HEC-RAS MODELING OF SEASONAL IRRIGATION WATER SUPPLY RELIABILITY UNDER CANAL BLOCKING MANAGEMENT

Abstract

The agricultural productivity of tidal swamp land in the Air Saleh Swamp Irrigation Area (DIR), Banyuasin Regency, South Sumatra Province, Indonesia is still sub-optimal. One of the causes is the lack of irrigation water supply in the 2nd and 3rd planting season. A significant effort to overcome this problem includes the construction of canal blocking that functions to maintain water level during high tide in channel and soil moisture on land used for rice growth. The construction of canal blocking is designed to maintain water level in channel and groundwater on agricultural land covering an area of 144 ha. Therefore, this research aimed to fulfill the availability of irrigation water using a combination of rainfall systems and canal blocking to improve agricultural land productivity. Canal blocking construction was made of coconut tree trunks, which were packed with sacks full of local soil to enhance structural solidity and reduce decomposition. On the outside, sacks were installed containing a mixture of sand and cement which functioned to withstand erosion by water flow. The construction of canal bulkhead was installed with 10-inch PVC pipes draining water into channel to regulate flow level during excessive rainfall. These trunks were used as the main construction material because of local availability, resistance to submersion in water, durability against shear and overturning forces. Furthermore, simulation and optimization of water management system were carried out by modeling using the HEC-RAS program. This allowed for analysis of water level during irrigation with sediment transport and accumulation when flushing and functioning as drainage.