Chapter-3. Study Area

Transcription

1 Chapter-3 Study Area The study area is Gujarat coast, (including Daman and Diu UT) India and is located on the north-western coast of the Indian Peninsula (Figure 3.1). The Gujarat state lies between N to N latitudes and E to E longitudes. The state is bounded by the Arabian Sea in the West, Pakistan and Rajasthan in the North West, North and North East, Madhya Pradesh in the East and Maharashtra in the South and South East. The Tropic of Cancer passes through the Kachchh, Surendranagar and Ahmedabad districts. The State has an international boundary with the Pakistan at the North-Western fringe. The Gujarat coast extends from Western Ghats in Valsad to Kori creek on the coast of Kachchh in north. The area of continental shelf of the state is 1, 65,000 km 2 (SAC, 2012). Out of the three gulfs of the country, Gujarat has two gulfs namely Gulf of Kachchh and Gulf of Khambhat. The gulf provides the natural navigational and logical advantage to reach out to an enormous hinterland. The tidal range at Gulf of Khambhat is the largest along the Indian coastline and the second largest of the world after the Bay of Fundy. About % (28500 km 2 ) of the country s total tidal influence area is located in the Gujarat, which is the largest area among the maritime states of India (Garg et al, 1998). Gujarat produces 70 per cent of the country s salt production (Census of India, 2011). Mudflats, mangroves, marsh vegetation, coral reefs and saltpans cover a major part of the coastal wetland. Geo-morphological and climatic variation is very high on the Gujarat Coast. Rainfall varies from an average high of 2500 mm in the south to only 300 mm in Kachchh. Major sites of the ancient Indus Valley Civilization, such as Lothal and Dholavira are located in the Gujarat. Lothal is believed to be one of the world's first seaports. 34

2 Study Area Gujarat has the longest coastline among the maritime states of India where 12 districts (35 Talukas) have coastal border in varying lengths (MoEF&CC, 2009). Vulnerability mapping of Gujarat coast is very much essential because most of the human settlement and infrastructure/industries are located in close proximity to the coastline. About 549 villages with the total population of more than 30 million are situated along the Gujarat coast. The coastline of Gujarat is dotted with number of minor and major ports and industrial establishments and also is bestowed with fragile marine environments like coral reefs and mangroves. As huge infrastructure are located close to the coastline, even if only a small stretch of coastline is impacted due to predicted sea level rise, it can have a significant effect on the region. Environmental Parameters of Gujarat Coastline are summarised in Table Physiography of Gujarat Coastal Region The Gujarat coast provides a wide variety of coastal features due to varied physiography, geomorphology, coastal processes and river discharge into the sea. The Gujarat coast is broadly divided into five regions viz., the Rann of Kachchh, the Gulf of Kachchh, the Saurashtra Coast, the Gulf of Khambhat and the South Gujarat Coast, based on distinct variations in the wetland / landform categories (SAC, 1992). These variations are due to climate, substrate constituent and topography. The Rann of Kachchh is a unique region along the Gujarat coast comprising of the Great Rann and the Little Rann. It remains as saline desert for most of the year and inundated only during monsoons. The Great Rann and the Little Rann though separated from each other by the highland of Kachchh are interconnected. Most of the salt desert is occupied by the Great Rann. The deltaic plains are located along the northwestern side of Kachchh district and it is characterised by the tidal creeks (Kori creek), mangroves and tidal flats with or without salt encrustations. The shoreline of the Gulf of Kachchh has extensive mudflats and is highly intended with a number of cliffy, rocky islands and fringed by coral reefs at many places. Mangroves, algae, salt marsh, dunes and salt pans are dominant features along the Kachchh coastline.the main coastal features of the Saurashtra coast are numerous cliffs, tidal flats, estuaries, dunes, sandy beaches and bays. A row of dunes is present behind the cliffs near Mahuva, trending northeast southwest. Near Diu, sandy beaches, numerous spits, bars, bays, marshes and estuaries are prominent. Raised beach areas are located around Veraval and Porbandar (Sood et al. 1982).The ancient shorelines (strandlines) are mostly observed along the Saurashtra coast. The coast around the Gulf of 35

3 Chapter-3 Figure 3.1: Map showing the coastal zone of Gujarat. The Red line indicates the coastal segments under study. 36

