University of Cape Town “Deriving a policy document towards an Early Warning System for Estuaries in South Africa: Case study Great Brak Estuary, Eden District, Southern Cape”

Johan Stander

Supervised by: Professor Isabelle Ansorge Head of Oceanography Department, University of Cape Town

Associate Professor Juliet Hermes Manager, SAEON Egagasini node Associate Professor, Oceanography Department, University of Cape Town

A thesis presented for the degree of Doctor of Philosophy in Oceanography

University ofUniversity Cape Town of Cape Town June 2020

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The copyright of this thesis vests in the author. No quotation from it or information derived from it is to be published without full acknowledgement of the source. The thesis is to be used for private study or non- commercial research purposes only.

Published by the University of Cape Town (UCT) in terms of the non-exclusive license granted to UCT by the author.

University of Cape Town Abstract

South Africa’s estuaries and their surrounding communities are becoming increasingly vulnerable to storm surges and accompanied estuary flooding. These events are largely due to increasing severity of storm surges combined with growing housing and commercial developments. A particularly severe weather event in 2007/2008 highlighted the pressing need to understand the processes involved and the urgency to develop proactive response and management actions to mitigate the effects of future storm events on these coastal areas. Scientific research on estuarine flooding is limited not only for South Africa but within the international community as well and only recently has received committed attention from policy makers. It is clear that our current knowledge of South African estuary flooding events remains rudimentary; while necessary action to mitigate such events are poorly understood and planned. The aim of this PhD thesis is to devise and implement an Estuary Early Warning – Emergency Preparedness and Response Guide for stakeholders and government policymakers. This guide will target South Africa’s coastal region by analysing past information on storm surges and estuary flooding, particularly in the low-lying southern coast region of the Western Cape, South Africa.

The key objective of this thesis is to assess the best processes for the issuing of estuary alerts and to better standardise them so that the response remains in line with multi-hazard early warning standard procedures and practices within South Africa. A further aim is to provide a comprehensive national guideline on how best to effectively disseminate and communicate such information and to establish an Estuary Early Warning (EEW) – Emergency Preparedness and Response Guide (EPRG), which forms part of the South African Multi-Hazard Early Warning System (MHEWS). It is critical that this EEW meets general principles accepted internationally for an effective Early Warning System. This thesis addresses the following key elements namely: (1) Risk identification, (2) Key drivers and contributions to estuary flooding, (3) Monitoring and alert early warning system, (4) Alert dissemination and (5) Response actions. Such pioneering work is an essential tool to translate science into policy, a crossover field, which remains poorly implemented.

2 Plagiarism Declaration

The thesis is my own research work. Wherever contributions from others are involved, every effort has been made to indicate this clearly, with due reference to the literature. Aside from guidance from my supervisors, I have received no assistance except as acknowledged.

I have not allowed, and will not allow, anyone to copy the contents of this thesis with the intention of passing it off as their own work. It should be noted that the initial process was led by the author, an employee of the South African Weather Service (SAWS) in conjunction with Disaster Management (DM), Department of Environmental Affairs (DEA) Branch Oceans and Coasts (O&C), Cape Nature, Department of Water and Sanitation (DWS), Council for Scientific and Industrial Research (CSIR), various Municipalities and the South African National Parks Board (SANParks), which involved a three-day estuary workshop in George, Western Cape after the successful development and ultimate draft implementation of the early warning storm surge guide in 2012. The aim was to bring all interested parties together to share knowledge and best practice in predicting and managing estuary flood events along the coast, as well as to consider the advantages and disadvantages of establishing a Guide for South Africa. Follow-up workshops were held, led by the author, and a guidance framework was developed. The Guide was developed to function within the various sets of legislative frameworks pertaining to estuary management, however the guide could not be enforced as it was not scientifically tested through case studies.

3 Table of Contents

Abstract ...... 2 Plagiarism Declaration ...... 3 Table of Contents ...... 4 Table of Figures ...... 10 Table of Tables ...... 16 1. Literature review ...... 17

1.1 Rio de la Plata, Argentina as a case study integrating satellite altimetry and real-time tide gauge data for the prediction of storm surges ...... 18

1.2 Thames Estuary, case study of modelling storm surge flooding of build-up areas...... 20

1.3 Coastal modelling for flood defence – case study the Netherlands ...... 21

1.4 Estuarine flooding and managed retreat ...... 23

1.5 Investigating River-Surge interaction in idealised estuaries ...... 24 2. Introduction ...... 28

2.1 Understanding the catchment to coast and water flow of estuaries ...... 30

2.2 Impacts of floods on estuaries – Secondary effects ...... 32

2.3 Changing climate and land use planning ...... 33

2.4 Proactive risk identification and subsequent risk reduction and mitigation ...... 34

2.5 The need for estuary early warning guideline for policymakers ...... 34 3. Data and methodology ...... 37

3.1 Key drivers of estuary flooding ...... 37 3.1.1 Meteorological drivers...... 37 3.1.2 Oceanographic ...... 38

3.2 Factors contributing to forecasting estuary flooding ...... 38 3.2.1 Predicted rainfall intensity within the catchment region ...... 38 3.2.2 Land use and bathymetry ...... 38

4 3.2.3 Estuary water level and beach berm height ...... 39 3.2.4 Sea-level rise ...... 39 3.2.5 Waves and storm surges ...... 40 3.2.6 Beach berms ...... 41 3.2.7 Numerical model information ...... 41 4. Results 1 - Why the need for an estuary early warning guide? – Case study of the Great Brak estuary in the Eden district ...... 43

4.1 Rainfall conditions over the Eden region ...... 43

4.2 Description of the events leading up to significant flood events in Eden estuaries – Case study the Great Brak estuary...... 46 4.2.1 Flooding event June 2011 ...... 48 4.2.2 Flooding event September 2008 ...... 52 4.2.3 Flooding event August 2006 ...... 54 4.2.4 Flooding event May 2002 ...... 55 4.2.5 Flooding event March 2003 ...... 55 4.2.6 Flooding event November 2007 ...... 56 4.2.7 Comparison of the 22nd November 2007 and the 8th June 2011 flood events depending on estuary mouth ...... 57 5. Results 2 - What is required for a successful policy to ensure that flooding events at Great Brak are minimal in damage? ...... 61

5.1 What is meant by artificial breaching? ...... 61

5.2 Artificial breaching events at the Great Brak estuary ...... 62 5.2.1 Planned and emergency breaching ...... 62 5.2.2 Planned artificial breaching on the 12th July 2012 prior to expected severe weather conditions ...... 63 5.2.3 Artificial breaching time sequence ...... 64

5.3 Identification and mitigation of high risk estuaries such as the Great Brak estuary .....66 5.3.1 Assessing the risk ...... 66

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5.3.2 Methods of identification of high risk estuaries such as the Great Brak ...... 67 5.3.3 Mitigation of risks for the Great Brak estuary ...... 68

5.4 Multi-stakeholder estuary early warning, emergency preparedness and response guide for estuaries such as the Great Brak ...... 70

5.5 Availability of early-warning services ...... 71

5.6 Information and functions required during anticipated extreme events at the Great Brak estuary ...... 74

5.7 Inputs required for the estuary early-warning process flow ...... 75 5.7.1 Rainfall ...... 75 5.7.2 Catchment and river information ...... 76 5.7.3 Beach berm heights ...... 76 5.7.4 Monitoring responsibilities ...... 76 5.7.5 Data and research gaps for the Great Brak estuary ...... 77 5.7.6 Wolwedans Dam level ...... 77 5.7.7 The Great Brak estuary bathymetry ...... 77

5.8 Outputs required for the estuary early-warning process flow of the Great Brak estuary alert system ...... 78 5.8.1 Dissemination of weather alerts ...... 78 5.8.2 Primary recipients of Great Brak estuary alert ...... 78 5.8.3 Secondary recipients of Great Brak estuary alert ...... 78

5.9 Establishment of a Provincial or Municipal Joint Operational Centre ...... 79

5.10 Common alert protocol used when warning needs to be sent for the Great Brak estuary ...... 81 5.10.1 Issue of an Alert ...... 82 6. Results into action – Deriving and testing a policy document. A series of six case studies for the Eden district ...... 83

6.1 Successful artificial breaching August 2013 ...... 83 6.1.1 SAWS rainfall data ...... 83

6 6.1.2 DWS hydrological data...... 84 6.1.3 Wave and tidal information ...... 86 6.1.4 Discussion of August 2013 ...... 87

6.2 Successful artificial breaching October 2013 ...... 88 6.2.1 Numerical model precipitation ...... 88 6.2.2 SAWS rainfall data ...... 88 6.2.3 DWS hydrological data...... 89 6.2.4 Wave and tidal information ...... 91 6.2.5 SAWS weather warnings ...... 92 6.2.6 Discussion of October 2013 ...... 92

6.3 Successful artificial breaching January 2014 ...... 93 6.3.1 Numerical model precipitation ...... 93 6.3.2 SAWS rainfall data ...... 94 6.3.3 DWS hydrological data...... 95 6.3.4 Wave and tidal information ...... 97 6.3.5 SAWS weather warnings ...... 98 6.3.6 Discussion of January 2014 ...... 99

6.4 Successful artificial breaching July 2015 ...... 100 6.4.1 Numerical model precipitation ...... 100 6.4.2 SAWS rainfall data ...... 101 6.4.3 DWS hydrological data...... 101 6.4.4 Wave and tidal information ...... 104 6.4.5 SAWS weather warnings ...... 105 6.4.6 Discussion of July 2015 ...... 105

6.5 Successful artificial breaching September 2016 ...... 105 6.5.1 Numerical model precipitation ...... 106 6.5.2 SAWS rainfall data ...... 106 6.5.3 DWS hydrological data...... 107 6.5.4 Wave and tidal information ...... 109

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6.5.5 SAWS weather warnings ...... 110 6.5.6 Discussion of September 2016 events...... 110

6.6 Summary of the Great Brak estuary breaching case studies ...... 110 7 The importance of flood damage mitigation – what have we learnt in summary ...... 111

7.1 Oceanographic conditions impacting on the Great Brak estuary ...... 111

7.2 Development and engineering along the Great Brak estuary ...... 112

7.3 Human, financial and infrastructure resources ...... 112

7.4 Integrated fully-coupled numerical weather prediction model ...... 114

7.5 Artificial planning and/or emergency breaching ...... 114

7.6 Wave conditions ...... 115

7.7 Ground-breaking work for policy consideration ...... 115 8 Estuary Management plans, Limitations, and Recommendations ...... 116

8.1 Management Plans ...... 116

8.2 Limitations ...... 117

8.3 Recommendations and Future Work ...... 118 8.3.1 Climate Change ...... 118 8.3.2 Improved forecasting ...... 118 8.3.3 High risk estuary information ...... 120 8.3.4 Resource requirements ...... 121 8.3.5 Capacity building...... 122 8.3.6 Management of estuaries ...... 122 8.3.7 Automation of estuary warnings ...... 123 9 Acknowledgements ...... 124

ANNEXURE A: List of Definitions ...... 126

ANNEXURE B: List of Acronyms ...... 133

ANNEXURE C: Bibliography ...... 138

8 ANNEXURE D: Agenda of first consultation workshop ...... 149

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Table of Figures

Figure 1.1: Global risks landscape taken from the 2017 World Economic Forum in Davos in which impact against likelihood are compared. It should be noted that of highest impact is denoted by the blue circle, which identifies storm surges, estuary flooding as the greatest threat for extreme weather events...... 25 Figure 2.1: Map highlighting the Eden district, which is marked as a black square, is situated within the Western Cape Province of South Africa. Map provided by the Western Cape Provincial Disaster Management centre...... 29 Figure 2.2: (a) The Climatic regions of South Africa (Taken from Kruger, 2004). The area of interest in this research is Region 24 along the south coast of South Africa and demarcated as purple; (b) Rainfall district areas over South Africa as classified and provided by the South African Weather Service. The region of interest is marked as 11...... 32 Figure 4.1: Average monthly rainfall in mm for rainfall district 11 (see Figure 2.2b). The green line represents the long term average of 1921-2018 (mostly manual recording stations) and the orange line represents the monthly average from 2003-2018 (mostly automated rainfall recording stations and year when DM started logging severe events). The blue bar represents the maximum amount of rainfall measured for that month in mm and the red bar the lowest rainfall in mm measured for that month...... 44 Figure 4.2: Map of the Eden district. In the insert is the Swartvlei river and estuary, which are highlighted in red and the black arrow indicating the town of Sedgefield. Map provided by the Western Cape Provincial Disaster Management centre...... 47 Figure 4.3: A photo showing how the National road and railway line completely flooded during the Sedgefield flood of November 2007. Photo provided by the Eden district Disaster Management centre...... 48 Figure 4.4: Graph showing rainfall in mm for the month of June 2011. The data highlights rainfall registered at three separate stations in the Great Brak catchment area. The different colours refer to the three rainfall stations Jonkersberg Bos (blue), Jonkershoek ARS (red) and Grootbrakrivier ARS (green). Data provided by SAWS...... 49

10 Figure 4.5: Graph showing wave data from the CSIR Wave-rider in Mossel Bay from 00:00 on the 6th June 2011 until 21:00 on the 9th June 2011. On the 6th the significant wave height reached ~4.5 m between 09:00 and 12:00. Wave height in m is shown in blue (Hmo) and significant wave height in m is shown in red (Hmax)...... 50 Figure 4.6: Graph showing the water level in m of the Great Brak estuary on the 8th June 2011 peaking close to 3 m at 14:00, almost the same time as highest significant wave height of just over 4.5 m between 09:00 and 12:00 in Figure 4.5. Data provided by DWS...... 51 Figure 4.7: Map of the Eden district. In the insert highlights the positions of the CSIR Wave- rider (Green) in Mossel Bay and its close proximity to the Great Brak estuary, which is highlighted in red. Map provided by the Western Cape Provincial Disaster Management centre...... 52 Figure 4.8: Graph showing rainfall in mm for the month of August 2008. The data highlights rainfall registered at two separate stations in the Great Brak catchment area. The different colours refer to the two rainfall stations Jonkersberg Bos (blue) and Grootbrakrivier ARS (green). Data provided by SAWS...... 53 Figure 4.9: Graph showing rainfall in mm for the month of September 2008. The data highlights rainfall registered at two separate stations in the Great Brak catchment area. The different colours refer to the two rainfall stations Jonkersberg Bos (blue) and Grootbrakrivier ARS (green). Data provided by SAWS...... 53 Figure 4.10: Graph showing wave data from the CSIR Wave-rider in Mossel Bay from 00:00 on the 30th August 2008 until 21:00 on the 2nd September 2008. The Significant wave height reached ~7 m at 12:00 on the 1st. Wave height in m is shown in blue (Hmo) and significant wave height in m is shown in red (Hmax)...... 54 Figure 4.11: Graph showing rainfall in mm for the month of March 2003. The data highlights rainfall registered at two separate stations in the Great Brak catchment area. The different colours refer to the two rainfall stations Jonkersberg Bos (blue) and Grootbrakrivier ARS (green). Data provided by SAWS...... 56 Figure 4.12: Graph showing wave data from the CSIR Wave-rider in Mossel Bay from 00:00 on the 20th November 2007 until 18:00 on the 23rd November 2007. The significant wave height

11 reached ~7 m at 12:00 on the 21st. Wave height in m is shown in blue (Hmo) and significant wave height in m is shown in red (Hmax)...... 57 Figure 4.13: Water level in meters of the Wolwedans Dam prior and during the flood events on the 8th June 2011, blue line and on the 22nd November 2007, red line. Data supplied by DWS. 59 Figure 5.1: Typical example of an illustration how emergency artificial breaching is carried out courtesy of George DWS. Photo 1 is where the Bulldozer arrives at Great Brak. Photo 2 until 4 is where the channel is prepared. Breaching starts in photo 5 while in photo 6 is where the river flows freely into the ocean...... 63 Figure 5.2: (a) Water level of the Great Brak estuary in meters between 06:00 on the 12th and 00:00 on the 16th July 2012. The letters represent various activities as highlighted in the text from the time the estuary level increased until it beached and then dropped. (b) Water level in meters of the Wolwedans Dam between 06:00 on the 12th and 00:00 on the 16th July 2012. The letters represent various activities as highlighted in the text as the dam level rose until it spilled. Data supplied by DWS...... 65 Figure 5.3 Decision-making process flow for a successful estuary early warning guide to mitigate estuary flooding such as the Great Brak. On the left is essential input required for an informed decision-making process. On the right hand side is where alerts are disseminated and the feedback loop for revision of the alerts...... 75 Figure 5.4: The figure illustrates various actions to be considered at Disaster Management Joint Operations Centre after receiving weather warnings issued by the SAWS. The figure further provides actions to be considered for high risk estuaries such as the Great Brak and if breaching should be considered...... 81 Figure 6.1: Graph showing rainfall in mm for the month of August 2013. The data highlights rainfall registered at three separate stations in the Great Brak catchment area. The different colours refer to the three rainfall stations Jonkersberg Bos (blue), Jonkershoek ARS (red) and Grootbrakrivier ARS (green). Data provided by SAWS...... 84 Figure 6.2: (a) Water level in meters of the Wolwedans Dam between 00:00 on the 24th August until 00:00 on the 29th August 2013. The letters represent activities as highlighted in the text. Data supplied by DWS. (b) Water level of the Great Brak estuary in meters between 00:00 on

12 the 24th and 00:00 on the 29th August 2013. The letter A denotes the time when breaching occurred. Data supplied by DWS...... 85 Figure 6.3: Graph showing wave data from the CSIR Wave-rider in Mossel Bay from 00:00 on the 26th August 2013 until 21:00 on the 29th August 2013. Wave height in m is shown in blue (Hmo) and significant wave height in m in shown in red (Hmax). The letter A denotes the time the wave height was not significant when breaching occurred...... 87 Figure 6.4: SAWS Unified model output representing accumulative precipitation for the 20th and the 21st October 2013. The left hand side figure is the 48 hour Unified Model initiated on the 19th for the 20th indicated <10 mm of rainfall over the Eden district. The figure on the right is the 48 hour Unified Model initiated on the 20th for the 21st October 2013 indicated >30 mm of rainfall for the Eden district...... 88 Figure 6.5: Graph showing rainfall in mm for the month of October 2013. The data highlights rainfall registered at three separate stations in the Great Brak catchment area. The different colours refer to the three rainfall stations Jonkersberg Bos (blue), Jonkershoek ARS (red) and Grootbrakrivier ARS (green). Data provided by SAWS...... 89 Figure 6.6: (a) Water level in meters of the Wolwedans Dam between 00:00 on the 18th and 00:00 of the 22nd October 2013. The letter A denotes the peak level of the dam. (b) Water level of the Great Brak estuary in m between 00:00 on the 18th and 00:00 on the 23rd October 2013. The letter A denotes the peak of the estuary prior to breaching. Data supplied by DWS...... 90 Figure 6.7: Graph showing wave data from the CSIR Wave-rider in Mossel Bay from 00:00 on the 20th until 21:00 on the 23rd October 2013. Wave height in m is shown in blue (Hmo) and significant wave height in m is shown in red (Hmax). The letter A indicates the lower wave levels on the 22nd compare to the 21st wave levels...... 91 Figure 6.8: SAWS Unified model output representing accumulative precipitation for 6th, 7th, 8th, and 9th January 2014. The figure top left is the 48 hour Unified Model (UM) initiated on the 5th for the 6th indicated a possibility of >50 mm on rainfall. The figure top right is the 48 hour UM initiated on the 6th for the 7th indicated >50 mm. The figure bottom left is the 24 hour UM initiated on the 8th for the 8th indicated >50 mm rainfall just to the west of Eden district. The figure bottom right is the 24 hour UM initiated on the 9th January for the 9th January 2014 indicated >50 mm rainfall in places...... 94

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Figure 6.9: Graph showing rainfall in mm for the month of January 2014. The data highlights rainfall registered at three separate stations in the Great Brak catchment area. The different colours refer to the three rainfall stations Jonkersberg Bos (blue), Jonkershoek ARS (red) and Grootbrakrivier ARS (green). Data provided by SAWS...... 95 Figure 6.10: (a) Water level of the Great Brak estuary in meters from 00:00 on the 5th until 00:00 on the 10th January 2014 which remained below 1,5 m. (b) Water level in meters measuring instrument reading at the Wolwedans Dam from 00:00 on the 5th until 00:00 on the 10th January 2014. The letter A denotes the point where the Wolwedans Dam reached full capacity and spilled. Data supplied by DWS...... 96 Figure 6.11: Graph showing wave data from the CSIR Wave-rider in Mossel Bay from 00:00 on the 5th January until 00:00 on the 10th January 2014. Wave height in m is shown in blue (Hmo) and significant wave height in m is shown in red (Hmax). The letter A denotes the period of maximum wave height...... 98 Figure 6.12: SAWS Unified model output representing accumulative precipitation for the 20th July 2015. The left hand side figure is the 48 hour Unified Model initiated on the 19th for the 20th July indicated <10 mm of rainfall while the right hand side figure is the 24 hour Unified Model initiated on the 20th for the 20th July 2015 indicated <20 mm of rainfall...... 101 Figure 6.13: Graph showing rainfall in mm for the month of July 2015. The data highlights rainfall registered at three separate stations in the Great Brak catchment area. The different colours refer to the three rainfall stations Jonkersberg Bos (blue), Jonkershoek ARS (red) and Grootbrakrivier ARS (green). Data provided by SAWS...... 101 Figure 6.14: (a) Water level in meters of the Wolwedans Dam between 00:00 of the 17th and 00:00 on the 23rd July 2015. The letter A denotes the point where the dam reached full capacity. (b) Water level of the Great Brak estuary in meters between 00:00 on the 17th and 00:00 on the 23rd July 2015 peaking after the spill. Data supplied by DWS...... 103 Figure 6.15: Graph showing wave data from the CSIR Wave-rider in Mossel Bay from 00:00 on the 20th July 2015 until 21:00 on the 22nd July 2015. Wave height in m is shown in blue (Hmo) and significant wave height in m is shown in red (Hmax)...... 104 Figure 6.16: SAWS Unified model output representing accumulative precipitation for the 16th September 2016. The left hand side figure is the 48 hour Unified Model initiated on the 15th for

