Integrated Management of the Ganges Delta, India

Chapter 11

Integrated Management of the Ganges Delta, India Ramesh Ramachandran, Ahana Lakshmi, Swati Mohan Sappal, Bonthu S.R., Mary Divya Suganya, D. Ganguly, R.S. Robin, R. Purvaja National Centre for Sustainable Coastal Management, Ministry of Environment, Forest and Climate Change, Government of India, Anna University Campus, Chennai, India

1 INTRODUCTION The Ganges-Brahmaputra River delta began developing ca. 11,000 year B.P. when rising seas resulted in the flooding of the Bengal basin because of which the river’s discharge was trapped on the inner margin (Goodbred Jr and Kuehl, 2000). The plume formed by the sediments transported from the Himalayas into the Bay of Bengal was found to cover the entire floor of the Bay of Bengal (Curray and Moore, 1971). The delta currently ranks first (along with the Amazon) in sediment transport, which is of the order of 1 × 109 t/year (Milliman and Syvitski, 1992). The Ganges-Brahmaputra-Meghna (GBM) delta spans two countries, India and Bangladesh and is a particularly fertile region supporting one of the most densely populated regions in the world. However, the GBM, like all other coastal river deltas, is a hotspot of global climate change impacts (Day et al., 2016; Hagenlocher et al., 2018). In this chapter, the important challenges faced by the Indian part of the delta, for which data are available, are examined by focusing on the present trend and strategies for integrated management of the delta under changing natural and human-induced conditions are explored.

1.1  The Ganges and the GBM Delta The River Ganges originates in the Gangotri glacier in the Garhwal Himalayas at an elevation of 7010 m as the Bhagirathi River. At Devprayag, River Alaknanda joins Bhagirathi and the combined stream is known as the Ganges. From its origin, the river flows for 2525 km before reaching the Bay of Bengal at Ganga Sagar in the state of West Bengal, India (Fig. 1).

1.1.1  Ganges Basin The Ganges basin stretches over an area of 1,086,000 km2 across India, China (Tibet), Nepal, and Bangladesh. In India, it covers 11 states namely Uttarakhand, Himachal Pradesh, Uttar Pradesh, Delhi, Haryana, Rajasthan, Madhya Pradesh, Chhattisgarh, Bihar, Jharkhand, and West Bengal, draining an area of 8,61,452 km2, which is nearly 26% of the total geographical area of the country (Table 1). The basin is bounded by the Himalayas on the north, by the Aravalli on the west, by the Vindhyas and Chota Nagpur plateau on the south, and by the Brahmaputra ridge on the east. The Ganges and its tributaries have formed a large flat and fertile plain in north India whereas in the eastern part of the basin, migration of the tributaries has resulted in conspicuous back-swamp and meander bolt deposits. These sedimentological features play a dominant role in the hydrodynamics of the region (WRIS, 2018).

1.1.2  River Flow The Ganges joins the Brahmaputra from the east, and along with Meghna, forms the GBM delta. Together, these three rivers along with their tributaries drain a catchment area of 1.72 × 106 million km2, on the southern side of the Himalayas, stretching across India (64.02%), China (17.69%), Nepal (8.57%), Bangladesh (7%), and Bhutan (2.73%) (Table 1). The GBM dispersal system, sustained with south Asian monsoon and high Himalayan sources, carries 1.8–2.4 × 109 tons sediment yr−1 (Goodbred and Nicholls, 2004) and the deposition of silt occurs within a vast area of about 115,000 km2 (Coleman, 1969; Goodbred and Nicholls, 2004; Nicholls and Goodbred, 2005; Woodroffe et al., 2006). Coasts and Estuaries. https://doi.org/10.1016/B978-0-12-814003-1.00011-3 Copyright © 2019 Elsevier Inc. All rights reserved.

187

188  SECTION | B  Deltas

FIG. 1  Ganges-Brahmaputra-Meghna River Basin Map. (Source Joint Rivers Commission, Bangladesh).

TABLE 1  Country Catchment Areas in the Ganges-Brahmaputra-Meghna River Basin Catchment Area (km2)

Rivers

Total Catchment Area (km2)

India

Nepal

Bhutan

China

Bangladesh

Brahmaputra

552,000

195,000

–

47,000

270,900

39,100

Ganges

1,087,300

861,452

147,480

–

33,520

46,300

Meghna

82,000

47,000

–

–

–

35,000

GBM total

1,721,300

1,102,000

147,480

47,000

304,420

120,400

(%)

(100%)

(64.02%)

(8.57%)

(2.73%)

(17.69%)

(7%)

Data from Joint Rivers Commission, Bangladesh.

The Ganges delta receives an average annual rainfall between 1520 and 2540 mm and experiences typical hot tropical climate with strong cyclonic storms, both during pre-monsoon (March to May) and post-monsoon (September to October) seasons. The Brahmaputra and Ganges Rivers receive water from both monsoonal rainfall and melting of ice from the Himalayan glaciers. For the period 1993–2011, Papa et al. (2012) estimated the mean aggregate discharge as ∼32,000 m3 s−1; whereas the annual maximum monthly discharge had a mean value of ∼82,000 m3 s−1 for the same time period.



Integrated Management of the Ganges Delta, India Chapter | 11  189

1.1.3  Sediment Discharge The GBM river system delivers 30% of the world’s total load of river sediment (Milliman and Meade, 1983) to the Bay of Bengal. This is despite the fact that in the case of the Ganges and Brahmaputra, 55% of their combined annual sediment load is retained by their delta, with only 36% reaching the shelf and 9% reaching the deep sea (Syvitski, 2003). According to Subramanian and Ramanathan (1996) the sediment load for the Ganges River varies from 403 to 660 × 106 tons year−1 and consists predominantly of coarse silt to sand-size particles. About 88% of the annual sediment load is transported during the monsoon compared to 76% of the annual water discharge (Subramanian, 1996).

1.1.4  GBM Delta The GBM delta is the world’s largest and extends across two countries. Two-thirds of the delta is located in Bangladesh, and the rest in the state of West Bengal in India. The GBM delta extends from the Hooghly River on the west to the Meghna River on the east; extending approximately 18,000 km2 along and across the Bhagirathi-Hooghly River (the distributary of Ganges). The width of the delta is approximately 350 km across the Bay of Bengal coast and the surface area is over 100,000 km2. This delta is particularly fertile supporting one of the most densely populated regions in the world. The major land use categories in the GBM delta include irrigated croplands, rainfed and/or mosaic croplands as well as mosaic vegetation, mangrove vegetation, shrubland, broadleaved evergreen forests, and developed (urban) areas (Brown and Nicholls, 2015). It is estimated that at least 630 million people live in the GBM river basin. Two megacities, Kolkata (India) (population about 14.3 million) and Dhaka (Bangladesh) (population about 18.2 million) are located within the GBM delta. Population density in the GBM river basin varies; it is very low in China and Bhutan whereas it is 432 inhabitants/km2 in India and more than double that (1013 inhabitants/km2) in Bangladesh.

