Why many floods lead to disasters



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Sri Lanka has got 103 river systems and of them 20 belongs to the Wet Zone of the country receiving more rainfall from April to September. These Wet Zone rivers frequently generate severe floods ending in disasters affecting many people in low-lying flood plains. Such flooding mainly inundates floodplains and in extreme cases expands beyond to nearby areas occupied by people and properties. The country experienced similar flood situations many times in the recent past, especially after year 2000, and frequency of such events has an increasing trend due to the impacts of climate change.


Year No of affected people due to flood


1969 1,000,000


1983 1,250,000


2003 695,500


2011 1,060,324


2014 1,100,020


2016 493,319


2017 879,778


Source: Sri Lanka Post Disaster Needs Assessment 2016 & 2017


Kelani, Attanagalu, Gin, Nilwala and Kalu rivers generated floods that caused not only displacement of people and damage to property, but consequences such as economic setbacks and disruption of basic services, as these rivers flow through main cities. Some densely populated areas of Colombo, Gampaha, Galle, Matara, Ratnapura and Kalutara districts often go under water during floods of aforementioned rivers. Flood impacts of other rivers are also considerable as the majority of those affected are poor people, who deserve temporary accommodation, food and other basic needs after a flood disaster.


The flood risk


Any risk of floods is a combination of hazards, vulnerability and exposure, and reduction of the magnitude of any of these three inherent factors would abate the risk and vice versa. Flood hazards, even if showing an escalating trend due to climate change, do not always end up in disasters if there is no exposed vulnerability. Exposure can be defined as the situation where people, houses, industries, public facilities and other infrastructure are located in hazard-prone areas. Presence of aforementioned entities in hazard-prone areas, merely, is not sufficient to create a disaster unless they are vulnerable. For instance, a house constructed on elevated piers or on a land at an elevation above flood level would not be vulnerable, even if it is exposed to a flood hazard.


Vulnerable people


It is obvious the present increasing trend of flood disasters is partly due to the occupation of low-lying flood hazard-prone areas by people and industries due to the scarcity of lands. These kinds of developments cannot be prevented as existing laws and regulations do not have sufficient provisions to interfere with private property. On the other hand, most of the new occupants of low-lying areas, who migrated from other areas, are not aware of such flood risks, until they really experience the flood. If they had been properly informed of potential flood risk by the authorities, who approved building plans, these new comers would not have resided in such flood prone areas.


Although stream reservations have been declared under the Land Development Ordinance No: 19 of 1935, they are only applicable to state lands. As a result, time to time regulations by way of gazette notifications have been enforced by various authorities, which are varying from place to place and seem to be not strong enough to control land use.


Illegal encroachment of river reservations is the other side of the same coin, when flood disasters are concerned. Further, taking action by relevant authorities against encroachments and unauthorized land use is often hindered by the occupants, with the support of politicians.


British constructed several earth embankments on either side of Kelani river in 1930 to protect Colombo from floods. Since then, Colombo city was free from floods except in a few extreme cases, and those bunds now seem to be inadequate to mitigate ever escalating flood risks. Although exact statistics are not available, there are a large number of unauthorized houses constructed in the flood zones encroaching river reservations. Recent floods in 2016 and 2017 displaced a large number of unauthorized settlers within the area between the Kelani river and flood embankments, and similar situations can be observed in other parts of the country as well.


Lack of real time early warning is another problem we have today. If an effective and efficient early warning is given on the verge of a flood hazard, people can move out of the area with their movable property minimizing the exposure conditions.


Mitigation measures


Basically, mitigation of flood disasters is done either by keeping water away from people and property, or keeping people and property away from water.


As discussed previously, keeping people away from water obviously will involve land acquisition and resettlement measures. In a situation, where land acquisition has been a tough task even for a development project, removal of many thousands of people from our river flood plains would be far from reality. However, people living in most critical places, like river reservations, definitely have to be removed as they are taking all sorts of risks, including to their lives.


In order to discourage those who wish to construct new houses and other facilities in these flood-prone areas, authorities can take the following temporary action until proper laws and regulations come into play.


Firstly, relevant authorities have to develop flood maps and inform relevant local authorities and the public of the potential flood risk in the area, while demarcating flood zones physically on the ground according to the severity.


Keeping water away from people can be done by structural interventions. Construction of reservoirs in the upstream and construction of flood defense walls as already done in Kelani river are such measures, though some lands are to be acquired.


People also can intervene to mitigate their risks to certain level by taking individual actions. Those who wish to construct houses and new buildings in such flood hazard-prone areas can construct these structures so that lowest living floor space is above the projected water levels, while keeping the ground floor vacant allowing flood water to flow through. Hence, dwellers of this type of houses are safe from floods and need not to vacate their places during a flood.


As a non-structural method, development of a real time early warning system is of prime importance, and it should be capable of disseminating descriptive warnings to the right people at the right time. When the practical implications and high cost of implementing other structural mitigation methods are considered, early warning seems to be a solution that can be implemented sooner.


When hazards like floods are concerned, it is worth mentioning the saying, "It happens-what matters is how you deal with it".


ENG. THUSHARA DISSANAYAKE


(The writer is a chartered Civil Engineer, material based on personal views)


 
 
 
 
 
 
 
 
 
 
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