No abstract

Dinamika kawasan pesisir mencakup proses erosi dan sedimentasi merupakan hal penting untuk mengetahui kondisi pantai. Pesisir Kecamatan Brebes merupakan salah satu kawasan di Pantai Utara Pulau Jawa yang memiliki dinimika perubahan pesisir sangat kuat. Studi sebaran jenis sedimen yang dilakukan secara terpadu di perairan Kecamatan Brebes ditunjukkan untuk memberikan gambaran proses transportasi dan pengendapan sedimen berdasarkan distribusi ukuran butir sedimen. Penelitian dilakukan dengan pengambilan sampel sedimen dasar perairan secara acak dan tersebar di sepanjang pesisir dengan metode grab sampler, kemudian dilakukan analisis lebih lanjut dengan metode granulometri. Hasil penelitian menunjukkan bahwa secara umum, pola sebaran sedimen permukaan dasar laut Kec.Brebes didominasi oleh sedimen berukuran lempung-pasir. Jenis sedimen berdasarkan ukuran butirnya yaitu pasir, pasir lanauan, lanau pasiran dan lanau. Kondisi hidro-oseanografi yang fluktuatif memberikan nilai sortasi buruk hingga sedang, dominasi ukuran halus tersebar pada bagian Timur, sedangkan fraksi kasar tersebar dibagian Barat dekat dengan laut lepas.  Kondisi tersebut menjadikan salah satu faktor tererosinya bagian pesisir Kecamatan Brebes dengan dinamika hidro-oseanografi yang berubah-ubah.

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.

Mandeh Bay is threatened by sedimentation issue caused by the rapid development of marine tourism area which strongly impacts to the environmental degradation. Due to the semi-enclosed area of Mandeh Bay, the tidal current has a significant role in triggering vertical and horizontal transports within the bay. This study aimed to determine the characteristic of tidal current during the southwest monsoon. We developed a hydrodynamic model based on Navier-Stokes equations using a flexible mesh and tidal forecast in which the validation is performed by ADCP data. The simulation results will be used as the basic data to develop a model which depicts the elliptical pattern of tidal current constituents. Offshore rotary tidal currents which are originally semidiurnal reiterate the elliptical pattern every 6 hours and 12 minutes. The strongest semidiurnal current speeds are observed in the bay mouth ranged from 0.1-0.5 m.s-1. The tidal constituent ellipses are oriented more meridionally and in several areas oriented zonally. The current speed of  is the highest at all which the  speed is averagely one third of  magnitude. While, the two main diurnal tidal constituents ( and ) have the maximum speeds approximately one fifth of  magnitude. Thus, the domination of semidiurnal constituents may trigger sediment distribution and accumulation within the bay because of its twice tidal oscillations entering the bay.

The dynamics of erosion and accretion in the coastal area of Brebes Subdistrict have many impacts on mangrove destruction and coastal region. The erosion and accretion are influenced by oceanography parameters that can affect the distribution of coastal sediments. The aims of this research were to determine the characteristics of the phenomenon of erosion and accretion in coastal Brebes Subdistrict and shape appropriate mitigation to reduce the erosion. This research is done with the bed sediment sampling using grab sampler for 26 sampling point. Current and tide measurement are conducted wih ADCP deployment for 15 days' measurement. Sediment characteristic analysis done with granulometri and statistic analysis. The average of sediment sorting is 1.21, skewness is 0.088 and the kurtosis is 3.76. Generally, bed surface sediment distribution pattern is dominated by clay to sand, the grand size distribution of sediments are sand, silt, sandy silt and silty sand. Longshore current speed ranged between 0-0.12 m.s -1 at the spring tide condition and ranged between 0-0.08 m.s -1 at the neap tide condition, the domination of current direction towards to the East and Northeast. The mitigation is very needed to rearrange the mangrove areas, build the coastal protection and recover the main river line which is the sourceof the sediment materials, so that can be provide the supply of sediment deposition in the coastal area. ABSTRAK Dinamika kawasan pesisir Kecamatan Brebes berupa bencana abrasi dan akresi yang terjadi memiliki dampak besar terhadap kerusakan kawasan mangrove dan pesisir. Fenomena erosi dan akresi yang terjadi dipengaruhi oleh parameter oseanografi yang dapat mempengaruhi sebaran sedimen di pesisir. Penelitian ini bertujuan untuk mengetahui karakteristik distribusi sedimen dasar perairan sebagai upaya identifikasi bencana erosi yang terjadi di pesisir Kecamatan Brebes.Penelitian dilakukan dengan pengambilan sampel sedimen dasar perairan menggunakan metode grab sampler terhadap 26 titik pengambilan. Pengukuran kecepetan arus di lokasi penelitian dilakukan dengan pemasangan ADCP selama 15 hari. Analisis karakteristik sedimen dilakukan dengan metode analisis granulometri dan statistic sedimen. Nilai rata-rata sortasi 1.21, skewness 0.088 dan kurtosis 3.76. Secara umum, pola sebaran sedimen permukaan dasar laut Kec.Brebes didominasi oleh sedimen berukuran lempung-pasir. Jenis sedimen berdasarkan ukuran butirnya yaitu pasir, pasir lanauan, lanau pasiran dan lanau. Kecepatan arus sepanjang pantai hasil model pada kondisi purnama berkisar 0-0,12 m.s -1 dan pada saat perbani berkisar antara 0-0,08 m.s -1 , dengan dominasi arah arus menuju ke Timur dan Timur laut. Perlu dilakukan penataan ulang terhadap kawasan mangrove dan bangunan pelindung pantai serta melakukan pencodetan terhadap sungaisungai utama yang merupakan sumber pembawa material sedimen sehingga dapat memberikan suplay endapan sedimen di bagian pesisir.

