Typhoon Mindulle Research Articles

Sustainability-Based Construction of the Restoration Projects for the Guguan Hydropower Station

In Taiwan, the Dajia River is one of the most important rivers that provides hydroelectric energy. A couple of well-operated hydropower stations have been placed in different sections of this river for several decades. The 921 earthquake that hit central Taiwan in 2000 and Typhoon Toraji that attacked this area in 2001 caused severe damage to almost all hydropower stations. To continue to provide sufficient power for the public, the restoration of these power stations is necessary. Taiwan Power Company (Taipower) was responsible for the restoration projects. The Guguan hydropower station, which could provide 212.8 MW power, is one of the most damaged power stations. The Guguan power station restoration project, executed by the New Asia Construction and Development Corporation (NA Corp.), was started in April 2002. During the project, a series of typhoons and heavy storms attacked central Taiwan between 2004 and 2007 (especially Typhoon Mindulle in 2004). Consequently, the restoration work was greatly hindered; in particular, there was massive groundwater leakage from all external walls of the tunnel and powerhouse structures. The maximum leakage of groundwater was up to 84 tons/min. This situation not only caused extreme difficulty that interrupted the restoration work but also made the construction site a dangerous environment to continue restoration or future operation. In addition, the construction facilities were damaged, resulting in suspension of the restoration work. For safety construction of the restoration work, a series of temporary protection structures/platforms and a large quantity of grouting work had been performed. This power station was well restored and engaged in commercial operation in October 2008. In this paper, the detailed working procedures of the safety construction methods are presented.

Typhoon impacts on chemical weathering source provenance of a High Standing Island watershed, Taiwan

Chemical weathering source provenance changes associated with Typhoon Mindulle (2004) were identified for the Choshui River Watershed in west-central Taiwan using radiogenic Sr isotope (87Sr/86Sr) and major ion chemistry analysis of water samples collected before, during, and following the storm event. Storm water sampling over 72h was conducted in 3h intervals, allowing for novel insight into weathering regime changes in response to intense rainfall events. Chemical weathering sources were determined to be bulk silicate and disseminated carbonate minerals at the surface and silicate contributions from deep thermal waters. Loss on ignition analysis of collected rock samples indicate disseminated carbonate can compose over 25% by weight of surface mineralogy, but typically makes up ∼2–3% of watershed rock. 87Sr/86Sr and major element molar ratios indicate that Typhoon Mindulle caused a weathering regime switch from normal flow incorporating a deep thermal signature to that of a system dominated by surface weathering. The data suggest release of silicate solute rich soil pore waters during storm events, creating a greater relative contribution of silicate weathering to the solute load during periods of increased precipitation and runoff. Partial depletion of this soil solute reservoir and possible erosion enhanced carbonate weathering lead to increased importance of carbonates to the weathering regime as the storm continues. Major ion data indicate that complex mica weathering (muscovite, biotite, illite, chlorite) may represent an important silicate weathering pathway in the watershed. Deep thermal waters represent an important contribution to river solutes during normal non-storm flow conditions. Sulfuric acid sourced from pyrite weathering is likely a major weathering agent in the Choshui River watershed.

Impact of catastrophic events on small mountainous rivers: Temporal and spatial variations in suspended- and dissolved-solid fluxes along the Choshui River, central western Taiwan, during typhoon Mindulle, July 2–6, 2004

