Perpustakaan Digital ITB

Alas Strait, which separates Lombok Island and Sumbawa Island, has a role as outflow passage from the Pacific Ocean to the Indian Ocean and known as Indonesian Throughflow (ITF). This Strait has recently attracted attention for researcher due to its potential resources as a tidal power generation site. In this study, field measurements are taken by Vessel-Mounted (VM) Acoustic Doppler Current Profiler (ADCP) method which collected during three effective days. The aim of this survey is to determine the spatial characteristics and local phenomena of currents in the Alas Strait that were not captured by single-moored ADCP or numerical model. This survey is expected to elaborate the spatial pattern of current magnitude and direction along with their temporal cycle due to tides, hence describing how the channel functions to facilitate current circulation. The ADCP is deployed downward from a moving vessel to collect three-dimensional profiles of current at 0.5 m vertical resolution. As many as 13 transects of typically 10 km long separated about 1 km. Filtering and calculations are carried out to obtain depth-averaged velocity (DAV) and current flow discharge. The visualization and calculation results show that during the flood phase, the southward current magnitudes are uniformly distributed throughout the cross sectional transects. On the other hand, during the ebb phase, the magnitude of the northward tidal current is stronger on the shore side and much weaker in the center of the strait. During this phase, a slight southward current is observed particularly in the northern side of the survey area. These may indicate that the northward ebb current from the Indian Ocean entering the strait from the south is routed to the shallower side of the strait. The routing of the northward ebb current to the shallower side of the strait suggests that the middle of the strait is dominated by the permanent southward flow to the Indian Ocean. The results show that stronger currents of up to 1.74 m/s are observed southward during the flood phase in the middle of the strait, in this phase also show the highest total flow discharge amounts to 21 ×104 ????3/s (0.21 Sv) southward. Furthermore, during the ebb phase northward currents observed with velocity of 1.55 m/s and total flow discharge amounts of 22 ×104 ????3/s (0.22 Sv) northward. The flow discharge on the north and south side of survey area indicates a discrepancy that may be due to the presence of Gili Dua island on the southeast side of the survey area. The results of this study reveal local phenomena occurring in the Alas Strait spatially that have not been previously reported by presenting the zonation of tidal current flow in the Alas Strait during the ebb phase.