|
Ecological Characteristics and
Issues
 As a background to defining current resource management problems within
Chilika Lagoon, this section of the report describes the Lagoon ecosystem
and the current status of the aquatic resources. Relevant features of the
ecosystem directly supporting, or contributing to fisheries and
aquaculture production, are highlighted.
This includes a consideration of general features of lagoon ecology,
followed by a systematic review of information pertaining to lower
trophic levels and commercial aquatic resources. This is followed by; an
evaluation of several different forms of aquaculture of present or potential
significance within Chilika
Lake.
General Lagoon
Ecology
High nutrient concentrations are often present in Lagoons as a result of
both riverine nutrient inputs and effective nutrient recycling between the
sediments and the water column. Lagoons are, therefore, often highly
productive aquatic environments. A comparison of productivity land biomass
estimates for lagoons around the world (Tables 4.1 and 4.2 in Barnes, 1980)
clearly indicates that Lagoons are characterized by exceptionally high
productivity and biomass, compared to other aquatic ecosystems. The
following features provide lagoons with their distinctive characteristics.
·
the high degree of shelter from tidal and current action;
·
the relatively stable salinity gradients;
·
the soft mud and/or sand substrates;
·
the well-mixed nature of the water column through wind action;
·
extreme shallowness;
·
organic richness;
·
rapidity with which they change (over geological time scales);
in climates with seasonal rainfall, and where major inputs of
freshwater exist a pronounced seasonal variation in salinity and/or water
level.In comparison with estuaries, contributions of phytoplankton and
submerged macrophytes in lagoons are more important in production processes.
Most of the production is consumed within the system, and there is less
export of nutrients and organic material due to the closed nature of lagoons
and of the unimportance of tidal fluxes. Carbon sources include
phytoplankton, ;benthic and epiphytic algae and detritus derived from
macrophytes. The latter detrital source is especially important as a source
of carbon. The pond weed, Potamogeton ppectinatus decays very rapidly
within the lagoon environment. Studies by Howard-Williams and Davies (1979,
cited by Barnes 1980) suggest that under environmental conditions of 15-260
C temperature and 5-11 ppt salinity, most nutrient release from
Potamogeton occurred during its first week of decay, and decay processes
very largely complete within 128 days. Within lagoons, detrital enrichment
via bacterial heterotrophs is the dominant trophic pathway supplying energy
to biological consumers.
Most of the consumers are thought to acquire detritus, benthic algae and
epiphytes in an indiscriminate fashion via deposit feed and/or browsing.
Among vertebrates within lagoons (both birds and fish) most species are
opportunistic omnivores or carnivores.
In summary, lagoons are extremely productive environments due laragely to
high nutrient inputs from surrounding land drainages, as well as efficient
nutrient re-cycling. This high productivity supports lagoon fisheries for
both fish and shell fish. Lagoons are ephemeral environments (on geological
time scales) evolving rapidly into other types of semi-aquatic, habitats
(marshes, swamps). Simultaneous with this succession is a gradual shift from
high salinity conditions to freshwater. Human activities within lagoon
watersheds often serve to increase the succession rate of lagoons towards
their ultimate terrestrial end-state. Virtually all of these general
processes appear to be currently operating within Chilika Lake.
o
the high degree of shelter from tidal and current action;
o
the
relatively stable salinity gradients;
o
the soft mud and/or sand substrates;
o
the well-mixed nature of the water column through wind action;
o
extreme shallowness;
o
organic richness;
o
rapidity with which they change (over geological time scales);
o
in climates with seasonal rainfall, and where major inputs of freshwater
exist a pronounced seasonal variation in salinity and/or water level.
