Coastal
Zones: Ecology and Climate Change Need Concerted Attention for Sustained
Productivity1
H.S.Sen2
Former
Director, ICAR-Central Research Institute for Jute & Allied Fibres,
Barrackpore
24
Parganas (N), West Bengal, PIN 700 120
Abstract
Coastal ecosystem
poses a delicate equilibrium between land and water masses amongst its
different components but with high degree of vulnerability in spite of
bountiful natural resources. The equilibrium is further under serious threat
due to climate change and global warming, though on the other hand, it is
significant that coastal marshes tend to sequester carbon continuously with
increasing storage capacity and with time, and thus regarded as a valuable C
sink per unit area, particularly in the tropics, to negate adverse impacts due
to global warming. Planning for effective and sustainable development warrants
specific attention to maintain the equilibrium. This will require adoption of
integrated approach to soil and water management, in the first place, and through
it or otherwise, necessary measures to conserve the ecology. Piecemeal
approaches to reclaim location specific problems or interference with the
hydrology of the rivers per se for short term gains for increase of
productivity, disregarding completely the practices on integrated management of
different intervention areas and thereby conserve the ecology in coastal
plains, may offset the equilibrium, as experienced in different parts of the
world, leading to such adverse impacts, such as seawater intrusion into inland
areas, massive loss of mangroves, coral reefs, seagrasses and various other
aquatic plant & animal species, sedimentation & erosion, tidal
flooding, subsidence of land, etc. The influx of reckless application with fast
increasing dose of nitrogen or other inputs resulting in nutrient imbalance
through human activities in the adjoining inland and coastal areas are glaring
examples leading to such phenomena as eutrophication and formation of dead end
zones in the coastal water bodies. Policy approach for water budgeting of
different water resources, preferably on watershed basis, with minimal or
planned dependence on abstraction of the underground water should be an
essential strategy to be drawn in order to ensure sustainable increase in crop water
productivity as well as water productivity all along the coast.
Key words: Coastal
ecosystem, Sustained productivity, Ecology, Climate change, Integrated water
management, Hydrology & E-flow in Ganga, Seawater intrusion, Sedimentation
& erosion, C sequestration, Soil quality, Water budgeting, Nutrient
imbalance, Population &
climatic disaster, Future policy
Coastal areas in India and
elsewhere are by and large heavily populated. Nearly 40 % of cities larger than
500,000 population in India are located in the coast. Overall about 50-70 % of
the global population live within 100 km of the coastline covering only about 4
% of earth’s land (Poyya and Balachandran, 2008), thereby drawing heavily on
coastal and marine habitats for food, building sites, transportation,
recreational areas, and waste disposal. According to another estimate
(Wikipedia, 2009), coastal areas (within 200 km from the sea) share less than
15 % of the earth surface area, and this predicts that three-fourths of the
world population are expected to reside in the coastal areas by 2025.
Coastal ecosystem poses a
delicate equilibrium between land and water masses amongst its different
components but with high degree of vulnerability in spite of bountiful natural
resources. The equilibrium among the different components in the ecosystem is
further under serious threat due to climate change
_____________________________________________________________________________
1 Dr. J.S.P.Yadav Memorial Lecture during the National
Symposium on “Innovations in Coastal Agriculture - Current Status and Potential
under Changing Environment” being organized by Indian Society of Coastal
Agricultural Research, held at ICAR-Indian Institute of Water Management,
Bhubaneswar, 14-17 January, 2016
2 Present address: 2/74 Naktala, Kolkata 700 047, WB;
Email: hssen.india@gmail.com, hssen2000@hotmail.com; Mobile: 09874189762
and global warming. While there
are commendable progresses in the country affecting productivity of the
ecosystem at a given time, significant changes in relevant parameters on
spatial and temporal mode, are in sight drawing instances on the ecological
damage from related areas within and outside the country, which suggests to
concentrate our attention for effective and sustainable development in the long
run by maintaining equilibrium amongst different components. The paper is a
brief exposure to such direction of research in future.
