Shen, Su-Min; (2001) Geomorphological and tectonic controls on coastal erosion, Huatung, eastern Taiwan. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The Huatung coast, eastern Taiwan, is characterised by rapid uplift and well-developed marine terraces. Despite the high uplift rate, and associated negative sea-level tendency, this coast has long been subject to coastal erosion problems. Only limited scientific understanding of the rate and processes of erosion has been available to inform the increasing mitigative works and, despite heavy expenditure, land loss and damage to coastal property remain a serious problem. The aim of this study is to determine the rate and pattern of cliff erosion and to provide a geomorphologically-sound basis for future coastal management. This is accomplished through: 1. the first comprehensive geomorphological survey of the Huatung coast; 2. identification of major geomorphic units ('littoral cells') along the coast; 3. quantification of the rate and pattern of erosion, with particular reference to the rapidly retreating coastal section around Chengkung; 4. investigation of factors driving coastal change at various temporal and spatial scales. More than 150 km of coast have been investigated and field surveys conducted of cliff and beach morphology and material properties. The Huatung Coast exhibits a bay-headland configuration and a series of littoral cells are proposed, based upon morphological and sedimentological evidences. Rigorous comparison of sequential topographical maps and aerial photographs covering the period 1929 to 1990 for various stretches provides the first quantitative measurements of the rate of erosion on this coast. Although the distribution of retreating stretches various locally, the maximum retreat rate is up to 3 m yr-1 over the period 1951~1990. High retreat rates occur where the cliff-forming material is less resistant (mudstones) and/or where the fronting beach is poorly developed. Extreme events, in the form of summer typhoons, are believed to be the main agent of coastal change. Cliff retreat occurs through a combination of storm wave attack and slope failure during heavy rainfall and runoff. This study identifies the most rapidly retreating coastal sections and provides a conceptual basis for understanding their distribution. An idea of the potential for future erosion is obtained from consideration of both coastal profiles (the extent and composition of the various terrace units) and planforms (in relation to theoretical equilibrium curves and observed palaeo-shorelines). These findings will allow more informed planning of future developments and protection works.

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