Quantifying water balance of subak paddy field based on continuous field monitoring

Abstract

Subak had been known as superior and sustainable water management system in Bali’s paddy field, and had a long history as an interesting topic for study. Water management in Subak is more or less based on religious practices and the philosophy of the harmony among God, human and nature, that ensures equity and sufficiency of water diversion. Traditionally there is no water regulation in the meaning of gate operation as most Subak has their own water source from definite location, and fixed system was used for water diversion that defined portion of water discharge and not quantity. In this study, field monitoring system had been set up to continuously observe the water balance components such as: rainfall, evapotranspiration, percolation, field water status. With the available data, water balance equation can be used to obtain net inflow, which in this case only minimum, median and maximum for each particular month. These values were used to summarize total annual net inflow to the field, which ranges from 4575 to 7419 mm. This is accounted as total water use for rice production at the site and generally it can be concluded as the amount of water required to sustain the present paddy field of the Subak.