14 the 16th September indicated <20 mm of rainfall while the right hand side figure is the 24 hour Unified Model initiated on the 16th for the 16th September 2016 indicated <25 mm of rainfall...... 106 Figure 6.17: Graph showing rainfall in mm for the month of September 2016. The data highlights rainfall registered at three separate stations in the Great Brak catchment area. The different colours refer to the three rainfall stations Jonkersberg Bos (blue), Jonkershoek ARS (red) and Grootbrakrivier ARS (green). Data provided by SAWS...... 107 Figure 6.18: (a) Water level in meters of the Wolwedans Dam between 01:00 on the 1st and 23:00 on the 17th September 2016. The letter A represents the day the dam reached full capacity. (b) The water level in meters measuring instrument reading at the Great Brak Mouth between the 1st and the 17th September 2016. Rapid increase in the estuary level from the 13th after the spill and peaked on the 14th as denoted by A. The drop in estuary level after the letter A indicates the outflow towards the ocean. The constant up and down from the 15th co-insides with high and low tide levels. Data provided by DWS...... 108 Figure 6.19: Graph showing wave data from the CSIR Wave-rider in Mossel Bay from 00:00 on 14th September 2016 until 21:00 on 17th September 2016. Wave height in m is shown in blue (Hmo) and significant wave height in m is shown red (Hmax)...... 110

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Table of Tables

Table 1.1: Estuary responses to sea-level rise (taken from Townsend and Pethick, 2002)...... 24 Table 4.1: Summary of significant disaster events from 2003 to 2016 along the Eden district in the Western Cape Province, South Africa (excluding fires, drought and non-weather related) as logged by Disaster Management. No significant known social impacts and/or damages reported since 2015 due to successful preventative steps taken by DM...... 46 Table 4.2: Table highlighting the Wolwedans Dam flow and Great Brak estuary water-level data for the 8th June 2011 and the 22nd November 2007 flood events. Data provided by DWS...... 58 Table 5.1: Great Brak estuary levels in m and the Wolwedans Dam level in % between the 12th and the 14th July 2012. Once the Dam reached full capacity and spilled at 17:00 the estuary was breached which allowed the estuary level to drop and make allowance for additional water from the Dam after 17:00. Data supplied by DWS...... 66 Table 5.2: SAWS estuary flooding weather alert reference table as provided by SAWS articulating the various yellow, amber or red alert categories. The table further indicates what the lead-time for each alert category is. The author in consultation with SAWS and DM employees developed this table...... 74

16 1. Literature review

South Africa’s coastal communities, in particular those living in and around estuarine environments such as Great Brak, Swartvlei and Touws, are becoming increasingly vulnerable to flooding events due to the increased frequency and severity of adverse meteorological and oceanographic conditions. The impact of a flood event is often aggravated by inappropriate development within estuarine floodplains; particularly as many developers choose to build below the 1-in-100 year flood line. Intensifying this challenge, the incremental rise of sea level brought on by anthropogenically-driven climate change is likely to further elevate risks associated with estuary flooding along the South African coastline.

Sea-level rise is a global concern, which has severe impacts on all coastal regions. Bindoff et al. (2007) indicated that since 1993, global sea level has risen ~ 0.4 cm/year. However, there are large regional departures from this global-average value, and the South African coastline’s estimate for sea-level rise. Based on statistical data for the west coast from 1957 until 2006 the change is 0,187 cm/year, the south coast between 1957 and 2006 is 0,148 cm/year and the east coast of South African between 1967 and 2006 is 0,274 cm/year (Marther et al., 2009). Real-time sea-level data (collected from tide gauges) can only be realistically understood once global sea levels are appropriately monitored and decadal and inter-annual variations included in sea level calculations. Oceanographic processes such as ocean eddies, surface tides and currents as well as internal tides can be better understood by making use of real-time tide gauge data. In addition, these real-time data sets can be used to observe additional extreme events usually associated with storm surges and tsunamis, such as estuary flooding along the Great Brak on the south coast of South Africa, which lead to short-term coastal inundation.

Storm surges, driven by changes in atmospheric circulation, occur at a much higher frequency than sea-level rise and result in a fluctuation of the inland and coastal water levels, which can persist from minutes to days. Although the fluctuation periods of storm surge levels vary, storm surge periods are about 3 hours and centre at roughly 10¯⁴ cycles/second. In assessing the variability of storm surges for different periods and at different locations, atmospheric factors

17 such as the strength and direction of the storm, tidal signal and stratification of the water body are minor factors compared to the local topography (WMO-No. 1076, 2011).

The impact that weather systems such as cut-off lows have on storm surges and ultimately the coastline is significant. Such interactions are brought about primarily through changes in atmospheric pressure and dynamic intensification. At the centre of an intense weather system, surface atmospheric can drop by several 10s of hPa, leading directly to sea level rise of 10s of cm. This phenomenon is commonly known as the “inverse barometer effect” or “static amplification”.

The ‘inverse barometer’ effect has been considered however, for extremely low atmospheric pressure systems along our coastal areas, the effect will differ when one take into consideration: • at what latitude the system is moving; • how many closed pressure gradients can be found around the centre; • if there is any upper atmospheric support; • and how steep and to what height the upper level support is.

For each of these elements, the effects and impacts along the coast will be different. The focus of the study was not in describing various low atmospheric pressure systems but rather the effect of storm surges along the coast”.

Various methods and models to investigate storm surges have been successfully tested and implemented in a number of countries. The following case studies deal mainly with storm surges, from prediction to mitigating factors to reduce the impact of storm surges.

1.1 Rio de la Plata, Argentina as a case study integrating satellite altimetry and real-time tide gauge data for the prediction of storm surges One area that is most likely to experience irregular sea-level rise during specific weather events is the east coast of Argentina and particularly in close proximity to the Rio de la Plata (Etala et

18 al., 2015). In this low-lying region, the conditions are favourable for surge generation to occur on the furthest northern area where the shallowest part next to the estuary mouth can be found.

Extratropical cyclones, which the general public know as intense cold fronts, pass over the region and result in continuous strong winds, which lead to storm surges that extend to the central parts of Rio de la Plata. The most severe events are storm surges, which occur in Buenos Aires, when localised extremely strong winds blow alongside the shallow estuary.

The main effects of these storm surges could be summarized as follows: a) due to the strong south-easterly winds the estuary water is pushed back (due to positive storm surge / increase in ocean-water level) resulting in severe flooding over low-lying areas of Buenos Aires; b) due to strong north-westerly winds, Buenos Aires experiences negative surges, which have a massive impact on sea-navigation safety (sea level drops and therefore ships can get stuck) and fresh water supply in the estuary due to dropping of estuary water level. Etala et al. (2015) indicated that a negative surge can be predicted in advance (from hours to a day) by monitoring water levels higher up in the estuary as well as anticipated weather patterns.

In Argentina, a wave/surge numerical prediction system at the Naval Meteorological Service (SMARA) was implemented (Etala et al., 2015) to forecast storm surges. The expected time of the storm surge in extremely low-lying areas, such as the City of Buenos Aires, allows for the identification of these differences (positive and negative surge) by monitoring the deviations from the norm in the real-time data from hours to days prior to the event. Etala et al. (2015) found that the integration of storm surge data and short-range storm surge prediction had a positive impact on their conclusions. Once the integration of the forecaster cycle was introduced it was found that the error in the storm surge level forecasted declined significantly.

The initial results (Etala et al., 2015) suggested that the numerical prediction of storm surges along the Argentine coastline would benefit by making use of integrated real-time observations

19 and the availability of this data is critical. Their research findings confirmed the influence of an improved original data field in short-range forecasts. Integrating data gathered from the middle and mouth of the estuary suggested an improvement in storm surge forecasting especially when the warnings criteria / levels are expected to be triggered.

To date, research has focussed mainly on storm surges and the impact on estuaries in Argentina and not in addressing warning criteria for estuary flooding, but only warning criteria for storm surge levels and therefore could not be used for the South African context where the storm surge data, hydrological, meteorological, astronomical and integrated early-warning systems are considered.

1.2 Thames Estuary, case study of modelling storm surge flooding of build-up areas Brown et al. (2007) used an overland flow and coupled storm surge model to simulate dangerous coastal flooding of Canvey Island, which is situated at the mouth of the Thames Estuary in south east England. It is a low-lying flat and muddy area and the height of Canvey Island is ~ 1 m below the average high-water level (Marsland, 1986).

Storm surges in the Thames Estuary actually originate from the atmospheric pressure gradients situated over the North Atlantic and to the northwest of Scotland (Pugh, 1987), due to the width of the continental shelf and high energy associated with the wind systems. Brown et al. (2007) explained that the surges formed when winds blow over the North Sea move southwards with the semi-diurnal tide towards the southern parts of the North Sea following the coastlines of the UK.

The waterfront at Canvey Island is protected by reinforced concrete walls as well as various secondary structures, and a further line of stone and sand banks protect the island against flooding. During storm surges these barriers need to be closed ensuring the reliability of the scheme is not undermined.

20 The variable heights of 6,35 m and 7,15 m of the sea defences were based on an analysis of statistical tidal data gathered over 140 years (Suthons, 1963), with mean sea level projected until 2030. However, this excludes the ‘‘1 in a 1000 year’’ water level estimations. It further stated that although the risk remains for future flooding as sea level rises, no study was conducted to verify that the sea defences will be breached or not.

Brown et al. (2007) concluded that a number of processes may lead to extensive flooding: • storm surge and tidal forcing of the ocean and atmospheric processes that generates long waves; • interaction variation between shallow water and the surge tide; • development of short waves and the spread of these towards coastal areas; • spilling over and the defences of the sea having been breached; • the flow of water in built-up areas, in the direct path of the water body and subsequent water directed by means of drainage and channels. It was further noted that various physical processes, however, could result in modelling uncertainties (Brown et al., 2007).

The Thames Estuary case study was basic and did not provide any details. The process could have been assisted by making use of a combined 1-D/2-D modelling approach. A limitation of their research (Brown et al., 2007) was that although it focussed on how models can accurately predict a storm surge and related flooding, their study did not address preventative estuary flooding and/or the implementation of an early warning system for estuary flooding.

In summary, the paper did not address the development and/or introduction of an early-warning system for estuary flooding based on meteorological and oceanographic conditions.

1.3 Coastal modelling for flood defence – case study the Netherlands Flooding is a well-known phenomenon in the Netherlands (Battjes and Gerritsen, 2002) and various methods have been developed to manage these floods. At present, there continues to

21 be debate over future approaches, with the understanding that land will continue to sink and that sea level will continue to rise. Ensuring that the Netherlands remains protected from coastal flooding, Battjes and Gerritsen (2002) presented a synopsis of current and modern developments in numerical modelling of extreme physical processes. The Battjes and Gerritsen (2002) case study especially highlighted wind waves, storm surges and once a post-flood event occurs the modelling of water and the forces acting on solid bodies immersed in water and on their relative motion.

Battjes and Gerritsen (2002) restricted their research by focussing on wind waves, storm surges and the physical phenomena of tides. Their paper provided a summary of policies addressing accepted levels of flooding risk and the statistical reanalysis of numerical hydrodynamic modelling combined with historical storm surge data. Their intention was to improve the likelihood of estimating high-water levels occurring along the coast of the Netherlands.

There are three different types of short-lived transitions of tides: (i) those between the tide and dry land, (ii) between basic tides in channels or rivers and basically surface tides over land, and (iii) dangerous tides. A numerical code was developed and operationalized (Stelling et al., 1998; Stelling, 2000) as the Delft flooding system package of Delft Hydraulics, based on the protection of form and motion and the positivity of the water depth applied on a staggered grid. The model provides accurate and constant results in calculating the tide on vertical slopes such as dykes in the Netherlands.

In the Netherlands, operational storm surge forecasting is an automated process at the Royal Netherlands Meteorological Institute. The output of the High Resolution Limited Area Model (HIRLAM) is used by the Dutch Continental Shelf Model (DCSM) to drive the storm surge forecasts (Gerritsen et al., 1995). By making use of the Netherlands Wave Model (NEDWAM), which is a general Wave Model (WAM) (Komen et al., 1994), wind-wave forecasts are generated.

In the closing comments of their paper (Battjes and Gerritsen, 2002) a clear indication was given that further research is required with regards to research challenges that exist in both the

22 modelling of wind-induced flows and in modelling inundation. In relation to research issues in modelling of tides as a result of wind, it is essential to evaluate and assess the flood risk in a changing climate. The modelling of atmosphere-ocean interaction (fully coupled) processes was outstanding when using a quadratic friction law. However, Battjes and Gerritsen’s (2002) paper did not address the development and/or introduction of an early-warning system for estuary flooding based on ocean and meteorological conditions.

1.4 Estuarine flooding and managed retreat The UK experienced a risk increase of floods in estuaries due to the increase of commercial, housing and agricultural activity along estuaries (Townsend et al., 2002). The same also holds true within South Africa such as the Great Brak. In the paper by Townsend et al. (2002) the risk of floods and their successful mitigation was addressed. The paper deals specifically with ‘managed retreat’ where it is wished to restore reclaimed land to reduce the risk of floods within estuaries.

One cannot simply accept that estuary flooding is a combination of atmospheric and oceanographic processes. Events can change the estuary shape and hence the tide circulation and eventually the level of adverse and/or extreme events. Modifications in the shape of the estuary can influence the outflow. Therefore, tidal propagation can be affected by activities such as soft and hard engineering (i.e. gabion basket fencing) along the estuary.

Townsend and Pathick (2002) defined the term “rollover”, as indicated in Table 1.1, as the response of an estuary to sea level rise. In a rollover the estuary adjusts to maintain its form, and in doing so, migrates towards the land (Allen, 1990; Pethick, 1996 and Long et al., 2000). The Bruun model adopts this term in relation to the response of beaches to sea level rise (Bruun, 1962). The loss of sand at the berm provides sand deposits to the lower parts of the beach and therefore its profile remains the same in relation to the stationary estuary water. It is a two- dimensional (2-D) cross-shore model and therefore longshore processes are not effectively explained. Similar theories can be used following the deepest area of an estuary. We should keep in mind that the 3-D form of the estuary will determine where piling and erosion will happen.

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Sea-level rise No Flood defences mean water level tide will flood low-lying areas increases hydraulic depth of channel amount of water in estuary increases one may expect floods to occur more one may expect ebb dominance frequently expect an increase of sediment and removal on enhances erosion of channel the intertidal zone and export of sediment with the increase of sea shore elevation then when the size of the waterway increases one the sea shore size of the estuary declines would expect an increase in depth of the hydraulic regime changes to dominance in ebb occurrences changes to floods to dominate

Table 1.1: Estuary responses to sea-level rise (taken from Townsend and Pethick, 2002).

Townsend et al. (2002) describe in detail the conceptual models of estuary response with i) the irregularity of tides and flood-ebb dominance, and ii) estuary transgression or rollover. However, their research lacks guidance on how to deal with estuary flooding when considering both atmospheric and marine effects and/or the implementation of an early-warning system for estuary flooding.

1.5 Investigating River-Surge interaction in idealised estuaries The interaction between river and surge was conducted by Maskell et al. (2014) and their study noted that along coastal areas, especially where development has taken place along the estuary front, the combination of high river-flow and storm surge can result in severe flooding. The combination of storm surge and dangerous river flow flooding risk is more noticeable in estuaries where the origin of the river flow comes from catchments. This is especially so in mountainous areas, where the amount of river outflow and the sea-level height is important (Svensson and Jones, 2004). The Great Brak river along the South African south coast is one such example.

The focus of the work by Maskell et al. (2014) was for the River Eden (in Northern England), which is dominated by mountainous and rocky terrain and thus results in a rapid run-off during heavy

24 rains. They anticipated an increase in risks (ocean and terrestrial) brought about by an increase in the occurrence of hazardous weather events (Figure 1.1).

Research on both global scales, such as the Intergovernmental Panel on Climate Change (IPCC), (IPCC, 2007, 2010 and 2018) and local scales (Woodworth et al., 2009) has indicated that the risk on coastal properties and infrastructure is increasing as the scale of extreme Sea Level Rise (SLR) results in an increase in storm surges.

Figure 1.1: Global risks landscape taken from the 2017 World Economic Forum in Davos in which impact against likelihood are compared. It should be noted that of highest impact is denoted by the blue circle, which identifies storm surges, estuary flooding as the greatest threat for extreme weather events.

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As regions, particularly low-lying areas, become more vulnerable due to increased storm surges and river flooding, there will be an increase in social-economic threats (Nicholls, 2002). For example, the current protection against floods in certain areas of the UK, such as the Thames Estuary, might not be sufficient in the future to resist any projected increase in severe weather and/or ocean events.

The most effective way to plan the development along floodplains is to simulate, in an operational model, various combinations of anticipated storm surges, expected waves, anticipated river outflow and associated coastal inundation. During extreme sea levels, driven by similar weather systems, it is essential to grasp the fact that extreme river discharge can develop in a nonlinear manner (in which the change of the output is not proportional to the change of the input). While it is important to the control of hydraulic discharge in two-layer flows (Armi, 1986), it could not be determined what the relevance between flood and tide flow is in the estuary and/or the area of the interaction between them, neither the effect it had that resulted in inundation.

There are many similarities between the work undertaken by Maskell et al. (2014) and South Africa’s environment. For instance, challenges in South Africa such as topography and the combination of ocean-terrestrial impact on estuary flooding are similar in that they experience severe flooding during storm surges and high river levels. However, Maskell et al. (2014) do not specifically address permanently open-close estuaries, as is needed for the South African context, nor do they specify the amount of precipitation required for significant and/or dangerous run-off. The focus is more on idealised model data, which may assist in the forecasting of flooding in an estuary based on ocean and hydrological information. However, in South Africa there was, until 2018, no operational storm surge and/or inundation model, neither is there real- time hydrological information available to weather forecasters. The work by Maskell et al. (2014) does not address the introduction of any early-warning system, despite model data being able to suggest possible flooding in the estuary.

26 A clear limitation in the various studies outlined in this chapter is that, while flooding events are discussed in the context of storm surges and sea-level rise, there is almost no information or recommendations regarding early-warning systems for estuary flooding. One local example is the research (Bornman and Adams, 2005) carried out on the flooding along the Keurbooms / Bitou and Piesang estuaries in South Africa, despite no storm surge early-warning systems being put in place for anticipated flooding events.

The Keurbooms river is subject to substantial flooding events (Duvenhage and Morant, 1984). Despite past research on the impact that tidal-flooding events will have on the estuarine ecosystem and on local communities, to date no management or early-warning guidelines are available. It is thus essential to design and develop an effective early-warning system for use along the South African coastline.

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2. Introduction

Global mean sea-level has risen by ~ 1,7 mm per year between 1901 and 2010 resulting in a total sea level rise of 0,19 m, as a result of an increase in ocean temperatures brought about by a warming planet (IPCC, 2018). The IPCC further states that the rate between 1993 and 2010 was very likely higher than 3,2 mm. However, on a regional scale, sea-level rise rates vary considerably, with significant sea-level rise increasing coastal inundation especially around low- lying regions and estuaries such the Great Brak on the south coast of South Africa. Naturally, major consequences of this is damage and/or loss to wetlands, biodiversity, valuable infrastructure and most importantly, human life (IPCC, 2007, 2010 and 2018). In addition to anthropogenic climate change, natural phenomena such as strong El Niño–Southern Oscillation (ENSO) events combined with higher ocean temperatures i.e. the recent 2015/16 El Niño, affect not only local winds, ocean circulation and occurrence of storm surges, but also sea level along the coastlines (National Research Council Report, 2012). This combination of both natural and anthropogenic induced factors further underpins the critical need to understand the long-term requirements for coastal planning and mitigation. Global model projections (IPCC, 2007, 2010 and 2018) demonstrated that sea-level rise will increase the impact of storm surges and high waves around coastal areas for the next 20-50 years (IPCC 2010 and 2018). The IPCC (2018) specifically states that it is likely that annual mean significant wave heights will increase because of enhanced wind speeds.

South Africa, in particular the Eden district of the Cape south coast (Figure 2.1), is well known for its significant weather and flood events despite being divided into different homogeneous rainfall areas. The coastal zone of Eden is influenced by maritime weather patterns i.e. the cooling and warming effects of the sea, resulting in an overall temperate climate. According to the South African Weather Service, data from 1993 shows that the mean maximum and minimum temperatures indicate an average winter minimum temperature of 8 °C, while for summer it is 15,5 °C. The average maximum temperature in winter is 19,9 °C, while in summer it is 24,7 °C, although temperatures can be higher during local berg-wind conditions. The highest ever recorded maximum temperature for George is 42,9 °C, while the lowest maximum

28 temperature is 8,2 °C. The extreme minimum temperature is 1,0 °C while the extreme highest minimum temperature is 25,1 °C.

Figure 2.1: Map highlighting the Eden district, which is marked as a black square, is situated within the Western Cape Province of South Africa. Map provided by the Western Cape Provincial Disaster Management centre.

In response to this growing concern, especially by Disaster Management practitioners in Eden, a multi-stakeholder approach, including the South African Weather Service (SAWS), Department of Water and Sanitation (DWS), Disaster Management (DM), Department of Environmental Affairs (DEA), Ethekwini Municipality, Nelson Mandela Bay Municipality, CapeNature, Council for Scientific and Industrial Research (CSIR) and the South African National Parks (SANParks), was deemed necessary to address the concern and is the core input of this thesis. This was achieved through various workshops and meetings where risks were identified and an effective

29 management plan developed. The workshops were coordinated and led with a direct aim towards gathering input towards an early warning estuary guide.