1.1.5  The Ganges Delta In India, the Ganges delta is located within the state of West Bengal and the delta begins at the Farakka Barrage (CWC and IMD, 2015). About 40 km downstream of Farakka, the river splits into two arms; the left arm, Padma, turns eastward and enters Bangladesh and the right arm, Bhagirathi, flows southward. After Nabadwip, it is known as Hooghly, and enters the Bay of Bengal about 150 km downstream of Kolkata. The Hooghly River, which is the lower tidal stretch of the Bhagirathi River, flows past the megacity of Kolkata and forms a vast mangrove-enriched estuarine delta before entering the Bay of Bengal. This is the Indian part of the Sunderbans covering an area of about 9630 km2 (Ray et al., 2011). Important tributaries entering the Ganges in West Bengal include Ajay, Dwarka, Damodar, Rupnarayan, and Haldi (CWC, 2014). The Ganges delta in West Bengal covers nine districts, draining an area of 71,485 km2. On the coast, the Sundarban mangrove forests rise up to 2.1 m above mean sea level, providing stabilization and enabling accretion of new land.

1.2  Challenges in the Ganges Delta Worldwide, delta sustainability is increasingly being challenged because of the multiple stresses that they are being subjected to, including rising populations, intensive agricultural activities, engineering projects that change water and sediment delivery, sea-level rise (SLR) and flooding from rivers and intense tropical storms, groundwater and hydrocarbon extraction, delta subsidence and submergence, and coastal erosion (Syvitski, 2008; Tessler et al., 2015; Brondizio et al., 2016; Renaud et al., 2016; Day et al., 2016). Recent research has indicated that the GBM delta is most prone to multiple natural hazards (i.e., flooding, droughts, salinity intrusion, cyclones, and storm surges), with the highest exposure of social-ecological systems among the major deltas of the globe (Hagenlocher et al., 2018). Because of the enormous size of the Ganges basin and the GBM delta, and the wide variation in physiography (from the high Himalayas through plains to the low-lying delta), changes in the upstream areas can have a tremendous impact on the delta. Simultaneously, the deltaic coast is under stress from rising seas and intensification of hazards of hydro-meteorological origin as well as human impacts. Hence, the major challenges to the sustainability of the Ganges delta can be broadly classified into Upstream Effects and Coastal Effects (Fig. 2).

2  UPSTREAM EFFECTS 2.1  Water Flows Rainfall, subsurface flows, and snowmelt from glaciers are the main sources of water in River Ganges and its tributaries. As the Ganges flows from its source toward the coast, it is joined by a large number of rivers including the Yamuna, the Ramganga, the Ghaghra, the Gandak, the Burhi Gandak, the Kosi, the Mahananda, and the Sone. From December to May are the months of low flow in the Ganges. There is considerable variability in water flows as seasonal rainfall in the

190  SECTION | B  Deltas

FIG. 2  Classification of challenges in the Ganges Delta.

catchment plays a major role in the amount of water flowing through the delta’s river systems. This means that during the rainy season, the Ganges becomes a large single channel while during the dry months it reverts to a sandy braided course. The Central Water Commission (CWC) has divided the Ganges basin into the Upper Ganges, Yamuna, and Lower Ganges basins. The mean annual available water resources of Ganges basin are 509.52 billion m3 (BCM), while it is 192.60 BCM in the Lower Ganges basin which extends from the eastern margin of the Punjab in the west to the Bangladesh border in the east (Fig. 3). The Lower Ganges basin (288,283 km2) is divided into 10 subbasins which include the combined delta (50,525 km2) as a single subbasin.

FIG. 3  Ganges and its major tributaries. Numbers indicate average annual flows in 106 m3. (Modified from Jain SK. Impact of retreat of Gangotri glacier on the flow of Ganges River. Curr. Sci. 95(8): 1012–1014, 2008.)



Integrated Management of the Ganges Delta, India Chapter | 11  191

The barrage at Farakka in Murshidabad district of West Bengal was constructed in 1974 with the primary purpose of diverting adequate quantity of water from the Ganges via a 40-km feeder canal which discharges into the Bhagirathi-Hooghly River for flushing out the sediment deposition from the Kolkata harbor without the need of regular mechanical dredging. The inflows at Farakka are about 459 × 109 m3 (Jain, 2008) whereas observed discharge at Farakka between 1985–86 and 2014–15 was between 200 and 400 × 109 m3 (CWC, 2017b). Measurements at Farakka indicate that while the flow remains low through most of the year, high flows occur during the wet season (Jul.-Oct.) including several peaks of very high discharge (Singh, 2008). The average bed slope from Farakka to Nabadwip (deltaic nontidal plain) and from Nabadwip to the outfall (deltaic tidal plain) is 1:23,000 to 1:24,000 (Jain, 2008); as a result intense rainfall during the monsoon causes flooding because of the slow movement of water. During dry seasons, there is hydrological drought. Most of the deltaic plains are confined to the southeast part of the North and South 24 Parganas districts covering about 60% of the coastal area of West Bengal (Chakrabarty, 1995). These low-lying marshy lands with elevation below the high tide mark get submerged under brackish water during high tides. The Ganges delta is tide dominated with a macro tidal range (>4 m). The districts of North and South 24 Parganas are traversed by a number of moribund rivers, which are primarily spill channels of the Hooghly River. Six major estuarine rivers, namely Muri Ganga, Saptamukhi, Thakuran, Matla, Gosaba, and Herobhanga discharge to the Bay of Bengal and are interconnected with each other through numerous creeks and small rivers creating about 102 islands of which 54 islands are inhabited while the rest are still part of the Sundarbans mangrove ecosystem. These tidal estuarine rivers carry seawater from the Bay of Bengal during high tide and inundate the mangrove forests at regular intervals. River Hooghly in the west is the main river carrying freshwater from upstream reaches of lower Ganges delta into the Indian part of Sundarbans as most of the other estuarine rivers have lost their earlier connections with River Ganges over time (Morgan and McIntire, 1959).