Major coastal ecosystems of the
world
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Table 1. Surface area of the
main coastal ecosystems in the world |
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|
System
|
Surface area
(106 km2 ) |
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Estuaries
|
1.4
|
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Macrophyte-dominated
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2.0
|
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Coral reefs
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0.6
|
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Salt-marshes
|
0.4
|
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Mangroves
|
0.2
|
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Remaining shelf
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~21
|
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Total
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26
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The main ecosystems
of the coastal ocean are: estuaries, macrophyte communities, mangroves, coral reefs, salt marshes and the remaining continental shelves (Table 1). These
areas are only approximately known, and there is some double-counting among the
ecosystem types. For example, coral reefs, estuaries and the "remaining
shelf" all include macrophyte-dominated communities, totaling
approximately 26 x106 km2 area (Encyclopedia of Earth,
2007).
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Table 2. Estimated
coverage with largest mangrove areas (Source: ITTO/ ISME, l993)
|
|
Country
|
Mangroves
(‘000 ha)
|
Global
% area
|
|
Indonesia
|
4250
|
30
|
|
Brazil
|
1376
|
10
|
|
Australia
|
1150
|
8
|
|
Nigeria
|
970
|
7
|
|
Malaysia
|
641
|
5
|
|
Bangladesh
|
611
|
4
|
|
Myanmar
|
570
|
4
|
|
Vietnam
|
540
|
4
|
|
Cuba
|
530
|
4
|
|
Mexico
|
525
|
4
|
|
Senegal
|
440
|
3
|
|
India
|
360
|
3
|
|
Colombia
|
358
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3
|
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Cameron
|
350
|
2
|
|
Madagascar
|
327
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2
|
|
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Coastal
plain: Major Features and Management Issues
Coastal
plain, within the ecosystem, is the landward extension of the continental shelf
or the sea and used for agriculture and allied activities as well as for few
other occupational purposes but is not always distinctly differentiated with
sharp boundaries from the other ‘main’ components referred in Table 1.
Characteristics
& Distribution, and Factors Affecting Productivity in India
Coasts are dynamic systems,
undergoing changes in form and processes in time and space in response to
oceanographic conditions and geomorphic features. Indian coastline, stretching
over 7,500 km along ten states and two archipelagos, is the sixth one in the
world and has been subjected to many spells of sea level changes since the Last
Glacial Maximum. The east and west coast are markedly different in topographic
setup, tectonic features and geomorphic framework. The west coast is relatively
narrow as compared to east coast and lacks any major delta formation. Of the two coastlines in India length of the
East coast is higher than that of the West. The continental shelf is more
stable than the coast. The continental shelf of 0-50 m depth spreads over
1,91,972 sq km and between 0-200 depth over 4,52,060 sq km. The shelf is wide
(50-340 m) along the East coast. The Exclusive Economic Zone is estimated at
2.02 million sq km.
Practically
no systematic study was earlier made in India to demarcate the coastal soils
based on well-defined scientific indices. Notable among the past works,
however, was that of Yadav et al.
(1983) who suggested 3.1 million hectare area (including mangrove forests),
while Szabolcs (1979) suggested 23.8 million hectare under coastal salinity in
India. The coastal saline soil has been referred by various workers almost
synonymously with coastal soil which is not correct since all coastal soils are
not saline in nature. None of the above estimates appears to have been made on
sound scientific basis. However, the latest compilation made by Velayutham et al. (1998) on the soil resources and
their potentials for different Agro-ecological Sub Regions (AESR) in coastal
tracts of India show total 10.78 million hectare area under this ecosystem
(including the islands), which was the first scientific approach for
delineation of the coastal ecosystem. Different factors limiting agricultural
productivity in the coastal plains are listed as (1) Excess accumulation of
soluble salts and alkalinity in soil, (2) Pre-dominance of acid sulphate soils,
(3) Toxicity and deficiency of nutrients in soils, (4) Intrusion of seawater into
coastal aquifers, (5) Shallow depth to underground water table rich in salts,
(6) Periodic inundation of soil surface by the tidal water vis-à-vis climatic
disaster and their influence on soil properties, (7) Heavy soil texture and
poor infiltrability of soil, (8) Eutrophication, hypoxia and nutrient
imbalance, (9) Erosion and sedimentation of soil, and (10) High population
density, etc.
Salinity Build-up in Soil and Soil Quality
Salinity
build-up in soil due to salinity ingress of ground water aquifers takes place
through the following major processes: (1) excessive and heavy withdrawals of
ground water from coastal plain aquifers, (2) seawater ingress, (3) tidal water
ingress, (4) relatively less recharge, and (5) poor land and water management.