4 Study Area Table 3.1: Environmental Parameters of Gujarat Coastline (Merh, 1995) Block Kachchh Saurashtra Mainland Gujarat Segment Jakhau-Kandla Jamnagar -Okha Dwarka-Diu Diu-Bhavnagar Cambay - Dahej Hansot-Umergaon Shoreline Indented Highly dissected Straight with Indented Indented Indented configuration small river mouth tidal flats Trend WNW-ESE to Almost E-W NW-SE NE-SW to NNW-SSE Almost N-S almost E-W almost N-S Shoreline Morphology Extensive mudflats on the W and E, narrow sandy beaches in S with small lagoonal tidal muds at river mouths Extensive mudflats with occasional beaches and coral reefs, offshore islands, rocky platforms with narrow beaches Continuous beach with projecting rock mounds, wave-cut platforms, occasional cliffs, backshore dunal ridge complex of calcareous sand and tidal creeks Mudflats, cliffs, rocky platforms, beaches with coastal submerged dune Vast mudflats backed by prominent alluvial cliffs, drowned river mouths and alluvial plains Drowned alluvial plain, mudflats and prominent estuarine river mouths marked by alluvial cliffs 37

5 with backshore Chapter-3 tidal flats Drainage Sluggish streams with Prominent towards Jamnagar, Fairly well developed, Sluggish streams with detritus load Active; detritus laden Active; detritus laden low detritus load sluggish streams, the higher orders of which show drowning lineament controlled, sluggish streams with poor detritus load Substrate Muddy soft Coralline Hard miliolitic, Hard miliolitic, Soft alluvial Soft alluvial, sandy (Tertiary rocks and alluvium) Trappean and Tertiaries; hard and uneven to soft uneven muddy and uneven, soft (Quaternary) rocks Gradient of Low Very low to low Low Very low (1 to 2 Negligible low ( 1 Low ( 1 to 2 m) littoral zone m) to 2 m) Nature of Silty and sand Thin veneer of Loose carbonate Terrigenous Silt Silt and sand littoral zone calcareous mud with occasional sand & clay sands over miliolite sandy shingle, mud rocks Width of the Variable Variable more Variable 400 to 1.5 to 2.5 km 4 to 6 km 4 to 6 km 38

6 littoral zone between 50 m and 2 km towards Jamnagar (5 to 10 km) decrease towards Okha 500 m 1200 m Study Area Energy conditions Moderate to high wave Low wave energy but fairly high High wave energy, strong Low wave energy with high Low wave energy with high tidal Moderate to high wave energy energy in the west and low in the Gulf tidal energy surf action tidal energy energy Tide Moderate to Moderate to high Very low (2 to 3 Moderate ( up to Very high ( up to High (8 to 9 m) high (3 to 8 m ) (3 to 5 m) m) 6 m) 10 m) Currents Shoreline currents Shoreline currents Long shore current Shoreline currents (tidal) Shoreline currents (tidal) Shoreline currents as well as long shore currents Climatic conditions Semi-arid, low rainfall Semi-arid, low rainfall Semi-arid, low rainfall Semi-arid, low rainfall Semi-arid, moderate rainfall Temperate moderate to high rainfall Salinity Saline to hyposaline Hyposaline Saline Saline to hyposaline Hyposaline Hyposaline to saline Turbidity Clear to turbid Turbid Clear Clear to turbid Turbid Turbid to clear 39

7 Chapter-3 Khambhat is indented by estuaries and consists of extensive mudflats, dunes, patch mangroves, salt marsh, saltpan and patches of sandy beaches. All these features are manifestation of high-tidal range in the Gulf. The South Gujarat coast is comparatively uniform and is broken by few indentations. The dominant coastal features of south Gujarat are series of estuaries, creeks, mudflats, beaches and marsh vegetation. Saurasthtra and Kachchh coast is characterised by predominantly ephemeral drainage. The perennial prominent rivers forming estuaries along the Gulf of Khambhat are the Shetrunji, Sabarmati, Mahi, Narmada, Tapi, Damanganga, Par, Purna, Aurunga, Ambica and Mindhola. 3.2 Climate The study area, being located on the tropic of cancer, falls in the sub-tropical climatic zone. A large portion of the state lies between 35 o C and 45 o C isotherms, the rainfall in the state is moderate. Sub-humid climate is observed in south Gujarat where as the moderately humid climate is observed in the central Gujarat (i.e. between Narmada and Sabarmati). The southern coastal regions of Saurashtra experience humid and sultry climate. Regions of central Gujarat, north of Ahmedabad and parts of central Saurashtra are in dry climatic condition. The arid and semi-arid types of climate are observed in north Gujarat and Kachchh. During March the temperature start rising till it reach the maximum, as high as 45 o C, in some parts of the state and January is the coldest month in the year in all parts of the state with maximum temperature never exceeding 30 o C and the minimum temperature remaining around 8 o C to 10 o C, occasionally dropping to as low as 4 o C. Gujarat receives much of its rainfall from the Southwest monsoon during the period between June and September and its maximum intensity being in the months of July and August. The southernmost portion (part of Valsad district) receive annual rainfall as high as 2500 mm. The rainfall gradually decreases northward and in the extreme northwest is as low as 300 mm. From the point of view of annual rainfall, the state is divisible into the following four major zones: 1) Rainfall above 1000 mm: (districts of Valsad, Dangs, Surat and the eastern parts of Bharuch). 2) Rainfall between 800 mm and 1000 mm: (districts of Vadodara, Panchmahals, Kheda and southern part of Ahmedabad). 3) Rainfall between 400 mm and 800 mm: (northern part of Ahmedabad district and whole Saurashtra). 40

