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CHAPTER 2

STUDY AREA : VEMBANAD LAKE

2.1 INTRODUCTION

Kerala, cradled between the rugged ranges of Western Ghats on the

eastern border and Arabian Sea on the western border, has a unique

physiographic setting in the Indian Union. Several minor rivers originate from

the Western Ghats enhance the greenery and natural scenario of Kerala. This

strip of land has a coast that runs some 590 km in length and is bestowed with

coastal landforms such as a chain of brackish lagoons, estuaries, islands,

marshlands, flood plains and alluvial plains. About 16.4% and 54.2% of

landforms are within 0–10m and 10–300m elevation from mean sea level,

which are comprised of coastal plains and lagoons (Menon et al 2000).

The Vembanad Lake system that lies in the above category is the

largest estuarine-lagoon system in Kerala. This lake consists of a complex

system of backwaters, marshes, small islands, mangrove forests, and a

network of canals. Considering its ecological significance and high

biodiversity, it had been designated as the Ramsar Site-1214 at the

Convention on Wetlands organized by the UNESCO in the Iranian city of

Ramsar in 1981. Besides, it is classified as an “Ecologically Sensitive Zone”

as per the Environmental Protection Act 1985 (29 of 1986), by the Ministry of

Environment and Forests, India (Subramanian et al 2002). In and around this

lake is one of the highly populated coastal zones, where people depend

directly or indirectly upon this ecosystem for their livelihood. It houses the

35

second largest port (Kochi Port- established 1936) in the west coast of India,

and the recently added Vallarpadam Container Terminal which functions as a

nerve centre for distribution of goods and is of high economic importance.

2.2 GEOGRAPHY

Vembanad Lake situated between Lat. 9º30 46 –10º11 11 N and

Long. 76º09 48 –76º25 45 E is distinguished by its long axes running parallel

to the coast and is separated from the sea by barrier spits interrupted by tidal

passes. This oxbow shaped lake extends for a distance of 96 km from

Azheekode in the north to Alappuzha in the south with a Northwest–

Southeast orientation (Figure 2.1). It is spread across three central districts of

Kerala, viz, Ernakulam in the north, Kottayam in the east and Alappuzha in

the south and covers an area of 241 km2(Subramanian et al 2002).

Figure 2.1 Location map of Vembanad Lake system

36

The lake is connected to the Arabian Sea in the west through two

inlets, with one channel at Kochi (400 m) and another channel further north at

Azheekode (250 m). The lake consists of two major arms, i) Northern arm

(Kochi barmouth to Azheekode barmouth) which is 32 km in length and

ii) Southern arm (Kochi barmouth to Alappuzha) which is 64 km in length.

Width of the lake is generally more (0.8-6.9 km) towards southern arm but

becomes narrow (0.05-0.5 km) towards northern arm. The average depth of

the lake is 2.1 m and it occupies a volume of 0.55 km3 (Gopalan et al 1983).

The bathymetry varies considerably from place to place. In most of the places,

the depth ranges from 2-6 m except in the main channel which is used for

navigational purposes where the depth is 10-13 m (Qasim 2003). The three

dredged navigational channels are: main approach channel (10 km) oriented

along the east–west direction and two inner channels located on either side of

the Willingdon Island, i.e. Ernakulam channel (5 km) on eastern part of

Willingdon Island and Mattancherry channel (3 km) on western part of

Willingdon Island.

Two artificial hydraulic barriers were constructed at

Thanneermukkom (43 km south of Kochi inlet) and Pathalam (28 km

northeast of Kochi inlet) respectively. Thanneermukkom bund is 1447 m

long. It was built in the southern arm in 1974 and made functional in 1976.

The bund acts as a barrier which partially cuts off tidal water causing the

system to behave as two entirely different ecosystems with the brackish Kochi

backwaters (Thanneermukkom bund to Azheekode) and the freshwater lake

(Thanneermukkom bund to Alappuzha) (Gopalan et al 1983). Pathalam bund

is a temporary barrage erected only during the dry season. The northern arm

consists of islands like Vypeen, Vallarpadam and Bolghatty whereas

Willingdon, Perumbalam, Kumbalam and Pathiramanal are distributed along

the southern arm. Many small islands are scattered across the lake.

