Coasts and Estuaries

The following sections are included:

• Dedication
• Preface
• About the Authors
• Acknowledgments
• Contents

Vast lengths of coastlines around the world are experiencing threats that have led to the loss of infrastructure and livelihood of the community and, in several instances, loss of lives. Coastal erosion is caused by either nature or anthropogenic activities along the coastal belt. In addition to planning for combating the hazards, a rapid progress in coastal development has emphasized the need for coastal management information to understand the physical parameters that are responsible for shoreline stability, which is the focus of Coasts and Estuaries: Management and Engineering. This book encompasses monitoring parameters such as waves, currents, wind, tide, bathymetry, beach profile, shoreline, sediment characteristics in the near shore, as well as in case of estuarine coasts, riverine data such as river current, discharge, conductivity, temperature and depth. Three coastal sites along the southern Indian peninsula with different coastal features — Devaneri in Tamil Nadu, Ponnani in Kerala and Karaikal in Puducherry — were selected for this purpose, the salient details of which are reported in this chapter.

Coastal developments across the globe have been rapid, in keeping pace with the growing infrastructure for ports, inland waterways, trade and commerce, tourism, fisheries, a hub for power plants, etc. This has resulted in an increase in population density along the coastal stretches. Such developments are bound to lead to instability in the shoreline, apart from the natural causes of coastal hazards. The process of erosion as well as accretion in the vicinity of approach channels of harbours, confluence tidal inlets or seas can either be natural, man-made or a combination of both. Excessive erosion or accretion problems need to be handled carefully without causing adverse effects along the adjoining shoreline, although it is a challenging task. Several such issues and the measures to combat the problems are well understood through case studies. To counter or minimize coastal erosion, the protection measures are broadly classified as hard and soft measures. A few case studies based on both approaches are considered, their performance characteristics are presented, and the merits and demerits of both methods are highlighted in this chapter.

This chapter describes a coastal and marine data information system that can be used for Maritime Spatial Planning. The system takes advantage of Internet mapping and web services technology to publish data as maps. These maps are created dynamically and enable the visualization of a diverse and growing collection of environmental data. Capabilities of the system include (i) visualization of environmental parameters on 2D maps; (ii) visualization of location-specific depth profiles of selected parameters; (iii) time animation of grids of environmental parameters and (iv) preparation of digital elevation and cultural object data sets for 3D terrain visualization (Durairaju et al., 2003, 2010). The function and interaction between key components of the system are described to illustrate the working of the system. The use of a mature map publishing engine greatly eased the development of these capabilities into a web-based system.

The vast amount of wave data obtained from physical measurements require systematic analysis to derive useful information for design and other widely varying applications such as sediment transport. The time-domain statistical analysis and frequency-domain spectral analysis provide the necessary characteristics of data sets for various applications. Further, the temporal variation of frequency distribution of energy could be explored by different methods such as phase-time, Hilbert transform and wavelet analysis.

It is essential to have real-field measurements of the ocean waves both for understanding the environment as well as for validation/calibration of numerical modeling exercises. The pressure measurement of free surface elevation provides the temporal variation of wave height. Further, to resolve the direction of the wave, the vector information on propagation components is essential, which can be derived from the measurement of either velocity or wave slope in either direction. An in-situ measurement is spatially discrete. However, the remote sensing radar measurements complement for spatially rich data.

Sandy beaches and alluvial estuaries are some of the most dynamic environments on the earth, and inspecting coastal morphodynamic behaviour through multidisciplinary approaches and techniques will throw significant light on its physical process. In addition, understanding the physical geomorphology of the coast in response to the hydrodynamic driving forces, it is also an important benchmark in shaping both the visible coasts and the invisible underwater/seabed features. The changes in the coastal geomorphology can be identified by taking appropriate, continuous and repeated measurements. The rate of changes can be reckoned by comparing measurements of the first with the last/latest. Controlled measurement and monitoring of changes in water depths and quantum of water and sediments in a water body could go a long way in understanding the morphodynamics behaviour and respective physical processes.