2.2  Sediment Transport Collision tectonics of the Himalayas control the Ganges system and are responsible for the formation of the vast Ganges plain, the world’s largest delta and the world’s largest submarine fan—the Bengal Fan (Singh, 2008). The basin area of the Ganges in the Himalayas is undergoing intense erosion which annually contributes a huge amount of sediment via tributaries into the main river; a large portion is carried as bed load. The Ganges plain acts both as a sink and source for sediment in transport to the delta and the submarine fan through initial deposition as channel bars and subsequent downstream movement especially during the wet season. According to Goodbred and Kuehl (2000) the sediment discharge of the GangesBrahmaputra system during 7–11,000 years BP was twice that deposited in the following 7000 years. Throughout Pleistocene times, the site of active deltaic sedimentation has switched. Today, the Ganges merges with the Brahmaputra, and the site of active sedimentation lies to the east, where large bell-shaped distributaries can be discerned. The major area of abandoned deltaic plain lies to the west and is the site of one of the largest mangrove regions in the world, the Sunderbans. The abandoned delta is approximately 1.6 times the size of the active delta plain. Numerous abandoned channel scars dominate the surface morphology of the abandoned delta plain. These scars are apparently remnants of former courses of the Ganges River and many of its distributaries. Most of the scars indicate that a meandering channel was dominant, now extensively modified by humans. Channel scars are of similar size to channels presently active along the Ganges and its distributaries. Many of these former riverine channels are now tidally dominated (Coleman et al., 2008). Wasson (2003) developed a suspended sediment budget for the Ganges-Brahmaputra catchment according to which of the 794 × 106 tons yr−1 transported in the rivers of the Ganges catchment, over 80% comes from the High Himalayas. According to him, the rivers of the Ganges plain catchment appear to be aggrading, thereby exacerbating the annual overbank flood. Aggradation may be because of enhanced sediment delivery to the rivers due to land use, rainfall change, or neotectonics in the Himalayas. It could also be caused by neotectonics on the Plain, warping the riverbed. According to Akter et al. (2016) in the last five decades, this delta has prograded at a rate of 17 km2 yr−1, whereas most large deltas elsewhere in the world have suffered from sediment starvation.

2.3  Impacts of Changes in Water and Sediment Transport Regimes on the Ganges Delta The Ganges River system is considered as one of the most engineered with almost 800 projects including irrigation, dams, hydroelectric projects, lift systems, and barrages (WRIS, 2018). Overall, because of the reduction in flows due to dams and consequently, less water reaching the delta, there are periods of drought within the delta while during the monsoonal heavy rains, there is flooding not only because of excess storage being diverted but also because of embankments that have been built to channel flows which often result in flooding as they are unable to contain flows (Jain, 2008).

Change in mangrove forest cover (%)

192  SECTION | B  Deltas

3 Change in mangrove forest cover (%)

2 1 0

1989 1991 1993 1995 1997 1999 2001 2003 2005 2009 2011 2013 −1 −2 −3

FIG. 4  Biennial change in Sundarban mangrove forest cover. (Data from FSI, 2013; ISRO, 2015.)

In the Ganges delta, there is a distinct variation in the water flows within the delta. The altered flow regimes have resulted in the variation in salinity in the different sectors of the delta. Here, salinity is mainly regulated by natural factors like siltation, tilting/subsidence of the delta, rising sea levels as well as by anthropogenic factors such as barrage discharge, run-off from the adjacent landmasses, many polders, etc. A study conducted by Trivedi et al. (2016) on the surface water salinity in the Ganges delta during 1984–2013 reveals that salinity has decreased by 0.63 and 0.86 yr−1 in the western and eastern sectors of the delta respectively, whereas in the central sector, it has increased by 1.09 yr−1. The western region of the delta was found to be hyposaline owing to the freshwater discharge from the Farakka barrage. The decadal average discharge (1999–2008) from the barrage into the western part of the delta was found to be 3.7 ± 1.15 × 103 m3 s−1 with maximum discharge during the monsoon season. Similarly, hyposaline conditions in the eastern sector of the delta were caused because of fresh water carried by several creeks and channels from the Harinbhanga Estuary of Bangladesh’s Padma Meghna River basin. On the contrary, the central sector experiences complete obstruction of fresh water due to heavy siltation and minimal fresh water discharge in the Bidyadhari and Matla Rivers (Cole and Vaidyaraman, 1966; Chaudhuri and Choudhury, 1994; Mitra, 2013). As a result, the central sector is hypersaline with tidal inflow of seawater being the only source of water (Trivedi et al., 2016). As a consequence of salinity changes, enhanced saline intrusion northward is evident in the coastal stretches of the Ganges delta which has been found to adversely impact mangroves and other associated flora and fauna. Gradual disappearance of fresh water species like Heritiera fomes and Nypa fruticans is a confirmatory test of such salinity variation (Gopal and Chauhan, 2006). The biomass of mangroves and species composition of phytoplankton and fish are also influenced by salinity fluctuation. Fig. 4 shows the declining trends in mangrove forest cover in the Sunderbans over the last 25 years. A study by Raha et al. (2012) indicates that the growth of dominant mangrove flora is more in the western sector of Ganges delta than the central sector due to changes in the salinity regimes, which also affects species composition and distribution. Increased salinity caused reduced growth in Sonneratia apetala whereas salinity did not influence the growth of Avicennia alba and Excoecaria agallocha due to their salt excretion capability and thus better adaptation to hypersaline conditions. Similar observations were made for fish production and diversity in the deltaic region where changing salinities have changed the fish assemblage and distribution (Raha et al., 2012). Fresh water fish (such as Tenualosa ilisha), due to the hypersaline conditions in the central sector, have changed their course and breeding grounds to the western sector; while trash fish which can survive in the stressful conditions are abundant in the central sector.

