Determination of mechanisms and hydrogeological environments of Gangxianlane landslides using geoelectrical and geological data in central Taiwan

Electrical resistivity tomography (ERT), single-point-resistance logging with time-lapse, and geological and groundwater level data, are utilized to determine the mechanism of, and a hydrogeological model of, the Gangxianlane landslide in the west-central part of Taiwan. The rock surface and geometry of the colluviums were found by integrating ERT and borehole data. The iso-resistivity line in the bedrock broadly followed the bedding plane, indicating that the contribution of lithology to resistivity exceeds that of groundwater. The results of single-point-resistance logging with time-lapse and borehole data reveal that the bedrock has low permeability, which is associated with poorly developed joints and fractures. The fine grain content part (including the clayey layer), almost parallel to the bedding plane of the bedrock and between the colluvium and the bedrock in the upper part of the landslide, served as the slip surface and is believed to have been recently produced. It can block and retain water in the colluviums. Accordingly, this slip surface has the potential to re-slip in the future. Another slope failure involved rock collapse by a well-developed open release joint close to the Huoshaoping Terrace. It is also related to groundwater flow over a large gradient from the Huoshaoping Terrace. It is a key to determining whether this landslide will expand in the future.     

Estimates of present-day erosion based on sediment transport in rivers: a case study in Taiwan

We discuss the present-day sediment transport by rivers, and hence the erosion rate in upstream basins, based on the example of Taiwan Rivers where large datasets are available. After data correction, the values of the suspended sediment load in the lower Kaoping River are nearly three times smaller than those from the literature. On the other hand, we add the bed load evaluated from numerical modelling, despite limitations from data and models. Whereas the contribution of the chemical denudation rate in Taiwan is minor, the bed load is significant and must be evaluated. We point out that biases in data collection may favour high values of suspended load data, and that large series of datasets are needed to reduce uncertainties and smooth the time variability effect. To cite this article: F.-C. Li et al., C. R. Geoscience 337 (2005).     

Inundation Potentials Analysis for Tsao-Ling Landslide Lake Formed by Chi-Chi Earthquake in Taiwan

Without any omen, massive landslides induced by the Chi-Chi earthquake blocked up gorges of Ching-Shui creek, and produced a new landslide lake.Although emergency spillways have been constructed to prevent dam failures,overtopping and possible breaching may still occur due to excessive inflows in raining seasons. As a result, the downstream valleys will have serious inundation and the safety of people and properties will be in immediate danger. The purpose of this work is to simulate and to analyze the inundation potentials downstream of Tsao-Ling landslide lake using a hydrologic/hydraulic approach and GIS (Geographic Information System) technology. Hydrologic analysis is employed to describe regional rainfall-runoff characteristics andto design rainfall/runoff scenarios. One-dimensional dam break flood routings are performed with different return periods of rainfall events and dam failure durations for downstream creeks. The depletion hydrographs of dam break routings are applied into two-dimensional overland flow simulations for downstream lowlands. The results of hydraulic computations are evaluated with GIS maps for inundation potentials analysis, which can be usedto assist the planning of emergency response measures.     

Slip monitoring of a dip-slope and runout simulation by the discrete element method: a case study at the Huafan University campus in northern Taiwan

Slope failure is a widely observed phenomenon in the mountainous areas in Taiwan due to rainy climatic and fragile geological conditions. Landslides easily occur after intense rainfall, especially from typhoons, and, accordingly, cause a great loss of human life and property. At the northern end of the Western Foothill belt in northern Taiwan, Huafan University is founded on a dip-slope about 20° toward the southwest composed of early Miocene alternations of sandstone and shale. Data from continuous monitoring using inclinometers and groundwater gauges reveal that 6–10 mm/month of slope creeping occurs, and a potential sliding surface is then detected about 10–40 m beneath the slope surface. To understand the potential runout process of the dip-slope failure at the campus, particle flow code 3D models based on a discrete element method are applied in this study. Results of the simulation reveal a critical value of the friction coefficient to be 0.13 and that more than 90% of the campus buildings will slide down in 100 s when the friction coefficient is reduced to half the critical value. The weakening of the shear zone due to the rise of groundwater during rainstorms is assumed to be the main factor. Some suggestions for preventing landslide disasters are to construct catchpits to drain runoff and lower the groundwater table and to install a sufficient number of ground anchors and retaining walls to stabilize the slope.     

Design and experiment of a small boat track-keeping autopilot

A real time kinematic (RTK), GPS-based, track-keeping control of a small boat is discussed in this paper. The internal model control (IMC) method is adopted in the autopilot design and the controller is recast in the PID controller format that is characterized by its simple structure and relative ease of implementation. The track-keeping mission is achieved through a sequence of course-changing maneuvers and the reference heading is computed with the line-of-sight (LOS) guidance law. Path planning based on Bezier curves to achieve obstacle avoidance is investigated. First, computer simulations are carried out to find the feasible controller design parameter that achieves satisfactory simulation results. Then the feasible controller design parameter is applied in the small-boat-based experiments to demonstrate the practical use of the proposed autopilot design method.     

Phytoplankton community reorganization driven by eutrophication and warming in Lake Biwa

We compiled and analyzed long-term data, including chemical, physical and phytoplankton community data, for the Lake Biwa ecosystem from 1962 to 2003. Analyses on environmental data indicate that Lake Biwa had experienced intensified eutrophication (according to total phosphorus concentration) in the late 1960s and returned to a less eutrophic status around 1985, and then exhibited rapid warming and thus increased water column stability since 1990. Total phytoplankton cell volume largely followed the trend of total phosphorus concentration, albeit short-term fluctuations existed. However, phytoplankton community shifted dramatically in response to those changes of environmental states. These shifts were cause by changes in trophic status driven by phosphorus loadings and physical properties in the water column driven by warming. Moreover, most phytoplankton species did not show a strong linear correlation with environmental variables, suggesting nonlinear transitions among different states.     

Modeling high-order statistics in the turbulent Ekman layer

Results from a direct numerical simulation (DNS) of the neutral and unstable turbulent Ekman layer at a Reynolds number of 1000 were used to evaluate turbulence closure models. For the neutrally stratified Ekman layer, the higher-order moments of velocity were examined and the accuracy of a kurtosis model was assessed. For the unstable Ekman layer, the analysis of higher-order moments was extended to temperature-velocity correlations. Model coefficients were optimised using DNS data and it was shown that the optimised models accurately captured the distributions of all fourth-order moments. These low-Reynolds number results can be extrapolated to higher Reynolds numbers to parameterise turbulence in other flow fields with rotational effects such as the atmospheric boundary layer.