Background: The Tsunami of 26 December 2004 inundated northern Sumatra and dumped vast amounts of sea-water, sediments and debris and destroyed a large proportion of the infrastructure. Under ADB Grant Number 0002-INO the Earthquake and Tsunami Emergency Support Project (ETESP) was set-up to assess the situation and propose remedial measures to assist the area recover. Uniconsult International Limited (UCIL) was awarded Package 3 – Agriculture Component and staff mobilised in early September 2005 to commence work. The Desalinisation and Soil Improvement Specialist mobilised in October 2005.
What was done: Initially very little data was located about the soils, salinity and sediment problems brought about by the tsunami however, there was limited information available – mostly within the ADB GIS Mapframe system. Raw data for an EM38 salinity survey compiled by the Soil Research Institute (ISRI), Bogor from a survey funded by the Australian Centre for International Agricultural Research (ACIAR). through BPTP (Balai Pengkajian Teknologi Pertanian) was made available and used. Field visits etc allowed scenarios of the various problematic areas to be built up and reclamation interventions designed.
What was found: The data from the salinity survey had not been fully assessed or used and no, or very few, interventions to improve the condition of the land had been put in place or designed, apart from supplying the farmers with standard inputs of seed, fertiliser and other agricultural materials. Many of these inputs that were applied to salt damaged land were totally wasted and no or very poor crops grew.
Salinity and Drainage: At some point “someone” said – “there is NO SALINITY problem” in Aceh and technical people stopped thinking. However, there was, a “chronic”, low grade salinity problem. Generally, soil EC values are < 4dS/m, usually an easy problem to overcome. Something that virtually everyone missed, or ignored, was the WATER TABLE levels which were very high in many places. High water tables mean any soil drainage has to be “lateral” in nature and, as the Tsunami affected area is virtually flat and drainage lines and channels were blocked, damaged and not operating the land drainage system was NOT operating. In fact very few locations had been badly salinised and usually those that were lay very close to the sea or coastline.
Sediments: The perceived large problems caused by depths of saline sediment appear to be unfounded in most cases since salinity levels were not too high. Many sites on land with drainage have been restored to farming following natural desalinisation and after the sediments were thoroughly mixed in with the native soil with the addition of organic matter in the form of FYM or compost. Most of the fine textured sediments would not have come from the sea but would have been topsoil material picked up and redistributed by the tsunami wave as it crossed the land. These topsoil deposits would have been saline but only from the sea water that carried them. Sandy, or coarse textured, sediments, found mainly close to the coast line, would have originated from the sea-bed, would have been saline but, being sandy in nature, could not contain vast amounts of salt and were easily cleaned-up by leaching. However, there is a problem in places by the depth of sand, and other sediment, that has been deposited in that the land is now out-of-command by the irrigation system.
The final compilation by the Soil Desalinisation and Improvement Specialist was to compile a tool for assessing the problems of salinity and sediment depth and propose routines and interventions to help get agriculture back on track.