In comparison with estuaries, contributions of phytoplankton and submerged
macrophytes in lagoons are more important in production processes. Most of
the production is consumed within the system, and there is less export of
nutrients and organic material due to the closed nature of lagoons and of
the unimportance of tidal fluxes. Carbon sources include phytoplankton,
benthic and epiphytic algae and detritus derived from macrophytes. The
latter detrital source is especially important as a source of carbon. The
pond weed, Potamogeton ppectinatus decays very rapidly within the
lagoon environment. Studies by Howard-Williams and Davies (1979, cited by
Barnes 1980) suggest that under environmental conditions of 15-260
C temperature and 5-11 ppt salinity, most nutrient release from
Potamogeton occurred during its first week of decay, and decay processes
very largely complete within 128 days. Within lagoons, detrital enrichment
via bacterial heterotrophs is the dominant trophic pathway supplying energy
to biological consumers.
Most of the consumers are thought to acquire detritus, benthic algae and
epiphytes in an indiscriminate fashion via deposit feed and/or browsing.
Among vertebrates within lagoons (both birds and fish) most species are
opportunistic omnivores or carnivores.
In summary, lagoons are extremely productive environments due laragely to
high nutrient inputs from surrounding land drainages, as well as efficient
nutrient re-cycling. This high productivity supports lagoon fisheries for
both fish and shell fish. Lagoons are ephemeral environments (on geological
time scales) evolving rapidly into other types of semi-aquatic, habitats
(marshes, swamps). Simultaneous with this succession is a gradual shift from
high salinity conditions to freshwater. Human activities within lagoon
watersheds often serve to increase the succession rate of lagoons towards
their ultimate terrestrial end-state. Virtually all of these general
processes appear to be currently operating within Chilika Lake.
Bird Ecology
The bird ecology of Chilika Lake is summarized in a recent report
commissioned by the Feasibility and Design Mission, undertaken by Associates
Project Bihang (Dev 1991), an NGO based in Bhubaneswar, actively involved in
ecological research on birds in Chilika Lake. The following statements on
bird ecology are abstracted from this source.
The bird fauna of Chilika
Lake is diverse, and includes 151 species belonging to 26 families (Table
2.3). The avifauna is predominated by 22 species of ducks and geese, 52
species of plovers and sandpipers belonging to 8 families, 14 species of
gulls and terns, 13 species of eagles and 11 species of herons and egrets.
Due in part to the importance of Chilika
Lake for migratory species of Arctic
and Central Asian waterfowl (e.g. flamingoes), the site is internationally
important as one of two Indian wetland conservation sites designated under
the Ramsar convention. Out of the 151 species, 92 species are considered by
Dev (1992) as long-distance migrants, and the rest are considered resident
or local migrants. Chilika is particularly important to migratory waterfowl
as a wintering habitat, during which time both bird numbers, as well as a
bird diversity, show seasonal peaks (Figure 2.9). Specific information
concerning bird feeding requirements, habitat selection, protection and
research requirements are summarized in Dev (1992).
Socio-economic Characteristics and Issues
Community Dependence on the
Lake
Chilika
Lake has 132 fishing villages with a total population of more than ten
million not including the surrounding area which has about 273 villages.
About 30% (33,300) of the fishing village population are active fishermen,
although many others depend indirectly on the fisheries. The specific
methods of fishing are a reflection of the particular caste characteristics
of the community.
The complex mix of resources in and around the Lake, water, fish, land,
forests and fauna, have an interrelated effect on community life. It is
difficult to precisely arrive at a geographical area, and consequently, at
the communities which should be included in a resource management plan for
the Lake. More specifically, farm
land, mostly paddy fields, is spread all around the
Lake and irrigation water with pesticides like Thimet and Ecalux and
fertilizers drain straight into the Lake. The forest area is
spread over the entire western side up to 30 km distance, denudation of
which for fuel and timber purposes add to the sedimentation of the
Lake. Thus many communities, with very different socio-economic backgrounds,
are one way or another linked to resources in and around the Lake.
