By Arief Santosa, M.Sc. – (Thesis M.Sc. Unesco-IHE, Delft, Netherland, 2014), Supervised by Prof. Charlotte de Fraiture Ph.D., M.Sc., Prof. Ir. Robiyanto H. Susanto, PhD., M.Agr.Sc. and Laszlo Hayde, PhD., M.Sc.
In many developing countries, forest areas suffer from illegal logging, wildlife hunting, illegal agricultural practices and forest encroachments. With increasing pressure on land use for human activities, natural forests have been converted and exploited into other land uses such as settlement, agricultural area, fish pond, and plantation estates. Lowland protected forest areas also threatened by this situation since people continue to expand their exploitation inside the forest area. Muara Air Telang in Banyuasin Region, South Sumatra Province is an estuary area which has been exploited by Bugis people (Buginese) since the 1970s. They opened the lowland forest for fish ponds and also coconut plantation by creating canals, called “parit” from the river into the middle of the forest. In order to prevent further lowland forest degradation, social forestry can be implemented, where local community are involved in the forest management activity. Farmers can utilize the land inside the forest area for agricultural purposes based on arranged mechanism and still consider the sustainability of the forest ecosystem.
This study deals with water management of Lado canal in Muara Telang area in Banyuasin Region that has been used by the Buginese for their coconut plantation estates for many years. Evaluation of the existing canal conditions was carried out to find out the water availability in different seasons (wet and dry) for social forestry implementation. There is a potential local tree species (indigenous species) that can be used for social forestry program in lowland areas which is Jelutung (Dyera polyphylla Miq. Steenis). In order to ensure that the plantation trees and crops can grow optimally, water management improvement is required. DUFLOW and MODFLOW computerized simulation of the surface and groundwater flows were used to visualize and describe water flow in the system. Modelling was used to simulate both surface water flow and groundwater flow during wet season and dry season. Several scenarios were generated to simulate both existing and improved conditions of the canal. The first scenario was the Lado canal in its existing condition without any improvement in both wet and dry seasons. The second scenario is the improvement of Lado canal through control structure installation for Jelutung cultivation in social forestry program. The third scenario is Lado canal system improvement for social forestry of Jelutung trees and also companion crops cultivation through agroforestry scheme.
According to DUFLOW model simulation result of existing condition during wet season, flood occurs in upstream area after 14 hours of rainfall and flooding the area for almost 24 hours with ±13 cm maximum flood depth, while during dry season, some tertiary canals are empty especially in the middle part of the Lado canal during low tide. Water flows inside the tertiary canal only for about 7 hours, while the remaining 17 hours there is no water inside the canal. On the other hand, MODFLOW simulations result shows tertiary canals mainly drain the fields from excess water from the precipitation during the wet season. From the model simulation it can be seen that average groundwater level rise is 2 cm/day. While during dry season, groundwater level depletes with 3 cm/day depletion rate. In order to solve the flood and drought problems, some improvement have to be carried out in the canal network. To solve flood problem during extreme wet season, construction of embankments or levees can be carried out along the canals at the suffered area. For the drought problem, the installation of water level control structure in the tertiary canal can be done to keep the water inside the tertiary canals.
For the purposes of social forestry development with Jelutung tree as selected species, it is important to regulate the groundwater level at a certain level that will not inundate the plantation root and also provide sufficient soil moisture for optimum growth. Jelutung seedlings will have optimum growth if groundwater level is regulated properly at the most recommended groundwater level, 30 cm below the ground/surface. Based on the MODFLOW modelling, installed stoplogs in the tertiary canals have to regulate surface water level at 0.7 m below surface level in wet season. During the dry season, water level has to be maintained at 0.25 m below surface level. By maintaining water level in tertiary canals in those levels during wet and dry seasons, groundwater level in the field can be maintained at 0.30 m below surface level with relatively small fluctuation. Planting for Jelutung seedling should be carried out in the beginning of wet/rainy season around November. Planting activity in the beginning of wet season related to the water level rising has been proven successfully for Jelutung seedlings growth and survival.
For agroforestry implementation in Lado canal, farmers can cultivate onion and pineapple in the first year together with the Jelutung seedlings plantation. Water level in the tertiary canals for the first year has to be adjusted at 0.7 m below surface level (wet season) and 0.25 m below surface level (dry season). In the second year, cabbage and potato can be cultivated with water level adjustment of 0.75 m below surface level (wet season) and 0.33 m below surface level (dry season). Tomato and bean can be grown in the third year with water level of 0.82 m below surface level (wet season) and 0.40 m below surface level (dry season). For the forth and coming years, farmers can cultivate crops with deeper or shallower root zone or can again cultivate previous crops since Jelutung trees are mature enough to adapt with groundwater changes and roots inundation.
For the purpose of social forestry, alley cropping arrangement with alternate rows layout is more suitable to be implemented in Lado canal since it will grow more trees in the field. Besides that, for long time period it will gain better soil conservation improvement to the area. Jelutung trees plantation spacing has to be determined to optimize crops growth and 7 x 7 m plantation spacing is more preferred. With this spacing design, it will generate good microclimate where the canopy of the trees will not cover the crops and allow sunlight to pass through. Implementation of social forestry and agroforestry in the Lado canal has a potential to improve farmers’ livelihood. By implementing agroforestry, besides the resin from the trees, farmers still can obtain additional income by growing agricultural crops in the same area. Eventually, water management improvement of the Lado canal becomes very important to ensure the success of the social forestry and agroforestry programs.
Keywords: Lowlands, Social Forestry, Agroforestry, DUFLOW, MODFLOW, Jelutung