The need for an estuary early-warning system is essential given the severe and often- unpredictable weather conditions in Eden. Elements such as a) high precipitation through cut- off lows, b) increased run-off brought about by growing communities and c) agricultural pressures on the land in each catchment. All of these result in highly variable and seasonal volume flow in rivers and estuaries across South Africa. In addition, the combination of storms, associated ocean conditions and water levels in estuaries can result in catastrophic flooding events impacting an already fragile state.

Although these events are a natural occurrence, the growing population and development of coastal habitats exists within the estuarine floodplain poses a real threat to life and infrastructure. Understanding and predicting these events, developing alerts and establishing a preventative mitigating intervention document are now critical. Of major concern is that South Africa does not currently have policies guiding Municipalities on how to mitigate estuary flooding in a coordinated and efficient fashion across its multi stakeholders. This thesis aims to address this limitation by establishing a policy document that highlights the measures needed to ensure an efficient warning system is developed.

As the Eden district is the area where most estuarine flooding occurs, it was agreed between Disaster Management and SAWS that the estuary early warning guide will be tested in this area.

2.1 Understanding the catchment to coast and water flow of estuaries An estuarine system is a receiving environment for fresh water flowing out of a catchment area as well as sea water pushing in from the ocean side. The freshwater flow rates reaching the estuary are determined by key drivers such as weather events, rainfall intensity within the catchment area, topography, soil porosity and ground cover. These natural influences can be further influenced by man-made interventions such as channel depth, instream channel constructions, e.g. bridges, impoundments, debris, hard structured shorelines, land use and

30 development in the catchment, e.g. hardened surfaces within cities. Thus, the response of an estuary to increased inflows and flooding will be determined by the above processes, which vary across regions.

Estuary mouth conditions regulate the access and rate of flow of fresh water to the sea, the interaction between fresh and salt water within the estuary, as well as the level of the water in the estuary. Therefore the condition of the estuary mouth plays a critical role with regards to estuary functioning. South Africa presents two forms of estuary systems. Permanently open (accounting for 30% of all estuaries) and temporarily open/closed (70%) (Whitfield and Bate, 2007).

Temporarily open/closed estuaries are generally at a higher risk of flooding, especially when there is development (i.e. housing) within the floodplain. The closure of an estuary mouth during periods of low freshwater inflow/outflow results in a significant increase in water level during wet periods, when freshwater outflow is restrained. The associated sand berm responsible for closing the estuarine mouth, naturally controls the level of flooding within each region (e.g. Holloway et al., 2010 and CSIR, 1990). The Great Brak Estuary is considered as a temporarily open/close estuary.

Permanently open systems are less prone to flooding, as there is little fluctuation in estuarine water level with the main changes brought about by tidal events. These estuaries are often fed by larger catchments, which result in a greater outflow of water. Yet, despite having permanently open mouths, such estuaries are subject to occasional large floods, e.g. during 1:100-year flood events. Permanently open estuary mouths also allow for ongoing intrusion of salty ocean water and are thus dependant on tidal state as well as storm surges. One such example is the Keerbooms estuary.

For both open and closed systems, changing climatic conditions may bring about an increased likelihood of accelerated flood events that require immediate response strategies to prevent loss

31 of both life and infrastructure. The area to be used in this research (Figure 2.2a) falls within climate region 24, known as the southern Cape (Kruger, 2004).

2.2a 2.2b

Figure 2.2: (a) The Climatic regions of South Africa (Taken from Kruger, 2004). The area of interest in this research is Region 24 along the south coast of South Africa and demarcated as purple; (b) Rainfall district areas over South Africa as classified and provided by the South African Weather Service. The region of interest is marked as 11.

Region 24 is characterised by high rainfall of between 800 and > 1000 mm per annum with the heaviest precipitation falling in October. According to the homogeneous rainfall district classification of the South African Weather Service, this region falls within district No. 11 (Figure

2.2b).

2.2 Impacts of floods on estuaries – Secondary effects In estuaries with a high-density population such as the Great Brak, flood damage will result in secondary (but of no less importance), impacts such as failure of sewage pumps, damage to electrical connections, water lines, transport infrastructure and communications. Furthermore, flood events will have a destructive socio-economic impact, particularly in areas where properties extend onto the floodplains such as the Great Brak estuary. Property can be seriously damaged either through major structural failure or less seriously through water ingress into building interiors. Socio-economic activities could be indirectly affected due to flooded seaside industrial areas, caravan parks, sports fields and fishing. Long-term consequences of repeated

32 flooding can include declining property values, inability and/or difficulty in obtaining insurance and financing for assets within these areas.

Flood events form part of the natural catchment process. Measures taken to manage flooding may have a negative influence on natural processes if not considered properly. Ongoing inappropriate estuarine mouth manipulation practices (e.g. lack of approved Mouth Management Maintenance Plans linked to Estuary Management Plans) can be a significant negative factor for ecological functioning and habitat preservation for the Great Brak. Natural flooding cycles form an essential part of a functioning estuarine system and its associated species, e.g. water plants, invertebrates, fish, birds and mammals. Flood mitigation measures may disrupt migration routes, reproduction cycles and change salinity regimes. All these factors require consideration in the development of an Estuarine Management Plan (EMP) for the Great Brak estuary, which must be drawn from the National Estuarine Management Protocol (NEMP). Further developing of the estuarine mouth-management protocol, which will be encapsulated in a Mouth Maintenance Management Plan (MMMP) referenced in the EMP, is required.

Additional negative ecological consequences include secondary impacts. For example, sewage- nutrients possibly leading to subsequent anoxia in closed systems as well as other water quality problems, debris being distributed throughout the environment, lack of scouring of channels for this instance of premature breaching, and erosion of remaining natural habitats caused by modified flow patterns in developed estuaries such as the Great Brak.

2.3 Changing climate and land use planning As a result of the increased intensity and frequency of adverse weather conditions, South Africa’s coastal and/or estuarine communities are becoming increasingly vulnerable. The flood risk to inappropriately-located developments in estuary floodplains is exacerbated by the disregard of the 1-in-100-year flood-line restrictions (National Water Act No. 36 of 1998). Provisions can be found in the Integrated Coastal Management Act (ICMA) for coastal setback lines/management lines to prevent and address inappropriate coastal and estuarine developments. Severe estuary flooding (e.g. Eden district Municipality 2007/2008/2011/2012) (Holloway et al., 2010) has

33 highlighted how vulnerable South Africa’s coastal and estuary communities are to the impacts associated with such events, as well as the negative secondary impacts (e.g. ruptured sewage pipes leading to pollution in the estuary). Given the growing need brought on by climate change and increasing social pressures on the coastlines, there is clearly an urgent need for effective and proactive actions to minimise the negative impacts of estuarine flooding, whilst maintaining a functional ecosystem (Van Niekerk and Turpie, 2012). One such example is the Department of Science and Technology’s (DST) SA Risk and Vulnerability Atlas (Palmer et al., 2011).

2.4 Proactive risk identification and subsequent risk reduction and mitigation A concurrent, proactive approach to Disaster Risk Reduction (DRR) and mitigation is urgently required within South Africa. This approach should focus on those estuary systems most at risk with respect to damage of infrastructure and property, socio-economic activities and most importantly loss of life, due to flooding from land and sea, and associated secondary risks such as pollution. Based on this, the Great Brak estuary can be considered a high risk estuary. The integrity of the associated ecological infrastructure should not be sacrificed in the process except under predetermined emergency conditions.

2.5 The need for estuary early warning guideline for policymakers This thesis presents, for the first time, an effective and tested early-warning system guideline for an Estuary Early Warning - Emergency Preparedness and Response system. The aim is to provide a guideline to policymakers that can be used to assess any threat of estuarine flooding against the backdrop of changing climatic conditions. Such a response is crucial for South Africa, given the country’s socio-economic pressures and the need to predict and manage expected change in the frequency and intensity of these natural disasters.

Coordinated and proactive interventions, which will assist with the management of future flood events, include the determination of estuarine flood lines, coastal and estuary management lines and coastal retreat policies. Their implementation will require political support from the National and Provincial Departments of Environmental Affairs (DEA) as well as Water and Sanitation

34 (DWS) as well as the Provincial Departments for Disaster Management (DM) with specifically allocated funds for these hazards.

The research conducted by this study will furthermore assist in the mitigation of flood damage specifically in Climate Region 24 (Figure 2.2a) through the combined effects of oceanographic, hydrological, meteorological and hydrographical disasters by addressing the following key questions: 1. Why the Great Brak is chosen as case study? 2. Did the case study of Great Brak indicate the necessity for a guideline for policymakers? 3. Who could benefit from such a guideline and ultimate policy? 4. What is the most appropriate guide for South Africa and what is required for such a guide to be successful? and most importantly, 5. Will the guide be successful when implemented?

In consideration of these questions and the socio-economic needs of South Africa, mitigating interventions, as part of the Risk Reduction Programme, are included in this thesis. Furthermore, this investigation will define the critical implementation needed for relevant institutions (i.e. Disaster Management) in order to issue estuary alerts during disaster scenarios such as extreme flooding events.

This thesis will furthermore identify, understand and for the first time nationally standardise the procedures and processes used to describe and predict extreme-weather events such as: 1. What is the amount and duration of rainfall expected? 2. How full is the dam and level of the estuary? 3. Is the estuary open or closed? 4. What is the height of the tide and what is the height of the waves?

In doing so, the associated issuing of estuary alerts in South Africa, in line with the standard multi- hazard early-warning system processes, will be created to minimise impacts of flooding of high- density, low-lying estuarine areas. This research will form part of the Estuary Early Warning –

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Emergency Preparedness and Response Guide for South Africa (EEW-EPRG) and thereby act as a guideline for the dissemination and communication of information across all communities as well as proposed actions aimed at addressing each issue. This guide will be the first nationally and internationally attempt and will lead the way forward for all high risk estuaries across the globe.

36 3. Data and methodology

It should be noted that various stakeholders kindly provided data used in the following chapters. A description of each follows. The South African Weather Service (SAWS) provided all weather- related information such as rainfall, temperature, weather forecasts, weather warnings and numerical-model data. The Hydrographic office of the South African Navy based in Simonstown provided tidal information. The Council for Scientific and Industrial Research (CSIR) shared their wave data archived from the Mossel Bay wave rider, the Department of Water and Sanitation provided all the hydrological data such as estuary and dam level data, while the records of severe weather events were obtained from Eden Disaster Management. The above-mentioned variables all contribute towards estuary flooding either as single or combined factors. Real-time information regarding these physical variables contribute towards minimising the risks of estuary flooding.

3.1 Key drivers of estuary flooding In the context of this thesis, drivers are considered those factors that have a direct influence on estuary flooding such as rainfall, sea-level height and tidal state.

3.1.1 Meteorological drivers Rainfall, both measured and predicted, is a critical measurement in terms of the estuary flooding process. Monitoring of rainfall at varying timescales (i.e. from hours to months) is not as important for estuary flooding when compared to the monitoring of rainfall intensity, especially over shorter periods i.e. less than a few hours. Greater meteorological drivers are extra-tropical storms of very low atmospheric pressure, which are over hundreds of kilometres in width. These weather systems may last for several days and affect large stretches of the coastline resulting in heavy rains, rough seas and potentially damaging cut-off low systems.

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3.1.2 Oceanographic The impact of the magnitude of estuary flooding relates to the state of the ocean at the time of estuary discharge. Sea-level rise, high-tide levels, storm surge and wind waves all contribute to magnifying and exacerbating the overall risk and extent of estuary flooding. 3.2 Factors contributing to forecasting estuary flooding There are a number of factors specific to each catchment that require consideration in determining the risk and impacts associated with estuarine flooding and are discussed in more detail in Chapter 6. The most significant adverse factors, which have been shown to be historically associated with estuarine flooding, are listed in the sections below.

3.2.1 Predicted rainfall intensity within the catchment region There is a need to provide rainfall forecasts in both the medium (i.e. up to 5 days) and short (i.e. up to 2 days) term. Initial forecaster assessments use medium term forecasts of rainfall in the catchment area. As the lead-time ahead of the event becomes shorter, so the focus shifts to short-term forecasts integrated with real-time observations of rainfall quantity and intensity. Information regarding high rainfall intensity over periods of an hour or less has been identified as an essential input into the prediction of flood peaks. The South African Flash Flood Guidance System (SAFFGS), managed by SAWS, is an essential guidance component to monitor such risk on a “drainage-basin” scale. Understanding the impact of rainfall in the catchment over the proceeding period of up to 10-20 days is vital. Rainfall events affect the catchment soil moisture, which in turn influences the amount and ease of rainfall run-off.

3.2.2 Land use and bathymetry Understanding the nature of land use within each catchment is critical, as there is a vast difference between rural areas and constructed areas. Rural areas, where conservation agriculture occurs and where wetlands remain intact, will be able to absorb greater quantities of rainwater than catchments with hardened surfaces such as cities and roads. High rainfall (>50 mm) within the catchment of a long or big river, such as the Breede river, may produce less of a flood risk along the estuary than a similar event within the catchment of a small or short river such as the Great Brak, Touw and Sandvlei.

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3.2.3 Estuary water level and beach berm height The severity of potential flooding within the estuary is influenced by three main factors. Firstly, high-water levels in the system (estuary and dams) reduce the system’s ability to buffer the flood. Secondly, the presence of a fully-functional estuarine flood plain or functional zone will act as a buffer to flooding events by absorbing incoming freshwater into a large surface area. Thirdly, the presence of a large intact beach berm will result in the natural damming of the inflowing fresh water, which in turn results in rising water levels until the beach berm is breached. In the event that a flash flood occurs, the buffering effects of the water level and berm height become irrelevant.

3.2.4 Sea-level rise Sea-level studies along the South African coastline intensified in the 1990s due to previous limited and poorly constructed data (Woodworth et al., 2009). The trend of sea-level along the South African south coast indicates a rising of ~ 0,148 cm/year between 1956 and 2006, while the eustatic sea level trend is 0,157 cm/year for the south coast (Mather et al., 2009). Mather (2009) stated that that Mossel Bay tide gauge indicated a sea level change of -0,040 ~ 0,019 cm/year. However, global tidal-gauge records and altimetry show that the global sea level has risen by a concerning rate since 1990s (IPCC 2007, 2010 and 2018 and Blake, 2010). The South African coastline estimate for sea-level rise is about 0,12 ~ 0,04 cm/year based on 30-year statistical data (Brundrit, 1995). Accurate sea-level observations are essential as they can be used to examine extreme events associated with estuary flooding, which may lead to coastal inundation. Given the lack of an expansive tidal-gauge network around South Africa’s coastline, the impact of these large waves on coastal regions cannot be significantly resolved.

Approximately 30% of South Africa’s population live near or along the coastline (Theron and Rossouw, 2008) therefore sea-level rise along the coastline has extensive socio-economic and ecological implications through erosion, coastal inundation and flooding resulting from increased frequency of storm surges.

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3.2.5 Waves and storm surges Storm surges can be explained as follows: “An abnormal rise of the sea level generated by a storm, over and above the astronomical spring high tides.” (Stander et al., 2011). Extreme weather events in the Eden district may lead to such a storm surge. Globally it has been found that storm surges are more frequent than anticipated coastal hazards and tsunamis (Stander et al., 2011). Phenomena such as these usually occur in South Africa during austral winter and are driven by extra-tropical storms (i.e. strong cold fronts). In contrast, during summer and early autumn they may be driven by tropical cyclones (common off the east coast of South Africa). When sustained strong winds blow onto the coastline, in combination with low atmospheric pressure, storm surges are likely to occur. Their long duration results in further elevated water levels at high tide.

The understanding of the criteria for issuing storm surge alerts, as articulated by Stander et al. (2011) remains valid because storm surges are one of the components that impact on estuary flooding. Until an operational storm surge model is developed for South Africa, a combination of the following criteria can be used only as a recommendation to issue a storm surge alert: a) When the water level is anticipated to be between 0,8 and 1,0 m above the mean level of tides during astronomical spring high tide conditions along the coast as per the South African tide tables supplied annually by the Hydrographic office. b) As an interim guideline when an offshore significant wave height of at least 3 m is expected. One would normally expect this with: i) a deep cold front (mid-latitude cyclone) and/or the passage of a well-established cold front; ii) the centre of a slow-moving tropical or extra-tropical surface low-pressure system (i.e. cold front) is below 1004 hPa and close to the coast; and iii) extremely fast cyclogenesis of a deep low-pressure system. c) When determining the storm surge water level one should consider the influence of waves as they move closer to land as well as atmospheric conditions and their local affect.

40 It was concluded that a storm surge alert should be issued when the calculated surge value is in excess of 0,5 m and it coincides with spring high tide as well as an expected offshore significant wave height of 3 m. This was shown to occur around 04:00, South African Standard Time (SAST) and 16:00 SAST when spring high tide is expected.

3.2.6 Beach berms The beach berm controls the flow rate of water in and out of the estuary. If the berm is intact, the waves are likely to spill over the berm and introduce salty water into the estuary. However, when the berm is breached, seawater in the form of a tidal flow and/or waves can travel upstream into the estuary, resulting in raised water levels and increased wave erosion. Elevated sea and/or estuarine levels due to waves and storm surge reduce the ability of fresh and salty water in the estuary to flow out to sea. This restriction results in the back flooding of the estuarine system, with the floodplain becoming completely inundated. A functional estuarine floodplain will be able to absorb these increased volumes unless development has taken place in this zone, in which case the buffering potential will be reduced.

3.2.7 Numerical model information In addition to the aforementioned factors, accurate weather prediction is an essential tool in the forecasting of estuary flooding. Numerical weather prediction models are an essential tool used by operational forecasters to accurately forecast the weather by comparing model-output data with real-time data and local knowledge obtained. The South African Weather Service (SAWS) uses the in-house Unified Model (UM) as the numerical weather prediction model. Although there are other weather prediction models run by SAWS, UM is their main operational model. The UM is the suite of atmospheric and oceanic numerical modelling software developed and used at the UK Meteorological (Met) Office (https://www.metoffice.gov.uk/research/modelling- systems/unified-model).

The UM is designed to run either in a fully coupled mode, ocean only or in atmospheric only mode. It further contains sub-models, which can be used as stand-alone model/s, or as additions to the main model. For climate, numerical modelling the prediction phase may be from tens to

41 thousand years, while for the numerical weather forecast the model run varies from a few hours until a week ahead. The horizontal and vertical resolution are random as it may be different for the user. Computing power and standard resolutions will determine the user’s resolution required (https://www.metoffice.gov.uk/research/collaboration/unified- model/partnership).

At SAWS, UM is run on two modes namely, data assimilation and non-data assimilation and at different horizontal resolutions – 12 km, 15 km and 4 km. The model forecasts, which are used for specific case studies are produced by 12 km horizontal resolution and non-data assimilation configuration. The model uses initial start files and frames, which are downloaded from the UK Met Office daily to produce daily 48-hour forecasts.

SAWS runs the atmospheric component of the UM and it is run over different domain sizes. The domain of interest here is from the Equator to 55° S and between 10° W and 55° E. This domain covers the Sub-Saharan Southern African region including Madagascar and the adjacent Atlantic and Indian Ocean basins. The 12 km UM at SAWS has a grid of 12 km x 12 km and extends from the surface up to 10 hPa (~26,5 km) with 38 quasi horizontal levels, hence forth called Unified Model South Africa 12 km (UMSA12). The UMSA12 run uses initial dumps and lateral boundary conditions which are downloaded from the UK Met Office daily. It is run daily and initialised at 00:00Z. UMSA12 produces forecasts for many variables such as geopotential height, cloud, wind, temperature at 500 hPa and accumulated total rainfall.

This chapter has identified the key drivers and variables needed to successfully focus and/or predict estuary flooding events. It demonstrated all the various atmospheric and oceanographic elements required and further underlines the importance of the estuary berm. This thesis focuses on severe flooding along estuaries in South Africa. The attention in the next chapter will be on the Great Brak estuary in order to identify which contributing factors are the main drivers for catastrophic flooding.

42 4. Results 1 - Why the need for an estuary early warning guide? – Case study of the Great Brak estuary in the Eden district

In this chapter a number of extreme flooding events at the Great Brak estuary are highlighted. It is very clear from the listing (Table 4.1) that, had improved data logging and weather forecasting been available and had direct action been taken, much of the damage brought on by the flooding events between 2003 and towards the end of 2012 could have been avoided. The aim of this chapter is to highlight the regularity of flooding events in the Eden district and to emphasize the objective of this thesis to design an early-warning policy for all stakeholders.

4.1 Rainfall conditions over the Eden region The Eden district (Figure 2.1) receives rainfall throughout the year with higher rainfall periods in austral autumn (March), winter (June – August) and spring (October and November) (Figure 4.1). The graph illustrates the long-term average of rainfall since 1921 until 2018 where rainfall was mostly measured manually until 2003 when the system became automated. The average rainfall (Figure 4.1) for the period 2003 until 2018 was chosen as this was the period where Disaster Management (DM) started logging severe storms and where the rainfall amounts were mostly measured electronically.

In spring, the high rainfall is associated with the combination of frontal systems moving across the country during late winter and the effect of orographic rainfall in close proximity to the coast. Rainfall during autumn is caused by weather systems moving eastwards. Since 2003, Disaster Management have logged 24 severe storms along the Eden district (Table 4.1), which have led to damaged homes, infrastructure and social hardship during a period where resources, especially financial, were limited and urgently required.

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Figure 4.1: Average monthly rainfall in mm for rainfall district 11 (see Figure 2.2b). The green line represents the long term average of 1921-2018 (mostly manual recording stations) and the orange line represents the monthly average from 2003-2018 (mostly automated rainfall recording stations and year when DM started logging severe events). The blue bar represents the maximum amount of rainfall measured for that month in mm and the red bar the lowest rainfall in mm measured for that month.