Three distinct communities can be identified as having crucial linkages to
the Lake and its resource management:
a.
the fishermen (traditional and non-traditional),
b.
the farmers who live around the lake, and
c.
those who depend on the forest resources in the Lake
catchment area for both their livelihood and to meet their fuel/timber
requirements.
Traditional Fishermen :
Their caste and status
The traditional fishermen are Harijans - the "Untouchables" and hence they
occupy the lowest social position in the society. In addition, their poverty
continues to reinforce this lower social position as, in the changing Indian
village scenario, social status and economic power go hand in hand.
There are seven
sub-castes of fishermen
Keuta (also known as Kaibarta or Khatia) - constitute 68% of the fishing
population; generally fish only with nets.
Kandara - constitute 14% of the fishing population; operate traps like
Dhaudi and Thattas for catching prawns and crabs;
Tiar - (also known as Ghadi) constitute 7%; generally use bamboo traps
called bejas and menjhas;
Nolia - constitute 7%; Telegu fishermen who catch mainly marine fish and
fish near the Lake mouth; use drag nets and
cast nets;
Niary (Niaries) - constitute 2.3%; operate nets but do not use traps;
Gokha - constitute less than 1%; operate drag nets.
There is significant status differentiation between the subcastes primarily
related to economic status. But between Khatia and Tiara there are only
marginal differentiations. While Khatias claim that they occupy the highest
position, others challenge this. Kondras are the lowest of the sub-castes.
The fishermen still live separately from the caste-Hindus. Some ten to
fifteen years ago, the fishermen were not even permitted to enter the
caste-Hindu villages and untouchability prevailed. Things have since changed
significantly; the fishermen take baths in the village open pond where
caste-Hindus also take baths and celebrate certain village temple festivals
together. However, in a few places, some discriminations still prevail. For
example, drinking water wells are separate, separate vessels are kept for
them in the hotels, they have to carry the bridge for marriage, play
traditional music, etc. Social awareness, education and economic development
are crucial aspect which can enhance social status in the society.
Forests
There is a large forest area both on the coastal side and around the lake
which quote successfully is being covered by casuarina (near the sea shore),
eucalyptus and cashew under both a SIDA-supported and the government's own
social forestry programme. But the tribals and the local communities
entirely depend upon the forest to meet their own fuel requirements and they
also cut and sell it in the local market. Also, the tribals supply bamboo to
the fishermen to make fishing tools and leaves to make leaf-plates. Some
fisherwomen, while returning after selling the fish in the villages around,
cut and bring home fuelwood. In some fishing communities, women spend five
to seven hours almost everyday to bring leaves to meet their fuel
requirement. Fuelwood is in short supply and hence it provides employment to
a large number of families. The caste-Hindus cut and bring fuelwood in cart
and cycle loads whereas the Harijans and the tribals bring in head-loads.
The number of families live exclusively on the forest. It was stated by the
people that they have to go deeper and deeper into the forest as forests are
getting cleared and denuded. It contributes to floods and sedimentation in
the Lake.
Hence, the forest is significantly linked to the Lake
and the fishing community in many ways. The linkage between poverty and
environment is quite obvious, for they said that they had to depend upon the
forest for their livelihood and that given an alternate income source they
would change their occupation. These relationships need to be further
understood.
Thus, there is a need to intensify the forest and soil conservation
programme and provide alternative income generation and energy sources for
those who depend upon the forest for both livelihood as well as to meet the
local energy requirement. The proper energy planning is essential.
Agricultural Land
The area around the Lake, not covered by
human settlements and forest, is under intense farming - mainly cashew in
dry land and paddy cultivation in wetland. Water from these farms, carrying
fertilizer and pesticide residues, drain straight into the
Lake. Moreover, the farming community, which is the most powerful
economically, socially and politically, has taken over by force the lands
around the Lake which have become dry due to the shrinkage of the Lake, and
is bringing them under agriculture or aquaculture. These farmers have also
taken to fishing, money lending (to fishermen) and fish marketing. This has
led, on the one hand, to conflict between the traditional and the
neo-fishing communities and, on the other hand, to the dependence of the
fishing community on the non-fishing communities making the latter more
powerful. This enables them to control the pricing of fish in their favour
which keeps the fishermen poorer.
