The vast and dream like Chilika Lagoon is situated on the east-coast of India. It is the largest brackish Water Lagoon with estuarine character that sprawls along the east coast. It is the largest wintering ground for migratory waterfowl found anywhere on the Indian sub-continent. It is one of the hotspot of biodiversity in the country, and some rare, vulnerable and endangered species listed in the IUCN Red List of threatened Animals inhabit in the lagoon for atleast part of their life cycle. The total number of fish species are reported to be 225 (Dean and Saaltink, 1991). Along with a variety of phytoplankton, algae and aquatic plants, the Lake region also supports over 350 species of non-aquatic plants (Panda and Pattnaik, 1988). By a recent phytodiversiy survey by CDA ( 2002) 710 number of plants identified from Chilika( within the waterbody, including the Islands and shoreline plants) . A survey of the fauna of Chilika carried out by the Zoological Survey of India in 1985-87 recorded over 800 species in and around the lagoon. This list includes a number of rare, threatened and endangered species, including the Barakudia limbless skink. On account of its rich bio-diversity, Chilika was designated as a "Ramsar Site", i.e. a wetland of International Importance. The Nalaban Island within the lagoon is notified as a Bird Sanctuary under Wildlife (Protection) Act, the National Wetlands, mangroves and coral reefs Committee of Ministry of Environment & Forests, Government of India, have also identified the lagoon as a priority site for conservation and management. The Lagoon is a highly productive ecosystem, with rich fishery resources. The rich fishing ground sustain the livelihood of more than 0.15 million fisherfolk who live in and around the Lagoon.
 

The waterspread area of Chilika varies between 1165 to 906 sq.km during the monsoon and summer respectively. A 32 km long, narrow, outer channel connects the main lagoon
 

to the Bay of Bengal, near the village Motto. The mouth connecting the channel to the sea is close to the north eastern end of the lagoon. High tides near this inlet mouth drive in salt water through the channel during the dry months, from December to June. With the onset of the rains, the 52 river and rivulets  falling into the Chilika are in spate, causing fresh water currents which gradually push the sea water out. Due to littoral drift prevailing along the east coast the inlet mouth constantly changes position.
 

The lagoon itself can be broadly divided into four natural sectors based on salinity and depth: the southern zone, central zone, northern zone and the outer channel. A number of islands are present in the lagoon with habitation and without the habitation, prominent among which are Krushnaprasad, Nalaban, Kalijai, Somolo, Honeymoon, Breakfast and Birds Island.
 

Chilika supports some of the largest congregation of migratory birds in the country, particularly during the winter. Flocks of migratory waterfowl arrive from as far as the Caspian Sea, Lake Baikal, Aral Sea, remote parts of Russia, Kirghiz steppes of Mongolia, Central and South East Asia, Ladakh and the Himalayas, to feed and breed in its fertile waters. In 1989-90 an estimated two million birds visited the Lake.Recently based on the survey by the BNHS ( 2002) 205 species of birds were listed from the lagoon.
 

Flora :- Phytoplankton flora – 43 sp, algal communities – 22 sp, Vascular plants 711 sp.

Fauna :- Fishes – 225 sp, Protozoa – 61 sp, Platyhelminthes- 29 sp, NematodesNematodes – 37 sp, Polychaetes –31 sp, Mollusca – 136 sp,–   Crustacea m- 28 sp., Decapoda – 30 sp., Amphibian & Reptile – 37 sp, Birds – 205 sp, and Mammals – 118 sp.

MORE  ABOUT CHILIKA

Location and Topography

Chilika Lagoon lies in the districts of Puri ,Khurda and Ganjam of Orissa State along the eastern coast of India. It is well connected to the Chennai and Kolkata through National Highway No 5, and the Chennai Kolkata  rail line passes along the western bankof the Lagoon Balugaon, with Balugaon, Chilika and Rambha being the main stations along the Western shoreline of the lagoon. Chilika lies about 50 km southwest of the city of Puri from where it is connected by road up to Satpara on the eastern bank.

Chilika is a shallow lagoon with estuarine character. It can be divided in to four ecological sectors i.e. the Northern, Cental, Southern and Outer Channel. The major part of the lagoon (the Nothern sector) has a depth of less than 50 cm, while the maximum depth of 3.7m is encountered in the central sector. The link between the lagoon and the outer channel (Muggermukh) was 20cm and was preventing the exchange of water between sea and the lagoon. The pear-shaped lagoon is about 64.5 km long and its width varies from 18 km to 5 km (Das and Samal 1988). The lagoon is connected to sea by a 32 km long, channel with several shoal restricting the flow and head loss . About 1.5 km wide, the channel runs parallel to the Bay of Bengal and is separated from it by a narrow spit whose width very between 100m to several kilometers. The channel opens to the sea near village Motto which is extremely narrow .Recently a new mouth was opened by CDA which is only 14 Kms away from the lagoon as per the recommendation of the CWPRS ,Pune.

