MORPHODYNAMICS OF CHILIKA MOUTH- STUDY ON SHIFTING OF TIDAL INLETS AND ASSESSMENT OF SHORELINE CHANGE ALONG EASTERN COASTAL INDIA, USING GEOSPATIAL TECHNIQUES AND DSAS EXTENSION

This study is focused on the spatio-temporal change in shoreline along Chilika coast and migration of tidal inlet of Chilika lagoon using multi temporal satellite images from the year 1972-2019. This study is carried out over decadal analysis with utilization of EPR and LRR system of DSAS model. For this change analysis studies the Landsat satellite images and IRS-P6 LISS-III images has been used. From the study it reveals that there is one new mouth opening in 2019 after occurrence of cyclone Fani. Based on calculations, the mouth of Chilika mostly has shifted in northward direction. It may due to frequently occurrences of cyclonic storm surges, which usually associated with winds and tidal actions over the coast. This study shows the high erosion trend along 8.3 km in northern part of shoreline. The accretion found along 6.5km in central part of shoreline. The coastal region is now more vulnerable to natural disaster as well as manmade disaster. Most of the areas are prone to floods. This problem may become very serious due to rapid increase in population. Every year the eastern coastal region is destroyed by cyclone and floods.


846
In the present study, IRS P6 LISS-III and Landsat multispectral images has been used for identification of shoreline change along Chilika coast in temporal scale of 60 years interval. The spatio-temporal change in Shoreline were analysed using Remote Sensing and GIS.

Study Area
The study area ranges from 19°28' and 19°54' N latitude to 85°05' and 85°38' E longitude in state of Odisha, one of the eastern coastal state of India. Chilika Lake is the largest brackish water lagoon in eastern Coastal India which spreads over Khurda, Puri and Ganjam districts. It covers an area almost 1165 sq.km.in summer and 906 sq.km. in winter at the mouth of DayaNadi and flowing towards Bay of Bengal. It receives the fresh water from various rivers like Daya, Bhargavi, Malaguni, Nuna and other distributaries of Mahanadi River and saline water from Bay of Bengal.

