Deltas on the move; Making deltas cope with the effects of climate c

KvR report 001/20067.3 AdaptationAdaptation measures can be implemented in deltas where it would not be effective totake physical measures regarding sediment and water management. This may bethe case in deltas where:- physical measures are simply not possible, for example because there is nophysical space or sediment available;- the costs of physical measures are out of proportion with the damage and/orlosses that would be suffered as a result of flooding.In these deltas, measures tackling or compensating for the consequences of floodingare much more effective than physical measures that aim to prevent that flooding.Some indicators for deltas where this is the case include (see 6.4):- the size of the coastal plain and the amount of space available: wider delta plainsoffer more options for adaptation measures such as the relocation of people andindustries, the restriction or directing of land use types etc;- GDP: in places with a low GDP, it will be cheaper to pay out compensation forlosses than to take physical measures. This can be determined by means of acost-benefit analysis.The Ganges-Brahmaputra deltaThe Ganges and Brahmaputra rivers form one of the largest river systems on Earth.The delta is also one of the largest in the world, covering some 105.640 km 2 (seephoto). The main area of abandoned deltaic plain lies to the west and is home to oneof the largest mangrove regions in the world, the Sundarbans. The site of activedeltaic sedimentation lies to the east. Wave energy in the delta is relatively low and,as a result, few beaches are present along the shoreline and muddy tidal flats arecommon. The coastline is extremely irregular as a result of the large number of tidalchannels that dissect the coast. Broad mud and silt flats border the coast. Theoffshore slope in front of the delta is extremely low. The Ganges-Brahmaputra deltais subsiding by more than 1.5 mm per year.Lower Deltaic plain of the Ganges-Brahmaputra delta (Hart & Coleman,2004).<strong>Deltas</strong> on the moveThe Ganges-Brahmaputra delta is one of the world’s most densely populated deltas.Humans therefore have a major impact on the delta. The inland part of the tidal plainis now protected by dikes, and the former saline lands have been converted intovarious agricultural and marine farming areas. Originally, the entire surface of theabandoned delta formed a vast expanse of mangrove forests, but large areas of theoriginal wetlands have been converted for agricultural use. The only areas in whichagricultural expansion has not taken place are those areas where saline tidal watersintrude into the delta plain, such as the Sundarbans. Yet even here, agricultural landis being expanded by means of the construction of levees to prevent salt waterintrusion.Fishermen at the Sundarbans (Left: www.zipcon.net/~beckyd/grapefruit -archives/fisherman_sunderbands.htm, right: www.grandpoohbah.net)Due to the high population density in the coastal area, the situation in a subsidencezone and the expected significant rise in the sea level, the number of peoplepotentially at risk of flooding as a result of climate change is high. There is thereforea great necessity to take measures.Physical measures in the Ganges-Brahmaputra delta in terms of sediment and watermanagement would appear to be virtually impossible now, despite the enormoussupply of sediment. Due to the high population density, there is hardly any space leftfor any intervention measures. Even an adaptation measure such as the relocation ofpeople from the most vulnerable areas of the delta would be difficult as there is solittle suitable and available land beyond the delta plain.Due to the low GDP, it would therefore probably be more cost-effective to takeadaptation measures, which could consist of:- the construction of hills and refuge mounds to limit the consequences of floods;- offering financial compensation for losses resulting from flooding;- setting up an early warning system to warn the inhabitants in case of disasters.7677