Coastal zone is a central attraction for coastal engineers, scientists and coastal community due to economic and developmental activities of the coast. Kerala has 593 km of coastline. More than 50% of the coast is occupied with artificial structures such as ripraps, groins, seawall, ports and fishing harbours. These coastal protection structures and developmental activities played a major role in altering the shoreline position significantly. Therefore, periodical analysis and monitoring of shoreline change is the primary requirement for effective planning and management of the coast. This paper provides the primary requirement of shoreline change rate for the past 26 years using geo-spatial technology and field investigation for proper management of the coast. Landsat 5 and 7, Resourcesat 1 and 2 and Cartosat-1 data set were used as primary data source. Long-term shoreline change rate (1990–2016) was calculated using weighted linear regression statistical method. The morphological study was carried out to substantiate the shoreline change pattern. For detailed investigation, the study area was divided into five sediment sub-cells. The analysis revealed that the maximum erosion of  54% was noticed  in sediment sub-cells II, followed by  IV (52%) and  III (43%) respectively. The result also indicated that the accretion/erosion pattern of shoreline change on either side of breakwaters was varying from place to place. The effectiveness of the coastal protective seawall was very minimal. This indicates that proper planning of any artificial structures is the basic requirement for effective management of the coast. The overall shoreline change status of Kerala coast indicates that 45% of the coast is eroding and 34% of the coast is in stable condition. Only 21% of the coast is of  accreting nature. The field survey was carried out to validate the analysed results for entire coast, specifically along the coastal structures. The study demonstrates that the combined effect of satellite data and field investigation can be a reliable approach for shoreline change analysis for these complex environments.

Shoreline change along Kerala, south-west coast of India, using geo-spatial techniques and field measurement

We estimated shoreline changes over the last five decades in a part of the southeast coast of India at Cuddalore by using multitemporal satellite images from six different time-windows (i.e. 1972, 1980, 1990, 2000, 2010 and 2020) and the digital shoreline analysis system tool (DSAS 5.0). The linear regression rate and end point rate quantified the maximum erosion at rates of 6.8–7.2 m/year and the maximum accretion at rates of 3.9–4.2 m/year at different sites along the 42 km stretch that was affected by several disasters in the recent past and has a substantial industrial presence. The net shoreline movement analysis identified the sites that experienced about 340 m of erosion and about 203 m of accretion. The Kalman filter model predicted up to 274 m of the shoreline erosion at Chinna vaaikaal until 2040. Similarly, the shoreline at Puthupettai could be accreted up to 538 m over the same interval. The outcome of this research demonstrates that studies similar to ours should be carried out in different parts along the vast Indian coastline to understand the shoreline evolution in order to prepare a better coastal management strategy.

Shoreline changes over last five decades and predictions for 2030 and 2040: a case study from Cuddalore, southeast coast of India

Detailed investigation on texture and mineralogy of beach sediments helps to understand their nature of deposition and potential targets of strategic mineral deposits. The beach sediments from the ...

Satellite-based spectral mapping (ASTER and landsat data) of mineralogical signatures of beach sediments: a precursor insight

The beach sands of the Varkala-Kovalam coast, south-west India, are enriched with heavy minerals with a high concentration of ilmenite followed by sillimanite, monazite, rutile, zircon, and garnet....

Raman-XPS spectroscopy, REE chemistry, and surface morphology of Fe-Ti oxide heavy mineral sands: a case study from Varkala-Kovalam coast, south-west India

The present study has considered the shoreline morphological changes following the construction of coastal structures, viz, groins and breakwaters along the southwest coast of India Shoreline modifications adjoining breakwaters and groins can be utilized as an indicator of the nature of sediment transport, as direct measurements involve tedious and sophisticated methods The 590 km coastline of Kerala is characterized by complex coastal hydrodynamic and morphological features along with coastal protection measures Shoreline modifications were estimated using multidated maps, images, and GPS shoreline mapping The net sediment transport is northerly along southern and some part of the northern sectors, while no net sediment transport is observed for many other parts of the northern sector The central sector shows net southerly sediment transport In general, the sediment transport along the Kerala is a complex, multi-directional, and dynamic process Moreover as the sediment transport is site-specific, appropriate analysis of sediment dynamics at a small scale is thus crucial for any coastal engineering work along this coast

Estimation of longshore sediment transport direction from varying coastal morphodynamics due to shore structures

Shoreline changes are largely dependent on coastal morphology. South-west coast of India is a high energy coast characterised by monsoon high waves, steep beach face and medium-sized beach sand. Waves are generally from west and west south-west during rough monsoon season and from south-west during fair weather season. Shoreline change along this coast is studied with reference to coastal morphological features. Various morphological features, modifications and chronological positions of shoreline are analysed with the information derived from multidated satellite imageries, toposheets and GPS shoreline mapping along with extended field survey. Image processing and GIS techniques have been used for the analysis of data and presentation of results. Sediment accumulation on the leeward side of artificial structures such as harbour breakwaters and groynes is used as a sediment transport indicator. Artificial structures such as seawalls, groynes and harbour breakwaters modify morphology. Shoreline south of headlands/promontories and breakwaters are stable or accreting due to net northerly longshore sediment transport while erosion tendency is observed on the north side. Lateritic cliffs fronting the sea or with seasonal beach undergo slumping and cliff edge retreat as episodic events. Spits adjoining tidal inlets are prone to shoreline variations due to oscillations of inlet mouth. Interventions in the form of inlet stabilization and construction of coastal protection structures trigger erosion along adjoining coasts. Seawalls constructed along highly eroding coasts get damaged, whereas those constructed along monsoon berm crest with frontal beaches for protection against monsoon wave attack are retained. Fishing gaps within seawalls are areas of severe temporary erosion during rough monsoon season. Accretion or erosion accompanies construction of harbour breakwaters in a stable coastal plain. Close dependence of shoreline changes on morphology necessitates detailed understanding of impacts on morphology prior to introducing any intervention in the coastal zone.

Noujas Varangalil

Papers

Coastal morphology and beach stability along Thiruvananthapuram, south-west coast of India