Unit Tamban is one of the reclaimed lowlands in the tidal irrigation area, which is included in the food estate program located in Block D, Central Kalimantan. The water system used in the area is a fork-type with a settling pond at the end of each primary canal. Most of the soils are acid sulfate type with a pyrite depth of more than 50cm. Sedimentation of the canal causes the water supply and drainage processes to slow down, which compromises the water quality. At high tide, there is a process of acid water dilution, while at low tide, acid water will be evacuated out of agricultural land through a network of canals. The study was conducted of examining the effect of tides on water quality as indicated by the characteristics of pH, Total Dissolved Solids (TDS), and Electrical Conductivity (EC). Measurements were done at four points along the primary canal during spring tide and neap tide in the wet season. Water level and water quality were measured simultaneously for 27 hours. The results showed that water level fluctuations had a significant influence on the water quality in the canal. When it comes to peak tide during spring tide, the pH of the water increases while the EC and TDS values decrease. Rainfall at high tide also affects the quality of the canal surface water, which raises the pH.

Unit Tamban is one of the tidal swamp irrigation areas located in the ex-PLG area, precisely in Block D of Central Kalimantan. The productivity of Unit Tamban is very low, with only one planting every year due to the low water quality in the canal and the unfinished land reclamation process. The volume of freshwater from the tide is only 229,788 m3, while the leaching of acidic sulphate soils requires 248,000 m3. Unit Tamban has a dominant hydro-topography of types B and C, so some agricultural land uses rainwater as an irrigation water supply. The study aimed to examine the effect of rain discharge on the existing irrigation network as an additional water supply in the leaching of acidic sulphate soils in the swamp irrigation area of Unit Tamban. This study used dependable rainfall for calculating rain discharge and one-dimensional hydraulic modelling using HEC-RAS. The water volume in rainy conditions can meet the needs of acid sulphate soil leaching, while there is a deficit of 7% in existing conditions. The availability of dependable rain can meet the need for acid sulphate soil leaching so that the reclamation process can run well.