Delineating Sediment Cells to Improve Coastal Stability and Conservation

Overview

Coastal zones are dynamic in nature. They are subjected to interactions from marine, terrestrial, atmosphere, biosphere, and fluvial systems apart from tectonic processes and human interventions. The stability of the coast is, therefore, an area of concern. Coastal stability is chiefly governed by the availability of sediments and coastal processes. Each coast is unique to its geographical location and set of physical interactions between land and oceanic parameters. Understanding these interactions is challenging and complicated in the perception of its sustainability.

A central concept in developing such a holistic approach is to view the coast as discrete functional units termed ‘Sediment Cells’ rather than viewing it as a single continuous stretch of land surface. A sediment cell can be defined as a stretch of coast between boundaries, which partly or wholly contains sediment movement and any change in the sediment movement within a cell does not significantly affect the sediment flow of the adjacent cells except in hazardous situations. It is the basic functional unit of the coast with the source, flow path and sink of sediments confined within the boundary.

Within its boundaries, the coastal processes act as a coherent and integrated system. An understanding of how this system function allows us to identify the impacts of development and mitigate to effectively manage the coastal stretch. The “sediment cells” concept is unique and is the first of its kind attempted for India under the ICZM phase I. The sediment cells approach will provide a better understanding of the interrelation between the functions of the short-term coastal processes and the long-term response and recovery of the coast.

Vision: To delineate discrete functional units along the west and east coasts of varying spatial scales. The identified coastal sediment cells can be used in Integrated Coastal Zone Management (ICZM) especially to deal with shoreline changes and in the preparation of Shoreline Management Plans (SMP).

Objectives

The aim of the study is to delineate the coastal sediment cells along the East and west coasts of India for better management and conservation of beaches and associated coastal landmass

Stakeholders Involved

Society of Integrated Coastal Management (SICOM, nodal agency for the Integrated Coastal Zone Management (ICZM) Project), World Bank, NCSCM and State Project Management Units (SPMU) of Odisha, West Bengal and Gujarat, Institute of Ocean Management (IOM) Anna University, Chennai. Solution and Implementation

The State project management units of Odisha and West Bengal used the primary cells and sub-cells obtained from the study for the preparation of their Integrated Coastal Zone Management plans. The ICZM plans for other coastal states using sediment cell boundaries of the study are planned to be undertaken in Enhancing Coastal and Ocean Resource Efficiency (ENCORE) programme in the subsequent period.

The movement of sediment along a coast does not proceed indefinitely but is interrupted by boundaries of different natures such as rigid, partially rigid, and free boundaries. Characteristics of sediment cells depend on the nature of the boundaries. Sediment cells with rigid boundaries that evolved due to long-term morphological processes are classified as “Primary cells” (PC). Key parameters considered for the delineation of primary cells are i) Coastal geomorphology ii) Source of sediments iii) stores of sediments and iv) interface of rocky-muddy and sandy coast.

Sediment cells with partly rigid boundaries within primary cells due to short-term coastal processes are classified as “Secondary or subcells” (SC). Key parameters considered for the delineation of sub-cells include i) Changes in littoral drift ii) changes in coastal alignment iii) decadal shoreline changes iv) man-made littoral barriers and v) Tidal inlets/river mouths.

Sediment cells with relatively free movement of sediments within sub-cells due to dominant land use activities are classified as “Management Units” (MU). Key parameters considered for the management units are the dominant land use activities along the coast. In comparison, MU are more dynamic due to the rapid changes in the coastal land use activities. Defining the boundaries of a sediment cell and its functioning demands considerable knowledge and experience of long-term morphological evolutions, coastal processes, and human interventions.

Use of Geospatial Technologies

The primary and subcells were delineated by reviewing the land use/land cover features, coastal morphology, coastal and marine habitats, shoreline changes, numerical model simulations, data on coastal processes such as ocean-atmospheric circulation features, wave dynamics and longshore current patterns and littoral drift obtained from authentic data sources. The movement of sediment was assessed using a variety of methods,