Sediment Accumulation Rate in Sayung Coast, Demak, Central Java Using Unsupported 210Pb Isotope

Abstract

Some efforts have been done to cope with coastal erosion and rob in Sayung Coast including mangrove plantation, hybrid engineering (HE), and hard structure protection. However, those efforts are not considered to be the best solution in reducing the impacts of the hazards. This study aimed to determine the sediment accumulation rates based on natural isotopes 210 Pb dating and hydro-oceanographic modeling technique. According to 210 Pb analysis, we calculated the sediment accumulation rates at Surodadi and Timbulsloko of 0.145 cm/year and 0.06 cm/year, respectively. The sediment compositions are dominated by terrestrial sediment typified by clay deposits. The sedimentary rate average of Sayung Coast prior to HE installation (2011-2013) was 0.195 cm/year. The rate of sediment accumulation rose to around 0.4 cm/year in 2016 in accordance with the increase of Mangrove area from around 409 hectares in 2013 to about 455.79 hectares in 2015. The increase of sedimentary rate recent years became an evidence that mitigation efforts to reduce abrasion temporarily succeeded.

Pemetaan Morfologi Dasar Perairan dan Pola Arus Pasang Surut di Teluk Bungus, Kota Padang

“…Saat memasuki mulut teluk, dengan kecepatan berkisar antara 1-2 m/s, aliran arus mengalami deformasi (pembelokan arah) kerena morfologi dasar perairan dan pantai dengan kecepatan yang lebih rendah yakni berkisar antara 0-0,6 m/detik. Mekanisme transport yang cenderung lemah diduga akan meningkatkan potensi pengendapan sedimen (Gemilang et al, 2020). Sedimen yang berasal dari daratan yang melalui sungai dan muara di dalam Teluk Bungus, akan mengendap dengan mudah karena tekanan aliran arus pasang yang menekan ke arah daratan dan rendahnya mekanisme transport dalam teluk.…”

“…Mekanisme transport sedimen pada kondisi purnama akan lebih intens terjadi, kecepatan arus pasang surut yang cukup tinggi mampu memindahkan massa air yang membawa sedimen menuju area lain di sekitarnya, sehingga pada suatu kawan akan terjadi kesetimbangan antara sedimentasi maupun abrasi (Ramkumar et al, 2016). Jika dilihat lebih mendetail, pada (Gambar 7A dan 7B) , arus sepanjang pantai terbentuk dari pembelokan arah arus setelah melewati mulut teluk, dinamika arus sepanjang pantai ini merupakan faktor utama yang memicu pengikisan pantai, pada area lain di dalam teluk dimana kecepatan arus sepanjang pantainya lebih rendah, sedimen hasil pengikisan sebelumnya akan didendapkan pada lingkungan pengendapan (sedimentasi) (Gemilang et al, 2020).…”

Hydrodynamics Sabang Bay and Its Influence on Near Shore Sediment Transport, Weh Island, Indonesia

“…The RMSE was 7.83 %, proving that the simulated model results can be used for further analysis. According to Gemilang et al (2020), the error of a developed model can be accepted to represent the field condition if it is not more than 15 %. If we see in more detail, even though during spring tidal conditions, the deviation of the symmetrical tidal phase is higher, but during neap tidal conditions, the surface depiction is likely to reflect an erratic fluctuation probably caused by the influence of waves.…”

“…Northerly and easterly sea currents commenced entering the bay, which possibly brought coarse sediments from the sea provenance. According to Gemilang et al (2020), the relatively coarse sea-sourced sediments will potentially be transported by reliable energy of currents by which the residue will be settled in the deposition environment near the coast in which the sea-current features tend to be weak. Asymmetrical currents are observed in the southern Rubiah, and Klah Island, wherein the current direction is oppositely formed.…”

“…If we compare the spring and neap phases of tidal, it is predicted that the sediment transport will mostly take place during spring conditions, whereby the current features are pretty much more reliable than the neap one. The coarse sediments will be transported toward the coast during flood tides, which tends to be settled due to its more significant mass (Gemilang et al, 2020). Otherwise, the finer-sized sediment sourced from river and land will be dominating the coastal area during ebb tides (Gemilang et al, 2018), which triggers resuspension resulting in the higher suspended sediment within Sabang Bay .…”