Marine Geology 363 (2015) 202–219 Contents lists available at ScienceDirect Marine Geology journal homepage: www.elsevier.com/locate/margeo Morphological change in the Pearl River Delta, China Wei Zhang a,b,c,⁎, Yang Xu b, A.J.F. Hoitink c,M.G.Sassid,JinhaiZhenga,b, Xiaowen Chen e, Chi Zhang a,b a State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Hohai University, Nanjing 210098, China b College of Harbor, Coastal and Offshore Engineering, Hohai University, Nanjing 210098, China c Hydrology and Quantitative Water Management Group, Department of Environmental Sciences, Wageningen University, Wageningen, Netherlands d Royal Netherlands Institute for Sea Research, NIOZ, Den Burg, Netherlands e Xijiang River Administration, Zhuhai, 519090, China article info abstract Article history: Morphological changes in the Pearl River Delta (PRD) have been investigated using bathymetric charts, underwa- Received 2 July 2014 ter Digital Elevation Models, remote sensing data and Geographic Information Systems. Water depths were ex- Received in revised form 16 February 2015 tracted from digitized charts to explore the accretion–erosion characteristics of three estuarine environments, Accepted 21 February 2015 and to provide quantitative estimates of changes in sediment volumes. Multi-temporal satellite images have Available online 26 February 2015 been used, in combination with topographical data, to analyze the coastline changes. PRD has gained an abundant amount of sediment of almost 9.45 × 105 km3 above the 10-m isobath in the period roughly between 1970 and Keywords: 4 3 Morphological change 2010; the average sedimentation rate was 3.15 × 10 km /yr. Between 1976 and 2006, the coastline extended Sedimentation seaward by 579.2 m on average, with a mean net extension rate of 19.3 m/yr. The results suggest that the PRD Land reclamation experienced a major phase of accretion, with net erosion only in some local zones. Coastline extension, associated Coastline with major morphological changes, has accelerated in recent decades. Changes in boundary conditions, such as Pearl River Estuary sea-level rise, seem to have relatively minor impacts on the dramatic changes in the morphology of the estuaries. The seaward extension of the coastlines shows an increasing trend whereas the sediment supply from the delta displays a decreasing trend. A detailed comparative analysis demonstrates that land reclamation in the PRD is the most significant factor that progressively alters the delta morphology, overwhelming the effects of subsidence and sediment supply. © 2015 Elsevier B.V. All rights reserved. 1. Introduction system (Jabaloy-Sánchez et al., 2010) and the Yellow River Estuary (Cui and Li, 2011). Syvitski and Saito (2007) selected a consistent database of The morphological changes in the hydrodynamical and hydrological fifty-one deltas, which covered the global parameter range of rivers enter- regime of rivers for estuarine zones are considered to be the cause of a ing all major coastal seas and oceans, to characterize key environmental major interference for estuarine zones, especially in morpho- and sedi- factors known to control delta morphology. The feedback of morphologi- ment-dynamics. The likely long-term impacts of physical factors con- cal changes may alter the morphodynamic regime. For instance, a delta trolling the morphological changes include sea-level rise (Ferla et al., may initially develop as a tide-dominated system, but gradually become 2007), wave fields (Pratolongo et al., 2010), tidal circulation (Wang a wave-dominated system as it progrades onto the open, continental and Townend, 2012), river flow (Inglis and Allen, 1957), sediment dis- shelf (Ta et al., 2002, 2005). Therefore, understanding the long-term mor- charge (Jiang et al., 2013) and storm surges (Riddin and Adams, phological changes in estuarine zones is of great value, not only because 2010). Intensive anthropogenic activities, such as channel dredging the knowledge provides insights to the historical characteristics of estuar- (Pinter et al., 2004), dam construction (Yang et al., 2006), sand excava- ies and facilitates the predication of future estuarine evolution, but also tion (Luo et al., 2007), and land reclamation (Chen et al., 2011)arealso because it enables researchers to assess the impact of natural changes significant causes for morphological changes. These factors were subject and anthropogenic activities on the coastal system. to study in a wide variety of delta and estuarine systems, including the Hydrodynamic models combined with sediment transport and a Senegal River Estuary (Barusseau et al., 1998), the Haringvliet Estuary morphodynamic module (‘bottom–up’ models) are widely used to pre- (Tönis et al., 2002), the Mersey