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2.3 GEOLOGY

The state of Kerala is covered mainly by four major rock units

namely precambrian crystallines, tertiary sedimentaries, laterites and the

recent to sub-recent sediments. The coastal plain of the region is of recent

geological origin, with its formation dating back to the early tertiary period,

whereas sedimentary formations on the coast are recent and sub-recent. The

lake was formed due to the initial tectonic movement followed by

sedimentation processes affected by waves and currents from the sea (Mallik

and Suchindan 1984). The present configuration of the lake was shaped

during fourteenth century A.D. following a catastrophic flood modifying the

drainage area of the rivers. The formation of parts of the present coastal

districts like Ernakulam and Alappuzha and the separation of this distinct

body of water from the sea happened after the intense flood in 1341 A.D.

(Gopalan et al 1983). Figure 2.2 illustrates the morphological changes in the

lake for the past few centuries, which has suffered severe shrinkages over the

years.

Figure 2.2 Morphological change of Vembanad Lake over centuries

(Source: Balachandran 2007)

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Kerala consists of mainly 10 broad groups of soils, tertiary,

quaternary sediments and offshore sediments in the Kerala-Laccadive basin

mixed with laterite. Lateritic and red soils cover the major portion of the

drainage basin of lake. Kaolinite, montmorillonite and illite are the major clay

mineral deposition in the bed of the lake, influenced by the riverine inputs

(Soman 1997).

2.4 LANDUSE

The land use/land cover map for the study area during the year

2008 is shown in Figure 2.3. Satellite images (IRS1C/1D) and Survey of India

toposheets were used in the preparation of map. The area around the lake

comprises a variety of unevenly distributed landforms under thirteen main

classes. These include mudflats, cropland, plantations, fallow land, sandy

beach, water logged area, settlement with vegetation, settlement and

industries. Human settlement is distributed all along the banks of study region

and is dense in the Kochi area. Population density (2011 census) in the study

region is higher (1103/km2) compared to the national average (382/km

2), and

is one of the most populated coastal zones of the world.

Of the total mapped area of 1989 km2, cropland consists of 15.3%.

Rice cultivation is one of the major occupations in this region and nearby

districts. Major share of cultivation land was mainly reclaimed from the lake

area during the last decades (Balachandran 2007). Plantations in the nearby

region occupy 7.1% of the land. The dominant plantations are of coconut and

tapioca while banana, cereals, millets, red gram, groundnut and papaya are

grown successfully as intercrops. Water body area covers 14% with a

seasonal waterlogged area of 4.6% and mudflat area <1% during the

monsoon. Settlement and settlement with vegetation cover 9.1% and 43.7% of

the total area respectively. Most of the settlements that are distributed along

39

the banks of the lake are associated with vegetation. Fallow land and sandy

beach occupy 1.1% and <1% respectively. Mangrove patches are also seen in

a very small area. Industries are mainly concentrated in the northern part of

the lake and on the riverbanks. Developmental activities in this area cause

changes and stress the land use pattern in this region.

Figure 2.3 Landuse map of the Vembanad Lake

2.5 METEOROLOGICAL FACTORS

The area experiences a more or less uniform temperature

throughout the year with less seasonal variations. High temperatures occur

40

during March–May varying from 30-34ºC and are lowest in December

22-24°C. The study region has the highest percentage of humidity in air

(70-90%). Humidity values are high all through the year, with lower values

during winter months and higher during the monsoon period.

The speed and direction of winds in the study region was found to

be regulated by season and by the temperature differences between land and

sea. The wind direction remains predominantly west to southwest during

southwest monsoon (June-September). From October to May, wind direction

changes from northeast in the morning hours to west during the afternoon and

evening. Southwest monsoon winds of marine origin are stronger than those

of continental origin of the northeast monsoon. Land breeze is not dominant

during June–December, but shows some influence during the summer.

The presence of Western Ghats, which obstruct the southwest

monsoon winds, results heavy rainfall in this region. Kerala receives heavy

rainfall for major part of the year and the mean climatic conditions can be

separated into two; i) dry season (Non-monsoon), which stretches from

approximately January to May and ii) rainy season in two phases – the first

from June to September (Southwest monsoon) and the second, from October

to December (Northeast monsoon). The total annual average rainfall of the

region is 320 cm (Qasim 2003). The climate is typical of the tropics with

southwest monsoon yielding 60% of the total rainfall and northeast monsoon

yielding 25%.