3  COASTAL EFFECTS 3.1  Floods and Inundation The state of West Bengal is vulnerable to multiple natural disasters. Floods and cyclones occur on an annual basis inflicting large losses of life and property. Such floods may be caused by tropical cyclones or by monsoonal rains, especially in the catchment areas as well as in the delta. Opening of sluice gates of dams during intense rainfall may result in flash floods. About 42% of the total geographic area of West Bengal state and 69% of its net cropped area is prone to floods. The floods actually bring sediment that has not only shaped the delta but also has allowed high agricultural production with relatively less input. However, the high population density as well as the increase in engineered structures has resulted in an increase in the number of flood-related disasters. Flooding episodes due to severe cyclonic storms over the Bay of Bengal also pose severe hazards to lives and livelihoods. A 26% increase has been documented over the last 120 years in the frequency of cyclones over the Bay of Bengal, intensifying in the post-monsoon period. Cyclones bring strong wind, heavy rainfall, and flooding, resulting in severe



Integrated Management of the Ganges Delta, India Chapter | 11  193

coastal erosion and embankment failure. From 1999 to 2005, while there were a number of cyclonic depressions, only three materialized into severe and super-cyclonic storms. However, in the next 4 years, seven such cyclonic storms were generated from a similar number of cyclonic depressions in the Northern part of the Bay of Bengal. This was found to be closely related to the increase in the sea surface temperatures (Singh, 2007). Track data were obtained for 56 cyclonic depressions over the GBM over a 25-year period (1990–2015) based on historical cyclone records from the India Meteorological Department (IMD). Out of these, 42 were deep depressions and 14 were severe tropical cyclones with intensity greater than 34 knots. Some of these cyclones had a major impact on the deltaic regions of India and Bangladesh. Documentary evidence is available to indicate extensive changes in geomorphological features due to the storm surges and heavy floods (Singh, 2007).

3.2  SLR and Delta Subsidence A major challenge for the Ganges delta is related to the global issue of rising sea levels. The Ganges delta is experiencing SLR at an average rate of 3.14 mm yr−1 near Sagar Island (Fig. 5) in the western deltaic region (Hazra et al., 2002; WWFIndia, 2010) and may rise up to 3.5 mm yr−1 in the next few decades (Hazra et al., 2002). The increase in eustatic SLR combined with the intense land subsidence due to the compaction of unconsolidated deltaic deposits can further aggravate relative SLR as much as 10–20 mm yr−1 in the seaward sectors of the Ganges delta (Allison, 1998). This is a serious cause of concern for the ecosystem dynamics and sustainability in the Ganges delta.

3.3  Coastal Erosion The Ganges delta is an extremely dynamic ecosystem and the process of erosion and accretion occurs almost simultaneously in different parts of the deltaic lobe. Studies have reported that the islands of the western delta are gradually eroding which may be attributed to sediment run-off, water flow, and current patterns regulated mostly by the Farakka barrage. By contrast, the islands of the central part are expanding owing to the absence of any head-on discharge, siltation on the riverbed, and land subsidence. The net effect, however, is inclined toward coastal erosion (Fig. 6) in the lower stretches of the delta (Ganguly et al., 2006; Raha et al., 2012). Along the east coast of India, the terrain has resulted in the formation of many large deltas. It is useful to compare the status of shoreline change of the Ganges delta with other large deltas. Here we compare the change in the shoreline of the Mahanadi, Godavari, and Ganges deltas. Shoreline change patterns between 1972 and 2015 were analyzed after extraction from appropriate remote sensing imagery. Fig. 7 shows the comparison of the shoreline in the three cases. Coastal embankments are seen only in the case of the Ganges delta. In the Mahanadi and Godavari deltas, erosion and accretion are more or less balanced, while in the case of the Ganges, erosion is greater than accretion indicating that the trend is net loss of land. In the Ganges delta, the shoreline change rate range varies from −98 to 165 m−1. High erosion areas are largely in Dalhousie, Bhangaduni, Bulchery Island, Chulkati Reserve Forest, east of Ajmalmari Reserve Forest, west of Matla Reserve Forest, and west of Gosaba River.

3.4  Impacts of Coastal Effects on the Ganges Delta Flooding is a regular occurrence in the Ganges delta. Riverine floods are beneficial as they bring in fresh silt that supports crop production without additional inputs. However, dams and other engineered structures have resulted in the ­reduction

FIG. 5  Relative mean sea level at Sagar Island, Ganges Delta. (Data from Survey of India, unpublished data.)

194  SECTION | B  Deltas

FIG. 6  Shoreline changes along the Hooghly, Matla, and other rivers of Ganges delta in comparison with other deltaic systems along the east coast of India.

Mahanadi

Ganges

Godavari

Shoreline change (%)

50.0 40.0 30.0 20.0 10.0 0.0

Ganges

44.3

Artificial coast 5.8 0.7

Godavari

41.0

0.0

Mahanadi

Erosion 36.1

Embankmen 0.0

Stable 12.8

Accretion 45.3

7.4

28.3

19.3

0.0

13.1

45.9

Type of change FIG. 7  Comparison of erosion/accretion characteristics in major deltas along the east coast of India based on average of 38 years (1972–2010).

in water flow and consequently the delta is increasingly sediment starved as well (Allison, 1998). Dams also get silted up rapidly because of the high sediment levels in the water reducing their storage capacity. Thus, during periods of heavy rainfall, large quantities of water may have to be released to prevent dam bursts. For example, in 2013 and 2018, there was widespread flooding in many districts of West Bengal due to heavy rainfall and water release from dams of the Damodar Valley Corporation just upstream of where the rivers enter West Bengal. The release also coincided with high tide (SANDRP, 2015).



Integrated Management of the Ganges Delta, India Chapter | 11  195

FIG. 8  Land loss in the most vulnerable islands of the Ganges Delta.

Cyclonic storms can cause extensive damage across large swathes of land because of the strong winds, heavy rain, and storm surge. Cyclonic storms and storm surges as well as extensive coastal erosion are key factors in contributing to water salinity especially in North and South 24 Parganas districts apart from increase of salinity in the estuaries of the Sunderbans due to reduced upland discharges. During Cyclone Aila (2009), damage to sluices and breaching of embankments by the storm surge resulted in large-scale flooding as well as intrusion of salt water into agricultural fields (CWC, 2017b). In Bangladesh, large areas remained under water for 2 years until the embankments were repaired, but it is possible that the tidal influx deposited sediment equivalent to decades’ worth of normal sedimentation (Auerbach et al., 2015). Fig. 8 provides the extent of land loss in some of the most vulnerable islands in the Indian Sunderbans.

