Perubahan Morfologi Sungai Porong Berdasarkan Karakteristik Sedimen Dan Fluktuasi Aliran Akibat Perubahan Musim (Studi Kasus: Lusi Sebagai Sumber Sedimen Tambahan)

Yanti, Rossana Margaret Kadar (2026) Perubahan Morfologi Sungai Porong Berdasarkan Karakteristik Sedimen Dan Fluktuasi Aliran Akibat Perubahan Musim (Studi Kasus: Lusi Sebagai Sumber Sedimen Tambahan). Doctoral thesis, Institut Teknologi Sepuluh Nopember.

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Abstract

Sungai Porong dipengaruhi oleh fluktuasi hidrodinamika akibat perubahan musim dan suplai sedimen tambahan dari pipa buangan Lumpur Sidoarjo (LUSI). Penambahan sedimen tersebut mengubah keseimbangan antara kapasitas angkut aliran (transport capacity) dan ketersediaan sedimen (sediment supply), sehingga memengaruhi distribusi sedimen, mekanisme transpor sedimen, dan perubahan morfologi sungai. Penelitian ini bertujuan menganalisis pengaruh variasi hidrodinamika musiman dan suplai sedimen LUSI terhadap distribusi sedimen, mekanisme transpor sedimen, serta perubahan morfologi Sungai Porong. Penelitian dilakukan melalui pengamatan lapangan setiap bulan selama satu tahun pada sembilan stasiun pengamatan. Parameter yang diamati meliputi kedalaman dan kecepatan aliran, konsentrasi sedimen tersuspensi (Suspended Sediment Concentration, SSC), karakteristik sedimen dasar, sediment core, dan Sub-Bottom Profiler (SBP). Data lapangan dianalisis secara statistik dan diintegrasikan dengan hasil sediment core, SBP, serta simulasi numerik menggunakan Delft3D. Hasil penelitian menunjukkan bahwa variasi musim mengontrol kondisi hidrodinamika melalui perubahan kedalaman aliran hingga 3,8 m, kecepatan aliran dari 0,04–0,72 m/det, tegangan geser dasar hasil pengamatan lapangan sebesar 5,59–394,91 N/m², dan unit stream power sebesar 0,134–13,503 W/m². Perubahan tersebut mengendalikan kapasitas angkut sedimen sehingga pada kondisi berenergi tinggi sedimen mengalami transport dan redistribusi ke arah hilir, sedangkan pada kondisi berenergi rendah sedimen terakumulasi dan mengalami deposisi di sekitar groundsill. Saat LUSI beroperasi, SSC di sekitar STA 2+775 mencapai 8,403 kg/m³ dan menurun menjadi 0,193–0,221 kg/m³ pada segmen hilir akibat proses transport, pencampuran, dan deposisi, disertai perubahan ukuran butir median (d₅₀) dari 0,001–0,002 mm menjadi 0,120–0,250 mm yang menunjukkan berlangsungnya hydraulic sorting. Mekanisme transport sedimen berkembang melalui siklus erosi, penyimpanan sementara, remobilisasi, dan deposisi yang dikendalikan oleh interaksi antara kapasitas angkut, suplai sedimen, dan kontrol hidraulik groundsill. Hasil simulasi menunjukkan bahwa keberadaan LUSI mengubah respons morfologi pada STA 2+775 dari erosi sebesar −0,085 m menjadi deposisi sebesar +0,095 m (Δ perubahan morfologi 0,180 m), sedangkan segmen tengah hingga hilir mengalami peningkatan deposisi sebesar 300–510% dibandingkan kondisi tanpa LUSI. Penelitian ini menunjukkan bahwa perubahan morfologi Sungai Porong dikendalikan oleh keseimbangan dinamis antara kapasitas angkut aliran, suplai sedimen, dan groundsill sebagai local morphodynamic control, yang mengatur penyimpanan sementara, remobilisasi, dan redistribusi sedimen sepanjang sungai.
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The Porong River is influenced by hydrodynamic fluctuations caused by seasonal changes and additional sediment supplied from the Sidoarjo Mudflow (LUSI) outfall. The addition of sediment shifts the balance between transport capacity and sediment supply, affecting sediment distribution, transport mechanisms, and river morphology. This study analyses the impact of seasonal hydrodynamic variations and LUSI on sediment distribution, transport mechanisms, and morphological changes in the Porong River. The study was conducted through monthly field observations over one year at nine observation stations. The observed parameters include flow depth, velocity, suspended sediment concentration (SSC), bed sediment characteristics, sediment cores, and Sub-Bottom Profilers (SBP). Field data were statistically analysed and integrated with results from sediment cores, sediment bathymetry profiles (SBP), and numerical simulations using Delft3D. The study results indicate that seasonal variations significantly influence hydrodynamic conditions. These variations caused changes in flow depth, which can reach up to 3.8 meters; flow velocity ranging from 0.04 to 0.72 meters per second; bed shear stress observed in the field between 5.59 and 394.91 N/m²; and unit stream power varying from 0.134 to 13.503 W/m². These changes control the sediment transport capacity. Under high-energy conditions, sediment is transported and redistributed downstream, while under low-energy conditions, sediment accumulates and deposits around the groundsill. When LUSI operates, the SSC around STA 2+775 reaches 8.403 kg/m³ and decreases to 0.193–0.221 kg/m³ in the downstream segment due to the processes of transport, mixing, and deposition, accompanied by a change in the median grain size (d₅₀) from 0.001–0.002 mm to 0.120–0.250 mm, indicating continued hydraulic sorting. The sediment transport mechanism works through a cycle of erosion, temporary storage, remobilisation, and deposition, controlled by the interaction among transport capacity, sediment supply, and the hydraulic control exerted by the groundsill. Simulation results show that the LUSI changed the morphological response at STA 2+775 from erosion of −0.085 m to deposition of +0.095 m (Δ morphological change of 0.180 m). At the same time, the middle- to downstream segments experienced a 300–510% increase in deposition compared to conditions without LUSI. This study shows that the morphological changes of the Porong River are controlled by a dynamic balance between flow transport capacity, sediment supply, and groundsill as the local morphodynamic control, which regulates the temporary storage, remobilisation, and redistribution of sediment along the river.

Item Type:	Thesis (Doctoral)
Uncontrolled Keywords:	Groundsill, Hidrodinamika Musiman, Lumpur Sidoarjo (LUSI), Respons Morfodinamika, Sungai Porong. Groundsill, Seasonal Hydrodynamics, Sidoarjo Mud (LUSI), Morphodynamic Response, Sungai Porong.
Subjects:	Q Science > QE Geology > QE571 Sedimentation and deposition. Sediment transport. Erosion.
Divisions:	Faculty of Civil, Planning, and Geo Engineering (CIVPLAN) > Civil Engineering > 22001-(S3) PhD Thesis
Depositing User:	Rossana Margaret Kadar Yanti
Date Deposited:	04 Aug 2026 04:17
Last Modified:	04 Aug 2026 04:17
URI:	http://repository.its.ac.id/id/eprint/142965

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