Sedimen merupakan material yang tidak terkonsolidasi yang dihasilkan dari proses pelapukan batuan melalui proses mekanis maupun kimia. Distribusi jenis dan tekstur sedimen merefleksikan karakteristik hidrodinamika yang terjadi pada lingkungan pengendapannya. Penelitian ini bertujuan untuk menganalisis jenis dan tekstur sedimen serta mengetahui profil hidrolika sedimen berdasarkan analisis kurva Hjulstrom. Sebanyak 25 sampel diperoleh dengan menggunakan metode pengambilan sampel untuk lamun di 5 transek (5 titik tiap transek), yang melintang (cross section) pada posisi reef flat Masimbung dan pengukuran sedimen menggunakan skala segitiga tekstur GSM (gravel, sand, mud). Selain sedimen, turut diukur arus, jenis, kondisi tutupan, serta kerapatan vegetasi lamun di lokasi sampling. Pengambilan sedimen menggunakan sedimen core sampler, lamun menggunakan transek kuadrat, dan kecepatan arus menggunakan layang-layang arus. Selanjutnya dilakukan analisis fraksi butir sedimen untuk memperoleh jenis dan tekstur. Selanjutnya dilakukan analisis gradistat untuk memperoleh segitiga tekstur sedimen dan parameter statistik sedimen. Selanjutnya jenis dan tekstur sedimen divisualisasikan dalam bentuk peta menggunakan bantuan prangkat lunak Q-GIS 3.3.45 dan Surfer 25. Hasil analisis data jenis dan tekstur sedimen yang didapatkan didominasi oleh pasir berkerikil (gravelly sand) dengan nilai antara 381,4-723,3 mm, dan pasir sedikit berkerikil (sligthly gravelly sand) dengan nilai 315,2-676,7 mm. Berdasarkan hasil penelitian diketahui jenis sedimen di reef flat Masimbung dominan Pasir (sand) sebanyak 90,3%. dengan berat rata-rata keseluruhan ukuran butir 1%, selanjutnya plot hubungan ukuran butir sedimen dan kondisi arus pada diagram Hjulstrom pada seluruh titik lokasi pengambilan menunjukkan kondisi deposisi atau pengendapan. Lebih lanjut hasil penelitian mengindikasikan bahwa keberadaan vegetasi lamun yang mengkoloni dasar perarian memberikan pengaruh dalam mempertahankan kestabilan sedimen dasar perairan.

Kata Kunci: Hidro-Oseanografi, Kepulauan Derawan¸ Lingkungan Pengendapan, Pasir Laut

Sediment is an unconsolidated material resulting from the weathering of rocks through mechanical and chemical processes. The distribution of sediment types and textures reflects the depositional environment's hydrodynamic characteristics. This study aims to analyze the type and texture of sediments and determine the hydraulics profile of sediments based on Hjulstrom curve analysis. A total of 25 samples were obtained using the seagrass sampling method in 5 transects (5 points per transect), cross-sectioning the Masimbung reef flat position and measuring sediments using the GSM texture triangle scale (gravel, sand, mud). In addition, the current, type, cover condition, and density of seagrass vegetation at the sampling location were also measured. Sediment was collected using a sediment core sampler, seagrass using a transect quadrat, and current velocity using a current kite. Furthermore, sediment grain fraction analysis was carried out to obtain the type and texture. Furthermore, gradistat analysis was carried out to obtain sediment texture triangles and statistical parameters. Furthermore, the type and texture of sediments were visualized in the form of maps using Q-GIS 3.3.45 and Surfer 25 software. The results of data analysis of sediment type and texture obtained were dominated by gravelly sand with a value between 381.4-723.3 mm and slightly gravelly sand with a value of 315.2-676.7 mm. Based on the study's results, it is known that the dominant sediment type in the Masimbung reef flat is sand (sand), which is as much as 90.3%, with an overall average grain size of 1%. The plot of the relationship between sediment grain size and current conditions on the Hjulstrom diagram at all points of the retrieval location shows deposition or deposition conditions. Furthermore, the results indicated that seagrass vegetation that colonizes the bottom of the water influenced the stability of bottom sediments. Keywords: Hydro-Oseanography, Derawan Islands, Depositional Environment, Marine Sand