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Marine Environmental Impact Assessment for Re-routing the 42 Sour Gas Pipeline Segment of ONGC in the Nearshore and Intertidal Areas of Umbhrat, Navsari District SPONSORED BY OIL AND NATURAL GAS COMMISSION, JANUARY 2015

Marine Environmental Impact Assessment for Re-routing the 42 Sour Gas Pipeline Segment of ONGC in the Nearshore and Intertidal Areas of Umbhrat, Navsari District Project Leader M.A.Rokade

Associate Project Leaders V.S.Naidu Sabyasachi Sautya B. R. Thorat

JANUARY 2015

CONTENTS

Project team i Executive summary ii List of tables xxi List of figures xxiii List of plates xxiv Common abbreviation xxv 1 INTRODUCTION 1 1.1 Background 1 1.2 Objectives 1 1.3 Scope of work 1 1.3.1 Evolve prevailing marine environment off Umbhrat as follows 2 1.3.2 Assessment 2 1.4 Approach strategy 2 1.5 Studies undertaken 3 1.5.1 Sampling locations 3 1.5.2 Sampling frequency 4 1.5.3 Physical processes 4 1.5.4 Water quality 4 1.5.5 Sediment quality 5 1.5.6 Flora and fauna 6 2 PROJECT DESCRIPTION 8 2.1 Present activity 8 2.1.1 Pipeline 8 2.1.2 Purpose for re-routing the pipeline and EIA 8 2.13 Cargo: sour gas 9 2.2 Proposed activity 9 2.2.1 Installation of new pipeline 9 2.2.2 Submarine pipeline segment 10 2.2.3 De-commissioning of redundant pipeline 11 3 STUDY AREA 12 3.1 Tapi estuary 12 3.2 Mindhola Estuary 14 3.3 Umbhrat coast 15 4 PREVAILING MARINE ENVIRONMENT 16 4.1 Bathymetry 16 4.2 Physical processes 16 4.2.1 Tides 16 4.2.2 Currents and circulation 16 4.3 Water quality 17

4.3.1 Temperature 17 4.3.2 pH 18 4.3.3 Suspended Solids (SS) 20 4.3.4 Salinity 21 4.3.5 DO and BOD 23 4.3.6 Phosphorus and nitrogen compounds 24 4.3.7 PHc 29 4.3.8 Phenols 31 4.4 Sediment quality 32 4.4.1 Texture 32 4.4.2 Metals 32 4.4.4 Phosphorus 35 4.4.5 Petroleum Hydrocarbons (PHc) 36 4.5 Biological characteristics 36 4.5.1 Mangroves 37 4.5.2 Bacteria 39 4.5.3 Phytoplankton 40 4.5.4 Zooplankton 45 4.5.5 Macrobenthos 48 4.5.6 Fishery 52 4.5.7 Corals 54 4.5.8 Birds 54 4.5.9 Reptiles and Mammals 54 4.5.10 Sand dunes 54 5 POTENTIAL ENVIRONMENTAL IMPACTS 55 5.1 Construction phase 55 5.1.1 Physical process 55 5.1.2 Water quality 55 5.1.3 Sediment quality 56 5.1.4 Flora and fauna 56 5.2 Operational phase 57 5.2.1 Leak quantities 57 5.2.2 Fate of gas leak 58 5.2.3 Probable movement of leaked gas 58 5.2.4 Impact on water quality 58 5.2.5 Impact on sediment quality 58 5.2.6 Impact on flora and fauna 59 6 MITIGATION MEASURES 60 6.1 Design considerations 60 6.2 Construction phase 60 6.3 Operational phase 61 6.4 Potential marine environmental impacts 62 6.4.1 Construction phase 62 6.4.2 Operational phase 63

6.5 Mitigation measures 63 6.5.1 Design considerations 63 6.5.2 Construction phase 63 6.5.3 Operational phase 64 6.6 Implications CRZ Notification 64 7 SUMMARY AND CONCLUSIONS 65 7.1 Background 65 7.2 Project description 66 7.3 Study area 67 7.4 Prevailing marine environment 67 7.5 Potential environmental impacts 69 7.6 Construction phase 69 7.6.1 Physical processes 69 7.6.2 Water quality 69 7.6.3 Sediment quality 70 7.6.4 Flora and fauna 70 7.7 Operational phase 71 7.7.1 Leak quantities 72 7.7.2 Probable movement of a leakage 72 7.7.3 Impact on water quality 72 7.7.4 Impact on sediment quality 72 7.7.5 Impact on flora and fauna 73 7.8 Mitigation measures 73 7.8.1 Design considerations 73 7.9 Construction phase 73 7.10 Operational phase 75 7.11 Potential marine environmental impacts 75 7.11.1 Construction phase 76 7.11.2 Operational phase 76 7.12 Mitigation measures 77 7.12.1 Design considerations 77 7.12.2 Construction phase 77 7.12.3 Operational phase 77 7.13 Implications CRZ Notification 78 8 RECOMMENDATIONS 79

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PROJECT TEAM M.A Rokade V.S.Naidu Sabyasachi Sautya B.R.Thorat S.N Gajbhiye Soniya Sukumaran Anirudh Ram S Jaiswar Rakesh P.S Abhay S Fulke D.S Bagde Mohammed Ilyas Jairam Oza Tejal Vijapure Suman Ghadigaonkar Nageshwar Rao Aditya Patwardhan Ajay Yadav Divya Majithiya Shailesh Salvi Vaibhav Joshilkar Archana Kamble Parul Chemburkar Gaurav Gavade Dipali Kanekar Edna Desouza Kiran M Manish Stephen M Salazar Archana Dhumal

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EXECUTIVE SUMMARY 1 INTRODUCTION ONGCs Hazira Plant receives sour gas from Mumbai offshore through

a 42 SBHT pipeline for processing. The pipeline segment of 769 m at Umbhrat, District Navsari got exposed due to high tides and cyclonic storms in 2011-12. ONGC carried out protection measures using Geotextile tube, Geobags and Gabion boxes on the basis of suggestions of EIL. Again in June 2014 its 500 m segment got exposed. EIL then recommended relocation of the segment for which Department of Environment & Forests, Govt. of Gujarat, Gandhinagar instructed ONGC to conduct EIA study including impact on mangroves. ONGC therefore contracted CSIR-NIO to conduct EIA study with the following objectives.

2 Objectives a) To establish the prevailing marine environmental status in respect

of water quality, sediment quality and biological characteristics including mangroves for marine environment off Umbhrat.

b) To assess probable impact of proposed pipeline laying on the marine environment and ecology. c) To suggest Marine Environmental Management Plan (MEMP) including

mitigation measures. 3 Studies undertaken Investigations were conducted during October 2014 at 3 subtidal

stations each at Umbhrat and Umbhrat - Hazira coasts and at 2 intertidal transects in respect of physical processes, water quality, sediment quality, flora and fauna including fisheries and mangroves etc.

4 Project description Sour gas The gas (specific gravity 0.74) mainly contains methane (C1) in 79%

while C2 and C3 hydrocarbons are 11.8%. Other high derivatives are in trace quantities. H2

S is upto 200 ppm due to which the colourless gas has a typical odour.

Proposed activity The proposed activity involves installation and laying of a 42 dia, 1.9

km long pipeline between two hook-up points HK1 and HK2, and new sectionalizing valve (SV) station.

A segment of 800 m between hook-up point : HK1 and the landfall

point shall be installed through the marine environment using open cut and trenching method in a 20 m corridor. The sediment side cast during trenching will be used for back filling and the contour of the intertidal area shall be

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restored after the construction activity is over. The re-routed pipeline shall be hooked up with the existing pipeline. Afterwards inertisation and nitrogen purging of the existing isolated pipeline shall be done. All the materials shall be confirming NACE quality as per specifications. Welding of the pipeline shall be carried out as per specifications/standard API 1104/ASME B3.18. All the welded joints shall be tested by radiography and other non-destructive tests (NDT) as specified. The pipeline shall be subjected to hydrostatic test pressure of 1.5 times of the design pressure. It shall then be followed by dewatering and swabbing operations as per specifications.

All the waste materials shall be disposed off properly. The back-filling

of the excavated areas and clean-up/restoration of the site shall be done on completion of the work. EGP and cathodic protection shall be carried out as per specifications laid.

The redundant pipeline shall be retrieved and cut at welding joints of

every 12 m and transported to ONGC storage yards. 5 Study areas The nearshore coastal waters off Umbhrat i.e. the project area located

10 km southward of Hazira includes Umbhrat beach, and coastal waters of Tapi and Mindhola estuaries. They are described below.

Tapi Estuary Tapi, a major perennial river of the west coast of India, is an important

source of freshwater to the region. The 720 km long river (Figure 3.0.1) originates near Multai in the Betoul District of Madhya Pradesh and commands a catchment area of 65,145 km2 of which around 4000 km2

is in Gujarat. During seaward course, the river meanders through the hilly terrain of the Western Ghats before entering the coastal alluvial plains of Gujarat to meet the Arabian Sea near Hazira. The shallow and wide lower segment of the river exhibits characteristics of a typical estuary with strong currents associated with significantly high tidal influence upto 25 km upstream. Further inland however, the seawater excursion is restricted due to creation of a causeway at Rander which also hinders the freshwater outflow.

The estuary and nearshore areas of Hazira exhibit a typical character of South Gujarat coast with (a) vast intertidal regions composed of poorly sorted sediment made up sand silt and clay with isolated rocky outcrops, (b) supralittoral region either barren or dominated by salt tolerant plant species of Prosopis, Acacia and Zyphus, (c) gently sloping continental shelf with uneven seafloor often strewn with sand bars, and (d) high tidal influence due to the proximity to the Gulf of Khambhat.

