USE OF DRAINMOD TO DETERMINE SPACING BETWEEN CANALS FOR SUBSURFACE DRAINAGE SYSTEMS AT LOWLANDSErry Koriyanti, Robiyanto H. Susanto, Dedi Setiabudidaya, Ngudiantoro and F.X. Suryadi
Lowlands have a huge potential to be utilized as productive agricultural lands. The success of agricultural activity in lowlands is heavily impacted by water table fluctuations. Subsurface drainage system can be implemented to control water table in lowlands. But implementation of subsurface drainage in lowlands requires good planning, considering the water management needs and construction costs. Drainmod models can help planning by simulating water table fluctuations in lowlands after subsurface drainage implementation. A Drainmod model allows planning based on climate and soil conditions without having to do trial and error in the field. This in turn allows planning of cropping patterns and types of plants to cultivate in the lowlands. Approach method is used to calculate the hydrological component of subsurface drainage, infiltration, evapotranspiration and runoff. Drainmod model validation was conducted prior to the implementation using the correlation coefficient between the water table fluctuations prediction from drainmod simulation results and direct field observations. The value of the correlation coefficient is 0.81, indicating an excellent correlation between Drainmod simulations and real-world observations. It is concluded that Drainmod simulation models can be used to determine the spacing between canals to obtain water table fluctuations that ranges from 0.6 m to 0.7 m below ground surface. The simulation results shows that the implementation of subsurface drainage at a depth of 0.7 m below the ground surface with 25 m spacing between canals is able to maintain the water table as needed in the plant root zone. A proper drainage system in lowlands will increase the index of agriculture and the productivity of the lowland increases.
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