Mariental Floods: A Perspective


By Dr M. Amweelo IN global terms the most frequent kinds of natural disasters are flooding, earthquakes, cyclones and droughts. Volcanic eruptions, tornados and landslides are less frequent. Flooding is not unusual, both in industralialized and in developing countries. A flood in China in 1938 washed away a whole city and one million people died (UNEP IE/PAC, 1992). Natural disasters cause many deaths both in developed and developing countries. Factors affecting the risks are: population density, building structures, how long the event lasts, how sudden and unexpected the event is and how often such events occur and number of incidents which preceded it. Example of hazards in connection with natural disasters are dams, seismically active areas, river banks and mountainous areas. The extent to which people can minimize the effects of a natural disaster depends on how well informed they are about the likelihood of a disaster and the damage that could be caused. People’s perception of risk plays an important role in this. Mariental town, situated to the southern part of Namibia, was plunged into chaos on Saturday morning February 24, 2006 when the sluice-gates were fully opened to release water from the dam which had reached an alarming 110% of its capacity after heavy rainfall of 130mm was experienced in the region, which increased the inflow into the dam. The inflow peaked at 3000 cubic metres per second and maintained levels of 2500 cubic metres per second for a period of 14 hours. Hardap Dam was constructed in 1962 and has a total capacity of approximately 300 million cubic metres of water. The purpose of the dam is to supply irrigation water to the Hardap Scheme, as well as purified water to Mariental town. Prior to the construction of the dam, flooding is reported to have occurred during flood events in 1923 and 1934, but since the construction of the dam, major flood events were experienced in 1972, 1989, and 2000. The flood peak experienced in 1972 was the highest instantaneous flow, whereas the present flood had the second highest peak inflow in history (New Era, Wed. 1 March 2006). Problem It is estimated that, on average, natural disasters claim more than 25,000 lives and cause damage valued in excess of U$3 million per year globally. There are great geographical variations in the risk that an individual is exposed to. About 95% of all natural disasters occur in developing countries (UNEP IE/PAC,1992). Namibia is a victim amongst these developing countries and this natural disaster that recently occurred in Mariental town destroyed the people’s property. It was reported in the local newspapers that all of the 27 farmers working on the 2 200 hectares of land had damages ranging from crop ruin to immense infrastructure destruction. Two of the farmers who had the most severe damages mentioned losses of approximately N$8 million to N$10 million each, while the lump sum collectively tops N$300 million. The maize fields and grape vines are facing drought as the whole irrigation infrastructure has been destroyed. Twenty hectares of onion fields that were ready for harvesting are perished in the floods. The pump station of the Visser Boerdery collapsed (New Era, 1 March 2006, The Namibian, 01/03/2006). Organisation The problem of disaster mitigation/relief is of stupendous magnitude and involves coordination of large numbers of agencies concerned with different aspects. Industry and government need to establish the task force to study various aspects involved in it, which will suggest a number of mitigation measures. Various other agencies such as Namwater, University of Namibia, Polytechnic of Namibia, etc., also need to work out mitigation measures in specific areas of risk management. Natural disasters do not confine to the administrative boundaries of one settlement or the other and hence they cannot be managed by the limited resources of one urban body. Hence planning for disaster prevention and mitigation calls for harmonization of the plans and programmes of a number of local bodies in urban and rural areas. Control measures While it may be difficult to predict precisely or avert natural disasters totally like rains and floods, some measures could however be taken to mitigate such disasters in order to minimize their impact. Interference of man with the natural process without any regard for possible negative consequences also cause disasters such as the green house effect, the construction of dams in unsuitable areas disturbing the ecology, high-rise buildings, deforestation, disposal of industrial effluents, habitation in flood plain areas, etc., which need to be controlled and managed to minimize their negative effect. A broad spectrum of mitigation measures and risk control management strategies are outlined below: – For flood forecasting and control measures, variations in hydraulic and sediment responses of the river water and flood-prone rivers should be regularly monitored by the concerned agencies. – For providing flood protection to the community certain engineering measures comprising of storage methods, conveyance methods, proper drainage, etc., should also be developed as control measures. – Mariental residents also suggested proper urban and rural land use facilitating more absorption of surface run off, control on occupation of flood plains by identifying prohibited zones, restricted zones and warning zones and modification in building regulations incorporating the design ability to withstand water inundation and high velocity. – New rivers to be formed around the area. – Other flood mitigation measures suggested includes proper siting and soil bearing conditions, good drainage system, additional protection measures for