Department of Environmental and Geographical Science
Honours Thesis
Susceptibility of municipal infrastructure and related services to extreme weather events in the Western Cape: A comparative study of 3 towns
By Janine Bauer
Disaster Risk Science Honours 2006
Abstract:
Climate change predictions have indicated that there will be an increase in the frequency of extreme weather events. The Western Cape is recurrently experiencing extreme weather events. These result in significant losses to municipal infrastructure. In April 2005, Bredasdorp was affected by a cut-off low pressure which caused widespread flooding and significant damage to municipal infrastructure. Both Montagu (March 2003) and Heidelberg (December 2004) extreme weather events have shown similarities with Bredasdorp. These similarities extend not only to the type of infrastructure that is being damaged but also factors that are leading to the damage.
By establishing strategies for the prevention and mitigation of the impacts of extreme weather events and resulting floods, there will be a greater capacity for adaptation to the climate change scenarios predicted for the Western Cape.
2 Declaration:
I, Janine Bauer hereby declare that this thesis is my own work and each significant contribution to, and quotation in; this thesis from the works of other people has been attributed and has been cited and referenced.
3 Table of Contents
Abstract 2 Declaration 3 List of Figures 5 List of Tables 5 Acronyms 6 Definitions 6 Acknowledgements 7
Chapter1: Introduction 8 1.1 Public Infrastructure and Disaster Risk in the Western Cape. 8 1.2 Exposure of infrastructure to extreme weather in the Western Cape 8 1.2.1 Climate Change Impacts: 8 1.2.2 Evidence of extreme weather events in the Western Cape (since 2003): 8
1.3 Focus of this thesis 9 1.3.1 Aim and Objectives: 9 1.3.2 Limitations: 10 1.3.3 Ethical Considerations 10 1.3.4 Organisation of this thesis 10
Chapter 2: Context for the Research 12 2.1 Introduction 12 2.2 Extreme weather in the Western Cape 12 2.3 Capacity of existing municipal infrastructure 12 2.4 Overberg and Bredasdorp cut-off low 13
Chapter 3: Literature Review and Conceptual framework 15 3.1 Introduction 15 3.2 Climate change in the Western Cape 15 3.3 Cut-off low phenomena 17 3.3.1 Meteorology 17 3.3.2 Documented impacts 17 3.4 Current vulnerability status of municipal infrastructure in the Western Cape 18 3.5 Risk exacerbating conditions: Focus on debris 19 3.6 Established methodologies for disaster loss estimation 20
4 3.7 Conceptual Framework for this study: Pelling 20
Chapter 4: Methodology 24 4.1 Introduction: Case study of April 2005 cut-off low Bredasdorp 24 4.2 Collection and compilation of secondary data 24 4.2.1 Meteorological data (sources) 24 4.2.2 Impact information 24 4.2.3 Economic loss information 24 4.3 Field research in Bredasdorp 25 4.3.1 Semi- structured interviews 25 4.3.2 Direct Observations 25 4.3.3 Georeferencing of storm impacts 25 4.4 Analysis of Infrastructural Impacts: Application of Pelling’s Model of Vulnerability 25
Chapter 5: Findings and Analysis 26 5.1 Introduction 26 5.2 Extreme weather risk profile of Bredasdorp 26 5.2.1 Historical Rainfall: 26 5.2.2 Topography and infrastructure: 28 5.2.3 Fire and Drought Profile 30 5.3 Description of April 2005 Cut-off Low 30 5.3.1 Rainfall 30 5.3.2 Description of flood process 31 5.3.3 Warnings Issued 31 5.3.4 Reported or Recorded impacts and associated economic losses 32 5.4 Respondents perceptions of flood risks 33 5.4.1 Location and siting of the sloot 33 5.4.2 Vulnerability and maintenance of the stormwater system 33 5.4.3 Heavy debris loads and management 34 5.4.4 Expansion on the town: 35 5.5 Cut-off low occurrences in Heidelberg and Montagu 35 5.5.1 Heidelberg December 2004: 36 5.5.1.1 Recorded Infrastructural Impacts: 36 5.5.1.2 Factors exacerbating flooding: 36
5 5.5.2 Montagu, March 2003 38 5.5.2.1 Recorded Infrastructural Impact 39 5.5.2.2 Factors exacerbating flooding 39 5.6 Comparison of events 40 5.7 Application of Pelling’s model to April 2005 cut-off low 43
Chapter 6: Discussion and Recommendations 46 6.1 Introduction: 46 6.2 Recurrent infrastructural loss patterns and exacerbating flood risk factors 46 6.2.1 Infrastructure losses: 46 6.2.2 Factors exacerbating flooding: 47 6.2.3 Flood Mitigation Strategies in Bredasdorp: 47 6.3 Relevance of findings to Pelling’s vulnerability framework and ECLAC loss estimation model 48 6.4 Future research and risk reduction: 48
References: 50 Appendix A: Weather: 10-12 April 2006 52 Appendix B: Georeferencing of storm impacts 54 Appendix C: Photographs 56
6 List of Figures Figure 1: Map of the Overberg ...... 15 Figure 2: Pellings vulnerability framework: Components of environmental risk ...... 24 Figure 3: Diagram of framework used in the context of infrastructure ...... 25 Figure 4: Graph of recorded rainfall for April from 1878 to 2000 ...... 29 Figure 5: Map of rough estimate of the route of the sloot ...... 31 Figure 6: Map of the Drinkwaterkloof and river ...... 32 Figure 7: Infrastructure damaged during April 2005 event...... 57 Figure 8: Infrastructure damaged in surrounding areas ...... 58 Figure 9: Damage to culvert and road between Napier and Bredasdorp ...... 59 Figure 10: Debris loading during the April 2005 event...... 59 Figure 11: Kogmanskloof pass damaged during March 2003 event ...... 60
List of Tables Table 1: Years with April Recording 100mm or more rainfall between 1878 and 2000 in Bredasdorp...... 30 Table 2: Comparison of Montagu, Heidelberg and Bredasdorp cut-off lows...... 44 Table 3: Application of Pelling's Framework ...... 46 Table 4: Daily record from 10-12 April ...... 56
7 Acronyms DiMP Disaster Mitigation for Sustainable Livelihoods Programme DWAF Department of Water Affairs and Forestry ECLAC Economic Commission for Latin America and the Caribbean MIG Municipal Infrastructure Grant SAWS South African Weather Service.
Definitions: Adaptation: Adjustments or changes made by humans in response to a changing or new environment Climate Change: A change in climate which is attributed directly or indirectly to human activity that alters the composition of the global atmosphere and which is in addition to natural variability observed over comparable time periods. (Midgley et al 2005) Cut-off low: A cold low which has become displaced out of the basic westerly current, and lies to the south of this current. (SAWS 2005) Debris Loading: Debris banking up against structures. Exposure made up largely a product of physical location and the character of the surrounding built and environment. (Pelling 2003, 48) Mitigation: Measures taken to reduce the effects of a disaster. Sloot: A water channel. Sustainable Development: A broad concept referring to a country’s need to balance the satisfaction of near term interests with the protection of the interests of future generations. (Midgley et al 2005) Resilience The ability of a person to deal with or adapt to a hazard (Pelling 2003, 48). Resistance reflects economic, psychological and physical health and their systems of maintenance, and represents the capacity of an individual or group of people to withstand the impact of a hazard.” (Pelling 2003, 48) Vulnerability: Conditions that increase the susceptibility of a person, structure or area to the impacts of a disaster
8 Acknowledgements:
I would like to extend my deepest thanks to Dr Ailsa Holloway for all the help and guidance she has given me for this thesis. I really appreciated all the time and assistance that she has provided me.
I would like to express my gratitude to Mr Reinard Geldenhuys for making time available to assist me in my research and providing invaluable information. I want thank Mr Groenewald, Mr G Hugo, Mr H Matthee, Mr J Daniels and anyone else who provided me with data.
I would like to thank the University of Cape Town and the Department of Environmental and Geographical Science for making funds available.
9 Chapter1: Introduction
1.1 Public Infrastructure and Disaster Risk in the Western Cape. Appropriate and robust public infrastructure is essential prerequisites for economic growth and development. Its contribution to the overall social and economic development in the Western Cape has been clearly defined in the Province’s Strategic Infrastructure Plan (Province of the Western Cape, 2006). However, sustained growth in the Western Cape is also influenced by the Province’s capacity to withstand and recover from recurrent natural and other threats that potentially undermine its development potential. In this context, public infrastructure plays a critical role in minimizing the province’s disaster risks, particularly those generated by extreme weather. The need for increased attention to the vulnerability of public infrastructure within the province has been underlined since 2003 by recurrent disaster occurrences that have had costly impacts. Moreover, there is increasing evidence that infrastructure in the Western Cape will come under even greater pressure as a result of future climate variability.
