ANALISIS LONGSOR DI SUNGAI CIPUNAGARA SUBANG DAN DESAIN PENANGANNYA

Abstract

ABSTRAKS

Pada hari Jumat 18 desember 2015 telah terjadi longsoran pada tebing sungai Cipunagara Desa Pesanggrahan, Kecamatan Kasomalang, Subang. Longsor menyebabkan rusaknya lahan pertanian dan membendung sungai sehingga banyak ikan di kolam mati. Penelitian ini bertujuan untuk menganalisis penyebab longsor dan menentukan metode penanganannya. Lokasi longsor mempunyai karakteristik material tanah berupa material lepas. Longsoran terjadi pada tebing sungai dengan kemiringan lereng 1:1. Pemicu longsoran diindikasikan karena daerah tersebut merupakan zona infiltrasi air dari saluran irigasi, hujan, genangan sawah, dan juga karena erosi pada tebing sungai. Berdasarkan faktor penyebab longsor maka untuk menjaga agar diperoleh lereng yang stabil, disampaikan 5 (lima) rekomendasi yaitu membuat saluran irigasi kedap air, membuat area pertanian kering, membuat struktur penguat tebing/pengarah aliran sungai (krib), membuat subsurface drainase. Pada lokasi longsor perlu dibuat terasering. Perlu dilakukan usaha mencegah longsor pada lokasi lain yang berpotensi longsor dengan mencegah terjadinya infiltrasi air permukaan ke dalam tanah. Dari analisis stabilitas lereng, nilai FS = 0,306 dan apabila dilakukan penguatan tebing maka nilai FS= 1,022

Kata kunci: Longsoran, Infiltrasi, Stabilitas Lereng, Subsurface Drainase

ABSTRACT

On Friday, December 18^th 2015, a landslide occurred in the Cipunagara River in the Pesanggrahan Village, Kasomalang District, Subang Regency. Landslides cause damage on agricultural land and dammed the river causing plenty of fishes in the pond dead. The aim of this study is to analyze the causes of landslides and determine mitigations methods that need to be applied. The landslide in the area is contained and formed by loose materials as its characteristics. Landslide occurred on the river bank having 1:1 slope. The triggers of the landslide are excessive water as it infiltrate the area through flowing water from irrigation canals. The second cause was rainfall, a puddle of paddy fields, and also the erosion in the river banks cutting the lower part of the hill. Based on the causing factors, to increase slope stability, there is five (5) recommendations which are to create the impermeable for irrigation channels, make the dry farming area, construct gabion to slope strengthness, arrange directional flow of the river (crib), and create a subsurface drainage. At the location of landslide, it is needed also to make some terraces. Also, to prevent landslides in other locations, we need to prevent water infiltration into the soil. Furthermore, from the slope stability analysis before the occurrence, we have the value of FS = 0.306 and after making the slope stronger by (gabion), the value of FS becoming = 1.022

Keywords: Landslide, Infiltration, Slope Stability, Subsurface Drainage