8 Study Area 4) Rainfall less than 400 mm: (districts of Kachchh, Banaskantha and western part of Sabarkantha). The relative humidity in all parts of the state is low, though in the coastal areas it is moderately high. Winds are generally light to moderate, increasing in the intensity during the late summer and monsoon seasons. Coastal areas experience stronger winds. The winds blow from W or SW during the monsoon months and NE to NW from October to April (Merh, 1995). 3.3 Geology of Gujarat The geological environment of Gujarat is the result of complex interactions between tectonism and sea level changes during the Cenozoic (Chaymal et al., 2003). The basic framework was formed due to sequential fragmentation of the western continental margin of the Indian plate during the Late Mesozoic as it collided with the Eurasian plate in the north (Biswas, 1987). The breakup of the margin resulted in the formation of the Kachchh, Cambay and Narmada rift basins along the Delhi, Dharwar and Satpura trends (Biswas, 1987). Major part of the Tertiary sediments in these basins is of marine origin and Quaternary sedimentation has been largely fluvial (Merh, 1993). The Saurashtra peninsula remained as a foundered horst during this period (Biswas, 1982) and hence is devoid of Quaternary sedimentation except in its fringe areas. Figure 3.2 shows the geology of Gujarat Kachchh The Kachchh region exhibits four major geomorphic zones:the Ranns; the Banni plain; the Island Belt, and the Mainland (Chaymal et al. 2003). The Ranns of Kachchh form a flat, salt-encrusted terrain rising up to a maximum of 4 m above mean sea level. Within the Great Rann, a slightly uplifted area is present to the north of Allah bund, which is known as the Bet zone. The Ranns are submerged annually under a shallow layer of water during the monsoon. The Little Rann is a former extension of the Gulf of Kachchh. The plain of Banni is a low tableland reaching heights of 3 10 m above mean sea level (Merh, 1995). The Island Belt includes the Pachcham, Khadir, Bela and Chorar Islands comprising of Jurassic and Tertiary rocks. The Jurassic and Cretaceous rocks occupy half the area of Kachchh in the east-west direction, and are restricted to the northern and central parts of the peninsula, they are also exposed further north in the islands of the Rann of Kachchh, where mostly older 41

9 Chapter-3 parts of the Jurassic sequence are present. Tertiary rocks are located in the south west portion of the Kachchh (Kulkarni, 1985). The coastline has extensive mudflats in the east and welldeveloped beaches and backshore regions from Mandvi to Suthri. Further west, mudflats reappear with rocky cliffs abruptly rising above the mudflats. These are the Quaternary deposits Saurashtra The Saurashtra peninsula is marked by flat-topped ridges typical of trappean areas. The coastline of Saurashtra is highly varied and is characterised by the presence of a narrow belt of low ridges and cliffs of miliolite limestones and other shore deposits (Chaymal et al. 2003). The southern coast is marked by m vertical cliffs of these rocks. The northern coastal area has a gentle seaward slope with tidal flats dominating the landscape. The coastline of the Dwarka Okha area exhibits cliffs of Tertiary rocks up to m high. The coastline from Porbandar to Kodinar is straight and is noted for some of the best exposures of miliolite rocks. The coast is irregular and dissected further east up to Diu. Extensive tidal flats are observed to the northeast of Diu Island. The southern coast of this island is cliffy. Beyond Diu, the coast is characterised by a rocky foreshore with occasional beaches and miliolite cliffs. Locally extensive mudflats are seen near Jafrabad. Thirty to forty metres high miliolite cliffs and several sea stacks are the major features of the coast further east. The miliolites completely disappear near Bhavnagar and the Tertiary rocks extend right up to the coast (Merh, 1995). North of Bhavnagar to the mouth of the Sabarmati, the coast is muddy with several tidal channels Main land The alluvial zone shows a gentle slope towards the southwest. The geomorphology of the area to the south of the Narmada River is slightly different. A well-defined alluvial zone is absent. The width of the alluvial plain decreases to km to the south of Narmada River compared to its width of about 200 km to the north. Although the fluvial geomorphology is similar to the area north.the geomorphology around the various river valleys of Mainland Gujarat shows three distinct geomorphic surfaces: the alluvial plain and the ravine surface 42

