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    Topic review

    Urbanization Impacts, Water bodies Wetlands

    Subjects: Geography
    View times: 159
    Submitted by: Mythili Madhusudhan

    Definition

    The impact of human habitation on ecosystems with reference to the particular case of a wetland situated in the city of Chennai, India is the focus of this paper. As the city grew the wetland site is known to have gained attention and simultaneously, the overall region which was viewed by the government with a development agenda, leading to an influx of population and a massive scale of urban growth. Appropriate monitoring of environmental resources will determine ways to evolve a methodology for a sustainable management of the region. Time series data from Landsat images and historical cadastral maps from the same initial time period are used for analysis. Trend analysis, studies from secondary sources, field observations and interviews with various members of the public including long term and new residents has culminated in this research which evaluates the present condition of the region and highlights the major issues and defines some recommendations for the public and for decision-makers and authorities.

    1. Introduction

    The transformation of eco-social landscapes (1), the drivers responsible and its consequences has caught the attention of ecologists, landscape and urban planners and engineers alike. “The suburb is a place where someone cuts down all the trees to build houses, and then names the streets after the trees" is a relatable statement by Bill Vaughan. This statement reflects what, in many countries, is the current state of development, often green areas lost to burgeoning city growth. Indian cities have shown a similar propensity for putting economic growth in the forefront, and in the case of Chennai, one can see the city boasting of ‘Lakeview roads’ in historical suburbs and modern peripheral areas which are built on reclaimed land, once water bodies. Incidentally, land reclamation is not an uncommon occurrence in many cities in India, such as Mumbai (2), Kolkata (3), Bengaluru (4), Hyderabad (5) besides Chennai (6). This paper addresses and approaches water bodies and wetlands from a regional perspective giving due attention to recent research which highlights the possibility of the emergence of ‘novel ecosystems’ (7) or ‘hybrid ecosystems’(7) through dialectic interaction of competing human occupation and natural processes.

    Wetlands are known to have biological and sociological implications on the lives of people. Wetlands may be inland or coastal land-forms, and human-made wetlands (such as rice-paddies, dams, reservoirs and fish ponds) also find their way into this category. Wetlands are central to water and food security of the region. Many large cities are dependent on wetlands for their water supply, e.g., Bhopal in Madhya Pradesh (8) and Kollam in Kerala, (9) and wetlands like the East Kolkata Wetlands are famous for their fish production (3,10,11). Wetlands act as buffers against extreme events, for instance the Deepor Beel which cushions the city of Guwahati from the floods of the River Brahmaputra (12). Wetlands are found to have deep connections with culture and traditions in India such as associations of ‘mother’ (Loktak lake, Manipur) and ‘wish fulfilling’ (Khecheopalri lake, Sikkim) and uses of tourism as in Kodaikanal (Tamilnadu) and Nainital (Uttar Pradesh) have also been established. Wetlands also serve as habitat for a number of plant and animal species including those of high conservation value (13–15). On a global scale, the aggregate value of the ecological services generated by wetlands has been estimated to be $4.9 trillion/year (16).  In all, these comprise the various ecosystems provided by wetlands, which are of provisioning, regulating, cultural and supporting (13,17) nature. The Millennium Ecosystem Assessment identifies 14 ecosystem services(18), nevertheless certain other sources give larger numbers.

    Wetlands are coalesces of land and water, combining the characteristics of terrestrial and purely aquatic ecosystems, the primary characteristics of which include the presence of water at or near the surface at least for part of the year, plants sensitized to wet conditions (hydrophytes), and soils that are saturated or flooded long enough to develop anaerobic conditions (hydric soils) (13). The Ramsar Convention (1971), an institutional framework for conservation of wetlands, uses a broad approach for defining these ecosystems as “areas of marsh, fen, peatland or water, whether natural or artificial, permanent or temporary, with water that is static or flowing, fresh, brackish or salt, including areas of marine water, the depth of which at low tide does not exceed six metres”.

    The threats to wetlands stem from various kinds of man-made activities: lack of attention, neglect and permitting incompatible neighbours to harm the landscape and pollute the lands, surface and groundwater; construction of roads and infrastructure fragmenting pristine lands, destruction of water resources (3,8,12,19) and affecting the upstream and downstream catchments by various activities, siltation affecting water-holding capacity, exploiting groundwater resources, unmanaged urbanisation and permitting building on wetlands thus increasing impervious cover, both by the government and individuals causing impacts at unimagined scales. As they are vital resources in the urban landscape, wetlands need to be able to withstand the impacts of urbanization. Research has shown that in wetlands the world over, the city wields greater power because of the convincing argument of economic growth and promise of increased prosperity. In China,(20) in spite of establishing more than 550 National Wetland Nature Reserves and 100 National Wetland Parks the annual rate of disappearance of wetlands is still around 1%. In certain parts of the USA, wetlands are being conserved by mitigation in alternative sites (21) or by ‘habitat conservation plans’ (22) including ‘no surprises rules’ for property owners who will not be burdened by financial or other restrictions on account of the wetlands if they have entered into an agreement. In Bogota, (23), Kakadu wetlands, Australia (24), biodiversity has garnered attention and in Lagos (25), Zimbabwe (26), Dhaka (27) and SriLanka (1,28), there exist various cases of urbanization impacting wetlands negatively, with instances of encroachment or myopic development plans on the part of the government. At this juncture, one recalls Henry Lefebvre’s theory of the production of space and right to the city, in which he argues that urbanization is a significant part of the changing world, with reference to conflicts over land (29).