2.6 HYDROLOGICAL FACTORS

2.6.1 River Systems

The rivers joining the Vembanad Lake are small compared to other

major rivers in the Indian sub continent. Six perennial rivers, which originate

41

from the Western Ghats flow westwards and drain into the lake before joining

the Arabian Sea. The rivers are Achenkoil (128 km), Pamba (176 km),

Manimala (90 km), Meenachil (78 km), and Muvattuppuzha (121 km) which

join at southern arm of the lake and a branch of Periyar (244 km) which joins

at the northern arm (Basak 1995). Combined drainage area of the six rivers is

12,724 km2 (Basak 1995). Drainage areas of these rivers are variable

(Figure 2.4a) depending on the land use pattern, habitation, nature of

vegetation, establishment of industrial units and other human activities. A

graphical representation of the individual river drainage areas is provided in

Figure 2.4b.

Periyar river bifurcates into two at Alwaye, one branch which

discharges nearly half of the river drains directly into the Arabian sea at

Azheekode barmouth whereas the other branch which flows toward Kochi

barmouth passes through the industrial belt at Eloor and discharges into the

Vembanad Lake. Muvattupuzha River discharges into the Kochi backwater

region between the Thanneermukkom bund and Kochi barmouth. Among the

remaining four rivers, Meenachil joins the middle east of the Vembanad Lake

after the bund while Manimala, Achankovil and Pamba join the extreme south

of the lake in Alappuzha.

Nearly 33% of the total river discharge into the estuary is from the

Periyar, which is the longest and has largest catchment area, and drains the

highest amount of water into the lake. Percentage contribution of water input

to the lake from Muvattupuzha, Achenkovil, Pampa, Meenachil and

Manimala (Srinivas et al 2003a) are shown in Figure 2.4c. Monsoonal flows

through the rivers of Kerala show strong seasonal characteristics during June

to the December. On the other hand, summer flow in the rivers forms only a

small fraction of the total runoff. More than 60% of the river discharge

(2.0 x 1010

m3

yr-1

) occurs during the southwest monsoon, 10-25% during the

42

northeast monsoon and the remaining during the rest of the year

(Srinivas et al 2003b).

Figure 2.4 a) Drainage area of rivers joining the Vembanad Lake

b) Drainage area graph in (km2)

c) Percentage contribution of river water input to

Vembanad Lake

2.6.2 Tides

Every estuary has its own tidal characteristics, which influences the

mixing, circulation and hydrodynamic processes of the system. In Vembanad

Lake tides enter and exit through two perennially open narrow inlets with

43

cross sectional area of 4234 m2 at Kochi mouth (Joseph 1996) and the

Azheekode mouth of lesser area. The tides are usually mixed semi-diurnal

with two high and two low waters that occur daily with inequalities in range

and time. The maximum amplitude is 1 m, and the magnitude of tides

progressively decreases with increase in the distance from the barmouth. The

flood and ebb currents are comparatively higher in the Ernakulam channel than

in the Mattanchery channel (Strikwerda 2004). The northern arm frequently

develops flow-restrictions due to converging tides entering from two adjacent

inlets, whereas tidal amplification is noticed in the southern arm

(Balachandran et al 2008). During summer, seawater reaches the head of the

estuary (Alappuzha), but is restricted to 25 km during monsoon.

2.6.3 Hydrodynamics

Vembanad Lake is a positive type estuary with the riverine inflow

and precipitation exceeding evaporation. Intermixing of tidal water and river

water gives the lake the characteristics of a tropical estuary (Balchand and

Nair 1994). The topography of the lake regulates the circulation pattern,

which behaves distinctly in the two arms of the lake. There is a significant

difference in the runoff and tidal influence during different seasons and

generally is referred to as monsoonal estuary; the west coast of India mainly

consists of this type of tropical monsoonal estuaries (Shetye et al 2007).

During the monsoon, the system conditions are dominantly of a freshwater

body and after that, the system gradually changes into brackish water with

marine conditions dominating during summer.

Fluvial supply from rivers result in high siltation and the sediment

flux from the catchments is about 32 x 106 tonnes yr

-1 (Thomson 2002).

Hydrodynamic conditions regulate the mode of accretion and siltation, which

causes shrinkage of the estuary. The exchange volume of the estuary has also

44

been reduced by 90 Mm3 per tidal cycle from 1960 to 1985 (Balachandran

2007). In addition, hydrodynamic aspects of the system are influenced by

various anthropogenic activities and its dynamics are not completely

understood.

