Coastal defence is national defence

The Bay of Bengal is one of the world's sixty-four Large Marine Ecosystems (BOBLME) bounded by eight countries viz. Bangladesh, India, Indonesia, Malaysia, Maldives, Myanmar, Srilanka and Thailand. The Bay is a relatively shallow or embayment of the north-eastern Indian Ocean covered by the southern part of Bangladesh. It occupies

an area of 2,173,000 Km2 with an average depth of 2600 meters and is 1600 kilometer in width. About one-quarter of the world's population live in the littoral countries of the Bay of Bengal with approximately 400 million in its catchment area subsisting at or below the poverty level. The Tsunami 2004 on 26 December has freshly panicked the BOBLME countries.

Bangladesh's coast is hydrologically aggressive and prone to extreme cataclysms with eventual vulnerabilities to the hard core poor. It has 710 km long coast along the northern tip of the Bay of Bengal. The coast of Bangladesh, based on geomorphologic conditions and hydrological features, can broadly be divided in three distinct regions: the eastern, the central, and the western. It has 25,150 Km2 of internal water up to base line. The territorial water of the country is 9,100 Km2 up to 12 nautical miles. The estimated total marine water is 166,000 Km2. The coastal population is 33 million with about same density as compared to the rest of the country. The poverty rate is higher and access to common facilities is lower over every sphere of livelihood. The tide along the coast of Bangladesh is of semi-diurnal type. The variation in tidal range is less than 2 m to about 6 m. The maximum current velocities vary from approximately 0.1 m/s to 4 m/s in tidal channels.

Under the prevailing south-south easterly winds with average speed of about 8 m/s, the average significant wave height ranges from 0.6-1.5 m in the near shore zone to 0.1-0.6 m in the landward zone of the coast. During monsoon, wave heights can exceed 2 m with periods greater than 6 seconds. Higher waves occur mainly during cyclones. About one-sixth of the tropical storms generating in the Bay of Bengal hit the coast. Cyclones occur at a frequency of 1.3 per year. Severe cyclone generates wind speeds of more than 150 km/hour and surges are 9 m above the astronomical tide. Climate change impacts on the coast of Bangladesh were investigated through the simulation of the possible situation in 2030 allowing for information derived from a number of Global Models. The analysis indicated an increased surge height

of between 5 and 20 percent. Other factors such as possible changes in the severity and frequency of cyclone events were not incorporated. An indication of the impact of severe cyclone events on the coastal population demonstrates that at 100-year return period 3.92 million people will be at high risk of devastation from saline flooding arising out of extreme hydraulic events.

The 654-km of sea-facing saline embankment along the coast of Bangladesh gradually built over the last four decades is the living geometry enhancing the degree of safety to life and property of coastal population against the cyclone and cyclone generated storm surges. These embankments are still principally considered as a safety bar to coastal agriculture only. The frontline saline embankment along the coast has seldom been seen or learnt to have been overtopped by the past storm surges. The tsunami in media term Asian Quake Disaster in the hard hit countries has not surpassed the damages caused by cyclone in terms of cutting the lives and properties in Bangladesh during 1970 cyclone.

The geographical location of Bangladesh in relation to the fault line in the Indian Ocean has itself made the nation's coast less prone to tsunami. Bangladesh has no device for detecting tsunami and monitoring the sea level rise or recording the storm surge heights. It should therefore join hands with the multinationals in the venture of installation of tsunami detecting device in the Indian Ocean for sharing the benefits. The development strategy contained in the National Water Management Plan "continue as at present" approach is a less viable option for the existing coastal embankment system than it is for inland schemes. Unless increased funding for adaptation to changing nature is provided and beneficiary participation in maintenance is increased, the coastal defense system will deteriorate, with increased vulnerability to saline flooding, cyclone surges, and tsunami.

On social grounds alone, it would seem unacceptable to allow the nation's coastal defence to degrade to the extent whereby they ceased to provide adequate protection to life and property. The government's sag at any time therefore may not appear to be rational, as millions of coastal population cannot be left at the vagaries of nature. Handing over of the coastal embankments system to beneficiary is likely to be as difficult as for inland schemes in the immediate days. As in other countries, therefore, the coastal defence system must be expected to remain largely the responsibility of the government. If it is accepted that the coastal defence system must be preserved, 'rehabilitation and improvement' is the only viable option for the existing coastal embankments system in the perspective of deadly disasters. Most land at risk from saline flooding is already protected, but new polders are required for newly accreted land. In any event, accreted area should be undertaken only when natural accretion processes are substantially completed and should provide for periods of further inter-tidal play to restore drainage system and raise the land. Afforestation to provide some protection against wave action and to promote accretion is an important part of this process. The National Water Management Plan in the backdrop of slower accretion of coastal lands recommends that coastal reclamation projects will be less attractive in the next 25 years. Yet there is no denying the realisation that coastal defence is the national defence -- with or without tsunami.

Md. Saeedur Rahman is Chief Engineer, BWDB, Dhaka.