    The Pallikaranai marsh, one of the few and last-remaining natural marshes of South India (30), extended to more than 5000 hectares as recently as 60 years ago (6,30,31) and has been reduced to one-tenth of its original area as it was subjected to various human-centric activities like development of roads and urban infrastructure and also due to its non-recognition as a wetland. The anthropogenic impacts include division by means of a road construction across the body of water with provision of culverts below to maintain flow and water level. Additionally the establishment of a corporation dumpyard on the water body, contaminating the groundwater and encroachment by various individuals, government and citizens and acquisition of lands all around are the stressors on the marshland. After various activist responses by the public and various non-governmental organizations (NGOs), the government initiated a move towards protection of the marshland and 620 ha (initially 317 ha) was declared as protected land and brought under the control of the Forestry department. It is notable that the marsh though encroached upon and damaged by various agencies, has evoked a certain degree of public awareness, maybe due to its size though shrinking and its historical significance.

    This study illustrates the use of remote sensing and GIS techniques in the analysis of wetland catchment (32–34) as a prerequisite for outlining restoration measures. The methodological focus of this paper is the utilization of cadastral maps worked with Arcgis software (35) and Landsat satellite images used to perform a study of land use conditions over four decades before and after governmental intervention. Even though numerous studies of the Pallikaranai marsh by various individuals and agencies exist, they are primarily of water quality studies, groundwater, environmental impact assessment, and also on biodiversity, but this study is of a socio-spatial kind and deals with the impacts effected by external agencies on the overall scale and the marsh itself. The study presented here, based on an understanding from existing literature and field conditions, official reports and newspapers, analysed land-use conditions enabling trend analysis from Landsat archives and cadastral maps and analysis from secondary sources.

    In this entry we address three research questions investigating the social and land-use drivers and consequences of ecological transformation of the wetland under question.

    • What are the kinds of eco-social changes occurring in the wetland?
    • What are its drivers and consequences?
    • How did incremental ecological changes add up over time into an overall transformation of ecological and social character of the wetlands?

    The entry is structured as follows: firstly, the introduction and statement of objectives followed by description of study area, followed by the methodology adopted and analysis by geospatial techniques, which is followed by an explanation of results obtained and discussion based on issues relating to the eco-social changes and environmental drivers as discussed in the research questions, concluding with recommendations.

    2. Materials and Methods

    2.1. Study area

    Pallikaranai Marsh, situated on the geo-coordinates of 12.949371°N latitude and 80.218184°E longitude, is among the last existing natural wetlands of Chennai city. Locally known by the generic Tamil name ‘Kazhuveli’ which translates to ‘marsh’ or water logged area (6), the marsh is bound in the east by Old Mahabalipuram Road (OMR), in the west by Tambaram-Velachery road, Velachery village and Velachery lake in the north and by Medavakkam-Karapakkam road on the southern side. It drains about 250 km2 area through two outlets viz., Okkiyam Madavu channel and the Kovalam creek and empties into Bay of Bengal. The marsh area had spread to an extent of 6000 ha (60 km2) around the 1906s, of which there is a 90% loss of habitat resulting in the presence of only 593 ha of marsh (30). In 2007, the State Government, responding to a science based advocacy programme of a concerned NGO and civil society network (30), part of the advocacy programme viz. ‘Save Pallikaranai Marsh Forum’, notified the southern portion of the marsh spanning 317 ha initially as reserved land, which was later upgraded to Reserve Forest.

    Chennai, the capital of the state of Tamil Nadu, currently houses a population of 8.6 million  (36). Similar to many Indian cities, Chennai’s growth has occurred mostly in recent decades. The greater Chennai area covers approximately 550 square kilometers (37) of  built up surface which happens to be substantially larger than its 176 sq.km municipal corporation boundaries (37) and is extending to the larger (1189 sq.km) Metropolitan Development Authority area. The first master plan for Chennai Metropolitan Area came into effect in 1975 for a period of 20 years till 1995 (38). The much-delayed second master-plan was approved by the government only in 2008 (38,39). Apparently it strategized augmentation of urban water and improvement of an open space network according to the plan chapters. In 1993, Chennai Metropolitan Development Authority (CMDA), the predicated planning authority of the state engaged consultants to study Pallikaranai and propose measures for drainage of the region and facilitated a Flood Relief Storm Water Drainage Master Plan Study (41,42). The consultants’ study recommended that the ‘Pallikaranai Development Area’‘could be developed as a light/medium scale industrial area without much adverse environmental impact’. This sums up the planning history of the Pallikaranai region from the governmental perspective.

    As for the public perspective, this part of the city  achieved a hitherto unforeseen popularity as a real estate destination for buyers big and small, following the construction of the road, hereafter referred to as 200 ft Radial Road and a series of grandiose residential projects in the early 2000s (43,44). Since then, due to proximity to the airport and the development of other roads, its popularity arose. This was in spite of its former lack of identity which may be attributed to the fact that one would never really build near or on a wetland if one had the choice.