The drainage basin of Chilika covers an area of over 4,300 sq. km (Das and Samal 1988), including about 1,100 sq. km of the lagoon itself.  
 

Watershed

52 number of rivers and rivulets drain into Chilika Lagoon. The details of the problem of siltation is sited in para 5.1. About 0.65 million cum of silt is pumped into the Lagoon by the above rivers and rivulets. It is essential to control siltation by appropriate catchment  treatment with an water-shed approach. As siltation is considered to be one of the most alarming factor for degradation of the Lagoon  ecosystem. Chilika Development Authority (CDA) sponsored a project titled “ Land Transformation studies in Catchment areas of Chilika Lagoon” to Orissa Remote Sensing Application Centre (ORSAC) to carry out a comprehensive action plan map to carry out the soil conservation measures based on the latest satellite imagery. The plan  prioritizes the areas which need to be treated on priority basis. The total western catchment area of Chilika  is 4,14,558.5 ha. which includes both forest and non-forest areas ( map- m-  ). Soil conservation measures covering most vulnerable and erosion prone area to an extent of 47,072.5 ha in the above catchment area need to be treated on a priority basis based on the action plan prepared by ORSAC. An integrated holistic approach is needed to address the problems faced by the Lagoon and it’s environs, involving the stake-holders as well as the state-holder Government Departments, NGOs, Village level institutions. The rational use of the natural resources in a holistic manner will solve this problem to a great extent. As observed from the land use and land transformation data that the degradation of the land is prevalent in the catchment area, resulting in decline in the productivity and accelerating the poverty and unsustainable pressure on the natural resources leading to further depletion the resource and decline in the productivity. The thrust of the present approach adopted by CDA is treatment of the catchment in a holistic manner on micro watershed basis in a participatory manner involving the watershed community and indigenous people  and to address not only the  the land, water, management but also focus on the appropriate management of the natural resources and its wise use.
 

Experience from the past has shown that watershed development projects often failed to achieve their objective because of inappropriate approach and inadequate management skills of the implementing agencies. Even in cases where progress has been satisfactory, development has not been sustainable in terms of operation and maintenance of assets created and the common property resources because of inadequate participation by the communities and user groups. The concept of participatory management of watershed is relatively a new concept for management of the watershed of Chilika. So to begin with, an innovative participatory micro watershed based approach was envisaged for management of the catchment of the lagoon. The participatory approach adopted is a deviation from the conventional approach of implementing rather than facilitating. Watershed rehabilitation is conceived as a resource-based approach, with an objective to livelihood enhancement. The micro watershed concept aims to establish an enabling environment for the integrated use regulation and sharing of water and land resources of the watershed based ecosystem to accomplish resource conservation, arrest soil erosion thus reduce the silt load in to the lagoon and enhance biomass production. The overwhelming evidence from natural resource management projects is that without people’s involvement the benefits are not sustainable in the long-term. In particular, the impact of watershed treatments has been impaired because of lack of co-ordination between line agencies. So the basic approach adopted in this project is to create an enabling environment, by capacity building at the community level through a series of training programmes to facilitate the integrated and holistic management of micro watersheds. The above preparatory process, facilitates the community to formulate the site specific micro-plan with a major input in form of their indigenous technical knowledge and skills, which is supplemented through learning from various training programmes organized under the aegis of the project, with an objective of empowerment and the capacity building of the community and the community based organisations at the grass root level.

Climate

The catchment of the lagoon enjoys a typically tropical climate with an average annual Maximum temperature 39.9 ⁰c, Minimum temperature of  14.00⁰c The lagoon which experiences South-west  and North-east monsoons during June to September and November to December respectively. During December and January cold wave conditions prevail for a couple of weeks due to Western disturbances in North India.  In the inland hilly tract, the climate is comparatively drier with higher temperature during the hot months and slightly cooler in winter. December to February is the winter season which is  followed by hot season from March to May. The period from June to September is the monsoon season while October and November months are the post monsoon transition months. The average rainfall in the catchment is 1238.8 mm with 72 rainy days. The rainfall generally decreases from northeast to southwest. The monsoon starts by about the second week of June and withdraws early in October. About 75% of the annual rainfall is received during the monsoon months from June to September. The Krushnaprasad Block receives the lowest rainfall of about 107.5 cm, the lowest in the State.

