Shoreline changes

Abstract

Shoreline, a part of coastal land in contact with estuarine or ocean waters, undergoes various morphodynamical changes. The shorelines migrate landward or seaward depending on changing sea level or uplift or subsidence of coastal regions. The cyclic and noncyclic processes change the position of shorelines over time scales, from the daily and seasonal interaction of winds and waves to over thousands of years due to secular sea-level changes. Tidal ranges affect the shoreline configuration, and vice versa. Monsoons also play an important role in shoreline changes. Wave refractions and the resulting longshore currents are the primary agents of sediment transport and deposition on shorelines. Rivers are the major sources of sediment supply and littoral drift of sediments along shorelines. The breaking waves and currents in the nearshore zone are responsible for the transport of coastal sediments resulting in shoreline change. Anthropogenic activities such as construction of coastal structures (harbors, breakwaters, seawalls, and vented dams across the rivers), mining of sand and shells, and urbanization and industrialization also contribute to the shoreline changes. Sea-level rise during the late Pleistocene and Holocene dramatically altered the physiography of the coastlines around the world. The high rate of sea-level rise during early to mid-Holocene time, high sediment discharge, and wave energy regime favored the preservation of transgressive depositional sequences. Shoreline-change analysis is very important to understand coastal processes and morphodynamics, as well as to predict the future shoreline changes. The most effective and economic instrumentations used for shoreline mapping and shoreline-change monitoring are satellite sensors, Global Positioning Systems (GPS), and all-weather sensors. Shoreline change studies using remote sensing techniques are highly accurate and cost-effective. Satellite-imaging systems have increasingly improved image resolution including the new generation of the high-resolution satellite imagery such as QuickBird and IKONOS. Various methods, such as end-point rate, average of rates, linear regression, jackknife, and average of eras rates, are used to estimate shoreline changes.