Abstract

The Chi-Chi earthquake of 1999 in Central Taiwan caused significant vertical uplift and ignited a dynamic fluvial erosion system in the Taan River. In order to understand the geomorphologic changes in the Taan River after the Chi-Chi earthquake, this study uses multi-temporal aerial photos to produce orthoimages and surface models to derive regional three dimensional movements from 2001 - 2009. The Particle Image Velocimetry (PIV) technique is applied to identify the horizontal movements from both orthoimages and digital surface models (DSMs). While PIV can provide estimates for the channel change direction and magnitude; vertical analysis such as river incision rate derivation could be performed using the height difference between multi-temporal surface models. The results from these two approaches are then integrated for river geomorphological interpretation. It is observed that the proposed scheme is capable of identifying three river evolution stages from the extracted movements in the Taan case. These stages are: years 2001 to 2003, 2004 to 2006, and 2007 to 2009, respectively. The total incision between 2001 and 2009 is about 10 m. This study demonstrates that both PIV and DSM subtraction are effective in river geomorphological change identification. The integration of these two approaches could provide more information when observing the evolution of river morphology.

Highlights

  • River landform is shaped by erosion and deposition processes, and influenced by external forces, such as climate change, tectonics, and human factors

  • Twelve ground control points (GCPs) were collected with static GPS in 2009 to support the aerial triangulation. These GCPs are all road-side features that can be identified from most images and spread over a much larger area than that of the study site

  • For the LiDAR-derived digital surface models (DSMs) and its accompanied orthoimage, the orthoimage is generated from images taken during the LiDAR mission with a medium camera

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Summary

Introduction

River landform is shaped by erosion and deposition processes, and influenced by external forces, such as climate change, tectonics, and human factors. Natural disasters such as earthquakes and typhoons frequently dramatically change the erosion and deposition mechanisms of a river. In 1999, the Chi-Chi earthquake (Mw = 7.6) struck Central Taiwan, causing many surface ruptures. The Taan River experienced co-seismic displacement due to this earthquake. The displacement was induced by reverse fault across the main river and changed the local fluvial system equilibrium. The fault scarps across the rivers had a vertical slip (up to 10-m) (Lee et al 2003; Huang et al 2013) and initiated the morphological channel evolution

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