    Another aspect to be considered is, with respect to Chennai, the water scenario is of much concern, with the city experiencing water insecurity even with 700mm and 1100mm annual rainfall (45). Pallikaranai region is over-exploited in this respect because it lies in an area where ground water was extracted from the peri-urban villages and supplied all over the city (46). Goldman and Narayan (47) have analysed, with respect to Bengaluru, shifting urban trajectories, existing agrarian relations and their interlinkages with water. It is intended to make a similar case with respect to Chennai, examining the role of the region under study and the trajectories revolving around it.

    Figure 1. Selection of Study Area

    As mentioned earlier the CMDA commissioned a study in 1993 (41) to identify the causes of flooding in the region. With reference to this study on drainage and the subsequent Environmental Impact Assessment (EIA) (42) addressing the wetland area south of the marsh leading to Kovalam estuary which drains into the Bay of Bengal, it is intended to address this associated wetland area. Thereby, a study area surrounding the Pallikaranai village [1] including the adjacent seven villages which share a boundary in the draining directions, viz. east and south comprising an area of 5657.032 ha has been identified. 

    Table 1. Details of Study Area

    S.No.

    Name of Village

    Administrative Status

    Area (Hectares)

    Population (2011 Census)

    Population density

    per sq.km (2011 Census)

    1.

    Perungudi

    Town Panchayat

    455.1882

    43111

    9471.0275

    2.

    Pallikaranai

    Town Panchayat

    1654.9443

    43493

    2628.0711

    3.

    Seevaram

    Village

    73.5311

    Not Available

    Not Available

    4.

    Okkiyamthuraipakkam

    Census Town

    657.9500

    76600

    11642.222

    5.

    Jalladampettai

    Census Town

    232.6998

    19100

    8208

    6.

    Karapakkam

    Village

    267.2412

    8958

    3217.33

    7.

    Sholinganallur

    Town Panchayat

    1559.5862

    35602

    2282.18

    8.

    Perumbakkam

    Village

    755.8911

    Not Available

     

    Initially, we performed a more general survey of the overall context. For the year 1975, the Survey of India topo sheet [2] T66D1  was digitised and the roads, buildings, open areas, and  water bodies were delineated. For 2005, the most recent topo sheet by Survey of India D44U1,5 was procured and digitized and the settlement boundaries, roads, water bodies, agricultural land were obtained as per the topo sheet. These have been visually compared to observe the changes, growth in urban land cover and decrease in open area.

    Figure 2. Incremental transformational changes in the region: 1975& 2005

    Thus, two topo sheets for the years 1975 (T66D1) and 2005 (D44U,5) have been digitised wth the help of Arcmap software and compared visually. The extent compared is the same in both the cases and the vector maps are spatially adjusted to the actual geo-coordinates. The 1975 topo sheet displays two major roads, the current Velachery Tambaram Road on the western side  and the current Old Mahabalipuram road on the eastern side, the Buckingham canal, certain water bodies, few buildings and trees which have been marked as point features on Arcmap, The rest is open area, comprising agricultural area or other open areas, and marshland. In the 2005 map, where the entities have transformed into a more complex matrix, there is a definite shrinkage in the outline of the marsh, while the lost areas have been taken over by settlement, agricultural patches with marsh areas interspersed in the matrix. Incidentally, most studies about wetland water quality pertain to the impervious cover especially road density of the surrounding area (48).

    In an effort to study the available records relating to water bodies from older revenue maps, the maps procured for the year 1985 were personally obtained from the Survey and Settlement Department, Survey House, Chennai. These maps were scanned to a resolution of 300 dpi and joined and stitched together using Adobe Photoshop software. The tiff layer comprising the merged maps was then georeferenced. The procured maps from the year 1985 are used to create a layer comprising of the water bodies in Arcmap, acknowledging a reference to Madry et.al., (35). This layer of water-body polygons gives the location, exact outlines, areas of the water-bodies from vector format and was digitized in a scale of 1:8500 from the cadastral maps. This layer acts as a database for the period before the present spate of urban development in the area and the number and area of water bodies in the abovementioned eight villages is available in the Arcmap attribute table.

    In order to determine extent of various land-uses and to obtain changes in water extent, remote sensing methods have been used. For this boundary, denoted in Fig 1(e), Land Use Land Cover (LULC) classification was performed. Landsat images were acquired from USGS Earth Explorer and processed. Post-monsoon imagery from the month of February for all four decades were used. The dates and types of images are as listed below:

    Table 2. Satellite Data

    S.No.

    Date of acquisition

    Satellite / sensor ID

    Path/Row

    Spatial Resolution / Cell size (m)

    Sources

    1.

    06 Feb 1988

    Landsat 5 “TM”

    142/51

    30m

    USGS

    2.

    17 Feb 1998

    Landsat 5 “TM”

    142/51

    30m

    USGS

    3.

    29 Feb 2008

    Landsat 5 ”TM”

    142/51

    30m

    USGS

    4.

