PERBANDINGAN MODEL UNSTEADY DAN STEADY FLOW ALIRAN BANJIR SUNGAI WAY LAALA SEBAGAI DASAR SOLUSI PENANGANAN PASCA BENCANA

Abstract

Abstrak:Tujuan Penelitian ini memberikan acuan dasar pemilihan solusi pengendalian banjir dengan melakukan perbandingan permodelan aliran banjir unsteady flow dan steady flow. Metode analisis data hidrologi menggunakan software HEC-HMS serta hidraulika dengan software HEC-RAS 5.0.7. Perhitungan curah hujan rata-rata wilayah diambil dari data hujan BMKG, Kairatu dan diperoleh hasil 144,69 mm. Sedangkan untuk perhitungan hujan rencana digunakan metode distribusi Log Person Tipe III dan didapatkan curah hujan rencana 25 tahun sebesar 290,46 mm. Keabsahan data hujan diuji dengan Smirnov-Kolmogorov dan Chi Kuadrat. Analisis hidrologi menggunakan program bantu HEC-HMS dan Microsoft excel 2019 dengan membandingkan 3 metode hidrograf satuan sintetik. Hidrograf dibandingkan antara metode SCS, Snyder, dan Nakayasu dengan data kondisi dilapangan saat permodelan banjir untuk kalibrasi data. Hasil permodelan HEC-HMS didapat nilai debit puncak metode SCS sebesar 42,9 m3/s, dan metode Snyder sebesar 60,8 m3/s, sedangkan hasil perhitungan dengan ms. Excel 2019 metode Nakayasu didapat nilai debit puncak sebesar 158 m3/s. Analisa hidraulika menggunakan program bantu HEC-RAS 5.0.7 membutuhkan data berupa cross section, long section, data terrain, serta data hidrograf kala ulang 25 tahun hasil permodelan HEC-HMS metode Nakayasu. Analisis HEC-RAS dibandingkan antara model aliran steady flow dan model unsteady flow. Dari HEC-RAS didapatkan hasil bahwa kondisi Sungai Way Laala terjadi overtopping setinggi 0.5 – 1 m pada aliran steady flow dan menggenang permukiman warga di Desa Loki pada simulasi unsteady flow. Hasil permodelan HEC-RAS menunjukan bahwa profil elevasi muka air rata-rata dari permodelan steady flow lebih tinggi dari elevasi yang dihasilkan permodelan unsteady flow. Elevasi muka air rata-rata permodelan steady flow sebesar + 30.519 m, sedangkan untuk permodelan unsteady flow sebesar + 29.849 m. selain itu kecepatan aliran permodelan steady flow juga cenderung lebih tinggi daripada model unsteady flow. Kecepatan rata-rata model Steay flow diperoleh nilai sebesar 2,791 m/s, sedangkan pada model unsteady diperoleh nilai 2,025 m/s.

Kata-kata kunci: debit banjir, pengendalian banjir, unsteady flow, steady flow, Sungai Way Laala

Abstract: The purpose of this study is to provide a basic reference for selecting flood control solutions by comparing unsteady flow and steady flow flood flow models. Hydrological data analysis method using HEC-HMS software and hydraulics with HEC-RAS 5.0.7 software. The calculation of the regional average rainfall was taken from BMKG, Kairatu rain data and the result was 144.69 mm. Meanwhile, for the calculation of the planned rainfall, the Log Person Type III distribution method was used and the 25-year planned rainfall was 290.46 mm. The validity of the rain data was tested with Smirnov-Kolmogorov and Chi Square. Hydrological analysis used the HEC-HMS and Microsoft excel 2019 programs by comparing 3 synthetic unit hydrograph methods. Hydrographs are compared between the SCS, Snyder, and Nakayasu methods with field condition data during flood modeling for data calibration. The results of the HEC-HMS modeling show that the peak discharge value of the SCS method is 42.9 m3/s, and the Snyder method is 60.8 m3/s, while the calculation results with ms. The Excel 2019 Nakayasu method obtained a peak discharge value of 158 m3/s. Hydraulic analysis using the HEC-RAS 5.0.7 program requires data in the form of cross sections, long sections, terrain data, and 25 year return period hydrograph data from the HEC-HMS Nakayasu modeling method. The HEC-RAS analysis was compared between the steady flow model and the unsteady flow model. From the HEC-RAS, it was found that the Way Laala River was overtopped as high as 0.5 – 1 m in steady flow and inundated residents’ settlements in Loki Village in the unsteady flow simulation. The HEC-RAS modeling results show that the average water level profile of the steady flow model is higher than the elevation produced by the unsteady flow model. The average water level for the steady flow model is + 30,519 m, while for the unsteady flow model it is + 29,849 m. besides that the flow velocity of the steady flow model also tends to be higher than the unsteady flow model. The average speed of the Steay flow model is 2.791 m/s, while the unsteady model is 2.025 m/s.

Keywords: flood discharge, flood control, unsteady flow, steady flow, Way Laala River