By : Yan Restu Freski and Darmadi (Taman Pintar Science Club)
The Winner of Special Award and Outstanding Achievement For Ability and Creativity In Science and Engineering Project – China Association for Science and Technology (Intel International Science and Engineering Fair (IISEF) 2011)
This research idea arises when facing the fact showed by the map. Many rivers in Bantul until Cilacap Regency, Java, Indonesia, have the trend to deflect to the west before come in to the ocean. One of them is Opak River in Bantul, Special Region of Yogyakarta, Indonesia. This research aimed to know the factor affecting the deflection of Opak River before it ends in Hindian Ocean and to know the process of deflection of Opak River on its condition.
Methods used in this research were observation, library research, and documentation. The samples were put in the research field tested in granulometric analysis. It was supporterd with stereo-microscopic analysis. Observation was focused on sedimentation process. To analyze the data, analytic descriptive was used, that is interpreting the data qualitatively.
The result of the research explained that there were many factors that affect the deflection such as wind, wave, long-shore drift, sedimentation from the river, lithology (rock formation), neo-tectonic setting, and geomorphology. Wind creates the wave that will break and crash the beach. It causes swash and back-swash shaping long-shore drift to the west. The sediment in this natural process moves to the western beach blocking the stream. The rock formation supports the process by its resistance. The formation of rock both in the East Java and West Java do not support the deflection of rivers in its surrounding. There was a fact about the subduction zone lies along the Java island and its southern beach. The latter always be uplifted as it belongs to the Eurasia plate. It construct the geomorphology of the beach in the mouth of Opak River.
