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Chapter 6

An Assessment of Physiographic Habitats, Geomorphology and Evolution of Chilika Lagoon (Odisha, India) Using Geospatial Technology Ashis Kr. Paul, Sk. Majharul Islam, and Subrata Jana

Abstract The coastal lagoon ‘Chilika’ along the Bay of Bengal shore (Odisha state, India) support a productive wetland ecosystem that influences the livelihood of local people by providing large scale fishing activity within the lagoon water body, pasturing in the lagoon fringe marshes by rearing livestock and promoting ecotourism in the islands and spits of the lagoon system using nature as magnet of attractions. The lagoon is shore parallel elongated water body enclosed with barrier spits and narrow tidal entrances, and extended in between Mahanadi deltaic distributary channels to the north east and Rishikulya River to the southwest. The average water spread area of Chilika is 1,165 km2 during rainy season and gradually it shrinkages to 906 km2 during summer months with average depth ranges from 1.70 to 3.70 m. Physiographically, the lagoon habitats are categorized as (i) Daya-Bhargavi deltaic flats with extensive fresh water wetlands, (ii) brackish water marshes and tidal flats, (iii) islands with marshes and transition vegetation, (iv) islands with mangrove swamps, (v) fresh water weeds of lagoon fringes, (vi) sand spits and dunes, (vii) and lagoon water bodies. All these habitats are showing significant variations related to geological, sedimentological, hydrological, climatic and ecological factors. Northeastern parts of the lagoon water body have been swallowed by deltaic sedimentation; barrier back shores, islands and other lagoon fringes have shrunk as the result of bordering accretion and encroachment of marshes, weeds and swamps; however, southwestern parts of the lagoon are narrowed, and in some places near-segmented by growth of spits and coalescence of headlands and islands. Opening of tidal inlets have been

A.Kr. Paul (*) • Sk.M. Islam • S. Jana Department of Geography and Environment Management, Vidyasagar University, Midnapore 721102, West Bengal, India e-mail: [email protected] C.W. Finkl and C. Makowski (eds.), Remote Sensing and Modeling: 135 Advances in Coastal and Marine Resources, Coastal Research Library 9, DOI 10.1007/978-3-319-06326-3_6, © Springer International Publishing Switzerland 2014

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shifted from one place to other place with time across the enclosed barriers to achieve the balance between water levels of the lagoon and open marine shelf, and as a result of interaction of fresh water from rivers with salt water from the sea during floods and cyclones in the region. Historically, the habitats of Chilika lagoon provided favorable conditions for maritime trade and commerce, as well as modern fishing related livelihood support system to the local people; but dynamic landscape changes of the lagoon with sedimentation have produced significant effects on human systems by changing salinity regime and eutrophication of enclosed water body. The paper highlights the gradual changes of coastal lagoon systems with variety of habitats influenced by sedimentation, fresh water inputs, local sea levels, tidal mixing and dynamic wetland geomorphology. Chilika habitats, their geomorphologic changes, ecologic responses, and evolution of the lagoon itself are studied in the present paper using geospatial technology with temporal image data, as well as with available archaeological remains of past maritime activities and existing dating records for better management option and conservation of degraded habitats.

6.1

Introduction

The coastal lagoon of Chilika (Odisha state, India) is subject to variable rates and types of geomorphological change and create a variety of habitats which are colonized by marsh plants, mangroves, other coastal plants of sand strand, weeds and algae. Chilika lagoon section of the coastal region is subject to low tidal range (below 2 m), a hot and humid climate with monsoonal rainfall, frequent landfall of Bay of Bengal cyclones, and high rates of sediment discharge of Daya and Bhargavi rivers particularly in the monsoon months. These four factors with open marine environment adjacent to the lagoon are largely responsible for the nature of geomorphic change which occurs within the lagoon system. Rishikulya river mouth to the extreme southwest of Chilika also contribute a high rate of sand size sediment discharge which takes part in the deposition of modern barrier spits dominated by north ward long shore drift. Types of plants and weeds are distributed throughout the area in a variety of physiographic habitats. It is the objective of this paper (i) to identify and assess the wetland habitats of the coastal lagoon, (ii) to discuss about the spatial variation of wetland vegetations, (iii) to examine the geomorphic change in response to various processes, and (iv) to explore the lagoonal deposits associated with sea level movements in the Holocene and Late-Holocene phases (Fig. 6.1).

