Nelson Mandela Bay Municipality:

Disaster Management

Flood Hazards

According to the investigation conducted by SRK Consulting, the three highest priorities are for the following hazards:• Floods• Hazardous materials; and• Environmental degradation.

4High

Environmental degradation: loss of biodiversity

3Very HighSevere wind2Very HighFloods1Very High

Industrial hazards, spillages; Explosions and related fires

Prioritisation (1 = very high; 17 = very low)

Perceived hazard priorityHazard

Spatial distribution of the dominant dwelling types in the NMMM

Details as indicated by client & SRK inside the 100yr floodline (L, M, H respectively), for major rivers where there is no 100yr floodline available, buffer the major rivers by 200m and other rivers by 50m and make these areas "unknown", rest = none; Major stormwater outflow channels = HFloods

Severity delineation proposed methodology

Hazard Name

Hazard Severity Mapping Guidelines

Flood Hazards

� Perceived Priority: Very High

� Future Expected Problems: � Flood line areas are not really perceived to be the

problem, but storm water reticulation system inadequacies are problematic

� Storm water system can not handle the run-off; this is probably linked to increased development. It will only get worse as the metro grows, especially with the Coega development

Flood Hazards - Severely Vulnerable Areas:

� Widespread - the entire bay area- generally referred to as the "Chatty River Delta" -detention pond areas.

� Specific flood lines are available, specific areas within the Chatty river flood lines were indicated on the maps as especially high hazard zones.

� Specific areas are the detention pond structures, where people go and live in the flat areas behind the pond structure. This sometimes occurs with road crossings, where the detention is part of the embankment. Uitenhage and Despatch area along the Swartkops river.

R11 150 000R6 600 000R4 550 000Total

R9 200 000R5 100 000R 4 100 000Permanent

R1 950 000R1 500 000R 450 000Temporary

TotalRoads & Stormwater

Water & Sanitation

Type of Repair

Floods: 22 December 2004

1. Infrastructure Damages

2. Electricity Damages: Total cost (approx) R380 000.00

Estimated total damages: R 11 530 000.00

Floods: 22 December 2004

• 282 informal- and 149 formal housing structures were affected

• Structural damage to roofs and substantial damage to super structure of formal houses. An average estimate for repairs: R 6000.00 per house.

• Loerie Dam, from having a capacity of 66% to overflowing by 2 metres within a matter of few hours.

December 2004

December 2004

December 2004

Blue Horizon Bay

1:100 year flood

Floods 2006

• Extreme weather conditions triggered by a powerful cut-off low system on the 2nd and 3rd of August 2006 resulted in massive flood damage and hardship in the metropolitan area

• 9 confirmed fatalities

Aug 2006: Infrastructure Damages

LONG TERM IMPROVEMENTSR 109 300 000

MEDIUM TERM REPAIRS /

IMPROVEMENTSR 26 660 000

TEMPORARY REPAIRS /

REHABILITATIONR 3 705 000

Aug 2006

Aug 2006

Aug 2006

Aug 2006

Aug 2006

Aug 2006

Aug 2006

Aug 2006

Risk Assessment: Specific Action Points / Recommendations (SRK)

• Current hazard severity maps and vulnerability maps have to be further refined and verified through field work.

• Flood hazard maps need to be developed along major water courses

• Early warning systems should be implemented, especially for flood-related hazards

Recommendations:

• That the need for and prioritisation of, early warning systems be assessed according to the Risk Assessment outcomes and prioritisation.

• That the flood warning system be integrated with the South African Weather Services (SAWS) rainfall monitoring stations.

Current Projects

• The NMBM has currently got 16 automatic weather stations within the metro area– Web-based– Project to be expanded to provide greater

coverage• A disaster management system is been

compiled by SYSMAN and will be active at the NMBM Disaster Management Centre.

Weather Stations

Current Projects

• Risk and Vulnerability Assessment study has been completed.

• Flood studies on Swartkops and Chatty River Systems being conducted by SRK

• Direct fibre optic link between Weather Service Office and Disaster Management Centre

• Early warning: Remote camera’s

Meeting held on 6 March 2006: Flood Forecasting System Implementation- main aims

• To develop a GIS based technology to estimate possible high water levels and associated flood hazard zones using outputs of the National Flood Forecasting System as inputs to a flood level prediction model which has already been partly developed by SRK.

• To enhance technology transfer of the study on the “National Flood Nowcasting System towards an Integrated Mitigation Strategy” by enabling and capacitating our disaster management centre to issue scientifically based flood warnings to our most vulnerable people at risk of severe flooding and possible loss of life.

Flood Forecasting System Implementation: main aims (cont.)

• To aid in proactively mitigating one of the identified high hazard categories, namely flooding.

• To aid in developing a pilot study within the NMMM area which can then be applied on a national basis and used by other local authorities.

• To compile a database of rainfall-runoff data.

Further study requirements would include:

− Determine status quo of current instrumentation and monitoring systems at the NMMM

− Determine the need for additional monitoring instruments and communication systems

− Establish modelling needs for real-time runoff predictions based on real-time rainfall data.

Further study requirements (cont.)

− Establish modelling needs for water level predictions along high risk watercourses which include:

(i) Chatty(ii) Swartkops(iii) Baakens(iv) Paapenkuils(v) Shark(vi) Sundays

Further study requirements (cont.)

� Establish software/hardware requirements for setting up the early flood hazard forecasting system at the NMMM Disaster Management Centre.

� Technology transfer to occur by enabling the forecasting system to be operated and maintained by NMMM personnel in conjunction with SAWS.

� Storm-water Related Risk Areas study (August 2002 by SRK) to be expanded