It was mentioned that the farmers in the western area took to fishing
because of failure of crops due to flooding in the last ten consecutive
years. The fishermen who had generated some surplus capital invested in
farmland because of less catch of fish. The farmers were anxious to get back
to farming if flooding could be controlled and adequate measures are made to
ensure irrigation but the fishermen would like to continue with farming. The
more fishing and prawn culture has become commercialized, the more farmers
have entered the fish business.
Thus, farming practices, the socio-economic profile of the farming
communities and the dynamics of the relationship between the traditional
fishing and the "neo" fishing communities are important areas of inquiry.
Indepth socio-economic studies need to be undertaken.
The data regarding use of fertilizer and pesticide reflect that within a
decade the use of fertilizer for agriculture purpose has become nearly
double. Out of the NPK, the amount of nitrogen far exceeds the amount of
potassium and prosperous, accounting for more than 80% of total fertilizer
used. The run off into the lagoon during monsoon has undoubtedly enriching
the bottom detritus leading to faster growth of aquatic vegetation.
Birds
The migratory birds during winter attract tourist, "birdwatchers". Poaching
of the birds is encountered in few pockets. Here again, there is a linkage
between poverty and nature. Hence, poaching needs to be studied from a
socio-economic perspective and alternative employment potentials need to be
identified for the poachers. An aspect which needs to be noted is that the
fishermen are bird-lovers. The birds not only help them identify the
location of fish but also bird abundance is associated with greater fish
production and hence fish catch.
Chilika Lake is famous for the vast numbers of migratory waterfowl that
flock there every winter, and the lake is reputed to support the largest
concentration of migratory waterfowl in India (Scott, 1987; Ram et al.,
1994). In the 1960s, the lake annually supported millions of ducks and
thousands of geese in the winter months, butover the past two decades
populations have declined considerably, although the numbers are still
impressive (Scott, 1987). As with many reports about Chilika Lake, various
sources provide quite different views, and species lits and total numbers
vary considerably. Scott (1987) reports "over 150 species" and "no
comprehensive counts have been made". Dean and Saltink (1991) report of
500,000 – 700,000 migratory birds annually, consisting of over 150 species.
Bandyopadhyay and Gopal (1991) record about 150 species of which 97 are
migrants, and that in 1989-90, when conditions were particularly suitable,
about wo million migratory birds visited Chilika Lake. Ram et al. (1994)
report of over 160 species, of which "atleast 97 species are migratory", but
do not give total numbers, other than quoting Bahdyopadhyay and Gopal
(1991). The Asian Waterfowl Census (Parennou & Mundkur, 1994) reports that
in 1992, Chilika was comprehensively counted, and that there were
indications that the area "supports up to a million waterbirds", although
they recommend count augmented by aerial surveys. In all, they report a
total of 103 waterbird species at
Chilika.
The first migrants, usually Golden Plover Pluvialis fulva and Green
Sandpiper Tringa ochropus, arrive in September when Nalaban Island is
still submerged – they converge on the periphery of the Lake, near Balugaon.
Ducks usually arrive by late September or early October and Nalaban usually
surfaces by January (pers. Comm.Acharya, 1997). During the present survey,
Nalaban had just barely surfaced, and consisted mainly of one large mudflat,
with some ‘ridges’ with several decimeters elevation, and a few
semi-artificial hillocks. The latter were observed to be mainly used by
birds of prey and ibis.
Due to disturbances in areas in and around Chilika Lake, about 75% of all
waterfowl (pers. Comm. Acharya, 1997) tend to converge on Nalaban Island,
which has been gazetted as a bird sanctuary and forms a safe haven. This
high concentration of birds can be observed during the winter, as much of
the 1,500 hectare island. However, as there are no hides, observers could be
seen from afar, and most birds species tended to keep at least 200-400
meters away. Flamingo’s were even more wary, staying at least 600-800 meters
away from the observer.