    25 Feb 2020

    Landsat 8 “OLI_TIRS”

    142/51

    30m

    USGS

    The images were classified with the help of Erdas imagine software and processed in Arcmap 10.0 as has been done by (49). An appropriate number of bands were classified in each case, including visible and near infra-red (and in Landsat 8, SWIR 2 also) to obtain a land-urban false colour composite showing vegetation, water and built-up areas. To obtain changes in land-cover dynamics, NDVI and NDWI were also mapped for the four years.

    • Classes identified

    For the LULC, five classes were identified in the images which decreased to four classes in the more recent images. The classes are, vegetation, water body, marshland, sand and built-up cover class.

    • Vegetation

    Vegetation cover identified from the imagery includes wetland vegetation, vegetation covering water, forest, urban vegetation, mangroves and scrub vegetation.

    • Water body

    Water body including shallow water is classified under this class which includes wetlands, tanks, streams, canals, lakes and shallow water.

    • Built-up

    These pixels indicate the built-up areas in the image and are thus classified including residential, commercial, industrial, transportation, mixed-use and utilities.

    • Marshland

    In the False Color Composite (FCC), marshland appears as brown color pixels and are seen in some regions around the water bodies.

    • Sand

    This includes sandy areas, mixed barren lands, empty river beds found around the marshland and along the coast.

    The watershed basin of the study area is also delineated with the help of Arcmap software using the DEM file from the National Remote Sensing Centre (NRSC) Bhuvan source. The basin profile for the study area is thus provided in the map. A study of the existing water-bodies from the 1985 revenue maps, the areas of which were ascertained from Arcmap software, and the state of the corresponding water-bodies in latter period, viz., 2008, sourced from the CMDA masterplan maps, whose data is ascertained by verifying the survey numbers  of  the water-bodies, exhibits certain trends (50).

    3. Results and Discussion

    The results demonstrate that Pallikaranai wetland and its associated regions were impacted both by government decisions to develop the region and encourage industrial growth and subsequent urban development, and public behaviour, viz., population dynamics, migration and occupation of lands in proximity to the water body, encroachments by public and private bodies and lack of attention. The land-use classes used to classify the satellite maps have been mentioned earlier.

    Figure 3. Land Use Land Cover analysis maps

    Table 3. Land use land cover data

     

    1988 (sq.m)

    %AREA

    1998 (sq.m)

    %AREA

    2008 (sq.m)

    %AREA

    2020 (sq.m)

    %AREA

    Vegetation

    14633191.52

    25.91

    12607537.82

    22.32

    12432253.8

    22.02

    11619196.8

    20.57

    Water body

    4756472.12

    8.42

    2414251.1

    4.28

    3300121.5

    5.84

    2675848.46

    4.74

    Builtup

    29186830.3

    51.68

    33077845.66

    58.57

    34881736.3

    61.77

    36906631.66

    65.35

    Marshland

    6142513.2

    10.88

    6212204.82

    11.00

    5852549.67

    10.36

    5272061.04

    9.34

    River sand

    1753872.1

    3.11

    2161517.2

    3.83

    0

    0

    0

    0

     

    56472879.24

    100.00

    56473356.6

    100.00

    56466661.2

    100.00

    56473737.96

    100.00

    Figure 4. Land Use Land Cover data

    These include the results from the LULC analysis. Simultaneously, the water bodies covering the whole study area were mapped for the years 1985 and 2008 from cadastral maps and second master-plan land use maps from the website of the CMDA (51) and the changes in the water extent according to this data is presented below.

    Figure 5. Hydrology map for the study area and Water bodies layer extracted thro Arcmap

    Figure 6. Water body analysis data

    Table 4. Analysis of Water bodies layer from 1985 and 2008

     

    Number of water bodies

    Largest water body area (sq.m)

    Smallest water body area (sq.m)

    Total area of water bodies (sq.m)

    Average area of water bodies (sq.m)

    Standard deviation of area of water bodies

    1985

    153

    6113780

    86

    9927123

    64883.156

    498298.184

    2008

    30

    3804695

    2742

    7206431

    240214.366

    683020.477

    On comparison between the 1985 and 2008 water bodies layer, the transformation in terms of the water extent viz., attributes of the water bodies for both years can be envisaged. The master-plan land use maps indicate that the water bodies have been converted to other uses over time and the land uses to which they have been changed proportionally with number of water bodies in the y-axis is plotted in the sixth graph in Fig 6. These land use maps were digitised and converted into kml format and the parcels which were originally water bodies in 1985 were observed in Google Earth. In Pallikaranai  Okkiyamthuraipakkam and Karapakkam the water bodies have been completely built upon to the extent of over 60%. In Pallikaranai, the marsh edges have been encroached upon and other water bodies have shrunk or dried up, whereas in other villages and within Pallikaranai also, buildings cover the previously existing water body sites in many cases. In Sholinganallur, on either side of the East Coast road, a large extent is zoned as restricted development area as it is an aquifer recharge zone, (as seen in the graph) but this is only on paper and there is found to be a gross extent of building activity in these regions also. Natham is a name for commons, and this land use is found in few villages.