Small mountainous rivers deliver disproportionately large quantities of suspended and dissolved solids to the global ocean, often in response to catastrophic events such as earthquakes or floods. Here we report on the impact of a major flood on the Choshui River, central-western Taiwan, generated by typhoon Mindulle, July 2–6, 2004, five years after the nearby Mw 7.6 Chichi earthquake. Water samples taken at 3-h intervals at three stations along main stem, as well as from two downriver tributaries, allow us to delineate the temporal and spatial variability in concentrations and fluxes of suspended and dissolved constituents within the middle and lower portions of the river in response to this flood. High suspended-sediment concentrations, some as high as 200g/l, reflected the rapid erosion of landslide scars and debris deposits generated by super-typhoon Herb in 1996 and the 1999 Chichi earthquake. Dissolved-solid and suspended-sediment discharges totaled 0.22 and 70million tons (mt), 50mt of which were discharged in just two days. Particulate organic carbon (POC) discharge, most of which was pre-modern in age, was 195,000t. More than half of the discharged water, POC and dissolved solids came from upriver, whereas about 70% of the suspended sediment and 60% of the dissolved nitrate came from two downriver tributaries, the Chenyoulan and Qingshui rivers. Spatial and temporal differences in the character and discharge of suspended and dissolved solids within and between rivers in the Choshui drainage basin reflect different geologies, landslide histories, the effects of human impact, and the abrupt draining of the Tsaoling landslide lake in the Qingshui basin, as well as the possible shifting of importance of groundwater vs. overland flow. Neither wind-blown pollutants nor sea salts appear to have contributed significantly to dissolved solid character or discharge. Sediment contribution from the landslides in the Chenyoulan basin generated by super-typhoon Herb and reactivated by the Chichi earthquake declined during Mindulle. In contrast, sediment erosion and discharge from the Qingshui basin, derived primarily from landslides generated during the Chichi earthquake and reactivated during Mindulle, remained elevated for several more years.

A case study of typhoon‐induced gravity waves and the orographic impacts related to Typhoon Mindulle (2004) over Taiwan

AbstractAtmospheric gravity waves (GWs) significantly influence global circulation. Deep convection, particularly that associated with typhoons, is believed to be an important source of gravity waves. Stratospheric gravity waves induced by Typhoon Mindulle (2004) were detected by the Atmospheric Infrared Sounder (AIRS). Semicircular GWs with horizontal wavelengths of 100–400 km were found over Taiwan through an inspection of AIRS radiances at 4.3 μm. Characteristics of the stratospheric gravity waves generated by Typhoon Mindulle were investigated using the Weather Research and Forecasting (WRF) model. The initial and boundary data were determined by the high‐resolution European Center for Medium‐Range Weather Forecasts reanalysis data. The WRF simulation reproduces the main features of Typhoon Mindulle and the significant GWs. The simulated GWs with horizontal wavelengths of 100–400 km match the AIRS observations: they propagate upward and eastward, and the westward components are mostly filtered in the stratosphere. By comparing the measured waves with a WRF simulation in the absent of orography (WRF‐FLAT), we find that the orographic gravity waves (OGWs) generated by the flow of Typhoon Mindulle over the Central Mountain Range (CMR) in Taiwan account for approximately 50% of the total wave momentum flux in the troposphere. The dominant orientation of the OGW wave fronts is parallel to the CMR rideline. When entering into the stratosphere, OGW propagation is determined by the position of the typhoon center relative to the CMR.

Temporal and spatial responses of river discharge to tectonic and climatic perturbations: Choshui River, Taiwan, and Typhoon Mindulle (2004)

Abstract. One reason that small mountainous rivers discharge disproportionately large quantities of sediment to the coastal ocean is because they are particularly susceptible to short-term episodic events, such as earthquakes and floods. The impact of such events, both temporally and spatially, however, has seldom been monitored. Here we report on the results of probably the most thorough monitoring of a flood ever undertaken: the effect of Typhoon Mindulle (2–4 July 2004) on the character of the water transported by the Choshui River, central western Taiwan, during which 74 million tons of sediment were discharged to the adjacent Taiwan Strait. Results from a series of 113 water samples obtained between 2nd and 4th July from five stations along the middle and lower reaches the river indicate that more than half of the suspended sediment was generated in nearby mountains before the river reached its flood plain. While the concentration of dissolved solids remained more or less constant along the mainstem of the river, the composition changed considerably, reflecting the imprints of local geology. An order-of-magnitude downstream increase in NO3− concentrations reflects the rapid draining of the Tsaoling landslide lake on the Chingshui River, as the 1999 earthquake-generated landslide dam was breached.