1.2 Exposure of infrastructure to extreme weather in the Western Cape
1.2.1 Climate Change Impacts:
Climate Change scenarios indicate that there will be an increased likelihood of extreme weather events. Possible implications of climate change in the Western Cape, based on current projections in South Africa, include: An increase in severe storms such as those associated with cut-off low-pressure systems will lead to more frequent flooding and consequent damage to farmlands, infrastructure and inhabitants of flood-prone areas (Weaver and Chapman ND).
There is also the prediction of more intense rainfall falling in few rainfall events. This will also mean that there will be an increased likelihood of flooding. (Midgley et al 2005)
1.2.2 Evidence of extreme weather events in the Western Cape (since 2003):
Since 2003, there have been a number of cut-off lows which have resulted in extensive damage in regions of the Western Cape. In March 2003, a cut-off low pressure caused
10 damage across towns in the Breede/Winelands Municipality. The total direct reported loss information associated with this disaster event, showing a total of R212 422 663 was sustained in direct economic losses. Of this, R95.5 million (45% of the total) were losses borne by Provincial Government Departments and R6.9 million (3.26%) were costs carried directly by district municipalities and selected municipalities in the weather-affected areas. (DiMP 2003)
During 2004, the Western Cape experienced 2 extreme weather events which resulted in damage. In August 2004, Cape Town was affected by two cold fronts which caused significant rainfall and resulted in significant flooding in many informal settlements across the Cape Flats. These floods incurred direct losses exceeding R 6.5 million (DiMP 2004). In December 2004, Heidelberg and surrounding towns suffered significant damage after being affected by a cut-off low pressure shortly before Christmas. The town sustained an enormous amount of damage due to the flooding of the Duiwenshok River and the Canal which flows through the town. This flooded 50% of the houses in the area and many businesses were also flooded. There was also an estimated R 2.5 million damage to the sewerage works. (DiMP 2005)
In April 2005, Bredasdorp and surrounding areas also experienced large scale flooding when they were affected by a cut-off low pressure.
Most recently, the Southern Cape has incurred an enormous amount of damage when they experienced two cut-off low pressures in August 2006. The damages sustained by the towns in the areas are predicted to run into billions of rands. (Department of Local Government and Housing 2006)
1.3 Focus of this thesis
1.3.1 Aim and Objectives: Recognising that infrastructure in the Western Cape will experience increasing climate variability in the future; this project aims to investigate 3 extreme weather events in the Western Cape and their impacts, in order to identify disaster risk and related vulnerabilities in critical municipal infrastructure of 3 towns.
11 In this context, the study’s specific objectives are: • To study and compare the biophysical characteristics of 3 cut-off low pressure systems that occurred in 2003, 2004, 2005. • To research the impacts sustained by critical municipal, provincial and other infrastructure as a result of these events. • To identify similarities and differences in the levels of vulnerability of exposed infrastructure of the 3 towns • To explain these differences by applying Pelling’s Framework on Vulnerability.
1.3.2 Limitations: There were a number of limitations that were encountered while conducting this research. The main limitation was language. As the Overberg is a predominantly Afrikaans speaking area it was difficult for an English-speaking researcher to understand and adequately communicate in Afrikaans. It also became problematic for respondents as although they were able to converse in English, they often were unsure of how to express their ideas in understandable English.
Another problem was the distance between Cape Town and Bredasdorp. Although the researcher made several field visits to Bredasdorp, distance and time constraints condensed these visits.
1.3.3 Ethical Considerations There are a number of ethical considerations that need to be taken into consideration when writing this thesis. All officials and local authorities will be identified by their official designation or title not their name in order to ensure confidentiality. There will be transparency. In adding, copies of this thesis will be sent to those interviewed as well as other stakeholders who requested a copy.
1.3.4 Organisation of this thesis This thesis is organized into 6 separate chapters. Chapter 2 describes the context for the research: Chapter 3 reviews relevant literature and presents the conceptual framework that informed the research
12 Chapter 4 outlines the methodology for collecting and consolidating information for the study. Chapter 5 presents qualitative and quantitative findings related to the cut off low which impacted Bredasdorp. Chapter 6 concludes the thesis through a discussion of findings and the presentation of recommendations.
13 Chapter 2: Context for the Research
2.1 Introduction The context for this research is informed by two major considerations, the first being the increasing exposure of municipal infrastructure to extreme weather within the Western Cape and the second, the limited capacity of existing municipal infrastructure to withstand and minimise the impact of extreme weather events.
2.2 Extreme weather in the Western Cape The Western Cape is highly disaster prone and experiences at least one destructive extreme weather event a year. Research has shown that southern Africa experiences on average eleven cut-off lows each year with the south western region of South Africa being the preferred location for these events (Singleton and Reason 2005). Studies of previous extreme weather events have shown that cut-off lows occur regularly and result in significant damage to Western Cape towns (Singleton and Reason 2005).
2.3 Capacity of existing municipal infrastructure While future climate change scenarios indicate an increased frequency of extreme weather, the Municipal Engineer in Bredasdorp reported that the municipal stormwater infrastructure in the Western Cape is normally designed to resist 1:2 or 1:5 year flood events, while that in outlying rural areas is designed for 1:50 year flood occurrences. This implies that existing municipal infrastructure is less likely to be able to cope with the run-off and river flows associated with an increased frequency of extreme weather events expected to accompany climate change.
Simultaneously, Municipal officials alleged that increased costs associated with civil engineering construction are lowering the standards of stormwater drainage design, furthermore, the costs required to increase the size and capacity of existing stormwater infrastructure exceeds the budgets of many municipalities within the Western Cape (per com. MIG official).
The consequences of limited municipal financial capacity to increase stormwater drainage infrastructure is that these systems are already unable to cope with the large volumes of water usually experienced during extreme weather events.
14 While funds for municipal infrastructure expansion are available through MIG approved by National Treasury, the level of funding available to the Western Cape is extremely limited. This is evident in the 2006/2007 MIG allocation for the Cape Agulhas region comprising of Struisbaai, Bredasdorp, Napier, Waenhuiskrans which reportedly amounts to R2.411 million (pers comm. MIG Official)
2.4 Overberg and Bredasdorp cut-off low The most damaging and destructive impacts of extreme weather in the Western Cape are experienced in the Province’s municipalities. In this context, the Overberg recurrently experiences cut-off low phenomena, including events in 2003 and 2005. In April 2005, a destructive cut-off low resulted in severe impacts specifically the town of Bredasdorp.
Bredasdorp is located in the Overberg in the Western Cape. It is situated along the R316 at the foot of the Heuningsberg. The town is surrounded by farming areas and the main crop grown in the area is wheat. Sheep farming is also common in the area. The town is known as the economic capital of the Cape Agulhas Region and has a number of businesses and service providers. The population of the town is 22 000. (Cape Agulhas Regional Visitors Guide 2006)
Figure 1: Map of the Overberg (Source All Cape Accommodation)
There is a non perennial river, Droë River which flows through the town. This river flows from the Drinkwater Kloof which is the main catchment above the town. The Droë River
15 joins the Kars River 3km outside of town on the Arniston Road. (pers com Municipal official)
In the context of the South Africa’s Disaster Management Act and Disaster Management framework (ND) which focus on the promotion of disaster risk reduction, Bredasdorp’s experience of the April 2005 cut-off low provides insight into the role of infrastructure and how it can minimise weather risks.
16 Chapter 3: Literature Review and Conceptual framework
3.1 Introduction This study is informed by seven significant areas of literature and publications. These include climate change and its consequences for the Western Cape, information on cut- off low phenomena. It is also shaped by factors that determine infrastructural vulnerability consideration and associated considerations such as debris flow. This study is similarly informed by methods for estimating disaster losses. The research has also been informed by Pelling’s (2003) vulnerability analytic framework.
3.2 Climate change in the Western Cape
Climate change projections show that there will be a definite drying trend in the Western Cape. One set of projections anticipates that there will be a weakening of winter rainfall with possibly slightly more summer rainfall (mainly in the east of the province). There will also be a shift to more irregular rainfall with a possibility of greater intensity. Across the Western Cape it is anticipated that there will be increase in the minimum and maximum temperatures. (Midgley et al 2005) An increased in intensity in rainfall events may be accompanied by increased runoff and riverine flooding (Midgley et al 2005). Future projections also anticipate an increase in extreme weather events such as droughts and flooding. (Midgley et al 2005)
Weaver and Chapman (ND) also concur with the Midgley et al (2005) on the effects of climate change in the Western Cape. They foresee drying out of the Western Cape along with an increase in the frequency of severe storms such as those associated with a cut-off low pressure. These severe storms may result in increased in flooding.
