| Summary: | ABSTRACT
Serang and Bogowonto mouths of river are located on the southern beach of Kulonprogo which directly connected to Indian Ocean. The distance between Serang and Bogowonto rivers is 6 kilometers and separated by sand dunes wind and beach deposits. The problem faced by the river surroundings is the annual flooding caused by unsuccessfully river outflow to the sea. The closing mouth of river on dry season is the main cause of the unsuccessfully river outflow. The 'mouth of river will open again after river flow highly raises in the rainy season. The closing and opening process of mouths of river have been happening for a long time and had shifted mouth of river to the west.
Exogenic factors which cause closing diver mouth are river flow, ocean wave, tide and wind. The intensity of each factor dependent on the season In the rainy season, the wind influenced by northwest monsoon wind which has wet characteristic. This will invite wave from southwest direction. The wave will generate the coastal currents and long shore currents to move to the east direction therefore the sediment will also move to the east. Due to stronger river flow than long shore currents, mouth of river always open in this season. On the contrary, in the dry season the wind influenced by southheast monsoon wind which has dry characteristic. This will invite many waves from the south and southeast direction. The wave intensity id generally strong and will generate long shore coastal currents to move to the west direction therefore sediment also move to the west direction. At this time river flow have decreased, therefore couldn't prevent sedimentation process on the mouths of river by long shore currents therefore the mouths of river will be closed.
Keywords Exogenic factor, mouths of river closing, mouths of river shiftingflooding.
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