    • Changes in wetland and watershed land-use
      • LULC change status 1988

    Vegetation is present covering both the water bodies and in the land area. A number of water bodies are also seen in this stage. A fair extent of marshland and sand cover class is visible all over the extent. Built-up cover class is seen occupying the rest of the area to an extent of 51.68% of the total area. Vegetation area totally occupies 25.91% of the total area. Water body area appears to be less, but is camouflaged by the vegetation layer as mentioned earlier. Another factor is, if we were to compare the 1988 LULC map and the 1985 water-bodies layer, the area of the water (covered by vegetation in this map) and the outline in the other map match in extent as to be expected.

    The prevalent landscape comprised of numerous water bodies as studied from the revenue maps, including the marsh and the channel, and wetland vegetation including grasses and other varieties supported it. These features predominated and further, marshland and sandy soil were present and only the rest was built-up cover class occupying 51.68% of the area boundary. In 1985, Pallikaranai was not yet identified for development by the government and the agricultural villages were present and water availability was copious. Numerous canals were found in the revenue maps in some villages and correspondingly the quantity of water in the LULC analysis is higher.

    • LULC change status 1998

    Vegetation is present covering both the water bodies and the land area, and like in the 1988 map, probably, both deep and shallow water areas. The extent of marshland and sand is still existent but decreased compared to the 1988 extents. Built-up cover class occupies the rest of the area and has shot up to an extent of 58.57% of the total area. Vegetation, in this analysis, occupies 22.32% of the total area. The extent of water body appears to have decreased.

    The marked change in the 1998 study happens to be the introduction and growth of the dump yard on the water body, seen in the north-eastern side of the marsh boundary. Vegetation has begun to disappear on the western side of the marsh and water bodies and vegetation on the eastern side of the marsh have also disappeared and are replaced by built up areas to an extent of 58.57%. Subsequently the marshland area has also been reducing along the edge. This may be the after-effect of the ‘Pallikaranai Development Area’ policy mentioned earlier.

    • LULC change status 2008

    The extent of vegetation is seen to have come down to 22.02%. The major difference in this decade is the introduction of the 200ft Radial road, dividing the marsh in the east-west direction, which can be seen in the map. This road was added in the early 2000s and as it divided the marsh physically, with a number of culverts beneath, to convey storm water flow and drainage channels along its sides, it has led to a plethora of inundation issues and with the passage of time, sedimentation and accumulation of deposit, with the reduction in availability of water due to various factors. In this map, more water extent is visible and is exposed (less covered by vegetation), so the area is greater than in 1998, but it may be shallower. Built-up area has increased compared to 1998 to 61.77% and marshland is still present (exhibiting) a decreasing trend. Areas which were classified as sand in the previous years have become urbanised in this stage and hence its value is zero.

    This is the period since the introduction of the east-west 200-ft Radial road, which divides the marsh into north and south. The growth in the dump yard can be visibly seen in this map. Connectivity between east and west has seen an improvement because of this road and hence urban development (to an extent of 61.77%) and subsequent disappearance of water bodies and vegetation.

    • LULC change status 2020

    Vegetation extent in this map covers an extent of 20.58% and has come down. The proportion of water body also has decreased compared to 2008 and built-up area exhibits a drastic increase to the extent of 64.94%, post economic and infrastructural development which characterize the region. The Old Mahabalipuram Road, also known as the IT [3] Expressway, which is home to a number of multi-national corporations and multi-storeyed buildings, the earlier-mentioned 200ft Radial road, which has catalysed a real-estate growth and the Velachery-Tambaram road, which connects to the south-western part of the city have spurred a city expansion at a relatively rapid scale. Incidentally, the Old Mahabalipuram road and the Velachery-Tambaram road, were identified from as far back as 1975 in the topo sheets that were digitized and surveyed in the previous studies. Built-up cover class has taken over completely (to an extent of 64.94%) and vegetation (20.58%), water body (5.89%) and marshland have dwindled. The dump yard also, seems to have grown as seen from its outline.

    The water body analysis reveals that from 1985 to 2008, a vast majority of water bodies have been removed from the map altogether, the total number having decreased from 153 in 1985 to 30 in 2008. Details of areas of the water-bodies, largest, smallest, total and  average area are presented in Fig 6.

    The map shows the overlay of the outline of water-bodies layer from the 2008 delineation on the LULC classification of the current data. From this we can observe the extent of water-bodies as per both datasets. The revenue maps outline shows the remnant water-body outlines and the classified data show the extent of available water as per recent data. How the two correlate is a direct visual observation. It can be observed that there is no coincidence of data in some places implying as we have been observing, that water bodies have disappeared, and in some places, water bodies have shrunk either marginally or grossly.