Seawater
Intrusion
India’s’first Aquifier Atlas, released by the Central Ground Water
Board (CGWB) recently, has further reiterated what other studies have shown
about Chennai city. Over-exploitation of groundwater has rendered it vulnerable
to sea intrusion in different pockets, putting to danger sensitive aquifers on
which a major chunk of the population depends for water. According to the
atlas, Chennai is one of the districts classified as Over-Exploited, with parts
having salinity content higher than permissible limits. However, what is
striking is the fact that the Aquifer Vulnerable Map, which is part of the
document, shows that the north of Chennai as one of only four pockets in entire
Tamil Nadu, which has seen significant sea water intrusion, with the other two
being pockets of Cuddalore, Ramanathapuram and Kanyakumari. Recent observations
have shifted their focus to South of Chennai in areas such as Adyar and Besant
Nagar, where officials pointed out that signs of intrusion are already showing
(http://www.ibnlive.com/news/india/sea-water-intrusion-a-big-challenge-for-city-aquifers-515082.html).
Modeling on ground
water behaviour: Salt water intrusion takes several
forms. Horizontal intrusion occurs as the saline water from the coast slowly
pushes the fresh inland ground water landward and upward. Its cause can be both
natural (due to rising sea levels) and man induced, (say, by pumping of fresh
water from coastal wells) (Fig. 1a). Pumping from coastal wells can also draw
salt water downward from surface sources, such as tidal creeks, canals,
embayment (Fig. 1b). This type of intrusion occurs within the zone of capture
of pumping wells, which is local in nature, where significant drawdown of the
water table causes induced surface infiltration. A third of intrusion is called
‘upconing’. Upconing also occurs within the zone of capture of a pumping well,
with salt water drawn upward toward the well from salt water existing in deeper
aquifers (Fig. 1c) (Maimone, http://cms.ce.gatech.edu/gwri/uploads/proceedings/1999/MaimoneM-99.pdf).
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|
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(a)
(b)
(c)
Fig. 1. Different forms of salt water
intrusion (a) horizontal movement towards supply well, (b) induced downward movement from
surface sources such as creeks, (c) upconing beneath a supply
well (Source: Maimone, http://cms.ce.gatech.edu/gwri/uploads/proceedings/1999/MaimoneM-99.pdf)
|
Management models and
control of seawater intrusion:
Indiscriminate use of water resources, particularly
under ground, thus poses a major threat to destabilize
the ecosystem. Different management models at varying degrees of success have
been reported in the literature by various workers to find out developing
withdrawal management methodologies for determining the number of viable
locations for wells and the quantities of water which can be pumped from
coastal aquifers while protecting the wells from seawater intrusion in order to
satisfy the demand (social dimension), maximizing the economic benefits
(economical aspects), and controlling the saltwater intrusion (environmental
concern). One such optimisation model
was developed for planning and managing saltwater intrusion (Da Silva et al., https://repositorium.sdum.uminho.pt/bitstream/1822/8682/1/Optimal%20Management%20of%20Grondwater%20Withdrawals%20in%20Coastal%20Aquifers.pdf)
into coastal aquifer systems using the simulation/ optimisation approach for
managing water resources in the areas, suggesting the best location of the
wells with specific flow rate, and thereby, the best policies to maximize the
present value of economic results of meeting water demands, and to keep under
control the saltwater intrusion.
Various
engineering methods are in use worldwide for the control of coastal seawater
intrusion. In India sporadic work has
been done, as for example in Tamil Nadu (Chennai) and along Saurashtra Coast in
Gujarat state (Mangrol-Chorwad-Veraval area). Methods that may be employed for
control of seawater (Sen, 2011) ingress into aquifers are listed and
described as: (1) Modification of ground
water pumping and extraction pattern, (2) Artificial recharge, (3) Injection barrier, (4) Extraction barrier, (5) Subsurface barrier,
(6) Tidal regulators/ Check dam/ Reservoirs.
For
an effective and long term solution to the problem of seawater intrusion into
ground water aquifer in the coastal plain it is necessary to develop
location-specific optimization model to decide on suitable locations of the
pumping wells and rates of withdrawal of the ground water from these wells
after due consideration of the relevant factors. Attempts for suitable
constructions either by pushing saline water front further seaward through
check dams or injection barriers, and/ or allowing more surface water
infiltration to recharge the ground water through creation of reservoirs behind
the dams, or through subsurface barriers, etc. are mostly in experimental stage
though worth consideration, and its adoption is subject to economic viability.