Weaver and Chapman (ND) further state that there will be the following implications for the Western Cape as a result of climate change: • Drying of the Western Cape leading to increased water stress and loss of agricultural production, while the eastern parts of South Africa may become wetter • Increased frequency of extreme fire hazard will impact negatively on forestry and the fynbos floral kingdom
17 • An increase in severe storms such as those associated with cut-off low-pressure systems will lead to more frequent flooding and consequent damage to farmlands, infrastructure and inhabitants of flood-prone areas • Rising sea levels and an increased frequency of storms at sea will lead to damage along low-lying coastal regions • The large number of category-five hurricanes in the western hemisphere has led to severe damage to infrastructure and oil production and a concomitant increase in insurance premiums; the South African insurance industry is sensitive to extreme weather events such as hailstorms over Gauteng, so similar trends in premiums could be expected
The implications of these projections are that increasing storm severity will have serious impacts for infrastructure as well as coastal developments. Roads, stormwater drainage and water supply will have to be adapted in order to withstand these future stresses and demands. For example, regional and local government will need to ensure that structures built are able to survive flooding. These improvements will be costly but imperative in order to meet the demands of not only climate change but also the increase in population. (Midgley et al 2005)
Studies of previous devastating extreme weather events in the Western Cape have shown that at the present the damage and financial losses that were incurred, particularly by the roads authorities and agricultural sectors have indicated high levels of vulnerability to such processes. (Midgley et al 2005) Moreover, regular ongoing maintenance of stormwater drainage is required in order to prevent exacerbating flooding. Much of infrastructure in the Western Cape has been under designed and has not considered the likelihood of more frequent flood events. (Midgley et al 2005)
In addition, roads and railways that have been built in low lying areas will be vulnerable to flooding during heavy storms and storm surges in areas close to the coast line. The subsequent damage sustained to this infrastructure from flooding is expensive to repair as well as inconvenient to commuters. Delays resulting from damage or repairs can also negatively affect businesses and people who rely on transport. (Midgley et al 2005)
18 3.3 Cut-off low phenomena The South African Weather Services (2003) defines a cut-off low as a cold low which has become displaced out of the basic westerly current, and lies to the south of this current. Cut off lows can remain stationary for several days or longer until they are rejoined to the Jet stream. They are associated with particularly destructive impacts.
3.3.1 Meteorology Southern Africa experiences on average eleven cut-off low pressures each year with the most common occurrence between March and May. Cut-off low pressures are associated with deep moist convection and can lead to very heavy rainfall over a short period of time. This makes them conductive to flash flooding. Examples of this are August 2002 when more than 300mm of rainfall fell over East London in 24 hours (the monthly average for August is 78mm) and in April 2003, when the town of Montagu suffered significant damage when a cut-off low tracking east along the south coast of South Africa received 200mm in 24 hours compared to the monthly average for March which is just 19.5mm. (Singleton and Reason 2005, 3-4)
Cut-off lows form when a trough of cold, high latitude air in the middle –upper troposphere becomes cut-off from its source region. Over South Africa, a cut-off low aloft is typically accompanied by a strong ridge of surface high pressure to the south of the system with a near surface depression to the east of the cut-off low aloft giving rise to a baroclinic structure. (Singleton and Reason 2005, 5)
3.3.2 Documented impacts Reports and research that have been conducted on previous cut-off low pressures that affected the Western Cape show that our infrastructure is very susceptible to cut-off low pressures. In December 2004, the Western Cape experienced a cut-off low which caused widespread damages in the Overberg and more specifically Heidelberg. The most expensive cost was the damage to the Heidelberg sewerage works. The sewerage works were completely flooded and resulted in sewerage being released into the Duiwenshoks River. The majority of the damage was due to a pipe which transports sewerage over the river was washed away by flood waters. The Overberg also received damage to its roads and bridges. Large parts of Heidelberg were extensively flooded when the canalized Klip River which runs through town bursts its
19 banks. This resulted in many properties being flooded and walkways and road surfaces being ripped up by the force of the water. (DiMP 2005)
The Western Cape town of Montagu received significant damage when they were affected by a cut-off low pressure in March 2003. Many bridges in area were damaged due to overtopping, scouring the embankments and debris loading. Water supply and sewer lines failed due to washing away of infrastructure due to scour. (DiMP 2003)
Most recently, the Southern Cape and specifically the Eden and Hessequa Municipalities received millions of rand damage when they experienced a devastating cut off low in August this year. The Eden District Municipality has incurred damages of R6.8 million and the Hessequa Municipality sustained damages of R 19.4 million. During the storm, there was also damage to stormwater drainage, water, sanitation as well as other municipal structures. (Western Cape Local Government 2006)
3.4 Current vulnerability status of municipal infrastructure in the Western Cape While repeated extreme weather events have exacted severe losses on infrastructure in the Western Cap, the overall status of municipal infrastructure within the Province is extremely poor.
The Strategic Infrastructure Plan (2006) has reported that in the Western Cape alone the local municipalities have a backlog of more than R 740 million for road maintenance and rehabilitation. Another major concern is the backlog of subterranean infrastructure, namely sewerage, water and stormwater. Regular on going maintenance to address breakages and blockages is imperative in extending the life of the infrastructure. If this does not form part of a scheduled programme the life expectancy of the infrastructure is drastically reduced. (Strategic Infrastructure Plan 2006)
The vulnerability of the municipal infrastructure can be attributed to many reasons. These include: • Poor design: The Bredasdorp Municipal Engineer reported the municipal infrastructure within towns is designed for 1:2 or 1:5 year floods, while infrastructures in the surrounding rural areas are designed for 1:50 year floods.
20 • The lack of human resources. Outside of Cape Town there are only 6 Engineers in the whole of the Western Cape. (per com MIG authority) • Lack of regular maintenance. (per com Bredasdorp Municipal Engineer)
3.5 Risk exacerbating conditions: Focus on debris With specific reference to the exposure of municipal infrastructure in mountainous areas to extreme weather, a critical driver of risk is the presence of debris. Internationally, debris flows and floods are seen as a major hazard which can be very destructive and usually result in extensive damage to infrastructure. Cannon et al (2000, 1103) reports that debris flows pose a hazard distinct from other sediment laden flows. This is because their unique destructive power allows them to occur with little warning, resulting in great impulsive loads on objects in their paths. Even small debris flows can denude vegetation, block drainage ways, damage structures and endanger lives. Wilford et al (2004, 1) further elaborates that debris flows, debris floods and floods in mountainous areas are responsible for loss of life and damage to infrastructure.
Debris floods are essentially high stream loads with large quantities of mud, rocks and debris. Stream flows water flows play a dominant role in the down ward movement process of debris floods. (Cheng et al 2005, 167)Debris floods are triggered by peak flows and debris slides from hill slopes. They carry additional inorganic and living and dead materials from streambeds and stream banks. These result in damage to structures and loss of life. (Cheng et al 2005, 165)
Debris flow and floods usually occur at the time of high accumulated rainfall and very high rainfall intensity. (Cheng et al 2005, 165) Land use conditions and changes caused by human and natural factors have been identified as a factor contributing to hazardous debris flows. Activities contributing to debris flows are improper slopeland cultivation, removal of vegetation cover and road construction (Cheng et al 2005, 165).
Also relevant to the Overberg, is the relationship between fire occurrence and subsequent risk of debris flows. It is reported that fire has can increase the likelihood of flooding as the vegetation removed by the fire results in decreased rainfall interception and infiltration resulting in an increase in surface runoff and even accelerated erosion of hill slopes. (Cannon et al 2000, 1113) In addition, fires cause damage to vegetation and
21 result in a loss in the strength of the roots to anchor sediment. This contributes to the soil having reduced effective soil cohesion and leads to accelerated erosion. (Cannon et al 2000, 1113)
Debris flows are also increased by the specific features of a drainage basin. Cannon et al (2000, 1113) reports that a rugged drainage basin form coupled with a steep channel gradient and steep, rough hill slopes are conducive to the generation of debris flows while less rugged basin, gentler channel gradient and long smooth hill slopes produce significant flooding.
