http://www.academia.edu/4378845/Chilika_Lake_-_Environmental_Impact_of_Dredging_and_New_Mouth_Opening

ENVIRONMENTAL IMPACT OF DREDGING OF OUTER CHANNEL AND CREATION OF A NEW MOUTH OPENING TO CHILIKA LAKE WITH THE BAY OF BENGAL, ODISHA, INDIA

R. Jagadiswara Rao, M.Sc., Ph.D.

Professor of Geology Retired, Sri Venkateswara University, Tirupati, Andhra Pradesh, India Email: rjagadiswara@gmail.com

Mobile: +91-944-018-4012

Chilika Lake (or Chilka Lake) (19°28’ and 19°54’ N latitude and 85°05’ and 85°38’ E longitude) is the largest lake (or lagoon) on India’s east coast spread over the districts of Puri, Khurda and Ganjam in Odisha (or Orissa), India. Formed a few thousand years ago, the lake used to receive fresh water from inland rivers and saline water from the Bay of Bengal in varying amounts to result in a wide range of fresh, brackish and saline water environments supporting an exceptionally productive ecosystem. The lake is pear-shaped with a maximum linear axis of 64.3 km parallel to the coast and a mean width of 20.1 km, a storage volume of 4 cu km, and water-spread area ranging from 1165 sq km in monsoon to 906 sq km in summer. Land reclamation for agriculture, aquaculture and human settlements, along with sediment inflow from the catchment, has reduced the average lake area to 760 sq km. The Daya, Bhargavi, Malaguni, Makra, Nuna and other distributaries of Mahanadi River with a drainage area of around 4300 sq km discharge at around 800 cu m/sec of fresh water and deposit around 1.5 million tonnes/year of sediment. The rivers joining the lake from the west discharge at around 536 cu m/sec of fresh water and deposit 0.3 million tonnes/year of sediment (www.chilika.com, http://en.wikipedia.org/wiki/Chilika_Lake & Ghosh and Pattnaik, 2005). A map of Chilika Lake prepared by the Remote Sensing & GIS Division, Chilika Development Authority (CDA), Bhubaneswar is shown in Figure 1. In conformity with the Survey of India maps, this map must have also been prepared using the Indian Geodetic Datum (i.e., Everest Spheroid of 1880 revised last in 1956). The Bay of Bengal, the largest bay in the world, is connected with Indian Ocean and surrounded by India, Bangladesh, Myanmar, Thailand, Indonesia, Malaysia and Sri Lanka and has long, gently sloping shelves with shallow water depths. It has a maximum length of 2090 km, maximum width of 1610 km, surface area of over 2.17 million sq km, maximum depth of 4694 m and average depth of 2600 m. The sea currents flow towards north in a clockwise circulation pattern known as "East Indian Current" from January to August bringing depressions, which rarely turn out as severe storm surges, contributing significant rains during the South West monsoon. In the remainder of the year, the flows are towards southwest in a counter-clockwise pattern known as “East Indian Winter Jet” bringing occasional severe cyclones and storm surges bringing cloudburst rains and flash floods during the North East monsoon. The long shore sediment transport (littoral drift) along the sea coast is estimated at 0.1 million tonnes annually, which has been shifting the lagoon mouth opening to the sea in a northeast direction. The lagoon mouth opening was near the village Arakhakuda in the year 2000. This shifting of the mouth opening has led to the development of a 32-km long barrier island with a width ranging from 100 to 1500 m bordered by the Bay of Bengal towards east and the narrow outer channel of Chilika Lake towards west. The work of Stone and McBride (1998) has indicated that barrier islands play a profound influence in protecting wetlands bordering the coast from the fury of storm surges and tsunamis. For example, the effect of the 1999 Odisha cyclone that hit the coast on 29 Oct 2013 – the first cyclone in India for which the Indian Meteorological Department (IMD) gave the meteorological label “super cyclonic storm” causing deaths of over 15,000 people and damages worth US$ 4.5 billion dollars appears to be quite low in the Chilika Lake region compared to the surrounding areas.

Figure 1: A map of Chilika Lake prepared by Remote Sensing & GIS Division, Chilika Development Authority (CDA), Bhubaneswar showing the northern, central and southern sectors and outer channel of the lake, communications, the northern Mahanadi catchment and its distributaries and the minor rivers from the west joining the lake, the 32-km long barrier island bordering the lake and the location of old mouth towards northeast and new Mouth towards southwest near Satapada opened by CDA on 23 Sep 2000 (both closed).

