Disaster Prevention Plan for South Africas Flooding Likelihood
South Africa has been ridden with a history of flash flood disasters that have come at the cost of loss of lives, displacement of thousands of families from their homes and a national economic burden due to; humanitarian demands post flooding, infrastructural and environmental rehabilitation demands. Climatic disasters in South Africa such as flooding and droughts have been the major disaster phenomena that have come as an economic growth obstacle.
Flash floods are defined as an unexpected event where theres a rapid rise volume of water that occupies a certain area of land and travels at rapid speed (NOAA, 2018). The key factors that influence flash floods are the volume of water and the topography of the area that the water occupies. The water is usually from the excessive rainfall over a short duration, overflowing dams and rivers or breaking off banks and levees are most times the source of these great volumes of discharge.
The topography may also create hydrological problems as it attributes to intensifying the accumulation of water. Construction of hard surfaces such as roads, bridges, pavements and buildings inhibit the infiltration of water into the ground. Furthermore, soils in dry regions have a low infiltration capacity, once saturated, the excess water remains as runoff.
Disasters are defined as events with consequences that disrupt human lives and financial, environmental and social and economic structures that help with the functioning of societies.
To this end, communities are not able to support or assist themselves in the face of such events. (Mohammad Valli Moosa, 1998)
The table below provides a record of the past ten years of the flash floods that have occurred in different regions of the country. Whereby in most cases, the occurrence of a flash flood event has hit the country in more than one province at the same time.
Table 1: Showing flash flood history of South Africa in the past 10 years Date Highest rainfall intensity Areas affected Loss of Lives Displaced people Cost of damage (CNY)
23 January 2011
90 mm in 24 hrs
5 March 2014
97 mm in 24 hours
28 July 2016
142 mm in 24 hrs
Millions (Specific amount undisclosed)
9 November 2016
90 mm in 3 hr with hail marbles of 20cm depth
6 fatalities, 1 missing
(Specific amount undisclosed)
11 October 2017
145 mm in 24 hrs
(specific amount undisclosed)
Figure 1: Image showing 2016 flash flood event in South Africa
South Africa has a climate that varies between arid and semi-arid, which also attributes to the flash flood disasters that the country has faced. The mean annual rainfall intensity in past years before the experience of flash floods has been 500mm. The drastic change in weather has been reported by climatologists to be due to global climate change and more specifically the La Nina affect. Table 1 illustrates that there has been a reduction in the number of provinces affected, the number of lives lost and the amounts of economic costs lost to the damages. However, the varying displacement of people only shows that reactive measures have been taken for such disasters instead of proactive ones.
Causes of Flash Floods in South Africa
South Africa has a comprehensive amount of policy framework on disaster management and prevention. However, the disaster events that have occurred in the past years have been of similar nature and in some instances have hit the same provinces more than once; this is a clear indication of poor implementation of these policy frameworks (Bongumusa M. Zuma, 2012) In
view of this, disasters have been re-defined as the consequence of poor risk management and implementation of preventative and mitigation measures. The consequences of flooding in all of the events described in table 1 have been due to the breaking of river banks, culverts that have been blocked off by debris due to no maintenance and ineffective channels of communication with the community. In addition, the developing of South Africa has also left many loop holes in terms of addressing disasters that come along with it. For instance, the biggest challenge facing South Africa is that with the development of the major cities, more of the poorer communities living on the outskirts are migrating into the cities and building informal housing on the flood plains for access of water. Furthermore, more formal housing developments and companies are encroaching onto the flood plains, reducing the surrounding vegetation and replacing them with impervious surfaces. This demonstrates that in a developing country, not only does climate contributes to natural disasters but also underlying issues such as the socio-economic status of the country and the countrys infrastructural capacity to deal with a disaster such as flooding.
Hazard Identification and Risk Assessment
The first step to developing a disaster prevention plan is by identifying the hazards, the risks that are linked to them, the root causes and thereafter providing preventative measures.