6 An Assessment of Physiographic Habitats, Geomorphology and Evolution. . .

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Fig. 6.1 Location map of Chilika lagoon and its adjacent areas (Odisha, India)

6.2

Methods of Study

Stratigraphic sections from the field stations; waves, winds and tides related data from INCOIS and CDA; Landsat OLI, ETM+, TM, MSS, ASTER and QuickBird images from NASA; historical records of geo-archeological remains from existing literatures; total station survey of sample areas of Sea mouth of modern spits; SOI toposheets and Geological maps of the study area; textural analysis of sediments

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collected from Chilika lagoon habitats; vegetation identification from different physiographic habitats are considered for the purpose of present study in Chilika lagoon and adjacent areas.

6.3

Geomorphology of Chilika Lagoon

The largest brackish water lagoon is physiographically associated with four or five diverse landform units at or along the Bay of Bengal coast. Geomorphological diversity of these landform units can indicate the direction of changes by which the lagoon was evolved over a temporal scale with interactive and interplaying processes of coastal environment (Fig. 6.2). The major landform units of the coastal lagoon include: (a) the spits and tidal inlets, (b) the lagoon fringe areas, (c) the lagoon water body with wide and elongated basin, (d) the distributaries fan lobes of Daya and Bhargavi Rivers (Mahanadi delta), and (e) open marine shelf adjacent to spits. The minor landform

Fig. 6.2 Seasonal water covers areas and wetland types of Chilika lagoon


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Fig. 6.3 Geomorphic divisions of Chilika lagoon and its fringe area

units, associated processes and possible age of their formation are estimated in the following ways (Fig. 6.3, Table 6.1). 1. There are two major groups of sand spit as barrier against the open marine environment and sheltered lagoonal environment parallel to the present day shoreline of Bay of Bengal. The landward older spits (Satapada-Puri section) are originated from Mahanadi delta side and extended towards south of the lagoon shores as viewed from the images and S.O.I. toposheets of the present study area. The length, width and elevation of these spits indicate the high volume of sediment input capacity of Mahanadi distributary Rivers (Devi River and Chandrabhaga River) into the coastal zone at different sediment abundant phases and dominant long shore drift for shaping the spits from the north east direction. Chandrabhaga River was abandoned at the later stage and Devi River discharged its sediment plumes into the sea in north east ward direction as evidenced from drainage features of Mahanadi delta, and for which the supply of sediment was reduced into the landward spits with south ward weakened longshore drift in the region. The sea ward younger spits are however, developed and extended from both sides with seasonal change of longshore drifts (from north west in winter and from south west in summer months), and supply of sediments from Rishikulya River and Devi River in the modern period. In width the younger spits range from 300 to 500 m and they are backed by beach ridges and sand dunes in most of the places except in south

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Table 6.1 Landform assemblages of Chilika coastal lagoon Sl. No. Major landform units 1. The spits and tidal inlets

2.

The lagoon fringe areas or lacustrine fringes

3.

The lagoon water body with wide and elongated basin

4.

Distributary fan lobes of Daya and Bhargavi Rivers

5.

