By Nur Azis, M.Sc. – (Thesis M.Sc Unesco-IHE, Delft, Netherland, 2014), Supervised by Prof. Charlotte de Fraiture Ph.D., M.Sc. Prof.Dr.Ir. Robiyanto H.Susanto, M.Agr.Sc. and F.X. Suryadi,M.Sc,PhD
Peat swamp is unique ecosystem which has multiple interrelationships that provides a wide range of important natural functions and environmental services. Tropical peat swamps has a typical characteristic as an ombrogenous system that receives water mainly from rainfall and mostly found as convex surface shapes. Refers to those important roles and functions, it takes the ecosystem under increasing pressure from national development interest. Indonesia which has 10% of peatland from the total land area has been utilizing it for national development and economic growth through altering the area for agricultural fields, settlement project, and other purposes. Since it was done, peatlands and peat swamps had been severe damaged and degraded that cause detrimental effects to the environment, economics, and socio culture.
In Central Kalimantan, the intensive damages occurred since the Mega Rice Project (MRP) launched in 1996. Almost 1.5 million ha of peat swamp and peatland area is changed into agriculture land use in order to increase the national production and compensate the land use change of rice fields in Java. The construction of huge and complex drainage canals networks causes worse conditions that indicated by land cover changing, lowering groundwater table, fire, several drought accidents, land subsidence, etc. Fire occurrences increase as consequences of the drop of groundwater table, land subsidence, increasing oxidation peat layer. Degraded peat swamps with all the potential damages make rehabilitation trials on that area facing complex difficulties. Peat swamps rehabilitation has shown a high failure number due to the technical obstacles in the field level and the lack programme of rehabilitation in national scope.
The study area represents all those conditions. It is located in Sei Ahas, Block A of Ex Mega Rice Project with total area around 1,000 ha, and part of upstream area of Kapuas river basin in Central Kalimantan. The area has peat dome shape which has to be maintained in proper way to hold its function naturally. Drainage network systems surrounding the area cause severely decreasing water table of peatland and damaging natural habitat of endemic peat swamp flora and fauna. Meanwhile, agricultural activities and other productive purposes that were expected by opening that area are totally failed. All the remaining land use in the area is the bare land in some parts as former logging area dominated by shrubs and ferns, land burnt caused by fire accident few years ago, and rubber plantation owned by surrounding people that are not in well maintained condition. Fires and drought due to over-drained become potential threaten for its existence. Moreover, there are no measures to control ground water table fluctuation in that area.
Those existing conditions make the area as a fragile environment that is very sensitive from the human interventions and natural changes. One of the measures that can be chosen to deal with those conditions is managing of the hydrological condition surrounding the study area. Degraded peat swamp in the area will results in the conditions that water cannot reach the level that is needed to support plant life in drier months whilst water runoff becomes faster in the wet months that lead to new problems like flooding of adjacent land and downstream area. Moreover, the risk of fire will increase, which is not only burn all of the plants on the surface layer but also penetrate the underlying peatland. In order to manage the hydrological factors in the area, the analyses and modelling software’s are prepared to deal with the problems; Duflow would be utilized to simulate the surface water level in the canals; and Modflow model will be prepared to find the distribution and the characteristics of the groundwater table in the field.
The result of the application of the two models shows that in dry season, study area is suffered in drought because groundwater table drops more than 1 m below the surface and varies from 1.2 m in the downstream part to 2.7 m in the upper part of the study area. This condition should be taken into account that some measures should be done in order to control the groundwater table that should not drop too far from the surface level. One of measures that can be done is related to water management in surrounding canals of the study area. The purpose is to keep the water level in canals high as possible in order to elevate or hold groundwater table. Two scenarios are prepared to deal with those conditions.
Scenario 1 that applied canal blocking installation at downstream part of Secondary Canal 3 and Canal 4 shows that the rise of groundwater table near the structure can reach at 0.40 m below the surface and after 15 days with no-rain condition, level drop to 0.50 m below surface level. Middle and upper part of study area are still having gaps difference that have varies gaps ranging from 2.0 m to 3.0 m below surface level. Meanwhile, Scenario 2 that installed cascade weirs along Secondary Canal 3 and Canal 4 shows the increment of surface level in the canals and groundwater level in almost each section on the field, but it is still remain the problem of gaps of groundwater level particularly in the field which has peat depth higher than 5 m +MSL. By installing cascade weirs, groundwater table can be elevated up to near surface level in downstream part; 1.30 m in middle part, and 0.70 m in upper part.
According to the result, effort of peat swamp rehabilitation by managing (ground) water level remain near surface level through two scenarios is not totally solved all problems in the area. Even though the result will be different, if it simulates in wet season when recharge from rainfall taken into account, some other measures should be applied such as other water management approaches, silviculture programmes and socio-economic empowerments. In silviculture approach, some appropriate procedures and techniques should be applied to improve land cover quality and quantity that support its natural hydrological function on this area. Intensive planting should be applied in the field through lane planting system. Planting fast growing species (i.e. Asam-asam (Ploiarium alternifolium), Garunggang (Cratoxylon arborescens) and Tumih (Combretocarpus rotundatus)), endemic species (i.e. Belangeran (Shorea belangeran), Jelutung (Dyera lowii), and Pulai (Alstonia pneumatophora), and the plant that could be survive in severe condition, Galam (Melaleuca cajuputi Roxb.) are recommended to be planted in some parts of study area that still have problem of lower groundwater table in dry season. Furthermore, socio-economic empowerment (creating alternatives incomes and job opportunities) to local people surrounding the area can be played as a significant role to reach a successful rehabilitation programme. Finally, by integrating those three approaches, success factors of peat swamp rehabilitation would be optimized.