Severe weather events along the Western Cape southern coast, and in particular in the Eden district, are a common occurrence and the social impact remains significant as shown in Table 4.1. Prior to 2010, the severity of storm events led to a recognition of the need to develop an EEW-EPRG. Following the successful implementation of an early warning storm surge guide across South Africa, a request was made by the Eden Disaster Management to develop a similar policy document for estuaries in the region.

Affected areas (District, Known Dates Type of event Social Impact(s) Municipality / Damage (R mil) Metropole) March 2003 Cut-off low Cape Winelands, Eden 3 fatalities, 343,4 and Overberg districts 3000 people evacuated December 2004 Cut-off low system Cape Winelands, Eden 3 700 homes and 40 83,3 and Overberg districts business premises damaged

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January 2005 Flooding due to severe Mossel Bay No social impact 2,6 weather reported July / August Cut-off low systems Cape Winelands, 5 fatalities, 691,4 20061 Eden, Overberg and 1 600 people Central Karoo districts displaced November 2006 Hailstorm Haarlem No social impact 9,3 reported November Black south-easter and Cape Winelands, 2 fatalities, 1 191,5 20072 Cut-off low system Overberg, Central >2 400 people Karoo and Eden provided with relief districts especially or evacuated Swartvlei September 2008 High seas and coastal Eden Coastal Area No social impact Unknown erosion reported November 2008 Black south-easter and Overberg, Cape 1 fatality 1 138,7 Cut-off low system Winelands and Eden districts June 2011 Cut-off Low Cape Winelands, 1 fatality, 348,0 Central Karoo, Eden >1 400 people and Overberg districts evacuated

February 2012 Coastal erosion Mossel Bay, Glentana No social impact Unknown reported July and August Cut-off low combined Cape Winelands and 5 Fatalities, 377,7 2012 with a low-level cold Eden districts 2 000 affected front October 2012 Heavy Rainfall. Weather Eden Coastal areas No social impact Unknown system not logged by DM reported November 2013 Cut-off low in City of Cape Town, >19 000 people 167,5 combination with Cape Winelands, affected warmer tropical air mass Overberg and Eden from the north and a districts low-level low pressure system January 2014 Cut-off low in Central Karoo, Eden People trapped and 4 465,5 combination with a and Overberg districts fatalities in Cape tropical low-pressure Winelands system September 2014 Cloudburst due to Kannaland Heavy downpours of Unknown thunderstorms rain and hail resulting in 47,8mm in less

1 http://www.riskreductionafrica.org/assets/files/South%20Coast%202006_Complete%20Report%20(1).pdf. 2http://app01.saeon.ac.za/PLATFORM_3/SARVA/Documentation/Integration/4.6%20Draft%20Eden%20Case%20Stu dy%20final_YS.pdf.

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than an hour. 57 households temporarily displaced March 2015 Heavy rainfall reported Meiringspoort Bus and vehicle Unknown entrapped, one fatality July 2015 Heavy rainfall reported Eden District No damages reported Unknown August 2015 Heavy rainfall reported Eden District No damages reported Unknown September 2015 Heavy rainfall reported Eden District No damages reported Unknown November 2015 Heavy rainfall reported Eden District No major damages Unknown were reported Several roads were closed due to flooding March 2016 Flash Flood reported Oudtshoorn No damages reported Unknown April 2016 Heavy rainfall reported Eden District No damages reported Unknown July 2016 Heavy rainfall reported Eden District No damages reported Unknown September 2016 Hail storm reported due Ladismith 68 informal Unknown to thunderstorm settlements 118 adults and 68 children affected Table 4.1: Summary of significant disaster events from 2003 to 2016 along the Eden district in the Western Cape Province, South Africa (excluding fires, drought and non-weather related) as logged by Disaster Management. No significant known social impacts and/or damages reported since 2015 due to successful preventative steps taken by DM.

The Eden district experienced 24 severe weather events between 2003 and 2016, resulting in damage exceeding R4,8 billion to properties and infrastructure. The most potentially damaging weather systems affecting the South African coastline and particularly in this region are cut-off lows which, due to their transboundary influence, result in entire stretches of coastline and estuaries being affected. The summary of events outlined in Table 4.1 highlights only the significant weather and flood events that were logged by Disaster Management for the Eden district. No significant known social impacts and/or damages reported since 2015 (Table 4.1) due to preventative steps taken by DM. These preventative steps include the proactive and early warning of communities and artificial breaching of estuaries.

4.2 Description of the events leading up to significant flood events in Eden estuaries – Case study the Great Brak estuary On the banks of the Swartvlei estuary in the Eden district (Figure 4.2), lies the coastal village Sedgefield, situated between George and Knysna.

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Figure 4.2: Map of the Eden district. In the insert is the Swartvlei river and estuary, which are highlighted in red and the black arrow indicating the town of Sedgefield. Map provided by the Western Cape Provincial Disaster Management centre.

The region is prone to flood damage as shown by the November 2007 event in which large parts of the town, the main National road (N2) and the railway line flooded and a rail embankment across Swartvlei estuary (Figure 4.3) were washed away. Although the June 2011 event was more extreme, the National road (N2) and railway line were not flooded. These storms resulted in repeated flood damage (Table 4.1).

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Figure 4.3: A photo showing how the National road and railway line completely flooded during the Sedgefield flood of November 2007. Photo provided by the Eden district Disaster Management centre.

The Great Brak Estuary Management programme interim report (van Niekerk and Huizinga, 2011) identified the six highest flood levels recorded in the Great Brak estuary between 1988 and 2011 in order of disaster as: 1) 8th June 2011, 2) 1st September 2008, 3) 1st August 2006, 4) 20th May 2002, 5) 25th March 2003 and 6) 22th November 2007. These events are individually discussed in the following sections in order of damage and highlight not only the ferocity and frequency of storm damage to the region, but also emphasise the importance that such an early- warning system would have on the region.

4.2.1 Flooding event June 2011 The flooding incident on the 8th June 2011 was caused by a cut-off low and was the highest recorded since 1988 with a flood level of 2,913 m above Mean Sea Level (MSL). The maximum inflow into the Wolwedans Dam was 630 m3s-1 and resulted in a maximum flow rate over the dam wall of 340 m3s-1. This was one of the highest in and outflows on record for the dam. The inflow depends on the amount of rain in the catchment area while the outflow depends on the dam capacity and inflow.

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Figure 4.4: Graph showing rainfall in mm for the month of June 2011. The data highlights rainfall registered at three separate stations in the Great Brak catchment area. The different colours refer to the three rainfall stations Jonkersberg Bos (blue), Jonkershoek ARS (red) and Grootbrakrivier ARS (green). Data provided by SAWS.

In the run up to the severe flooding, significant amounts of rainfall of 193 mm fell at Jonkersberg Bos between the 6th and 8th June (Figure 4.4). No rain was registered at Jonkershoek Automatic Rainfall Station (ARS) as it was faulty on those three days while Grootbrakrivier ARS registered 140 mm over the same period. The significant wave height of ~5 m further peaked on the 8th (Figure 4.5) hindering any water outflow from the estuary into the open ocean.

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Figure 4.5: Graph showing wave data from the CSIR Wave-rider in Mossel Bay from 00:00 on the 6th June 2011 until 21:00 on the 9th June 2011. On the 6th the significant wave height reached ~4.5 m between 09:00 and 12:00. Wave height in m is shown in blue (Hmo) and significant wave height in m is shown in red (Hmax).

Despite the storm, the estuary level was already 1,3 m above MSL on the 1st June 2011 due to a closed estuary. Should the estuary mouth be open or controlled water released from the dam prior to the forecasted rainfall, the level of the estuary would have been manageable at less than 0,3 m above MSL before the 8th June 2011 (Figure 4.6).

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Figure 4.6: Graph showing the water level in m of the Great Brak estuary on the 8th June 2011 peaking close to 3 m at 14:00, almost the same time as highest significant wave height of just over 4.5 m between 09:00 and 12:00 in Figure 4.5. Data provided by DWS.

It is most likely that flooding could have been prevented if these measures were put in place, arguing for an urgent need for an estuary early warning. Thus the dangerous combination of heavy rainfall, dam overflow, storm surge and an already high estuary level, contributed towards the flooding. The position of the CSIR wave rider is situated close to the Great Brak estuary indicated in red (Figure 4.7).

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Figure 4.7: Map of the Eden district. In the insert highlights the positions of the CSIR Wave-rider (Green) in Mossel Bay and its close proximity to the Great Brak estuary, which is highlighted in red. Map provided by the Western Cape Provincial Disaster Management centre.

4.2.2 Flooding event September 2008 Unlike previous floods, the event on the 1st September 2008 (2,429 m above MSL) was not due to rainfall-induced river flooding but due to large waves (Figure 4.10) sweeping over the berm on the 1st where the wave height was ~4 m and the significant wave height reached ~7 m.

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Figure 4.8: Graph showing rainfall in mm for the month of August 2008. The data highlights rainfall registered at two separate stations in the Great Brak catchment area. The different colours refer to the two rainfall stations Jonkersberg Bos (blue) and Grootbrakrivier ARS (green). Data provided by SAWS.

Only 5 mm of rain was recorded at the end of August (Figure 4.8) at Jonkersberg Bos and Grootbrakrivier ARS. No rainfall was recorded at the beginning of September 2008 (Figure 4.9).

Figure 4.9: Graph showing rainfall in mm for the month of September 2008. The data highlights rainfall registered at two separate stations in the Great Brak catchment area. The different colours refer to

53 the two rainfall stations Jonkersberg Bos (blue) and Grootbrakrivier ARS (green). Data provided by SAWS. On the 1st September 2008 the mouth was closed and the maximum water level recorded at the railway bridge was 2,429 m above MSL, an increase of 1 m since the day before. The closed mouth most likely dampened the effects of the storm waves. The event was categorised as the second highest (van Niekerk and Huizinga, 2011) flooding event on record for the Great Brak.

Figure 4.10: Graph showing wave data from the CSIR Wave-rider in Mossel Bay from 00:00 on the 30th August 2008 until 21:00 on the 2nd September 2008. The Significant wave height reached ~7 m at 12:00 on the 1st. Wave height in m is shown in blue (Hmo) and significant wave height in m is shown in red (Hmax).

4.2.3 Flooding event August 2006 The flooding event that occurred on the 1st August 2006 and its associated flood level of 2,245 m above MSL resulted from 200 mm of rain, which fell within 48 hours. However, within the first

54 24 hours more than 150 mm was recorded in the Great Brak catchment area. This excessive rainfall resulted in a flow rate of 245 m3s-1 over the dam wall resulting in 1-in-10 year flood for post dam conditions (Council for Scientific and Industrial Research (CSIR) Report EMA-C9036 and Department Water and Sanitation (DWA report V/K100/08/E002). Dam-level data indicated that the dam was close to 100% capacity the day prior to the event and the estuary level was at a critical level of 1,4 m above MSL. The Great Brak Environmental Committee (GEC) had issued a warning that the region is prone to flooding and people with low-lying properties must take precautions (CSIR, 2006).

4.2.4 Flooding event May 2002 The flood event of the 25th May 2002 resulted in a flood-level height of 2,24 m above MSL and is comparable to the flood level recorded on the 25th March 2003 (section 4.2.5 below). Similarly, to the event of the 1st September 2008, the damage was brought on by excessive ocean waves flowing over the berm and can result in far greater flood levels at the Great Brak estuary. Unfortunately, it was not possible to obtain real-time wave data for this period from the CSIR as there were no data recorded or archived.

4.2.5 Flooding event March 2003 The flood event on the 25th March 2003 recorded a level of 2.24m above MSL. On the 16th March 2003, the mouth of the Great Brak river closed (van Niekerk and Huizinga, 2011), entraining all estuarine flood water. Heavy rains in the catchment area of this district caused the dam to overflow at a rate of 145 m3s-1, resulting in the river mouth eventually breaching. Unfortunately, due to technical problems daily recordings were not obtained from the Grootbrakrivier ARS and the 200 mm recorded on the 25th is an accumulation of 5 days; however, the Jonkersbergbos rainfall station depicts daily rainfall for this period (Figure 4.11).

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Figure 4.11: Graph showing rainfall in mm for the month of March 2003. The data highlights rainfall registered at two separate stations in the Great Brak catchment area. The different colours refer to the two rainfall stations Jonkersberg Bos (blue) and Grootbrakrivier ARS (green). Data provided by SAWS.

4.2.6 Flooding event November 2007 The flooding event of the 22nd November 2007 had a level of 2,194 m above MSL with a maximum inflow to the dam of 626 m3s-1 and outflow from the dam 409,5 m3s-1. This event was caused by excessive rainfall of 400 mm between 21st and 22nd November (Figure 4.12) as well as a moderate ocean state of ~4 m waves and a significant wave height of ~7 m on the 21st subsiding to respectively ~3 and ~5 m on the 22nd (Figure 4.12).

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Figure 4.12: Graph showing wave data from the CSIR Wave-rider in Mossel Bay from 00:00 on the 20th November 2007 until 18:00 on the 23rd November 2007. The significant wave height reached ~7 m at 12:00 on the 21st. Wave height in m is shown in blue (Hmo) and significant wave height in m is shown in red (Hmax).

4.2.7 Comparison of the 22nd November 2007 and the 8th June 2011 flood events depending on estuary mouth The conditions of the 2007 and 2011 flooding events were comparable in terms of wave height and significant rainfall data, however in 2011 the estuary was closed prior to the flood whilst in 2007 it was open. Table 4.2 and data available from the Department of Water and Sanitation highlights the importance of an open estuary mouth during the comparable flooding events in 2007 and 2011.

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8th June 2011 22nd November 2007 Mouth Closed before flood Open before flood Inflow 630 m3s-1 626 m3s-1 Outflow 340 m3s-1 405 m3s-1 Dam volume before 88,48 % 64,15 % Volume of flood ~ 9450 Million m3 ~ 44,15 Million m3 Highest water level 2,913 m above MSL 2,194 m above MSL Table 4.2: Table highlighting the Wolwedans Dam flow and Great Brak estuary water-level data for the 8th June 2011 and the 22nd November 2007 flood events. Data provided by DWS.

Information provided by the Department of Water and Sanitation indicated that the inflow into the Wolwedans Dam in June 2011 was 630 m3s-1 and in November 2007 it was 626 m3s-1, more or less identical and the highest on record. The estuary maximum flood level in 2007 was 2,194 m above MSL although hardly any flooding of property occurred in comparison to June 2011 where the estuary maximum flood level was 2,913 m above MSL and serious flooding of properties occurred.

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Figure 4.13: Water level in meters of the Wolwedans Dam prior and during the flood events on the 8th June 2011, blue line and on the 22nd November 2007, red line. Data supplied by DWS.

The period between the rainfall in the catchment and the flood coming through was much shorter in June 2011 than in 2007. The dam level prior to the flood in June 2011 was much higher than the dam level prior to the November 2007 (Figure 4.13) flood. However, the rainfall intensity in November 2007 was much higher over a short period of time therefore resulting in a larger flood peak period with smaller volume of water over a certain period. The period from start to end of significant dam level increase is less than 24 hours and underlines the fact that

59 water volume upstream as well as period of intensity needs consideration during severe weather-related events.

In all cases, it is clear that if the estuary had been opened prior or at the time of the rainfall, flood damages could have been prevented. These case studies further emphasise the need for an effective policy-driven guide that would assist in mitigating such disasters.

While it is clear that catastrophic events leading to the loss of life and cost to infrastructure and properties have been logged, it remains important to identify procedures and policies, which help to mitigate these disasters in order to minimise further risks. The following chapter will deal with factors, which can be considered as mitigating factors in cases where estuary flooding is expected. The implementation of such a guide is notably essential to limit the impact of flooding along the Great Brak estuary.

60 5. Results 2 - What is required for a successful policy to ensure that flooding events at Great Brak are minimal in damage?

In the previous chapter the variable nature of historical flooding events at the Great Brak estuary were described. One factor that must be considered is the importance of artificial breaching and how this can be achieved in a coordinated way with the inclusion of all stakeholders e.g. the SAWS, Disaster Management, Mossel Bay Municipality, Department of Environmental Affairs and Department of Water and Sanitation. The coordination will further ensure that all the critical criteria such as estuary level, conditions of mouth (i.e. open or closed) and its berm height, anticipated rainfall, wave height, time of low and high tide and level of the dam have been met prior to breaching.

One other factor that may be considered is dredging of the mouth of the Great Brak estuary. Dredging is a common approach to maintaining estuary openings in many parts of the world. It will require each district municipality to obtain several of these machines, something our district municipalities and South Africa, as a developing country, can simply not afford. This will require further permanent engagement between various government departments to obtain such approval. The option of dredging was further not mentioned and or considered by stakeholders during the consultation process.

5.1 What is meant by artificial breaching? Artificial breaching is the forced opening of an estuarine mouth to allow free river flow into the ocean. This thesis has identified the Great Brak estuary as an ideal case study to test how estuaries can respond to extreme weather conditions. Weather conditions, estuary and dam- level data, as well as tidal and wave information were available for all the dates where extreme weather was expected and the thesis identified the very same estuary that has experienced severe floods in the past. Since 1814, artificial breaching at this estuary has been conducted annually through a digging process to avoid flooding of the river crossing.

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The need to artificially breach the Great Brak estuary was due to the high unpredictability of rainfall and subsequent run-off from the catchment area. Frequent flooding events compounded by an increase in the development in the low-lying areas along the estuary may result in extensive risks to infrastructure, property and human life. The risks may be higher in specific areas run-off such as holiday resorts and housing developments along the estuary. Advance warnings of potential flooding are required to mitigate these risks. It is thus essential to put into place strategies and procedures that will minimise the socio-economic damage. Such measures must be able to address efficient and effective evacuation plans, including the breaching of the Great Brak estuary at short notice. There are negative impacts with regards to artificial breaching such as ecological reasons, however for the Great Brak it is critical to understand that, South Africa is a country with scarce water resources and regular breaching cannot be considered given the uncertainty for sufficient rainfall to refill the dams.

5.2 Artificial breaching events at the Great Brak estuary Guidelines included in the CSIR (2004) report, indicate that breaching occurs when water levels exceed ~2,0 m above MSL. Although the preferred time for mitigation is when these levels are closer to the natural breach MSL of ~2,8-3,0 m. Such steps enable maximum outflow and flushing of sediment from the estuary. Where possible, breaching should occur 2-3 days before the spring tide to maximise the outflow of water prior to these high spring levels.

5.2.1 Planned and emergency breaching Breaching protocol addresses two types of breaching; planned and emergency breaching. Planned breaches are normally required at the start of the austral spring/summer season and are designed to open the estuary mouth in time to allow the water level to drop prior to the onset of anticipated rainfall.

The results obtained from Disaster Management for estuaries along the Western Cape south coast have shown the Swartvlei, Great Brak and Touw estuaries are highly susceptible to flooding as described in the previous chapter and therefore the importance for planned breaching is high.

62 The estuaries are influenced mostly by a combination of rainfall run-off from the mountain, rainfall on the estuary itself, infrastructure along estuaries and/or crossing estuaries, permanent open/close phenomena of the estuary and storm surges and waves. Successful artificial breaching events of the Great Brak estuary are explained in the following sections.

5.2.2 Planned artificial breaching on the 12th July 2012 prior to expected severe weather conditions A sequence of photos (Figure 5.1) illustrates how a planned breaching event is carried out successfully at the estuary. The first step of this process involved planning when disaster management received sufficient information and weather-warning messages from SAWS, confirming that extreme weather and accompanying heavy rainfall are expected in the Eden district. The time taken from receipt of weather information to the completion of the bulldozer work was 5 hours for artificial breaching (Figure 5.1).

1 2 3

4 5 6

Figure 5.1: Typical example of an illustration how emergency artificial breaching is carried out courtesy of George DWS. Photo 1 is where the Bulldozer arrives at Great Brak. Photo 2 until 4 is where the channel is prepared. Breaching starts in photo 5 while in photo 6 is where the river flows freely into the ocean.

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5.2.3 Artificial breaching time sequence In light of anticipated heavy rainfall and the likelihood of flooding, a planned estuary breaching was considered for the 12th July 2012 (Figure 5.2a) when representatives of Mossel Bay Municipality, Petroleum Oil and Gas Corporation of South Africa (PetroSA) and DWS met at (A) 08:30. At the time the estuary level was noted to be at a height of 1,540 m. By 09:00 (B), the Mossel Bay Municipality bulldozer started preparing the trench and at 12:00 (C) the PetroSA bulldozer started with the excavation of an emergency channel. At this point the water level remained at 1,540 m. At 06:00 on the 13th (D) the estuary level had risen to 1,550 m while all role players receiving an updated weather forecast and warning from SAWS at 16:00 (E). At 20:47 the estuary level rose to 1,586 m and at 02:00 on the 14th (F) the level rose to 1,618 m. At 07:11 (G) the estuary level alarm automatically activated at 1,7 m. The mouth was breached at 12:40 (H) with a height of 1,857 m in the estuary and the flood peaked at 17:00 (I) and with a recorded estuary level at 2,037 m. The mouth opened after the artificial breaching process. Experience from this event highlights the importance for early mitigation and timeous artificial breaching at the mouth.

During these events at the estuary, the level of the Wolwedans Dam (Figure 5.2b) remained under constant observation. The initial dam level during the site meeting (A) was measured at 87,88%, by 03:12 on the 14th September. The dam had risen to 88,64% (B) after 48 mm of rain was recorded and after a further 60 mm at 06:24 (C) the dam was at 89,49%. By the time the mouth was breached (D) the dam was at 94,26%. An additional 78,4 mm of rain was registered at 14:12 as the dam rose to 98,07% (E). The dam eventually spilled (F) at 17:00 and peaked at 21:48 (G) at 101,54%.

