www.cerf-jcr.org Coastal Embayment Long-Term Erosion/Siltation Associated with P-A Relationships: A Case Study from Jiaozhou Bay, China Yunling Liu { , Ya Ping Wang {{ *, Yan Li { , Jianhua Gao { , Jianjun Jia 1 , Xiaoming Xia 1 , and Shu Gao { { School of Geographic and Oceanographic Sciences Nanjing University Nanjing 210093, China ypwang@nju.edu.cn { State Key Laboratory of Marine Environmental Science Xiamen University Xiamen 361005, China 1 Second Institute of Oceanography State Oceanic Administration Hangzhou 310012, China ABSTRACT Liu, Y.; Wang, Y.P.; Li, Y.; Gao, J.; Jia, J.; Xia, X., and Gao, S., 2012. Coastal embayment long-term erosion/siltation associated with P-A relationships: A case study from Jiaozhou Bay, China. Journal of Coastal Research, 28(5), 1236– 1246. Coconut Creek (Florida), ISSN 0749-0208. The sedimentary environment of a large coastal embayment, Jiaozhou Bay, eastern China, in terms of erosion/siltation, has been assessed on the basis of seabed bathymetry and coastline data sets from sea charts (1936–2002) and Landsat-5 TM images (1986–2011). Nine types of sedimentary environment are identified according to the sedimentation rate. The results indicate that slow siltation was generally present from 1936 to 1963, with exceptions of some patchy, slightly eroding areas within the embayment. Transformation to a slow erosion pattern occurred in the main channels over the central embayment in 1963, and such a situation continued until 1982. Subsequently, since 1986, most of the coastlines extended toward the sea at a rate of 10 1 –10 2 my 21 ; this was mainly attributable to human activities, including reclamation over the NW tidal-flat and harbour construction along the east and south coastlines. Using the same data set, patterns of changes in tidal prism and deposition rate within the entrance channel were established. An equivalent friction coefficient (K) is proposed to evaluate the P-A relationship of the large tidal inlets in Jiaozhou Bay. The K value increases gradually over time, indicating a trend toward stable equilibrium in Jiaozhou Bay. This coefficient can be used to examine the status of morphological stability and equilibrium of coastal embayments. ADDITIONAL INDEX WORDS: Environment assessment, erosion and siltation, P-A relationship, equivalent friction coefficient, coastal embayments, tidal inlets, Jiaozhou Bay. INTRODUCTION A coastal embayment is a well-marked indentation, which contains certain land-locked waters and constitutes more than a mere curvature of the coast (O’Connell and Shearer, 1982). The area of the embayment also include the intertidal area (between high and low water levels), in addition to the water areas below the theoretical depth datum (namely the local hydrographic zero) (Wu and Wang, 2000). Thus, this type of coastal system contains wide-ranging natural resources such as deep channels for navigation and beaches for tourism. Being susceptible to natural changes and anthropogenic activities (Syvitski and Saito, 2007; Syvitski et al., 2005; Tudhope et al., 2000), the coastal zone, including coastal embayments, is often subjected to geologic hazards, e.g., seawater intrusions, coastal erosion, and port siltation (Huang et al., 2009). Therefore, the coastal embayment is regarded not only as a sensitive and susceptible zone of environmental variations, but has been also an integral part of the nearshore coastal waters to which attention has been paid in several international research programs (e.g., Land Ocean Interactions in the Coastal Zone [LOICZ]) (Cicin-Sain and Knecht, 1998; Newton and Icely, 2008). Hazardous geology represents a variety of geological phe- nomena that are likely to cause losses of human lives and property (Liu et al., 2000). The environmental assessment focusing upon the hazardous geology is crucial for sustainable coastal development, which is associated with a procedure of evaluating the environmental implications before any deci- sions are made with regard to coastal development (ECE, 2001). In the present study, we attempt to evaluate the environ- mental influences of erosion and siltation in a large coastal embayment, Jiaozhou Bay, North China. In response to continuous reclamation undertaken since the 1950s, the intertidal area of this embayment had decreased to 75 km 2 by 2005, with a reduction of the coastline length. As a result, the tidal prism, which is vital in maintaining the clearance water depth for a harbour, has decreased (Wang, 2000; Yang et al., 2003b). However, the consequences of such changes regarding the navigation channels, the harbours, and the nearby sandy beaches are still poorly understood. Thus, it is necessary to DOI: 10.2112/JCOASTRES-D-11-00158.1 received 25 August 2011; accepted in revision 26 February 2012. Published Pre-print online 6 June 2012. *Corresponding author. ’ Coastal Education & Research Foundation 2012 Journal of Coastal Research 28 5 1236–1246 Coconut Creek, Florida September 2012