    On an enquiry by means of application citing the Right to Information Act (2005), the information obtained reveals that in the village of Okkiyamthuraipakkam, 14 water bodies are still existing out of the 32 identified in from the 1985 map all of which are found to have been converted to other land uses in the masterplan. In Pallikaranai 6 water bodies out of the 14 numbers identified from the 1985 map are still existing while other water bodies have transformed into builtup areas (it is interesting how the streets in these built up areas follow the shape profile of the preceding water body), and in Karapakkam, 3 water bodies out of 10 are still existing all of which are shown as other land uses in the master plan. This could also be because the concerned department records were outdated, but as mentioned, an observation from Google Earth engine reveals that these parcels are existing as shrunken water bodies or regions which get inundated in monsoon and remain dry otherwise. Further, the website of the Chennai Metropolitan Development Authority was visited to collect details from the available dates viz., 2001 onwards, for the villages under study. Predominantly in the cases of Perungudi and Jalladampettai, and also in Pallikaranai, Perumbakkam there are mentions of land registration to residential use and rarely to other uses, adjacent to water bodies as can be ascertained from the survey numbers of parcels (51). Also in Perungudi village one of the water bodies extending to an area of 6.23ha has now physically transformed into a residential area known as ‘Ambedkar Nagar’, which was noticed while comparing the revenue and land-use maps and this became the empirical motivation of this paper.

    • History of land-use and other changes in the wetland area and associated regions

    Baden Powell, while tracing the revenue history of Madras Presidency, traces two periods, early and modern settlements: the period after 1858 being the modern, when the settlement department was established and witnessed the use of rigorous criteria involving survey and settlement officers who mapped the lands. Even though the exercise seemed to encourage land under cultivation and individual ownership, the process mainly involved claiming ‘wasteland’ and bringing it under state control. Lands excluding forests were classified under patta, assessed dry and wet waste, unassessed waste and puramboke [4] lands (revenue and forest). Assessed dry and wet wastelands were kept uncultivated until an official allotment was made by the revenue department and included marshes and seasonal wetlands (30). It is also noted that, in the colonial times in Madras, there was a move towards commercial agriculture for cash crops in addition to paddy, and farmers hugely appreciated the government digging bore wells and introducing pumps, even if they were expensive, according to Christopher Baker who has outlined the economic history (52). In his paper, he also discusses that the landed gentry viz., hegemonic interests sought favours with the government and this led to a divided society. Though it is not the focus of this paper, it is relevant in a study of eco-social changes at the household and community levels and the ensuing land-uses.

    As mentioned earlier in this paper, the proposal to promote a ‘Pallikaranai Development Area’ came out of the consultations held by CMDA with various agencies from 1990s and following this, urban growth of an industrial nature, in consequence of the economic up thrust because of various sectors and the resulting migration into this area, spurted in the establishment of the dump yard on the marsh itself. The construction of the 200ft Radial road to improve connectivity between the eastern and western regions surrounding the marsh contributed to a massive real estate growth as mentioned earlier though this spurred on other issues of landscape fragmentation and difficulties in conveyance of floodwaters. There was also a notable attention towards protecting the marsh by few individuals but they were few and far between. Nevertheless, the efforts undertaken towards protection of the marshland are to be examined.

    As early as 1985-86 Pallikaranai was identified by the Government of India as one of the 94 wetlands under the National Wetland Conservation Programme (NWCMP) (53,54). In 2007, the state government (30,54) declared [5] a portion of the Pallikaranai marsh (3.17 sq.km) as a reserve forest under Section 4 of the Tamil Nadu Forest Act, 1882 after understanding the ecological importance of the marsh in the city context (6). In 2012, 115 wetlands were listed under the National wetland conservation programme by MoEF [6] and this list includes Pallikaranai (55).

    Public movements like the ‘Save Pallikaranai Marsh Forum’ gained a lot of attention and attracted media support and also response from the government. In 2011, an Adaptive Management plan for the Pallikaranai marshland was prepared by Chennai-based NGO [7] Care Earth in order to ecologically conserve the marsh. In the same year, the process of handing over the marshland following a request from the forest department was initiated and the forest department plan was to undertake restoration of the marshland. In 2018, the state government announced that it would commence the restoration of 695 hectares of the wetland under the National Adaptation Fund for Climate Change over 5 years from 2018 to 2023 (56). But there are shortcomings in the pertaining law particularly with the ‘wise-use of wetlands’ as stipulated by the Ramsar convention. The Wildlife (Protection) act of 1972 provides for the establishing of sanctuaries and wetlands which fall within the protected area are protected. But grazing is strictly banned within a sanctuary, and this reduces human impact and influences the wetland ecosystem once it is declared as a national park. This and other aspects of the functioning of the forestry department implies that the areas with highest protection are not capable of protecting in the manner of ‘wise-use of wetlands’ (57).

    • Hydrological changes and history of flooding

    As discussed, the 200ft Radial road divides the marsh into two fragments and constrains the flow of water from north to south. Its behaviour during floods has been discussed below. As per a study conducted in 2014 by Ramalingam, it was ascertained from the Airborne Laser Terrain Mapping (ALTM) data, flood volume generated in west Velachery is around 11.5 MCM and from east Velachery is around 32 MCM, amounting to 1.54 TMC (58).

    The culverts on Radial Road were found to be inadequate. The flood of about 7000 cusecs was found being conveyed as a sheet flow over Pallikaranai marsh over a width of 2.3 km. 7 pipe culverts and 10 RC box culverts of 2 to 3m width totalling 59m of linear waterway provided were assumed to be in operation. Thus the percentage of waterway provided is only 2.6% (58).The Velachery flood flow channel (constructed before 2014)  parallel to the Velachery-Tambaram bypass could not convey maximum flood flows.