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Figure 5.2: (a) Water level of the Great Brak estuary in meters between 06:00 on the 12th and 00:00 on the 16th July 2012. The letters represent various activities as highlighted in the text from the time the estuary level increased until it beached and then dropped. (b) Water level in meters of the Wolwedans Dam between 06:00 on the 12th and 00:00 on the 16th July 2012. The letters represent various activities as highlighted in the text as the dam level rose until it spilled. Data supplied by DWS.

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Comparing the estuary time sequence and dam level time sequence (Table 5.1) it is noted that the estuary dropped significantly by the time the dam was at its peak therefore preventing flooding.

South African Date Great Brak estuary level Time Wolwedans Dam level Standard Time 08:00 1,540 m 08:00 87,85% 08:30 1,540 m 08:30 87,88% 12th July 2012 09:00 1,540 m 12:00 1,540 m 06:00 1,550 m

13th July 2012 20:47 1,586 m

02:11 1,618 m 03:12 88,64% 06:11 1,676 m 06:24 89,49% 11:40 1,857 m 11:40 94,26% 14th July 2012 14:12 1,880 m 14:12 98,07% 17:00 2,037 m 17:00 100,00% 22:00 1,347 m 21:48 101,54%

Table 5.1: Great Brak estuary levels in m and the Wolwedans Dam level in % between the 12th and the 14th July 2012. Once the Dam reached full capacity and spilled at 17:00 the estuary was breached which allowed the estuary level to drop and make allowance for additional water from the Dam after 17:00. Data supplied by DWS.

5.3 Identification and mitigation of high risk estuaries such as the Great Brak estuary 5.3.1 Assessing the risk Disaster risk assessment is a process that determines the risk level by identifying and analysing potential hazards and/or threats, assessing the conditions of vulnerability that increase the chance of loss for particular elements-at-risk (i.e. environmental, human, infrastructural, agricultural, economic and other elements that are exposed to a hazard, and are at risk of loss); and determining the risk level for different situations and conditions, helping to set priorities for action.

66 It is essential to assess risks associated with estuary flooding in order to provide all stakeholders direction in defining the likelihood and extent of damage and loss to the community living along the coastline.

In consultation with stakeholders, eight main tasks in the risk assessment procedure was identified: i) define the geographical scale and extent of the assessment, ii) define the temporal scale of the assessment, iii) incorporate geospatially-referenced hazard-exposure information and probabilities with assessed vulnerability, iv) translate integrated hazard and vulnerability output into levels of risk for each vulnerability dimension in respect of each hazard; assess risk for separate vulnerability dimension or aggregated taking all dimensions and deficiencies in institutional preparedness into account, v) produce risk maps for the designated coastal management area in respect of selected hazard scenarios, vi) analyse and evaluate uncertainties, vii) assess future risks taking preparedness and mitigation measures into account and viii) communicate risk assessment to policy and decision makers.

5.3.2 Methods of identification of high risk estuaries such as the Great Brak The current approach is structured to reduce the risk to human life/infrastructure losses through an early-warning system. It would be preferable that steps be taken to mitigate or reduce the risk completely by guiding new housing developments in respect of the flood level along the estuary and at least 1:100 years setback lines along the coast and the placement of infrastructure. Chapter 4 highlighted the risks associated with the Great Brak and it is essential that these new developments should be incorporated into the Mossel Bay Municipality’s Integrated Development Plan (IDP) or their Land Use Management Plan or Spatial Development Framework, (SDF).

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A reliable disaster-risk assessment for a specific threat, such as the Great Brak flooding, should answer the following pertinent questions; • What is the likelihood that the same disaster and/or incident will happen and at what frequency? • Who are most at risk within the community or area? • What will the impact be on the local area and/or community? • How vulnerable is the community? • What is the community’s socio-economic standing as this may increase the risk? • Do you find that the risk identified is escalating? • Are there any resources available and/or capabilities of the Municipality to deal with the risk? • Will further development by the community be hampered by the risk? And if that is the case, should the management of the risk not be a development priority? • Are there any other risks which may impact on the community affected by the risk?

This thesis identified the need for real-time data such as hydrological data in an early-warning system. The Department of Water and Sanitation (DWS) has real-time data sources and plays a critical role in providing hydrological data to other stakeholders. Their data can be linked within the Joint Operations Centre (JOC), which will enable effective decisions regarding the development of a proactive DRR and flood mitigating procedure to be made. Data collected during monitoring programmes and the decision-making processes included local estuary management planning.

5.3.3 Mitigation of risks for the Great Brak estuary Sustainable risk mitigation or reduction should be the decisive objective for an effective risk- management strategy. It requires the selection of strategic management options for the risk reduction that are appropriate to the scale of the designated coastal-management area, balancing social and economic pressures against environmental considerations, including sustainability over the long term.

68 High waves are one of the main coastal risks identified in Chapter 4.2.2 for the Great Brak estuary. A risk assessment for the Great Brak estuary is essential. To date, such a task has not been accomplished. As soon as the risk assessment has been completed, Disaster Management should articulate mitigating factors for each risk identified. Selected strategies in mitigating flooding disasters need to be robust. It is very unlikely that a single mitigation approach would be effective by itself for the Great Brak estuary.

Many factors influence a community’s vulnerability along the Great Brak estuary. These include the location of critical infrastructure, vulnerable populations and key economic centres as well as environmental considerations. Policy makers should develop hazard mitigation responses for specific areas based on the concentration of development and critical ecosystems at the specific estuary. Where regulation is required, enforcement and control may be a problem due to pressure on decision makers to adjust, especially in relation to infrequent storm events. In addition, vulnerabilities are affected over time as the Great Brak estuary population, infrastructure, development and land use patterns change. Therefore, policy makers must recognise and introduce the Estuary Early Warning - Emergency Preparedness and Response Guide (EEW-EPRG) at the Great Brak estuary. The guide must recognise that natural hazards change over time and therefore the EEW-EPRG must remain a living document and open to revision. Once risk assessments for all estuaries have been concluded in Eden, policy makers may consider implementing the EEW-EPRG at high risk estuaries.

Risk-mitigation strategies that are available and applicable to all estuary hazards, and especially valid for the Great Brak, can broadly be classified into three main types: protection, accommodation and retreat. When dealing with a small and/or homogenous coastal- management area such as the Great Brak, policy makers may implement a mix of these approaches for an affective and practical response applicable to the Great Brak estuary. These strategies include both structural and non-structural measures.

Structural measures refer to any physical (natural or artificial) construction to reduce or avoid possible impacts of hazards. Structural measures can range from engineered structures that are

69 added to the landscape to protect development and infrastructure from hazards, to buildings that are designed or modified specifically to better withstand estuary impacts. The thesis highlighted in Chapter 2 that various types of infrastructure such as housing, railway lines and a national road can be expected along the Great Brak.

Non-structural measures refer to policies, regulations and plans that promote good estuary- management practices to minimise risks from estuary flooding. Protection involves the use of natural or artificial measures to protect landward development and/or attempts to hold the estuary/shoreline in its existing position in an effort to reduce the hazard impact.

Traditionally, protection against estuary flooding has been approached by hard structural engineering such as estuary and sea walls. However, it is not always an ideal solution due to regular disturbance from sand movement within the estuary, which can exacerbate erosion rates further downstream from these structures. To accommodate different protection methods it is necessary to include how development is undertaken on land and how people are able to adapt in response to estuary hazards.

5.4 Multi-stakeholder estuary early warning, emergency preparedness and response guide for estuaries such as the Great Brak Chapter 4 articulated the need for an Estuary Early Warning - Emergency Preparedness and Response Guide (EEW-EPRG), for estuaries such as the Great Brak. The findings in the chapter further suggested that such a guide must form part of the South African Multi-Hazard Early- Warning System. In line with the general principles of effective Early-Warning Systems, the EEW- EPRG needs to address the following five conclusive elements: i) risk identification, which includes high risk estuaries identified, institutional arrangements, specific weather indicators identified and risk-reduction system for the Great Brak, ii) monitoring and warning system, which includes information flow before and during incidents, emergencies and disasters, institutional arrangements, requirements for monitoring and real- time data acquisition and infrastructure and equipment requirements for the Great Brak,

70 iii) alert dissemination, which includes information flow prior and during incidents, emergencies and disasters, institutional arrangements and infrastructure and equipment requirements for the Great Brak area, iv) response actions, which include institutional arrangements as well as roles and responsibilities of role players and stakeholders, and v) reporting and evaluation, which include institutional and information flow as well as infrastructure and equipment. Once the EEW-EPRG addressed the risk identification, monitoring, dissemination of a warning, the response and ultimately reporting, it is essential to introduce and early-warning service.

5.5 Availability of early-warning services This thesis underlined in Chapter 4 the importance of an early-warning system for the Great Brak estuary and in Chapter 2.2, the importance of the development of a Great Brak EMP was highlighted. In addition, the Great Brak EMP needs to identify flooding as a risk and relate it to the mouth condition and mouth-management interventions. Furthermore, the Great Brak EMP needs to include the need for the Management Authority to develop a mouth-management protocol for the Great Brak, which will be in the form of a MMP authorized by the appropriate Provincial Department. The mouth-management protocol should reference early-warning procedures as well as Disaster Management plans and interventions for the Great Brak estuary.

The provision of early-warning facilities to the Great Brak coastal communities is a key part of the development of the preparedness of its local communities in coping with the rapid onset of flooding or a potentially catastrophic hazard. The other crucial part of the community preparedness is understanding and taking on an appropriate reaction in the event of a warning or alert being received from SAWS. WMO regarding the effect of coastal risks in developing countries, such as South Africa, (WMO No. 558) highlighted the fact that insufficient preparation and response to emergency situations has increased the loss of lives and extensive damage. In some cases this is a flaw brought on by the absence of effective communication of warning hazards.

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It remains the responsibility of the Disaster Management team (DM) to establish a DMC (Disaster Management Act, Act 57 of 2002, sections 44 and 47). The DMC must promote an integrated and coordinated approach to disaster management with special emphasis on early warning, prevention and mitigation. To act as an advisory body and a conduit for information concerning any impeding disasters that will impact on the state, statutory functionaries, the private sector, non-governmental organisations as well as communities and individuals along the Great Brak estuary, DM has to disseminate early warnings to relevant parties. It is essential that all mandated Departments participate in the DMC and the Joint Operation Centre (JOC) established as a coordinating platform as well as implementing the process and actions identified by the JOC when such an event is expected in the Great Brak area.

A severe weather early-warning capability should not be used to justify future unwise (i.e. housing) activities or development of estuaries, because the weather warning will only mitigate potential problems and not prevent their occurrence. Disaster Management needs to ensure that a local Disaster Management Plan exists for the identified estuaries such as the Great Brak. The SAWS makes use of a colour coded alert system as per Table 5.2. This table was developed by the author of this thesis in consultation with SAWS and DM employees as reference table for the forecasters to determine when and what type of alert should be send when estuary flooding is expected.

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Severe Weather Alert Levels of estuarine conditions which are potentially dangerous to coastal communities and activities on the water GREEN YELLOW AMBER RED Alert No alert Advisory Watch Warning Category Awareness None Be aware Be prepared Take action level expected Threat No Early warning of Weather Hazard is already hazardous potential conditions are occurring somewhere weather hazardous likely to or is about to occur expected in weather deteriorate to with a very high next few hazardous levels confidence days Risk No Estuary A risk that an Moderate risk Estuary flooding is flooding is Estuary flooding that an Estuary imminent, or already expected may occur flooding will occurring. occur Impact A potential risk A moderate risk A high risk of damage of damage to of damage to to infrastructure and infrastructure infrastructure disruption of local and disruption and disruption of activities. of local local activities. activities. Advice Be alert and Be vigilant and Be extra vigilant of follow the latest follow the latest dangerous conditions alert bulletins alert bulletins as and follow the advice issued by the issued by the SA given by the SA South African Weather Service. Weather Service and Weather Prepare for a Disaster Management Service. possible Authorities. evacuation. Evacuation Prepare the imminent/likely channel

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Confidence Nil Low to Moderate to high Very high or occurring of event moderate occurring Lead-time Alert Category Estuary 2 to 5 days Nil Advisory flooding alerts 1 to 3 days Nil Advisory Watch 24 hours or Nil Watch Warning less Table 5.2: SAWS estuary flooding weather alert reference table as provided by SAWS articulating the various yellow, amber or red alert categories. The table further indicates what the lead-time for each alert category is. The author in consultation with SAWS and DM employees developed this table. 5.6 Information and functions required during anticipated extreme events at the Great Brak estuary The results in Chapter 4 (Table 4.1) indicated the likelihood of flooding and associated damage and/or loss of life along the Eden district and in particular the Great Brak. Therefore, the first consultation workshop with stakeholders (i.e. SAWS, DEA, DM, CSIR, SANParks) to discuss issues which can assist in mitigating the risks of flooding along the Eden district estuaries was held from the 31st July to the 2nd August 2012 (Annexure D). During the consultation process it was clear from all stakeholders that a process flow, based on needs analysis, is required for a successful guide. The process flow was developed (Figure 5.3) through a consultative process. On the input side it is essential to make sure of the storm surge guide (Stander et al., 2011) unless an operational storm surge model is used, a list of identified high risk estuaries, real-time weather, hydrographic and oceanographic data as well as SAWS weather warnings is available. The primary role players / decision makers should all report to the JOC where it is agreed what the alert level will be and the way forward actioned while continuous feedback is required to the JOC to re-evaluate the warnings issued or actions taken accordingly.

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Figure 5.3: Decision-making process flow for a successful estuary early warning guide to mitigate estuary flooding such as the Great Brak. On the left is essential input required for an informed decision-making process. On the right hand side is where alerts are disseminated and the feedback loop for revision of the alerts.

5.7 Inputs required for the estuary early-warning process flow Various critical elements are required for an effective early-warning guide. The consultation group identified that, apart from inputs such as numerical weather forecasting models, satellite data, radar and astronomical tide data, the following factors are also to be considered critical as they are the main drivers for the Great Brak estuary flooding.

5.7.1 Rainfall Rainfall data is required at a number of temporal scales in the Great Brak catchment area. Firstly, advance warnings at extended time scales of up to five days is undertaken to inform assessment. As the weather systems start to impact, the rainfall data needs to be available in the Great Brak catchment in real-time to rerun the catchment run-off models, which can be compared against the real-time rainfall and stream-gauge data for this region. It is critical that real-time rainfall

75 data is disseminated to disaster-management structures. The case studies presented in Chapter 4 articulate the importance of anticipated and real-time rainfall as this may assist Disaster Management in activating artificial breaching and warn the Great Brak community of possible flooding.

5.7.2 Catchment and river information The Great Brak catchment receives variable rainfall however, it also receives severe weather (Chapter 4.1). The contribution by rainfall to potential run-off is a function monitored and assessed within the Great Brak estuary. This function is currently been performed by SAWS using the South African Flash Flood Guidance System (SAFFGS) for the entire country which includes the Great Brak river. Vegetation cover (or lack of vegetation following large fire incidents), antecedent moisture conditions, slope steepness and profile are obviously critical in modelling the rates of run-off at various locations within the catchment. Many of the aforementioned factors are incorporated into the SAFFGS. Of further importance is the requirement to identify other major infrastructure that could be at risk (i.e. the N2 crossing the Great Brak). River-flow data would be required for the Great Brak, anticipated numerical model rainfall and real-time rainfall as well as estuary level data are further elements identified as essential for an effective early warning guide.

5.7.3 Beach berm heights The Great Brak water levels often influence and control the height of the downstream beach berm as described through the case studies in Chapter 4. The height of the berm is critical in providing insight into the risk profile of the extent of flooding in the estuary. On way to monitor the berm height is to install a camera relaying the information to SAWS and DM.

5.7.4 Monitoring responsibilities Given the past severe weather events in which immediate action for the Great Brak estuary was needed, it is essential that the Great Brak estuary has a monitoring programme which can be clearly identified and communicated to the responsible management authority for the estuary. The Great Brak is a high risk estuary and thus it is essential to ensure that an Estuarine

76 Management Plan is developed (or possibly in the interim, a shorter disaster/mouth- management plan) together with all responsible management authorities including SAWS, DM and DEA.

5.7.5 Data and research gaps for the Great Brak estuary For a management plan to be successful it is essential for stakeholders to better understand the timing needed to open the Great Brak estuary mouth. Quantitative relationships between rainfall, catchment characteristics, run-off, estuary water levels, mouth and berm status, and ocean impacts must be understood as well as the role of estuary vegetation and floodplains in mitigating flooding. Also important is the role of catchment activities in exacerbating flooding (e.g. fire, vegetation not cleared in the lower reaches and agricultural practices), which speed up run-off, or cause erosion and estuary sedimentation. There is a lack of understanding of the links and relative contributions between land-and sea-flooding events; furthermore there is also a need to understand temporal coincidence (probability of joint events). It is important that the guide is flexible ensuring it can be updated as required, following additional research done into the Great Brak estuary and/or other estuaries.

5.7.6 Wolwedans Dam level The level of the upstream Wolwedans Dam level needs to be included in the risk calculation for the appropriate downstream Great Brak estuary. An empty dam will add to the flood buffering capacity of the catchment. Factors like the volume of the dam, surface area of the upstream catchment as well as the calculated possible run-off related to predicted rainfall events need to be included in the risk calculation.

5.7.7 The Great Brak estuary bathymetry A flood event results in sediment originating in the catchment being transferred to the estuary and eventually to the ocean. The incoming sediment that is deposited in the Great Brak estuary impacts on the existing bathymetry of the estuarine channel and floodplain. In principle, a shallow estuary will create a greater flood risk for the floodplain area.

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5.8 Outputs required for the estuary early-warning process flow of the Great Brak estuary alert system 5.8.1 Dissemination of weather alerts The Great Brak does not receive area specific weather alerts. Rather it receives weather alerts, which form part of the alerts disseminated for the Eden district. The SAWS should be the lead stakeholder responsible for the issuing of weather alerts to all the primary role players as per SAWS Act, Act No 8 of 2001 as amended. These alerts must focus specifically on high risk estuaries such as the Great Brak. Municipal Disaster Management Centres (Section 43 of the Disaster Management Act, Act No 57 of 2002), will be responsible for the cascading of these alerts to secondary role players (listed below in section 5.8.3).

Notwithstanding the Disaster Management Act, SAWS should assist in the dissemination of these warnings to the general public, utilizing well-established links to various media platforms. Estuary alerts based on the minimum criteria as defined in Section 5.7, will be issued for each local Municipality along the coastline.

5.8.2 Primary recipients of Great Brak estuary alert While the National and Provincial Disaster Management authorities will receive all warnings, the Provincial and District Disaster Management Centres, such as the Western Cape Provincial Disaster Management centre and the Eden district DM centre, will be the only primary recipients of alerts for the Great Brak estuary.

5.8.3 Secondary recipients of Great Brak estuary alert A recommendation from the events outlined in Chapter 4 is that secondary recipients must include those affected by anticipated floods. This function is the responsibility of Disaster Management to identify those recipients and distribute the warnings to them.

It is now known that the appropriate management authority needs to ensure that a Great Brak estuary management plan is developed in line with the National Estuary Management Plan (NEMP) to improve advance planning and communication with regards to breaching for the this

78 area. If the planning and the DM process identify flooding as an issue and if the condition of the mouth of the Great Brak estuary is seen to largely influence the estuary state then a specific mouth-management protocol must be developed in the form of a Maintenance Management Plan authorized by the Provincial Government. The plan needs to identify a Disaster Management Plan as part of the mouth-management protocol. These plans will then be provided to the DM to integrate into the Disaster Management systems and processes.

5.9 Establishment of a Provincial or Municipal Joint Operational Centre Consultation with Disaster Management for the Great Brak estuary and its risk of flooding has indicated that 72 hours are required to initiate any mitigation plans. A recommendation is that once the DM has been informed of severe weather events in the Great Brak area and it is evident that the situation will demand various human, equipment or organisational capabilities and/or decision-making, a Joint Operational Centre (JOC) must be established.

The management scope of the JOC extends across all jurisdictional boundaries. It includes executive decision-making and the invoking of extraordinary statutory powers necessary to deal effectively with each situation.

The authority is exercised by the Head of the relevant Disaster Management Centre supported by the Management team represented in the Disaster Operations Centre.

The activation and management of a local and Provincial JOC is the responsibility of Disaster Management (Disaster Management Act, Act No 57 of 2002). The JOC must, when activated and during any pro-active and response operations perform the following functions and report to the Disaster Management Centre (DMC): i) follow the step–by-step action guidelines (Figure 5.4) drawn up in consultation with Disaster Management, ii) initiate the relevant contingency plans, iii) decide on emergency measures and priorities, iv) assess impact,

79 v) request emergency partner assistance / invoke mutual aid agreements, vi) issue public warnings, orders and instructions, protect the health and safety of emergency responders, vii) co-ordinate response with relevant authorities, viii) co-ordinate response with non-governmental disaster-relief organisations, neighbourhood and community organisations, ix) identify persons/organizations to contribute to emergency response, x) provide information to the media for dissemination to the affected population(s) and the general public, xi) co-ordinate information for public release with emergency partners’ communications staff and xii) respond to inquiries from the media and public.

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Figure 5.4: The figure illustrates various actions to be considered at Disaster Management Joint Operations Centre after receiving weather warnings issued by the SAWS. The figure further provides actions to be considered for high risk estuaries such as the Great Brak and if breaching should be considered.

5.10 Common alert protocol used when warning needs to be sent for the Great Brak estuary Communication is crucial when severe weather is expected, during severe weather and when evacuation procedures are activated. The Common Alert Protocol (CAP) will be used as the basis

81 for preparing warning information. It is an international standard that addresses the long- standing need to coordinate all the dissemination mechanisms used for warnings and alerts. It defines a standard format used internationally, allowing for all kinds of hazards and a variety of relevant information. The format can be used universally to convey and display warning information. Alert messages will automatically be converted by software into the CAP standard format by web xml applications and warning generators.

