HYDRODYNAMIC MODELING FOR FLOOD HAZARD ASSESSMENT IN TELOMOYO CATCHMENT, CENTRAL JAVA, INDONESIA

FRIETA DAMAYANTI, S.Si, Dr. rer.nat. Djati Mardiatno, M.Si.

2011 | Tesis | S2 Geografi

Banjir merupakan bencana yang dapat menimpbulkan kerusakan parah di dataran banjir di hampir seluruh belahan dunia. Bencana banjir juga merupakan bencana dengan intensitas kejadian yang sangat tinggi dengan distribusi yang relatif luas sehingga manajemen risiko bencana banjir sangat diperlukan untuk dilaksanakan. Penilaian bahaya banjir merupakan langkah awal dalam rangkaian manajemen risiko bencana banjir. Model hidrodinamika telah menjadi alternative praktis dalam penilaian bahaya banjir karena dapat memberikan keuntungan dalam memprediksi kejadian banjir yang tidak pernah terjadi sebelumnya. Pemodelan ini membantu dalam memahami bahaya banjir dan merupakan alat yang juga berguna dalam melakukan tindakan mitigasi. Model banjir didasarkan pada empat kala ulang yang berbeda yaitu 2, 5, 10, dan 25 tahun. Model elevasi digital (DEM) merupakan komponen penting dalam pemodelan hydrodinamika. Analisis geostatistik digunakan dalam pembuatan DEM yang didasarkan pada interpolasi kriging. Model simple kriging dapat menghasilkan DEM dengan simpangan baku yang terkecil. Hasil pemodelan banjir menunjukkan bahwa banjir hanya menggenangi 15% derah penelitian, baik pada banjir dengan kala ulang 2 tahun maupun 25 tahun. Semakin besar kala ulang banjir, semakin luas genangan banjir. Kedalaman banjir hasil dari model dan data observasi menunjukkan perbedaan sebesar 35 cm. Tingkat kesalahan DEM hasil interpolasi sebesar 31 cm mempengaruhi akurasi model banjir, khususnya untuk kedalaman banjir sebesar 64 cm.

Flooding is considered as one of the most devastating events in many parts of the world. In terms of its frequency and distribution, river flooding remains as a frequent disaster that has to be faced by civilization in the floodplain. Due to the periodical occurrence and adverse impact that may be generated, flood risk management is necessary to conduct. Flood hazard assessment is the preliminary step in conducting the flood risk management. A coupled 1D2D hydrodynamic modeling has become a popular practical method in flood hazard assessment due to its advantage in predicting the flood events which did not occur in history. This modeling helps to understand the flood hazard and serves a tool which also useful in understanding the effect of mitigation measures. The flood model was based on four different retun periods (2 yr, 5 yr, 10 yr, and 25 yr). Digital elevation model (DEM) is substantially important in conducting such flood model. Geostatistical analysis was preferred to do DEM generation. Three interpolation methods were used in this study and the results were compared. The Simple Kriging was the best geostatistical predictor since it embedded the least SD, RMSE, and unbiased interpolation. The result of the flood model showed that the flood, either from low magnitude (2 yr) and high magnitude (25 yr) only inundated 15% of the study area. The positive relationship of the inundation area and flood magnitude was identified. The comparison of the flood model and the observed data in term of the flood depth showed 35 cm differences. The DEM error interpolation by 31 cm propagated in the flood modeling and doubled the error of the flood depth by 64 cm.

Kata Kunci : model hidrodinamika, DEM, kriging, bahaya banjir