Modelling shallow landslides: the importance of hydrological controls and lateral reinforcement

Shallow landslides are important as geomorphic agents of erosion, sources of catchment sediment and potential hazards to life and infrastructure. The importance of these mass movements is difficult to define using solely field- based approaches because these are often too limited in both duration and resolution to fully determine the magnitude and frequency of these processes. Modelling is a powerful alternative tool for providing insight into underlying processes governing shallow landslides and for testing new hypotheses regarding environmental and land-use change impacts. The explanatory power of models is a function of their process representation and predictive ability. Current models suitable for catchment-scale application provide valuable probabilistic information on failure, but not detailed deterministic predictions. Using the English Lake District as a study area, this thesis addresses three issues necessary to provide the process-basis of these probabilistic analyses. First, poorly constrained or spatially variable input parameters such as soil depth, root reinforcement or material properties are often used to explain the locations of failure within a larger area that has a high, sometimes equal, probability of failure. The thesis develops rigorous new methods to quantify and minimise error in these parameters, representing them as distributions to capture both their natural variability and the error in their measurement. Results suggest that lateral root reinforcement even for grasses and shrubs may provide important additional strength (as much as 6 kPa) in the top 0.5 m of the soil. Second, infinite slope stability analysis neglects important additional lateral friction and root reinforcement effects at the margins of an unstable block. More sophisticated three-dimensional stability analyses can represent this process but are limited in their applicability by computational and data resolution requirements. This thesis derives from first principles a set of analytical governing equations for three-dimensional analysis; tests these against benchmark geotechnical methods; and applies them to establish key landslide scaling relationships. Third, shallow landslides in the UK are almost exclusively hydrologically triggered, resulting from local high pore water pressures. In line with the current paradigm existing stability models assume that the topography plays a dominant role in defining the spatial pattern of soil moisture and therefore pore water pressures in the landscape. This hypothesis is tested: first at the hillslope scale (10(^1) km(^2)) with a network of ֊100 wells; then the catchment scale (10(^2) km(^2)) using high resolution orthorectified aerial photographs to identify vegetation indicative of wet habitats and applying these as a proxy for soil moisture. These studies indicate that, for the case-study, wet areas are controlled at the landscape scale by a set of broad topographic limits in terms of slope and contributing area. Within these there is considerable scatter, resulting from the interplay of local factors such as: bedrock topography, preferential flow and soil stratification. Lateral root cohesion represents an important source of additional strength which can be included within analytical stability equations to create a threshold dependence on landslide size. Patterns of instability will then depend on the spatial pattern of other influencing factors (e.g. soil strength and pore pressure). At present the limits to available data and our understanding of hillslope hydrology constrain our ability to predict slope instability in environments like the Lake District. Future research might usefully identify landscape scale controls on this predictability

Which methodologies of science are consistent with scientific realism?

This thesis sets out to examine which methods it would be most consistent for a scientific realist to adopt when practising mature science, given his philosophical predilections. Moreover, it aims to establish the means by which the closely related question, "Is there any support for the philosophical stance known as scientific realism, given the methods that the modern scientist does, in fact, employ?” might be answered. In order to do this, it is first necessary to examine scientific realism in detail, and to compare it with competing philosophical positions on science; this is the role of chapter one. Scientific realism is seen to involve four distinct theses: metaphysical, semantic, epistemic, and teleological. The vital role which induction plays in justifying each of these theses is then illustrated, in part by elucidating the limitations of Popper's anti-inductivism, and of subsequent critical rationalist positions. Second, it is necessary to examine how the methods which one adopts when practising science might be affected by one's philosophical viewpoint. This is the task undertaken in chapter two, where the distinction between normative methods, in which all scientists must take part (in order to practice anything which might be justifiably thought of as a mature science), and auxiliary methods, which are dependent upon the psychological state of the individual practitioner, is established, based on plausible demarcation guidelines between science and pseudo-science. It is clearly shown that different auxiliary methods are adopted by realist and anti-realist scientists: the construction of the quantum formalism in the 1920s, which is mentioned at several points throughout the thesis, is used as the primary example. The final chapter consists of the conclusions, which are as follows: (i) Scientific realists who are also practising scientists should be metaphysical realists of a Lowean variety, and employ metaphysical analysis in order to delimit ontological possibilities, before using experience (e.g. experiment) to choose between those possibilities; (ii) The question of whether there is support for scientific realism from the practice of modern scientists rests on whether there is really any legitimate distinction to be made between belief and acceptance; (iii) The semantic thesis of scientific realism is just as plausible as the metaphysical thesis of scientific realism, given that a practising scientist must behave as if both are true (viz. instrumentalism appears to be a highly dubious position)

Physics for Iowa schools, 1966.

The purpose of this physics guide is to assist the teacher in developing his own course to meet the needs of two types of students: (1) those who plan for further study, and (2) those who will terminate their formal education with high school graduation