Geomorphic Evolution Of Chilika
Chilika lagoon is the largest brackish water body in east coast of India. From the history of Orissa the ports located around Chilika lagoon had an important role in expanding the Indian culture to other countries. Hydrologically, it has been observed that three subsystems have an influence on Chilika. Those are the Mahanadi river system, rivers flowing from the western catchment in to the lagoon, and the Bay of Bengal. The lagoon receives freshwater from a series of 52 channels. The lake is about 64 km long. It extends from the southeast corner of the Khurda district into the adjoining district of Ganjam. However, the formation of sand bars, spits are due to changes in the hydrodynamic regime.
From history over 4 th century AD, Chilika was appeared due to the sudden inflow of water into the sea. Most commonly Chilika lagoon hasexperienced both coastal submergence and emergence. According to (Gazetteer 1908) the Chilika lagoon was formed as the sea receded for a couple of miles and at the same time flooded over a greater part of Puri district.
According to a school of researchers Chilika lagoon may have been formed towards the end of Pleistocene period. Post, Pleistocene period the coastline might have receded due to marine and fluvial activities. This geomorphological activity in the Bay of Bengal might have created a shallow, brackish-water inshore lake connected to the Bay of Bengal through a narrow mouth. According to B. N. Sinha the evolution of Chilika is parallel with the origin of Eastern Ghats. Through the researches of geologists, can be said that when Gondwana land started to move in north eastern direction, the Tethys Ocean got folded up into present Himalayas during Tertiary period. The peninsular India was formed when the land drift stabilized upon touching the Tibetan plate. Simultaneously, the Western Ghats was formed through a massive N-S fault which when stabilized & subsided balanced with a tilt to the eastern side. This resulted in the rivers flowing from west to east.
During the same stage the Deccan land plate drifted from East coast of Mozambique towards the Indian land mass. While through the creation of Western Ghats the volcanic lava in the Deccan flowing to the eastern coast of India. The rivers now started flowing from the higher altitudes of Western Ghats giving rise to numerous gorges along the Eastern Ghats, during its formative time. Hence, evolution of Eastern Ghats is a very important landmark in the history of Peninsular India.
As Rambha spur in Eastern Ghats, the Gondwana strike line changed its direction towards and entered into Bay of Bengal. This spur gave rise to the present day Palur hills, which may be attributed of having given birth to Chilika. Evidence show that the river Mahanadi was draining into the Bay of Naraj and not into Bay of Bengal. The Mahandi delta was formed much later forming the NE of the present Chilka. The SE frontier of the Chilka is attributable to the advancing of the delta formed by Daya, Luna and Bhargavi, distributaries of Mahandi.
In later years, the silt deposited by the river Salia, Mandakini, Malaguni, Dhanua etc. delivered the western margin of the Lagoon. In the north east from Palur hills there was a formation called bar, which is built by the silt and sand carried by Rushikulya river and wave action during south west monsoons aided by strong current from the Coromondal coast. The sea wind drifted the sand dunes from Bay of Bengal coast to Chilika, forming numerous islands due to this Aeolian action. This bay bar and islands developed through stages and not continuously, but continually. This phenomenon is evident through the presence of the ten mouths as identified in the satellite imageries. Thus mouth of Chilika was open from Palur hills to Arkhakuda. After the formation of Malud Island 847 there was a constricted opening and the free flow of salt water from the Bay of Bengal was obstructed and thus Chilika started to deteriorate in its ecosystem.
The presence of the headland and bay topography, the sea cliffs and sea stacks along the western and southern margins of Chilka indicates that it was exposed to open wave action during the geologic past, there by shifting the coast line. The erosional features evident in the periphery of the Lake are presumed to have resulted towards the end of Pleistocene or latest, during the time of the maximum Holocene transgression, before the beach ridge on the eastern side of the lake. A possible neotectonic activity might have resulted in the prominent lineament trending in NE-SW direction parallel to the long axis of the lake, as interpreted through the satellite imagery.
The deposition of the bidge ridges and the spit which enclosed a body of sea water resulting in the formation of lagoon Chilika took place during later part of the Holocene.  In the present study according to predefine objective, the satellite images for the years of 1970s, 1980s, 1990s, 2000s, 2010s & 2020s has been used for assessing the movement of shoreline. The detail of data used in present study has been mentioned in table 3.1. In this study the US Toposheet for the year of 1930-35 has been used as primary reference for extract shoreline and the location of mouth along Chilika. Based on that toposheet the change in position of shoreline (erosion/ accretion) and shifting of tidal inlet has been identified.
The LANDSAT satellite images (L1 MSS, L5 TM, and L7 ETM+ & Sentinel) have been downloaded from United States Geological Survey (USGS) and used. The LISS III image has been downloaded fronBhuban, ISRO site and used for preprocessing.
The focus of this study is assessment of historical change of shoreline along Chilika coast form various of year intervals i.e. 1972-1980, 1980-1990, 1990-1999, 1999-2012 and 2012-2020. All the images have been preprocessed in geo-tiff format, and geo-corrected in the WGS84 datum through Arc GIS 10.1. The visual interpretation and band rationing process has been done. The layer stalk and subset process of images has been made according to study area.
Then need to digitize the shoreline from Landsat satellite images using Arc GIS software in line feature to identify the movement of shoreline.
To quantify the erosion and accretion rate the year wise shoreline has been digitized in line feature from multi temporal satellite imagery.
The overlay analysis for different year of satellite images has been done to delineate differences in year wise increase and decrease of shoreline length.Then the displacement of shoreline has been measured in time series format. The landward movement of shoreline is identified as erosion and seaward movement in shoreline is known as accretion.
The Digital Shoreline Analysis System (DSAS) model as an extension of Arc GIS software is applied for the study of coastal behaviour and shoreline change rate.
There are different methods of DSAS system i.e. net shoreline movement (NSM), end point rate (EPR), linear regression rate (LRR) has been used which is helpful in evaluation of historical change in shoreline position.
For this study the transect layer has been created by considering 50 meters of spacing as fixed distance. In this method the uncertainty of results increases by high spacing of transects and massive data values occurs along low distance spacing.
So here by 50mtr spacing has been taken for the study. In the present study to calculate the distance of movement of shorelines from 1972-2019, three statistical methods has been use. Such as -End Point Rate (EPR), Net Shoreline Movement (NSM) and Linear Regression Rate (LRR).
End Point Rate is calculated by dividing the distance of shoreline movement by the time between the oldest and recent shoreline.