An index to describe the earthquake effect on subsequent landslides in Central Taiwan

Chelungpu fault reactivation produced the 1999 Chi-Chi earthquake in Central Taiwan in 1999, triggering many landslides over a broad area. The ground damage caused by the Chi-Chi earthquake still influences successive rainfall-triggered landslides. The landslide distribution triggered by heavy rainfall during typhoon Mindulle in 2004 has a high correlation to the landslide sites triggered by the previous Chi-Chi earthquake. This research calculated and ordered landslide data for both the area and distance from the Chelungpu fault. The rank correlation coefficient for measuring two covarying variables is employed to quantify the degree of correlation between the landslide distribution and the Chelungpu fault. A high rank correlation coefficient value demonstrates a highly correlated relationship between the subsequent landslides in 2004 and previous Chelungpu fault activity in 1999.

Topographic Correction of Wind-Driven Rainfall for Landslide Analysis in Central Taiwan with Validation from Aerial and Satellite Optical Images

Rainfall intensity plays an important role in landslide prediction especially in mountain areas. However, the rainfall intensity of a location is usually interpolated from rainfall recorded at nearby gauges without considering any possible effects of topographic slopes. In order to obtain reliable rainfall intensity for disaster mitigation, this study proposes a rainfall-vector projection method for topographic-corrected rainfall. The topographic-corrected rainfall is derived from wind speed, terminal velocity of raindrops, and topographical factors from digital terrain model. In addition, scatter plot was used to present landslide distribution with two triggering factors and kernel density analysis is adopted to enhance the perception of the distribution. Numerical analysis is conducted for a historic event, typhoon Mindulle, which occurred in 2004, in a location in central Taiwan. The largest correction reaches 11%, which indicates that topographic correction is significant. The corrected rainfall distribution is then applied to the analysis of landslide triggering factors. The result with corrected rainfall distribution provides better agreement with the actual landslide occurrence than the result without correction.

Assessing impact of Natural Disasters on Tourist Arrivals: The Case of Xitou Nature Education Area (XNEA), Taiwan

Tourist arrivals represent popularity of a recreation site. However it could be changed due to accessibility, weather, and natural disaster. These factors are complex and their effects on tourist arrival are mixed. This study applies switching regression approach to assess impact of natural disasters on tourist arrivals in the popular forest recreation and education site, Xitou Nature Education Area (XNEA), Taiwan. Natural disaster in a tourist destination cause environmental changes which impact short- and long-term changes on tourist arrivals. Precisely estimating the impacts on tourist arrivals could therefore provide an insight to management. The results show that (1) Typhoon Herb reduced tourist arrivals by an estimated 530 thousand over three years; (2) the Chichi earthquake caused a 2.59 million loss in tourist arrivals over seven years; (3) Typhoons Toraji and Nari resulted in a 360 thousand reduction in tourist arrivals over three years; and (4) Typhoon Mindulle reduced tourist arrivals by 80 thousand over a one-year period.

Landslide-induced levee failure by high concentrated sediment flow — A case of Shan-An levee at Chenyulan River, Taiwan

Typhoon Mindulle struck northeast Taiwan on July 2, 2004, and brought an abundant air current in the following days that caused serious flood disasters to the mountainous areas in central Taiwan. One of sever flood events during Typhoon Mindulle was about hundreds of hectares of farmland loss induced by an 1620 m break of Shan-An levee at the Chenyulan River. This paper examines the nature and causes of Shan-An flood by integrating catastrophic investigation and scenario simulation. The catastrophic investigation of the disaster scene, including field survey, outcrop investigation, and remote sensing image interpretation, was executed to reveal the inundation for disaster response and recovery. SPOT-IV and FORSAT-II satellite images and airborne images provided temporal and spatial information for inundation investigation. The HEC-RAS hydraulic model was applied to estimate the water surface profiles of Shan-An levee around the lower reach of Chenyulan River. Also, the impacts of debris and water in the hyper-concentrated sediment flow were estimated to illustrate the effects of sediment yield on Shan-An levee. The result shows that the levee was designed to sustain the heavy rainfall bought by Typhoon Mindulle but failed to the impact of high concentrated sediment flow induced by sediment yield from the landslide. The seismic-triggered landslide on the left riverside was reactivated by intensive rainfalls to deposit a great amount of sediments on the riverbed that narrowed down the river width, increased the impact force, and diverted water toward Shan-An levee. The levee failure should draw more attention from engineers while designing a new flood control structure in the waterway of Chenyulan River due to the occurrence of the hyper-concentrated sediment flow and landslide residuals after the Chi-Chi earthquake (M L 7.3). In addition, the perceived investigation and analysis of an earthen levee failure provides essential information to setup a proper recovery plan of Shan-An levee and a basin management strategy of Chenyulan River in the future.