The wind speed is high during the month of March to July and speed is low during the winter season. The wind speed mostly from North and north easterly direction and during monsoon month it is mostly southerly and southwesterly direction due the influence of the South-west monsoon and the wind speed varies from  5.3  to  16.0(Km/Hour).

Hydrology

Hydrology is the single most dominant factor governing the ecological processes and functions of Chilika Lagoon. It has a large catchment area constituted by two river systems. The first is the deltaic drainage of the Mahanadi river system into the lake via rivers of more recent origin including Bhargavi, Daya, Nuna, Makra etc. which contributes the major part of the freshwater and silt input to the lagoon. The Mahanadi River trifurcates at Cuttack into three branches (Fig 4) :

• Northern Mahanadi branch, which flows to Paradwip and carries about 28% of flood flows. This branch is controlled by gates.

• Central Debi branch, which is the main distributary, carried about 60% of flood flows. This branch is a controlled byh gate.

• A southern Khukhai branch which breaks into three branches, the Kushbhadra, the Bhargavi and the Daya, the latter two flowing into Chilika Lagoon. The Khukhai branch takes about 12% of the flow during floods, and of this the Bhargavi and Daya take about 35% each. 

-            According to assessment made by CDA  (2000), the distributaries of Mahanadi accounted for about 61% (850 cum/sec) of the total fresh water inflow into the lagoon. During monsoon when high flood past over the Naraj weir, they fill the Kathjuri and Khukhai river thereby influencing the hydrology of Chilika. In the dry seasons, these branches are only fed by subsurface drainage, as the entrance to Khukhai is dry. The second drainage system is that of the older rivers which drains the Eastern Ghats. All these streams/ rivers are non – perennial and accounts for 39% (536 cum/sec) of the total fresh water inflow into the lagoon.   Kansari, Kusumi, Janjira and Tarimi are some of the important rivers of this drainage system.

All total there are 52 rivers/ steams flowing into the lagoon (Fig 5). The total surface freshwater from these rivers/ streams into the lagoon is estimated to 1,760 MCM annually. The direct precipitation, estimated at 870 MCM annually, on the lake surface also makes significant contribution to the freshwater input to the lake due to its relatively large size. The total evaporation loss from the lagoon surface estimated at 1,286 MCM annually by ORSAC (1988), is quite substantial.

Very little reliable data is available on the extent of erosion and sediment transport from the catchment and its deposition in the lake. No reliable estimates of sedimentation rate are available, although sediment yield is now being monitored on the major rivers and streams. About 30 – 40 years ago, the lake was 3 – 4 meters, and even as deep as 5 – 6 meters in some places, but now much of the lake’s depth masures a mere 1 – 1.5 meters (Das, 1997). There are four sources of silt: sand blown from the coast into the lake, silt carried from the sea by the tidal action, rivers from the Eastern Ghats and the Mahanadi distributaries. Out the four, the greatest source of silt is the Mahanadi distributaries, which in its lower course splits into a number of distributaries.

As per survey carried out by CDA (2000), during the monsoon 3,65,500 tonnes of sediment are discharged into the lagoon. While the distributaries of the Mahanadi contribute 75% (2,75,297 tonnes), the rivers/ streams from the western catchment are responsible for only 25% (90,203 tonnes) of the silt load in to the lagoon. It is apparent that the high sediment load contributed by the distributaries of Mahanadi are creating rapid sedimentation in the North western part of the lagoon and the inlet channel.

• A reduction in freshwater flow in the lagoon may lead to increase in salinity. The link between the freshwater input and the lagoon characteristics has not been examined, yet flow of Mahanadi river is controlled through some regulations by Hirakund Dam built in 1961 and weirs which have existed for many years. 

• Mahanadi river bifurcate at Cuttuck into three branches. A northern Mahanadi branch, which flows to Paradweep and carries about 28% of flow water. The central Devi branch, which is main distributory carries about 60% floods, flows. A southern Kuakhai branch, which breaks into three branches Kushbhadra, the Bhargavi and the Daya. The Kuakhai branch takes away 10% floods during floods and of this Bhargavi and Daya take about 35% each. 

• The total catchment in Mahanadi river to Cuttuck is 1.41 x  10⁵ sq km of which 0.83 x 10⁵ sq km is behind the Hirakund Dam. Hirakund dam impounds 14 % of Mahanadi River. 

• Lagoon water level is recorded by Irrigation Department since 1960s near Balugaon along with the sediment data.  8 gauging stations have been set up to collect data. 

