|
|
|||||
1.1.
General The project activities concerned
with the installation of the desalination plant comprise of: i)
site preparation, ii) drawing sea water of 237 MLD (10000 m3/hour)
through an intake system comprising of intake head and submarine
pipeline (or) from the existing NCTPS intake collection sump located
inland (which would receive sea water from Ennore Port basin),
iii) pump house, iv) pre-treatment including flocculation-coagulation,
gravity settling, two steps filtration, ultra-filtration and chemical
dosing, v) desalting of sea water using reverse osmosis, vi) discharge
of brine of 137 MLD (5700 m3/hour) at sea using submarine pipeline
and diffuser ports outfall system, and vi) related electrical
and mechanical installations. The general layout of the plant facilities is shown in Fig. 3. The options are envisaged for drawing seawater viz., (i) The sea water will be drawn by gravity flow from the sea through a sea water intake head and pipeline laid on the sea bed (or) (ii) sharing with NCTPS seawater intake which is drawn from Ennore Port basins. A capture tower will be installed at the shore end in order to avoid the entry of sand and floating debris. The water will be pre-filtered through rotating filters and chlorinated by applying a dose of sodium hypochlorite in the underwater intake channel and in the pump aspiration chamber. In order to eliminate suspended matter and colloids present in the sea water, a dose of ferric chloride (coagulant) will be applied, enabling the formation of flakes. The suspended solids will be eliminated in gravity settlers. The seawater will then be filtered in two stages i.e., through the sand filters and anthracite filters. Sulphuric acid addition is made to reduce the pH of sea water and prevent precipitation of carbonates and bicarbonates, as well as to generate sufficient CO2 for post-treatment with dolomite. Sodium bisulfite dosing is added in order to eliminate residual chlorine from the dose of sodium hypochlorite. In order to prevent the precipitation of ferric hydroxide, calcium fluoride, calcium sulphate and strontium sulphate salts, an antiscalant will be metered to prevent the formation of crystalline networks. Due to the characteristics of raw water, and in order to prevent fouling in the reverse osmosis membrane, an ultrafiltration unit will be installed. It goes through then energy recovery equipment consists of high-pressure pumps, a unit for recovering energy from the brine with hyperbaric chambers, and recirculation or booster pumps to increase the pressure of the rest of the water transferred in the direction of the reverse osmosis membranes. The water discharged from the reverse osmosis modules is used to feed the hyperbaric/compression chambers, thus achieving maximum energy economy due to the performance of these groups. The pH levels will be adjusted between 6.5 and 8.5 by means of treatment with dolomite. The plant will also be equipped with fire prevention system, communications system and laboratory. The Desalination plant is proposed to be set up about 4 km north of Ennore Port, which is 22 km north of Chennai. The project site lies in Kattuppalli village, Minjur, between the Buckingham canal and the Bay of Bengal. The Land Fall Point (LFP) of the water intake pipeline will be located approximately at latitude 13o 19’01” N and longitude 80o 20’25” E (WGS 84). The Pulicat Lake, second largest brackish water lake in India, lies north of the project area, with its mouth located about 15 km north of this region. The region inland of the project area is a plain and barren land with thorny bushes and sparse wild vegetation. On the eastern side of the area, we have a long and nearly straight coastline that is exposed to an open sea, the Bay of Bengal. This coastal region comprises of fairly wide beaches with well-defined foreshore, elevated backshore and with small dunes at some places. The morphology of this region is influenced by 3 climatic conditions, viz., southwest monsoon (June – September), northeast monsoon (Mid October to Mid March) and fair weather period from April to May. Unlike the northern part of the east coast of India, this part of the coast is influenced more by the northeast monsoon weather conditions than those during the other two seasons. The nearshore remains relatively steeper due to the action of high waves during monsoon seasons. The seabed in nearshore primarily comprises of sand without any complex bathymetric features. Sand banks are observed at offshore which perhaps have been formed over the geological period from sediments transported through the Ennore creek and the Pulicat Lake. The newly constructed Ennore Port breakwaters also influence the littoral drift in this region in recent years. 1.4. Proposed marine facilities The development of marine facilities consists of a sea water intake system with chlorination pipe, and a brine reject outfall system with a submarine pipeline and outfall diffuser. The lay out of various marine facilities are shown in Figs. 3, 4 and 5. Seawater intake: The intake is designed to draw the seawater having the ambient salinity of around 35 PSU, at the rate of 237 MLD (10000 m3/hour) through an intake system having two options: Option 1- drawing through a gravity flow system from an intake head located offshore with chlorination pipe and HDPE submarine pipelines, 3 nos. X 1400 mm dia. (or) 2 nos. X 1600 mm dia. with a pump house at shore, and Option 2- sharing seawater from the existing NCTPS intake collection sump located inland (which would receive sea water from Ennore Port basin) and transport to the project site through on land buried pipeline. Brine reject outfall: The brine
reject will be of the order of 137 MLD (5700 m3/hour) with a salinity
of 70 PSU released into the sea using HDPE submarine pipeline
of 1 no X 1400 mm dia. and diffuser ports outfall system which
will be designed to have mixing in order to attain ambient salinity
within a short distance. The fishery potential of the region off the project area is relatively good. The nearshore supports certain type of demersal fishery with moderate bottom animal community. In general no inhabitation is
found in the project region. Fishing is one the main occupations
of the people living at far away surrounding villages. Scanty
agricultural and limited aquaculture activities in certain parts
of the coastal belt also take place away from the project region.