In any case, it is obvious that Chilika Lake is of great importance to
migratory birds, and in addition to supporting large to very large numbers
of waterfowl, it also provides a refuge for certain rare and
endangered
species, such as the Spoon-billed Sandpiper Eurynorphynchus pygmaeus,
Asian Dowitcher Limnodromus semipalmatus and Goliath Heron Ardea
goliath. Birds of prey seen at Chilika include the Brahminy kite
Haliastur indus, the Pariah Kite Milvus migrans, Crested
Honey-buzzard Pernis ptilorhynchus, Black-shouldered Kite Elanus
caerulens, Sparrow-hawk Accipiter nisus, White-bellied Sea-eagle
Haliaeetus leucogaster, White-backed Volture Gyps bengalensis,
Pale Harrier Circus macrourus, Pied Harrier Circus melanoleucos
and Marsh Harrier Circus aeroginosus, but also rare species such
as Palla’s Fish-eagle Haliaeetus leucoryphus and Osprey Pandion
haliaetus.
Dolphins
The Irrawaddy Dolphin (Orcaella brevirostris), is a somewhat elusive
species, found in various large rivers, bays and estuaries in South and
Southeast Asia. It’s IUCN Red Data Book status (Groombridge, 1993) is
‘undetermined’, but suspected to be Rare, Vulnerable or Endangered and it is
listed in CITES Appendix II. Irrawaddy Dolophins are found in Chilika Lake,
but it’s status is somewhat uncertain as reports are conflicting. Ram et al
(1994) report that this species was once abundant in the Lagoon but today it
is endangered, although it can occasionally be seen near the Lake mouth.
Others, however, are more optimistic. Dean and Saaltink (1991), for
instance, report that 60-70 dolphin can regularly be seen in the channel
between Satapada and the Bay of Bengal, while Patnaik (Principal Chief
Conservator for Wildlife, MoEF Orissa State, pers. Comm.1997) report of a
total population of 157 dolphins. The MoEF Research Scholar based at Chilika
for 21/2 years, Ms Smita Acharya, reports that about
50-60 dolphins occur, mainly in the southern sector, which is the deepest
part of the Lake (Acharya, pers. Comm., 1997). Fishermen at the Lake inlet
confirmed that dolphins used to occur at the Lake mouth, but now were found
only in the deepest part of the Lake.
Irrawaddy Dolphin in Chilika Lake are likely to be affected by the various
recent changes in Chilika Lake, and their long-term survival appears
threatened. The three most important factors affecting the species are: the
apparent drastic decline in fish numbers (endangering their food supply,
siltation, and decline in water quality. Most abundantly the Dolphins are
spotted along the outer channel upto the Satapada. The detail ecology of the
animal is not yet studied.
Physical Characteristics and Issues
Geomorphic Features and Coastal Processes
Many of the current management issues within Chilika relate to its status as
a lagoon ecosystem. A general overview of lagoon ecology is provided by
Barnes (1980) who compared a large number of lagoon ecosystems around the
world. Lagoons are highly dynamic, ephemeral aquatic systems, which once
formed, persist for time periods of between hundreds and thousands
of years. The lagoon lifespan is believed to be positively correlated with
size. Thus large lagoons like Chilika may persist for considerably longer
than 1000 years. Barnes (1980) makes the point that lagoon biology can only
be understood within the framework of lagoon formation, evolution, and
subsequent decline.
Lagoons are usually formed when a portion of the sea is enclosed by offshore
or lognshore barriers. Sand is a common barrier material which can form into
a spit which extends across inlets or bays of the sea, thereby forming a
lagoon. Lagoons are shallow systems with maximum depths rarely in excell of
10m. Because of their shallowness, lagoons are ralatively easily converted
into swamps, marshes and ultimately land by plant colonisation and
encroachment (except in more saline lagoons). Many of these successional
trends are currently operating within Chilika Lake.
