SAND SPIT MORPHODYNAMICS ON RIVER MOUTH

• Main Author: Fadlan Abida, Rizal
• Format: Theses
• Language: Indonesia
• Subjects: Ilmu kebumian
• Online Access: https://digilib.itb.ac.id/gdl/view/73826
• Institution: Institut Teknologi Bandung

The coastal inlet is a channel that travels along the shore and joins the river to the sea. The biological and socioeconomic circumstances surrounding the coastal inlet are significantly influenced by the dynamics of the channel. The deposition of sediment from the transport of sediment by waves, erosion owing to the washing of silt in the coastal inlet induced by river flow, and human activities all affect the dynamics of the coastal inlet. Research on coastal inlet at the Opak and Bogowonto Rivers mouth is crucial because these two rivers have a significant impact on the morphology of southern coastal Java Island. While the Bogowonto River mouth resides in Purworejo Regency, Central Java, the Opak River discharges into the Indian Ocean first and is located in the Gunung Kidul district of Yogyakarta. Both of these rivers have data that can be researched further, particularly in anticipating changes in the coastal channel, particularly in the Opak and Bogowonto coastal channels. This data is particularly available daily for river discharge. This study identifies beaches for 21 years, related with wave conditions and river flow, with the aim of analyzing the growth trend of sand spit. The morphodynamics of the coastal inlet on South Java Island in general, as well as its effects on the surrounding area and the local community, are all given in this study's overview. Landsat 7 and 8 imagery data, as well as Sentinel-2 satellite data, were used for the investigation of the coast. The mNDWI algorithm is used to identify the coastline by image interpretation, and four classifications are used for categorization. After processing satellite imagery data, the shoreline is confirmed with SPOT 4/5 imagery data, which has a greater resolution and a similar or almost identical capture time. A mathematical model that predicts the closure of coastal inlet makes use of the interaction between river flow and waves, assuming that river flow erodes material out of the coastal channel while waves impact the incursion of silt into the channel. Sand spit growth in the coastal inlet of Bogowonto and Opak follows a seasonal pattern. Sand spit growth in the Opak tends to move westward, as shown by the growth rates of sand spits there from 2000 to 2008 of 65.78 m/year , from 2008 to 2013 it was 415 m3/year and from 2013 to 2020 it was 127.79 m3/year, respectively. Two (two) breaches of the sand spit in the Opak coastal waterway happened in 2008 and 2013. Due to the geometry of the water pool in the Bogowonto coastal channel, which is shorter than the Opak lagoon, the growth of the sand spit there is more open and closed. Longshore currents, which are created by waves, carry sediments along the coast and deposit them in inlet, closing coastal inlet in the process. River flow, on the other hand, erodes sediments in inlet, eroding sand spit. In order to analyze the topographical changes that took place between 2000 and 2020 in the Opak River estuary, the model was applied to the area. applying the coastal channel closing and opening to the model to make necessary adjustments. With the help of this model, it is easier to comprehend how river mouth width changed between 2001 and 2014, taking into account the effects of coastal channel closure and opening. With a 0.54 coefficient of determination, an RMSE of 27.23 m, and a bias of 37.08 m, the Opak coastal inlet opening and closing trends may be anticipated.