3.6 Established methodologies for disaster loss estimation Estimating losses attributable to extreme weather and other natural hazards has been a critical area of study especially in Latin America. In this context the United Nations Economic Commission for Latin America and the Caribbean (1999) has established a method to calculate direct damage to infrastructure as a result of natural hazard events. This approach, known as the ‘ECLAC’ Model, views direct damage as “all damage sustained by immovable assets and inventories (of finished and semi-finished products, raw materials and other materials). Direct damage refers mainly to the loss of infrastructure.” (United Nations Economic Commission for Latin America and the Caribbean 1999, 13).
According to the ECLAC Model, the estimation of direct damage to infrastructure requires on-site visits to verify the losses. (United Nations Economic Commission for Latin America and the Caribbean 1999, 175)
ECLAC also recognises that a range sources can be used to estimate infrastructural losses such as governmental entities and the media. However, it cautions that governmental entities may underestimate actual loss in part to avoid causing local panic and to avoid disclosing the true magnitude of damage. (United Nations Economic Commission for Latin America and the Caribbean 1999, 175)
3.8 Conceptual Framework for this study: Pelling For the purpose of this study Pelling’s analytic framework on urban vulnerability will be applied to municipal infrastructure within Bredasdorp. While normally applied to human
22 vulnerability the framework conceptually provides a systematic lens for examining the exposure, resistance and resilience of infrastructure to extreme weather.
In Pelling’s (2003) framework, vulnerability is conceptualised in three dimensions exposure, resistance and resilience. In this framework, exposure is seen as “largely a product of physical location and the character of the surrounding built and natural environment.” (Pelling 2003, 48). Resistance of a person to a hazard is shaped by their livelihood and their health. “Resistance reflects economic, psychological and physical health and their systems of maintenance, and represents the capacity of an individual or group of people to withstand the impact of a hazard.” (Pelling 2003, 48) The resistance of an object or person is linked to their ability to withstand a hazard. If their resistance is low, they will be unable to withstand even the smallest of hazards. The most successful efforts to enhance resistance will not directly target disasters vulnerability, but focus on the wider goals of economic, social and political inclusion. (Pelling 2003, 48) Resilience is the ability of a person to deal with or adapt to a hazard. It is a product of the degree of planned preparation undertaken in the light of potential hazard, and of spontaneous or premeditated adjustments made in response to a felt hazard, including relief and rescue (Pelling 2003, 48). These three dimensions to vulnerability are shaped by access to rights, resources and assets. Access profiles are in turn rooted in local and global political and socio-economic structures. Through the relationship between these components of vulnerability may not always be reinforcing, this is often the case, so that the opportunities of resilience tend to be less common when resistance is already low and exposure is high, and vulnerability increases with each successive disaster event.
23
Figure 2: Pellings vulnerability framework: Components of environmental risk (Source: Pelling 2003 )
In this study however, the focus is less on human vulnerability, with greater emphasis on infrastructure. In this context, Pelling’s framework has been slightly modified so that infrastructural vulnerability is informed by: • Exposure (specifically geographic location and the character of the surroundings) • Resistance (specifically the parameters which shaped the initial construction of individual infrastructure as well as the quality of ongoing maintenance and upgrading) • Resilience (specifically preparedness measures taken in advance of an impending extreme weather event and protective responses during the event).
For the purpose of this study, particular focus will be placed on the exposure and resistance components of municipal infrastructure.
24
Vulnerability
Exposure Resistance Resilience
Geographic Character of Initial Maintenance Preparedness Protective Location Surroundings Construction Measures Responses Parameters
Figure 3: Diagram of framework used in the context of infrastructure
25 Chapter 4: Methodology
4.1 Introduction: Case study of April 2005 cut-off low Bredasdorp On the 10, 11 and 12 of April 2005, Bredasdorp experienced a cut off low which resulted in a large amount of precipitation and produced widespread flooding. The damages due to this extreme weather event were extensive and not only houses in the area were flooded but much of the infrastructure in the town and surrounding area had significant damage. This event provided a case study opportunity to investigate the vulnerability of municipal infrastructure to extreme weather.
A combination of methods was used to undertake this study. These included the collection and compilation of secondary data and field research in Bredasdorp.
4.2 Collection and compilation of secondary data
4.2.1 Meteorological data (sources) Meteorological data were obtained from two different sources. Data were received from the South African Weather Service via email. The other source of meteorological data was the local meteorologist in Bredasdorp. This meteorologist has his own webpage on the Overberg Agricultural website where he provides short term and long term forecasts. He was able to provide accurate historical rainfall and data for the April event for Bredasdorp as he has a weather station in the municipality.
4.2.2 Impact information Impact information on past cut-off low events was obtained from information and reports which has already been compiled for the 2003 and 2004 cut-off lows by Disaster Mitigation for Sustainable Livelihoods Programme. Information concerning the April 2005 event obtained from unpublished sources such as minutes of the Provincial Disaster Management Committee meetings, as well as from the Cape Agulhas Municipality Situation Analysis reports.
4.2.3 Economic loss information This information was obtained from records from Cape Agulhas Municipality
26 4.3 Field research in Bredasdorp
Field research involved the following methods
4.3.1 Semi- structured interviews Semi-structured interviews were conducted both in Cape Town and Bredasdorp. In Bredasdorp, interviews were undertaken with the Overberg Disaster Manager, an official in the Roads Department, the Municipal Engineer as well as other Municipal official. The local meteorologist was also interviewed in order to obtain information around the meteorology of the event.
4.3.2 Direct Observations Observations and information concerning the infrastructure were taken while driving through the affected area during visits to the Bredasdorp.
4.3.3 Georeferencing of storm impacts GPS co-ordinates were taken at each of the sites where damage to infrastructure occurred. These positions were then plotted using the ArcView and Map Source computer programs.
4.4 Analysis of Infrastructural Impacts: Application of Pelling’s Model of Vulnerability Infrastructural losses associated with cut-off low impacts were analysed using Pelling’s Model of vulnerability. This framework focuses specifically at the exposure and resistance of the individual infrastructures to the extreme weather event.
27 Chapter 5: Findings and Analysis
5.1 Introduction This chapter is organized into seven sections. Section 5.2 presents the extreme weather risk profile for Bredasdorp. Section 5.3 describes the April 2005 cut-off low, focusing on extreme rainfall, associated flood process and reported impacts and losses to municipal infrastructure. Section 5.4 then presents respondents perceptions of the risk factors that exacerbated flooding occurrences in Bredasdorp. Section 5.5 summarises comparable cut-off low experiences for Heidelberg and Montagu and in 5.6 consolidates these with findings draw from Bredasdorp. Section 5.7 concluded this chapter by applying Pelling’s vulnerability framework to all three events to identify recurrent patterns in infrastructural vulnerability to extreme weather.
5.2 Extreme weather risk profile of Bredasdorp Bredasdorp extreme weather risk profile is shaped by many factors including a changing rainfall pattern, topography and municipal drainage system. It is also in part affected by the municipality’s exposure to fire and drought occurrences.
5.2.1 Historical Rainfall: Bredasdorp historical rainfall records show that the average rainfall for the area is 42.8mm for the month of April. These records reflect the monthly rainfall data spanning 1878 to 2000.
28 Rainfall for April for the period 1878 to 2000 180.0 160.0 140.0 120.0 100.0 80.0 60.0 40.0 20.0 Amount of rainfall (mm) rainfall of Amount 0.0 1878 1886 1894 1902 1910 1918 1926 1934 1942 1950 1958 1966 1974 1982 1990 1998 Year
Figure 4: Graph of recorded rainfall for April from 1878 to 2000
April’s records show that there have been intermittent years where over 100mm of rain has fallen during the month. These years are becoming much more frequent. Between 1878 and 2000, there have been 10 years where April has recorded more than 100mm of rain. In the earlier years, there was a greater period of time elapsed between these years.
29 Year Amount of Rainfall Number of Years elapsing (mm) between high April rainfall 1892 107.1 1908 123.4 15 1942 103.3 32 1959 129.4 17 1967 135.3 7 1981 133 13 1982 161 0 1989 100 6 1993 134 3 1998 109.7 4
Table 1: Years with April Recording 100mm or more rainfall between 1878 and 2000 in Bredasdorp (Source: Bredasdorp meteorologist)
Table 1 indicates an increasing frequency in rainfall occurrence during April in Bredasdorp.
5.2.2 Topography and infrastructure : Bredasdorp is situated at the foot of the Heuningsberg Mountain. Directly above the town is the Drinkwater Kloof. During heavy rainfall the resulting river runs into the town and is fed into a sloot that runs through the town. The sloot runs alongside many houses and when the sloot intersects with the main road, it runs beneath the road and under a building. When the sloot was constructed, in order to accommodate already existing houses and buildings, it was constructed with a number of kinks and bends in order to avoid such obstacles. The sloot is 2.5m wide and 1.2 deep.