Chilika Lake is a classical tidal lagoon, created by a beach barrier berm
that developed by the accretion of coastal sediments following the
stabilization of sea levels some 3,000-4,000 years ago. It differs from some
lagoons because of the large influx of fresh water, particularly during the
mornsoon season, which gives the lagoon a brackish characteristics.
Geomorphic features are shown on Figure 2.1. The lagoon owes its existence
to three principle geomorphic features :
-
The weathered hills that anchor the southwestern limit of the lagoon;
-
The delta of the Mahanadi Riever to the northeast : and,
The barrier berm.
The weathered (denudational) hills are comprised of hard, metamorphic rocks,
that trend from the coast toward the northesast. Prior to the emergence of
the contemporary shoreline, it is likely that the seaward extremity of these
hills jutted into the bay of Bengal forming a promontory and a large
embayment on the leeside of the prevailing southwest monsoons. The rock
promontory was subsequently encaptured by sediments, leaving a cliff facing
the sea in an area presently referred to as the Palur Hills.
Although monsoon winds also blow from the northeast, wind and wave records,
together with the alignment of coastal features, indicated the prevailing
direction of winds, waves and sediment transport along the coast is from
south to north. Based on an analysis of ship-based wave observations, the
National Institute of Oceanography (NIO), estimated the net coastal sediment
transport is about 1.5 x 10 6 m 3 per year, with the majority of this
movement taking place in the months of March to October. A reversal in the
direction of transport occurs in the months of November to February (Chandramohan
et al, 1989).
This northerly sediment transport, which ranks as high as any location in
the world, delivered coastal sediments from the south, past the Palur Hills,
pushing them into the bay which was later to become the existing lagoon. It
is likely the coastal sediments would have initially been transported in a
more northerly direction than at present, following the alignment of the
rocky hills into the bay. The sediments formed barrier islands under the
combined interactive processes of wave refraction,, wind (aeolian)
transport, and emergence of the rocky hills. An sediments accreted, and the
barrier formations increased in size, the alignment of the barrier features
swung more to the northeast, seeking to be parallel to the incident
southerly waves.
Concurrently, the delta of the Mahanadi River prograded into the Bay of
Bengal distributing sediments to the coast via a classical "birds-foot"
delta, comprised of multiple distributary channels that nature uses to
discharge excessive sediments more efficiently to deep water. Two
distributary channels, the Daya and Bhargavi, presently discharge into
Chilika Lake.
Some of the sediments delivered to the coast by the Mahanadi River would
have been transported southward, eventually intermingling with the sediments
from the south, participating in the coastal processes, and forming barrier
berms and coastal dunes.
Fine sediments from the Mahanadi and other rivers may have laid down a layer
of silt and clay over which the existing fine to medium sized sands have
formed as the barrier spit. Vankatarathnam (1970) makes reference to
observing an exposed clay base north of the inlet following beach erosion
associated with the southeast monsoon season.
Sediments delivered to the lake thorought the Daya and Bhargavi Rivers,
after the coastal barrier was developed, infilled about 400 km 2 of the lake
leaving between 900 to 1,200 km2 of water surface area at present. Thw water
surface area at a particular time depends upon the prevailing water level.
Landsat imagery indicates the mouth of the Daya River was about 30 km north
of its present position following stabilization of sea levels (ORSAC pers,
comm.).
Attempts have been made to calculate the loss of water area since the turn
of the century. However, this data may be questionable because of the
sensitivity of the water area to the water level, and also, as pointed out
by Dean and Saaltink (1991), area has been lost to prawn culture operations.
Documentation reviewed, estimated the present rate of siltation in Chilika
Lake is 735,000m 3 annually, based on some underfined empirical formulae.
