Rifai

Rahman Rifai 2009

Spatial Modeling and Element at Risk Assement of Sidoarjo Mud ...

Spatial Modeling And Element At Risk Assement Of Sidoarjo Mud Volcanic Flow

On 29 may 2006 mud volcano occurred in Sidoarjo-east java 23 km south of Surabaya. This is a geological phenomenon due to over-pressurized sub-surface mud layers. This muderuption appears to have been triggered by drilling of over-pressured porous and permeable limestone at a depth 0f -2830 m below the surface (Davies, 2007). The discharge is very high with a rate of 7 /000 – 115,000 m3 / day, and has inundated 4 adjacent villages and so far 7000 people have displaced (UNDAC/ July 2006). In June 2006 the government built a dike around the centre of eruption to protect the surrounding environment from flood and inundation. Today more than 12 month after the start of the eruption, the mud volcano remains have high flow rates. This condition is very dangerous because if the dike breaks or the mud overtops, a wider area has high risk of being flooded by the mud. To better understand which areas might be at risk or being flooded due by the mud, a prediction tool is needed to simulate the mudflow. Simulation of the inundation might be used for predicting what will happen in the future to know where inundation will takes place in certain time to come. If one then knows what elements are at risk of being flooded and if the vulnerability of the area is known, element at risk assessment can be done. Quantification of element at risk is needed as input for preparation, evacuation, rehabilitation and reconstruction. In this study, a 1D2D hydrodynamic model using SOBEK was implemented to create mud flow modeling. In the modeling approach five time scenarios of mud flow was generated represent five different condition of flowing of the mud. Four time scenarios were represented four times the dike break and one time scenario to represents the prediction of inundation without the dike. The scenarios have been implemented also used to test the behavior of mud flow compared with waterflood using SOBEK, since this software is designed to model waterflood. The model result mostly give 40% agreement on the inundation extent. This result was achieved by comparing the inundation extent from the model with inundation extent from recorded event which was captured in the IKONOS image. The model also has output of inundation depth, but the result only gives 15%. These probably because of the SOBEK do not include of rheological properties of the mud such as viscosity, and land subsidence which was occurred in the study area. The land subsidence factor was ignored in this study because the magnitude and direction of land subsidence have spatial and temporal variations. The element at risk assessment also be done is this study by analyzing the result of inundation extent and integrate with element at risk. The information of elements at risk was calculated from topographic map and IKONOS imagery.