Pemodelan Efektivitas Hutan Pantai di Cagar Alam Pananjung Pangandaran Sebagai Buffer Tsunami

Abstract

Kawasan pantai selatan Jawa merupakan daerah pesisir yang rawan terjadi tsunami. Tahun 2006 tsunami dengan kekuatan gempa 6 skala Richter melanda daerah Pangandaran termasuk Cagar Alam Pananjung. Terdapatnya hutan pantai di Cagar Alam Pananjung mampu mereduksi kekuatan tsunami sehingga efek merusak tsunami dapat diminimalkan. Penelitian ini dilakukan dengan tujuan untuk memodelkan efektivitas hutan pantai Cagar Alam Pananjung Pangandaran sebagai buffer tsunami dengan berbagai faktor pereduksi tsunami. Nested sampling digunakan untuk pengambilan data karakteristik vegetasi dengan intensitas sampling 4%. Luas hutan pantai 38 ha, sehingga digunakan petak ukur sebanyak 38 petak ukur persegi dengan ukuran petak ukur untuk tumbuhan bawah 1 m x 1 m, semai 2 m x 2 m, sapihan 5 m x 5 m, tiang 10 m x 10 m, dan pohon 20 x 20 m. Petak ukur ditempatkan secara purposive dengan mempertimbangkan lokasi genangan tsunami dan kerapatan vegetasi. Kerapatan vegetasi dilakukan dengan analisis citra Sentinel 2-A tahun 2017. Efektifitas hutan pantai sebagai buffer tsunami dianalisis menggunakan persamaan matematis menggunakan konsep Harada dan Imamura (2003) dan dimodelkan dengan Spatial Multi Criteria Analysis (SMCA) dengan kriteria lebar hutan pantai, kerapatan vegetasi, diameter pohon, dan kerapatan tumbuhan bawah. Hasil penelitian menunjukkan nilai-nilai parameter hutan pantai pereduksi tsunami di Cagar Alam Pananjung berupa kerapatan vegetasi > 2000 ind/ha, rata-rata diameter pohon yaitu 15,94 cm, dan lebar hutan pantai antara 120– 325 m. Ketinggian tempat hutan pantai Cagar Alam Pananjung bergelombang antara 0–59 m dpl. Hasil pemodelan menunjukkan efektivitas hutan pantai Cagar Alam Pananjung sebagai buffer dalam meredam energi tsunami memiliki nilai reduksi sebesar 41,18%, sehingga termasuk kategori efektif. Effectiveness Model of Coastal Forest in Pananjung Nature Reserve, Pangandaran as Tsunami Buffer Abstract The southern coast of Java is a coastal area prone to tsunami. In 2006, a tsunami with a magnitude of 6 Richter scale happened in Pangandaran area including Pananjung Nature Reserve. The presence of coastal forest in the Pananjung Nature Reserve reduced the force of the tsunami so that the destructive effect of the tsunami can be minimized. This research aimed to model and assess the effectiveness of coastal forest in Pananjung Nature Reserve as a tsunami buffer. Nested sampling was used to collect vegetation data with 4% sampling intensity. Extensive coastal forest of 38 ha was measured in 38 square forest sample plots with the size of the plot for the understorey 1 mx 1 m, seedlings 2 m x 2 m, saplings 5 mx 5 m, poles 10 m x 10 m, and trees 20 x 20 m. The plots were located purposively by considering the location of tsunami inundation and vegetation density. The vegetation density was performed by image analysis of Sentinel 2-A2017. The effectiveness of coastal forests as tsunami buffers was analyzed using mathematical concepts according to Harada and Imamura (2003) and modeled with Spatial Multi Criteria Analysis (SMCA) with width coastal vegetation criteria, vegetation density, tree diameter, and density of understorey. The results showed that in Pananjung Nature Reserve has vegetation density > 2000 ind/ha, average tree diameter of 15.94 cm, and coastal forest width between 120 m - 325 m. Topography of coastal forest Pananjung Nature Reserve waved between 0 m asl - 59 m asl. It was found that the effectiveness of coastal forest Pananjung Nature Reserve in reducing energy tsunami was in the value of 41.18%, thus it was included in the effective category.