2.7 FLORA AND FAUNA

This Ramsar site No.1214 has a unique environmental habitat

which supports rich and diverse species of flora and fauna. Both freshwater

and saline water species are present in this tropical estuary, and consist of 194

species of phytoplankton and 135 species of zooplankton (Subramanian et al

2002). Diatoms and Copepods are the dominant groups among the

phytoplankton and zooplankton community respectively. The major aquatic

plants present in this lake include Eichhornia crassipes (water hyacinth) and

Salvinia molesta (giant salvinia, kariba weed) which are widely distributed

and are a threat to the ecosystem. Small isolated patches of mangrove

vegetation are present at Kumarakom, Vypeen, Kannamali and Chettuva

regions of this estuary.

Faunal diversity includes a large variety of fishes, prawns, clams,

reptiles and birds. Fishes present in this lake are mainly oligohaline and

estuarine fishes which migrate from the Arabian Sea to the lake and vice

versa. Marine penaeid prawns, clams like Villorita cyprinoids and Mertrix

meretrix are exploited more from this region of the Kerala coast. Polychaetes,

crustaceans and molluscs are the major members of benthic community in the

lake. This ecosystem supports the third largest population of waterfowl in

India during the winter months (Rajan et al 2008). Numerous species of

resident and migratory birds are found visiting this area for breeding and

feeding. Rich insect biodiversity is also found with butterflies forming the

majority.

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2.8 ECONOMIC SIGNIFICANCE

2.8.1 Navigation

The Port of Kochi, a natural port/harbour located near the Kochi

barmouth, which handled about 15.7 x 106 tonnes during 2007-08

(www.worldportsource.com/ports/IND_Port_of_Cochin), is busy throughout

the year. Recently, an international container trans-shipment terminal facility

is being developed at Vallarpadam, described as a milestone in infrastructure

development logistics. This has placed India in a key position in the world

maritime map. Inland navigation through the national waterway (Kollam-

Kottappuram segment) and lower reaches of rivers is a major means of

transportation in this area.

2.8.2 Tourism

Extensive network of rivers, lakes, canals, and lagoons fringed by

lush green coconut groves and paddy fields, harbouring rich avifauna; water

sports like the famous snake-boat race and the calm and pleasant environment

with boating facilities makes Vembanad Lake one of the top 50 destinations

on the global tourism map. This helps the flourishing tourism industry in

Kumarakom, Alappuzha and Kochi region and also provides employment

opportunities. However, tourism facilities like resorts and hotels are being

developed without any concern for the natural system increasing the pressure

on the ecosystem.

2.8.3 Fisheries

Vembanad Lake supports rich fishery resources and provides

feeding, spawning and nursery grounds for large numbers of commercial fish

and shellfish. About 32.5% of the fisherman population of the state is

46

concentrated on the banks of the lake. Lake production per year consists of

5000 tonnes of fish and almost same quantity of prawns, and 300-400 tonnes

of giant fresh water prawn. Over fishing, use of banned fishing gears and

massive reclamation has resulted in the decline of the fishing area and has

also affected the productivity of fishing grounds. Unnithan et al (2001)

reported decline in annual landing of fisheries from 16,000 tonnes per year

during late seventies to about 7,200 tonnes in recent years. Further confirms

by the decrease in fish species from 150 to 62 in the recent survey on 2008 by

Priyadharshanan and Latha (2009).

2.8.4 Clam Mining

Clams are widely distributed and form vast deposits between the

Pathiramanal Island and Vaikom region. Clam deposits are quarried by

various industries. This is in addition to live clam collection, one of the major

occupations of women and children in this area. Clam meat forms a cheap

protein source for the poor people of this locality. There is a decline in clam

shell production and landing from 2500 tonnes to 1300 tonnes (Arun 2005).

Uncontrolled mining of shells from the lake is also posing a threat to the

ecosystem.

2.8.5 Coir Industry

About 0.35 million workers mainly from socially and economically

backward communities in this region depend on the coir cottage industry.

Brackish waters of the Vembanad Lake are used as coconut husk retting yards

by coir manufacturing industries and Alappuzha acts as the nerve centre of

Kerala’s coir industry. It is important in Kerala’s economy and accounts for

70% production of the coir products in India.