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The riverine discharge to the sea is controlled by the Ukai and Kakrapar dams constructed on the river at 141 and 115 km upstream respectively. Mean runoff of Tapi was 1.7982 x 1010 m3/y in 1975. After the construction of dams, it has reduced to an average of 7.301 x 109 m3/y during 1982-91. In 1995 a weir-cum-causeway was constructed across the river at Rander that prevented seawater incursion further inland. In recent years the river discharge of 8000 m3/s during monsoon decreases to 10 to 45 m3

/s during November-May leading to stagnation in the riverine and inner estuarine segments, during the dry season.

Due to proximity of the Gulf, the region experiences significantly high tidal influence with mean spring and neap tidal ranges of 5.7 and 4.3 m respectively at Hazira. The tidal influence however decreases with distance into the estuary with spring and neap tidal ranges of 2.3 and 0.4 m respectively at Surat. During the period of freshwater dominance the flood duration of 6 h in the openshore reduces to 4 to 5 h in the mouth segment of the estuary and decreases to barely 2 h at Surat with corresponding increase in the ebb period. Decrease in flood period though to a lesser extent occurs in the landward direction during the dry season also.

The Tapi River is subjected to sporadic floods associated with heavy

rainfall in the catchment area during July-September. When the flood coincides with spring tide, the water level rises substantially inundating vast areas. A level of 10 m with respect to CD has been recorded at Magdalla during one such flood in the past. The construction of two dams on the river has however reduced the flood fury to a great extent.

Currents are largely tide-induced during dry season and are

considerably influenced by the riverine discharge during monsoon. At times when the runoff is heavy, the flow is unidirectional in the estuary throughout, irrespective of the tide. During dry season, the maximum flood and ebb speeds often exceed 1 m/s with the tidal excursion of 7 to 20 km within the estuary and 11 to 13 km along the open coast. The direction of flow is predominantly decided by the channel geometry that reverses with the change in the tidal phase. The u component of the current is dominant throughout a tidal cycle and net negative u component favours seaward transport. The v component is considerably weak as expected for estuaries under high tidal dominance.

The lower segment of theTapi Estuary is well flushed with flushing time

of less than 2 tide cycles calculated based on the tidal prism method. Flushing time of 3 tide cycles during spring for both freshwater flow conditions reveals the dominance of tidal influence over freshwater flow during spring tide. However, during neap when the seawater incursion in the estuary

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greatly reduces, the flushing time increases to 7 tide cycles when the river discharge decreases to 10 m3

/s.

The water quality of the estuary has deteriorated after the industrialization time though not severely. Considerable depletion in DO with values decreasing to

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Umbhrat coast Purna River having a winding channel and shallow depths is situated

10 km southward of Umbhrat which is a low plan of sand. This Umbhrat beach is almost barren with absence of mangroves and

other vegetation. Umbhrat village is located eastward between the beach and the Highway. The beach ends at Danti further northward along the Mindhola Estuary which has confluence to sea with Tapi estuary.

6 Prevailing marine environment The prevailing marine environment was evolved in respect of physical

processes, water quality, sediment quality, flora and fauna etc for the Umbhrat coast. It is the project areas which were investigated during October 2014. The recent data generated for the Hazira-Umbhrat coast during January 2014 (postmonsoon) and May 2014 (premonsoon) were also assessed for the purpose. The data generated since 1983 and available with CSIR-NIO has been employed for comparison with the present results so that variations, if any due to natural or otherwise causes would be indicated for the prevailing marine environment which has been described in detail below.

Bathymetry

The Mindhola and the Tapi Estuaries which meet at the mouth region is exposed during the low tide. Bathymetry shows two channels namely east and west channels at the mouth region. Depths of 2 and 10 m are available at a distance of 1.7 km and 2.7 km, respectively. At the mouth, in the eastern side between Danti and Bhimpur, there is a channel which leads to the Mindola River. The width of the river at this point is around 3 km and the length of the river is around 6 km.

Physical processes Due to the proximity to the Gulf, the region experiences significantly

high tidal influence (1.7 - 7.4 m). The tides are semi-diurnal type with two high and two low waters with unequal amplitudes occurring or each tidal day. The maximum flood and ebb speeds varied from 0.4 to 0.8 m/s. The u and v components of the currents denote that the v component dominated the u component, showing the currents are parallel to the coast. The tidal excursion indicates an elliptical circulation pattern with the major axis with excursion lengths varying from 6 to 19 km and the track parallel to the shoreline and the minor axis perpendicular to the coast during an average tide.

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Water quality: Temperature: Temperature of the Umbhrat-Hazira coast varied 20 to 33oC

range indicating seasonal variations. However, spatial variations were not marked. Temperature of the project area i.e. Umbhrat coast varied from 29.0 to 32.2oC (av 31.1oC) during October 2014. It is comparatively higher than that of the Hazira-Umbhrat coast during the period possibly because of low depths of the nearshore waters. Hence, average temperature was 22.4 to 31.5oC during 1983-2013 indicating clear seasonal variations. The present data are in similar range and also indicate similar seasonal changes. These temperatures are below 35o

pH: pH of the Hazira-Umbhrat and the Umbhrat coasts was 7.8-8.2 (av 8.1) and 7.8-8.2 (av 8.1) respectively during 2014 indicating spatial as well as seasonal variations. The lower pH for the areas could be possible because of drainage of contaminated waters through the estuaries particularly during low tide. The data though were in similar ranges that recorded since 1983, lower average values upto 7.7 were recorded in several instances because of the polluted outflow from the Tapi estuary.

C which is below the threshold for the aquatic biota to impart any harmful effects.

SS: SS was highly variable from 92 to 2265mg/l (av 1170 mg/l) and 250 to

1612 mg/l (av 763 mg/l) for the Hazira-Umbhrat coast and the Umbhrat coast respectively during 2014. The content clearly indicated spatial as well as seasonal variations particularly due to rain runoff and erosion of banks in the estuaries. It is comparatively low along the Umbhrat coast as the coast is not erosion prone.

Average SS varied from 96 to 1433 mg/l for the Hazira region during

1990-2013. The content recorded in the present study was comparable with the earlier data as illustrated in the above table.

Salinity: During 2014 salinity varied in the ranges of 25.9 to 33.9 ppt (av

31.1ppt) and 27.3 to 29.2 ppt (av 28.7 ppt) for the Hazira-Umbhrat coast and the Umbhrat coast respectively indicating comparable salinity for both the coasts. The lower salinities were recorded during monsoon revealing the impact of rain runoff through the estuaries. They were higher during premonsoon because of high evaporation rates and negligible land drainage having low salinity. Hence seasonal as well as spatial variable were marked for the area. Average salinity of the Hazira-Umbhrat coast varied in the range of 25.7 to 39.0ppt during 1983-2013. The data of 2014 possess similar range as illustrated in the above table.

DO and BOD: DO was highly variable from 2.0 to 7.3 mg/l (av 5.5 mg/l) and

3.8 to 6.1 mg/l (av 5.8 mg/l) for the Hazira-Umbhrat and the Umbhrat coast

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respectively during 2014. The lower content for the Hazira-Umbhrat coast particularly during monsoon indicated negative impact of the polluted drainage through the estuaries due to which spatial as well as seasonal variations have been noticed. In comparison the content was higher for the Umbhrat coast possibly because of low influence of the drainage through the estuaries. With the average DO of 4 mg/l since 1983, the coastal waters of Hazira-Umbhrat region were well oxygenated indicating healthy environment. The content observed during 2014 was comparable with the earlier data as presented above. BOD was low (av 2.5 mg/l) and 2.7 mg/l) for the Hazira-Umbhrat as well as the Umbhrat coasts during 2014. The seasonal and spatial variations were not significant. High average BOD shows that organic load entering through the estuaries is efficiently oxidized by incoming tidal water in the coastal waters. It indicated good oxidising conditions in the coastal waters.

Phosphorus and nitrogen compounds: Phosphate was highly variable in

the Hazira-Umbhrat coast (1.6-15.2 mol/l) during 2014 possibly attributed to the drainage of contaminated waters through the estuaries, hence indicating spatial variations. The content along the Umbhrat coast was comparable though in lower range. The content also indicated seasonal variations. Phosphate was present in a low range of 1.1 to 5.3 mol/l in the Hazira-Umbhrat coast during 1983-2013. The seasonal and spatial variations were not marked in the content which is comparable with the records of the present study.

Nitrate was highly variable in the study area of the Hazira-Umbhrat

coast during 2014 (6.6-23.2 mol/l). The concentrations indicated spatial as well as seasonal variations. The levels at the Umbhrat coast were higher (25.6 - 38.9 mol/l) as compared to those for the Hazira-Umbhrat coast.

Average nitrate content was 0.6 to 34.8 mol/l during 1983-2013.

These concentrations are in the similar range as that of the present study. Nitrite levels in the Hazira-Umbhrat and the Umbhrat coast were low

(0.3-3.8 mol/l (av1.2 mol/l and 0.1-2.5 mol/l, av 0.9 mol/l) during 2014. It is known that Tapi and Mindhola estuaries possess high nitrite content because of high organic load entering in the estuary. However, it is negative influence on the coastal waters was not evident because the waters are highly oxygenated. Hence spatial as well as seasonal variations were not seen. Similarly the levels at the Umbhrat coast were low during 2014 indicating good oxidising conditions.

The nitrite content in the Hazira-Umbhrat coast was low of 0.2 to 2.4

mol/l during 1983-2013.

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Ammonia in the Hazira-Umbhrat and the Umbhrat coasts was in the comparable (1.1 - 5.6 mol/l) low ranges during 2014. Some adverse impact of drainage through the estuaries has been visible in the coastal waters off the Hazira-Umbhrat. Spatial variable were evident in the content. However, seasonal variations were not marked in the content. The low values were attributed to the good oxidising conditions in the waters.