    The physical measures to be provided proposed were, a study of retention of run-off of the 13 tanks in the catchment area of Pallikakaranai swamp to be conducted separately and intra-linked plus storage capacity to be increased. Additional culverts in the affected area were also proposed. The flow width between Centre for Wind Energy (a government organization, also a major encroacher on the water body) boundary and the solid waste dump in the marsh should be enlarged (to at least 500m, which currently is not more than 167m). As discussed the presence of physical obstructions like the road, pipelines, encroachments and siltation have resulted in inundation and a decrease in the flow passage over time.

    According to Andimuthu et.al., (59) the assessment of Velachery drainage system response to storm events of varying return periods under present and future climate change scenarios relates the vulnerable hot-spots including critically flooded channels and outflows. The highest peak discharge has been observed in Outfall 1 which is located close to Velachery lake and joins with Pallikaranai marshland. Highest flooding has been noticed at junction VB-179 , located very near to Velachery Lake. Out of 234 nodes/junctions, 9 nodes present themselves as hotspots and flooding has been noticed under all storm events. These nodes are inundated for nearly 24 hours. It has been recommended that proper maintenance should be undertaken routinely in order to create a free passage to drain out the flow and to avoid the blockages in storm drains.

    Increasing the size of the Okkiyam Maduvu weir width from 120 m to 200 m, will help reduce the depth of the flow over the weir from 3.43 m to 2.44 m for 100 yr return period rainfall thus reducing the backwater effect, according to them. At Okkiyam Maduvu, minimum width of 200 m in the downstream channel is essential to ensure the free flow of flood water. The carrying capacity of the channel is suggested to be improved by removing vegetation and blockages and lining with stone pitching.

    • Changes in vegetation and ecological characteristics

    The landscape surrounding the Pallikaranai marsh was a predominantly agricultural landscape and the oft-repeated statement by local people who have been over time a part of these villages that they grew paddy and horticultural crops using only water that inundated the area, without dug-out wells or ponds in their vicinity is sufficient evidence. The wetland habitat constitutes aquatic grass species, scrub, marsh and water-filled depressions. The abundantly growing Typha and other aquatic macrophytes have been found to serve as biofilter for the wastes discharged into the wetland. The species inventory carried out in the preparation of the report by Centre for Climate Change and Advanced Research (CCC & AR), Anna University (n.d.,) states that 90 species belonging to 77 genera of 36 families are found to be present in the marshland. Of these, Euphorbiaceae family having 6 genera belongs to 9 species and Poaceae family having 7 genera belongs to 8 species. Habitat types found in the Pallikaranai marsh include open water pockets that attract the diving water-birds, islands and mounds that are used as breeding ground for a number of species, shallow waters and mudflats which act as feeding areas for migratory waders and emergent sedges, reeds and grassy bank areas which attract wading birds (30). The marsh being a source of income to many locals has been discussed in a 2007 report which explains that inhabitants of seven villages partially depend on the wetland for subsistence, of these some ethnic groups are highly reliant, including fishing and reed-gathering, grazing and agricultural groups (43).

    • Demographic and Socio-economic changes

    The population density of Chennai city changed from 186.65 P/Ha in 1981 (40) to 265.53 P/ha in 2011 (36). The population density of Pallikaranai town panchayat [8] changed from 2.225 P/ha in 1981(40) to 25.05 P/ha in 2011(36). According to the 2020 data, the population of Chennai as a percentage of India’s population is 0.312%. The population of Pallikaranai as a percentage of the city population has increased from 0.12% in 1981(40) to 0.613% in 2011(36) which implies that the average decadal increase in population of Pallikaranai town panchayat is 0.164%. Key-informant interviews and discussions with members of the local population revealed that there has been a huge migration into this region since 2000 onwards.

    Data reveals that in the environs closer to the marsh and also to other water bodies, the proportion of low-income dwellings is higher. In addition in the area east of the marsh, adjacent to Okkiyam Maduvu, are numerous tenements constructed by the government in order to rehabilitate inhabitants affected by the tsunami, squatter settlements on river banks and settlements displaced by the construction of the Mass-Rapid transit system. In the case of the eastern side, where the Old Mahabalipuram road runs north-south, approximately within 2km of the edge of the marsh (near the point where Okkiyam Maduvu originates), multi-storeyed buildings on the road are functioning in very close proximity to an ecologically sensitive site, and invariably as only very large projects are equipped with onsite sewage treatment facilities, the amount of wastewater which may be drained into the marsh goes unmonitored. Also to be taken into consideration is the common practice of a number of household sewage connections being led into public storm a water drain which appears to be a fairly common practice in some areas in the vicinity. Compounding these problems is the common grievance of many residents regarding the laying of roads by the corporation periodically, thus raising the external road level to an elevation above the ground level of the houses and hence water from the roads enters the individual plots.

    Figure 7. Change in Marsh condition 2002 and 2020

    The images from Google Earth historical imagery show the southern portion of the marshland including the channel, Okkiyam Maduvu, the extent of urban growth and nature of the water body on 17-09-2002 (above) and 28-11-2020 (below).

