The relative scarcity of arable land in Indonesia means that wetlands are increasingly likely to be converted to agricultural and commercial forestry uses. However, typical land uses such as forest plantations, oil palm and rice cultivation all generally require extensive drainage. As a result of this development path, much of Indonesia’s peat swamp forest landscape has been drained for agriculture and forestry purposes, leading to peatland subsidence and enhanced flood and fire risks over large areas.

Josh Estey/AusAID

If drainage-based land use continues then peatlands will subside until they are no longer drainable and will be too flooded for any further economic use. This problem is already emerging in some locations and will extend over vast areas in the coming 30-50 years under a business-as-usual scenario. On the other hand, if the canals are blocked and the drainage is prevented, the peat will become wetter so that emissions will be greatly reduced and the peat fires will become a rare event. Thus, emissions and soil subsidence can be slowed down first, and then eventually stopped and potentially reversed through restoration of the eco-hydrology of the peatland. 

Rewetting programs therefore seek to block all drainage canals, and there are three main methods in which this work is performed: (a) by building box dams; (b) by creating compacted peat dams; and (c) by infilling canals with local materials in combination with creating palisades.

Box dams are usually constructed by government agencies, NGOs and local communities. Box dams create local employment and usually include spillways, allowing for some limited passage of boats. However, each dam takes considerable time and effort to construct and they are relatively expensive as materials such as timber and sand bags need to be brought to the site. By contrast, the building of compacted peat dams and the infilling of canals both require the use of heavy equipment such as excavators, and these methods are usually only carried out by plantation companies. Compacted peat dams are significantly cheaper than box dams, as the infilling material is easily available on site.

Anything short of full rewetting means that oxidation will continue. For this reason, careful study is required on the effectiveness of each of these canal blocking types in raising water tables; and how long these dams may last without maintenance. Effectiveness depends to some extent on the local geography and history of drainage: as subsidence is greater closer to canals, the end result after one or two decades of drainage may be the formation of mini-domes between canals, and some subsidence may still continue even after complete blocking of a canal until a new equilibrium is reached.