UNCORRECTED PROOFS CHANGE DETECTION OF GRAVEL MINING ON RIVERBEDS FROM THE MULTI-TEMPORAL AND HIGH-SPATIAL-RESOLUTION FORMOSAT-2 IMAGERY CHENG-CHIEN LIU, a * CHJENG-LUN SHIEH, b CHIAO-AN WU b and MING-LIN SHIEH b a Department of Earth Sciences, Institute of Satellite Informatics and Earth Environment, Earth Dynamic System Research Center, National Cheng Kung University, 701 Tainan City, Taiwan, ROC b Department of Hydraulic and Ocean Engineering, National Cheng Kung University, 701 Tainan City, Taiwan, ROC ABSTRACT Gravel mining from river channels is conducted in many countries around the world, yet ground-based monitoring of these activities requires considerable manpower and is not very effective. Therefore, innovative and effective approaches to monitoring gravel mining are urgently required. Deployed as a high spatial resolution sensor in a daily revisit orbit, Formosat-2 has proved to be an ideal satellite for site surveillance. Using one known event of gravel mining in the Tseng- Wen River, Taiwan, between March 2004 and March 2005, we analysed nine Formosat-2 images taken during this period to summarize three characteristics of gravel mining in the images. Based on these characteristics, a standard procedure for processing Formosat-2 imagery to detect gravel mining is proposed. This procedure is validated against ground truthing collected by an unmanned helicopter flying at low altitude. The evolution of this gravel-mining event in the Tseng-Wen River is described by processing all historical Formosat-2 imagery using the proposed procedure. This standard procedure has been successfully incorporated into the Formosat-2 automatic image processing system and has been used to monitor gravel mining on a daily-basis. Copyright # 2008 John Wiley & Sons, Ltd. key words: remote sensing; gravel mining; riverbed; river management; monitoring; image processing; Formosat-2; change detection Received 10 October 2007; Revised 9 July 2008; Accepted 18 September 2008 INTRODUCTION Gravel mining from river channels is conducted in many countries around the world (Wyzga, 2001; Rinaldi et al., 2005). Particularly in regions with higher erosion rates, such as in Taiwan (Dadson et al., 2003) where tremendous amounts of gravel are washed into the rivers and deposited after heavy rains, resulting in a valuable source of construction materials (Sear and Archer, 1998). However, large-scale excavation of gravel from river channels inevitably modifies the topography and changes the river flow pattern (Kondolf and Swanson, 1993; Kondolf, 1994). The resulting sediment transport could have an unpredictable and devastating impact on piers or other structures rooted in the riverbed (Rovira et al., 2005). From the biological/ecological view point, in-stream mining destroys in-channel alluvial features important for habitat and their diversity (Rinaldi et al., 2005). In addition, the human activity generally results in increased fine-grained sediment delivery to rivers and increased sediment transport in rivers (Owens et al., 2005), which also poses a threat to the water quality if the sediment enters a reservoir. A comprehensive discussion of the effects of sediment mining on channel morphology and environment is provided by (Rinaldi et al., 2005). The general strategy to monitor gravel mining on riverbeds requires considerable manpower and is not very effective (Gilvear et al., 2004; Rinaldi et al., 2005). Therefore, seeking an innovative and effective approach to monitoring gravel mining on riverbeds is one of the most urgent considerations in the management of rivers and watersheds (Rinaldi et al., 2005). Rivers in Taiwan are typically short, with small drainage basins, steep gradients with rapid flows. A tremendous amount of gravel is washed into the rivers and deposited on the riverbed every year. As a result, serious disasters RIVER RESEARCH AND APPLICATIONS River. Res. Applic. 24: 1–17 (2008) Published online in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/rra.1210 *Correspondence to: Cheng-Chien Liu, Department of Earth Sciences, Institute of Satellite Informatics and Earth Environment, Earth Dynamic System Research Center, National Cheng Kung University, 701 Tainan City, Taiwan, ROC. E-mail: ccliu88@mail.ncku.edu.tw Copyright # 2008 John Wiley & Sons, Ltd. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56