3.5  Anthropogenic Challenges 3.5.1  Population Pressures The population supported by the GBM delta is large. In the Indian part of the delta, which falls in the state of West Bengal, the population in the nine districts has increased from 9.2 million in 1901 to 16.3 million in 1951 and 57.08 in 2011—a fivefold increase in a century; while the population density (persons per square km) has increased from 3722 in 1991 to 4165 in 2011 (Census of India). Fig. 9 shows how the population in the delta districts has increased since 1901 while Fig. 10 shows the increase of population in the delta districts paralleling the increase in the population of West Bengal state. In the case of Kolkata, a megacity, the population density went up from 23,783 persons per km2 in 1991 to 24,760 in 2001 but decreased marginally to 24,348 a decade later. The population in 1991 was 4.39 million in 1991, rising to 4.57 million in 2001 and 4.5 million in 2011. Within the districts, urban populations have been increasing faster than the rural population owing to mass migration, greater employment opportunities, and improved infrastructure facilities in urban centers. This has put greater stress on available resources including access to water which serves as a good indicator for well-being. According to the 2011 census, the sources of potable water include tap water (treated/ untreated source); wells (covered/uncovered); hand pumps, tube wells/boreholes; springs; rivers/canal; tank/pond/lake, and other sources. Hand pumps are the most common sources of potable water except in Kolkata where tap water accounts for over 85% of water supplied. In the context of arsenic contamination of groundwater in certain blocks, as well as saline intrusion into groundwater especially in coastal areas, the need to ensure protected water supply is important for well-being. Chronic arsenic toxicity is caused by drinking arsenic contaminated groundwater and results in a variety of systemic manifestations. Arsenic contamination has been reported extensively from all districts except Burdwan (SOES, 2006; Mazumder and Dasgupta, 2011).

3.5.2  Land Use Change The primary land use in the delta districts is for agriculture. The large number of tanks, ponds, and other water bodies are used for inland fish culture/capture. The change in the different land use classes between 2003 and 2013 shows the decadal change in land cover for the same time period. Land cover in the delta indicates a reduction in the area under mudflats and marsh vegetation and an increase in the area under industry and aquaculture (Figs. 11A and B).

196  SECTION | B  Deltas

FIG. 9  Population growth in the Ganges Delta Districts (1901–2011).

Integrated Management of the Ganges Delta, India Chapter | 11  197



100 90 80

Population (in Million)

70 60 50 40 30 20 10 0

1901

1911

1921

1931

1941

1951

1961

9 Delta Districts combined

1971

1981

1991

2001

2011

West Bengal

FIG. 10  Population growth in the Ganges Delta districts vs state of West Bengal. (Data from Census of India.)

FIG. 11  (A) and (B) Land use and land cover pattern of the Ganges Delta-2003 and 2013 (Farakka Barrage to Bay of Bengal). (Continued)

198  SECTION | B  Deltas

FIG. 11, CONT’D

3.5.3 Livelihoods West Bengal is predominantly an agrarian state. Comprising of only 2.7% of India’s geographical area, it supports nearly 8% of its population. There are 7.123 million farm families of whom 96% are small and marginal farmers. The net cropped area is 5.205 million ha which comprises 68% of the geographical area and 92% of arable land. The rapid growth in West Bengal’s agricultural production beginning in the early 1980s can be attributed to the adoption of high-yielding variety of seeds and chemical-based farming practices. Food grains and oilseeds have shown the highest increase in yield rates over the years and have grown by over 75% and 100%, respectively, between 1980 and 2008. The area under production of pulses (lentils) has shown a decline but yield levels have managed to improve over the years. Between 1990 and 2014, there was a steady increase in the consumption of fertilizers (Nitrogen fertilizers dominate); however, the total consumption of fertilizers in the delta districts (Fig. 12) is just over half of the total consumption in the state and in fact has come down, albeit marginally, from almost 58% in 1991 to 55% in 2014 (GoWB, 2015). The decline in area and increase in yield due to fertilizer-based farming practices could have adverse impacts on the pollution load in the delta region. Cropping intensity has decreased in most of the districts. The agricultural sustainability in the Ganges delta is also vulnerable to the changing climate. Rice is the main food crop cultivated in the deltaic region. Three crop cycles are generally observed, namely rabi (starting from November-February to March-June), kharif (beginning of the Southwest Monsoon and harvested in the autumn months), and autumn or pre-kharif (from March-May to June-October). Rice cultivation needs differential water supply especially during the sowing time which is largely governed by the seasonal rainfall in this region. Reliable water resource is a prerequisite for rice cultivation, and any change in the pattern and potential magnitude of precipitation in the delta may affect the crop yields. On comparing the rice yield with the seasonal rainfall in the 24 Parganas districts between 1998 and 2010, it was found that there is a strong dependency of crop productivity on precipitation in this region and any alterations in the precipitation patterns affects the agricultural productivity in the delta region. In the inland districts of the Ganges delta, freshwater fisheries dominate. The state has a 158 km

Integrated Management of the Ganges Delta, India Chapter | 11  199



FIG. 12  N-Fertilizer consumption in the delta districts.

80

250

70 200

40 100

30

(103 ha)

50

150

Available water spread area

Fish production in (103 tonnes)

60

20 50 10

0

North 24 South 24 Murshida Burdwan Parganas Parganas bad

Hoogly

Nadia

Malda

Howrah

2011–12

169308

172041

130690

78734

93173

59695

56929

36105

2012–13

182280

164030

136791

79680

83337

88543

58351

42341

2013–14

180055

164293

137168

103062

96168

96505

63006

33822

2014–15

194380

179684

140629

113147

96180

98329

60758

38420

2015–16

201955

186870

146253

120794

100988

100880

62581

39947

Available water (ha)

61378

66996

33135

20599

20153

10260

14132

5673

0

FIG. 13  Inland fish production vs available water spread in the delta districts. (Data from GoWB. Handbook of Fisheries Statistics 2015–16. Department of Fisheries, Directorate of Fisheries, Government of West Bengal, 2016.)

coastline. The estimated annual fish production in 2015–16 was 1.671 million MT (GoWB, 2016). Fig. 13 provides data on fish production over the last 5 years in the delta districts. The production more or less corresponds to the water spread area available in the district (GoWB, 2016). South 24 Parganas is the only district with a coastline. The fish production reported from this district appears to be leveling off in the last 2 years after showing a steep increase between 2012–13 and 2013–14. Analysis of fish catch data indicates declining trends of most fishes in the marine fisheries realm. Hilsa is an important fish in the West Bengal fishery. After seeing declining catch from both inland and marine fisheries, a sharp increase from marine catch may be noted in 2010–11 after which the catch data once again have fallen to their 2007 values while inland catch shows a continuing declining trend (Fig. 14). This may be attributed to the changing hydrology of the river due to construction of dams and weirs that obstruct the passage upstream as the Hilsa is anadromous, as well as changing water regime. In the post Farakka period, between

200  SECTION | B  Deltas

60

Hilsa production (103 tonnes)

50 40 30 20 10 0

2005–06 2006–07 2007–08 2008–09 2009–10 2010–11 2011–12 2012–13 2013–14 2014–15 2015–16

Marine

19061

16072

9430.64

11744

10560

54265

20949

7699

9407

8908

13405

Inland

8520

7156

5207

4256

3445

5530

3172

980

1029

984

1127

FIG.  14  Hilsa production in West Bengal. (Data from GoWB. Handbook of Fisheries Statistics 2015–16. Department of Fisheries, Directorate of Fisheries, Government of West Bengal, 2016.)

