A Proposed Improvement of Belanti II Tidal Irrigation Scheme, Kalimantan, to Support Leaching of Acid Sulphate Soil Reclamation

The reclamation process of acid sulphate soil of the Belanti II tidal irrigation scheme remains unfinished. During ebb tide, the upstream acidic drainage water retains and settles in the irrigation canals. During high tide, the acidic water flows back into some parts of the agricultural land and reduces rice productivity. The measured pH is about 2.5 ~ 3.5 and the measured electric conductivity is about 0,25 ~ 0,35 mS/cm. Sedimentation in the middle to the end of the primary, secondary, and collector canals and tidal pond at the upstream end of the primary canal, preventing the leaching process of sulfuric acid soil. Primary canal normalization as an alternative solution to increase the capability of acidity leaching is proposed. Leaching the acidic soil of Belanti II irrigated area of 3.976 ha requires 500 m 3 /ha/day of freshwater, equivalent to 1.998.000 m 3 /day. The one-dimensional HEC RAS mathematical model is used to evaluate the hydraulics performance to support the leaching process. The hydraulic analysis was carried out using two tidal cycles on the existing channel and the normalized channel. Channel normalization has succeeded in reducing the water supply deficit to support the leaching process from 39% to 9%.