Shorelines are of great importance to coastal engineers and planners. They are the line of action for planning coastal protection measures and act as the first line of defence during extreme weather events. The intensity of a storm on the coast can be estimated by calculating the changes in the shoreline. The prominence of shoreline changes is further stressed in the planning of ports and harbours and other coastal installations. There are various sources of data available for shoreline extraction from field surveys to satellite image extraction. The analysis of collected data is performed using statistical methods of Linear Regression Rate, End Point Rate and Weighted Linear Regression Rate. In this chapter, the various sources of data collection and analysis and the role of remote sensing and Geographical Information System (GIS) in shoreline change studies are discussed using case studies. In addition, the advantages of various shoreline mapping techniques and the errors and uncertainties involved in performing a remote sensing study are discussed.

Beaches undergo gradual changes continuously. The changes over an open beach differ from that over a beach adjoining natural or manmade obstructions. The beach profile changes are of importance in the understanding the coastal processes. This chapter presents the beach profile changes in an open coast and near an estuary quantified through field investigations over a couple of years. The changes in the beach profiles are compared temporally and spatially. The data has been collected on the first spring tide of every month using Real Time Kinematic Global Positioning System (RTK-GPS) from January 2017 to December 2018. The accuracy of data collected using RTK-GPS is 8–15 mm. The study areas considered an open coast in Devaneri, Tamil Nadu, and near an estuary with its mouth being trained by a pair of training walls in Karaikal, Puducherry. Both sites are situated along the southeast coast of Indian peninsula and 300 km apart. The open coast has remained constant with minor changes in the variations in its profile, whereas the one near an estuary undergo major changes seasonally and spatially. It is observed that the presence of coastal structures dictate the erosion/accretion process. Irrespective of the type of coast, northeast monsoon brings forth significant changes along the coast.

The importance of investigating the sediment characteristics along an open coast and in an estuary are discussed through a comprehensive literature review. The sediment characteristics along an open coast and near an estuary situated on the southeast coast of India are quantified through field investigations conducted over a couple of years. The temporal and spatial variations are discussed. The seasonal variations for both the above-stated environments are also presented and discussed in this chapter.

The most dynamic part of the ocean environment is the wind-wave. It has the maximum energy content among all the ambient environmental forces in the ocean. The prediction of such wave climate is of prime importance for various scientific and engineering applications. It is possible to estimate the integrated wave parameters through analytical equations in an unbounded domain with constant wind fields but it requires numerical models for the prediction over complex domain and varying wind conditions. It is always required to establish the operational wave climate for several day-to-day activities and extreme wave climate for the estimate of the design wave. In this chapter, a brief introduction to the historical understanding on the prediction of wave climate to the state-of-the art numerical wave models is presented. The extraction of design wave climate is highlighted.

Longshore sediment transport (LST) plays a vital role in dictating the stability of a shoreline. The estimation of LST rate poses problems due to assigning the value for the driving parameters and the method adopted. In this chapter, the driving parameters, i.e., the wave characteristics, predicted from the field-measured wind data for a year were considered for the estimation of LST. The predicted wave data was initially validated with the field measurements, acquired by deploying a bottom-mounted directional wave recorder. LST were evaluated with five different empirical formulae, the details of which are discussed in this chapter.

Tidal inlets are ecologically sensitive coastal features, where its opening along the shoreline permits free exchange of water through flooding and ebbing flow. The shoreline openings may constitute bays, lagoons, marsh or estuaries. The formation of sandbars, spits, and shoals is more common at the inlet mouth particularly along the coasts dominated by longshore sediment transport. These formations act as a barrier, blocking the entrance of tidal inlet and thus restricting flow/exchange of water. The sandbar and spit formation are usually minimized by construction of a pair of training walls, prior to which monitoring the local hydrodynamics at the inlet vicinity is essential. In the case where the tidal inlet meets an estuary, the volume of water exchanged at the inlet mouth are governed by the inlet dimensions and rate of littoral transport. After a comprehensive discussion on the hydrodynamics and morphodynamics of estuaries, its application is considered through a detailed investigation of a micro-tidal inlet at the Arasalar estuary, a tributary of the Cauvery river, in Karaikal (10° 54′ 52″ N; 79° 51′ 09″ E), situated along the southeast coast of the India. The numerical model using the finite volume method is applied to estimate the siltation rate and its distribution within the domain, driven by the tide-induced currents and riverine discharge and validated through field measured data. This chapter provides the procedures to be followed in identifying the problem of siltation and arriving at a suitable mitigation measures to reduce siltation within the inlet to facilitate smooth navigation.

The following section is included:

• Index