EPR (m/yr) = distance/ (time between the oldest and recent shoreli
Net shoreline Movement is used to calculate the distance. It denotes the distance between oldest and recent shoreline.

NSM (m) = distance between the oldest and recent shoreline
850 Linear Regression Rate is determined by fitting a least squared regression line to all shoreline points for a particular transects. LRR is the slope of line.

Results &Discussion:-
The administrative map of Chilika Lake and movement of Shoreline at Chilika coast in 50 years of duration is shown in map 4.1 & 4.2. The detailed shoreline lengths have been measured and presented in table-4.

Periodic River Mouth Dynamics
Identification of shoreline change is due to periodic mouth dynamics and erosion/ accretion along the study area for the period of 50 years interval from 1972 to 2019 using remote sensing and GIS.From past literatures found that many cyclonic storms have been occurred along Chiika coast and shifting of tidal inlet takes place. Here in this study the past cyclonic storms along Chilika have been listed out and the detail shifting of mouth relating to cyclone has been identified.  In the present study, the location of mouth demarcated on US Topo by Army Map Services, US department of Defence in the year of 1931 has been taken as standard point and the shifting of mouth along years from 1972-2019 has been measure with respect to that. In the image of 1972 Nov. it has been observed that there are 3 mouths opening to Bay of Bengal and the mouth 1 is found to be shifted 1.72km in southward direction where other 2 mouths are shifted in northward direction. It may occur due to cyclonic storm on Sept, 1972 which touched the land at Gopalpur coast. On Jan, 1980 it is found that there were only 2openings which was displaced by 670.60 m and 1.19 km in northward direction. On Feb, 1990 it is observed that the mouth has shifted around 3-4km in northward direction. On Nov, 1999 it is observed that there is only 1 mouth opening to Bay of Bengal, which has shifted 7.7 km towards north. Again on July, 2019 there is a significant change along coast after occurrence of Cyclone Fani. Ii is found that there is one new mouth opening. Other 3 mouths have shifted by 4.5, 3.7 & 3.5km in southward direction. There also field verification has been done by collecting GCPs and the compilation of remote sensing data has been done. It is observed that there is a deposit of slit, mudflats clay with fine sand along Chilika Coast. This study reveals that the instability motion of sandbar due to water waves is the important element of mouth dynamics. The wind direction along Chilika coast causes wave approach to the shoreline and give rise to shifting in position of mouth

Erosion and Accretion
The present study reveals that the shoreline change has dynamic behaviour which has been influenced by the occurrences of cyclonic storms and wave height.    The coast may be affected due to storm surge generated by the cyclones and the wave height ad wind pressure in the Bay of Bengal.
Here maximum erosion occurred at northern part of Chilika coast. Somehow central part of the Chilika coast is accreted and erosion is mostly observed in northern and southern part.

Conclusion:-
From this study it concludes that, application of remote sensing and GIS is very helpful in monitoring periodically shoreline change with high accuracy. The state Odisha is considered as highly vulnerable state in eastern coastal India. Odisha has been facing cyclonic hits more frequently now days. This causes increase in coastal erosion in recent years. The deficiency in forest and vegetation cover may aggravate the vulnerability of coast. As a result, the cyclonic winds may affect the land without any restriction. The coastal areas are highly populated and that may cause more vulnerable to infrastructure and human health. Chilika coast has undergone accretion in central part and erosion is in northern direction, which seems the ocean current and wind direction is northward flowing. A GPS survey with geo tagging application may be carried out for accurate shoreline change detection and morphological assessment.

Further scope of study
The more specific micro level study including land form change and characteristics of agricultural and aquaculture activities can be taken for consideration. Studies of sediment dynamics from land into oceans by rivers in this region may be suggested for future study.Further, the impact of wave energy and other meteorological factors on the erosion and accretion process were also measured.