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2.9 ANTHROPOGENIC INTERVENTION AND THREATS

Human intervention started in 1888 in the form of land being

reclaimed for agriculture in the southern parts of the lake (Balachandran

2007). Then, during 1920-1936 there was reclamation and creation of

Willingdon Island and dredging to maintain the shipping channel for the

harbour. Subsequently during 1940’s, industries were allowed to be

established along the upper reaches of the estuary which led to intense

reclamation for human settlements since 1940. During 1955, Thottapally

spillway was constructed to divert the floodwaters of Achankovil, Manimala,

Pamba and Meenachil directly to sea. Thanneermukkom Bund (1976) was

built to improve agricultural output, and a temporary barrage in Pathalam

bund was constructed on the Eloor branch of Periyar River since 1981.

During 2011, the first phase of the International Container

Transhipment Terminal at Vallarpadam was constructed to handle

international cargo. The region is still witnessing many engineering

modifications like construction of houses/factories on reclaimed land,

waterways development, erection of bridges and deepening of shipping

channels, required to support rapid economic development. All these

anthropogenic activities have led to the shrinking of the water spread area of

the backwaters from 365 km2 to 256 km

2 (Balachandran 2007). These

interventions have had significant effect on the hydrodynamic aspects of the

system leading to dispersion of pollution and diminishing of the bioresources

of the system.

2.9.1 Agricultural Activities

Rising requirement for food has resulted in intense agriculture in

the Kuttanad (rice bowl of Kerala) region. The fertilizer consumption in

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Kuttanad region alone is reported to be 20,239 tonnes yr-1

(Nair 2002). A

large amount of chemical fertilizer has been added to the other variety of

plantation and crops in the nearby regions to maintain high production. These

all seems to an increase in use of nitrogen/phosphorus containing fertilizers in

these areas. Intense agricultural practices are responsible for the reclamation

of lake area, inputs of fertilizers and pesticides and fall in soil fertility.

2.9.2 Domestic Sewage

Industrialization and commercialization attracts a lot of migrants

and this increase in population has resulted in the enhanced discharge of

260 m3

d-1

of organic waste in to the Cochin estuary (Balachandran et al

2005). Urban sewage from Kochi city including slaughter house wastes, and

wastes from the markets and hospitals as well as domestic wastes reach the

lake through the network of natural and artificial canals. Discharge from

motor boats, resorts and houseboats directly into the lake are a major source

of organic pollutants.

2.9.3 Artificial / Engineering Construction

Thanneermukkom bund, constructed to prevent salinity intrusion

into Kuttanad farmland for high crop yield, has resulted in the reduction of

population of fish and shrimps. This artificial barrier produces negative

impacts like arresting the tidal flushing which results in the trapping of

agricultural pollutants, increased growth of water hyacinth and severe

environmental degradation. Drastic ecological changes have been reported

particularly south of the Thanneermukkom bund, thereby affecting the

ecology and distribution of the living resources in the estuary (Menon et al

2000, Arun 2005). The Kochi shipyard and port activities release sizeable

quantities of waste oil, paints, metal and paint scrapings. Various engineering

49

activities by Vallarpadam terminal and the annual dredging of Kochi

navigation channel (l0 x 106 m

3) have adverse effects on the circulation

pattern, sedimentation rate and the ecology in the estuarine region (Rasheed

1997).

2.9.4 Industrial Pollution

Kochi, the industrial capital of Kerala, has a lion’s share of

chemical industries, which are situated on the banks of river Periyar and also

in the upper and mid reaches of the system. The industrial typology includes

fertilizer, pesticides, radioactive mineral processing, chemicals and allied

industries, petroleum refining and heavy metal processing, food and drug

manufacturing and fish processing. It is estimated that nearly 104 million

litres of partially treated and untreated industrial effluents generated every day

by various industries (Menon et al 2000, Balachandran et al 2006).

Small-scale industries on the banks of the lake like coir industry, where

processing is carried out through traditional retting practices and fermentation

of coconut husk contributes to the organic load entering the system.

Overall, the Vembanad Lake, an economically important system is

undergoing a great deal of environmental alterations due to various activities

induced by economic gain and development. The quest for economic gain

without concern for the environment has resulted in adverse environmental

impacts and a fast declining ecosystem. This is mainly caused by improper

management and lack of awareness, which provide challenges for coastal

managers and policy makers in future.