Ammonia concentrations in the coastal waters off Hazira-Umbhrat were

ND to 6.5 mol/l during 1983-2014. These and present data were comparable. PHc: The average PHc levels were 0.3 to 43.1 g/l in the coast during 1983-

2013. The levels reported for the present study were in the lower range. Phenols: The phenols content in the Hazira-Umbhrat and the Umbhrat coasts

were in the low range of 63 to 210 and 55 to 119 g/l respectively during 2014. The levels suggested that negative effect of the runoff through the estuaries was not marked in the coastal waters. Average levels of phenols in the coast were 2 to 129 g/l during 1990-2013. These concentrations recorded since 1990 were comparable with the present results.

Sediment quality: Texture of the Umbhrat coast during October 2014 was

mostly sandy (62.9 - 96.2%) with variable percentage of silt and clay. Spatial variations were clearly evident. Texture of the Umbhrat coast was also sandy (86.4 - 93%, dry wt) with meager content of silt and clay. The variations in the content were narrow.

The results of the present study were comparable with the earlier data. Metals: The results of metal content indicated considerable variation in the

trace metals of concern such as chromium, nickel, copper, zinc and mercury along the coast making the assessment difficult. Variations in lithogenic fraction of metals in sediment along the west coast in space and time are common due to various factors such as variable inputs of SS through land drainage, littoral transport, sediment movement due to tides etc. The variations in the concentration of trace metals are also because of changing levels of aluminium and iron in sediment which generally influence the concentration of trace metals. The results of monitoring are to be addressed in this context. The metal content in the sediment of the Hazira-Umbhrat coast was highly variable. Station 4 which was located close to the estuarine mouth exhibited mostly higher content indicating spatial changes in the content. The seasonal variations however were not marked.

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Similarly, the metal content at the Umbhrat coast was also highly variable but comparable with the content of corresponding metal levels as illustrated in the above table.

The average concentrations of selective metals as given in the

table also indicated variation in wide ranges. The results of the present study however were within the range of levels of metals recorded since 1997. They did not reveal any gross accumulation of the metals in the sediment of the study areas.

The contents in the intertidal sediment were highly variable and they

were comparable with accumulation in subtidal sediment of the Hazira-Umbhrat and the Umbhrat coasts reported for 2014. They indicated that the intertidal sediment of the project area was grossly uncontaminated.

The build-up of Corg

in the sediment of the study areas was negligible indicating uncontaminated sediment and low influence of organic matter originating through the estuaries on the coastal sediment. The concentrations of 0.1 to 3.7%, dry wt recorded for the Tapi Estuary and the Hazira-Umbhrat coast during 1990 to 2013 also suggested that the sediments were uncontaminated and compared well with the present results.

Phosphorus: The phosphorus contents were low and compared well with the contents of 238 to 1014 g/g, dry wt reported for Hazira-Umbhrat during 1998 to 2013. The levels showed that the organic load flowing through the estuaries did not impact the coastal sediment of the study area.

PHc: PHc in subtidal and intertidal sediment of the Umbhrat coast and

subtidal sediment of Hazira-Umbhrat coast during 2014 was low upto 0.3 g/g, wet wt. PHc in the subtidal sediment of the Tapi Estuary and the Hazira-Umbhrat coast was 0.1 to 4.8 g/g, wet wt during 1999 t0 2013. These concentrations compared well with the present results.

The above results revealed low PHc accumulation in the sediment

though the area experiences traffic of barges and ships. In areas receiving anthropogenic petroleum residues such as oil terminals, the PHc concentration in sediment often exceeds 10 g/g; wet wt.

Apart from changes in the physico-chemical characteristics of water

and sediment environments that a coastal development may induce, the ultimate concern is invariably the biological resources as described below.

Mangroves: Mangroves are absent at the development site at Umbhrat.

However small bushes and shrubs at the proposed site have been observed.

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A large area of mangroves (about 27 ha) dominated by Avicennia marina exists along the open coast outside the mouth of Tapi estuary which is located about 12 km away from the present study sites. These mangroves are under considerable stress due to heavy sand deposition and inadequate tidal flushing due to human induced changes in morphology.

Water: The TVC counts in water varied widely from 107102 to 5600 x102

CFU/ml with the highest count of 5600x102 CFU/ml recorded at the stations during post monsoon period. No clear trend in their distribution was observed. TC (NG-300 CFU/ml) (NG- No Growth) and FC (NG-30 CFU/ml) also varied with nominal ranges without any trend. Overall average of TVC counts (2300102 CFU/ml) during the postmonsoon period were much higher that that during monsoon (395102 CFU/ml at Hazira-Umbhrat segment and 1057102 CFU/ml at Umbhrat segment) and pre monsoon (860102

CFU/ml) periods; whereas TC counts was highest during monsoon (av120 CFU/ml) at Hazira-Umbhrat segment.

Bacterial counts viz; TVC, TC and FC were high in sediment than water. No clear spatial trend in the distribution of TVC, TC and FC was noticed. However, monsoon period sustained higher number of pathogens at Umbhrat coast than any other season and area of the year 2014.TVC which gives a quantitative idea about the presence of microorganisms such as bacteria, yeast and mould was reported to high throughout the coastal areas during the present study. Water quality criteria set by Central Pollution Control board (CPCB) require TC to be 500 MPN/100ml or less for outdoor bathing (organized). Concentration of chl a ranged from 0.1 to 3.2 mg/m3 averaging at 0.8 mg/m3. Overall highest average values were recorded during monsoon (av 1.2 mg/m3) followed by monsoon (av 0.9 mg/m3) and premonsoon (av 0.4 mg/m3

). The average values of chlorophyll a and phaeophytin were low in the coastal area of Umbhrat-Hazira area. In most of the stations average phaeophytin values were lower than that of chlorophyll signifying that production was more than disintegration. The temporal studies showed narrow tidal variation in chlorophyll distribution. The phaeophytin also did not show marked temporal variation. Seasonally, higher concentrations of phytopigments were recorded during premonsoon season.

Pre-industrialized average concentration of chlorophyll a varied in 0.3 to 2.5 mg/m3 ranges for the coastal water. These concentrations have not changed significantly seasonally though high values were occasionally observed. The concentrations of chlorophyll a, however, increased dramatically during May 2003 indicating eutrophication and hence an environment under stress due to increase in the concentration of nutrients probably associated with sewage release. The average concentration of

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phaeophytin was often lower or comparable with the concentration of chlorophyll a as commonly observed for coastal waters of South Gujarat.

Highest average cell count as well as number of genera were found

during October 2014 (monsoon) followed by May 2014 (premonsoon) and January 2014 (postmonsoon). The decrease in cell count was associated with low chlorophyll a. Genera like Cylindrothe Caclosterium, Thalassiosira, Navicula and Nitzschia were present in all the segments and during all the seasons. Premonsoon season represented by mainly Cylindrothe caclosterium, Thalassiosira, Nitzschia, Navicula, Thalassiothrix, Coscinodiscus, Guinardia by contributing more than 78% of phytoplankton population. Overall 46 genera of phytoplankton were encountered during the monsoon periods dominated by Skeletonema costatum, Cylindrothe caclosteri. During postmonsoon season total 42taxon of phytoplankton were recorded dominated by Cylindrothe caclosterium, Thalassiosira, Nitzschia etc. Overall 64 species from 46 genera of phytoplankton were encountered during 3 seasons of 2014 and compared well with the earlier reports, although all of them do not occur at any single station or in one season.

The seasonal variability and generic diversity of the phytoplankton

population recorded during the present study compared well with the other season. The populations of phytoplankton were generally dominated by Cyclindrotheca, Thalassiosira, Skeletonema, Nitzschia and Navicula.

Zooplankton: The average standing stock of zooplankton in terms of

biomass and population was relatively higher during monsoon period than the premonsoon period, whereas in terms of population count, higher abundance was recorded during premonsoon period. The table indicates a fluctuating trend in all the segments of the coastal segment. The community structure revealed the dominance of copepods (86.2 % in January), chaetognaths (8.1% in January), gastropods (45.7% in October), lamellibranches (12.4% in October), decapods(7.9% in October) and polychaetes (0.3% in January). The composition was fairly diverse and the number of faunal groups varied between 12 and 15 (av 13 groups). Overall, 19 groups of zooplankton encountered, however all the groups were not present at any given time or station. Other less common groups encountered were foraminiferans, siphonophores, medusae, ctenophores, mysids, ostracods, cumaceans, amphipods, Lucifer sp, stomatopod, cephalopods, isopods and marine insects.

The average baseline biomass of zooplankton (4.1-8.0 ml/100 m3) in

the coastal segment had increased in the period between April 1997 and November 2003 and decreased thereafter. The overall trend suggested gross changes in the current study as compared with pre-industrial baseline (9.1-9.5

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ml/100m3). In the coastal segment which receives industrial effluents, on the contrary, the trend fluctuated and there was no clear evidence for impact of the effluents on the zooplankton biomass. In the off Umbhrat-Hazira coastal segments sea off the mouth of the estuary, the post-industrial average biomass was variable (0.1-9.5 ml/100m3

) and high during mid tide (Figure 4.5.20).

The results since 1984 indicated a fluctuating trend in the coastal segments of Umbhrat-Hazira. The number of zooplankton components (no) varied randomly. The baseline for the coastal segment as a whole did not reveal any gross variations in the zooplankton diversity with the number of zooplankton components of the current study falling in the range of 7 to 15 no.

Macrobenthos: The results revealed not significant spatial variations in the

intertidal macrobenthic standing stock. The intertidal macrobenthic standing stock in terms of abundance (0-500, av 154 no/m2) and biomass (0 1.1 g/m2, wet wt av 0.4 g /m2

) varied widely. The faunal diversity varied between 0 and 3 (av 2) and mainly dominated by the polychaetes. Overall, about 3 groups of intertidal fauna were recorded during the present investigation.