30
Figure 5: Map of rough estimate of the route of the sloot (Source : The Map 2005) (Key: Blue line represents the Sloot) At the bottom of the town, lies the Droë River. This is a non-perennial river that only flows during significant heavy rainfall. The Droë River is a very shallow and only about 2m wide. This river flows between the main part of the town and the low income area of Kleinbegin.
31 Figure 6: Map of the Drinkwaterkloof and river (source: Department of Land Affairs)
All the rivers in the area feed into the Agulhas Flats (vlakte) where they flow in to the sea at an estuary at De Mond. These Flats have very poor drainage and the water stands still for some time after heavy rain fall. Although Bredasdorp is not situated on the Agulhas flats, it is very near to this area. The closest perennial river to Bredasdorp is the Kars River which flows 2-3 km outside of town. The Droë River feeds in to the Kars River in east of the town.
5.2.3 Fire and Drought Profile Bredasdorp’s extreme weather risk profile is also exacerbated by its exposure to recurrent fire and drought risks. During the period of 1 April 2002 to 31 March 2003, the Overberg Municipality experienced 875 wild fires. (Dowry 2003)
5.3 Description of April 2005 Cut-off Low 5.3.1 Rainfall On the 10, 11 and 12 of April 2005, Bredasdorp was hit by a cut-off low pressure that resulted in large part of both Bredasdorp and the surrounding area being flooded. Over the duration of the event, rainfall of 228mm was recorded.
32 5.3.2 Description of flood process During the heavy rainfall experienced during this extreme weather event, the roads in the area were described by residents as ‘becoming rivers’. As the town is built on the slopes of the Heuningsberg the roads in the higher income area are at a steep incline. These roads channeled excess water down them and this water also flowed into the Droë River exacerbating the situation.
The Droë River flows within close proximity to Kleinbegin, a low income housing settlement. In this area any excess water which is flowing down the roads is forced to flow through houses in order to reach the river. These roads have been built in a U shape so houses have been built between the road and the river. This led to flooding of houses at the end of these roads.
The sloot’s course makes a number of bends and kinks. These kinks were the one of the main factors that led to flooding within the town. In the April 2005 cut-off low, the sloot flowed at full capacity with any excess water in the sloot overtopping its edges and continuing in a straight line. The path of this water was straight into the middle of the town. The water in the sloot runs down the length of the town and ends up the Droë River.
5.3.3 Warnings Issued The Disaster Management Department in the Overberg makes use of 4 different weather services for their weather forecasts and warnings, namely, Fire Warning and Weather, Buoy Weather, Giel se (Local Weather page on the Overberg Agriculture website) and the South African Weather Service.
Warnings: Extreme weather
Giel se has a weather forecast which is accessed via the Overberg Agriculture website and is released every Thursday and providing a weekly and monthly forecast.
Giel se first started to forecast a significant impending rainfall event on 31 March 2005. Although at the time that this forecast first was issued, it could not accurately predict the day which the rainfall event would occur. On the 3 April 2005, a more accurate forecast and warning was issued
33 The forecast predicted that there was a probability of rain through out the day with an 80% chance of rain from 17h00 onwards. There were also predictions of rainfall and thunderstorms on the 11 April 2005.
The South African Weather Service also issued a number of warnings by sms to the District Disaster Management Centre. However it was reported that these did not give adequate fore warnings in order for preventative measures to be taken. For example, on the 10 April 2006 at 10:59 am, a warning was issued for that day that heavy showers were predicted. (South African Weather Service 2005).
In the comparing the warnings, Giel se was able to provide more advanced, timely and accurate warnings than the South African Weather Service but results from field research did not indicate that flood preparedness strategies were taken even though warnings were issued..
5.3.4 Reported or Recorded impacts and associated economic losses The cost of repairing damage to infrastructure due to the April 2005 cut-off low in the Cape Agulhas Municipality was R 5.46 million. The Cape Aulhas Municipality includes Bredasdorp, Napier, Struisbaai, L’Agulhas and Suiderstrand. (Daniels 2005) Within Bredasdorp, two bridges were damaged. Repair to the bridge in Ou Meuleweg was R 210 135 and to the bridge in Baadjiesstraat was R 50 000. Repairs to the sloot at Fletcher Street were the most expensive, costing the Municipality R 1.53 million. A number of roads and side walks also required repairs. This amounted to R 924000. (Daniels 2005)
Other non municipal infrastructure damaged by the flooding Bredasdorp was isolated from the surrounding towns due to road closures resulting from the flooding. The main access route between Napier and Bredasdorp was closed due to the road and culvert collapsing. This culvert was “washed away” as a number of smaller non perennial rivers converged at this point. It was reported by authorities that this culvert is able to cope under normal rainfall conditions. Part of a bridge between Bredasdorp and Napier was also washed away.
34 Bredasdorp was also cut off from Struisbaai due to the Swellendam Road being closed as it was under water. The usual protocol by the Bredasdorp Roads Department is to close roads as soon as there is water moving over them (Pers Com Bredasdorp Department of Roads Official) In the outlying region, a number of culverts and low lying bridges sustained damage.
5.4 Respondents perceptions of flood risks
The official interviewed attributed the severe flooding to four main factors; the location and siting of the sloot, the vulnerability and poor maintenance of the stormwater system, the heavy debris loads in runoff and the impact of expansion of the town.
5.4.1 Location and siting of the sloot Those interviewed agreed that the sloot which runs through the older part of town also contributed significantly to the flooding. The Droë River is the main catchment above the town and all the water feds into this sloot the water in the sloot runs down the length of the town and flows into the Droë River. In the sloot’s course there is a number of bends and kinks. These kinks were the one of the main problem that led to flooding within the town. With such large volumes of rainfall (228 mm over 3 days), the water overflowed the sloot and resulted in a number of houses being flowed especially along Fabriek Street. Sand and other objects also obstructed the flow of the water. The sloot was constructed with a number of kinks in, in order to accommodate the houses in the area. During the April 2005 cut-off low, it was reported that as the water approached a “kink”, the water overflowing left the channel and continued flowing straight. This resulted in roads and houses being flooded. The post office was flooded as it lay in the pathway of the water before the water rejoined the channel.
5.4.2 Vulnerability and maintenance of the stormwater system Maintenance: At the time of the floods, there was no regular maintenance of the stormwater drainage system or the sloot and river that flow through the town. Litter, rubble and other dumped objects all contributed to the flooding. These objects obstructed stormwater pipes and streams and resulted in flooding.
35 During this particular flood, it was later found that many of the inlets were blocked by sand further compromising the ability of the system.
Inadequate Stormwater Capacity: When the extreme weather event in April 2005 occurred, the flooding and the inability of the storm water system to deal with the water was exacerbated, particularly in the Kleinbegin area, by runoff and streams all feeding into the stormwater drainage. There were 2 different streams as well as the stormwater drainage from the informal settlement all feeding into the stormwater system that flowed through the area. A stream from the lime works vicinity and a stream from the farming area which lies to the north west of Bredasdorp all fed into the stormwater system.
Exposed Soil: As April is the main planting time for wheat in the area, large tracks of land had been ploughed and prepared in order to plant. This resulted in a large amount of both runoff and top soil coming off the land. This is due to no crops or vegetation having been planted so there was nothing to bind the soil or absorb excess runoff. This would have ended up in the stormwater system. Although the fields are constructed in such away to minimize runoff, during periods of heavy rainfall this would not have been able to cope with the large amounts of runoff due to lack of vegetation in the area.
5.4.3 Heavy debris loads and management The Bredasdorp authorities suggested that the debris loading was the main cause of infrastructure failure and damage. They have indicated that main cause in the increase in the debris load was due to the DWAF’s Working for Water Programme which removes alien vegetation from the rivers and surrounding areas. It was the opinion of those interviewed that their actions were indirectly responsible for most of the damage sustained by bridges and culverts. During alien vegetation clearing, the cleared alien vegetation is left on the banks of the river to decompose. This is done as the removal of the vegetation is costly and in some areas, vehicle access is limited. With an event such as this the increased runoff and river volume would have swept the debris in and along with the rivers. Any debris in the rivers or washed into the rivers by the flood water gets carried along with the water. These braches, trees and other debris obstructs culverts and channels
36 and obstruct the water’s path. Officials reported that the only option for the water to flow over or around the structure. When the water is forced to flow over the road and structure the down stream side usually is damaged. This is due to the soil underneath the road surface becoming saturated. This causes the soil to lose its firmness and compactness and results in the road surface subsiding or lifting due to the power of the water. When the water is forced to go around a structure, the force of the water erodes away the ground beneath the supports of the structure. This causes the structure slip and may result in the road collapsing.
