Analisis Perubahan Morfologi Sungai Tawing, Trenggalek, Jawa Timur Menggunakan HEC-RAS 2D

Sayoga, Rizqi Septian (2025) Analisis Perubahan Morfologi Sungai Tawing, Trenggalek, Jawa Timur Menggunakan HEC-RAS 2D. Diploma thesis, Institut Teknologi Sepuluh Nopember.

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Abstract

=Pengendapan sedimen secara masif di Sungai Tawing berpotensi mengubah alur sungai, merusak tebing, dan meningkatkan risiko banjir. Pemerintah merencanakan pembangunan bangunan pengendali banjir berupa retaining wall dan bronjong, namun konstruksi ini dapat memengaruhi dinamika aliran dan pola sedimentasi. Penelitian ini bertujuan menganalisis perubahan morfologi Sungai Tawing akibat pembangunan bangunan pengendali banjir dan mengevaluasi alternatif penanganan dengan pemodelan hidrodinamika dan angkutan sedimen menggunakan HEC-RAS 2D.
Analisis hidrologi dilakukan dengan metode Poligon Thiessen dan Hidrograf Satuan Sintetik (HSS) Nakayasu untuk menentukan debit rencana, dengan hasil Q50 sebesar 220,59 m³/detik. Kalibrasi debit menggunakan metode FJ Mock menunjukkan nilai NSE sebesar 0,90, yang mengindikasikan kinerja model sangat baik. Kalibrasi hidraulik menggunakan nilai koefisien Manning (n) sebesar 0,035 untuk daerah aliran sungai dan 0,025 untuk sungai utama menghasilkan akurasi tinggi, dengan perbedaan kecepatan maksimum antara simulasi dan pengukuran hanya 0,09 m/s masih dalam batas toleransi standar ±10–15%. Hasil simulasi menunjukkan bahwa kecepatan aliran meningkat dari 1,14 m/s menjadi 1,35 m/s pascaproyek, sehingga terjadi kenaikan sebesar 0,21 m/s yang berpotensi meningkatkan erosi, terutama pada belokan luar sungai.
Sebagai solusi teknis, dilakukan analisis efektivitas krib dengan dua variasi jarak (10,5 m dan 14 m) berdasarkan standar SNI 8453:2017. Hasil simulasi menunjukkan bahwa krib berjarak 10,5 m lebih efektif dalam menurunkan volume dan area erosi pada kondisi baseflow, yakni dari 19.076 m³ menjadi 12.169 m³ (penurunan ~36%) dan dari 0,419 km² menjadi 0,3987 km². Namun, pada debit ekstrem (Q50), krib dengan jarak 14 m justru memberikan pengurangan area erosi yang lebih signifikan, meskipun volume erosi masih cukup tinggi. Pola deposisi dominan terjadi pada belokan dalam akibat rendahnya kecepatan aliran dibanding kecepatan kritis sedimen. Secara keseluruhan, struktur krib terbukti efektif dalam mengelola dinamika sedimen dan memperbaiki stabilitas morfologi dasar sungai, terutama di segmen yang rawan degradasi akibat aliran ekstrem.
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Massive sediment deposition in the Tawing River has the potential to alter the river course, damage the banks, and increase the risk of flooding. The government plans to construct flood control structures in the form of retaining walls and gabions, but these structures may affect flow dynamics and sedimentation patterns. This study aims to analyze changes in the morphology of the Tawing River due to the construction of flood control structures and evaluate alternative management options using hydrodynamic modeling and sediment transport analysis with HEC-RAS 2D.
Hydrological analysis was conducted using the Thiessen Polygon method and Nakayasu's Synthetic Unit Hydrograph to determine the design flow rate, with a Q50 value of 220.59 m³/s. Flow rate calibration using the FJ Mock method yielded an NSE value of 0.90, indicating excellent model performance. Hydraulic calibration using Manning's coefficient (n) values of 0.035 for the river basin and 0.025 for the main river resulted in high accuracy, with a maximum velocity difference between simulation and measurement of only 0.09 m/s, still within the standard tolerance range of ±10–15%. Simulation results show that flow velocity increased from 1.14 m/s to 1.35 m/s post-project, resulting in an increase of 0.21 m/s, which has the potential to increase erosion, particularly at the outer bend of the river.
As a technical solution, an analysis of the effectiveness of the weir was conducted with two variations in distance (10.5 m and 14 m) based on the SNI 8453:2017 standard. Simulation results indicate that the 10.5 m spacing krib is more effective in reducing erosion volume and area under baseflow conditions, from 19,076 m³ to 12,169 m³ (a reduction of ~36%) and from 0.419 km² to 0.3987 km². However, under extreme flow conditions (Q50), the 14-meter spacing krib provided a more significant reduction in erosion area, although erosion volume remained relatively high. Dominant deposition patterns occurred at the inner bend due to the low flow velocity compared to the critical sediment velocity. Overall, the weir structure proved effective in managing sediment dynamics and improving the morphological stability of the riverbed, especially in segments prone to degradation due to extreme flows.

Item Type:	Thesis (Diploma)
Uncontrolled Keywords:	Morfologi sungai, sedimentasi, HEC-RAS 2D, erosi, krib. River morphology, sedimentation, HEC-RAS 2D, erosion, cribs.
Subjects:	T Technology > TC Hydraulic engineering. Ocean engineering > TC175.2 Sediment transport
Divisions:	Faculty of Vocational > Civil Infrastructure Engineering (D4)
Depositing User:	Rizqi Septian Sayoga
Date Deposited:	04 Aug 2025 01:35
Last Modified:	04 Aug 2025 01:35
URI:	http://repository.its.ac.id/id/eprint/126380

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