There are 42 point sources of sediment loading, 5 of which are larger rivers
or streams, The extent of flocculation occurring in the system is not known,
whereby clay material aggregates into largerr, more settleable, particles
upon contact with saline water. Data on the density of settled solids in the
lake bottom was not seen in documents reviewed.
The barrier berm, or spit, associated with Chilika Lake is about 60 km long
with an average width of 150 m. The southern portion is generally wider and
higher than the northern section where the inlet is presently located .
Backshore dunes are well developed along the southern half of the spit
reaching heights of 9 to 15 m above the beach in two or three parallel
series. Along the northern half there is generally just a single dune, which
is less developed toward the outlet.
The beach along the foreshore of the spit is comprised of fine to medium
sized sand, 0.25 to 0.5 mm diameter. The beach slope is variable depending
upon activity, tending to be steeper , at a slope of about IV (vertical): 6H
(horizonatal), during the period of June to October, and somewhat flatter,
IV: 8H to IV:12H, during November to February. The offshore slope, below low
tide, is IV:50H, or flatter.
Although not described in any documentation reviewed, the coastal dynamics
will be greatly affected by major cyclones in the area. Large waves, coupled
with a rise in the sea level sometimes exceeding 2 m, result in substantial
erosion of the beach profiles and overtopping of the spit at one or more
locations. Shifts in the location of the inlet would be associated with
major storms that breach the spit.
The inlet to a lagoon is a product of interaction between waves, currents
and sediments. O'Brien (1971) was the first to point that dynamic
equilibrium develops at inlets with the cross-sectional area of an inlet
being related to the tidal prism, or volume of water exchanged on a tidal
cycle. The tidal prism is approximately the product of the surface area of
the lagoon times the tide level fluctuation. The tidal prism, and the
cross-sectional area of the inlet, decrease with a reduction in lagoon
surface area. The tidal fluctuation in Chilika Lagoon is about 0.2 to 2.4 m.
Chilika Lagoon also receives the benefit of the Mahanadi River flows in
Keeping the tidal inlet open. The lagoon level increases by up to 2 m, by
one report, during the monsoon season.
Usually, the but not always, the location of an inlet migrates in the
direction of the shore transport of littoral sediments. Incident waves
generate longshore currents which convey sedimants. The sediments lengthen
the spit and encroach on the inlet channels. Sediments driven into the
channel are either carried inshore to form a bar, or channel shallows or are
swept offshore to a bar which acts as a sediment transport link between the
downcoast and upcoast sides of the inlet.
As the inlet migrates the channel connected to the inlet lengthens. This is
the case for Chilika Lake where the inlet is connected to the lake through a
25 km long channel. Quite ofter the inlet migrates to a point where flow
resistance in the channel is too great and hydraulic forces act to open a
new inlet with a shorter connecting channel, such that the process of
migration, and subsequent breaching, commence again. Alternatively, multiple
breaks can occur in the spit during a storm event, which will be closed
leaving a single inlet during more quiescent periods.
The location of the inlet to Chilika Lagoon exhibits the effect of the
prevailing northerly littoral sediment transport, and a large bar is located
offshore on the inlet mouth. Historical records show the inlet has been
located in the same general area, within about 10 km, since at least 1914.
Estimates of the location of the inlet relative to the village of Arhhakuda
are as follows :
1914 - 6 km NE
1965 - 8 km NE
1986 - 41/2 km NE
1991 - 51/2 km NE
The historical records indicate multiple inlets have opened, on occasion,
and siltaion had temporarily reduced the inlet cross-section.
Although not substantiated by historical records, the bathymeetry seaward of
the spit opposite Satapada, some 20 km south of the present inlet, would
indicate the inlet to the lake was located at this location for many years.
The 5 and 10 m depth contours show a concave outward fan, typical of a
subaqueous point source discharge of sediments, attached to a submarine
ridge extending north from the fan.
|