KARAKTERISTIK DAN DISTRIBUSI LUMPUR SIDOARJO SEPANJANG SUNGAI, ESTUARI DAN PERAIRAN PORONG

Semburan lumpur Sidoarjo (Lusi) di daerah Porong menambah fungsi Sungai Porong menjadi sarana untuk mengalirkan lumpur ke arah laut, karena kemampuan tanggul – tanggul penghalang di sekitar lokasi semburan sangat terbatas. Kondisi ini berdampak pula terhadap terbawanya lumpur lapindo ke perairan Porong. Penelitian ini bermaksud untuk mengetahui sebaran sedimen di sungai, muara dan perairan sekitar Porong terutama yang bersumber dari luapan lumpur Sidoarjo. Materi yang digunakan dalam penelitian ini adalah sebanyak 30 sampel sedimen hasil sampling yang diambil di lokasi sungai – muara sungai Porong dan 30 sampel sedimen permukaan dasar laut di perairan sekitar muara sungai Porong. Distribusi umum sebaran sedimen di perairan Porong menunjukkan sedimen lumpur ditemukan di pinggir sungai dan sedimen pasir ditemukan di bagian tengah sungai. Distribusi umum sedimen dasar perairan di sekitar muara Porong berupa pasir, lempung dan lempung lanau pasiran. Hasil analisis mikroskopik dan SEM menunjukkan bahwa sedimen yang berasal dari luapan lumpur Sidoarjo ditemukan di sepanjang aliran Sungai Porong sampai muara, namun belum ditemukan di perairan luar sekitar muara Porong. Sedimen Lusi yang sampai ke muara Porong berukuran butir sampai 2,5 mikron. Deskripsi megaskopis menunjukkan sedimen Lusi pasir - kerikil umumnya berbentuk pipih (halus– agak halus). Hasil SEM menunjukkan bahwa sedimen yang berasal dari lumpur Sidoarjo umumnya seragam dan didominasi berupa smectite. Berbeda dengan sedimen sungai, hasil SEM yang diperoleh dari sampel laut yang menunjukkan sedimennya beragam, berupa montmorilonite, kaolinite dan illite. Kata Kunci : Sedimen, Porong, lumpur Sidoarjo The Sidoarjo mudflow in the Porong area increases the functions of Porong River as media to drain the muds towards the sea, because the ability of embankments in the area as a barrier is very limited. This condition intends to determine the presence and distribution of sediment in rivers, estuaries and waters originating from the Lusi mudflow. The materials used in this study are the sediment sampling results as many as 30 samples taken from the river and off the river mouth and 30 samples of sea surface sediments in the surrounding waters. General distribution of sediments in the Porong River shows the form of mud sediments are generally found in the riverside and sandy sediment found in the middle of the river, while the distribution of sediments in waters Porong form of sand, clay and sandy silt clay. The results of microscopic and SEM analysis showed that the sediments derived from the Lusi mudflow found along Porong River till estuaries, but they have not reach surrounding water of Porong estuary. The Lusi sediment that reached the estuary Porong sized to 2.5 micron. General megascopic description show the shape of the Lusi sediment as sand-gravel is a flat-shaped (rounded - sub rounded). SEM results showed that the sediments derived from the Lusi is generally uniform and dominated by smectite. In contrast to stream sediments, the SEM results obtained from marine sediment samples show a variety of sediments, in the form of montmorillonite, caolinite and illite. Key words: Sediment, Porong, Sidoarjo, Mud Overflow (Lusi)

KAJIAN DINAMIKA PANTAI SELATAN BANYUWANGI BERDASARKAN HASIL PENAFSIRAN CITRA SATELIT LANDSAT TM

Hasil kajian citra satelit Landsat Thematic Mapper (TM) menunjukkan daerah pantai selatan Banyuwangi mempunyai empat karakteristik dinamika pantai, yaitu daerah akresi, terjadi di muara Sungai Gonggo, Sungai Baru, dan Sungai Pergaul yang terjadi karena tingginya aliran (run off) dari sungai. Daerah abrasi terjadi di Teluk Grajagan yang terjadi karena adanya arus menerus dari laut sehingga sedimen dari Segoro Anakan tidak bisa diendapkan di daerah teluk dan hanya di muka sungai. Daerah abrasi dan akresi terdapat di teluk Rajegwesi dan Pancamaya yang mempunyai daerah akresi di muara sungai dan daerah abrasi di bagian sisi teluknya. Daerah stabil, terdapat di daerah-daerah yang menjorok ke laut dan sepanjang pantai Alas Purwo. Daerah akresi maupun abrasi umumnya terjadi di daerah topografi rendah, landai dan berupa aluvium, sedangkan daerah stabil terdapat pada daerah dengan topografi bertebing dan batuan penyusun berupa batuan keras. Kata kunci : sedimen, dinamika pantai, Landsat TM, pantai selatan Banyuwangi The result of the assesment of Landsat TM imageries show that the coastal area of south Banyuwangi have four coastal dynamic characteristics those are: accretion, abrasion, accretion and abrasion, and stable areas. Accretion area, is located in the river estuary of Gonggo, Baru, and Pergaul rivers that occur by run off from river. Abrasion area, is located in Grajagan Bay caused by continuous current from the sea so that the sediment from Segoro Anakan cannot precipitate in the bay area but only in the river mouth. Abrasion and accretion areas are located in Rajegwesi and Pancamaya Bays where the accretion area is in a river estuary but the abrasion area is in the side shares of the bay. Stable area is located in the peninsula area and along the Alas Purwo coast. Generally the accretion or abrasion areas were occurred in low relief topography and occupied by alluvium, whereas the stable area is characterized by the high relief topography consisting of hard rock. Key words: sediment, coastal dynamic, Landsat TM, south coast of Banyuwangi.