The municipality does clean and maintain rivers that flow through the town but are unable to do the same for rivers outside of towns as this was reportedly a difficult and expensive exercise.
Those interviewed also reported that a fire which occurred on the slopes of the Heuningsberg above the town also contributed to increased runoff. After the fire, there was an increase in runoff and water flowing into the sloot that runs through the town and into the Droë River.
5.4.4 Expansion on the town: As the town has grown and expanded there has been an increase in man made surfaces. These surfaces range from tarred roads to cement and roofs. Many of these surfaces have replaced natural vegetation and resulted in a reduction in the natural infiltration process. Instead these surfaces increase the surface runoff and add to the stress of the stormwater system.
5.5 Cut-off low occurrences in Heidelberg and Montagu Since 2003, the Western Cape has been significantly affected by four cut-off low systems. This section reviews the impact of cut-off low phenomena in Montagu (2003) and Heidelberg (2004)
37 5.5.1 Heidelberg:
In December 2004, the Western Cape was hit by a cut-off low pressure which caused widespread flood. One of the towns which suffered significant flood and flood related damage was Heidelberg which recorded 168mm rainfall in 3 days.
5.5.1.1 Recorded Infrastructural Impacts: This event resulted in significant damage to the Sewerage Works in Heidelberg. This was due to the complete flooding of the facility as well as the destruction of the pipeline carrying sewerage across the river. This also had serious consequences on the river as sewerage was being discharged into the river while repairs were hampered by workmen unable to cross the fast flowing stream. The cost of repairing and rehabilitating the affected facility cost R 3,944,400 (DiMP 2005). Reports from the March 2003 cut-off low which also affected Heidelberg show that the same facility sustained damage during this event (estimated at R2.4.72 million). (DiMP 2003)
The storm water channel that runs through Heidelberg also had significant damage due the raging flood waters pulling up the channels surfaces. The rehabilitation of the existing tar and concrete storm channel and concrete drifts cost R2, 275,000. (DiMP 2005)
A number of roads in the area were also damaged due to the heavy rain and flooding. Roads and pathways along side the Klip River were damaged and destroyed when the river burst its banks flooding adjacent properties and areas. The force of the water ripped up cement and tore out pieces of the tar on the roads. Some of the storm water pipes were also washed away by the force of the water. (DiMP 2005) The cost of repairing the roads and stormwater drains in the area was R 2.3 million. (DiMP 2005)
Electricity cables were also washed away as well as 3 substations were badly damaged by the flood waters. (DiMP 2005)
5.5.1.2 Factors exacerbating flooding: Five critical factors were identified as key risk factors for exacerbating the severity of flooding in Heidelberg. They include debris loading, canalisation of the Klip River,
38 proximity of the settlement and critical infrastructure to the river, increased runoff due to hardening of surfaces and decrease in vegetation cover and poor maintenance of stormwater channels.
Debris loading: In a few years prior to the event, DWAF’s Working for Water program had removed alien vegetation from the catchments and along the banks of the Buffelsjag and Duiwenshok Rivers. One of the consequences was that the removed vegetation was left on the banks of the river, where it was swept up in the flood waters and contributed to the December 2004 load of the river. It is this load that obstructs the river pathways and dams up against bridges resulting in failure. (DiMP 2005) The second consequence of the Working for Water Programme was that the removal of vegetation led to the ground being susceptible to erosion until new plants can become established in the area. This also led to increase sediment load in the rivers. (DiMP, 2005)
Increased Runoff: The removal of vegetation also increases flood volume. Plants absorb a lot of rainfall and runoff, thereby reducing the amount of water that flows into the rivers. By removing vegetation, you remove the nature’s ability to reduce runoff therefore leading to increased flood volumes (DiMP, 2005). Hardening of the environment is also another factor that is contributing to flooding. As town are made up by majority of tar, cement and other man made surfaces, the environments ability to absorb excess runoff is severely compromised. These hard surfaces lead to greater runoff in the area (DiMP, 2005).
Canalisation of the Klip River: Another factor that increased the town’s vulnerability to flooding as the canalisation of the Klip River which is a tributary of the Duwenshoks River as it flows through the town. The canal under normal rainfall is able to contain the river and thus protect the town and its inhabitants from flooding. During an event such as the one experienced in December 2004, the canalisation of the river becomes a major problem as these smooth surfaces increase the speed of the increased water volume. Usually sediment and vegetation slows down the speed of the water. (DiMP, 2005)
39 Proximity of the settlement and critical infrastructure to the river: The proximity of the town to the river led to increased flooding. Heidelberg is situated at the junction of two rivers. When the rivers are in flood, there is a backwash of water that flows through the town. This causes major flooding the town and the infrastructure is unable to deal with this large volume of water. (DiMP, 2005)
The Heidelberg Sewerage works has been built on a 1 in 50 year flood plain on the opposite side of the Duiwenshoks River to the town. In order to transport the sewerage from the town to the plant, it crosses the river via a pipeline. This pipeline is one of the contributing factors to its vulnerability as during high flood volumes this pipe is easily be washed away resulting in untreated sewerage being discharged into the river
Poor Maintenance of Stormwater channels Blocked storm water drains result the towns drainage system being unable to deal with the heavy rainfall. Towns take preventative measures at the beginning of the rainy season. These measures include clearing out the storm water drainage systems. As this event occurred during the summer, the drains had not been cleaned out and any debris in the drains would have contributed to the flooding in the area. (DiMP, 2005) Inadequate storm water drains in urban areas also result in lots of damage in large areas flooding. “These open drains are hardly adequate to deal with normal levels of rain, let alone extreme rainfall. In effect what happens during heavy rainfall is that the drains overflow, flowing over the roads and into the houses, thus creating damp houses at best and flooding houses at worst. This is exacerbated by litter and other blockages in these drains.” (DiMP, 2005)
5.5.2 Montagu, March 2003
During the March 2003 cut-off low pressure that affected the Western Cape, Montagu recorded 241mm rainfall over 3 days and sustained major infrastructural damage. (DiMP 2003)
40 5.5.2.1 Recorded Infrastructural Impact Most of the damage to roads was concentrated around Montagu. The most significant impact of the event was the damage to the Kogmanskloof Pass which connects Montagu and Ashton.
This was a major expense that had to be paid by the Provincial Roads Department. The reconstruction of this pass alone cost R59 million. During the flood there were a number of bridges damaged. It was seen that these bridges failed due to over topping, scouring of embankments or debris loading. Montagu also sustained damage to the electricity lines that supplies the town and surrounding areas. This cost R1.28 million to repair. The Winelands/Breederiver Municipality also suffered damage to the sewerage works. (DiMP 2003)
5.5.2.2 Factors exacerbating flooding Three critical factors were identified as key risk factors for exacerbating the severity of flooding in Montagu. They included debris loading, proximity of the town and critical infrastructure to the river and increased runoff due to hardening of the surfaces and decrease in vegetation cover.
Debris loading: Reed beds are also a contributing factor for floods and infrastructural failure. The reeds, in the rivers, cause greater resistance and result in higher flood levels. The reeds also increase the debris load in the rivers and this can result in the debris banking up against the structures and this often is the cause of structural failure. (DiMP 2003)
Proximity of the town and critical infrastructure to the river: As the town is situated on the convergence of the Kogmanskloof and Kingna Rivers, there are a number of infrastructures that have been built across or near to the rivers. As a result it was these structure that sustained damage. When a structure is built across a river there is an increase in the potential for damage due to flooding (DiMP 2003). This is caused by the structure restricting the flow of the water in the river. When the river is in flood, the water is then forced to either go around or over the top of the structure causing damage to either the supports, top of the structure (road surface lifting) or both.
41 Increased runoff: One of the contributing factors to flooding was the change in land use and land cover of the area. This leads to an increase in the frequency and severity of flooding. As the town has grown and expanded, more of the surrounding environment is being changed from natural vegetation to hard man made surfaces. This is a major problem as these hard man made surfaces do not have the absorptive and infiltration ability that vegetation has. Therefore, when it rains there is more surface runoff. (DiMP 2003)
5.6 Comparison of events There are many common characteristics are evident in the comparison of these three extreme weather events.