1975 and 2010, migratory Hilsa recorded at Patna (upstream of the Farakka barrage) declined even more dramatically from 234.7 to 1.38 kg km−2 (Pathak and Tyagi, 2010).

3.5.4 Pollution The Ganges River basin is one of the most fertile agriculture belts in the Indian peninsula, making it a focus point for massive human population growth and tremendous urbanization and industrialization (NRCD, 2009). The river basin is the main support system for the industries developed along its stretches and as many as 764 grossly polluting industries have been inventoried throughout the Ganges basin (CPCB, 2013) that utilize the river water and also directly discharge their wastewater into the river. The industrial units are classified into chemical factories, which mainly include fertilizer, petrochemical, pesticides, and pharmaceuticals; distilleries; dairy, food, and beverage industries; pulp and paper industries; sugar industries; tanneries; textile, bleaching and dyeing units; and other sectors like cement industries, slaughter houses, ordinance factories, packaging and printing units, paint industries, electronics and electrical, thermal plants, electroplating and metallurgical factories, automobile industries, etc. The wastewater generation by these industries is nearly 45% in terms of total water consumption. In the context of the deltaic region of West Bengal, a large number of industries are situated on the banks of the Hooghly estuary, namely paper, textiles, chemicals, pharmaceuticals, plastics, shellac, food, leather, jute, pesticides, etc. (UNEP, 1982). Though the water consumption of the industries here is comparatively less than the other states in the Ganges basin, their wastewater generation with respect to water consumption is considerably higher and, hence, alarming (CPCB, 2013). The Hooghly River receives 87 million liters per day (MLD) wastewater from 22 grossly polluting industries and as much as 70% of total wastewater generated comes from the chemical industries, followed by pulp and paper industries which discharge around 20% of total wastewater. Thus, large quantities of toxic and hazardous effluents are released into the deltaic ecosystems through these industrial units. In addition, about 360 outfalls on both sides of the river continuously discharge community sewage, virtually without any treatment (Mukherjee et al., 1993). The area supports large numbers of shrimp (Penaeus monodon) aquaculture farms often found coexisting with agricultural lands in the Ganges delta complex. Agriculture-based nutrient pollution is a well-established fact in the Ganges basin and the deltaic region (Banerjee et al., 2014). The region has seen exceptional growth in the agricultural sector in the recent decades, with an increase in the usage of nitrogenous fertilizers and consumption rate as high as 4961 kg-N km2 yr-−1 for the Ganges basin (Chanda et al., 2001). A study by Banerjee et al. (2014) and Swaney et al. (2015) concluded that the net anthropogenic nitrogen input into the basin was considerably high and it was mainly contributed by high agricultural fertilizer inputs. The huge nutrient load emanating from these activities along with the nutrient load from several nonpoint sources (such as discharges from fishing vessels and trawlers and run-off from adjacent landmasses) is leading to ecosystem collapse and problems like harmful algal blooms, eutrophication, hypoxia, and loss of biodiversity at the local scale. In addition to this, the Ganges delta houses one of the largest urban centers, the megacity Kolkata, with a population of about 14.5 million (Census of India, 2011). The densely populated city depends on the Ganges water for domestic needs. Also, the city of Howrah and the Haldia industrial belt on the bank of the Hooghly add to the anthropogenic stress on the



Integrated Management of the Ganges Delta, India Chapter | 11  201

Ganges delta. Apart from the localized pollution in the deltaic region, the river also brings substantial inputs of pollutants from the upper stretches all along its 2525 km course from Himalayas (CPCB, 2013).

3.5.5  Anthropogenic Impacts on the Delta The population of the Ganges delta has been rising steeply over time, especially in the 24 Parganas districts (north and south) as the delta has been able to support intensive agriculture. However, rising populations also mean increasing demand for land for settlements and agriculture as well as for resources, especially potable water supply. While the reach of protected water supply is high in urban areas, in rural pockets, dependence on wells is high; however, many of these are in areas of high arsenic contamination and this can have far reaching impacts on the health profile of the population in the delta as given in detail at Annex 1. The sewage generated by Class-I cities along the Ganges River in West Bengal is 1311.3 MLD whereas the treatment capacity is 548.4 MLD which means that more than half the sewage generated reaches the river systems in the delta. Pollution assessment by the CPCB (CPCB, 2013) indicates that West Bengal generates half of the total sewage generated by Class-I cities in the four Ganges basin states—Uttarakhand, Uttar Pradesh, Bihar, and West Bengal. Within West Bengal, the megacity of Kolkata generates 47% of the total sewage followed by Howrah (10%).This indicates that a significant amount of nutrients enter the river and coastal waters resulting in coastal pollution. The East Kolkata Wetlands (EKWs), a Ramsar Site, stretching over 12.5 km2 of the north and South 24 Parganas districts, nurture the world’s largest wastewater fed aquaculture system which comprises 254 sewage fed fisheries, agricultural land, garbage farming fields, and some built up area (Kundu et al., 2008). The EKW offer a solution that can be implemented on a larger, delta-wide scale to reduce pollution of water bodies as they function as waste stabilization ponds with the slow-moving canal system functioning as the anaerobic and facultative ponds while the fishponds are the maturation ponds. The EKW are under threat from growing urbanization and land reclamation. The construction of dams, weirs, and other structures along the river at many locations has resulted in not only altering the hydrology of the river but also fish diversity and thus, the profile of the fisheries sector. The construction of the Farakka barrage on the Ganges River resulted in a major stock change in the fishery at Lalgola center about 45 km below the Farakka barrage. From Hilsa being the main fishery (92%), its contribution dropped to only 16.8% post-construction of Farakka; with the niche being replaced by other species including major carps and large catfishes. Also, change in the salinity regime of the Hooghly estuary resulted in a sharp increase in estuarine fishery from 9482 tons (1966–75, pre-Farakka period) to 62,000 tons (1999–2000) (Pathak and Tyagi, 2010). This has not only a bearing on the economic status of fishermen but also resulted in a change in the consumption choice and preferences through the delta. Today, a lot of the fish is imported from other locations including Bangladesh and Myanmar (GoWB, 2016) as Hilsa is an important constituent of the diet of the delta communities.