Open marine shelf adjacent to spits

Associated processes Waves, long shore currents Landward spits Waves, long shore currents, tides Spit front beach Waves Spit back dunes Winds Tidal inlets Tides Back spit islands, flats, Wind waves, bars, marshes and winds and tides channel pans Terraced banks Surface runoff

Minor landform units Sea front spits

Emerged flats Marshes and weeds Tidal flats Islands Shoaling flats Basins Delta plains Marshes Channels Water bodies Tidal flats Shallow shelf Shelf break

Winds, runoff Water logging tides Sub-aerial Tidal Lagoonal Fluvial Fresh water Fluvial Flood water Tidal Marine Marine

Possible ages 30–300 YBP 1850–1300 YBP 2200–2100 YBP

3750–1850 YBP 4300–3100 YBP 4000–3500 YBP 5000–4000 YBP

8000–6000 YBP

central shores adjacent to ‘New mouth’ (new opening of tidal inlet). The spits are flat in form and ranging from 2 to 3 m in elevation and liable to flooding in high magnitude storm events in the Bay of Bengal coast. As the balance of coastal lagoon is significantly affected due to reduced supply of sediments and fresh water discharges by Daya and Bhargavi rivers in the near past the younger spits are breached in two another places and existing inlet is also shifted towards north east. Because of such dynamic behavior of the younger spits a spit back dune body of 20 m elevation and 270 m width is washed out within 2.5 years. Around the month of July, 2012 another mouth or inlet is also opened across the spit towards north of existing one. Ample of evidences of geomorphic signatures prove the wave reworking as well as over wash activities of the low lying spits in the raised water levels (period of storms, monsoon months, H.A.T. phases) and for which the spit front beaches are scarped and spit back dunes are cliffed in many places (Fig. 6.4, Table 6.2, Figs. 6.5 and 6.6). 2. The lacustrine fringe areas of Chilika lagoon is dominated by fresh water wetlands on the landward sides (particularly near river mouths of Daya, Bhargavi, Rishikulya and others) and brackish water wetlands on the barrier back margins parallel to the present shoreline of Bay of Bengal. More over the seasonal shrinkage of lagoon body (in the drier months) also produce a sub-aerial


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Fig. 6.4 Palaeo channels along the spits and islands of Chilika lagoon Table 6.2 Tidal inlet opening and variation of tidal prisms of Chilika lagoon

Year 1972 1980 1990 2000 2000 2004 2009 2013

Date 07 Nov. 18 Jan. 28 Nov. 12 Sept. 15 Nov. 02 Nov. 13 Sept. 26 Apr.

No. of opening 03 02 01 01 02 01 02 01

Tidal prisms 93,312,000 m3 62,208,000 m3 62,208,000 m3 38,880,000 m3 54,532,000 m3 62,208,000 m3 93,312,000 m3 202,176,000 m3

exposure of an extensive areas of temporal wetlands dominated by lagoon filled sediments. The lagoon water body of Chilika covers about 1,309.63 km2 areas in the monsoon month (September), and it reduces to 797.77 km2 in the month of April (Non-monsoon month). The average water spread area of Chilika is 790 km2 according to the Remote Sensing data of 1996, though according to Government of Odisha record, the area covered by the lake is around 1,055 km2 which swells to 1,165 km2 during the rainy season and gradually shrinks to 906 km2 during summer. The total area of islands inside the lake is 223 km2. The average depth of the lake varies from 1.73 to 3.70 m during rainy seasons and 0.93 to 2.60 m during summer. About 259 km2 areas of seasonal wetland emerge at the fringe of the lagoon in winter and summer months every year. Diversified wetland types are visible at the lagoon fringe with characteristic soils and vegetations. Peaty soils, sandy soils, clayey soils, loamy soils and humus rich organic soils are found in the back

Fig. 6.5 Variation of tidal prisms in a temporal scale at Chilika lagoon through the opening and closing of tidal inlets

Fig. 6.6 Barrier spit extension, hooking, breaching and retreat along the present day shoreline of Chilika lagoon