• No reliable estimate of sedimentation rate, although the sediment yield is now being monitoring on the major streams. Theoretical estimates were suggested that 13 m t is deposited annually.

• The important factors that contribute to the soil erosion from catchment area are over grazing, illicit felling and ruthless cutting, cultivation and clearance of vegetation  for various purposes.  It is quite apparent that high sediment loads are contributing by tributaries on the west side and the Mahanadi tributaries for the major sources of rapid sedimentation in the lagoon which is creating increased floodings and flood damages in the Daya and Bhargavi rivers.

• Major flooding problems exist during monsoon in the Mahanadi delta on the north side of the lagoon where sediment has reduced size and depth of the channel. The Kanas block in particular has an extensive area, which remains water logged for 3 months of the year and flood damages, and health problems have increased over the years along with flood levels. Flood plain wetlands in this area, which could have reduced the sediment, load entering into the lake and retention of nutrients to reduce eutrophication in the lagoon. 

• The Department of Soil Conservation has been undertaking a programme to reduce soil erosion in the west catchment area of the lagoon. The Chilika catchment area (excluding Mahanadi drainage) is estimated at 3211 sq km of which 37% is arable, 32% fellow, 26% forests and 5% wasteland. 

• CWRPS, Pune and NIO, Goa, have undertaken some studies on numerical modeling and coastal processes. A physical model was built and tested by CWRPS in 1994. CWRPS prepared a physical model in 1974 with the main consideration of reclaiming land in Chilika lagoon for construction of fisheries harbour. The model used was a fixed bed, with horizontal and vertical scale of 1/1500 and 1/60 respectively. The model tested a cut through the spit near Satpada (123 m by 2 m deep).  With the result that the tidal range at Satpada increased from 0.2 – 0.6 m. Although not tested they predicted that salinity will increase in the lake as a result of the cut.  They computed a cross section area of the inlet of about 150 sq km would likely be maintained due to current flow with the depth of 0.8 – 1 m. this computation was likely based on O’Briens work.

• More recently CWRPS has carried out addition studies to know hydrodynamic of the lagoon. A numerical model was developed and partially tested to know the hydrodynamics of the lake. Salinity has not been tested. 

• NIO has collected data on wave characteristics, monthly beach profiles, monthly long-shore current, daily littoral environment observations and monthly beach sediment observations. Reports without conclusion have been submitted.

Siltation has lead to a gradual reduction in the size of the lagoon, and this process has particularly taken hold over the past few decades. Dean and Saaltink (1991; see Table 3), has reported that the lake may have shrunk by 10-15 % by 1990 during the dry season. Landsat imagery indicates the mouth of the Daya River was about 30 km north of its present position following stabilization of sea levels (ORSAC per. Comm.)

Although monsoon winds blow from the northeast, wind and wave records together with the alignment of coastal features, indicate 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 10⁶ m³ 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.

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. As sediments accreted, and the barrier formations increased in size, the alignment of the barrier features swung more to the northeasterly alignment, seeking to be parallel to the incident southerly waves.

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.

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 surfacr area of the lagoon times the tide level fluctuation. The tidal prism, and the cross-sectional area of the inlet, decreases with a reduction in lagoon surface area. The tidal fluctuation in Chilika Lagoon is about 0.2 m, during non-monsoon periods, driven by a tide in the Bay of Bengal ranging from 0.9 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, but not always, the location of an inlet migrates in the direction of the longshore transport of littoral sediments. Incident waves generate longshore currents which convey sediments. 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 act 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 Lagoon where the inlet is connected to the lake through a 25 km long channel. Quite often 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, commences again. Or alternatively, multiple breaks occur in the spit during a storm event, only to 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 1914. Estimates of the location of the inlet relative to the village of Arhhakuda are as follows:

Salinity

Chilika undergoes a cyclical variation in salinity throughout the year, with different patterns seen in separate sectors.Thus a salinity gradient is maintained. This cycle is worth understanding in some detail, as it is extremely important for the biodiversity of the lagoon. It is this periodicity in salinity that allows freshwater as well as marine and estuarine species to thrive in the lagoon.

Salinity is measured in parts per thousand(ppt) and 10 ppt is equal to 1 per cent by weight. Thus a salinity of 10 ppt implies one gram of salt for every hundred grams of water. During the monsoon, the Northern and Central sectors show low salinity (1.8-2.0 ppt) as does the outer channel (3.5 ppt). In the Southern sector, salinity remains higher (6-10 ppt) as the freshwater input is much lower in this part of the lagoon and the sea water influx take place during the high tide through the Palur canal.