42 Town Month Rainfall Flooding Infrastructure losses Explanation of Losses Factors exacerbating flooding Montagu March 2003 Between 23-25 The Kingna Roads damaged in the Bridges failed due to over Change in the land use March 241 mm River was the area topping and scour of and land cover in the rain fell main Significant damage to embankments. area. An increase in the contributor to Kogmanskloof pass Debris loading resulting amount of tarred surfaces flooding. It was bridge, from reed beds and other increased runoff. thought to be a Number of other bridges vegetation was also a cause Increase in hard surfaces 1 in 50 or 1 in in the area failed of damage to a number of also reduces the amount 100 year flood. Sewerage works bridges. of runoff. suffered damage from Water and sewer pipes Town is situated at the flooding were washed away due to confluence of two rivers. Water and sewer pipes scour. were also washed away Sewerage works is built too close to the river. Heidelberg December 168mm of rain Flooding in the Sewerage works Debris loading: Authorities Canalised river running 2004 fell over a town was due received extensive have indicated that Alien through the town period of 3 to the damage. vegetation that was cleared contributed to flooding. days canalised Klip Stormwater channel was during the Working for An increase in tarred River as well damaged. Water Program is the major surfaces also reduces as the Significant damage to contributor to debris in infiltration and increase confluence of roads and stormwater rivers. runoff. the pipes. The Sewerage works was Blocked stormwater Duiwenshoks Damage to roads. located to close to the river. drains increased water and Blocked stormwater pipes. running through the town. Buffelsjags Infrastructure not built to The proximity of the town River resulted withstand such flooding to the river. in backwash events. “Removal of palmiet and flooding parts The infrastructure is built filling in of wetlands of the town. too close or across rivers. Clearing of alien vegetation – not enough time for regrowth Blockages in the river – e.g. vegetation debris, siltation, infrastructure Bad farming practices farming on the flood plain Alteration of the course of the river” DiMP (2005) Bredasdorp April 2005 10-12 April The flooding A number of roads in the Debris loading: Authorities Kinks and bends in the 228 mm of rain was due to the area were damaged. have indicated that Alien sloot resulted in excess was recorded. Droë river Bridges in the vegetation that was cleared water flowing straight and which flows surrounding area during the Working for flooded a number of through the suffered structural Water Program is the major houses and buildings. town. This non damage as well as a contributor to debris in Blocked stormwater perennial river number of culverts were rivers. drains resulted in flows from the washed away and Lack of regular insufficient drainage. main resulted in damage to maintenance resulted in a A fire a few years prior catchment the road above them. number of stormwater pipes above the town resulted in above the being blocked. increased runoff. town and is Land having been canalised as it prepared for planting also runs through reduced the infiltration the older ability of the soil. section of An increase in man made town. surface also resulted in increased runoff. Table 2: Comparison of Montagu, Heidelberg and Bredasdorp cut-off lows
(Information for March2003 and December 2004 from DiMP)
44 In comparing these events, all three of these cut –off lows recorded high amounts of rainfall over short period of time. A common characteristic of all 3 towns is there proximity to rivers. All three towns are situated on rivers. The proximity to the river all contributed the flooding in the area.
Debris loading has been identified in all 3 cases are the leading contributor to infrastructural failure and damage. In Heidelberg and Bredasdorp, the DWAF’s Working for Water Program was seen as a major contributor to debris in rivers. In both areas, the removed vegetation was left on the river banks and was swept up along with the water.
The hardening of the environment and an increase in tarred surfaces was seen as a factor exacerbating flooding in all three towns. The removal of the natural vegetation in order to be replaced by man made surfaces has contributed to a decrease in infiltration and an increase in runoff. Blocked stormwater drains and pipes have also been a common occurrence in these cases. Poor or lack of maintenance is often the leading cause of blocked drains.
In Heidelberg and Bredasdorp, a canalized river flowing through the town caused significant flooding and damage.
5.7 Application of Pelling’s model to April 2005 cut-off low In applying Pelling’s model to the April 2005 cut-off low, there will be a focus on the exposure and resistance of infrastructure to the event. Type of Damage Sustained Exposure Exposure Resistance Resistance infrastructure Physical location Environmental Not built to flood Poor Maintenance Surroundings resistant standards Bridges and Culverts Structural damage In the direct path of Debris loading was Not designed for Poor maintenance. and many culverts non perennial rivers. main contributor to flooding of this Resistance washed away failure. Debris calibre. Designed for compromised by obstructed the flow of 1:50 year floods in debris in rivers water through these rural areas and 1:2 or structures. 1:5 in town. Roads Road surface being In the path of flood Debris blocking Age and condition of ripped up. Surface water. Water running culverts resulted in road contributes to over culverts over the surface. roads collapsing or resistance. collapsing water flowing over Lack of regular the surface. maintenance. Stormwater drainage Blockages Stream being fed into Debris, sand and Built to cope with 1:2 Poor and lack of system the stormwater litter swept up into or 1:5 year floods. regular maintenance. system. the system. The pipes were unable to deal with such large volumes of water. Poor design. Table 3: Application of Pelling's Framework Destruction and damages sustained were due to infrastructure exposure to the flood water. Damage resulted from the structure being in the direct path of flood waters or streams. Debris was identified as a main contributor to infrastructure damage. The infrastructures resistance was compromised due to two factors. Firstly, the structures were not built to withstand such flooding events, and secondly, poor and lack of regular maintenance. Chapter 6: Discussion and Recommendations
The findings of this study highlight the considerable vulnerability of municipal infrastructure to extreme weather events within the Western Cape. This chapter revisits the original objectives for the thesis, identifying recurrent infrastructural loss patterns and exacerbating flood risk factors. It then relates findings to both the Pelling model which is applied in this study to identify the strengths and limitations of this approach in this context. The section concludes by outlining potential risk reduction measures to mitigate the impact of future weather events and areas of critical investigation and research.
6.1 Introduction: With climate change predictions indicating that there will be an increase in the frequency and severity of extreme weather (Weaver and Chapman ND), municipal infrastructure needs to be able to cope with large volumes of water, or else there is going to see repeated damage to the same type of infrastructure throughout the province. There are number similarities between extreme weather events which impacted Montagu, Heidelberg and Bredasdorp. These similarities extend not only to the type of infrastructure that is being damage but also the factors that are leading to the damage.
In Montagu, Heidelberg and Bredasdorp, each event recorded a high amount of rainfall over a short period of time. Each of these events lasted three days.
6.2 Recurrent infrastructural loss patterns and exacerbating flood risk factors
6.2.1 Infrastructure losses: In the comparison of these events, there were a number of types of infrastructures that are repeatedly recorded as sustaining damages. In both Heidelberg and Montagu, the sewerage works suffered damage from flooding. The proximity to the river was seen as a contributing factor for both these losses. Heidelberg and Bredasdorp both sustained damaged to canalised rivers. These canals were also seen as a factor which contributed to flooding in the towns. Roads in all three of the areas, sustained damage from flood waters. In both Bredasdorp and Montagu, bridges in the areas sustained damage. This was primarily caused by debris loading.
48 6.2.2 Factors exacerbating flooding: The locations of the towns and their proximity to rivers have been seen as a contributing factor to flooding. Both Montagu and Heidelberg are situated at the confluence of two rivers. Debris loading was recognised by authorities in all three towns as the main contributor. The proximity of the infrastructure and towns was also a common cause. Increased runoff due to reduction in vegetation and an increase in tarred surfaces, contributed to the flooding the areas. This finding is consistent with literature on debris flows. The literature explores these factors and reports that they are contributing factors which leads to infrastructure losses. (Cheng et al 2005, 165)
6.2.3 Flood Mitigation Strategies in Bredasdorp: The Bredasdorp Municipal Engineer highlighted a number of measures have been implemented by the municipality after the April 2005 extreme weather event in order to prevent future occurrences:
Measures to increase resistance to extreme weather: Plans have now been established for regular stormwater maintenance. These plans include cleaning out pipes and flushing them out with water in order to remove any sand or debris.
Improvements have been made to prevent the flooding in Kleinbegin due to the streams and stormwater that previously fed into the stormwater drainage system. The stream from the Lime works has now been connected to a retention dam (which was already built in April 2005). Water from the farming area and stormwater from the informal settlement both feed into the Padiathy stream. This stream now takes the water away from the town where it joins the Droë River along the Main Road to Arniston. This measure has reduced the stress put on other stormwater drainage during heavy rainfall.
Measures to increase resilience to extreme weather: When a warning of heavy rainfall is issued or when heavy rainfall is experienced, a protocol has been established. All the main channels are opened and any obstructions are removed in order to ensure free flowing movement of water.
49 A number of measures were taken during reconstruction after the April 2005 event, these include: Widening of the sloot and cement laid in the bottom of the channel. Gabions have been built on both the up and down stream of low lying bridges. This has been down in order to direct the water in the stream and prevent the erosion of the structures supports.