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Fig. 6.7 Nature of spit surface morphometry of Chilika near sea mouth with total station survey

spit lagoon fringes of Chilika. In most cases, the lagoon fill sediments of underlying areas are blanketed by fluvial, fluvio-marine, marine and windblown sediments at the lagoon fringes. A number of soil pits excavated at the lagoon fringe proves the above facts at Chilika (Figs. 6.7, 6.8, and 6.9). 3. The lagoon water body with wide and elongated basin occupies a larger part of embayed coast in this part of eastern India. Balance of the lagoon is achieved between fluvial discharge and sediment input, evaporation, precipitation, tidal link with prisms and sea level change. The lagoon was extended further towards northeast along the shoreline up to Puri even in the recent past in elongated form. Ample of geomorphic evidences prove the earlier extension of the lagoon which is partially filled up with deltaic sediments of Mahanadi distributaries (Daya R., Bhargavi R. and Nuna R.) to the north east and reshaped in the present form. The northeastern part of the lagoon is also relatively shallower in compare to the central and southwestern parts due to seasonal monsoon deposition of alluviums transported by Mahanadi distributary rivers in this part annually as lagoon filled sediments. Depth of the lagoon ranges from 0.50 to 1.80 m in northeastern shores and it is ranging from 2.40 to 3.50 m in the southwestern part. Northeastern part of the lagoon is affected by concentration of weeds due to shallowness of lagoon bed, seasonal wash deposition from nearby agricultural fields, buffering of phosphorus, nitrogen and sulphars, and presence of maximum fish firms with modern shrimp culture ponds. As long as the parts of spits, bars and associated sand dunes are unstable or dynamic they may act as the major source of sediment supply into the lagoon bed in the form of washover deposition, windblown deposition, and flood delta

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Fig. 6.8 Nature of spit surface morphometry of Chilika towards southwest section (total station survey)

deposition guided by inlet channels. The inlet to the lagoon is the product of interaction between waves, currents, tides and sediment bypassing. Gradually, the inlet is shifting towards the northeast close to the old mouth due to net sediment transport from southwest to northeast by longshore current at present. The lagoon is gradually decreasing in depth due to siltation process. The tidal fluctuation is recorded as 0.20 m in non-monsoon months and only 1.00 m in monsoon months in the lagoon that is driven by the occurrences of open marine Bay of Bengal tides ranging from 0.90 to 2.40 m in front of Chilika sand spit. The lagoon was formed in between 3,700 years and 5,000 years before present (YBP) when the shoreline was located towards west in the Pleistocene era. Later the shallow shelf of the embayed basin was enclosed by sand spit extending from the mouth of Rishikulya River to the mouth of Kushabhadra River of Mahanadi delta. The northeastern extension of the lagoon was filled by Daya and Bhargavi river system in the post Hirakud situation (a dam across Mahanadi at the off take of Mahanadi delta) that accelerated the sediment flow into the lagoon, causing high rate of siltation (Das and Jena 2008). Several palaeo stands in the form of indented terraces and topographic highs or ridges with formation of concretions and compact sediments are available off


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Fig. 6.9 Various slope aspects of Chilika barrier section measured by total station survey. Amount of slope varies from 0-39.61 in the section

Chilika offshores. These are termed as evidence of Holocene sea level still stands off Odisha coast by geologists (Bhattacharya et al. 1994). With the subsequent transgression of the sea the younger sediments are overlain by underlying compact sediments. Such underlying sediments with carbonate samples from 17 m depth off Chilika-Gopalpur-Nizampatnam areas are dated at 8200 + 120 YBP (Rao et al. 1990) which is very significant in this respect of sedimentation rate along the shallow shelf. If it is the beginning of the subsequent sedimentation around the shallow shelf and Chilika embayment, the overlying sediment column might have been deposited at the rate of 4 cm per 100 years. Furthermore, it can be extended as an estimated rate of sediment deposition for the case of Chilika lagoon till today. As Chilika lagoon or embayment is older of 5,000 years, the upper most sediment depositional column might be approximately 2.00 m in thickness. Gradually by subsequent transgression and regression processes the lagoon bed is filled up and lagoon margins are modified with sedimentation (Table 6.3). 4. Today the distriburary sedment fan lobes of Daya and Bhargavi rivers with palaeo channels can be identified from the satellite images of northern Chilika lagoon. The sediment plumes of both the rivers are extended into Chilika lagoon in the monsoon months, and such evidence proves the time, duration and

Samples 1.70 mm 1 mm 850 μm 500 μm 425 μm 250 μm 150 μm 125 μm 75 μm 38 μm