Integrated
Water Management
If
the water table, rich in salts, is present at a very shallow depth (generally
not exceeding a depth of 2 m below the soil surface), it contributes salts to
the root zone during the dry season through upward capillary rise in response
to evapotranspiration demand of soil moisture. The net salt loading in the root
zone will be positive (salinity will build up) or negative (desalinization will
take place) depending upon the relative rate of recharge of salts by upward
rise to rate of downward flux of salts through leaching. The relative salt
loading will thus be treated generally as positive during dry season, and negative
(waterlogging on the soil surface) during wet season due to high rainfall, and
the process will be repeated in the each year in a seasonally cyclic mode.
Sen
and Oosterbaan (1992) presented a practical working method on integrated water
management for Sundarbans (India) through surface gravity induced drainage
during summer/ wet season (through land shaping)-cum-excess rainwater storage
for irrigation during dry season. They computed for the same region drainable
surplus, which may be stored for irrigation during dry (deficit) period. Ambast
and Sen (2006) developed a computer simulation model and a user-friendly
software ‘RAINSIM’ for the same, developed primarily for Sundarbans region for
small holdings, based on the hydrological processes (Fig. 2), and the same
tested duly for different agro-climatic regions in India for (i) computation of
soil water balance, (ii) optimal design of water storage in the ‘On-farm
reservoir (OFR)’ by converting 20 % of the
|
Fig.2. Comprehensive
framework of hydrological processes at different scales (Source: Ambast and
Sen, 2006)
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Irrigation water resources:
In
spite of the coastal ecosystem presenting a delicate equilibrium among the
different components there is however no firm strategy, as of now, for
exploitation of water resources for irrigation and other purposes for long term
solution in any sector. The European Commission (2007) observed, based on a
study by Spanish researchers, how an inappropriately planned coastal
development could lead to increasing water consumption to unsustainable levels,
for which future planning for sustainable development, based particularly on
water resources, should be such as not to disturb the ecosystem in the long
run. The technological developments in this region should focus on the areas,
viz. artificial recharge of the aquifer, recycling of water, desalinzation of
seawater, weather modification, improved irrigation management practices, and
use of marginally poor quality water.
It is suggested that location-specific programme on water allocation under different sources should be drawn up for each
region, based on soil, climate, water, and crop parameters, with minimal dependence on abstraction of water
from the underground aquifer, but with increasing dependence on other means,
like use of surface water sources by recycling of rainwater stored and fresh
water available using innovative seawater desalination technology, and
conjunctive use of marginally saline water available, with overall target to increase water productivity and cropping intensity phasewise, and conserve the ecosystem at the same time.
With
a vision on source-wise water allocation for irrigation for higher productivity
and stability of the coastal irrigated plains in India, an analysis shows need for stepwise
increase in water use under different
|
Fig.
3. Percent water
allocation source-wise with respect to total amount of irrigation water of
the cropping
system and gross cropped area per year during coming four decades in the
coastal areas of India (Source: Sen et
al., 2012)
|
|
Fig.
3. Percent water
allocation source-wise with respect to total amount of irrigation water of
the cropping
system and gross cropped area per year during coming four decades in the
coastal areas of India (Source: Sen et
al., 2012)
|
modes
along with suggested increase in cropping intensity from 150 % to 225 % during
2020 to 2050. A Field Water Balance model has been utilized to estimate surface
water storage opportunities, which should gradually dominate over under ground
water use for stability of the coastal plain (Fig. 3). It is suggested to
introduce coastal watersheds having multiple components for computation of
overall water balance of the ecosystem through integrated approach (Sen et al., 2012).
|
Fig.
