

estimated

Other causes for flooding

♥ The setting: by the end of November1957 majority of irrigation tanks of the dry zone was spilling over or was near full capacity

♥ In early December rainfall was concentrated mainly on the North Eastern parts of the dry Zone

♥ From about 17th of December the zone of highest rainfall expanded gradually from a core area in the North East to encompass the entire Northern plains, and the Northern segment of the central highlands.

♥ The torrential rainfall that led to flooding began on 23rd December , and continued unabated until the 26th.

♥ Rainfall was heavily concentrated on Northern and Eastern parts of the dry zone. Daily total rainfall exceeded 400 m.m.

Floods of 1957

♥ Flood Levels: according to reports prepared by GA s, extensive areas in A’ Pura, Polonnaruwa, Vauniya, Mannar and Puttlam districts were submerged at places upto 30 feet or more.

♥ Localised floods in other parts of the country, excluding Southern Region

♥ Apart from the floods, landslides were reported in Kurunegala, Matale, Kandy Nuwara Eliya and Badulla

♥ Deaths: 171 (Annual Report for 1957- Dept. of Social Services)

♥ About 65,000, houses were either partially or totally damaged

♥ Irrigation Dept. reported serious damage to 35 major irrigation works, and minor damage to 53 others, in addition to breaching of more than 1300 village tanks.

♥ Exclusive damage to roads, bridges, railways, and to crops

Floods of 1957 ( Continued)

♥ According to Asian Disaster Reduction Center (ADRC) the 1978 cyclone alone affected

♥ More than one million people,♥ Killed nearly a thousand persons, ♥ Partially and completely damaged nearly 2,50,000 houses, ♥ Destroyed 90 percent of the coconut plantation in the Batticaloa

district (The government spent over Rs.600 million to bring immediate relief

to those affected.)♥ Also cyclones and floods of severe intensity struck Sri Lanka

in 1922, 1931 and 1964. ♥ Cyclone of 1978 incurred damages amounting to nearly 3.78

percent of the GDP while floods of 1992 caused losses close to 1.03 percent of the GDP.

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Floods of 1978

♥ Several flash floods occured recently, without giving much time for evacuation, and diminished within two to three days. In 2008, there were three flood events one in 29th April, 30th May and other in 19th July in Kelani, Kalu and Gin basins.

♥ Floods in Kelani river are important due to its outfall being near the capital city of Colombo.

♥ Flood area mapping in the lower reach of the Kelani river basin became a top necessity with frequent floods in Kelani River

♥ When the flood levels of Kelani are in between 5.0 ft. and 7.0 ft. at the Nagalagam Street gauge, they are within the limits of minor floods.

♥ When the level exceeds 7.0 ft. the flood is defined as a major flood

♥ When it exceeds 9.0 ft. the flood is considered to be dangerous.32

♥ Affected areas – Central, Northern, Eastern provinces, (specially Batticoloa and Trincomalee)

♥ Duration – One week (Due to Monsoon Rains)

♥ Deaths due to Flooding = 23 persons

♥ Over 541,000 persons were displaced and had to take shelter in 275 camps set up by the Government.

♥ This is stated to be worse than the Cyclone of 1978, which devastated the low-lying district of Batticaloa and displaced nearly one million persons. The worst disaster in the districts of Batticaloa and Ampara since 1913.

♥ The most devastating floods that had battered the Eastern coast of Sri Lanka and wreaked havoc in most parts of the island had cost the emerging economy a staggering Rs. 30bn or US $ 27mn.

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January 2011- Floods of Sri Lanka

Estimated precipitation over Sri Lanka for January 3 - 9. Up to 18 inches (525 mm) fell over eastern Sri Lanka. Image credit: NASA Earth Observatory.

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http://earthobservatory.nasa.gov/NaturalHazards/view.php?id=48515

♥ Recent past several flash floods occur, without giving much time for evacuation, and diminished within two to three days. So far, in 2008, there were three flood events one in 29th of April, 30th of May and other in 19th of July for Kelani, Kalu and Gin Ganga basins.

♥ Floods in Kelani river are important due to its outfall being near the capital city of Colombo.

♥ When the flood levels of Kelani are in between 5.0 ft. and 7.0 ft. at the Nagalagam (Colombo) gauge, they are within the limits of minor floods.

♥ When the level exceeds 7.0 ft. the flood is defined as a major flood

♥ When it exceeds 9.0 ft. the flood is considered to be dangerous.

♥Affected areas – Central, Northern, Eastern provinces

♥Duration – One week ( Due to Monsoon Rains

♥Flooding in Sri Lanka has resulted in deaths of about 23 persons during a week of monsoon floods in the Central, Northern and Eastern provinces especially Batticaloa and Trincomalee.

♥Over 541,000 persons were displaced and had to take shelter in 275 camps set up by the Government, bringing the total number of displaced persons to about 1,081,000.

January 2011- Floods

♥ The most devastating floods that had battered the Eastern coast of Sri Lanka and wreaked havoc in most parts of the island had cost the emerging economy a staggering Rs. 30bn or US $ 27mn.

♥ Affected areas – Central, Northern, Eastern provinces, (specially Batticoloa and Trincomalee)

♥ Deaths due to Flooding = 23 persons

♥ Over 541,000 persons were displaced and had to take shelter in 275 camps set up by the Government.

♥ This is stated to be worse than the Cyclone of 1978, which devastated the low-lying district of Batticaloa and displaced nearly one million persons. The worst disaster in the districts of Batticaloa and Ampara since 1913.

♥ During the period of 1974-2008, the highest

number of people affected was due to floods and next

highest number of people affected has been due to drought,

even though it was apparent as very insignificant in the

Profile of Different Disaster Categories.

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♥ The highest number of flood events was reported in 2003 totaling 255, and the average for the period was 77.

♥ The greatest number of people was affected by fl oods in 1994, 2003, 1990, and 1993. The largest number of houses damaged during the floods in 2003 totaled to 37,721 and in 1994 totaled to 19,857.

♥ The greatest damage to paddy occurred in 1994 (53,021 hectares), 1984 (51,034 hectares) and 1986 (47,564 hectares).

♥ Relief distribution was highest in 2003 (Rs.265,400,390) and in 2005 (Rs. 243,271,924).

♥ While the largest number of disaster events recorded; the

largest number of houses damaged or destroyed and the

largest amount of resources spent on flood relief was in 2003,

the largest number of people affected was in 1994, and the

greatest damage to paddy occurred in 1994.

♥ The Districts most prone to floods include: Kalutara,

Ratnapura, Colombo, Gampaha, Puttalam, Matara, Galle,

Ampara, Polonnaruwa and Hambantota.

The End

floods in sri lanka

Environment