The data indicated poor subtidal macrobenthic biomass (0-0.1 g/m2; av 0.1 g/m2, wet wt) and population (0-75 no/m2; av19 no/m2) in all the stations of the Umbhrat-Hazira coastal segment during all the three seasons while 0-175 no/m2; av44 no/m2

was observed at Umbhrat segment during monsoon season in the study year. This revealed that the prevailing subtidal environment was not conducive for the proliferation of macrobenthos due to the instability of the substratum associated with strong tidal currents and was probably the major factor for the low macrobenthic productivity of many coastal segments of Gujarat. The faunal diversity of macrobenthos was also poor throughout the study area. Polychaetes were the dominant group followed by Polychaete and pelecypods. In general, 5 groups of subtidal macrobenthos were recorded during the present investigation.

The data since 1984 indicated poor macrobenthic biomass in the coastal water in the pre-industrial (

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in macrobenthos. The overall trend suggested a stabilized poor structure of faunal density except one abrupt increase during October 2012, otherwise decrease in faunal components in the Umbhrat-Hazira coastal segment over the years. The faunal diversity was low and comparable with the earlier results indicating the absence of gross changes in the subtidal ecology during the post-industrialization period.

Fishery: The results of the experimental fishing operation carried out during

February-March 2013, October 2013 and January 2014 Tables 4.5.19 indicated a moderate fish catch rate suggesting a poor fishing potential off Umbhrat-Hazira.

The results confirmed low fishery potential in terms of catch per unit

effort as well as low to moderate diversity in the Tapi Estuary than the coastal segment off Hazira.

During the three seasons of 2013-14 (premonsoon, monsoon and

postmonsoon) these catches were represented by 47 species of fishes, 9 species of Prawns and 9 other species which includes Crabs, Squilla, Lobster and Cephalopod. Harpadon nehereus, Johnius glaucus, Thryssa mystax, Lepturacanthus savala, Cynoglos susarel, Coilia dussumieri, Arius caelatus, Hilsakelee, Pellonaditchela, Parapenaeop sissculptilis, Macrobrachium rosenbergii, Acetes indicus, Charybdis annulata and Scylla serrata occurred in most of the catches during all the seasons. During October 2013 the fish catch diversity was the highest and represented by 28 species of fishes, 9 species of prawns and 5 other species. However, composition was more or less comparable except for the exclusive occurrence of Arius megaloptera, Arius sp, Ilisha megaloptera, Johnius sp, Liza macrolepis, Lutjanus johnii, Opisthopterus tardoore, Periopthalmus sp, Polynemus heptadactylus and Polynemus tetradactylus. During January 2014 fish diversity was also high and represented by 26 species of fishes, 9 species of prawns and 9 other species. Species like Boleopthalmus sp, Carangoides malabaricus, Carcharhinus limbatus, Channa punctuta, Otolithes sp, Pomadasys kaakan, Protonibea diacanthus, Sardinella longiceps, Scomberoides commersonnianus, Thryssa hamiltoni, Trichiurus lepturus, Charybdis cruciata, Matuta lunaris and Portunus pelagicus were only encountered during the season. Overall, the study region revealed low to moderate fishery potential and results are comparable with that of the other areas of the Gulf. The low fishery status of the Gulf could be related to high turbidity associated with strong currents and the low biological potential at different trophic levels.

Corals: The Umbhrat-Hazira region does not have corals as the intertidal

area is largely sandy or muddy. Coral growth in the subtidal region is unlikely

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in view of the high suspended load in the water column, the conditions under which corals do not thrive.

Birds: The Hazira coast offers different marine habitats like rocky/sandy/muddy intertidal and mangroves for a variety of resident and migratory birds (Table 3.4.20). The birds use these habitats as their active feeding ground especially during low tide. Hectic activities of Gulls, Heron, Terns, Egrets, Kingfisher, Plovers, Avocets, Curlews, Whimbrels, Sand pipers, Shanks, Spoonbills and Bitterns are frequently seen in these coastal habitats. A large number of migratory species pass through Hazira and a small population of them in the form of juvenile and non-breeding adults take shelter in the coastal areas during summer. In all, the region is represented by 81 species of birds.

Reptiles and Mammals: Marine turtles are not common along the Hazira coast and have not been sighted during the field studies. The marine mammals are chiefly represented by Dolphin and Porpoise in the coastal waters of Hazira but whales are very rare. They were not observed during the field studies. Sand dunes: Sand dunes are present along the coast of Umbhrat as well as around the project site.

7 Potential environmental impacts The impacts during construction phase would be associated with

trenching and laying of the pipeline in the shallow water depths of 0 to 5 m to a small extent of 400 m and the remaining part in the intertidal area. Impacts during the operational phase would be the result of the sour gas transfer through the pipeline as described below.

Construction phase

Physical processes: The time period to execute the work was given as 3-4 months only and a very long trench would not be feasible.

Water quality: Dredging, trenching and pipelaying activities have a high

potential to increase turbidity due to increased rate of dispersal of fine grained sediment in the water column. Apart from affecting photosynthesis, DO as well as BOD levels may be altered and concentrations of trace pollutant in water could increase due because of the release of sediment interstitial water exposing the biota to relatively high levels of pollutants. However, it will be limited to a short period.

However, as discussed in Section 4 the sediment along the pipeline

corridor is unpolluted and hence the interstitial water is unlikely to have high

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levels of organic carbon and other contaminants. Thus DO and BOD levels would not be grossly influenced and the concentrations of trace pollutants would not enhance. Moreover, any transient perturbations would be effectively smothered under the prevailing dynamic conditions off Umbhrat and in the coastal waters. Hence, the overall impact during construction phase on water quality would be localised and minor. No adverse impact is envisaged.

Sediment quality: Backfilling and resettling of sediment may lead to

changes in sediment texture in localised areas particularly along the intertidal segments. However, these changes would be minor and nonconsequential.

Flora and fauna: The most likely impact during construction phase would

be on subtidal and intertidal habitats which could be temporarily destroyed along the pipeline route due to dredging, trenching and pipelaying activities. Moreover, if the dredge spoil spreads over nearby areas under the prevailing high tidal excursion (Section 4), the biota there would also suffer accordingly.

An increase in suspended load may marginally influence the

photosynthetic activity of phytoplankton, in localised areas. Hence, the damage to phytoplankton in the region would be localised, temporary and reversible and recovery would be fast once the construction phase is completed.

Impact on zooplankton standing stock although a localised, marginal

change in community structure and population counts may result. Such changes are temporary, highly reversible and do not reflect in the overall zooplankton productivity.

The trenching for the pipe laying would destroy the benthic fauna of the

area. However, it will re-colonise when the pipeline is buried and back filled. The process would however be slow in the trenched area. Damage to the subtidal and intertidal benthic fauna along the pipeline route would occur during construction period of 3 to 4 months.

The vegetation is scanty and shrubby in the nearshore belt of Umbhrat

- Hazira and hence not very attractive for birds. Hence, an increase in noise level during offshore construction would be of little consequence, though the birds would be disturbed by the noise of trenching operations. The impact however would be limited to construction period only.

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Operational phase: Major concern during the operational phase of the terminal would be the leakages of the sour gas under transfer that might occur in the case of pipeline damage only.

Leak quantities: The possible failures resulting in leaks can be attributed to

leaking valves and rupture of pipeline. Failure in the submarine pipeline can also be another source of the

leaks. The leaks and rupture of sub-sea pipelines can result from corrosion or due to gouge on the pipe during construction. However, pipelines designed, fabricated, laid and periodically inspected as per internationally accepted codes and practices are relatively safe and spillage of POL are rare during the design life of a pipeline. Nevertheless, in an unlikely event of pipeline rupture due to unforeseen events such as a severe cyclone, an earthquake or intentional third party intervention, the quantity of sour gas that may be spilled can be 8.75 to 14 m3

(7.5 to 10.4 t) if the rupture occurs under the bed (since sectionalising valves are provided on both the banks) which close within 210 sec.

Since the pipeline is buried all this leaked will not surface like a blob but leak slowly after gasification.

Fate of gas leak: Evaporation and dissolution are the major processes mainly

responsible for changing the quantity and composition of the spilled sour gas under water. The evaporation/gasification takes place mainly due to the decrease of pressure on the pressurized natural gas. Most of the leaked gas would escape from the shallow water column as the processes exerted by the few metres of water would not be sufficient to keep it in the pressurized state. Also the dissolution would not be substantial as the water column through which it travels is not much.

The transport of a leaked gas would be largely decided by wind apart

from the physical and chemical properties of the gas as these gasses are supported to be denser than the ambient air, it may spread like a sheet on the water surface and the intertidal area and eventually disperse catching fire is one of the possibilities.

The gasses are traced when leaked due to the presence of H2

S in ppm level. However, as the gasses are not refined, they may also contain traces of oil during the transportation and the oil would form slicks on the water surface to indicate a possible leak.

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Water quality: The solubility of hydrocarbons is low in water and the depth through which this sour gas travels is limited as the water depths in this case are < 5 m, the solubility is almost negligible to impact the water quality.

Sediment quality: If a spill occurs in the nearshore area or under the

intertidal area, traces of oil transported alongwith the sour gas may remain trapped in animal burrows and may get mixed with the sediment delaying its removal by tidal flushing apart from general contamination of large segments of surficial sediment. The sediment may sustain abnormal level of PHc for several days and even months. The weathered residue sinking through the water column in the event of a spill away from the shore may contaminate the subtidal sediment also. This impact would be relatively minor for a given product and given quantity since the weathered mass would be transported widely before settling on the seabed.

Flora and fauna: Populations and community structure of marine biota are

subject to considerable natural fluctuations due to changes in climatic and hydrographic conditions as well as the availability of food. Hence, it is often difficult to assess long term effect of a sour gas spill and to distinguish changes caused by the PHc from those due to natural variability. Moreover, the leakage of sour gas which does not have any oxygen in it may produce anoxic conditions in the oil depending on its pore city and the annihilation of the benthic organisms that come in direct contact of the gas.