3. Percent water
allocation source-wise with respect to total amount of irrigation water of
the cropping
system and gross cropped area per year during coming four decades in the
coastal areas of India (Source: Sen et
al., 2012)
|
With regard to soil fertility, the coastal soils
are usually rich in available K and micro-nutrients (except Zn), low to medium
in available N and are having variable available P status (Bandyopadhyay et
al., 1985, Bandyopadhyay, 1990, Maji and Bandyopadhyay, 1991). Major
portion of the applied N fertilizer is lost through volatilization (Sen and
Bandyopadhyay, 1987). Effect of salinity on
the microbial and biochemical parameters of the salt affected soils in
Sundarbans (India) was studied at nine different sites showing that the average
microbial biomass C (MBC), average basal soil respiration (BSR), and average
fluorescein diacetate hydrolyzing activity (FDHA) were lowest during the summer
season, indicating adverse effect of soil salinity. About 59%, 50%, and 20%
variation in MBC/OC, FDHA/OC, and BSR/MBC (metabolic quotient, qCO2),
respectively, which are indicators of environmental stress, could be explained
by the variation in ECe. The decrease in MBC and microbial
activities with a rise in salinity was ascribed as probably one of the reasons
for the poor crop growth in salt affected coastal soils (Tripathi et al., 2006). It was suggested that integrated nutrient
management should be very effective for increasing its use efficiency for
higher and sustainable yield of crops (Bandyopadhyay et al., 2006,
Tripathi et al., 2007).
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Fig. 4. Distribution
of rainfed lowland rice soil quality area in Asia. Each dot is coloured to
represent the assumed dominant soil class (Source: Haefele and Hijmans, 2009)
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The importance of improved soil quality in the
coastal plains through higher SOC level of the soils was highlighted by
Mandal et al. (2008). IRRI characterized lowland rice soils (excluding
deepwater rice) in Asia in respect of soil quality (Haefele and Hijmans, 2009),
which includes large areas under coastal plains (Fig. 4). They grouped soil
qualities into four categories. These were: Good, Poor, Very Poor and Problem
soils. ‘Good’ and ‘Poor soils’ represent those with different degrees of
weathering but without major constraints; ‘Very Poor’ represents soils with
multiple chemical constraints (acidity, deficiency of phosphorous, or
toxicities of iron and aluminum); while ‘Problem soils’ represent those with the
most frequently cited soil problems, including acid sulphate, peat, saline, and
alkaline soils, which partly cause low fertility, and partly soil chemical
toxicity.
Major Ecological Factors
Carbon
Sequestration
Modeling
C sequestration so far indicated that coastal marsh ecosystems tend
to sequester C continuously with increasing storage capacity as
marsh age progresses and its area increases. Thus, C sequestration
in coastal marsh ecosystems under positive accretionary balance acts
as a negative feedback mechanism to global warming. Choi and Wang (2004) were of the opinion that
dynamics of carbon cycling in coastal wetlands and its response to sea level
change associated with global warming is still poorly understood. However, they
also observed during their study at Florida that salt marshes in this area have
been and continue to be a sink for atmospheric carbon dioxide. Because of
higher rates of C sequestration and lower CH4 emissions, coastal
wetlands could be more valuable C sinks per unit area than other ecosystems in
a warmer world. Brigham et al. (2006)
stated that the estuarine wetlands sequester carbon at a rate about 10-fold
higher on an area basis than any other wetland ecosystem due to high
sedimentation rates, high soil carbon content, and constant burial due to sea
level rise.
In
India, possibly, the first ever study made by Bhattacharyya et al. (2000) about a decade back showed
SOC pool in two soil strata under different physiographic regions including
coastal areas. The data based on soil analyses covering 43 soil series showed
the SOC data varied from 2.4 Pg to 10.9 Pg from 30 cm to 150 cm soil depth. It
will be prudent to concentrate on elaborate studies in future on monitoring SOC
pool in different soil strata in coastal areas over a long period of time,
and relate them
with sea level
rise, extent and
nature of land submergence with water, seawater
quality, extent and nature of vegetative cover, relevant soil and climatic
parameters, nature and amount of agricultural, industrial and city effluents
discharged into the sea, and any other anthropogenic factors of the locality
likely to influence SOC, etc. It should also be possible to create databank on
SOC and related factors of the past using radiocarbon dating.
Sedimentation
and Erosion
The
dynamics of alluvial landscapes and natural sedimentation patterns that
determine the nutrient and energy flows in coastal areas are increasingly being
modified by human activities, in particular those that affect water flows
(dams, increased water extraction, deviation of rivers) and erosion, especially
due to deforestation. This prevents or slows down vertical accretion, thus aggravating
salt water intrusion and impairing drainage conditions in riverine, delta or
estuarine areas. It reduces or blocks sediment supply to the coast itself,
which may give rise to the retreat of the coastline through wave erosion. Beach
erosion is a growing problem and affects tourism revenue, especially in island
nations. In the Caribbean, as much as 70 percent of beaches studied over a
ten-year period were eroded (http://www.cep.unep.org/publications-and-resources/marine-and-coastal-issues-links/sedimentation-and-erosion).