5.10.1 Issue of an Alert General arrangements will determine issuing of the Great Brak estuary alert as the issuing of severe weather-related alerts and/or warnings as formulised by SAWS as discussed in section 5.5 above. Any successful alert mechanism requires proactive action by all relevant stakeholders. Any other significant information of interest to the wide public should be mentioned in a special release issued to the disaster management and the media by the National Disaster Management Centre or the South African Weather Service.

82 6. Results into action – Deriving and testing a policy document. A series of six case studies for the Eden district

Artificial breaching can only be effective if the response mechanism is successful once a weather alert is received. The information presented in this chapter will provide clear examples of how successful artificial breaching at the Great Brak estuary mouth can be achieved prior to any flooding event.

Although frequent successful artificial breachings have been conducted since 2013, specific examples of events in this region during the period 2013-2016 are presented to highlight the importance of such measures. This chapter further illustrates how successful artificial breaching can be achieved through a broad and inclusive consultative process. This chapter will prove that artificial breaching reduces flood risk, loss of life, damage to infrastructure and significant financial loss.

This thesis illustrates the success of artificial breaching during storm events and more importantly to provide policy makers more detailed information in the review of their current policies. Furthermore this thesis provides a compilation of test cases for the period 2007-2011, the work and testing undertaken that led to the early warning system. This highlights the fact that after 2013, as per Table 4.1, there was no estuary flood damage.

6.1 Successful artificial breaching August 2013 Heavy rainfall was expected over consecutive days in the Great Brak estuary catchment area and with the Wolwedans Dam at 100% capacity, high estuary level and a closed mouth, conditions were favourable for flooding.

6.1.1 SAWS rainfall data Heavy rain fell in the Great Brak catchment areas (Figure 6.1) during the early part of August 2013 when these areas registered over 100 mm during a 3-day period. Towards the end of August, additional rainfall exceeding 10 mm was recorded compounding to the risks of flooding.

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Jonkershoek ARS, in the Great Brak catchment area, recorded 131,8 mm, which was the highest rainfall for the month, while the lowest of 73,5 mm was measured further to the east at the Knysna Platboskop ARS.

Figure 6.1: Graph showing rainfall in mm for the month of August 2013. The data highlights rainfall registered at three separate stations in the Great Brak catchment area. The different colours refer to the three rainfall stations Jonkersberg Bos (blue), Jonkershoek ARS (red) and Grootbrakrivier ARS (green). Data provided by SAWS.

6.1.2 DWS hydrological data The dam-level data was obtained from the Department of Water and Sanitation (DWS) and indicates that from the 24th August 2013, (denoted as A Figure 6.2a), the Wolwedans Dam was close to 100% capacity after the initial rainfall in early August. With further rainfall anticipated towards the end of August, artificial breaching was conducted, resulting in an excess of 200 000 m³ of water being released from the Wolwedans Dam between 05:30 and 07:30 on the 28th August. Naturally, the release of dam water resulted in a significant decline in water levels as shown by B in Figure 6.2a.

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Figure 6.2: (a) Water level in meters of the Wolwedans Dam between 00:00 on the 24th August until 00:00 on the 29th August 2013. The letters represent activities as highlighted in the text. Data supplied

85 by DWS. (b) Water level of the Great Brak estuary in meters between 00:00 on the 24th and 00:00 on the 29th August 2013. The letter A denotes the time when breaching occurred. Data supplied by DWS. A key impact of any dam release is that further downstream, river levels will increase in height and this was observed with the Great Brak estuary rising to 1,935 m at 08:30. An additional 50 000 m³ of water was released from the Wolwedans Dam between 08:36 and 09:06 to force the mouth open.

The target for the 28th August was to raise the water level to the required 2,00 m above MSL (still below the flood level) so that the estuary mouth could be artificially breached at a level of 1,990 m above MSL. What was critical during this event was that the correct decision to artificially breach the estuary mouth was made timeously, and at 11:38 on the 28th August (as denoted by A in Figure 6.2b) the mouth was breached and water could flow easily into the sea.

The ongoing rainfall in the catchment area resulted in a further outflow rate of 0,45 m3s-1 from the 28th August until the 2nd September to ensure that the mouth remained open during the period of neap tides. On the 29th August at 07:30 the water level in the mouth dropped to 0,870 m while the water level of the Wolwedans Dam at 10:30 remained close to full capacity. The height of the water level was 52,474 m (full capacity is 52,700 m) proving that the planned release had little effect on the total capacity of the dam. The information above underlines the importance of planned emergency breaching involving quick decisions by all stakeholders and thus reducing any risk of the estuary exceeding its maximum level before flooding.

6.1.3 Wave and tidal information At the time of the emergency breaching on the 28th August, the wave height was very low ~1,5 m, (denoted as A on Figure 6.3), allowing the water from the estuary to run freely into the sea (Figure 6.2b).

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Figure 6.3: Graph showing wave data from the CSIR Wave-rider in Mossel Bay from 00:00 on the 26th August 2013 until 21:00 on the 29th August 2013. Wave height in m is shown in blue (Hmo) and significant wave height in m in shown in red (Hmax). The letter A denotes the time the wave height was not significant when breaching occurred.

6.1.4 Discussion of August 2013 On the 28th August 2013 the situation within the Great Brak estuary was critical. The estuary river level was high and the Wolwedans Dam at full capacity. With this as background, additional rainfall may eventually result in flooding in the estuary and the successfully artificial breaching of the mouth mitigated the risk of flooding for the anticipated rainfall.

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6.2 Successful artificial breaching October 2013 During the October 2013 event, heavy rainfall occurred in the catchment area. The Wolwedans Dam level and estuary level were extremely high with an accompanying closed mouth.

6.2.1 Numerical model precipitation Outputs of the Numerical Weather Prediction (NWP) model run at SAWS indicated accumulative precipitation (Figure 6.4) of 50 mm over a 48-hour period in the Eden district. The data proves that the model forecast and real-time rainfall data are comparable and further emphasise the importance of model data in its ability to forewarn any impending flooding event. The use of atmospheric models will undoubtedly assist key stakeholders in their risk assessment of better forecasting potential disaster events ahead of time and thus allowing communities to react accordingly.

Figure 6.4: SAWS Unified model output representing accumulative precipitation for the 20th and the 21st October 2013. The left hand side figure is the 48 hour Unified Model initiated on the 19th for the 20th indicated <10 mm of rainfall over the Eden district. The figure on the right is the 48 hour Unified Model initiated on the 20th for the 21st October 2013 indicated >30 mm of rainfall for the Eden district.

6.2.2 SAWS rainfall data Heavy rainfall was recorded within the first 48 hours between the 20th and 21st October; with 75 mm recorded at Jonkersberg Bos (Figure 6.5) as a result of a surface high-pressure system to the

88 southeast of the country and a surface low over the central interior with supporting lower atmospheric levels. The real-time rainfall recorded was higher than the numerical model rainfall predictions for the Eden area as discussed in 6.2.1 above.

Figure 6.5: Graph showing rainfall in mm for the month of October 2013. The data highlights rainfall registered at three separate stations in the Great Brak catchment area. The different colours refer to the three rainfall stations Jonkersberg Bos (blue), Jonkershoek ARS (red) and Grootbrakrivier ARS (green). Data provided by SAWS.

6.2.3 DWS hydrological data Initially 40 mm of rain fell in the Great Brak catchment area earlier in October 2013 (Figure 6.5), which contributed to increased dam and river levels. After the heavy precipitation event on the 20th October, emergency breaching was undertaken to reduce dam and estuary levels in time for the anticipated further rainfall expected between the 24th and 25th October.

During this period the maximum height of Wolwedans Dam at 101,1% capacity was 52,940 m (denoted as A on Figure 6.6a). This capacity equates to 16 000 l/s over the Dam’s spillway. On the 22nd October at 08:12, the Wolwedans Dam level continued to exceed its capacity at 100,8% with a water level of 52,880 m approximately 10 000 l/s over its spillway.

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Figure 6.6: (a) Water level in meters of the Wolwedans Dam between 00:00 on the 18th and 00:00 of the 22nd October 2013. The letter A denotes the peak level of the dam. (b) Water level of the Great Brak estuary in m between 00:00 on the 18th and 00:00 on the 23rd October 2013. The letter A denotes the peak of the estuary prior to breaching. Data supplied by DWS.

90 This event has shown that the need for breaching and continued monitoring of water levels between the 21st and 22nd October 2013 were essential to reduce any risk to the local communities. Breaching commenced at 17:15 on the 21st October and was completed by 21:30. The peak height of the estuary was 1,699 m above MSL at 01:54 on the 22nd October, (denoted by A on Figure 6.6b) when breaching occurred followed by a significant drop in estuary level as water started to flow out into the sea.

6.2.4 Wave and tidal information When breaching is considered, the wave height and tides must be factored in, as resulting high waves combined with a possible spring high tide will hamper the outflow of the river (Chapter 4). This is largely due to water being pushed back into the estuary on the flowing high tide. During this period of breaching, the tide height and conditions were considered and that the low wave height of ~1 m, with a total height of only ~2 m (denoted by A on Figure 6.7). The wave height continued to drop, allowing water from the estuary to flow freely into the sea, the risk of flooding was minimal.

Figure 6.7: Graph showing wave data from the CSIR Wave-rider in Mossel Bay from 00:00 on the 20th until 21:00 on the 23rd October 2013. Wave height in m is shown in blue (Hmo) and significant wave height in m is shown in red (Hmax). The letter A indicates the lower wave levels on the 22nd compare to the 21st wave levels.

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6.2.5 SAWS weather warnings It was critical to establish if SAWS issued a severe weather-warning timeously. Prior to the flooding (on the 19th October), SAWS predicted moderate rainfall (less than 50 mm within 24- hours) along the Cape south coast with associated 30-50 km/h south-to-south-easterly winds. Unfortunately, as only moderate rainfall was predicted by the weather forecaster. SAWS did not issue any warnings or alerts for the Eden district. This would undoubtedly leave the disaster management team on minimal alert and therefore unable to act timeously.

6.2.6 Discussion of October 2013 Only 36% of the rainfall stations for the region recorded rainfall in excess of 50 mm within the first 24 hours. The inability to record high-resolution rainfall across the region presents a further concern over the current infrastructure of the weather stations in the Eden district. Therefore, there remains sufficient proof that SAWS should have sent an early weather-warning for heavy rain along the Eden district and in particular the mountainous areas when the first real-time rainfall measured data became available.

The SAWS short-range forecast, issued on the 20th October, indicated a 60% probability of showers and thundershowers within the Eden district. As demonstrated throughout the thesis it is critical that whenever severe weather is expected, and during periods when dam and river levels are high, artificial breaching must be considered to avoid flooding. All of the above elements occurred following the heavy rainfall of the 20th October and in conjunction with the low-wave activity, it was decided to implement artificial breaching on the 21st in order to neutralise any possible flooding.

The event above has once again proven the importance and success of timeous artificial breaching. Furthermore, it should be noted that despite the absence of an SAWS weather warning, the importance of effective communication between all stakeholders is critical in order to successfully manage potential flooding events.

92 6.3 Successful artificial breaching January 2014 Heavy rainfall was expected during the peak summer season between December 2013 and January 2014. There was a critical concern over the impact such a flooding event would have along the riverbanks of the Great Brak estuary due to inundation of holidaymakers camping along the shore. Despite the high river and dam levels, the anticipated weather patterns emphasised the potential risk for a serious flooding incident along the estuary and this was prevented through artificial breaching.

6.3.1 Numerical model precipitation A sequence of numerical weather prediction model runs consistently suggested that between the 6th and 9th January 2014 rain in excess of 50 mm would fall within 24 hours (Figure 6.8), over most parts of the Eden district and moderate to heavy precipitation in the order of 50 mm for all four days over other areas. The top two figures are the 48 hour UM output to assist the forecaster with regards to the anticipated weather for the next day while the bottom two figures are the 24 hour UM output to assist the forecaster for the same day anticipated weather.

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Figure 6.8: SAWS Unified model output representing accumulative precipitation for 6th, 7th, 8th, and 9th January 2014. The figure top left is the 48 hour Unified Model (UM) initiated on the 5th for the 6th indicated a possibility of >50 mm on rainfall. The figure top right is the 48 hour UM initiated on the 6th for the 7th indicated >50 mm. The figure bottom left is the 24 hour UM initiated on the 8th for the 8th indicated >50 mm rainfall just to the west of Eden district. The figure bottom right is the 24 hour UM initiated on the 9th January for the 9th January 2014 indicated >50 mm rainfall in places.

6.3.2 SAWS rainfall data Within the Great Brak catchment area, heavy falls were recorded at all three stations (Figure 6.9), 92 mm of rain fell within 24 hours at Jonkersberg Bos. The same station recorded a total of 186,5 mm between the 6th and the 9th January. Additional moderate rainfall of between 20 mm to 45 mm fell over two days towards the end of January 2014.

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Figure 6.9: Graph showing rainfall in mm for the month of January 2014. The data highlights rainfall registered at three separate stations in the Great Brak catchment area. The different colours refer to the three rainfall stations Jonkersberg Bos (blue), Jonkershoek ARS (red) and Grootbrakrivier ARS (green). Data provided by SAWS.

6.3.3 DWS hydrological data The Department of Water and Sanitation (DWS) continued to monitor dam and estuary water levels. It was noted that the mouth started to close between the 30th and 31st December 2013. With the increased risk of flooding, the Department decided to implement a flush release from the Wolwedans Dam into the estuary to avoid closure and resulting in a relatively low estuary level (Figure 6.10a).

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Figure 6.10: (a) Water level of the Great Brak estuary in meters from 00:00 on the 5th until 00:00 on the 10th January 2014 which remained below 1,5 m. (b) Water level in meters measuring instrument reading at the Wolwedans Dam from 00:00 on the 5th until 00:00 on the 10th January 2014. The letter A denotes the point where the Wolwedans Dam reached full capacity and spilled. Data supplied by DWS.

96 The results of the actual measured rainfall and the Wolwedans Dam level confirmed that due to the high rainfall received between the 6th and 9th January 2014, the Wolwedans Dam spilled over. This spill occurred on the 7th January (denoted by A on Figure 6.10b) and was deemed sufficient by all stakeholders to keep the mouth open between the 8th and 12th January 2014. This opening coincided with neap tide. The mouth remained open with the Wolwedans Dam at 100% capacity until the 20th January 2014.

The January 2014 event has clearly shown that, as a consequence of the heavy rainfall, the water storage within the Eden district was more than 100% capacity and resulted in extensive overflowing during the course of this extreme weather event. The water levels overflowing from the Floriskraal Dam were only 1 m below the level recorded during the disastrous Laingsburg flood on 25th January 1981. It is clear that the artificial breaching was a success during the December/January holiday season.

6.3.4 Wave and tidal information In all flooding events, wave heights and tidal status must be taken into consideration when an estuary mouth is opened. High-wave heights combined with a spring tide may hamper the emergency flushing out of an estuary. Fortunately, during this event, it was neap tides and the wave height during the heavy-rainfall period from the 6th to the 9th January 2014 was 2 m with the maximum wave height at approximately 4 m (denoted by A on Figure 6.11).

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Figure 6.11: Graph showing wave data from the CSIR Wave-rider in Mossel Bay from 00:00 on the 5th January until 00:00 on the 10th January 2014. Wave height in m is shown in blue (Hmo) and significant wave height in m is shown in red (Hmax). The letter A denotes the period of maximum wave height.

6.3.5 SAWS weather warnings The January 2014 cut-off low resulted in serious impacts and losses across the Eden district Municipal area. Infrastructure damage extended to roads, informal and formal housing, bridges, commercial and subsistence farmers, storm-water drains, holiday resorts and dams amounted to R466 million. This negatively affected the local economies, infrastructure, property, the environment as well as the livelihoods of the affected communities while four people lost their lives (Table 4.1).

Initial weather warnings from SAWS indicated, “Heavy falls of rain is expected in places over the Eden district”. Further information received has shown that SAWS later upgraded their alert to “Heavy falls of rain leading to floods is expected in places over the Eden district”. Early indications may suggest that an alert could have been disseminated to the Eden district in advance although warnings were only issued on the 6th January. Moderate rainfall was expected in the weather forecaster’s lead-time.

98 6.3.6 Discussion of January 2014 On the 6th January 2014, the Eden Disaster Management Centre (DMC) activated their District Disaster Management Centre (DDMC). Disaster management practitioners, relevant role players at local Municipality and identified stakeholders, were informed that SAWS had issued a weather warning. The Eden DMC monitored and coordinated the event with further assistance from the Provincial Disaster Management Centre (PDMC) during the extreme weather event.

This section conclusively proves the vulnerability of the community and infrastructure along this area, which was at that stage enhanced by the fact that there was an additional risk of potential loss to human life and that DM should act decisively in warning the communities at risk.

Following SAWS weather warnings, ongoing communication between the Eden DMC and local Municipalities occurred. Advice regarding the weather event was provided. The overall management of the flooding event reflected a coordinated multi-sectoral and multi-disciplinary approach.

In discussions with Disaster Management they articulated that the emergency services rescue teams played a vital role in the rescue and evacuation operations throughout the Eden district. The coordination, cooperation and management between the local Municipalities and their respective rescue teams were excellent.

An alternative measure in dealing with major flooding incidents by the appropriate line departments, the declaration of a disaster in accordance with the Disaster Management Act (Act 57 of 2002) should be investigated to declare such a disaster at Provincial level in a short space of time.

The Disaster Management Act makes provision for the declaration of a local disaster. Although not a prerequisite, the declaration of a disaster could render access to emergency and central contingency funds, as well as to allow the applicable National, Provincial and Municipal Department’s budgets supplemented.

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For the January 2014 event specific areas within Eden district were declared a disaster area; fortunately due to prompt action in the emergency breaching of the estuary the impact on the loss to life and damage to property was reduced.

6.4 Successful artificial breaching July 2015 The Great Brak estuary was closed prior to the rainfall on the 20th July 2015 while the Great Brak estuary and Wolwedans Dam levels were high. Anticipated severe weather patterns led the disaster management to recommend that even with minimal rainfall of 10 mm there was a high risk to flooding and any additional rainfall may lead to spilling of the dam, which would increase the estuary level further due to the closed mouth. The mouth was opened to minimise the risk of flooding.

6.4.1 Numerical model precipitation Information on accumulative precipitation received from SAWS Unified model output anticipated rainfall of 30 mm within 24 hours over the Great Brak catchment area for the 20th July 2015 (Figure 6.12). However, the results from the model data have indicated that the rainfall and accompanying flooding would be of minimal threat based only on amount of rainfall (30 mm). Given the low risk, largely brought on by the low rainfall forecast, SAWS were not at liberty to issue a severe weather alert or warning for heavy rainfall.

100 Figure 6.12: SAWS Unified model output representing accumulative precipitation for the 20th July 2015. The left hand side figure is the 48 hour Unified Model initiated on the 19th for the 20th July indicated <10 mm of rainfall while the right hand side figure is the 24 hour Unified Model initiated on the 20th for the 20th July 2015 indicated <20 mm of rainfall.

6.4.2 SAWS rainfall data Rainfall measured at the Jonkersberg Bos, Jonkershoek ARS and Grootbrakrivier ARS, situated in the Great Brak catchment all registered less than 50 mm within 24 hours. Although the average for July is only 70 mm, two of the three rainfall stations in the Great Brak catchment recorded total precipitation in excess of 100 mm during July 2015 (Figure 6.13).

Figure 6.13: Graph showing rainfall in mm for the month of July 2015. The data highlights rainfall registered at three separate stations in the Great Brak catchment area. The different colours refer to the three rainfall stations Jonkersberg Bos (blue), Jonkershoek ARS (red) and Grootbrakrivier ARS (green). Data provided by SAWS. 6.4.3 DWS hydrological data The results obtained from section 6.4.1 and 6.4.2 indicated that while no heavy rainfall was expected over the first 24 hours, there was a strong likelihood that rainfall levels would increase over the following days. The DM decided that emergency breaching should be initiated. On the 17th July, the Wolwedans Dam was at a capacity of 98,9% while further downstream the estuary level was at 1,230 m above MSL and its mouth closed with a berm height of 2,03 m above MSL. As a precaution, DM requested the Mossel Bay local Municipality to have the necessary machinery such as an excavator and bulldozer on standby if required.

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Despite between 10 mm and 23 mm of rainfall recorded on the 8th July, the Wolwedans Dam was at 99,07% capacity on the 18th July 2015 at 13:00. After an additional 18 mm of rain fell in the catchment on the 18th it became very clear that the dam would spill and prompt emergency action was needed.

While the DWS continued to monitor the situation between the 19th and the 20th July, the Wolwedans Dam and estuary continued to increase to a 99,62% capacity and the river level rose to 1,332 m. By the 21st July the Wolwedans Dam had reached 100% capacity (denoted by A on Figure 6.14a) with the estuary continuing to increase to 1,476 m.

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Figure 6.14: (a) Water level in meters of the Wolwedans Dam between 00:00 of the 17th and 00:00 on the 23rd July 2015. The letter A denotes the point where the dam reached full capacity. (b) Water level

103 of the Great Brak estuary in meters between 00:00 on the 17th and 00:00 on the 23rd July 2015 peaking after the spill. Data supplied by DWS. At 08:40 on the 21st July 2015, a decision was taken to prepare the channel for emergency breaching. At 16:18 the estuary peaked with a height of 1,923 m (Figure 6.14b) when the breaching occurred. Despite that the dam was over 100% capacity on the 22nd and with an overflow rate of 5,753 m3s-1 the estuary level dropped to 1,125 m by 06:30; however, with ongoing rainfall the dam continued to spill allowing the mouth to remain open.