Chilika Lake remains a vital lifeline providing sustained livelihood for around 200 thousand fishermen and other people living in 141 villages bordering the lake and in several islands including Badakuda, Honeymoon, Kalijai Hill, Kanthapantha, Krushnaprasadrah (Old Parikuda), Nalabana, Nuapara and Sanakuda within the lake. The lake shelters a number of endangered species and wintering ground for more than a million migratory birds. This was the first wetland in India to be declared as a Ramsar site way back in 1981. The surface and underground runoff and sediment load entering into Chilika Lake are so large that the lake and the outer channel became shallow in course of time. The flow of seawater entering into the lake got so much reduced owing to a choked mouth that a good portion of the lake got transformed into a fresh water ecosystem with a remarkable decline in the over-all biodiversity, steep decline in fish production, and steep decline in the income obtained by the local people. This has prompted the Ramsar Bureau placing Chilika Lake under the Montreux degraded list in 1993. Concerned with the degradation of the lake, the Government of Odisha created Chilika Development Authority (CDA) in 1992 for the restoration and overall development of the lake. A credible management plan formulated by the CDA enabled to receive a grant of Rs. 270 million from a “special problem grant” from the Central Government under the 10th Finance Commission (1996-2000) and Rs. 300 million under the 11th Finance Commission (2001-2004). Based on the recommendations of Central Water and Power Research Station (CWPRS) of Pune, National Institute of Oceanography (NIO) of Goa, and Ocean Engineering Centre, Indian Institute of Technology (IIT), Chennai, and extensive consultations with the stakeholders, 58% of the grants was utilised towards improvement of water exchange and salinity gradient by dredging the outer channel based on certain mathematical and bathymetric data besides opening a new mouth near the village Satapada at a distance of about 18 km southwest of the old mouth on 23 Sep 2000 to enable seawater to enter into the lake by a shorter route. In addition, certain developmental works have been taken up in Chilka Lake with the funds made available under Orissa Water Resources Consolidation Project (OWRCP). The environmental impact assessment and monitoring by the NIO and the CDA indicated that there has been a marked improvement in the overall biodiversity with the lake retaining the original bathymetry and the original water salinity distribution, which in turn enhanced both fish production and income of the local people. This led the CDA to receive the Ramsar Wetland Conservation Award on 18 Nov 2002 and the Indira Gandhi Paryavaran Puraskar in the same year for outstanding achievements in the field of restoration, conservation and wise use of Chilika Lake through active community participation. The visit of SG Ananda Tiega to Chilika Lake from 19 to 22 Oct 2012 marks the first ever visit of a Secretary-General Ramsar Convention to India (www.ramsar.org/pdf/SG-Visit_Chilika-Lake.pdfv). Satisfied with the sustainable ecological restoration of Chilika Lake and sustainable high income levels of the communities depending on the lake, the CDA appears to have neglected the new mouth opened on 23 Sep 2000. The present study is aimed at a study of the barrier island bordering the outer channel of the lake together with the condition of its old and new mouth openings besides naturally-formed new mouths through a study of all the high-resolution Google Earth images available in the public domain. The Google Earth gets satellite images from a number of sources. On merging with GeoEye in early 2013, DigitalGlobe became the only commercial provider of high resolution satellite images of as high as 0.5 m to the Google Earth with TerraMetrics and Cnes/SPOT images providing lower-resolution satellite imagery for some regions. In addition, the Google Earth obtains Digital Elevation Models (DEMs) data of the NASA Shuttle Radar Topographic Mission (SRTM) with a resolution of around 90 m and a vertical error of around 16 m; and satellite data processed for preparing composite images by agencies such as Scripps Institution of Oceanography (SIO), National Oceanic and Atmospheric Administration (NOAA),

U.S. Navy, National Geospatial Intelligence Agency (NGA) and General Bathymetric Chart of the Oceans (GEBCO). The combination of satellites’ high-resolution map-accurate imagery, Google's search-and-display capabilities and Google Earth’s unique software solution uniting traditional satellite imagery, digital aerial photography and GIS resources allows users to have access to rich, interactive visual image maps of various parts of the Earth in very low to very high magnifications. Unlike the Survey of India maps and the satellite images captured by the Indian Space Research Organisation (ISRO) using the Indian Geodetic Datum (i.e., Everest Spheroid of 1880 revised last in 1956), the Google Earth images make use of the globally-used WGS 84 Datum revised last in 2004. The Google Earth satellite images captured in the present study are dated 4 May 2005, 8 Aug 2007, 1 Jun 2009, 10 Nov 2011, 18 Oct 2012 and 28 Apr 2013 (Figures 2-6). Figure 2 shows a Google Earth composite image captured on 4 May 2005 and 8 Aug 2007 showing both the old and new mouths, while Figures 3-6 show only the new mouth. It may be noted that the width of a mouth opening as seen in a satellite image shows high variation including its total absence depending on the capture time in relation to the prevailing tide conditions. For example, a satellite image may not show any mouth at all at a place where a field study reveals its existence. Mouths thus can be broadly classified into those that are visible at all times and those that are visible only at high tide but not at low tide. In the absence of the exact location details of the old and new mouths of Chilika Lake, their approximate location could only be shown in the Google Earth images studied. It is surprising to note that both the old and new mouths of Chilika Lake remain in a closed condition in all the Google Earth images studied. If they are seen now in the field, it must be then because of all the Google Earth images studied were captured during the low tide only. In the images captured on 4 May 2005 (Figures 2 and 6), the only mouth seen is located at a distance of 6.7 km northeast of the new mouth at an elevation of 14 m. The barrier island bordering the outer channel of Chilika Lake was having fairly good width and supporting good mangrove vegetation. In the images captured in the subsequent dates, there has been drastic reduction in the width and mangrove cover of the barrier island because of the disturbances caused to the barrier island by the closure and opening of old and new mouths with increased overall width of the mouths over time. The loss of mangrove cover is because of natural causes but not due to deforestation by human intervention. In the image captured on 31 May 2009 (Figure 3), there were two mouths separated by a distance of 1.1 km with the northeast mouth located at an elevation of 7 m at a distance of 7.8 km northeast of the mouth opened on 23 Sep 2000. In the image captured on 9 Nov 2011 (Figure 4), there were again two mouths separated by a distance of 0.7 km with the northeast mouth located at an elevation of 2 m at a distance of 8.4 km northeast of the mouth opened on 23 Sep 2000. In the composite image captured on 14 Oct 2012 and 28 Apr 2013 (Figure 5), there were three mouths separated by a maximum distance of 2.6 km with the northeast mouth located at an elevation of 1 m at a distance of 10.6 km northeast of the mouth opened on 23 Sep 2000. In the modified image captured on 4 May 2005 (Figure 6), the mouths seen on 4 May 2005, 31 May 2009, 14 Oct 2012 and 28 Apr 2013 are all shown. The distance between the extreme northeast and the extreme southwest mouths is 3.8 km. The image clearly shows that some naturally-formed mouths in recent years lie in the outer channel of the lake existing on 4 May 2005, indicating that a portion of the lake has already become sea.