Eutrophication, Hypoxia, Dead Zones
and Nutrient Cycle
Source:
World Resources Institute (2006)
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Table
3. Global
sources of Biologically Available (Fixed) Nitrogen
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The
World Resources Institute reported that driven by a massive increase in the use
of fertilizer, the burning of fossil fuels, and a surge in land clearing and
deforestation, the amount of nitrogen available for uptake at any given time
has more than doubled since the 1940s. In other words, human activities now
contribute more to the global supply of fixed nitrogen each year than natural
processes do, with human-generated nitrogen totaling about 210 million metric
tons per year, while natural processes contribute about 140 million metric tons
(Table 3). This influx of extra nitrogen has caused serious distortions of the
natural nutrient cycle. In some parts of northern Europe, for example, forests
are receiving 10 times the natural levels of nitrogen from airborne deposition,
while coastal rivers in the Northeastern United States and Northern Europe are
receiving as much as 20 times the natural amount from both agricultural and
airborne sources (Coastal Wiki, 2008).
Climate Change
Climate
change has a phenomenal influence through all the components on E-flows on
temporal scale. It is now well established that glaciers around
the world – and especially in the Hindu Kush Himalayas – are retreating due to
global warming, as a result the predicted water flow, based on Kathmandu-based
study of the International Centre for Integrated Mountain Development (ICIMOD),
from the glaciers to the basins would reduce by 25-50% by the end of this
century (the thirdparty.net).
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Fig.5. Global
average sea level rise since 1961 at
an average rate of 1.8 mm per year and since 1993 at 3.1 mm per year
(Source: Pachauri, 2008b)
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Population
Growth as the Driver
Apart from climate change
population growth is possibly the single most factor, other than those directly
or indirectly related to crop production, impacting livelihood in the coastal
ecosystem. Around the world maximum people die of drowning by storm surge. It
is just astonishing to note that in the cyclone of 1970 that struck Bangladesh
more than 300000 people met a watery grave. Similar things happen in Australia
too, but casualties were less because of lesser density of population on the
vulnerable areas (Joshi, 2007). A list of 5 deadliest natural
disasters on the coast is shown in Table 4.
It has been projected that number of people living within 100 km of
coastlines will increase by about 35 percent in 2050 as compared to that in
1995. This type of migration will expose 2.75 billion people to coastal threats
from global warming such as sea level rise and stronger hurricanes in addition to other natural disasters like
tsunamis (Goudarzi, 2006). In another estimate (Schwartz, 2005), the expected
change of the population (or population density) from 2000 to 2025 regionwise
shows increase in almost each coastal area. The
estimates (population within 100 km of the coastline) show increase by
25 % in Asia (except Middle East), 52 % in Middle East and North Africa, 81 %
in Sub-Saharan Africa, 20 % in North America, 31 % in Central America and
Caribbeans, and 32 % in each South America and Oceania, while there may be
decrease by 2.5 % in Europe. In India, according to the Department of Ocean
Development, there are 40 heavily polluted areas along the Indian coast (Dubey,
1993).
Ecological
impact: Deteriorating E-flow in Ganga on South Bengal
The Hooghly’s flow is
oscillating; the water level fluctuates twice a day, owing to the tides, and
changes its hydro-morphology. Its estuary below Diamond Harbour being
funnel-shaped, it restricts the optimum tidal influx which primarily governs
the channel regime and its navigability. The sediment movement in tidal estuary
of the Hooghly is the function of a complex fluvial system that can hardly be
governed by inducing 40000 cusec (1132 cumec) of flow. The available flow even
dwindled to 454 cumec in the first week of April causing declining in the
navigability for the Kolkata Port. The adverse effect in the Indian part could
be verified from the fact that the annual quantum of dredging increased from
6.40 MCM during pre-Farakka days to 13.24 MCM during post-Farakka days quoted
up to 1995, and then to 21.18 MCM quoted for 1999-2003 (Rudra, 2006). Besides, sediments are trapped in the
barrage-pond raising the level significantly and also encouraging the river
course to change its direction both upstream and downstream.
