RAHMA, Sukma Laksita and Sunarsih, Sunarsih and Mussadun, Mussadun (2023) EVALUASI KAPASITAS DEBIT SALURAN DRAINASE UNTUK MITIGASI BANJIR DI WILAYAH PERKOTAAN KECAMATAN NGANJUK, PROVINSI JAWA TIMUR. Masters thesis, UNIVERSITAS DIPONEGORO.

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Abstract

Kabupaten Nganjuk merupakan salah satu kabupaten yang terdampak banjir selama tahun 2019 hingga 2022. Kecamatan Nganjuk adalah ibukota kabupaten yang berada dalam kategori kerentanan sedang terhadap bencana banjir. Bencana banjir di wilayah perkotaan Kecamatan Nganjuk merendam jalan protokol, pasar, rumah sakit, sekolah, pemukiman, hingga perkantoran setinggi 20-30 cm. Salah satu penyebab terjadinya banjir tersebut adalah saluran drainase yang tersumbat sampah dan sedimen. Beberapa upaya pengurangan risiko banjir telah dilakukan pemerintah, namun belum efektif sehingga perlu adanya penelitian untuk mengetahui apakah kapasitas debit saluran drainase eksisting sudah sesuai dengan debit rencana dan bagaimana mitigasi banjir akibat ketidaksesuaian antara kapasitas debit saluran dan debit rencana. Wilayah penelitian meliputi empat Daerah Tangkapan Air (DTA), yaitu DTA Maria, Kuncir Kanan, Asri, dan Kuncir Kiri. Penelitian dilakukan melalui observasi lapangan dan kunjungan instansi. Analisis yang digunakan meliputi perhitungan debit rencana, perhitungan debit saluran drainase eksisting, evaluasi kapasitas debit saluran eksisting, dan penyusunan mitigasi banjir. Data curah hujan yang digunakan dalam analisis merupakan curah hujan harian maksimum selama 15 tahun terakhir dari tujuh stasiun penakar hujan. Debit rencana dihitung menggunakan Metode Rasional dan debit saluran eksisting menggunakan Persamaan Manning. Hasil perhitungan menunjukkan bahwa 66.187% saluran drainase eksisting memiliki kapasitas debit sesuai dengan debit rencana periode ulang 10 tahun. Debit saluran drainase eksisting bagian hilir DTA Maria saluran 68-72 (19.547 m3/detik) mampu menampung debit rencana periode ulang 10 tahun (6.201 m3/detik). Sedangkan saluran drainase bagian hilir DTA Asri saluran 162-163 (5.217 m3/detik) tidak mampu menampung debit rencana (9.506 m3/detik). Beberapa upaya yang dapat diterapkan di wilayah penelitian untuk mengurangi risiko banjir dibedakan berdasarkan masing-masing daerah tangkapan air. Upaya tersebut antara lain melalui normalisasi saluran drainase, penggunaan biopori, connecting embung Roro Suratmi dengan saluran drainase primer Asri, optimalisasi TPA, serta penyusunan regulasi dan kebijakan tentang upaya pencegahan banjir perkotaan.
Kata kunci: banjir perkotaan, debit rencana, debit saluran eksisting, mitigasi

Nganjuk Regency is one of the districts affected by flooding from 2019 to 2022. Nganjuk District is the capital of the district, which is in the category of medium vulnerability to flood disasters. The flood disaster in the urban area of Nganjuk District submerged main roads, markets, hospitals, schools, residential areas, and offices as high as 20–30 cm. One of the causes of flooding is drainage channels that are clogged with rubbish and sediment. The government has made several efforts to reduce flood risk, but they have not been effective, so research is needed to find out whether the discharge capacity of existing drainage channels is in accordance with the planned discharge and how to mitigate flooding due to a mismatch between the channel discharge capacity and the planned discharge. The research area covers four water catchment areas (DTA), namely Maria, Kuncir Kanan, Asri, and Kuncir Kiri catchments. Research was carried out through field observations and agency visits. The analysis used includes calculating the planned discharge, calculating the discharge of the existing drainage channel, evaluating the discharge capacity of the existing channel, and preparing flood mitigation. The rainfall data used in the analysis is the maximum daily rainfall for the last 15 years from seven rain measuring stations. The planned discharge is calculated using the Rational Method, and the existing channel discharge is calculated using the Manning Equation. The calculation results show that 66.187% of existing drainage channels have a discharge capacity in accordance with the planned discharge for a 10-year return period. The discharge of the existing drainage channel downstream of the Maria DTA channel 68-72 (19.547 m3/second) is able to accommodate the planned discharge for the 10-year return period (6.201 m3/second). Meanwhile, the downstream drainage channel of the Asri DTA channel 162-163 (5.217 m3/second) is unable to accommodate the planned discharge (9.506 m3/second). Several efforts that can be implemented in the research area to reduce flood risk are differentiated based on each water catchment area. These efforts include normalizing drainage channels, using biopores, connecting the Roro Suratmi embung with the Asri primary drainage channel, optimizing landfills, and preparing regulations and policies regarding efforts to prevent urban flooding.
Key words: existing channel discharge, mitigation, planned discharge, urban flooding

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