3.6  Integrated Management of the Ganges delta 3.6.1  The Interrelated Cascading Impacts It is clear from the above discussion that the delta is under threat from multiple causes and many of these are closely interrelated, with cascading and cumulative impacts (Fig. 15). Reduced river flow can have multiple first-level impacts—such as on agriculture, potable water supplies, saline intrusion and coastal erosion, and linking the social and ecological systems very closely. Reduced water flow in the river leads to reduction in crop production because agriculture becomes highly rain-dependent reducing the number of crops as availability of groundwater for an additional crop shrinks. This reduction in production results in reduced incomes for farmers and higher prices of food resulting in food security issues on the one hand, and heightened poverty and forced migration, on the other, setting off yet another chain of events. Reduced water flow also means reduced flow of enriched silty sediment. This may raise the demand for chemical fertilizers on the one hand, resulting in coastal erosion as there is insufficient sediment supply at the coast. This may also result in increased penetration of salt water with additional impacts due to rising sea levels as well as storm surges during the regular cyclones, affecting, among other things, diversity of coastal mangroves, which can have far-reaching implications on the structure of the entire Sunderbans ecosystem.

3.6.2  Delta Sustainability and Integrated Management Considering the intricate connections between the various delta components, the way forward for delta sustainability is an integrated approach, linking the various aspects including water and land management, conservation of ecosystems, ­ensuring that livelihoods are sustained, managing pollution without straining the delta’s water network and building a culture of disaster preparedness. Fig. 16 provides a few strategies under each major class of action that are required for ensuring delta sustainability.

202  SECTION | B  Deltas

FIG. 15  Example of cascading multiple impacts due to reduced river flow.

FIG. 16  Strategies for delta sustainability.

Foremost among these is the maintenance of an environmental flow in the river, essential for maintenance of the aquatic ecosystem (Jain and Kumar, 2014). However, the necessary data are not yet available. Even here, investigations have been confined to the upper reaches of the river while the requirements of the delta have been largely ignored. Even within the delta, as mentioned earlier, variation in the salinity regimes indicates how the central section of the delta is becoming hypersaline while the fringes are hyposaline. Thus, in addition to ensuring environmental flow in the major rivers, it is essential to examine and determine environmental flows for all branches of rivers within the delta. Wetlands and the flood plain of rivers are essential for storing water during peak flow, releasing the water during off-season as well as serving as breeding and nursery grounds for many riverine fish. Many of these are silted up and have lost their functionality and hence appropriate steps including planting of native species on riverbanks to control water (and silt) flow are needed. These will ensure not only regulation of water flows but also restoration of riverine fisheries (Pathak and Tyagi, 2010).



Integrated Management of the Ganges Delta, India Chapter | 11  203

Water use within the delta also needs to be effectively managed by promoting techniques such as decentralized rainwater harvesting that are eco-friendly and cost-effective especially in areas where there is seasonal high fluctuation in water flow. There must be a reduction in over-dependence on ground water, with ground water being utilized within the rechargeable limit to avoid delta subsidence. Land in the delta needs effective management, especially in the coastal areas where zoning is essential. Effective implementation of the Coastal Regulation Zone Notification 2011 that zones the coastal areas and regulates activities in the CRZ will help in conserving critical coastal ecosystems especially mangroves. Reclamation by landfilling, wholly or partly, of wetlands must be prohibited because such ecosystems (engineered or natural) provide services including flood control during floods and sewage treatment (EKWs) that reduce human stress on the environment/delta. Water and land management together play an important role in the state of the ecosystems, especially the mangroves that cover a large area of the delta. In the last several decades, large areas of the Sundarban mangroves have been converted into paddy fields and more recently, into shrimp farms (Gopal and Chauhan, 2006). The Sundarbans have been declared as Biosphere Reserve and there are several sanctuaries/national parks/protected areas in the Indian part of the Sunderbans under varying degrees of protection (Singh, 2003). Changes due to upstream controls in water flow have impacted the biodiversity of the Sunderbans. Additional threats are from reclamation and encroachments into the Sunderbans as a huge population (~2.5 million) is reportedly dependent on resources from the forests (Gopal and Chauhan, 2006). Using satellite data, Giri et al. (2007) noted that between 1973 and 2000, though the loss in total mangrove area was not significant in the Sunderbans, the change matrix showed that turnover due to erosion, aggradation, reforestation, and deforestation was much greater than net change. This means there is a constant stress on the ecosystem structure and functioning and potentially increased vulnerability, as well as reduced functioning in terms of services such as nutrient cycling, carbon sequestration, and shoreline protection. Recent studies (Ray et al., 2011) estimated the overall carbon storage in the Sundarbans mangrove forest reservoir to be 21.13 Tg C and in the soil reservoir (30 cm) 5.49 Tg C. The Sunderbans store 0.41% of the total carbon storage in the Indian forests (6621 Tg C) but their annual increase exhibits faster turnover than the tropical forests. The study also found that the overall annual increase in mean carbon stock across the Sundarbans mangrove forest could be partly due to an increase in resource availability favoring lighter-wooded mangrove species such as Aegialitis rotundifolia and Ceriops, now dominating in the eastern part rather than the heavier wood species such as Avicennia that dominate in the western Sunderbans. Pollution management through the entire delta has to be implemented with decentralized wastewater management especially for domestic wastes with emphasis on treating at source and recycling and reuse wherever possible. Pisciculture as carried out in the EKWs can be promoted in other suitable locations through the delta which will serve the double purpose of retrieving nutrients and enhancing food security and livelihoods for the local communities. Sustaining agricultural livelihoods is crucial as agriculture is the primary occupation of the delta inhabitants. However, dependency of crop yield on precipitation and temperature should be reduced. Instead, adaptive management strategies need to be taken up by farmers in choosing what crops to grow, during what time, what is the best suited land/soil type, and how to grow the crops (e.g., using system of rice intensification—SRI), for improving rice yields. Other strategies could include use of indigenous varieties requiring less water and promotion of organic agriculture with use of natural manure rather than chemical fertilizers. The latter may help reduce nutrient runoff into the waterways, consequently reducing eutrophication of coastal waters. Along with agriculture, other traditional resource-based livelihoods such as fisheries and honey collection from mangroves need to be sustained through better practices including market linkages. The main constraints are with reference to data availability especially with regard to water and sediment flows in the Ganges and the requirements of coordination when actions that can have large-scale impacts on the delta are planned. Very often, political decisions supposed to be for the good of the larger community are taken but the complexities of the ground situation are seldom taken into account resulting in unanticipated adverse impacts. From a broader perspective, sustainable delta management should be based insofar as possible on natural system functioning (Day et al., 2016).