It is true that there
are interferences of the Ganga’s regime due to construction of Farraka Barrage
giving rise to problems and disadvantages – changes with water level,
discharge, sediment movement, bed slope, etc. caused by aggradations and
degradation of the bed and the entire reach from Rajmahal to Farakka in the
upstream and from Farakka to quite a distance downstream. Alluvial fans formed
on the right side and the deep channel shifted to the left above the Barrage.
Bank erosion got worse and was usually highest during August and September.
There were direct and indirect effects of sedimentation pattern of the
Ganga-Padma in Bangladesh as well, which would eventually increase siltation
and erosion of the river beds and banks, ultimately affect the channel and
cause other morphological changes.
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Table
4. List of 5 deadliest natural disasters on
the Coast (Source: Wikipedia, 2009)
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The complacency of the
administration, on the other hand, looking the other way concentrated on
construction of roadways and bridges through silted up river beds in the Indian
Sundarbans in the name of development at the expense of drying up of the rivers
which is an antithesis to development blunderingly ignoring the ecology in the
area.
Way Forward
The lower Ganga delta face
threats due to dwindling water diversion via Farakka Barrage and deteriorating
water quality of the river in the upstream at different places in India. There
is need for a holistic and focused attention for which the following
suggestions are made to seek for a lasting solution (Sen and Ghorai, 2014).
·
There
appears to be a need for revisiting the design of the Farakka Barrage, as well
as the discharge and distribution norms of water in the interest of the two
countries, keeping in view of the predicted flow of upstream Ganga water in
long term perspectives, and if necessary, fresh norms to be decided.
·
Predicted
flow of water through Ganga-Brahmaputra, both originating in Tibet, river
system on account of retreat of glaciers and other parametric uncertainties due
to climate change needs to be studied and refined with appropriate climate
models in deciding the future norms for distribution of water via Farakka
Barrage with as much precision as possible in different time scales.
·
Need
for fresh installation of hydro-electric power and irrigation projects in India
must be given extremely careful consideration with stringent norms for
discharge of river water into the upstream so that ecology of the area is not
disturbed.
·
Past
hydro-electric power and irrigation projects in the upstream already in
commission need also to be reviewed in terms of the norms for discharge of
water decided, and if necessary, to be revised, scientifically so that ecology
of the area is not disturbed.
·
Provisions
should be mandatory to make impact analysis of the discharge of water from
different projects, be it hydro-electric power and irrigation projects or any
others, on the ecology of the area for all past and future installations in
India.
·
Strict
administrative vigilance to be maintained to stop acts on unscrupulous
diversion of water forthwith by private agencies in India.
·
Location
specific integrated water development and management schemes at strategic
points over the entire flow length in different time scales to be prepared and
their methods of implementation be worked out, with adequate participation and
vigilance from the local inhabitants, to ensure maintaining prescribed water
quality throughout the year.
·
Impacts
of the water flow at different strategic points into lower delta in respect of
salinity in soil & water, flow rate, tidal amplitude and fluctuations, sedimentation/
hydrological parameters, navigation through rivers, ground water table depths
and qualities, all important components of biodiversity, and any other related
parameters should be taken up and monitored with a holistic plan, over minimum
five year phases, through a central task force comprising of scientists, NGOs,
government officials, local inhabitants, and the same placed in public
domain.
It is believed, in
conclusion, that there may be no short-cuts to improve the ecology for sustained
livelihood of the inhabitants in this area other than ensuring E-flows via
Farakka Barrage, for which careful considerations may be given to the
suggestions made above.
Conclusion
Although management of soils due to salinity or other stress factors catches
immediate attention of all concerned for augmenting productivity in the coastal
ecosystem, the various ecological factors discussed above, to speak the least,
besides a few others, like under-sea tectonic movement along with off-shore and
on-shore protection measures required to be undertaken, demand that it should
be mandatory to give a holistic look to their interaction matrix, and not the
management of the stressed soils alone, to ensure lasting stability of the
ecosystem.
I am grateful to ISCAR for asking me to deliver the first lecture in the
series.
Tribute
I owe my deep indebtedness to Dr.
J.S.P.Yadav for anything I have learned on the subject, yet I must confess I
have garnered only to scratch on the surface. Hope future workers will further
lay bricks on the foundation, if at all I have been able to create it, to strengthen
our understanding in this complex area, which will be the best homage to him.
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