Though sand dunes are present in the vicinity, the pipeline route avoids

the sand dunes and no destruction to sand dunes is expected.

Mitigation measures: It is important that certain decisions are taken and supplemented beginning with the planning stage itself so that the risk factors during construction and operational phases are reduced to a minimum to protect marine ecology from anthropogenic shocks.

Design considerations: Major environmental concern at oil terminals is

accidental leakages of the POL. No technology is available to recover the sour gas once leaked. Hence, best approach is to prevent the leakages. Evidently, the design and operating philosophy of an oil terminal should be "No Leak" under normal operating situations which if deviate beyond preset norms, the pumping operations should automatically stop till normal conditions are reset. It should be ensured that internationally accepted codes and practices are followed for the sour gas transport through proper inspection, frequent evaluation and intensive testing of all critical components of the

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pipeline system. Likewise, vulnerable units such as fittings, valves, flanges, couplings etc should be rigorously tested and certified for their reliability.

The pipelines should be buried below scour level to keep the lines in

place as the intertidal areas often experience strong wave forces particularly during monsoon and cyclonic condition can erode the upper strata of the intertidal area considerably.

Construction phase: The key factors in minimising adverse impacts would

be the reduction in construction period and avoidance of activities beyond the specified geographical project area (50 m corridor for pipelaying) which should be kept to a minimum. Hence, as a part of the management strategy, it is important that various activities are well-coordinated and optimised to avoid time over-runs and to complete the project within an agreed time schedule.

Pre-treatment to the pipes such as coating, concreting etc and other

fabrication jobs should be undertaken in a yard on land located sufficiently away from the high tide line and transfer of materials to the site should be through a predecided corridor. Similarly, the movement of construction barges, ships, machinery etc should be restricted to the predecided operational area. However, the region should not be crowded with too many vessels and construction machinery to avoid accidents and subsequent spillages of materials and fuel.

The pipeline in the intertidal and nearshore subtidal areas should be

buried to a safe depth and the depth of burial should be ascertained through reliable seismic surveys to guarantee its safety.

The Umbhrat-Hazira region is prone to occasional storms with 6 severe

cyclones (wind speed 100 - 150 km/h) striking the region over the past 100 y. At such wind speeds a wave generated offshore can have pronounced effect on the coast as well as the nearshore subtidal zone. This factor should be taken into account while designing the subsea pipeline segment.

A large number of labourers and other personnel would be involved in

the construction phase. Temporary colonies of the work force etc should be established sufficiently away from the high water line and proper sanitation including toilets and bathrooms should be provided to the inhabitants to prevent abuse of the intertidal area. Sewage and other wastes generated in these settlements should not be released to the sea.

The operational noise level should be kept to minimum particularly in

the nearshore region through proper lubrication, muffling and modernisation of equipment.

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It should be ensured that the intertidal and supratidal areas are restored to their original contours after the pipe-laying activities are completed. General clean-up along the corridor, adjacent areas and intertidal and subtidal regions should be taken-up and extraneous materials such as drums, sacks, metal scrap, ropes, excess sediment, make shift huts and cabins should be cleared from the site.

Operational phase: The major concern during operations is the leakage of

sour gas. Another consideration in preventing spills is the provision and regular

testing of not only emergency shutdown devices but also the components vulnerable to fatigue or failure. Hence, it should be ensured that auto-shut off valves, couplings, hoses, pumps, sub-sea pipeline etc are periodically inspected for their integrity and to ensure their proper functioning in an emergency. Accurate records of all inspections, unusual findings, actions taken etc must be scrupulously maintained as a part of the overall record system.

Operation should commence only after optimum conditions are reset.

Provision for an effective and reliable communication between the production platform, landfall and storage tanks should be made to avoid ambiguities and time delays during pumping of POL.

Firefighting equipment should be readily available at the land fall point

to mitigate any exigencies due to a leak in the intertidal areas of the pipeline route during hook-up and welding jobs.

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LIST OF TABLES

2.1.1 Composition of cargo: sour gas (gas + condensate). 4.3.1 Water quality of Umbhrat-Hazira coast during October 2014. 4.3.2 Water quality of Umbhrat-Hazira coast during January 2014. 4.3.3 Water quality of Umbhrat-Hazira coast during May 2014. 4.4.1 Sediment quality of Umbhrat-Hazira coast during October 2014. 4.4.2 Sediment quality of Umbhrat-Hazira coast during January 2014. 4.4.3 Sediment quality of Umbhrat-Hazira coast during May 2014. 4.5.1 Taluka-wise status of mangroves (ha) of Surat District. 4.5.2 Microbial counts (CFU/mL) in water of Umbhrat-Hazira coast during 2014. 4.5.3 Microbial counts (CFU/g) in sediment of Umbhrat-Hazira coast during

2014. 4.5.4 Range and average (parenthesis) of phytopigments off Umbhrat-Hazira

coast during 2014. 4.5.5 Range and average (parenthesis) of phytoplankton off Umbhrat-Hazira

coast during 2014. 4.5.6 Percentage composition (%) of phytoplankton population off Umbhrat-

Hazira coast during 2014. 4.5.7 Range and average (parenthesis) of zooplankton off Umbhrat-Hazira coast

during 2014. 4.5.8 Percentage composition (%) of zooplankton population off Umbhrat-Hazira

coast during 2014. 4.5.9 Range and average (parenthesis) of intertidal macrobenthos of Umbhrat

during October 2014. 4.5.10 Composition (%) of intertidal macrobenthos of Umbhrat during October

2014. 4.5.11 Range and average (parenthesis) of subtidal macrobenthos off Umbhrat-

Hazira coast during 2014. 4.5.12 Composition (%) of subtidal macrobenthos off Umbhrat-Hazira coast

during 2014. 4.5.13 Marine fish landings of Gujarat State, Surat and Navsari Districts during

1977-2013. 4.5.14 Species-wise composition of marine fish landings of Gujarat State, Surat

and Navsari Districts during 2011-2012 4.5.15 Centre-wise marine fish production (t) for Surat District during 2012-2013. 4.5.16 Monthly calendar of marine fish landings (t) at Hazira in Surat District

during 2012-2013.

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4.5.17 Monthly calendar of marine fish landings (t) at Bhimpur in Surat District 2012-2013.

4.5.18 Fishing villages, fishermen, boats and fishing gears of Surat District (2007).

4.5.19 Fish catch in coastal water off Umbhrat-Hazira coast during 2013-2014. 4.5.20 Check list of birds around Umbhrat-Hazira coast.

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LIST OF FIGURES

1.1.1 Map of project area showing Umbhrat, Mindhola and Tapi estuary. 1.1.2 Schematic diagram of re-routing and redundant pipeline at Umbhrat. 1.4.1 Subtidal and intertidal sampling locations along Umbhrat-Hazira coast

during 2014. 3.0.1 Map showing marine environment of Umbhrat, Mindhola and Tapi estuaries. 4.2.1 Current speed (a) and components (b) observed at station 2 (Umbhrat-

Hazira coast) from 10 to 14 April 2010. 4.2.2 Drogue trajectory conducted at station 2 (Umbhrat-Hazira coast) (Fl-Eb-Fl)

on 8 November 2009. 4.2.3 Drogue trajectory conducted at station 2 (Umbhrat-Hazira coast) (Eb-Fl) on

13 April 2010. 4.2.4 Drogue trajectory conducted at station 2 (Umbhrat-Hazira coast) (Fl-Eb) on

8 April 2010. 4.3.1 Water quality at station 1 (Umbhrat-Hazira coast) on 9 October 2014. 4.5.1 Temporal variation in phytopigments at station 2 (Umbhrat-Hazira coast) on

2 October 2014. 4.5.2 Temporal variation in zooplankton at station 2 (Umbhrat-Hazira coast) on 2

October 2014.

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LIST OF PLATES

Plate 1 Pipe protection measures at Umbhrat Geobags (Figure a & b).

Plate 2 Pipe protection measures at Umbhrat - Geotextile mats and tubes.

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COMMON ABBREVIATIONS Av - Average B - Bottom BOD - Biochemical Oxygen Demand (mg/l) Corg

- Organic carbon (%)

DO - Dissolved Oxygen (mg/l) Eb - Ebb tide Fl - Flood tide Max - Maximum Min - Minimum ND - Not Detected NH4+

-N - Ammonium nitrogen (mol/l)

NO3-

-N - Nitrate nitrogen (mol/l)

NO2-

-N - Nitrite nitrogen (mol/l)

PHc - Petroleum Hydrocarbons (g/l) Phenols - Total phenols (g/l) PO43-

-P - Reactive phosphate phosphorus (mol/l)

S - Surface SS - Suspended Solids (mg/l)

NA - Not Analysed

1 INTRODUCTION 1.1 Background

Oil & Natural Gas Commissions Hazira plant (ONGC) receives sour gas and condensate from Mumbai Offshore through 36 and 42 South Bassein Hazira Trunkline (SBHT) pipelines (Figure 1.1.1) for processing and there after supplies sweet gas to HBJ line through Gas Authority of India (GAIL) spanning about 3000kmacrossthe northern states for downstream industries including CNG supply in Delhi and to local consumer industries like KRIBHCO, RIL, ESSAR, GGCL and GSPL.ONGC also produces and supplies products such as LPG, naphtha, HSD, and ATF and kerosene to consumers like IOCL, BPCL, HPCL, RIL etc. The 42 dia SBHT p i p e l i n e s e g m e n t w h i c h t r a n s p o r t s g a s got exposed due to high tides and cyclonic storm occurred to an extent of 769 m in 2011-12 at Umbhrat, Navsari District. ONGC carried out protection measures in 2012 with geotextile tube, Geobags and Gabion boxes on the basis of suggestions given by Engineers India Limited (EIL). The temporary protection measures taken have resulted in change of the erosion pattern in the vicinity of the pipeline and the geobags used for this purpose have moved into lower intertidal areas (Plates 1 to 2). Again in June 2014, the 42 dia pipeline got exposed to an extent of about 500 m due to high tides and cyclonic storms.