roofing, rigid frame construction, water proofing treatment, etc. – Growing of plants and trees in catchment areas and along the banks of rivers, development of flood plain zoning concept. – Another suggestion is to build an additional dam and canal, as well as to clear up the river that could minimize flooding in future. Proper planning and development imperatives The process of planning for flood disaster mitigation and risk management is generally comprised of the following stages. In the beginning it is the mitigation stage involving planning for reduction of risks to human health and safety followed by preparedness. In this stage emphasis is on preparation of development plans to reduce damage by intervention. Once the plan is prepared it would be followed by responses in terms of provisions of emergency relief in the aftermath of a flood disaster so that original functioning could be restored back. The community as such cannot be risk free and will have to function within the specific levels of tolerance of natural and man-made hazards. Alternatives to flood disaster prevention and mitigation may either be found in having development away from hazardous areas towards safer locations or enforcing structural measures aimed at resisting or deflecting the impact of natural phenomena. The physical planning, specifically proper land use planning, can contribute greatly in the reduction of both flood disaster risk and the vulnerability of human settlements. Land use planning and control are the key factors for orderly and safe growth of human settlements. In disaster prone areas the expansion of urban areas is of critical importance and its feasibility is directly related to the extension of infrastructure and other civic services linking with the core town. Land use control measures indicate the location, function and density of such urban extension areas. Keeping in view the nature and degree of the risk posed by the flood disaster and the potential impact on the human settlement a vulnerability analysis would be essential before formulating land use development policies. Generally, reduction of the intensity or the frequency of natural hazards in most areas is beyond control, however, the reduction of damage probability is well within reach. Hence, land use planning and control should primarily concentrate on reducing the risk of flood disaster by reducing damage probability by channelling future urban expansion away from the areas exposed to severe natural hazards. The up-to-date base maps indicating the hazardous area by type, intensity and frequency is the essential requirement for taking up systematic land use planning and development exercises. Once maps and criteria for land use regulation are available evaluation of future settlement sites could be made easily. Apart from directing the location of development activities in future the land use mapping should also identify the hazardous areas of the existing settlements so that priority could be assigned to the urban renewal programmes and disaster preparedness accordingly. The scale of risk mapping needs to be related to the size of the planning area. For example, at regional level mapping could be carried out at scale: 1:50000 to 1:250000 while at urban settlement level it may range from 1:2500 to 1:25000 and at the site level it could be the scale of 1:500 to 1:2500. Within the broad policy framework of urban and rural development at national level the detailed policies and programmes should be worked out at urban area level. For guiding the spatial distribution of human activities and for implementation of flood disaster mitigation programmes a package of plans consisting of long range perspective plans (15-25 years), short-term development plans (5 years) coinciding with Namibia third national development plan (NDP111) followed by annual action plans and specific projects and schemes should be prepared. The planning policies and programmes should integrate the structural and man-made environment so as to avoid the negative effects of unplanned growth. The success of various land use measures for preventing the settlements from further damage from the natural hazards would be facilitated by certain policy interventions. At international level awareness programmes would be of vital importance for the disaster prone areas. The international funding agencies should ask for a vulnerability analysis component while funding any project in disaster prone areas. Technical assistance needs to be provided for the taking up of such projects. Training and interaction programmes should be augmented. Mechanisms for inter-sect oral coordination need to be established on a sound footing. At national level, land use planning legislation for flood disaster prevention and mitigation need to be strengthened. At local level, land use development policies need to be harmonized with environmental, social and economic goals within the broad objectives of flood disaster prevention and mitigation. Land use patterns for settlement planning should, however, retain some resources free from development so as to be used at sites at the time of emergency after the flood disaster occurrence. Open spaces at town level should be linked penetrating through the entire built- up areas sub-diving it into smaller units. NB!!!!!! Depending on local conditions, the following natural forces must be considered by industry, local government and others in their land-use planning, their installation design, their processes, management, emergency plans, etc: earthquake, landslide, flooding, wind, waves and extreme drought. The effects of a natural disaster can be reduced by having early warning systems, safer building methods, reliable transport and contingency plans.