Figure 2: A Google Earth composite image prepared using the satellite images of the National Aeronautical Space Agency (NASA) and DigitalGlobe with the western part captured on 4 May 2005 and the eastern part on 8 Aug 2007 showing the locations of both the old and new mouths (now closed) separated by a distance of 18 km. The naturally-formed new mouth on 4 May 2005 is at a distance of 6.5 km due northeast of the mouth opened on 23 Sep 2000.

Figure 3: A Google Earth image captured by the DigitalGlobe satellite captured on 1 Jun 2009 showing two new mouths separated by a distance of 1.1 km with the northeast mouth located at a height of 6 m at distance of 7.8 km northeast of the mouth opened on 23 Sep 2000.

Figure 4: A Google Earth image captured by the DigitalGlobe satellite captured on 10 Nov 2011 showing two naturally-formed new mouths separated by a distance of 0.7 km with the northeast mouth located at a height of 10 m at a distance of 8.4 km from the mouth opened on 23 Sep 2000. A major portion of the barrier island shows sand devoid of any mangrove vegetation.

Figure 5: A Google Earth image captured by the DigitalGlobe satellite with the western part captured on 28 Apr 2013 and the eastern part on 18 Oct 2012 showing the location of three naturally-formed new mouths separated by a distance of 2.6 km with northeast mouth located at sea level at a distance of 10.6 km from the mouth opened on 23 Sep 2000. A major portion of the barrier island shows sand devoid of any mangrove vegetation.

Figure 6: A Google Earth image captured by a DigitalGlobe satellite captured on 4 May 2005 showing the location of all the naturally-formed mouths as on 4 May 2005, 1 Jun 2009, 10 Nov 2011 and 18 Oct 2012. They are separated by a maximum distance of 3.8 km. The image clearly shows that some naturally-formed mouths formed after 4 May 2005 lie farther into the outer lagoon, indicating that a portion of the lake has already become sea.

Conclusion The 32-km long barrier island that separates the outer channel of Chilika Lake from the sea is progressively getting degraded owing to gradual closure and opening of mouths since the opening of a new mouth by the CDA on 23 Sep 2000. The only consolation is that there is increased access of Chilika Lake to the Bay of Bengal for easy entry of seawater into the lake to maintain brackish salinity necessary for maintaining biodiversity. A 4-km stretch of the barrier island has already become barren of vegetation with the number of naturally-formed mouths increasing from one to three, heights of mouths reduced, and the cumulative width of the mouths developed getting gradually increased. In the absence of scientific intervention by the CDA, there is danger of the entire barrier island getting destroyed with the outer channel of the Chilika Lake becoming part of the Bay of Bengal. Acknowledgement The author is grateful to Mr. N.V. Sivarama Prasad, Divisional Forest Officer, Wild Life Management Division, A.P. Forest Department, Sullurpet, Andhra Pradesh for involving him in carrying out scientific investigations on the feasibility for ecological restoration of the Pulicat Bird Sanctuary through opening of mouths of the lake with the Bay of Bengal.

REFERENCES Ghosh, A.K. and Pattnaik, A.K., 2005. Chilika Lagoon – Experience and Lessons Learned Brief: http://iwlearn.net/iw-projects/1665/experience-notes-and-lessons-learned/chilikalagoon_2005.pdf/view Stone, G.W., and McBride, R.A., 1998. Louisiana barrier islands and their importance in wetland protection: forecasting shoreline change and subsequent response of wave climate: Journal of Coastal Research, v. 14, p. 900–915. http://www.jstor.org/discover/10.2307/4298843?uid=3737496&uid=2129&uid=2&uid=70&uid=4&sid=21102602459083