Risk assessment of debris flows in Songhe Stream, Taiwan

Typhoon Mindulle was the most severe typhoon across the Tachia River watershed following the 921 Chi-Chi earthquake, and resulted in extremely high precipitation of 1431 mm that induced many landslides, debris flows, and debris floods in affected areas. This paper analyzes the debris flows in the Songhe area induced by Typhoon Mindulle by employing a numerical model for debris flow simulation. The FLO-2D numerical program was adopted to simulate the flow conditions of debris flows in the Songhe area, including flow depths, flow velocities, and sediment depositions. Comparing the field data with simulation results, this paper defines an Index of Accuracy to examine simulation accuracy. Ignoring the influence of houses in the alluvial fans, the simulation accuracy was 79.3% and 61.4%, respectively for the First and Second Branches of the Songhe Stream. Considering the house effect in the Songhe area raised the simulation accuracy to 82.3% and 75.5%, respectively for the First and Second Branches. In addition, the simulation considering the hydraulic structures established after Mindulle was executed. This study also adopted 24 h accumulated precipitation at various recurrence intervals (10, 100, and 500 years) to perform scenario simulation of debris flows. Based on the method of Swiss Disaster Degree Classification, consisting of influential intensity and occurrence probability parameters, this study classified the risk degree of hazardous debris-flow areas into three categories, including high, medium, and low. The proposed approach generates the risk distribution map that may be used for setting up a disaster mitigation strategy for the Songhe area.

A study of extratropical transition and re-intensification of Typhoon Mindulle (2004)

In this study, the fifth-generation Pennsylvania State University-National Center for Atmospheric Research (PSU-NCAR) Mesoscale Model (MM5) is used to simulate Typhoon Mindulle (2004) at high resolution (3-km grid size). The data from measurements show that in the upper atmosphere the existence of an upper jet is important to the transition cyclone. When Mindulle moved to the area of the upper jet entrance, where high-altitude divergence existed, the pumping of the high-altitude divergence would enhance the vertical motion and low-level cyclone convergence. The enhanced vertical motion was confirmed by the simulation results and indicated that the existence of upper divergence enhanced the vertical motion which was favorable for the maintenance of Typhoon Mindulle. The process of extratropical transition (ET) and re-intensification always accompanies the process of cold air invasion. This process enhances the baroclinicity of the atmosphere and the formation of front at high altitudes, which converts baroclinic potential energy into kinetic energy and strengthens the cyclone vortex. The distributions of equivalent potential temperature (θe) and temperature anomalies show that the warm-core of the typhoon at the tropopause aids the re-intensification of the system. As the typhoon reenters the ocean, latent heat flux (LHF) increases in the north and west and the strong reflectivity and vertical motion occur in the east and southeast, and the west. With the re-intensification of the typhoon the wind field evolves from an oval to a circle at the lower atmosphere, the area coverage by high winds increases, and the distribution of the tangential wind shows an asymmetric pattern.

Prediction of Mountain Road Closure Due to Rainfall-Induced Landslides

The implementation of landslide probability analysis was undertaken in order to evaluate the impact of landsliding on closures of major mountain road networks in Guoshin Township in central Taiwan. To achieve this objective, an event-based landslide probability analysis method was adopted to establish a landslide prediction model using a set of training data from the landslides triggered by Typhoon Mindulle in July 2004. Landslide causative factors and triggering factors were selected in a logistic regression scheme so that the criteria for successfully distinguishing landslides from non-landslides were established. Landslide occurrence probability was mapped in the whole study area as well as along the road route. Locations of high potential for landslide occurrence were thus highlighted along the road route and were proposed for road closure during typhoon events. At last, the proposed locations for road closure were validated by historical road closures caused by subsequent typhoons after Typhoon Mindulle. Validation results show that the proposed model could be used in predicting road closures due to storm-induced landslides.