4 CONCLUSIONS The Ganges delta is the world’s largest and spans two countries. We have examined the major challenges to the delta in India that can be primarily construed to be related to the upstream activities that control the flow of the river and sediments. The other set of challenges are due to the coast-related phenomena including rising sea levels and increasing intensity of storms. Anthropogenic challenges are cross cutting across the deltaic landscape. We have also examined how an integrated approach is required to address the various challenges as they can have a cascading impact on the structure and function of the Ganges delta. Appropriate actions are urgently required as the delta is already tending toward a collapsed system.

204  SECTION | B  Deltas

ANNEX 1 Facts and Figures and Pollution Status Along the Coast of West Bengal with Particular Reference to the Ganges Delta No.

Coastal Information

1

Length of coast

200 km

2

Number of coastal districts

4

3

Cities along the coast

6

(a)

Major (Class 1)

Haldia Howrah Kolkata Bangaon Basirhat

4

Population in coastal districts

28.17 million

5

Rivers/estuaries

Ganges Hooghly

6

Dams

4

7

Number of ports

2

(a)

Major

1

(b)

Minor

1

8

Number of industries located on the coast

57

Major sources of pollution from the Ganges delta include: (a) (b) (c) (d) (e) (f) (g) (h) (i)

Sewage outfall (treated/ untreated) Solid wastes Industries Port-oil pollution Thermal power plants Agriculture Aquaculture Water quality Tourism

(a) Sewage Outfall (Treated/Untreated) Total Sewage Generated Million liters per day (MLD)

Sewage from Coastal Districts

2345.21

250.048

Capacity

Coastal Districts

No. of STPs (Coastal Districts)

In MLD

Quantity Treated

East Midnapur

–

16.3

6.7

10.35

South 24 Parganas

2

8.25

–

–

North 24 Parganas

9

114.46

-

-

of STPs

Total Untreated Sewage

Integrated Management of the Ganges Delta, India Chapter | 11  205



(b) Solid Waste

State

District

Quantity of Solid Waste Generated (TPD)

381.3 TPD

East Midnapur

13.2

–

–

–

–

South Parganas

7

–

–

–

–

North Parganas

361.1

–

–

–

–

Quantity of MSW Collected

Quantity of MSW Treated (TPD)

Number of Landfills

Landfilling Capacity (m2)

(c) Industries Category (Medium + large) Coastal Districts

Small

Medium

Large

R

O

G

W

Purba Midnapur

–

–

12

9

2

0

1

South-24 Parganas

–

7

2

1

2

2

North-24 Parganas

–

9

14

10

3

11

29

14 12

N.so

10

8 6 4 2 0 Purba Midnapur Red

South-24 Parganas Orange

Green

White

North-24 Parganas Others

ANNEX FIG. 1  District-wise categorization of Industries in the Ganges Delta, West Bengal.

(d) Port—Oil Pollution: No oil spill has been reported along the coast of West Bengal. There are two ports and one mooring point located along the coast of west Bengal. (e) Thermal Power plant Nuclear power plants

0

Thermal power plants

16

(f) Agriculture ● Total cropping area: 5.5 Mha—3.9% of total cropping area of India ● Total agricultural production: 19.65 million tons ● Fertilizer consumption: 2.82 million metric tons and consists of 5.72% of total fertilizer consumption in India ● Pesticide consumption: 3800 tons

206  SECTION | B  Deltas

(g) Aquaculture Estimated potential of West Bengal is 405,000 ha of which area developed consists of 50,405 ha with a production of 52,581 tons, all of which are concentrated in the lower part of the Ganges delta (h) Water Quality Index

River/Estuary

O2 (mg L−1)

BOD (mg L−1)

Turbidity (NTU)

Chlorophyll (μg L−1)

DIN (μmol L−1)

DIP (μmol L−1)

Hooghly

7.2

1.1

22.7

2.0

23.6

1.0

ANNEX FIG. 2  Water Quality Index of the River Hooghly.

Integrated Management of the Ganges Delta, India Chapter | 11  207



Trophic Index for Ganges Delta and coastal waters of West Bengal Nutrients may stimulate primary production under sufficient light and temperature regimes which may cause eutrophication when released in favorable conditions. The extent to which this process has influenced is reflected in Trophic State Index (TRIX). TRIX is an estimate of nitrogen and phosphorus, and chlorophyll pigments in a water body. It is defined by a linear combination of the logarithm of chlorophyll a, absolute percent deviation of O2 from saturation, DIN, and IP. TRIX = (log10(Chl a x × OD %× DIN × IP) = k)/m TRIX Value

State Water Quality

Level of Eutrophication

0
High

Low

4
Good

Medium

5
Moderate

High

6
Poor and degraded

Elevated

Eutrophication index calculated for West Bengal coastal waters was 4.7 indicating good seawater qualities with medium eutrophication level. The observed trophic index is indicative of high potential for algal blooms’

Harmful Algal Blooms Only one incidence of algal bloom has been reported off Kolkata in 2001 due to Trichodesmium erythraeum State/Place

Latitude

Longitude

Year

Species

Off Kolkata

21.3377

88.1036

April 25, 2001

Trichodesmium erythraeum

(i) Tourism Total number of beaches

14

Pilgrimage sites along the coast

0

(j) Ecologically Sensitive Areas in the Ganges Delta Area (km2)

Ecologically Sensitive Area Mangrove

202.81

Coral

0.00

208  SECTION | B  Deltas

Area (km2)

Ecologically Sensitive Area Seagrass

0.00

Salt marsh

0.00

Horseshoe crab habitat

41.05

Turtle nesting sites

2.87

Bird nesting sites

Sunderbans

Sand dune

2.69

Mudflat

216.35

Archaeological and heritage site

0.05

(k) Pollution Hotspots along the coast of West Bengal and Ganges Delta: The following pollution stretches have been identified in the Ganges Delta and the coast of West Bengal ● ● ●

Digha Diamond Harbor Sapthamukhi



Integrated Management of the Ganges Delta, India Chapter | 11  209

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210  SECTION | B  Deltas

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