6.4.4 Wave and tidal information At the time of this artificial breaching, the wave height was 1 m on the 20th July increasing to 3 m on the 22nd July (Figure 6.15). During the July 2015 event, the wave height by itself could have been a challenge if it had been spring tide, fortunately, it was neap tide and breaching was conducted just after low tide, therefore the outflow to sea was not hampered.

Figure 6.15: Graph showing wave data from the CSIR Wave-rider in Mossel Bay from 00:00 on the 20th July 2015 until 21:00 on the 22nd July 2015. Wave height in m is shown in blue (Hmo) and significant wave height in m is shown in red (Hmax).

104 6.4.5 SAWS weather warnings For the July 2015 event, SAWS did not issue a weather warning as there remained little evidence that either heavy rainfall or any other adverse weather conditions could be expected for the Eden district. However, from 17th July with the threat of thunderstorms, constant communication between SAWS and the DM at the Eden district occurred. In addition, SAWS suggested a strong possibility of a cut-off low with a potential of heavy rainfall (>50 mm) predicted. With the impending rainfall, the Municipality requested that an excavator be on standby to prepare the channel for emergency breaching.

SAWS soon proceeded to issue a special weather alert for high rainfall along the Cape south coast on the 23rd July 2015 through to the 26th July.

6.4.6 Discussion of July 2015 The numerical weather prediction models projected no heavy rainfall for a 24 hour period. There was a concern raised by the weather forecaster, in discussion with DM that more rain may be anticipated and that similar weather systems in the past have led to more adverse weather conditions than initially anticipated by the numerical model. This concern was based on the experience of the duty forecaster highlighting the importance of good communication between the SAWS and Disaster Management when the forecaster expects severe weather.

Emergency breaching was conducted successfully as most of the critical elements, as highlighted in Chapter 5.2, for breaching, were met.

These results emphasize how emergency breaching was undertaken successfully for this event based on clear communication between stakeholders, assessing the risks and mitigating those risks as indicated earlier.

6.5 Successful artificial breaching September 2016 Although the numerical models did not clearly demonstrate heavy rainfall for the Eden district, it was anticipated that the weather patterns may lead to heavy falls. Furthermore, the

105 anticipated high ocean waves, a full Wolwedans Dam, high estuary level and closed mouth were all contributing factors towards possible flooding of the estuary. The mouth was successfully breached preventing a flood.

6.5.1 Numerical model precipitation Research material received from SAWS indicated that the Numerical Weather Prediction (NWP) model had projected between 15 mm and 45 mm of rainfall for the 16th September 2016 (Figure 6.16). In cases like this, SAWS may simply indicate that good rainfall is expected; however, the possibility of 50 mm or more (characterised as a heavy fall) is always likely within mountainous areas.

Figure 6.16: SAWS Unified model output representing accumulative precipitation for the 16th September 2016. The left hand side figure is the 48 hour Unified Model initiated on the 15th for the 16th September indicated <20 mm of rainfall while the right hand side figure is the 24 hour Unified Model initiated on the 16th for the 16th September 2016 indicated <25 mm of rainfall.

6.5.2 SAWS rainfall data In the period from the 1st to the 3rd September 2016, between 14 mm and 51 mm fell across the Great Brak catchment area (Figure 6.17), while the remainder of the Eden district recorded heavier rainfall of between 41 mm and 99 mm.

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Figure 6.17: Graph showing rainfall in mm for the month of September 2016. The data highlights rainfall registered at three separate stations in the Great Brak catchment area. The different colours refer to the three rainfall stations Jonkersberg Bos (blue), Jonkershoek ARS (red) and Grootbrakrivier ARS (green). Data provided by SAWS.

On the 16th September, 52,0 mm fell at Farleigh Bos (height of 503 m above MSL), while Jonkersberg Bos (height of 325 m above MSL), recorded 16,5 mm. Farleight Bos is within Eden but not within the Great Brak catchment area, while Jonkersberg Bos is within the Great Brak catchment area. Most rainfall stations in the Eden district recorded between 17 mm and 49 mm during this period. The data proves that the model forecast and in-situ rainfall data are comparable and further emphasise the importance of model data in forewarning impending flooding events. During the month of September 2016, the Eden district rainfall stations recorded between 60 mm and 174 mm of rain.

6.5.3 DWS hydrological data On the 1st September 2016, the Wolwedans Dam was at a capacity of 95,7% with the estuary level at 1,360 m above MSL. By the 13th September, the Wolwedans Dam was at full capacity (denoted by A on Figure 6.18a) with the estuary level at 1,420 m above MSL. Further downstream the estuary mouth was closed while the estuary level was rising. As a precaution, and to mitigate the risk of flooding breaching was conducted.

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Figure 6.18: (a) Water level in meters of the Wolwedans Dam between 01:00 on the 1st and 23:00 on the 17th September 2016. The letter A represents the day the dam reached full capacity. (b) The water level in meters measuring instrument reading at the Great Brak Mouth between the 1st and the 17th September 2016. Rapid increase in the estuary level from the 13th after the spill and peaked on the 14th as denoted by A. The drop in estuary level after the letter A indicates the outflow towards the ocean. The constant up and down from the 15th co-insides with high and low tide levels. Data provided by DWS.

108 The Jonkershoek ARS, recorded 68,4 mm of rainfall from the 1st to the 12th September 2016 which contributed to increased dam levels and eventually spilling on the 13th September. An automated estuary high-level alert was issued and emergency breaching was placed on standby.

On the 14th September at 07:30 the estuary level increased to 1,620 m above MSL. Once the preparatory channel for breaching had been concluded, water was released from the dam. On the 14th September at 15:00, breaching occurred (denoted by A on Figure 6.18b) while the Wolwedans Dam remained above 99% capacity. Additional water was released from the Wolwedans Dam to enhance the scouring of sediments in the estuary. On the 16th, the dam was at 99% capacity and although good rainfall was expected there was no threat as the mouth was open.

6.5.4 Wave and tidal information The wave height during emergency breaching on the 16th was only about 0,5 m and the maximum wave height about 1 m (Figure 6.19). The minimal wave height and conditions had little impact on the outflow of the estuary despite coinciding with spring tide.

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Figure 6.19: Graph showing wave data from the CSIR Wave-rider in Mossel Bay from 00:00 on 14th September 2016 until 21:00 on 17th September 2016. Wave height in m is shown in blue (Hmo) and significant wave height in m is shown red (Hmax). 6.5.5 SAWS weather warnings On 14th September 2016 the SAWS issued a special advisory for heavy rainfall and for very rough seas. These warnings were further updated on a daily basis until the 16th September.

6.5.6 Discussion of September 2016 events The conditions were again favourable for flooding during September 2016 and reiterates the importance and success of artificial breaching. SAWS was correct not to have disseminated early warnings for heavy rainfall.

6.6 Summary of the Great Brak estuary breaching case studies The various events that occurred at the Great Brak between 2013 and 2016 have clearly indicated that the use of weather predictions would help access disaster events ahead of time. The combination of weather predictions and numerical models based on sound communication structures will undoubtedly help key stakeholders in their risk assessment to forecast potential disaster events ahead of time and allow communities to react accordingly (i.e. breaching of estuary). This research has shown conclusive results how emergency breaching was successfully undertaken for these events based on clear communication between stakeholders, particularly during events when concerns were raised by the weather forecaster that for some of these weather conditions, flooding could occur even through the model was not necessarily predicting heavy rain.

Chapter 2 and 4 have demonstrated that the Great Brak estuary is vulnerable to severe storms and flooding and therefore is a high risk estuary. The thesis in Chapter 5 described how and when breaching can take place. The various case studies in Chapter 6 clearly articulated the successes of artificial breaching since 2013. Because of artificial breaching, no flooding occurred along the Great Brak estuary since 2013. The following chapter will deal with a summary of what the thesis have proved to this point.

110 7 The importance of flood damage mitigation – what have we learnt in summary 7.1 Oceanographic conditions impacting on the Great Brak estuary Along South Africa’s coastline, the sea-level variability due to wave-height fluctuations and tidal differences is considerable. This variability ranges from periods of less than a second to years and is largely due to the nature of the coastline and also includes aspects of coastal morphology, local weather patterns, adjacent ocean sectors and the variation in latitude along the length of the coast.

The response by the Great Brak estuary to sea-level variability is dependent on the physical nature of the estuary and more specifically the nature of its mouth at any given time. Therefore, further changes of the estuary over time ultimately depend on the role and impact of atmospheric forcing on sea-level rise. However, it has been shown that the reaction by the estuarine system to changes in sea level is difficult to predict, and more importantly monitor, due to high variability of tide levels which further differ on various time scales.

Tides in the vicinity of the Great Brak estuary are the most regular sea-level variations and propagate from west to east along the South African coastline. Furthermore, this region is dominated by semidiurnal, micro-tidal tides with spring-tidal heights recorded to exceed 2 m, while neap tides, on occasions below 0,5 m.

At shorter wave periods, such as surface-gravity waves, sea-level deviations are not transferred upstream of the Great Brak estuary and appropriate measurements are difficult to assess due to the lack of specialised measuring equipment such as wave buoys and river-level equipment along the Great Brak. Funding remains a challenge for stakeholders such as SAWS, DWS and DEA to invest in this equipment as annual capital expenditure and operational costs provided by Government and/or Treasury is limited.

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In studying the Great Brak estuary, this thesis has identified two main considerations for any flooding events. 1) The mouth of this estuary and 2) the rate in which these different signals are able to propagate from the sea into the estuary through storm surges. The mouth of the estuary is important as it can be open or closed (Chapter 2.1) and if closed what is the berm height of the estuary (Chapter 5.7.3) .

7.2 Development and engineering along the Great Brak estuary Extreme weather events can be devastating for disadvantaged and low-income families living in or on the edge of the Great Brak estuary. One of the outcomes of this research is that growth and engineering planning concerning the development of low-income housing along estuaries, such as the Great Brak, can contribute significantly as strategic and front-line climate risk- management services for more efficient emergency response. The houses erected in the naturally flood-prone or low-lying areas such as this area are at risk as they have been erected as low-cost formal or informal settlements, and to date remain poorly equipped to deal with flooding events as they are not protected from rising river levels.

7.3 Human, financial and infrastructure resources With limited resources available there is an urgent need to address the emergency-response process in which stakeholders are sufficiently equipped to deal with automated information that will reduce the threat of future Great Brak estuary-flooding events. The following are considerations for SAWS to proactively provide effective severe weather warnings and for disaster management to succeed in their planning and operations: i) high importance, • aspects such as the Wolwedans Dam level • estuary water level of the Great Brak • major floods do occur in other estuaries and should be studied further • the Great Brak estuary flooding can occur when high waves are overtopping a closed berm (September 2008)

112 • amount of land-based rainfall expected and occurring over the catchment and the estuary itself • the sea state regarding the possibility of rough or high seas • astronomical tide information regarding tide phases • the likelihood of a storm surge occurring simultaneously with the predicted flood event • clearly defined criteria for the issuance of a Great Brak estuary flood warning and/or alert ii) medium importance, • berm height of the Great Brak, which require continuous monitoring and consideration • roles and responsibilities needs to be clear and the people living in high risk areas should be familiar with these responsibilities as well as who to contact 24/7 • certain considerations are essential such as open phases; however, closed phases are important for ecological cycles in estuaries • a closed mouth may provide protection at times iii) low importance, • CCTV monitoring of the Great Brak estuary • significant bush and veldt fires to factor the expected increase in run-off into planning • communities need to be informed regarding what is required of them during evacuations • communities need to receive weather alerts and know how to act accordingly • communities need to be kept informed on processes followed • insurance industry involvement (especially when development is done in high risk areas) A key recommendation of this research is sufficient human resources should be made available to SAWS. SAWS is the only entity capable of monitoring weather conditions all year round. Limited resources may impact negatively on the provision of an effective early-warning service as well the actions required by DM when severe weather is expected. It is essential that at all the

113 main weather forecasting offices have sufficient weather forecasters to work 24 hours, 365 days a year, with one forecaster at each regional office just focussing on severe weather.

It should be noted that an improvement in capacity by DM is essential to manage warnings provided to them after normal working hours. It is critical to maintain a professional and transparent working relationship between SAWS and DM to ensure that successful mitigation of flooding disasters are achieved.

7.4 Integrated fully-coupled numerical weather prediction model Ideally, SAWS should run a fully-coupled operational numerical model that integrates several factors including storm surge, wave, and river-flow forecasting, inundation forecasting and then simulates the combined influence of these factors, as an ideal scenario. The simulation of these combined factors can be used in an effective floodplain development planning for the evacuation of communities along the estuary and implementation of flood defences. It should be noted that SAWS has subsequently implemented an operational storm surge model towards the end of 2018, which was not the case during the research period.

7.5 Artificial planning and/or emergency breaching Conclusive results have shown that emergency breaching of the Great Brak estuary should be considered only when emergency conditions are expected to develop within 24 hours. These emergency conditions may include high intensity rainfall or a period of continuous rainfall in the catchment area, which could result in the Wolwedans Dam overflowing directly into the Great Brak river.

It is important to continuously monitor weather conditions within the catchment area of the river and dam as this will enable further weather warnings to be issued through SAWS, DWS and DM in order to continuously monitor the situation.

114 7.6 Wave conditions Large waves can make artificial breaching impossible as shown by the major flood event in September 2008. It is therefore critical that wave conditions particularly their height and period are considered in any decision-making process. In the Western Cape the principal responsibility of disaster risk management is to manage disaster risks and to minimise the loss of life as well as damage to infrastructure during these incidents. The storms described by Holloway et al. (2010) and the lessons learned will improve the management of risks faced during the current change in climate as there is not sufficient monitoring stations, while weather warnings do not often reach the communities most at risk.

7.7 Ground-breaking work for policy consideration The role of the EEW-EPRG for the Great Brak estuary was highlighted, which takes into consideration oceanographic aspects, hydrographic nature, hydrological information, meteorological information and a DRR (early warning) for the protection of life and property, a first of its kind in the world. Therefore, to ensure its prominence within the international arena the EEW-EPRG should be updated regularly following research within the subject matter and/or legislation, protocols etc. ensuring it remains relevant. This should eventually result in improved numerical weather prediction models, additional monitoring stations at sea and at land and improved communications between stakeholders such as SAWS, DWS and DM. It is important that the same message is communicated to communities at risk and to the media.

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8 Estuary Management plans, Limitations, and Recommendations 8.1 Management Plans The importance of swift and decisive intervention as emergency flooding conditions develop as well as the need for an emergency breaching have been highlighted in this thesis. Emergency conditions may be defined as periods of prolonged rainfall and/or intense rainfall (>50 mm within 24 hours) in the catchment area. In the case of the Great Brak region, this may result in the Wolwedans Dam overflowing (i.e. a large flood). It has been highlighted in Chapter 7 that for emergency breaching it is required to continuously monitor the general weather conditions, especially the amount of rainfall in the catchment area of the dam and river.

The stakeholders involved (i.e. SAWS, DM, local Municipality, Department of Water and Sanitation) should communicate regularly while monitoring any emergency situation. Fundamentals that require constant monitoring by the Department of Water and Sanitation are the water level in the estuary and the rate of its increase. The Wolwedans Dam level, which includes its rate of change as the inflow increases should also be monitored by them. It is key that SAWS provide the anticipated and real-time rainfall in the catchment, severe weather alerts, real-time and predicted wave and tidal conditions.

Disaster management and/or the Municipality should provide the width and height of the berm at the estuary mouth and the equipment available on short notice to breach the mouth. During the research period it was found that once SAWS issues a weather warning it is the responsibility of the Mossel Bay Municipality to communicate the warning to affected stakeholders including residents and businesses.

Chapter 6 highlighted that preventative steps should be taken with regards to emergency breaching once a yellow alert has been issued by SAWS and not during the red phase (warning) as a warning and/or red alert is only issued once there is certainty of the event occurring. The lead-time for preventative steps is not sufficient after receiving such an alert as they normally occur within 48 hours of the anticipated event.

116 It is strongly recommended that the preparation of breaching be done once a yellow alert is received. It is further strongly recommended that the implementation of breaching (opening of preparatory channel) occur once the orange alert is given and in adverse unexpected conditions when a red alert is issued by SAWS. It remains the responsibility of the Mossel Bay Municipality and in particular the Municipal Manager to order the emergency and/or normal breaching. The order to breach should be done in consultation with the Department of Water and Sanitation as well as the Department of Environmental Affairs. It is extremely important to note that the main focus of breaching is to mitigate the loss of life and damage to property / infrastructure. It is recommended that a report is compiled after each breaching to build a history for future studies and/or for the enhancement of models / warning services.

8.2 Limitations One of the major limitations within the development of an estuary warning system is the fact that rainfall measured by SAWS is point rainfall, and it is measured at certain fixed points in the catchment area therefore limiting an overall view of the differences between rainfall measured at various points in the catchment. Other individual rainfall-station measurements were undertaken manually and can only be compared with surrounding electronic stations for accuracy. In addition, ARS data can be accepted as these stations are frequently visited as part of a maintenance schedule ensuring quality as part of SAWS, ISO requirements.

During the period of this work, there were no operational storm surge models across South Africa. However, during the described events, larger wave heights and spring-tide periods were observed, and an operational 5 km high-resolution storm surge model that provides wave height, surge height and period would have assisted in determining whether a storm surge did occur. A recommendation of this thesis is to ensure that storm surge models can be backdated over several decades.

This work has shown that there is insufficient data coverage in terms of real-time measurements (rainfall, water-flow, wave height and estuary level), available from a central point for all critical

117 estuaries, such as the Great Brak. SAWS, which is operational 24/7, and responsible for issuing weather warnings only has access to real-time rainfall.

There is a lack of Estuary Management Plans for high risk estuaries. These plans should include the training of operational personnel on estuary dynamics and related subject matter, although critical water-height levels for all estuaries during conditions critical for flooding is lacking and the amount of water required for precautionary breaching is therefore unknown.

8.3 Recommendations and Future Work 8.3.1 Climate Change It is clear that, with climate change as highlighted in Chapter 13 of the IPCC 2018 report dealing with sea level change, higher sea levels will mean more frequent storm surges. Furthermore, the risk of more frequent adverse weather conditions (Figure 1.1) is increasing due to climate change and therefore higher flood levels will have an impact on the protection of low-lying properties. Achievable short-to medium-term actions should be taken, including: i) establishment of ecologically sound breaching levels and development of mouth- management protocols for all estuaries, ii) determination of high risk estuaries and their characteristics and the frequent update of the high risk estuarine register, iii) determination of appropriate rainfall thresholds for high risk estuaries, iv) determination and investigation into the optimum artificial-breaching site, v) case study after each estuary flooding, vi) annual review of the Estuary Early Warning - Emergency Preparedness and Response Guide and vii) the updating of the flood hydrographs, under the various operational rules, flowing into the estuaries as it underpins the systemic flood risk to certain areas.

8.3.2 Improved forecasting Given that the WMO implemented a Coastal Inundation Forecasting Demonstration Project (CIFDP) for countries such as Fiji, Bangladesh, Caribbean and Indonesia, it is recommended that

118 the SAWS seriously consider implementing Coastal Inundation forecasting for South Africa as it will enable them to improve on the following: i) hydrological forecasting for high risk estuaries as SAWS Flash Flood Guidance system is not suitable for estuary flooding, ii) ensure that SAWS implements an operational storm surge model and iii) to ensure that storm models can be backdated over several decades.

In 2017, SAWS started using, on a trial basis, Impact-based Forecasting (IBF). The implementation of IBF is imperative as it provides stakeholders such as DM, DWS and Municipalities with sufficient time to act when severe weather is expected. IBF should further be used as a tool to educate communities so they know what to do during certain severe weather conditions. The IBF became operational as from May 2019 and the impact of expected conditions along estuaries should be regularly updated.

Since SAWS is the only entity, classified as an essential service, able to perform throughout the year, a weather service and provide weather related warnings. It is critical that SAWS is identified and targeted as the stakeholder who should coordinate a collective funding request to treasury to enhance and optimise real-time monitoring of infrastructure, collection of data and ensuring it is available on a central database for SAWS, DM and DWS to monitor continuously. These elements should include but are not limited to: i) the level of the Wolwedans Dam, which includes the rate of change during severe weather, ii) expected weather conditions from SAWS with graphical illustration up to 5 days in advance, iii) investment in real-time weather monitoring equipment such as weather radars, wave radars, LDN, AWS, ARS, satellite images and high resolution numerical model, iv) warnings and/or alerts issued by SAWS, v) investment in real-time hydrological-monitoring stations such as water level measurements at various points in the estuary, vi) the dam level and rate of increase of water flow,

119 vii) CCTV cameras indicating the width and height of the sand berm at the Great Brak estuary mouth, viii) installation of real-time wave-measurement moorings and/or annual deployment of wave drifters in Mossel Bay and other high risk estuaries, ix) astronomical tide information regarding tide phases, x) various flood-level markers (1:50, 1:100, 1:200 etc.) and xi) operational numerical model that includes all factors which contributing to estuary flooding such as storm surge levels, wave levels, anticipated river flow, inundation forecasting, which simulates their combined affect as well as options to select various factors to simulate the influence.

The aforementioned information needs to be available in GIS shape-file format with the ability to activate and/or deactivate certain parameters, depending on what needs consideration or if all parameters are not required simultaneously.

8.3.3 High risk estuary information An additional recommendation is that DEA should ensure that the bathymetry of estuaries is refreshed at least once every 3 years. As well as this, critical estuary levels should be determined for each estuary, as in the case of the Great Brak, based on the amount of precipitation expected within 24 and 48 hours in the catchment area (i.e. when 50 mm of rain is expected the estuary level should not be higher than 1,8 m before the rainfall) to accommodate the amount of precipitation without flooding. The 1:50, 1:100 and 1:200 flood lines should further be determined for the Great Brak and other estuaries and therefore the flood level under different precipitation amounts should be determined under the assumption of closed-mouth condition at maximum berm height. The dam level should be considered as low amounts of rainfall may result in flooding if the estuary is full, the mouth is closed and there are high waves which may coincide with a high tide.