10 Fig.3.2: Geological map of Gujarat. (Source: modified from Merh, 1995). 43

11 Chapter-3 comprising Late Pleistocene sediments; and the Mid-Late Holocene valley fill terrace (Chaymal et al. 2003). The Decan trap area is observed south of Umergaon. 3.4 Agriculture Agriculture and allied sector plays an important role in the State economy. The two thirds of the population are engaged in agricultural activities. Agriculture is main source of employment in rural areas and its tool of progress of villages all around ( Gujarat is India s largest producer of cotton, castor, cumin and isabgul. The state is the second largest producer of sesame and groundnut in the country. The productivity of mustard, castor, cotton, onion and potato is highest in the state compared to other states in India. The productivity of groundnut, bajra and banana is the second highest in India (Swain et al. 2012). The state is divided into 7 sub agro-climatic zones based on the characteristics of their agriculture and climate. Output of agricultural sector in Gujarat State has been largely dependent on south-west monsoon. The State frequently experiences erratic behavior of the south-west monsoon, which can partly be attributed to geographic situation of the State. The wide variation in rainfall received by different parts of the state has been the characteristic feature of monsoon (GoG, 2013). 3.5 Transport The coastal area of entire Gujarat coast is well connected by road and rail. All parts of the state of Gujarat are easily accessible rail, road and air as the state has ell developed communication and transport system. Broad and Metre-guage rail-lines of Western Railways criss-cross the entire Gujarat State. Broad-guage rail connects Saurashtra and Kachchh to Delhi, Bombay and other cities of the country. National Highways No.8 and 15 pass through the State. In addition, the region of Gujarat has good networks of State Highways and District roads. Most of the roads are very good and motorable all through the year. Gujarat State Road Transport Corporation (GSRTC) is the primary body responsible for providing the bus services within the state of Gujarat and also with the neighbouring states. It is a public 44

12 Study Area transport corporation providing bus services and public transit within Gujarat and to the other states in India. There are also city buses in cities like Ahmedabad (AMTS & Ahmedabad BRTS), Bhavnagar (VTCOS) Vadodara (VTCOS), Gandhinagar (VTCOS), Rajkot (VTCOS), Anand (VTCOS) etc. The total length of railway lines in the State as on 31st March-2011 was 5271 route km, comprising of 3382 km of Broad Gauge (BG), 1205 km of Meter Guage (MG) and 684 km of Narrow Guage (NG) lines. The total length of roads is (except Non-plan, Community, Urban and Project roads) km at the end of Out of the total road length of Km, the length of surfaced roads was Km (96.96 percent), where as unsurfaced roads was 2345 Km, (3.04 percent) (GoG, 2013). 3.6 Vital Coastal Resources Gujarat has the largest mangrove area cover among the western states of the country and is the second largest in the country after West Bengal, where the total mangrove area in Gujarat is 1058 km 2 (Forest Survey of India, 2011). The mangroves are observed mainly along Kori creeks, along the Gulf of Kachchh, Gulf of Khambhat and South Gujarat coastline. Mangroves play a very significant role in maintaining the coastal environment, reducing the impact of wave action and erosion in the coastal areas, and also providing protection to the coastline from the impact of cyclones. Apart from these ecological functions, mangroves play a very significant economic role in the lives of the coastal village communities. The villagers are dependent on mangroves mainly for fodder, fuel-wood and fishing activities. Coral reef of the Gujarat is one of the four major coral reef areas of India. High species diversity and very high rate of biological productivity make coral reefs very important and unique marine ecosystem. Apart from its significant role as carbon sink, they also provide habitat and food for fishes, crabs, prawns and other marine life. Major coral reefs in Gujarat are observed only along the Jamnagar coast of Gulf of Kachchh. Coral reefs in the Gulf of Kachchh are the northern most in the Indian Ocean, but they are geographically isolated. Many islands in the Gulf support fringing reefs. The entire southern coast of the Gulf of Kachchh in Jamnagar district is ringed by a cluster of 42 islands and many of them are fringed by coral reefs and bear mangrove vegetation. It is estimated that the coral reefs area of Gujarat is about 460 sq km (SAC, 2012). The seaweeds are largely observed along the Saurashtra 45