Une contribution pratique à l'estimation du transport des sédiments dans un écoulement fluvial

Several computational methods of sediment discharge in open channel flows are reported in the existing literature. However, sediment transport is a complex procedure that implies several parameters which in some cases are difficult to estimate. Even if direct confrontations of methods used are published, it is difficult to draw significant conclusions that would help determine a model or the models likely to produce the best results for a specific case. To facilitate that choice, the authors have attempted to establish a classification of the various methods commonly used by determining their relative performance, and to improve the performance by proposing a new model which distinguishes the type of sediment transport and the nature of the bed. Key words: sediment discharge, sediment transport, open channel flow, model, performance.[Journal translation]

Studies on the Sediment of St. Margaret's Bay, Nova Scotia

A detailed examination of the sediment in a small area of St. Margaret's Bay revealed it to be composed of two main types of particles, mineral particles and particles of organic debris. Debris was also adsorbed onto the mineral particles. Particles generally had relatively low numbers of bacteria associated with them indicating that most of the organic carbon in the sediment is refractory. Variation in size distribution of the component particles with depth in the sediment was found to be minimal, but a slight decrease in the proportion of debris particles was seen. Variation in size distribution along a transect was also limited, but where the mineral particles became coarser the size range of the debris particles remained constant. The relative amount of debris particles along the transect varied little but values for total organic carbon (by weight) changed dramatically. Key words: sediment, particle composition, size distribution, organic carbon

The Intrusion of Fine Sediments into a Stable Gravel Bed

A rectangular flume was used to study variables affecting the intrusion of fine sands into a stable gravel streambed. The amount of intrusion by sand (median particle diameter 0.5 mm) was determined under varied conditions of discharge, depth, velocity, flume slope, and rates of sediment transport. During all experimental tests, sand particles were trapped in voids within the upper 10 cm of an initially clean gravel bed (median particle diameter 15 mm), forming a barrier to further intrusion. An analysis of flow variables showed that flow conditions, as indexed by Froude number, significantly (90% confidence level) affected intrusion amounts, possibly by influencing the rate and depth of formation of the sand seal. Intrusion amounts, expressed as a percent of total volume, varied from 2 to 8%. Two replications used a finer grade sand (median particle diameter 0.2 mm) that intruded more and, in one case, completely filled the gravel pore space (25% by volume), further indicating that particle size, and not hydraulic variables, may have a more important influence on the total amount of intrusion. Key words: sediment transport, intrusion, streambed, substrates, riffles, sedimentation

Importance of Sediment Working by the Deposit-Feeding Polychaete Arenicola marina on the Weathering Rate of Sediment-Bound Oil

The interactions between the polychaete Arenicola marina, a common deposit feeder in sandy intertidal areas, and sediment contaminated with the fresh API (American Petroleum Institute) reference oils and weathered Bunker C oil remaining from the 1970 Arrow spill were investigated in laboratory experiments. Worms can tolerate low concentrations of sediment-bound oil, although the sediment working rate is reduced depending upon oil type, concentration, and degree of weathering. Hydrocarbon concentrations, measured gravimetrically and by gas chromatography and fluorescence spectroscopy, were substantially lower (17–72%) in worm casts than in initial sediment. This loss can be accounted for by microbial degradation, which is stimulated by the worms' activity, uptake of hydrocarbons into worms, and perhaps dissolution. A large population (10–25/m2) of Arenicola is present at Black Duck Cove, N.S., living in sediment contaminated with weathered Bunker C oil remaining from the Arrow spill. These worms, which have spent their entire lives in oil-polluted sediment, do not have markedly elevated hydrocarbon concentrations and behaved no differently in experiments than worms collected from a clean environment. Calculations suggest that they are capable of removing the oil present in a square metre of sediment in 2–4 yr. After any oil spill, when concentrations reach tolerable levels, activities of deposit-feeding animals such as Arenicola can apparently accelerate the weathering rate of sediment-bound oil. Key words: sediment, Arenicola marina, polychaete, petroleum, weathering rate, pollution, hydrocarbon