The role of the sediment budget in understanding debris flow susceptibility

AbstractThis study proposes a sediment‐budget model to predict the temporal variation of debris volume stored in a debris‐flow prone watershed. The sediment‐budget is dominated by shallow landslides and debris outflow. The basin topography and the debris volume stored in the source area of the debris‐flow prone watershed help evaluating its debris‐flow susceptibility. The susceptibility model is applied to the Tungshih area of central western Taiwan. The importance of the debris volume in predicting debris‐flow susceptibility is reflected in the standardized coefficients of the proposed statistical discriminant model. The high prediction rate (0·874) for the occurrence of debris flows justifies the capability of the proposed susceptibility models to predict the occurrence of debris flows. This model is then used to evaluate the temporal evolution of the debris‐flow susceptibility index. The analysis results show that the numbers of watershed which are classified as a debris‐flow group correspond well to storage of sediment at different time periods. These numbers are 10 before the occurrence of Chi‐Chi earthquake, 13 after the occurrence of Chi‐Chi earthquake, 16 after the occurrence of landslides induced by Typhoon Mindulle (Typhoon M), and 14 after the occurrence of debris flows induced by Typhoon M. It indicates that the occurrence of 7·6 Chi‐Chi earthquake had significant impact on the debris flow occurrence during subsequent typhoons. Copyright © 2009 John Wiley & Sons, Ltd.

Increase in basin sediment yield from landslides in storms following major seismic disturbance

The landslide area along the Tachia River catchment of central Taiwan was investigated using the remote sensing images of various typhoon and earthquake events taken from 1996 to 2004 and the sediment discharge measured at hydrometric stations. Our findings indicate that 88% of the coseismic landslides triggered by the 1999 Chi-Chi earthquake were first-time occurrences. After the Chi-Chi earthquake, 59% of the landslide area was reactivated during typhoon Toraji and 66% during typhoon Mindulle. The landslides prone to reactivation were on the formations with closely spaced discontinuities. It is suggested that further rock-mass defects in the formations were added or opened by the earthquake, and that the landslide areas continued to extend until the end of 2004. Post-1999 rainstorms delivered large amounts of colluvial sediment into the main channel, leading to a 2-fold increase in post-seismic sediment discharge while the precipitation was only half that of the pre-earthquake rate.

The Secondary Low and Heavy Rainfall Associated with Typhoon Mindulle (2004)

Abstract This paper presents an observational and numerical study of Typhoon Mindulle (2004) as it affected Taiwan. Mindulle made landfall on the east coast of Taiwan at 1500 UTC 1 July 2004, and after 13 h, it exited Taiwan from the north coast. Severe rainfall (with a maximum amount of 787 mm) occurred over central-southwestern Taiwan on 2 July 2004. During the landfall of Mindulle’s main circulation, a secondary low formed over the Taiwan Strait. However, the secondary low, after it developed significantly (vorticity exceeded 5 × 10−4 s−1 over a 30-km radius), did not replace the original center as was observed in many other storms. Instead, it moved inland and dissipated after the original center redeveloped near the north coast of Taiwan. In this study, the evolution of the secondary low, the redevelopment of the primary center, and the processes leading to the severe rainfall were examined. Results showed that the processes leading to the formation and the development of the secondary low were similar to those described in previous studies. These processes include the leeside subsidence warming, the horizontal transport of vorticity around the northern tip of the Central Mountain Range (CMR), and the overmountain upper-level vorticity remnant. However, because of the northward track, Mindulle preserved some strong vorticity on the eastern slope of the CMR. This strong vorticity remnant was steered northward over the ocean offshore from the north coast where the redevelopment of the primary center occurred. This “quasi-continuous track” of Mindulle has not been documented in previous studies. The vortex interaction between the redeveloped primary center and the secondary low resulted in the northeastward movement of the secondary low, which then dissipated after making landfall. Analyses also showed that even though heavy rainfall would occur over the mountain area when only the southwesterly flow prevailed, as on 3 July 2004, Typhoon Mindulle and the secondary low provided extra convergence that resulted in the west–east-oriented convective bands. These convective bands and the orographic lifting of the circulation associated with the secondary low resulted in the heavy rainfall over the central-western plains area.