Table 2: Hazard Identification and Risk Assessment
? Torrential rains
? Agricultural land
? Damage of infrastructure e.g. roads, bridges, institutional facilities
? Flooding of toxic waste facilities e.g. mines, landfills and sewer treatment facilities
? Loss of lives and homes
? Loss of food supply
? Economic impact
? Possible cholera outbreaks or other deadly diseases
? The La Nina effect
? Informal settlement on flood plains
? Reduction of flood plains
? Narrowing river bends, removal of dykes and levees
? Breaking of river banks
? Socio-economic gap i.e. higher poor population unable to afford formal housing
? No harsh land use laws
? Commercial development along flood plains
? Reduction of coastlines
? Construction of impervious surfaces along coastline and river flood plains
? Removal of wetlands
? Easier access of ocean waters to communities
? Higher velocities of waters that drainage systems are incapable of draining
? No natural prevention of flooding
? No revision of land use zones with rapidly changing climate
? Under-designed sewer drainage
? Inability of drainage capacity to deal with 1-100, 1-200 year floods
? Erosion and weakening of roads, undermining of bridges rapid velocities of water on motorways
? No revision of drainage design manuals with recent rapidly varying climates
? Blocked drainage outlets
? Inability for areas to drain rain and flood waters
? Erosion and weakening of roads, undermining of bridges rapid velocities of water on motorways
? Homeless people living inside culverts and blocking off waterways
? Insufficient allocation of municipal funds to maintenance
? Flood awareness
? Lack of preparedness for communities
? Loss of life
? Displacement of people from homes
? Inadequate early warning systems of floods
? No proper communication channels to the public
Sustainable and Affordable Preventatives Approaches
Torrential rains and flash floods cannot be avoided however, the disasters or consequences that affect human life can be prevented. This is done through an integrated stakeholder involvement wherein; the government at policy making and at local levels are involved, civil engineering
institutions, emergency response teams e.g. fire and police brigade, weather forecasting institution, the community and media.
Due the encroaching of rapid industrial development on the river banks, and poorer communities erecting shanty houses, efforts should be made into restoring peat and wetlands. Where wetlands are already destroyed, artificial wetlands can be constructed in order to act as a sponge for intensive rainfall and swollen rivers.
South Africa is a country that suffers from cycles of droughts and floods, so dredging river basins, lowering dam levels will not be of any use as such flood waters usually help with increasing dam levels. However, more work can be done downstream to aid with flooding hazards. This includes; restoration of levees and building river dykes in community prone areas, creating more bends in the rivers in order to slow down high velocities of water and opening up river channels that have been straightened by communities that live along the river. These are only a few measures to decrease the flow rate of gushing streams.
According to research and surveys from designers, the design method that is used in calculating flood discharge for drainage design; is based on statistical mapping from 1987 (Du Plessis, 2015). This makes our current infrastructure under-designed for the current climate as the probability rainfall occurrence has changed, and the coefficients of concentration have also been altered due to the different spatial uses compared to those dated in 1987. A recommended use of a 1-100 or 1-200year flood return period with research efforts into revising South Africas drainage coefficients, will assist in future design of drainage systems (O J Gericke, 2012).
Non-maintenance of our drainage systems have made them obsolete. Removal of debris from drainage systems will ensure flow with no obstacles even during flooding. Poor people can be involved through employment to do labor-intensive work, in order to regularly clean out municipal storm water drains. This effort will result in; job creation and removal of poor people from informal homes and also raise community awareness of the importance of environment preservation.
Significant studies and implementations have been done on Sustainable Urban Drainage Systems (SuDs). The implementation of SuDs in South Africa has been growing in new developing cities in South Africa. However, nothing has been done to the older cities to ensure flood prevention. This is of great concern as the greatest impact of flash flooding occurs in these cities as the existing storm water drainages are bottle-necked due to poor-maintenance or under-design. The long-term solution for business and residential districts includes; removal of some impervious paving and replacing it with flood attenuation solutions such as swales, filter drains and pervious paving that run alongside hard surfaces (Neil Armitage, 2013), (Nor Zakaria, 2007). Furthermore, the construction of attenuation ponds is necessary in order to act as temporary storage. In this way overflowing sewer treatment plant on such flash flood event will be assisted with the amount of runoff from drainage systems.
South Africas coastal towns have encroached too close to the coastal lines and have destroyed sand dunes due to the demand of hotels for tourism purposes. However, these developments have suffered greatly due to floods.
The following actions need to be taken:
? Government municipalities need to revise their spatial use policies.
? Flood plains need to be reclaimed back from residents for their own safety.
? Sand dunes need to be restored to keep people separate from nature.
? In the case of informal settlements along the flood plains, stricter laws have to be enforced as currently government has no control over the growing communities that erect their homes along water sources.
The South African weather service has been efficient in reports of heavy rains, however, the methods of awareness for communities needs more attention. The poorer communities that live in poor conditions are the ones greatly affected by heavy rains or flooding. Assumptions of radio, television and newspapers as adequate methods of creating awareness is not accurate. More direct means of alerting communities are required so that they are able to prepare for potential floods. Uses of sandbags in low lying areas have proven to be successful in preserving lives and peoples homes. More affordable access to them needs to become a priority.
Flood prevention does not require only one solution, however, an integration of multiple solutions. It is the responsibility of everyone in a society to ensure that disasters as those mentioned in this paper are avoided in future. A living document on disaster prevention should be regularly updated as the global climate is changing as well. It is the role of each country to be proactive in predicting climate patterns and proactively designing cities accordingly. To this end lives and the countrys economic value will be preserved.
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