Evaporation causes a slight increse in salinity in the Northern sector (1.8-4.5 ppt) and the Central sector  during the post-monsoon period (October to December). The Southern sector shows a slight decrese in salinity (7-8 ppt ) due to slow mixing with the rest of the lagoon (Ramanadhan et al. 1964; Banerjee and Roychudhuri 1966). The outer channel shows remain almost fresh water during the monsoon due to the unidirectional flow of  freshwater from the lagoon.
 

During winter (November-March), the freshwater flow in to the lagoon is almost nil. Northerly winds fascilitate the  tidal water enter in the lagoon through  the outer channel, increasing the salinity. The salinity gradually rise in all the sector , ranging from 2-6 ppt (Northern sector), 8-13 ppt (Central sector) and 9-11 ppt (Southern sector) and in the  outer channel the rise in the salinity level is rather high and reaches almost sea level. During the summer, evaporation and prevailing southern winds cause greater salinity all over the lagoon. The Northern and Central sectors turn mesohaline (medium range of salinity), with salinity ranging from 5.5- 22 ppt and 7.5-27ppt, respectively. The Southern sector shows a slight increse (10-11 ppt) (Ramanadhan et al. 1964; Banerjee and Roychudhuri 1966). The outer channel is practically like seawater at this point, with salinity at 34-35 ppt (Mohanty 1975a)

Due to increased silt load, narrowing of the lagoon mouth and other factors, the overall average salinity for the whole lake was observed to have  dropped from 22.31 ppt in 1957-58 to 13.2 ppt in 1960-61 and  9.14-11.83 ppt in 1961-64, but appears to have stabilized after the rapid drop (Sarkar 1977). Such a decrease in salinity had a great adverse  impact on the  biodiversity as well as fisheries of Chilika.
 

Water and Sediment Quality
 

Limnological investigation including physico-chemical characteristics of water of Chilika Lagoon is regularly monitored by Chilika Development Authority in collaboration with Wetlands International. Several other organization including Orissa Remote Sensing Application Centre (ORSAC), Central Inland Fisheries Research Institute, Zoological Survey of India, other research institutes and universities located around Chilika Lagoon have collected information on water quality parameters.

The analyses of the data indicated that in general, lagoon water is alkaline with pH ranging from 7.1 – 9.6. Total alkalinity follows closely the salinity, the highest alkalinity value prevails in the southern part of the lagoon near Rambha. The bathymetry study of the lagoon carried out by ORSAC (1987), indicates extreme shallow depth profile particularly in the northern sector where a large percentage of the area is less than 1.5 m depth. The maximum depth of 3.9 m is found in the southern sector. The transparency values (9 – 155 cm) indicate high turbidity due to strong mixing of overlying water with sediments. Isothermal condition prevails throughout the lagoon water column. Water temperature follows closely the mean air temperature.

The salinity concentration levels show remarkable variations, both temporally and spatially. A complex combination of freshwater discharge, evaporation, wind condition and tidal inflow of seawater govern the seasonal changes in salinity levels. Salinity concentration in Chilika vary along the north – south gradient. Due to shallow depth of the lagoon the salinity concentration fluctuates between 1 – 3 ppt between the surface and bottom. The lagoon is brackish over most of its area nad varies from fresh water (0 ppt) adjacent to the Daya river mouth to hyper – saline level (42 ppt) in the outlet channel during the dry period (ORSAC,1990).

Based on salinity, the lagoon is broadly divided into 4 zones: the southern zone, central zone, northern and the outer channel. During monsoon a large volume of freshwater enters in the northern and central zones and passes through the outer channel into the Bay of Bengal. These three sectors contain freshwater and the current is strong enough to overcome tidal influx of seawater. The southern sector remains relatively undisturbed because water renewal is much slower, and hence brackish water condition prevails in this zone even during monsoon. However, during post monsoon period and in winter the northern winds help mixing of water in the southern sector with rest of the lagoon, thus decreasing salinity in the southern sector. The northerly winds also cause intrusion of seawater into the outer channel. In the summer water level of Chilika lagoon reaches its lowest level and hence intrusion of salt water from outer channel into the lagoon increases. Wind induced mixing by the predominantly the southern winds causes a general increase in salinity of the central and northern sectors. However, the salinity in the southern sector does not rise appreciably.

Higher concentration levels of phosphate phosphorus (0-0.4 ppm) and nitrate nitrogen (10-60 ppm) and silicates (1-8 ppm) have been recorded in the north and north-west part of the lagoon where most of the rivers discharge into the lagoon bringing huge amounts of silt and nutrients. The dissolved oxygen values have been recorded between 3.3-18.9 mg/l.