Assessment of disaster resilience capacity of hillslope communities with high risk for geological hazards

This study presents a novel preparedness assessment method for assessing hazard mitigation and environmental planning of hillslope communities. A professional questionnaire was utilized to weight each indicator. Communities in Hsinchu, Taichung and Nantou counties with debris flow hazards were taken as study samples. Debris flow risk and landslide susceptibility for each community were determined using Geographic Information System (GIS) technology and logistic regression analysis. Thus, a novel risk assessment method for evaluating disaster resilience capacity of hillslope communities was established. This method was then applied to assess casualties caused by Typhoon Herb in 1996 and Typhoon Mindulle in 2004. Additionally, the analytical results generated by this assessment method were discussed with the aim of developing references for implementation of risk analysis, increasing the effectiveness of disaster mitigation, and reducing future loss of life and property.

Extreme storm events, landscape denudation, and carbon sequestration: Typhoon Mindulle, Choshui River, Taiwan

Research Article| June 01, 2008 Extreme storm events, landscape denudation, and carbon sequestration: Typhoon Mindulle, Choshui River, Taiwan Steven T. Goldsmith; Steven T. Goldsmith * 1School of Earth Sciences, The Ohio State University, Columbus, Ohio 43210-1398, USA *E-mail: goldsmith.35@osu.edu Search for other works by this author on: GSW Google Scholar Anne E. Carey; Anne E. Carey 1School of Earth Sciences, The Ohio State University, Columbus, Ohio 43210-1398, USA Search for other works by this author on: GSW Google Scholar W. Berry Lyons; W. Berry Lyons 2Byrd Polar Research Center, Ohio State University, Columbus, Ohio 43210-1009, USA Search for other works by this author on: GSW Google Scholar Shuh-Ji Kao; Shuh-Ji Kao 3Academia Sinica, Research Center for Environmental Changes, Taipei 115, Taiwan Search for other works by this author on: GSW Google Scholar T.-Y. Lee; T.-Y. Lee 3Academia Sinica, Research Center for Environmental Changes, Taipei 115, Taiwan Search for other works by this author on: GSW Google Scholar Jean Chen Jean Chen 3Academia Sinica, Research Center for Environmental Changes, Taipei 115, Taiwan Search for other works by this author on: GSW Google Scholar Geology (2008) 36 (6): 483–486. https://doi.org/10.1130/G24624A.1 Article history received: 28 Nov 2007 rev-recd: 15 Feb 2008 accepted: 01 Mar 2008 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Steven T. Goldsmith, Anne E. Carey, W. Berry Lyons, Shuh-Ji Kao, T.-Y. Lee, Jean Chen; Extreme storm events, landscape denudation, and carbon sequestration: Typhoon Mindulle, Choshui River, Taiwan. Geology 2008;; 36 (6): 483–486. doi: https://doi.org/10.1130/G24624A.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract We have performed the first known semicontinuous monitoring of particulate organic carbon (POC) fluxes and dissolved Si concentrations delivered to the ocean during a typhoon. Sampling of the Choshui River in Taiwan during Typhoon Mindulle in 2004 revealed a POC flux of 5.00 × 105 t associated with a sediment flux of 61 Mt during a 96 h period. The linkage of high amounts of POC with sediment concentrations capable of generating a hyperpycnal plume upon reaching the ocean provides the first known evidence for the rapid delivery and burial of POC from the terrestrial system. These fluxes, when combined with storm-derived CO2 consumption of 1.65 × 108 mol from silicate weathering, elucidate the important role of these tropical cyclone events on small mountainous rivers as a global sink of CO2. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Heavy Rainfall and Southwesterly Flow after the Leaving of Typhoon Mindulle (2004) from Taiwan