    • State of anthropogenic changes affecting the environmental quality of the wetland: whether to the extent of an emerging ‘novel’ or ‘hybrid’ ecosystem

    Severe environmental degradation especially in terms of water quality, both groundwater and water in the marsh has been noted since the late 90s. The challenge involved with respect to this marsh is that the aquatic grasses or reeds may eventually transform into a terrestrial ecosystem which is part of the evolution process. As such, the influx of saline water from Okkiyam Maduvu and its mixing with freshwater is sustaining the marsh. Inundation, siltation, pollution of land and water are having an impact on the soil-water-vegetation nexus which is peculiar to the marsh and these effects may have compounded into the evidences of a ‘hybrid’ ecosystem (1,7), acknowledging the data on environmental quality from studies (6,53,60,61). How stable the ecosystem can be and to what extent will the impact of negative uses and activities be overcome is hard to predict.

    • Land-use and hydrological drivers

    The marsh topography is such that some storage of water is always retained, thus forming a classic wetland ecosystem. In recent times, due to increase in impervious cover in the surroundings of the marsh, and due to the inadequacy of the draining mechanism compounded by the 200ft Radial road and its culverts, inundation during rains has become a serious problem. Also, in the south, the drainage capacity of the Buckingham canal is so meagre, that water filling the canal takes, on an average, 10 days to drain into the Kovalam estuary according to various reports and articles. A short-cut canal directly from Okkiyam Maduvu to the Bay of Bengal was proposed as mentioned in the second master plan 2026, but abandoned because of the hindrances in acquiring lands from the villages which were occupied, by residences and also an amusement park. Since this is the only mode of drainage for the entire wetland, it has become a matter of grave concern to the authorities who are preoccupied with solving inundation problems and creating canals and drains. Thus, urbanization of the watershed has resulted in increased flooding and issues with direction of flow due to urban infrastructural elements.

    In this context, one needs to dwell upon certain key aspects resulting from this discussion. These aspects may be listed as (i) the Society-Nature Cartesian divide which has come about from western philosophy and engulfs our thinking where society is the one and nature is the ‘other’ will always evoke the same results and turns nature into merely a passivity (62). (ii) there needs to be a complete thinking through or rethinking or rather, unthinking of our convention-based understanding of the natural sciences and its relationship to sociology, and hence to society. This will emphasize the fact that the crisis we are witnessing is to be seen not as an environmental crisis but as a crisis of society or a crisis of modernity.

    4. Conclusion

    From the observations made, certain key points have emerged and that gives us a few lessons to be learnt, which conclude this discussion. A concerted effort to save wetlands and related natural resources mandates the following: importance should be given to the local people and the need for community engagement (29,63) should be highlighted. By commissioning a series of hydro-ecological studies on the condition and utilization of all wetlands, a real-time database for all efforts to reclaim and rehabilitate these systems can be maintained. There is a need to halt the forced eviction of squatter settlements and to relocate them in suitable places within 2-3km radius of their original location with their consent; need to halt dumping of solid and liquid wastes from STPs (sewage treatment plants) in commercial/ residential/ industrial sites into wetlands and water bodies and constructing viable sanitation facilities for communities lacking it; to halt the illegal appropriation of sand dunes, mangroves and other coastal commons for public and private sector projects like SEZs (special economic zones), industrial economic corridors and desalination plants; likewise, the need to halt the forcible acquisition of agricultural lands for development thereby dispossessing farmers and workers of their source of living and also exploiting natural resources like water from those villages; also needed are time-bound digitization and making available in the public domain all information pertaining to land and commons across the state of Tamil nadu; need to establish statutory registries of the common lands at watershed, up to basin levels based on the inputs from people-led studies, continuously updated by the commoners at the local level, with the facilities to digitize, compile and network all the information in open access mode; to set up disaster management infrastructure at every level, to deploy necessary early warning systems, integrating communities settled in vulnerable locations in risk reduction measures; and importantly, to free all water bodies, water courses and wetlands of any large-scale public or private encroachment by permanent structures that obstruct the drainage of water, disable recharge or displace flood waters or interfere in any way with hydro-ecological functions.

    As outlined in the introduction, from our analysis we have tried to bring out and discuss the eco-social changes in the region and drivers that led to the environmental and social modifications in the marshland and associated regions. Over the period from 1985 to the current times, incremental changes have compounded into an ecological transformation and this has led us to ponder how to address this region from the perspective of developing policies and to what extent the damages resulting from anthropogenic activities will be acknowledged in the context of decision making for the future.

    References

    1. Village is the term for the unit of administrative boundary, not implying rural attributes.
    2. Toposheet: a term for surveyed drawing
    3. IT refers to Information Technology indicating that the buildings on this road belong to this industrial sector.
    4. Puramboke is a vernacular term denoting ‘commons’, also of negative oral usage addressing the third person  pronoun.
    5. (Gazette notification GO. Ms. No. 52, Environment dated 9th April, 2007)
    6. Ministry of Environment and Forests
    7. Abbreviation for Non-Governmental Organization
    8. Town panchayat is the current administrative status of Pallikaranai which lies within the Chennai corporation.
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