Railings on bridges have now been designed to collapse when water or debris banks up against it. This is to allow for free movement of the water and prevent damage resulting from debris. Gabions have also been used as railings along the gravel roads in remote areas.
These measures to reduce impacts will greatly help the situation but a major problem facing municipalities is a lack of money. The money which is provided by Municipal Infrastructure Grant is insufficient in order to even repair damages sustained. For example, the Cape Agulhas municipality received R 2.411 million from Municipal Infrastructure Grant for the 2006/2007 financial year. In the April 2005 event which affected the region, the losses sustained were R 5.46 million. This is more than double the money located to the region. In order for these municipalities to be able to carry out maintenance and improve infrastructure to withstand such events more money needs to be allocated.
6.3 Relevance of findings to Pelling’s vulnerability framework and ECLAC loss estimation model
The findings of this study are closely consistent with the categories proposed by Pelling’s vulnerability framework. Although this approach was primarily developed for human vulnerability, the study shows the relevance of this to infrastructure. The model however requires adjustment with regard to the resistance category. ECLAC model is relevant in estimating that losses sustained to infrastructure as this model contains a specific focus on direct impacts. A limitation is that it is reliant on information issued by Government. There may be delays before this information is readily available.
6.4 Future research and risk reduction: Considerable effort has been invested to date in studying the possible impacts of climate change in the Western Cape. This study confirms the importance of such research, also 50 highlighting the need for more specific studies in the susceptibility of infrastructure to extreme weather. Specifically, there is need for further research into the capacity of municipal, provincial and national infrastructure to withstand all climate change predictions not only those associated with extreme weather
With respect to risk reduction measures, this study also underlines the need for urgent intervention to protect critical infrastructure in municipalities exposed to extreme weather. One of the major contributors of infrastructural damage, namely debris loading must be tackled in order to avoid the province costly expenses in the future. There is a critical need to remove debris from catchments exposed to flash flooding. This has been highlighted as an expensive exercise by authorities but in the long term it will save the municipalities money. If this practice of leaving debris and removed vegetation is continued we will see the same damages in the future. Bredasdorp Roads Departments Official has suggested that chipping the debris is the solution to the problem but this also has its disadvantages. These fine chopped up pieces will add to the sediment load in the rivers and also result in destruction. Transporting the vegetation out of the catchments is the only answer.
In order for towns to be able to deal with the increase in rainfall, runoff and floods, our stormwater system needs to have more attention paid to it. Ideally when stormwater pipes are fitted wider pipes need to be used but this is a costly exercise that municipalities do not have the funds for. It is imperative that routine maintenance takes place. The implementation of regular maintenance and cleaning will ensure that water can freely flow through our stormwater systems.
Bridges and culverts which have been damaged by past events should be repaired and incorporate mitigation strategies in to these repairs. Steps that can be taken is rebuilding infrastructure in order to withstand 1 in 50 or 1 in 100 year floods, culvert should be rebuilt bigger in order to allow more water to pass through which will reduce the likelihood of structural damage during flooding and bridges must be built with bigger openings to allow for more water to pass through.
Although the channels that flow through both Heidelberg and Bredasdorp can not be removed, widening these water ways and regular maintenance and cleaning will ensure that the water can move through easier and will reduce the amount of damage that these channels receive during flooding events. 51 By establishing such methods for prevention and mitigation of the impacts of extreme weather events and resulting floods, there will be a greater capacity for adaptation to the climate change scenarios foreseen for the Western Cape.
52 References: Cannon, S.H and Reneau, S.L 2000. Conditions for Fire Generation for Fire Related Debris Flows, Capulin Canyon, New Mexico. Earth Surface Processes and Landforms 25: 1103- 1121.
Chapman, A and Weaver, A. Not Date. Climate Change: A heated Debate. Science Scope
Cheng, J.D, Huang, Y.C, Wu, H.L, Yeh, J.L and Chang, C.H 2005 Hydrometeorological and landuse attributes of debris flows and debris floods during typhoon Toraji, July 29-30, 2001 in central Taiwan. Journal of Hydrology 306: 161-173
Cape Agulhas Regional Visitors Guide, 2006.
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Department of Local Government and Housing, 2006. Final Cabinet Submission Second Version.
Disaster Management Framework No Date. Available online at sandmc.pwv.gov.za/WebDocuments/framework/framework.pdf (2006. October 11)
Disaster Mitigation for Sustainable Livelihoods Programme (DiMP) University of Cape Town, 2003. March 2003 Cut-off Low: Consolidated Report.
Disaster Mitigation for Sustainable Livelihoods Programme (DiMP) University of Cape Town. August 2004 Severe Storm Event.
Disaster Mitigation for Sustainable Livelihoods Programme (DiMP) University of Cape Town. 2005. Disaster Debriefing
Dowry, C 2003. Western Cape Government contributes towards fire-fighting helicopter. Ministry of Local Government, Western Cape Provincial Government. Available on online at http://www.polity.org.za/pol/speech/2003/?show=45007 (2006. October 11)
Geldenhuys, R. 2005 Vloed Overberg Presentation.
53 Hugo, G. 2006 Giel se. Overberg Agricultural Website. Available online at: www.overbergagri.co.za
Midgley, G.F, Chapman, R.A, Hewitson, B, Johnston, P, De Wit, M, Ziervogel, G, Mukheibir, P, Van Niekerk, L.A Tadross, M, Van Wilgen, B.W., Kgope, B., Morant, P.D., Theron, A., Scholes, R.J., Forsyth, G.G. 2005. Status Quo, Vulnerability and Adaptation Assessment of the Physical and Socio-Economic Effects of Climate Change in the Western Cape.
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54 Appendix A: Detailed Daily Weather: 10-12 April 2006 10 April 2005: Light rainfall was experienced throughout the day. Most of the day had an hourly rainfall total of 0.2mm or more. As the day progressed, the rainfall become heavier and from 18h00 GMT (with the exception of 2 hours) the hourly rainfall was 1.4mm or more. 37.2 mm of rainfall fell during the day. The rain rained out of the south east.
11 April 2005: There was heavy rainfall through out the day with some periods having an hourly recorded rainfall of more that 15mm. From 15h00 GMT, the rain started to become much lighter. During the 11 th there was two periods of heavy rainfall namely 1h00 to 4h00 and 12h00 to 14h00 where the rainfall rate exceeded 24 mm/hour.
12 April 2005: By 9h00, the rain had stopped. Very light rainfall was experienced in the early morning. 10.8 mm of rain fell during the morning.
Throughout the 10 and 11 April, the wind was described as gusty from an easterly direction. On the 11 th , these gusts were on average 4m/s (14.4 km/h). These gusts did reach up to speeds of 6.3 m/s (22.68 km/h). These gusts of wind picked up throughout the day. The wind direction was south east to east south east.
On the 11 th , the average wind speed was 5.6 m/s (20.16 km/h). These gusts reached speeds of 8.5 m/s (30.6 km/h). As the day progressed the wind speed began to decrease and the direction started to change from south east to south westerly direction.
On the 12 th , the wind was blowing in a south westerly direction.
55 Date 10 April 11 April 12 April Type of rain Light becoming Heavy becoming Very light rainfall in heavier in the lighter in the the early morning evening afternoon stopping by 9h00. Hourly Rainfall rate 0.2 For most of the Periods when the Hourly rainfall rate day. Increasing to 1.4 hourly rate exceeded decreased or more during 24mm/hour. The throughout the heavier showers average rainfall rate morning. Between was 12.5 mm/hour 12am and 2 am it exceeded 3 mm/hr and then decreased to on average 0.8 mm/hr Amount of rain for the 37.2 mm 168 mm 10.8mm day Wind direction South Easterly to South easterly South westerly East South Easterly changing to south westerly in the evening Wind speed Gusty, increasing Gusty with Gusty with speeds up wind strength in the decreasing speeds to 6.3 m/s evening. towards the end of the day. Table 4: Daily record from 10-12 April (Weather Data supplied by Giel se)
56 Appendix B: Georeferencing of storm impacts
Figure 7: Infrastructure damaged during April 2005 event. (map source: Department of Land Affairs) Key: Red dot: Damage to infrastructure.
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Figure 8: Infrastructure damaged during April 2005 event area surrounding Bredadorp (Source: Map Source) Key: AWA: infrastructure washed away. Road: Road damaged Bridge: Bridge damaged Culvert: culvert damaged
58 Appendix C: Photographs
Figure 9: Damage to culvert and road between Napier and Bredasdorp (Source Disaster Manager)
Figure 10: Debris loading during the April 2005 event. (Source Disaster Manager)
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Figure 11: Kogmanskloof pass damaged during March 2003 event (Source Disaster Management)
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