EIL has proposed relocation of the pipeline segment as shown as in Figure 1.1.2 and ONGC has engaged L&T for laying of the pipeline and to carry out execution of re-routing scheme of 42 SBHT line at Umbhrat within the CRZ. Now Department of Environment & Forests (DOEF), Govt. Of Gujarat, Gandhinagar has instructed ONGC to conduct EIA study includingmarineaspectsand impactof theproject activityon themarine environment and mitigation measures, details of mangrove patches a n d impact of proposed activity on mangroves. ONGC therefore, contracted Council of Scientific & Industrial Research-National Institute of Oceanography (CSIR-NIO) to conduct the EIA study with the following objectives:

1.2 Objectives

a) To establish the prevailing marine environmental status in respect of water quality, sediment quality and biological characteristics including mangroves for marine environment off Umbhrat.

b) To assess probable impact of proposed pipeline laying on the marine environment and ecology.

c) To suggest Marine Environmental Management Plan (MEMP) including mitigation measures.

1.3 Scope of study CSIR-NIO has conducted several site-specific investigations in and around the Hazira-Umbhrat coast over the period (1984-2013) thereby generating an

2

extensive database for the area. Considering the availability of these data, the following studies are proposed:

1.3.1 Evolve prevailing marine environment off Umbhrat as follows: a) Physical processes: Physical processes like tides, currents and circulation also play a crucial role by controlling the extent to which many of the perturbations can influence the ecology. Hence, information available on currents, tides will be assessed to evaluate current and tidal fluctuations of the water level.

b) Water quality: Water quality at 3locations will be assessed based on salinity, temperature, pH, Suspended Solids (SS), Dissolved Oxygen (DO), Biochemical Oxygen Demand (BOD), nitrate, nitrite, ammonia, phosphate, Petroleum Hydrocarbons (PHc) and phenols. c) Sediment quality: Sediment from the intertidal and subtidal regions will be studied for texture, organic carbon, phosphorus, aluminium, chromium manganese, iron, cobalt, nickel, copper, zinc, mercury and petroleum hydrocarbons.

d) Biological characteristics: The status of flora and fauna in the subtidal and the intertidal zones will be established based on microbiology, phytoplankton pigments, population and generic diversity; zooplankton biomass, population and group diversity; macrobenthic biomass, population and group diversity; fisheries status; mangroves and their species diversity etc.

1.3.2 Assessment The impact assessment for the proposed projecton the marine ecology will be carried out based on the database generated and available with CSIR-NIO as well as other information made available by ONGC. Suitable mitigation measures will be suggested for adverse impacts, if any, in the form of Marine Environmental Management Plan (MEMP).

1.4 Approach strategy

Severity of negative impacts of developments in the coastal zone on associated marine ecology vary widely depending on many factors such as the extent, period and type of disturbance, anthropogenic perturbations, capacity of the receiving water to assimilate contaminants and extent of ecological sensitivity. Hence, the primary requirements for assessing adverse impacts due tore-routing the pipeline at Umbhrat are the baseline information for the coastal area off Hazira-Umbhrat in general and intensive site specific data for the nearshore waters off Umbhrat, in particular.

CSIR-NIO has been conducting general and site-specific studies for the

coastal waters off Hazira-Umbhrat region since 1983 with more frequent investigations in recent years due to several proposed and ongoing developments bordering the region. These data are adequate to describe general environmental

3

setting of the study areas and field data acquisition in the coastal waters off Hazira-Umbhrat and Umbhrat in the present investigationsis considered sufficient to meet the objectives.

CSIR-NIO monitors the coastal waters of Hazira at a few locations in the

vicinity of the proposed project area once every year since 1990 that has generated long term database for water quality, sediment quality and biological characteristics. This available information is assessed to plan field data acquisition for the present study. Accordingly, 6subtidal stations covering an area of 9.0 km2 of the openshore segment of Umbhrat-Hazira were sampled. Intertidal area has been also considered for the study and samples at 2 intertidal transects were collected. The sampling locations are illustrated in Figure 1.4.1.

This report is based on the field studies conducted off Hazira-

Umbhrat and Umbhrat coasts during October 2014 and the available immediate data of Jan 2014 and May 2014 for selected areas. Apart from this the available data of 1983-2014 with CSIR-NIO also used for long term comparison.

MEIA for the proposed project was conducted on the basis of information

provided by ONGC and that available in the literature. Mitigation measures including EMP were suggested for the adverse impacts, if any due to the proposed project.

1.5 Studies undertaken

Details of studies undertaken during October 2014 are as follows:

1.5.1 Sampling locations Investigations were conducted at 3 subtidal stations (1-3) and 3 subtidal

stations (4-6) in the Umbhrat coast i.e. the project site and Hazira-Umbhrat coast respectively. Sampling was done at 2 transects (I-II) at Umbhrat coast. The locations are illustrated in Figure 1.4.1 and their positions are given below.

Coast Area Station/

transect Position

Umbhrat Subtidal

1 21o0048.3N, 72o4349.4E 2 21o0033.7N, 72o4346.5E 3 21o0119.0N, 72o4332.6E

Intertidal I 21o0102.5N, 72o4342.3E II 21o0110.2N, 72o4340.1E

Hazira-Umbhrat Subtidal 4 21o037.7N, 72o4055.56E 5 21o029.90N, 72o4040.55E 6 21o0113.7N, 72o4122.38E

4

1.5.2 Sampling frequency Sampling was done at all stations in duplicate for water quality and

biological characteristics. Temporal measurements of 1 h frequencies over a tidal cycle were conducted at station 1.

Intertidal stations were sampled once along each transect in the area

between the Low Tide Line (LTL) and the High Tide Line (HTL).

1.5.3 Physical processes a) Tide: Available information on tides for Gulf of Khambat was assessed. b) Currents: Available information on Currents for Gulf of Khambhat was assessed c) Circulation Available information on circulation for Gulf of Kambhat was assessed

1.5.4 Water quality a) Sampling procedure: Surface water samples were collected using a clean polyethylene bucket while an adequately weighed Niskin sampler with a closing mechanism at a desired depth was used for obtaining subsurface water samples. Sampling at the surface and the bottom (1m above the bed) was done when the station depth exceeded 3 m. For shallow regions, only surface samples were collected. A glass bottle sampler (2.5 l) was used for obtaining samples at depth of 1 m below the surface, for the estimation of PHc. For shallow areas only surface water was collected.

b) Methods of analyses: Majority of the water quality parameters were analysed within 24 h of collection in the field laboratory. Colorimetric measurements were made on a Shimadzu (Model 1201) spectrophotometer. Shimadzu (Model 5301) fluorescence spectrophotometer was used for estimating PHc. The analytical methods for the measurements were as follows:

i) pH: pH was measured on a Cyber Scan (pH 510) pH Meter. The instrument was calibrated with standard buffers just before use. ii) SS: A known volume of water was filtered through a preweighed 0.45 m membrane filter paper (Millipore), dried and weighed again. iii) Salinity: GUILDLINES Autosal, Model 8400b-50 Hz, Sr. No. 71463, laboratory salinometer used for measuring salinity with the accuracy better than 0.002 equivalent practical salinity units (psu/ppm) was used for estimating salinity. iv) DO and BOD: DO was determined by Winkler method. For the determination of BOD, direct unseeded method was employed. The sample was filled in a BOD bottle in the field and incubated in the laboratory for 3 d after which DO was again determined.

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v) Phosphate: Acidified molybdate reagent was added to the sample to yield a phosphomolybdate complex which was then reduced with ascorbic acid to a highly coloured blue compound which was measured at 882 nm.

vi) Nitrite: Nitrite in the sample was allowed to react with sulphanilamide in acid solution. The resulting diazo compound was reacted with N-1-Naphthyl-ethylenediamine dihydrochloride to form a highly coloured azo-dye. The light absorbance was measured at 543 nm. vii) Nitrate: Nitrate was determined as nitrite as above after its reduction by passing the sample through a column packed with amalgamated cadmium. viii) Ammonia: Ammonium compounds (NH3 + NH4+) in water were reacted with phenol in presence of hypochlorite to give a blue colour of indophenol. The absorbance was measured at 630 nm. ix) PHc: Water sample (1 l) was extracted with hexane and the organic layer was separated, dried over anhydrous sodium sulphate and reduced to 10 ml at 30o C under low pressure. Fluorescence of the extract was measured at 360 nm (excitation at 310 nm) with Saudi Arabian crude residue as a standard. The residue was obtained by evaporating lighter fractions of the crude oil at 100oC for 30 min. x) Phenols: Phenols in water (500 ml) were converted to an orange coloured antipyrine complex by adding 4-aminoantipyrine. The complex was extracted in chloroform (25 ml) and the absorbance was measured at 460 nm using phenol as a standard.

1.5.5 Sediment quality

a) Sampling procedure: Subtidal surfacial bed sediment from all locations was obtained by a van Veen grab of 0.04 m2

ii) Metals: Sediment was brought into solution by treatment with conc HF-HClO4-HNO3-HCl and the metals were estimated on a Perkin Elmer (ICP-OES Model

area. The sample after retrieval was transferred to a polyethylene bag and preserved for further analysis. Intertidal sediment was sampled using a hand shovel. b) Methods of analyses: (i) Texture: Dried sediment (25 g) mixed with deionised water and 10 ml sodium hexameta phosphate (6.2 g/l) was sieved through 63 m sieve to retain sand and the passed material was dispersed in deionised water (1 l). The fraction (20 ml) picked up at 20 and 10 cm depth immediately and after 2 h 30 min respectively were considered as silt and clay after drying and weighing.

