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In 2009 typhoon Morakot with copious amounts of rainfall struck Taiwan and caused catastrophic disasters. Different disasters including flood, landslides, landslide dams and debris flow occurred in Siaolin Village. The extreme rainfall has changed the disaster type, from “single” type such as flood or debris flow into “compound” type. The so called “compound disaster” is defined as a disaster by which floods or sediment-related disasters of a large extent occur simultaneously or consecutively in an event at a site. What happened in Siaolin Village is a significant example. It challenges the present warning, forecasting and response system of debris flow. New concept and new procedure are necessary to cope with the compound disasters triggered by extreme heavy rainfall. The rainfall hydrograph shows long-duration, high-intensity, high-accumulation and large-extent characteristics. It suggests the correlation of each disaster type with the rainfall characteristics by reference to the report of eyewitness memory. The causality between those in Siaolin Village occurred disasters could then be deduced. In order to characterize the disaster and suggest a strategy, it is necessary to try to rebuild the temporal order and spatial distribution of the disaster processes. This paper describes briefly each single disaster, the relationship among those disasters and the approach to rebuild the disaster process by field investigation, topographic survey, sediment core analysis, experiments, numerical simulation and satellite image processing. The results serve to intensify the disaster prevention system of debris flow and shallow landslide which then could be applied to the warning system of deep-seated landslide and landslide dam. The derivative issues and the approach to compound disaster prevention are suggested. The related discussions, evaluation and assessment are also summarized as the reference of further tasks.

Typhoon Morakot accompanied strong southwesterly monsoonal flow brought extreme heavy rain over the southern half region of Taiwan in August 2009. The large extent, high intensity and long duration rainfall caused huge damage. The objectives of this paper are to evaluate the benefit of reconstruction and management for the main disaster catchment areas, to arrange the results of conservation management of the Soil and water Conservation Bureau in sediment-related disaster area and to review and amend those strategy and countermeasures. In response to the post-disaster reconstruction is necessary to grasp the change of the environment state and make a management process to follow the countermeasures and evaluate the risk. Settling basin, flood retaining zone are measures to protect the residents. The balance of sediment transport and the channel stability could be accelerated through dredging of unstable sediment. The recovery process of the disaster catchment areas struck by Typhoon Morakot could be proceed through the management.

type:text, Overpressure, fluid pressure higher than hydrostatic pressure, has developed below the middle Miocene formations in the north-central Western Foothills of Taiwan. To study the mechanism by which overpressure is generated and maintained in the Taiwan oil fields, we estimated the fluid pressure history and overpressure distribution by using a one-dimensional basin model incorporating laboratory-approximated hydraulic parameters. Transport properties of outcropping sedimentary rocks were measured at effective pressures of 5 to 200 MPa. All parameters showed apparent stratigraphic variation, decreasing with increasing burial depth. Permeability showed the strongest sensitivity to depth, decreasing by 6 orders of magnitude to 10-20 m2 at the bottom of the basin. A critical sealing layer was not identified in the geologic column. The basin model incorporates overburden loading due to sediment accumulation, aquathermal expansion of water, the dehydration reaction of expandable clay to nonexpandable clay, and oil generation. Predicted overpressure was generated dramatically from 3 Ma, when the accumulation rate increased rapidly as a result of tectonic collisions in the area. If we assume a fluid influx from the bottom of the basin, the predicted overpressure is consistent with the observed overpressure, implying that continuous inflow from depth, possibly along the décollement or normal faults, may be the main cause of overpressure generation in this area. Stratigraphic variation of transport properties, which decrease with depth, also influences overpressure trends in the Western Foothills, where overpressure is generated only in deeper horizons. The clay mineral distribution estimated by a kinetic smectite–illite dehydration model is consistent with the observed mineralogical data.

Overpressure, fluid pressure higher than hydrostatic pressure, has developed below the middle Miocene formations in the north-central Western Foothills of Taiwan. To study the mechanism by which overpressure is generated and maintained in the Taiwan oil fields, we estimated the fluid pressure history and overpressure distribution by using a one-dimensional basin model incorporating laboratory-approximated hydraulic parameters. Transport properties of outcropping sedimentary rocks were measured at effective pressures of 5 to 200 MPa. All parameters showed apparent stratigraphic variation, decreasing with increasing burial depth. Permeability showed the strongest sensitivity to depth, decreasing by 6 orders of magnitude to 10-20 m2 at the bottom of the basin. A critical sealing layer was not identified in the geologic column. The basin model incorporates overburden loading due to sediment accumulation, aquathermal expansion of water, the dehydration reaction of expandable clay to nonexpandable clay, and oil generation. Predicted overpressure was generated dramatically from 3 Ma, when the accumulation rate increased rapidly as a result of tectonic collisions in the area. If we assume a fluid influx from the bottom of the basin, the predicted overpressure is consistent with the observed overpressure, implying that continuous inflow from depth, possibly along the décollement or normal faults, may be the main cause of overpressure generation in this area. Stratigraphic variation of transport properties, which decrease with depth, also influences overpressure trends in the Western Foothills, where overpressure is generated only in deeper horizons. The clay mineral distribution estimated by a kinetic smectite–illite dehydration model is consistent with the observed mineralogical data.