120 8.3.4 Resource requirements Additional human capacity and funding is required for research, planning, and operational activities and modelling. There must be effective data collection in each quaternary catchment to estimate the respective contribution of water in rivers and rainfall to flood events. The identified data coverage includes: i) live-camera feeds to monitor estuaries visually, ii) weather radars for storm tracking, iii) soil moisture, which would assist in run-off calculations, iv) flow gauges in rivers and the estuaries to provide real-time data to SAWS, DWS and DM, v) rain gauges in specific catchments as there is not sufficient gauges along high risk estuary catchment areas, vi) berm height as this will impact the outflow of the river vii) estuary-level indicators for monitoring purposes and viii) real-time wave data for monitoring purposes.

During the consultation process with Disaster Management practitioners, they highlighted that since the introduction of the Disaster Management Act and framework (Act No 57 of 2002) of South Africa, it has become apparent to them that there is lack of implementation across all spheres of government. Questions are still raised regarding the practicality of the act and framework. In addition, Disaster Risk Managers has long been referred to as an unfunded mandate in the industry, providing challenges to practitioners to obtain budget for specifically Risk Reduction efforts. Although the Provincial and Metropolitan Disaster Management Centres, as well as National and Provincial organs of State, are in general adequately staffed by proficient practitioners, engineers and scientists, capacity often lacks at Local Level. It is at this level where implementation is of utmost importance, and it should therefore be taken into cognisance when addressing Disaster Risk Reduction.

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8.3.5 Capacity building During the research period all stakeholders expressed the need for training of operational personnel on estuary warnings, dynamics and related subject matter to better equip them for making informed decisions when issuing an estuary early warning.

8.3.6 Management of estuaries To prevent prolonged closures of the mouth and extensive build-up of the berm, it is essential that regular breaching is undertaken, which will result in longer open-mouth conditions. Considerably more water is needed for the management of any estuary than that presently considered. It is therefore critical that SAWS seasonal forecasts be incorporated when allocation of water and/or water used for regular breaching is discussed. South Africa is a country with scarce water resources and regular breaching cannot be considered, given there may not be sufficient rainfall to fill the dams again.

In Chapter 6, it was identified that precautionary breaching is imperative when conditions are favourable for water levels to be back to normal soon. An increase of the estuary water level will improve the effectiveness of a mouth breaching. It should however be expected that sometimes far less rain will fall than what was predicted and/or far more rainfall can fall than what was expected, therefore not all predicted heavy-rainfall events can automatically be treated as an emergency conditions. The dam levels, estuary water levels and berm heights would require continuous monitoring and consideration during each expected rainfall event and municipalities should consider not approving any development under the 5 meter above MSL.

Although the district municipalities in South Africa do not have the funds for dredging and was not considered as an alternative in the study, as mentioned at the beginning of Chapter 5, it would be wrong not to suggest that municipalities should consider this method as an alternative in the future.

122 8.3.7 Automation of estuary warnings During the research, particularly during discussion with SAWS and DM, the need for automation of all data was identified (see section 7.3) as, during lead up and during any weather events, especially significant weather events, SAWS and DM are extremely busy. It is therefore imperative that the Estuary Early Warning - Emergency Preparedness and Response Guide is automated through a policy for an effective and efficient disaster mitigation process saving life and protecting property.

In Chapter 2, it was articulated that this is the first policy driven thesis, which integrates meteorology, oceanography, hydrology, hydrographic data and a multi-hazard early warning system for estuaries. Prior to 2013 there was frequent flooding of estuaries as outlined in Chapter 4 but, since the implementation of the estuary early warning guide, (Chapter 6) there has been no experience of any flooding of estuaries along the Eden district and in particular the Great Brak. Ensuring that the forecasting of these mitigating successes continues, it is essential for the automation of real-time information (Chapter 7). Continued estuarine research must include a continuous improvement of the current estuary early warning guide. The investment in additional meteorological, oceanographic and hydrological instrumentation along high risk estuaries is essential. Finally yet importantly, Disaster Management authorities and weather forecasters should be capacitated to forecast and deal with estuarine flooding by training them for such phenomena.

The anticipated financial resources for the effective implementation of the three consideration levels, as articulated in Chapter 7.3, as well as those elements mentioned in Chapter 8.3, for the entire South African coastline, will cost in the region of US$35 million. The data available from the additional infrastructure will be of immense value to operational forecasters, disaster management and various research communities as atmospheric, hydrological and ocean data will be available for the same area.

It is hoped that this work will assist with the effective implementation by decision makers. The workshops held as part of this thesis, also worked towards an effective implementation.

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9 Acknowledgements

I would like to thank the University of Cape Town and in particular the Oceanographic Department under the leadership of Professor Ansorge, whose interpersonal relationship and friendly encouragement was a cornerstone in completing the research. The University has in Professor Ansorge a special person to drive oceanography forward. My co-supervisor, Professor Hermes, thank you for your continued friendly and constructive support. The road towards developing the (EEW-EPRG) started when the following people assisted me in developing the Storm surge guide for South Africa and they were AA Mather, S Brown, P de Villiers, K J Rae, E Poolman, A Matot, N Madlokazi, E Louw, H van Niekerk, S du Toit, G Otto, G Brundrit, E Schumann, T Khan, S W Carstens, S Visser, C J Malherbe, N G Kwela, C Fillis, M Rossouw. I would like to thank SAWS colleagues who provided me with relevant information and a special thank you to A Kruger, E de Jager, R Batties, R Smit, G Linnow, M Barnes, M de Vos, S Landman, D Ferreira and H van Niekerk who provided me with some excel training in graphs. The South African Naval Hydrographer, SA Navy as the supplier and copyright holder of tide information and, R Farre for the sea-level data at Mossel Bay. The Department of Water and Sanitation for water levels especially J Kriel, N van wyk and P Rademeyer. I further wish to acknowledge the wave data supplied by the CSIR, Stellenbosch, which was collected on behalf of the Transnet National Port Authority (TNPA) by U von Saint Ange, and S Haasbroek. A special thank you to the Eden Disaster Management colleagues, G Otto and W Jacobs for the Disaster-Related information along Eden as well as insight into the research area. A word of thank also go to Western Cape Provincial Disaster Management Centre and in particular S W Carstens who assisted with general DM processes and insight into operational practises while NtlekiI Khanya greatly assisted in the development of the GIS maps. I further wish to thank my former employer SAWS who allowed me time for my studies as it is not always easy to take extended leave. I wish to thank Dr W Jordaan and E de Jager for their time in proof-reading my thesis. I wish to thank my family who stood by me and believed in me even though they saw little of me, they understood how important it is. Finally yet importantly, I thank my Creator in whom I found peace.

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125

ANNEXURE A: List of Definitions

Alert Alert may respectively be classified as either an advisory, watch or a warning depending on (a) the lead-time ahead of the expected event as well as (b) the confidence level of the forecaster that the event will be realized. The SAWS issue, green, yellow , orange and red alerts.

Capacity The total amount of water that the Dam can be contained or store.

Catchment A ``catchment'', in relation to a watercourse or watercourses or part of a watercourse, means the area from which any rainfall will drain into the watercourse or watercourses or part of a watercourse, through surface flow to a common point or common points.

Disaster A natural or human-induced event, occurring with or without warning, and causing widespread human, material, economic or environmental losses, which exceed the ability of the affected community or society to cope with these effects using only their own resources. A disaster is a function of the risk process. It results from the combination of hazards, conditions of vulnerability and insufficient capacity or measures to reduce the potential negative consequences of the disaster risk.

Disaster Management Centre (DMC) A Centre established in a Municipal, Provincial or on National level in terms of the Disaster Management Act, No. 57 of 2002, to oversee all disaster risk reduction, response, relief and rehabilitation activities for the respective sphere of government.

126 Disaster Operational Centre A fully equipped dedicated facility within the disaster management centre of a particular sphere. Such a facility must be capable of accommodating any combination of emergency and essential services representatives, including all relevant role players and stakeholders identified in response and recovery plans for the purposes of multidisciplinary strategic management of response and recovery operations, when a local, Provincial or National disaster occurs or is threatening to occur.

Dredging Is the operation of excavating material from a water environment (sometimes temporarily created). Possible purposes of dredging include: improving existing water features; reshaping land and water features to alter drainage, navigability, and commercial use; construct dams, dikes, and other controls for streams and shorelines; and to recover valuable mineral deposits or marine life having commercial value. In all but a few situations the excavation is undertaken by a specialist floating plant, known as a dredger. Dredging is carried out in many different locations and for many different purposes, but the main objectives are usually to recover material of value or use, or to create a greater depth of water. Dredges have been classified as suction or mechanical.

Early Warning Timely and effective information, through identified institutions, that allows individuals, households, areas and communities exposed to a hazard to take action to avoid or reduce the risk and prepare for effective response.

Elements at risk Environmental, human, infrastructural, agricultural, economic and other elements that are exposed to a hazard, and are at risk of loss.

Emergency Preparedness

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A state of readiness, which enables organs of state and other institutions involved in disaster management, the private sector communities and individuals to mobilise, organize and provide relief measures to deal with an impending or current disaster or the effects of the disaster; and the knowledge and capacities developed by governments, professional response and recovery organisations, communities and individuals to effectively anticipate, respond to and recover from the impacts of a likely, imminent or current hazard event or conditions.

Entity (Primary role player) A governmental agency or juridical, private or public company, partnership, non-profit organisation, or other organisation that has disaster-risk management responsibilities.

Estuary A body of surface water that is permanently or periodically open to the sea in which a rise and fall of the water level as a result of the tide is measurable at spring tide when the body of surface water is open to the sea; or in respect of which the salinity is higher than for fresh water as a result of the influence of the sea, and where there is a salinity gradient between the tidal reach and the mouth of the body surface water. This should also include the estuarine functional zone which includes the open water as described above as well as specific estuarine habitat, e.g. mud and sand flats, and the estuarine floodplain, e.g. 1:100 year flood line, or the land area that exists between the open water and the 5 m contour line as a surrogate (GNR 546 Listing Notice 3, NEMA EIA Regulations (2010) identifies the estuarine functional zone as a sensitive area).

Estuary Management Authority Responsible Management Authority for developing EMP’s

Planned Breachings Undertaken as part of the Management of the estuary

128 Emergency Breachings Performed to avoid danger of flooding therefore minimizing the likelihood of the loss of life and/or property.

Flash Floods Quick response flooding event causing sudden flooding in small river basins, occurring within 6 hours of the causative circumstances, as defined in the SAFFGS.

Joint Operational Centre (JOC) A designated on-site facility, established at either an acceptable structure in the vicinity, or a mobile facility, which can be provided by the DMC or any other designated discipline, during a major incident, emergency or disaster situation. Rising floods or ‘pooling’ Rising floods’ or ‘pooling’ occur when there is an accumulation of water in an area that leads to general flooding, but without any significant river flow. In the Western Cape, rising floods occur most often in informal settlements located close to wetlands, or in high-water-table areas where there is limited or blocked drainage. While the term ‘rising floods’ is not typically used in conventional flood definitions, it does reflect the reality in many of the informal settlements in the Western Cape. In low-lying areas such as Masiphumelele and Philippi in Cape Town, or Power Town in the southern Cape, seasonal rising floods are a source of great hardship during the winter months.

Risk The probability of harmful consequences or expected losses (deaths, injuries, property, livelihoods, disrupted economic activity or environmental damage) resulting from interactions between natural or human-induced hazards and vulnerable conditions along the coast and estuaries. Conventionally risk is expressed as follows: Risk = Hazard x Vulnerability. Some disciplines also include the concept of exposure to refer particularly to the physical aspects of vulnerability.

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Risk Assessment A process to determine the nature and extent of risk by analysing potential hazards and evaluating existing conditions of vulnerability that could pose a potential threat or harm to people, property, livelihoods and the environment on which they depend.

River floods River floods occur when prolonged (i.e. over several days) heavy rain in an upper catchment increases water levels in river channels, leading to flood waves. Rising water levels eventually overflow a river’s banks, inundating adjacent areas before flowing downstream. River floods are serious transboundary processes, in which the consequences of poorly-managed flood risk in an upper catchment results in serious flood losses downstream. They can also be exacerbated by the sudden release of water from dams when sluices are opened to prevent them overtopping.

South African Flash Flood Guidance System The South African Flash Flood Guidance System (SAFFGS) is a software system utilized by forecasters at the South African Weather Service (SAWS) to provide short-term guidance for decision-making regarding potential flash-flooding of river channels. Within SAFFGS, each individual drainage basin across South Africa, defined in GIS shape-file format, is monitored continually, with the state of the drainage basin assessed every 1 to 6 hours. Rainfall contributions (either measured or predicted) to each drainage basin are also taken into account in near real-time. Radar as well as satellite sources of remotely-sensed rainfall estimation, rain- gauge data as well as predicted rainfall from numerical weather prediction (NWP) models are superimposed over each of the aforementioned drainage basins, allowing ongoing estimation of precipitation entering each basin. Estimates of soil moisture as well as modelled river levels are also incorporated into SAFFGS. Calculations are then made, per drainage basin, as to how much additional rainfall (in mm) would be required in order for the flow capacity of the main river channel (draining the basin) to be exceeded. On this basis, basins approaching saturation level are colour-coded (in a “traffic-light” system of yellow, orange and red) to indicate greater risk of imminent flash flooding.

130 Storm Surge An abnormal rise of the sea level generated by a storm, over and above the astronomical spring high tides.

Support Agencies (Secondary role player) The agency/entity tasked with secondary responsibility for a particular disaster risk management activity.

Temporarily open estuaries Sand bars often form in the mouths of these estuaries blocking off connection with the sea. Sandbars form as a result of a combination of low river-flow conditions and longshore sand movement on the adjacent coast. Flooding is frequently the cause of mouth opening, which also results in large amounts of sediment removal. However, infilling from marine and fluvial sediment can be rapid. Hyper-saline conditions occur in these estuaries during times of drought. Tidal and riverine inputs control the water temperature in these systems when the mouth is open, but is independent of them when the mouth is closed. Marine, estuarine and freshwater life forms are all found in these systems, depending on the state of the mouth.

Venue Operation Centre (VOC) A designated on-site facility, established at either an acceptable structure in the vicinity, or a mobile facility, which can be provided by any other designated discipline, during a major incident, emergency or disaster situation.

Vulnerability The degree to which an individual, a household, a community, an area or a development may be adversely affected by the impact of a hazard. Conditions of vulnerability and susceptibility to the impact of hazards are determined by physical, social, economic and environmental factors or processes.

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132 ANNEXURE B: List of Acronyms

ARS Automatic Rainfall Station(s)

ASCAT Advanced Scatterometer

AWS Automatic Weather Station(s)

CAP Common Alert Protocol

CIFDP Coastal Inundation Forecasting Demonstration Project

CPZ Coastal Protection Zone

CSIR Council for Scientific and Industrial Research

DCSM Dutch Continental Shelf Model

DDMC District Disaster Management Centre

DEA Department of Environment Affairs

DEA O&C Department of Environment Affairs, Oceans and Coast

DOC Disaster Operational Centre

DM Disaster Management

DMC Disaster Management Centre

DRR Disaster Risk Reduction

DST Department Science and Technology

DWS Department of Water and Sanitation

EEW Estuary Early Warning

EEW-EPRG Estuary Early Warning - Emergency Preparedness and Response Guide

EGRR EGRR Bracknell Centre, England

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EMP Estuarine Management Plan

EMS Emergency medical Services

ENSO El Niño–Southern Oscillation

EPRG Emergency Preparedness and Response Guide

EWS Early Warning System

GIS Geographic Information System

GEC Great Brak Environmental Committee

GMDSS Global Marine Distress and Safety System

HIRLAM High Resolution Limited Area Model hPa hectoPascal

IBF Impact Based Forecasting

ICMA Integrated Coastal Management Act

IDP Integrated Development Plan

IPCC Intergovernmental Panel on Climate Change

ISO International Organization for Standardization

I-STORM International Network for Storm Surge Barriers

JOC Joint Operational Centre km Kilometres

L/s Litre per second m meter(s) m3 Cubic metre m3s-1 Cubic metre per second

MDMC Municipal Disaster Management Centre

134 Met Meteorological

METAREA Meteorological Area

MHEWS Multi-Hazard Early Warning System mm millimetre(s)

MMP Management Maintenance Plans

MMMP Mouth Maintenance Management Plan

MSL Mean Sea Level

NAVTEX Navigational Telex

NCEP National Centre for Environmental Prediction

NDMC National Disaster Management Centre

NEDWAM Netherlands Wave Model

NEMP National Estuarine Management Protocol

NERC Natural Environment Research Council nm nautical miles

NOAA National Oceanic and Atmospheric Administration

NSRI National Sea Rescue Institute

NWP Numerical Weather Prediction

N2 National road 2 (two)

O&C Oceans and Coast

PetroSA Petroleum, Oil and Gas Corporation of South Africa

PDMC Provincial Disaster Management Centre

POL Plymouth Oceanographic Laboratory

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R South African currency in Rand

SAFFGS South African Flash Flood Guidance System

SAMSA South African Maritime Safety Authority

SANDF South African National Defence Force

SANHO South African Navy Hydrographic Office

SANParks South African National Parks

SAPS South African Police Service

SAST South African Standard Time

SAWS South African Weather Service

SDF Spatial Development Framework

SLR Sea Level Rise

The wave/surge numerical prediction system at the Naval Meteorological SMARA Service

SMS Short Message Services

SOLAS Safety Of Life At Sea

SOP Standard Operational Procedure

SPR Source-Pathway-Receptor

SST Sea Surface Temperature

The Protocol National Estuarine Management Protocol

UK United Kingdom

UKMET United Kingdom Meteorological Office

UM Unified Model

UMSA12 Unified Model South African 12km resolution

136 UN/ISDR United Nations International Strategy for Disaster Reduction

VOC Venue Operation Centre

VOS Voluntary Observing Ship

WAM Wave Model

WMO World Meteorological Organization

Z Universal time

137

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148 ANNEXURE D: Agenda of first consultation workshop

Record Ref #: 31-July 2012 to 2 Aug 2012 Agenda Estuary Early Warning guide

TITLE OF MEETING Workshop with stakeholders/clients in the development of an Estuary Early Warning Guide for South Africa PURPOSE Development of a National Estuary Early Warning Guide DATE 31 July 2012 – 02 August 2012 TIME/DURATION 08:30 – 18:00 daily VENUE Far Hills Hotel – George CHAIRPERSON/ Johan Stander FACILITATOR MINUTES To be identified MEMBERS SAWS Dept Water Affairs SANParks George Municipality Mossel Bay Municipality eThekwini Municipality Disaster Management (WC, EC, KZN)

DEA (Oceans and Coast)

INVITED PERSON/S Dr Monde Mayekiso DDG Oceans and Coast Geoff Brundrit Neil Malan Omar Parak Andrew Mather Eckart Schuman Sandiso Zide

149

Pierre de Villiers

Meeting Agenda

Time Day, Facilitator and Item Brought by

Monday 30 July 2012

20:00 Working Arrangements (Johan, Andrew, Colin, Nceba, Eckart, Schalk, JS Gerhard)

Finalizing Agenda (Johan, Andrew, Colin, Nceba, Eckart, Schalk, JS Gerhard)

Tuesday 31 July 2012 Facilitator: Johan Stander

08:30 Introduction and aims of workshop JS

08:35 Expectations by various stakeholders All

09:00 Presentation by representative of Dept Water Affairs

09:30 Presentation by representative of SANParks

10:00 Presentation by representative of George Municipality

10:30 Questions/Comments

11:00 TEA

Facilitator:

150 11:30 Presentation by representative of Mossel Bay Municipality

12:00 Presentation by representative of eThekwini Municipality

12:30 Presentation by representative(s) of Disaster Management

13:00 Questions/Comments

13:30 Lunch

Facilitator:

14:15 Presentation by representative of DEA

14:45 Presentation by representative of Department Environmental Affairs Alan (Oceans and Coast) Boyd

15:15 Presentation by Dr Eckart Schuman ES

15:45 Questions/Comments

16:15 TEA

Facilitator:

16:30 Presentation by Sandiso Zide SZ

17:00 Presentation by Pierre de Villiers PdV

17:30 Questions and Comments

18:00 Wrap up

Wednesday 01 August 2012 Facilitator:

08:30 Setting the Scene

151

08:45 Presentation on SAWS Severe Weather Guide, Alerts and Common Kevin Alert Protocol Rae

09:15 Presentation on SAWS Flash Flood Guidance (SAFFG) System Elke Brouwer s

09:45 Presentation on storm surges, marine warnings and other warnings Johan which may impact in estuaries Stander

10:15 Questions / Comments

10:45 TEA

Facilitator:

11:00 Mandates All

● SAWS ● DM ● Water Affairs ● DEA (Oceans and Coast) ● National Parks ● …….

12:00 Identification of responsibilities All

● SAWS ● DM ● Water Affairs ● DEA (Oceans and Coast) ● National parks ● ……

13:00 Information sharing and communication All

152 13:15 Lunch

Facilitator:

14:00 Identification of synergies between stakeholders wrt requirements / All need in an Estuary warning guide

15:00 Establishment of Working groups All

15:30 Tea

15:45 Working groups (Breakaway session)

Thursday 02 August 2012

08:00 Working Groups (Breakaway session continue) All

10:30 Tea

Facilitator:

10:45 Presentation by working group 1

11:30 Questions / Comments

11:45 Presentation by working group 2

12:30 Questions / Comments

12:45 Presentation by working group 3

13:30 Questions / Comments

13:45 Lunch

Facilitator:

153

14:30 Formulation of draft guide JS

16:00 Tea

16:15 Continue Formulation of draft guide JS

17:30 Adoption of Guide

17:45 Way Forward

18:00 Closing All

154