6

no OPTIMA-7300DV). Mercury was estimated by flameless AAS technique after digesting the sediment with aquaregia. iii) Corg: Percentage of Corg in the dry sediment was determined by oxidising organic matter in the sample by chromic acid and estimating excess chromic acid by titrating against ferrous ammonium sulphate with ferroin as an indicator. iv) Phosphorus:Dried and powdered sediment (20.5 g) was digested using HF, HC104, HNO3 and HCl. It was used for estimating total phosphorus as described under Section 1.5.3(b)(v). v) PHc: Sediment after refluxing with KOH-methanol mixture was extracted with hexane. The residue was subjected to clean-up procedure by silica gel column chromatography. PHc content was then estimated by measuring the fluorescence as described under Section 1.5.3 (b) (ix).

1.5.6 Flora and fauna

a) Sampling procedure:For microbial analysis, surface water was collected directly in a sterilised glass bottle. Sediment sample was obtained using van Veen grab and transferred directly into sterilised polyethylene bag.

Polyethylene bucket and Niskin sampler respectively, were used for sampling surface and bottom waters for the estimation of phytoplankton pigments and population. Samples for phytoplankton cell count were fixed in Lugol's solution.

Zooplankton samples were collected by oblique hauls using a Heron

Tranter net (mesh size 0.3 mm, mouth area 0.25 m2) with an attached calibrated TSK flow meter. All collections were of 6 min duration. Samples were preserved in 5% buffered formaldehyde.

Sediment samples for subtidal macrobenthos were collected using a van-

Veen grab of 0.04 m2

i) Microbes: Samples were analysed by plating and membrane (Millipore 0.22 m) filtration techniques for Total Viable Counts (TVC), Total Coliforms (TC), Escherichia Coli like Organisms (ECLO), Faecal Coliforms like Organisms (FCLO), Shigella like Organisms (SHLO), Salmonella like Organisms (SLO), Proteus, Klebsiella like Organisms (PKLO), Vibrio like Organisms (VLO), Vibrio

area. Intertidal collections between the HTL and the LTL were done with a hand shovel for muddy and silty substratum while quadrants of different sizes were employed for sampling rocky, sandy and areas of compact sediment. Samples were preserved in 5% buffered formaldehyde - Rose Bengal.

Experimental bottom trawling and gill netting were undertaken wherever

feasible using a high opening bottom net of 20.7 m (637 meshes of 50 mm) length and locally procured gill net.

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Parahaemolyticus like Organisms (VPLO), Vibrio Cholerae like Organisms (VCLO), Pseudomonas aerugenosa like Organisms (PALO) and Streptococcus faecalis like Organisms (SFLO). Colonies of TC, ECLO, VLO, VPLO and VCLO were counted separately. The media employed for growth of colonies were as follows: Nutrient agar for TVC, Mac Conkey agar for TC and ECLO, M-Fc agar for faecal coliforms, Xylose-lysine deoxycholate agar for SHLO, SLO and PKLO, thiosulphate citrate bile salts medium for VLO, VPLO and VCLO, cetrimide agar for PALO and M.Enterococcus agar for SFLO. ii) Phytoplankton pigments:A known volume of water was filtered through a 0.45 m membrane filter paper (Millipore) and SS retained on the filter paper were extracted in 90% acetone. For the estimation of chlorophyll a and phaeophytin the extinction of the acetone extract was measured at 665 and 750 nm before and after treatment with dilute 0.1 N-HCl. The concentrations of phytopigments were expressed as mg/m3. iii) Phytoplankton population:The cells in the sample preserved with Lugols solution were allowed to settle and transferred into a Sedgwick-Rafter slide. Enumeration and identification of phytoplankton were done under a microscope. The cell counts were expressed as number/litre. iv) Algae, seaweeds, mangrove and sand-dune ecosystem: Algal, seaweed and mangrove flora were assessed from upper to lower intertidal region along predecided transect. v) Zooplankton:Volume (biomass) was obtained by displacement method. A portion of the sample (25-50%) was analysed under a microscope for faunal composition and population count. Biomass and population were expressed as ml/100 m3 and nox103/100m3 respectively. vi) Fish eggs, fish larvae and decapod larvae:These groups were sorted out from zooplankton samples and counted. Frequency of occurrence and their percentage composition were then determined. vii) Benthos:The sediment was sieved through a 0.5 mm mesh sieve and animals retained were preserved in 5% buffered formaldehyde-Rose Bengal. Total population was estimated as number of animals in 1 m2 area and biomass on wet weight basis (g/m2). viii) Fishery:After trawling fishes were sorted out into different groups, weighed,and catch rate (kg/h) and composition were determined. A part of the catch was preserved in 5% formaldehyde for identification at species level. Fish landing data were obtained from the Department of Fisheries, Government of Gujarat, for assessing the fishery status of the region.

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2 PROJECT DESCRIPTION 2.1 Present activity 2.1.1 Pipeline

ONGC Hazira plant receives sour gas and condensate from Mumbai Offshorethrough36and 42 SBHT (South Bassein Hazira Trunkline) pipelines for processing (Figures 1.1.1 and 1.1.2) and thereafter supplies sweet gas to HBJ line through GAIL spanning about 3000km across all northern states for downstream industries including CNG supply in Delhi and to local consumer industries like KRIBHCO, RIL, ESSAR, GGCL & GSPL. Hazira plant produces and supplies products of LPG, Naphtha, HSD, and ATF and Kerosene to consumers like IOCL, BPCL, HPCL, RIL etc. Thus 36 and 42 dia SBHT lines from Mumbai to Hazira is lifeline of India and it is essential to secure safety, stability and security of the pipelines.

The 42 dia SBHT line t r a ns po r t i n g th e ga s got exposed to the extent

of 769 m (approx.) in 2011-12 at Umbhrat, District Navsari. Based on design and engineering by their consultant (EIL), ONGC carried out protection measures in 2012 with geotextile tubes, geobags and gabion boxes which has been approved by Gujarat Maritime Board (GMB).

2.1.2 Purpose for re-routing the pipeline and EIA

Meanwhile, due to high tides and cyclonic storm on 15-16 June 2014, about another 500 m of the 42 gas pipeline has got exposed, its previous protection measures got damaged and the line got shifted by 25 to 30 m towards seaside. ONGC carried out protection measures in 2012 with geotextile tube, Geobags and Gabion boxes on the basis of suggestions given by Engineers India Limited (EIL). The temporary protection measures taken have resulted in change of the erosion pattern in the vicinity of the pipeline and the geobags used for this purpose have moved into lower intertidal areas (Plates 1 to 2). Again in June 2014, the 42 dia pipeline got exposed to an extent of about 500 m due to high tides and cyclonic storms.In view of this, ONGC has engaged Engineers India Limited (EIL) as consultant for permanent remedial measures of the pipeline. EIL has submitted scheme of re-routing the line at Umbhrat as a permanent solution.

ONGC will implement re-routing the pipeline in about 1.9 km stretch which includes the exposed position on fast track for permanent solution to the problem of its exposure at Umbhrat beach and therefore has engaged L and T to carry out execution of re-routing scheme of 42 SBHT line at Umbhrat. ONGC has submitted application for permission to DOEF, Gandhinagar. DOEF has asked to submit EIA study report including marine aspects and impact of the project activity on marine environment and mitigation measures, details of mangrove patches and impact of the proposed activity on mangrove and CRZ Map in 1.4000 scale alongwith super imposition of proposed activity and technical recommendations/suggestions. Accordingly ONGC requested CSIR-NIO to carry

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out EIA studies along with details of mangroves and impact of pipeline laying on mangrove vegetation.

2.1.3 Cargo:sour gas Composition of the sour gas gas+condensate which is transported through

the pipeline (Table 2.1.1) is as follows: The gas with molecular weight of 21.42 and has specific gravity of 0.74 to

0.7418 under the pressure condition on the 60 - 80 kg/cm2. It mainly contains(%,mole) methane(C1) with 79%, other gases (C2 + C3) are 11.8. The higher hydrocarbon derivatives in the gas are lower of 2.6 while C6+ fraction is1%.

The condensate contains (% volume) (4:8.6, C5:12.9, C6:21.6, C7:25.2,

C8:13.4, C9:80, C10:4.5, C11:2.1, C12:31 and polynaphthalene: 0.7 hydrocarbons.

The gas (density 676 kg/m3) flows at a normal rate of 20 to 22 MMSCMD

under a operating pressure and temperature of 60 to 80 kg/cm.2g and 20 to 40oC respectively through the 42 O.D. pipeline. The condensate flows at the rate of 5000 to 8000 m3

The 400 m long pipeline portion prior to the entry of HDD having concrete weight coating shall be installed by open cut and trenching method. Another 400 m long section without concrete coating after HDD exit shall also be installed by the same method. The 1100 m long portion (HDD) between these sections shall be installed using Horizontal Directional Drilling (HDD) technique.

/d.

2.2 Proposed activity 2.2.1 Installation of new pipeline

Now ONGC has proposed to re-route the dislocated/exposed pipeline segment. Accordingly EIL has prepared the engineering plan for re-routing of the pipeline as shown in Figure 1.1.2.

The proposed activity includes installation and laying of the 42 dia, 1.9 km

long pipeline between hook-up points HK1 and HK2 (Figure 1.1.2). It also includes installation of new SV station having a 42, 900# ball valve; gas actuated; buried; remote and manually operated sectionalising valve (SV). Installation of a new insulating joint of 42 dia, 900 # (buried) will be near HK1. Hot tapping with stappling (double line stop with temporary by-pass) shall be carried out at HK1 and another at HK2 in the existing pipeline. The gas in the isolated section between HK1 and HK2 shall be flared off safely through the existing SV station.