This paper presents an observational and numerical study of the southwesterly flow and heavy rainfall associated with Typhoon Mindulle (2004). When Mindulle made landfall on the east coast of Taiwan on 1 July 2004, a secondary low formed over the Taiwan Strait. The low then dissipated after Mindulle moved out over the ocean north of Taiwan. Subsequently, the accompanying strong southwesterly flow brought extremely heavy rainfall over southern and central Taiwan. The modeling study of the 15-km and 5-km grids shows that the southwesterly flow, which resulted from a downgradient acceleration toward the low system over the Taiwan Strait, transported the convectively unstable air northeastward over the northern South China Sea. When low-level air convergence provided enough lifting, strong mesoscale convective systems (MCS) were triggered in this region. This contributed to the formation of a series of mesolows and mesohighs which prevented air from accelerating farther northeastward. Only after these MCSs dissipated and the Pacific high extended westward was the moist unstable air able to accelerate into the southern Taiwan Strait, where it converged with the westerly flow of the typhoon circulation, producing convective rainbands southwest of Taiwan. When moving over land, these MCSs were enhanced, resulting in heavy rainfall. It is concluded that although the typhoon circulation was critical on the rainband development, the importance of the southwesterly flow in bringing the moist unstable air to converge with the typhoon circulation can not be left out. The southwesterly flow was first induced by typhoon's low pressure system at early stage, and was enhanced as a result of the westward extension of the Pacific high at later stage. The moisture budget analysis further shows that the development of the MCSs was mainly contributed by the horizontal moisture transport in the southwesterly flow. Evaporation locally from the ocean played only a minor role.

Detection and Volume Estimation of Large-Scale Landslides Based on Elevation-Change Analysis Using DEMs Extracted From High-Resolution Satellite Stereo Imagery

A new technique for quickly assessing extensive areas of large-scale landslides that uses digital elevation models (DEMs) extracted from high-resolution satellite images is presented in this paper. The proposed technique observes the elevation changes by using multitemporal DEMs. Five-meter-resolution DEMs from SPOT-5 images are applied to two large-scale landslide disasters: the landslides triggered by the 2004 Mid Niigata prefecture earthquake (magnitude 6.8; a moderate-topography area in Central Japan), and the landslides caused by the 2004 typhoon Mindulle (a steep-topography area in Central Taiwan). Both events yielded elevation changes in excess of 10 m. We assess the DEMs produced by the proposed method and their landslide application. We find three main results. 1) The elevation difference error increases with the slope angle. The root-mean-square error was 4-5 m on slopes lower than 30deg in both areas, whereas it was 5-6 m for slopes that exceeded 30deg in moderate topographies and 5-9 m in steep topographies. 2) The proposed technique well delineated the large-scale landslides. The total rate of successful area detection was over 70% for slopes under 40 deg but under 40% for slopes that exceeded 40 deg. 3) The landslide volume could be roughly estimated in units of 100times10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . The developed technique well supports damage assessments of large-scale landslides because the location, depth, and volume can be quantitatively determined by remote sensing

Short-term changes in seafloor character due to flood-derived hyperpycnal discharge: Typhoon Mindulle, Taiwan, July 2004

During Typhoon Mindulle in early July 2004, the Choshui River (central-western Taiwan) discharged similar to 72 Mt of sediment to the eastern Taiwan Strait; peak concentrations were g= 200 g/L, similar to 35%-40% of which was sand. Box-core samples and CHIRP (compressed high-intensity radar pulse) sonar records taken just before and after the typhoon indicate that the hyper-pycnal sediment was first deposited adjacent to the mouth of the Choshui, subsequently resuspended and transported northward (via the Taiwan Warm Current), and redeposited as a patchy coastal band of mud-dominated sediment that reached thicknesses of 1-2 m within megaripples. Within a month most of the mud was gone, probably continuing its northward transit, but more mud appeared in late August in response to Typhoon Aere. Following autumn and winter storms, the entire nearshore area was again sand dominated by early spring.