Topography: The coastal zones of Aceh vary in width to a maximum of about10 kilometers inland. The area with elevations near sealevel generally extends for about 1-2 kilometer. The valley of Banda Aceh is 10 km wide and 30 km long (the flooding reached maximum about 3 km inland). At Sigli in the Pidi Plain the low coastal zone extends further and flooding reached here up to 14 km inland.
Geology: The low-lying coastal zones of Aceh consist of mainly clayey un-consolidated to semi-consolidated sediments intersected by coarser sediments along river valleys. Beach deposits along the shore have formed sandy ridges. Bandah Aceh is situated in a depression formed by two parallel NW-SE trending faults filled with clayey to sandy un-consolidated to semi-consolidated sediments. Sigli in the Pidi Plain is built on clayey coastal mud-flats. Meulaboh is situated on the remnants of a limestone reef. The islands Simeulue and Nias are composed of limestone.
Hydrogeology: The groundwater in the coastal zone is brackish to saline in many places. This water originates from the time that the land was below sea level. The land level of Sumatra rises relatively quick by uplifting and due to the low permeabilities of the clayey sediments, the saline groundwater is not flushed out by fresh water. Fresh groundwater is found near the coast in the sandy beach deposits and more inland, in alluvial fans along the rivers.
Vulnerability: Intrusion of saline water during the tsunami flood is to be expected especially along the south coast in areas with sandy sediments; remaining stagnant brackish water could have increased the period of intrusion; retreat of coastline will cause inland movement of salt water interface The salts in soils and aquifer will be removed in an estimated one or two years depending on rainfall quantities
Damage areas: All low lying areas along the shore of Aceh were hit by the tsunami. The sandy beach ridges along the coast were flooded everywhere and all water supply facilities were probably completely destroyed. Areas with shallow groundwater are expected to suffer from groundwater pollution caused by seawater and by contamination from waste disposals and pit latrines.
Water supply: Banda Aceh: town water supply wells are reported without damage, the distribution system is damaged in the center of town
Dug wells and handpumps are destroyed in many villages and towns. Other wells are heavily contaminated with salt water, mud and debris. Ref.: Preliminary Damage and Loss Assessment | CGI January 2005
Hydrogeological map of Aceh (Ref.: Hydrogeological map, 1:2,500,000, Dir. of Environmental Geology, 1983)