13 Chapter-3 coast. India s first Marine Sanctuary and National park was established in the Gulf of Kachchh, Jamnagar District in Gujarat. 3.7 Coast based Economic Activity India is the third largest salt producing country in the world after China and USA. Gujarat accounts largest, ie 70 % of the total salt produced in India. It is estimated that an average of 1.09 lacks labourers are employed in industry. In the state, salt is produced in Kachchh, Bhavnagar, Rajkot, Jamnagar, Anand, Bharuch etc. ( pdf/salt_in_guj.pdf). The world's largest ship breaking yard is in Gujarat near Bhavnagar at Alang. Reliance Petroleum operates the oil refinery at Jamnagar which is the world's largest oil refineries. India s only Liquid Chemical Port Terminal located at Dahej, Gujarat. Gujarat has two liquefied natural gas (LNG) terminals in the country (Dahej and Hazira) out of the three in the country. Two more LNG terminals are proposed, at Pipavav and Mundra in Gujarat. Currently, Gujarat has the highest number of ports in the country (i.e. 41) and these handle 20 per cent of India s cargo (WAPCOS Limited 2009). Gujarat has many tourist places along the coast such as Dwarka, Somnath, and Rann of Kachchh etc. Fish processing is also developed as an important industry. Gujarat is the second largest producer and exporter of processed fish in the country. Veraval, Porbandar and Mangrol have been developed as important fish processing centres ( 3.8 Sea Level Changes along the Gujarat Coast Hashimi et al studied the sea level fluctuations on the west coast of India and they reported that the sea retreat to about -120 m at 18 ka BP. As a consequence, the vast area of Gulfs of Khambhat, Kachchh and the Ranns were exposed to sub-aerial processes during this period of low sea level (Chamyal et al. 2003). The aeolian sediments suggest that the arid conditions in Mainland Gujarat prevailed up to at least 10 ka (Juyal et al. 2000). The sea level fluctuations which are indicated as strandline of the late quaternary period are very well recorded all along the Gujarat coastline. There are least two high strandlines (`+20 m and +6 to +10 m) related to early middle Pleistocene and Holocene transgression respectively and an intervening lower strandline (~ -20 to -30m) related to regression pointing to one of the still stands of late Pleistocene glaciations (Patel. 1991). Shoreline shift coupled with sea-level 46

14 Study Area change have always remained interesting aspects due to wider ramification for the populations living on the coast and there are different methods to understand and explain their causes and quantum (Gaur and Vora. 2007). Gaur and Vora had studied the shoreline and sea-level changes during the last 2000 years on the basis of archaeological evidence. They suggested that the following sequence of episodic sea level changes. I. Sea level was higher than the present one at around 6000 yrs BP and remained there until 3500 yrs BP. That time the whole Great and Little Rann was invaded by sea and connected with the Gulfs of Kachchh and Khambhat (Merh and Chamyal, 1993). The remnants of this sea are presented by the lakes of the Nal area (Merh and Patel, 1988). As a result of higher sea level, a large number of Harappan port towns in Gujarat and Pakistan are now located inland, far away from present- day shoreline and at a higher position than the present sea level (Gaur and Vora, 1999). II. Sea level continued at the present state from 3500 to 2300 yrs BP. Example, a wellknown early historical port town at Sopara, north of Mumbai (Ghate, S. 1988), was an active port and had international trade relations, is situated a little higher than the present high waterline III. After 2300 yrs BP, the sea level fell by 2 to 3 m. Example; Bet Dwarka coast is located below the present sea level. IV. Around medieval period (10th century AD), the sea level reached the present state when a number of ports came into existence along the Gujarat coast. Current status of sea level rise along the Gujarat coast is not well documented due to lack of data. According to Douglas et al. (2001), a record length greater than 60 years is desirable to determine trends in long-term sea-level changes. Unnikrishnan and Shankar (2007), reported that the inter-station consistencies among the tide gauge stations, situated along the Gujarat coast, are not significant and these tide gauge station data will not suitable for sea level rise analysis. They also reported that the Gujarat coast is facing tectonic activity so the stability of tide gauge station is questionable. 47