Estuary (Blott et al., 2006; Thomas dict the short-term (hours to days) morphological changes in estuaries et al., 2002), the Ribble Estuary (van der Wal et al., 2002), the Yangtze (Friedrichs and Aubrey, 1996; Green et al., 2000; Whitehouse, 2002; Estuary (Chu et al., 2013; Wang et al., 2008, 2013), the Adra River deltaic Hibma et al., 2004; Townend, 2005; Blott et al., 2006; Karunarathna et al., 2008). Geological and geomorphological evolution models (some- times referred to as ‘top–down’ models), such as the Historical Trend ⁎ Corresponding author at: State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Hohai University, Nanjing 210098, China. Analysis (HTA) and the Expert Geomorphological Assessment (EGA), E-mail address: [email protected] (W. Zhang). are considered to be a more effective approach to estimate long-term http://dx.doi.org/10.1016/j.margeo.2015.02.012 0025-3227/© 2015 Elsevier B.V. All rights reserved. W. Zhang et al. / Marine Geology 363 (2015) 202–219 203 morphological changes ranging from decades to a few hundred years et al., 2011; Duong et al., 2014; Fanget et al., 2014; Maselli et al., 2014; (Dennis et al., 2000; Tönis et al., 2002; Whitehouse, 2002; Hibma Samaras and Koutitas, 2014; Stollhofen et al., 2014; Tanabe et al., et al., 2004; Townend, 2005; Karunarathna and Reeve, 2008; 2003; Tessier et al., 2012). However, the booming economic develop- Karunarathna et al., 2008). However, top–down models have inherent ments have disrupted the natural balance of a large number of delta sys- limitations due to the lack of detailed physics (Prandle, 2004, 2006; tems worldwide and have caused the excessive exploitation of natural Townend, 2005; Blott et al., 2006; Wang et al., 2013). Therefore, the resources, e.g. Pearl River Delta (PRD). The PRD is located at the north- analyses of historical bathymetric charts, remote sensing data and GIS ern margin of the South China Sea (Fig. 1). With an area of no more (RS-GIS) integration, field measurements and topographical surveys than 0.5% of China's territory, this densely populated delta has a mature are still indispensable when analyzing the morphological changes economy that produces approximately 20% of national GDP. The re- (Thomas et al., 2002; van der Wal et al., 2002; Blott et al., 2006; Jiang markable achievement doesn't come without cost. The morphology of et al., 2012; Wang et al., 2013). These approaches are particularly suit- the PRD has changed greatly due to intensive human interventions, able for the study of the long-term morphologic evolution in real- such as the building of coastal defense structures, sand mining and world delta regions (van der Wal et al., 2002; Prandle, 2004; Blott land reclamation. Zhang et al. (2012) report that the sediment et al., 2006; Wang et al., 2008, 2013; Li et al., 2011). transported from the upper river has decreased significantly due to Global delta areas are inhabited by almost two thirds of the world's the upper rivers' dam construction, which is very likely to cause coast- population. There is no doubt that the evolution of delta morphology is line recession. To satisfy the need of land, large-scale land reclamation closely intertwined with socio-economic development. Delta morphol- took place between the 1970s and the 2000s (Chen et al., 2011). This ogy evolves as the combined result of both natural- and human-factors. in turn led to coastline extension. The ongoing construction of the Most researches on delta morphology focused on the response of delta Hong Kong–Zhuhai–Macao Bridge will undoubtedly exert a significant morphology evolution to global changes in climate, continent-scale up- impact on the hydrodynamics, and change the geomorphologic evolu- lift and sea level (Amsler et al., 2005; Anderson et al., 2014; Bruneau tion in this region. Therefore, as a research paradigm, the PRD offers Fig. 1. Geographic information of the study area with isobaths in colors including the following: (1) the map of China, which shows the location of the Pearl River; and (2) the major to- pographic features of the Pearl River Delta. The names of the three major rivers and eight outlets are shown on the map. Blue circles represent four metropolitan cities. 204 W. Zhang et al. / Marine Geology 363 (2015) 202–219 the opportunity to study morphological changes in delta regions under changes in this region. Details of 55 admiralty charts and 15 topographic rapid economic development around the world. The morphological maps are given in Tables 1 and 2 respectively. The surveys were mainly changes in the PRD increasingly attract substantial research efforts. In carried out during four periods: 1960s–1970s, 1980s, 1990s and 2000s. the Lingding Bay, the largest estuary of the PRD, coastline changes