Tidal Swamp development by Pump Irrigation and Gravity Drainage, Acid Sulphate Soils, Kalimantan, Indonesia

This report is a study on the possibilities of practising irrigation & drainage at a large scale in tidal lowlands with acid sulphate soils in the humid tropics. The first chapters concern lowlands and their development in Indonesia. It appears that many of these lands become unfertile shortly after reclamation due to oxidation of pyrite, resulting in acid (sulphate) conditions. A brief introduction into this phenomenon learns that higher yields can be obtained by: - Leaching -Water logging As water logging has a shorter term return of investment it is chosen to apply this technique. Rice is thus the chosen crop. To see how this can be done in practice, Pulau Petak, an "island" in South Kalimantan, Indonesia, surrounded by tidal rivers and the sea is taken as "case study". An introduction based on existing research programs pictures the general situation. Data such as topography and tidal effects in rivers are missing and have to be calculated or even estimated. Transmissivities are extremely high and even when water logging is applied as technique, some 10 mm water/day leaching are desirable. The water requirement for cultivation of two rice crops is much higher than what is presently available. with all of the above in mind, a layout is chosen for irrigation and drainage canals to satisfy the whole 200 000 ha. The water is allowed in at various places along the river, and is drained via a large canal running through the whole island down to the sea. Next, the possibilities of using the tidal force to drive the water onto the paddies and back into the sea are investigated. Low hydraulic gradients result in the necessity of canals with big cross- sectional areas. Due to high permeabilities and danger of oxidation the water levels must be kept high in the whole area including the canals. The tide is only so high fora short part of it's cycle. To irrigate by gravity large gates and especially a big reservoir would be necessary. The costs of this area (measured in lost income for farmers) are compared with those of pumping. The latter appears to be much cheaper. As all water levels are to be maintained high, there is more head at the outlets to drain by gravity than there is at the inlets. The main drain runs parallel to the rivers, and has a lower hydraulic gradient than the river at low tide. This makes that the head at which water can be discharged back into that river/sea grows with the distance travelled!Hydraulic EngineeringCivil Engineering and Geoscience