By Intan Nur Azizah, M.Sc. – (Thesis M.Sc. Unesco-IHE, Delft, Netherland, 2014),, Supervised by Prof . Charlotte de Fraiture, M.Sc, PhD, Prof.Dr.Ir. Robiyanto Hendro Susanto,M.Agr.Sc. and F.X. Suryadi, Ph.D, M.Sc.
Mangrove forest brings the important role for the global ecosystem. Mangrove forest spread in all the tropic and sub tropic areas in the world. Indonesia has the largest mangrove forest which is about 2.5 – 4.5 million ha or 25 % from the total mangrove area in the world, even some of them are in critical condition. These mangrove areas are spread in East Kalimantan (3.8 %), South Sumatra (3.6 %), South Kalimantan (3.4%), Papua (3.2%) and Riau (2.3%).
Deforestation in mangrove brings serious effects for the world because it releases carbon to the atmosphere and affects the global climate. Deforestation in mangrove area is caused by logging, forest fires, land use change (industry and resident) and also agricultural practices. In line with that problem, rehabilitation in mangrove area is needed. Rehabilitation in ex-mangrove in coastal area is very important to solve the problems that are caused by mangrove degradation and deforestation.
To ensure the rehabilitation project will be successful, water management is needed. Water is the most essential component of mangrove that is about 90% of total component. Unwise drainage and land use change in mangrove cause fires, land subsidence, and oxidation.
The study is conducted in Teluk Payo Village which is part of Air Telang Protected Forest, Banyuasin District, South Sumatra. This area has drainage system that was built by local people. This area is planned to do rehabilitation to improve and restore the original condition. The study area is located in flat area with surface elevation 0 – 7 m+MSL.
MODFLOW and DUFLOW software are used in this study. MODFLOW is used for groundwater flow fluctuation analyzes based on drainage space. DUFLOW is used for canal performance analyzes in order to reach the optimum groundwater for optimum mangrove growth. Three scenarios of DUFLOW are implemented in this study and two MODFLOW scenarios are implemented.
Based on MODFLOW simulation, the existing water management system in the study area is not suitable for mangrove growth especially in dry season. The groundwater flow for existing condition reaches 0.45 m below surface level. Meanwhile mangrove for 1 – 2 years stage has the taproot between 0.1 – 0.3 m. Therefore, set a steady flow in the canal for 2 m high is applied and can increase groundwater flow for 1.98 m in dry season or about 0.15 m below surface level. This condition is suitable for mangrove growth and can be applied to succeed the rehabilitation project.
Based on DUFLOW modelling, existing condition is suitable enough for 1 – 2 years mangrove growth which can tolerant of water logged until 0.3 above surface levels. Rhizophora apiculata can tolerant with water flooded until 0.3 m and can grow well with 10 – 19 times tidal flooded. This study area has diurnal tides which means will be flooded for about 14 – 16 tidal flooded in the area. This condition is suitable for R. apiculata growth.
In order to achieve the best water management regarding surface level and groundwater flow, installation of stoplog is one of solutions. This structure can be easily operated and not expensive. This structure will be closed in dry season to keep the minimum water level and be open in wet season as an existing condition.
Keywords: mangrove, rehabilitation, protected forest, water management, DUFLOW, MODFLOW.