3 Post-tsunami assessment and restoration of soil and water
Water quality and assessment
The 2004 tsunami caused major changes to Aceh’s water systems. Coastal drainage patterns changed, particularly on the west coast, which was closer to the earthquake epicentre and hence more affected by the tsunami. Some land rose, other areas subsided, and the scouring action of the tsunami altered the coastline dramatically. Changes in coastal drainage closed estuaries in some areas; attempts to dredge them open to allow drainage were not successful, possibly because of changed land levels from subsidence or uplift. In many areas, former freshwater catchments became affected by high tides, saline groundwater or waterlogging, making them permanently unsuitable for agriculture (Figure 10).
Delays in reconstructing irrigation and drainage channels meant that areas remained waterlogged or were unable to access irrigation water. There was a general shortage of irrigation water in dry areas, and a lack of local rainwater storage for rainfed rice production. Some sites needed pumps to remove saline water from storages and to pump fresh river water into dams; some dams needed cleaning and deepening.
A common problem was poor growth due to salinity in low-lying fields. These ‘basins’ accumulated salts that would dissolve into the first irrigation water. Farmers therefore needed to drain water and accumulated salts away from the fields.
In some areas, salt water entered freshwater aquifers, and water testing was needed to ensure that salt water was not used on crops. Groundwater salinity in West Aceh fluctuated markedly—it declined rapidly after the tsunami, then rose repeatedly in response to seasonal variation in rainfall and the intrusion of saline water during flooding (Marohn et al. 2012). In the district of Bireuen, irrigated rice experienced more problems than dryland rice, possibly because of salt in the water used for irrigation. Water with an EC greater than 3 dS/m may cause significant crop damage.
In areas with poor drainage, improving the irrigation and drainage systems was an important priority for local government and non-government organisations. Irrigation was vital to ensure that farmers could plant and finish rice crops through flowering and seed set. On the east coast of Aceh, rice crops that were well established in August 2005 failed to yield well in October. A lack of sufficient irrigation water reduced salt leaching, leading to increased soil salinity and plant water stress. Irrigation systems must be surveyed to ensure that levels have not been affected by earthquake or tsunami damage.
The New South Wales Department of Primary Industries has produced guidelines for testing the salinity of water (NSW Agriculture 2000).