HK1 shall be located minimum 100 m upstream of the existing land fall

point (LF2, (Figure 1.1.2). The re-routed pipeline section of 400 m length from HK1 to HDD entry point shall be gradually lowered to HDD entry point matching the depth of 6 m at HDD entry point.

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The re-routed pipeline segment shall be hooked up with the existing pipeline by cold field bands at both the ends using manual cutting and welding. Afterwards inertisation and nitrogen purging of the existing isolated section shall be done.

The pipeline shall be 42 O. D. X 32.4 mm W.T., APISL Gr x 60 PSL2,

NACE, LSAW. The 1100 mm portion (HDD) shall be installed minimum 12 m below lowest natural ground level.

All the materials shall be confirming NACE quality as per specifications.

Welding of the pipeline shall be carried out by semi automatic/automatic/manual (including Auto UT) method as per welding specification. Fresh WPS/PQR/EQT and other procedure qualifications shall be carried out as per specification/ standard API 1104/ASME B3.18. Production test also be carried out at acceptable limit. All the welded joints including cutting edge preparation, fit-up, bending, preheating etc. shall be tested by radiography and other non-destructive tests (NDT) as specified.

All the waste materials like gabions, stones, boulders, geobags and

geotubes etc lying on the seashore shall be disposed of properly. Surplus excavated soil trench outside ROU and bentonite shall be disposed suitably with the permission from the concerned authorities. The back-filling of the excavated areas and clean-up/restoration of the site shall be done on completion of the work. EGP (Calliper Run) and cathodic protection (CP) shall be carried out as per specifications laid.

The pipeline and the new SV stations shall be subjected to hydrostatic test

pressure of 1.5 times the design pressure. It is then followed by dewatering and swabbing operations to be carried out as per specifications.

2.2.2 Submarine pipeline segment The existing pipeline segment between hook-up point HK1 and landfall

point LF2 in the marine environment shall be re-routed in the proposed project (Figure 1.1.2) of the total length of 800 m of the segment, the 500 m long portion shall be in the subtidal area while the 300 long portion shall be in the intertidal area (Figure 1.1.2).

The 42 O.D. 800 m long segment which shall have concrete weight

coating for 400 m length shall be installed by open cut and trenching method in a 20 m wide corridor. The sediment side cast during trenching shall be used for back-filling. The excess sediment is expected to be dispersed by the tidal action. The contour of the intertidal area shall be restored after the construction activity is completed.

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2.2.3 De-commissioning of redundant pipeline De-commissioning of the redundant pipeline between hook-up points HK1

and HK2 and existing SV station valves shall be carried out. The old pipeline shall be retrieved and cut at welding joints at every 12 m. All the materials including the valves shall be transported to the ONGC storage yards. The dismantled area in the existing SV station including the valve pit shall be restored to the levels of the adjoining areas.

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3 STUDY AREAS The coastal waters off Umbhrat located 10 km southward of Hazira forms

the project area (Figure 3.0.1). The Hazira-Danti region is the confluence of Tapi and Mindhola estuaries with area (Figure 1.1.1). Hence Tapi Estuary, Mindhola Estuary and Umbhrat coast are described below.

3.1 Tapi Estuary Tapi, a major perennial river of the west coast of India, is an important

source of freshwater to the region. The 720 km long river (Figure 3.0.1) originates near Multai in the Betoul District of Madhya Pradesh and commands a catchment area of 65,145 km2 of which around 4000 km2 is in Gujarat. During seaward course, the river meanders through the hilly terrain of the Western Ghats before entering the coastal alluvial plains of Gujarat to meet the Arabian Sea near Hazira. The shallow and wide lower segment of the river exhibits characteristics of a typical estuary with strong currents associated with significantly high tidal influence upto 25 km upstream. Further inland however, the seawater excursion is restricted due to creation of a causeway at Rander which also hinders the freshwater outflow.

The estuary and nearshore areas of Hazira exhibit a typical character of

South Gujarat coast with (a) vast intertidal regions composed of poorly sorted sediment made up sand silt and clay with isolated rocky outcrops, (b) supralittoral region either barren or dominated by salt tolerant plant species of Prosopis, Acacia and Zyphus, (c) gently sloping continental shelf with uneven seafloor often strewn with sand bars, and (d) high tidal influence due to the proximity to the Gulf of Khambhat.

The riverine discharge to the sea is controlled by the Ukai and Kakrapar

dams constructed on the river at 141 and 115 km upstream respectively. Mean runoff of Tapi was 1.7982 x 1010 m3/y in 1975. After the construction of dams, it has reduced to an average of 7.301 x 109 m3/y during 1982-91. In 1995 a weir-cum-causeway was constructed across the river at Rander that prevented seawater incursion further inland. In recent years the river discharge of 8000 m3/s during monsoon decreases to 10 to 45 m3

/s during November-May leading to stagnation in the riverine and inner estuarine segments, during the dry season.

Due to proximity of the Gulf, the region experiences significantly high tidal

influence with mean spring and neap tidal ranges of 5.7 and 4.3 m respectively at Hazira. The tidal influence however decreases with distance into the estuary with spring and neap tidal ranges of 2.3 and 0.4 m respectively at Surat. During the period of freshwater dominance the flood duration of 6 h in the openshore reduces to 4 to 5 h in the mouth segment of the estuary and decreases to barely 2 h at Surat with corresponding increase in the ebb period. Decrease in flood period though to a lesser extent occurs in the landward direction during the dry season also.

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The Tapi River is subjected to sporadic floods associated with heavy rainfall in the catchment area during July-September. When the flood coincides with spring tide, the water level rises substantially inundating vast areas. A level of 10 m with respect to CD has been recorded at Magdalla during one such flood in the past. The construction of two dams on the river has however reduced the flood fury to a great extent.

Currents are largely tide-induced during dry season and are considerably

influenced by the riverine discharge during monsoon. At times when the runoff is heavy, the flow is unidirectional in the estuary throughout, irrespective of the tide. During dry season, the maximum flood and ebb speeds often exceed 1 m/s with the tidal excursion of 7 to 20 km within the estuary and 11 to 13 km along the open coast. The direction of flow is predominantly decided by the channel geometry that reverses with the change in the tidal phase. The u component of the current is dominant throughout a tidal cycle and net negative u component favours seaward transport. The v component is considerably weak as expected for estuaries under high tidal dominance.

The lower segment of theTapi Estuary is well flushed with flushing time of

less than 2 tide cycles calculated based on the tidal prism method. Flushing time of 3 tide cycles during spring for both freshwater flow conditions reveals the dominance of tidal influence over freshwater flow during spring tide. However, during neap when the seawater incursion in the estuary greatly reduces, the flushing time increases to 7 tide cycles when the river discharge decreases to 10 m3/s.

The water quality of the estuary has deteriorated after the industrialization

time though not severely. Considerable depletion in DO with values decreasing to

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3.2 Mindhola Estuary Mindhola River which originates in the Western Ghats follows a westward

but meandering course before meeting the Arabian Sea at Danti adjacent to the mouth of the Tapi Estuary (Figure 1.1.1). The river though narrow, broadens into a wide estuary below Nanod, which is about 25 km inland from the sea. The estuarine region has extensive sandbanks and mudflats that get submerged during flood tide. The network of tributaries that get periodically filled with tidal water harbour a variety of edible mudskippers, crabs, mullets and prawns. Intertidal region, which is generally muddy, supports a rich growth of Typha and other plants except in the mouth region where no vegetation except halophytes occur.

Industries located in Palsana and Choryasi talukas discharge their treated

wastewater through Kadodara/Kakra/Bhedwad, Gabheni/Unn and Hanuman/Lajpore Khadis in the Mindhola estuary. Besides, majority of sewage from in and around Surat City is also discharged in the estuary through some natural creeks. Baleshwar/Gangadhar/Itarva Kankarakhadis also carry effluents from nearby areas to the estuary apart from direct release of effluents from industries of Maroli Udyognagar in Navsari District.

A variety of industries release their effluents in Bhedwad and Kakra

Creeks; the tributaries of the Udhna Khadi, which in turn transports this load to the Mindhola estuary near Budiya roughly 15 km from the estuary mouth.

The Mindhola Estuary is under considerable tidal influence with the spring range at the mouth of 5.5 m decreasing to 1.9 m at 32 km inland. The respective neap ranges are 2.5 and 0.5 m. The flood period decreases from 4 to 5 h at the mouth to 2 to 3 h at 32 km upstream with the ebb extended over a period of 7 to 10 h. High tidal influence generates strong currents with maximum speeds of 0.8 to1.9 m/s in the mouth segment. The excursion length during spring decreases from 17 km at the mouth to 12 km at Budiya where Udhna Khadi meets Mindhola. During neap the respective distances are 11 and 8 km. The excursion lengths of 3 to 5 km further inland indicate the possibility of accumulation of pollutants in the inner estuary during periods of weak riverine flows.

Maximum intrusion of salinity occurs upto 25 km inland during April (lean period of freshwater flow) and decreases to 15 km during September (when the riverine flow is substantial). The water is generally well mixed vertically though occasional stratification is recorded in the mouth area when the freshwater flow is significant. The flushing time of the estuary is estimated to vary between 4 and 8 tide cycles in April, based on salinity distribution. Based on this, the effluent load retained in the estuary has been estimated to be 2.2 to7.3 times the load introduced per tide cycle.

The SS entering the estuary through river discharge during dry season is

below 160 mg/l. There is a marked increase in the estuarine zone and the

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concentrations are widely variable. The anthropogenic organic load entering the estuary influences the DO balance in the system. There is a general tendency for DO to increase with flood tide and decrease as the ebb progresses even during September when the riverine flow is good. The values around 2 ml/l are commonly recorded in the mid-estuarine zone during April. BOD increases markedly during low tide and values of 4-8 mg/l are common in the mid-estuary. No marked increase in the levels of phosphate and nitrate as compared to other estuaries of South Gujarat is evident though the concentrations of nitrite and ammonium are often high