Sabang coastal bay becomes the area of significance where the development centered in the semi-enclosed area. Sabang Bay is well-known as the center of marine economy (Aquaculture, Harbor, and marine tourism). Recently, there is a planning initiated by Ministry of Marine Affairs and Fisheries (MMAF) to install the floating fish cage aquaculture (KJA) in the offshore area of Sabang Bay which the planning becomes a controversy between local people, local government, and researchers as well. This study aims to evaluate and discuss the impacts that will be happened if KJA is applied. Field surveys on hydro-oceanography aspects were done measuring currents, tides, waves, winds, bathymetry, water quality, as well as tourism condition. Based on those hydro-oceanography conditions, Sabang Bay categorized into calm water area where the sea current is weak (ranging from 0-0.12 m/s), whilst the high values of pH, salinity, and temperature are identified within the bay during low tidal condition. If KJA is installed within the bay, automatically it will pollute the water due to the accumulation of remaining fish feeder wastes. Moreover, within the bay, there are several attractive marine tourisms such as diving sites, the conservation area of Sophie Rickmers shipwreck site, and hot bubble (fumaroles hydrothermal vent). The presence of KJA will possibly disrupt marine tourism activities so that the implementation of KJA needs to be considered the impacts before installation.

Beberapa upaya mitigasi terhadap bencana erosi yang terjadi di kecamatan Brebes telah dilakukan dengan penanaman mangrove, pemasangan hybrid engineering, alat pemecah ombak, namun dari keseluruhan upaya tersebut masih dianggap belum menjadi solusi terbaik mengurangi dampak bencana erosi pantai. Penelitian ini bertujuan untuk mengetahui tingkat rata-rata kecepatan sedimentasi berdasarkan umur absolut sedimen dasar laut yang dianggap mewakili daerah penyelidikan. Penentuan umur absolut sedimen berdasarkan aktifitas kandungan isotop alam 210 Pb pada sedimen. Hasil perhitungan laju sedimentasi tersebut dikorelasikan dengan data debit sungai dan kondisi hidrooseanografi yang berperan dalam sistem sedimentasi. Berdasarkan profil unsupported 210 Pb pada lokasi IST-01 (Muara Pemali) dan IST-02 (Muara Nipon) rata-rata laju sedimentasinya berturut-turut 0,224 cm/tahun dan 0,211 cm/tahun, debit Sungai Pemali sebesar 14,4-48,1 m 3 /s, kecepatan arus pada stasiun IST-01 berkisar antara 0,001-0,1 m/s dan kecepatan arus pada stasiun IST-02 berkisar antara 0,001-0,08 m/s. Kondisi hidro-oseanografi daerah penelitian yang fluktuatif memberikan pengaruh besar terhadap proses sedimentasi. Besarnya debit sungai memiliki korelasi terhadap peningkatan besarnya nilai laju sedimentasi di Muara Pemali dan Muara Nippon. Hasil penelitian tersebut dapat dijadikan bahan rekomendasi upaya mitigasi bencana erosi di kecamatan Brebes

ABSTRAK Kawasan pesisir Pademawu yang beralih fungsi menjadi pusat pertanian garam menimbulkan beberapa dampak negatif yang salah satunya adalah permasalahan kerentanan sumber daya air tanah. Beberapa sumur gali milik penduduk sudah berubah menjadi payau hingga asin. Evaluasi terhadap kualitas air tanah di kawasan tersebut sangat dibutuhkan untuk mengetahui kerentanan air tanah. Penilaian kerentanan air tanah dilakukan berdasarkan parameter hidrogeokimia dan indeks kualitas air Water Quality Index (WQI). Fasies hidrokimia air tanah didominasi oleh fasies CaHCO3 kemudian NaHCO3 dan NaCl. Nilai rasio Na/Cl dan Cl/HCO3 menunjukkan bahwa dalam air tanah daerah penelitian telah terjadi proses pencampuran air laut ke dalam akuifer dengan kategori penyusupan air laut sedikit hingga agak tinggi. Kondisi tersebut didominasi oleh proses infiltrasi air tambak garam ke dalam akuifer. Nilai Water Quality Index (WQI) berkisar 46,69-736,42, kategori WQI good water mendominasi wilayah penelitian sebanyak 45,45%, excellent 27,28%, poor water 18,18% dan satu sampel air masuk kategori 9,09%. Lokasi dengan kategori poor water dan very poor water berada di sumur gali penduduk yang berdekatan dengan garis pantai dan tambak garam. Pengaturan tataguna lahan antara kawasan pemukiman dan tambak garam sangat dibutuhkan sehingga tidak memperluas area kerentanan air tanah di pesisir Pademawu.