Saltpans are observed far from the project site on the southwestern
side. The increased industrial and transport activities associated
with the recently developed Ennore Port are seen about 10 km away
on the southern side of the project region. The acute drinking water supply
of the rapidly developing Metropolitan Chennai City has the only
viable option of augmenting with desalination plant. The project
region is a dry and barren land without any inhabitation. Further,
the region surrounding the project area remains economically under
developed. The proposed desalination plant if commissioned would
invite defined improvement in the community of the region and
in the land use. The proposed project related activities are mainly
concerned with the marine environment and thus a marine EIA study
will be essential in order to identify the impacts and mitigation
measures and plan an appropriate Environmental Management Plan. The proposed activity in the
identified coastal region will have a direct relevance on the
key issues like fishing - marine pollution - land use - industrialization
- human welfare. The oceanographic investigations and the marine
EIA must focus on deciphering these issues. The latest tools should
be used to study the environment and thus the associated impacts
with relevant mitigation measures. i) Drinking water supply can be explored from different sources, but no such sources are available to meet the acute shortage of drinking water supply of the Chennai city. ii) Ground water source is also not viable to meet such large requirement. The meager quantity of existing potential of ground water also remains very brackish. Continuous drawl of ground water will seriously hamper the environment by large scale sea water intrusion. Types of mitigation: Suitable mitigation has to be worked out with least anticipated impact. In the present case, there is no alternative other than installing the desalination plant with seawater intake and brine reject outfall system at the project region. The main reasons are: i) the Chennai metropolitan city has the long history of acute shortage of water supply in India, ii) there is no possibility of obtaining fresh water from alternate sources like nearby rivers etc. , and iii) there is only limited ground water potential, which had already turned brackish due to sea water intrusion.
If the project is not installed, the effect will be more detrimental to: i) drinking water supply, ii) economical growth of the Chennai Metropolitan city and in turn the Tamilnadu state, iii) human welfare and iv) regional development. On the other hand, the cessation
of such developmental project, may, to a very limited extent help
in maintaining the marine environment. The marine environment off the project region as shown in Fig. 1, has been studied for the evaluation of baseline information as per the norms stipulated by the Ministry of Environment and Forests, Govt. of India. The baseline data were collected along three transects separated each by 2.5 km apart with three sampling stations (1 km, 2 km, and 3 km off the coast into the sea) along each transect. The study area covers around 30 km2. The details of the sampling locations are presented in Table 1 and also shown in Fig. 6. The details of the studies carried out in the coastal region on physical, chemical and biological aspects are explained below. The field studies were conducted in August 2005 representing the southwest monsoon period of the project region. Physical parameters Water quality parameters Temperature, Sediment quality parameters Sediment structure, Biological parameters Primary Productivity, Environmental study Assessment of fishery resources
in the area, The data collection was carried in August 2005 covering the southwest monsoon season in order to prepare the Rapid Marine EIA report. 6.2. Method of collection / analysis Wind To understand the wind pattern prevailing in the project region, the data on daily variation of wind speed and direction at 0830 hours and 1730 hours available for Chennai region were compiled from the Bay of Bengal Pilot (1978). Storm The information on cyclonic storm is essential for the environmental assessment. Occasional occurrence of severe cyclonic storm is found to occur in this region. Based on the IMD data on the Tracks of Storms and Depressions in the Bay of Bengal and the Arabian Sea, (1979), and the Addendum (1996) published by IMD, the details on the storms occurred between 1877 and 1990 were compiled. Waves The ship reported visual observations documented in Indian Daily Weather Reports (IDWR) published by the India Meteorological Department, Pune, compiled over the period from 1968 to 1986 were used for the base line data. The data reported for the region between the latitude 10°N - 15°N, and longitude 80°E - 85°E were considered for the present project (Chandramohan, et.al., 1990). Tides Aanderaa WTR9 is a Self Recording Tide Gauge, manufactured by Aanderaa Instruments, Norway was used for the measurement of tides. It has a pressure sensor which is based on a high precision quartz crystal oscillator. The pressure is measured every 0.5 seconds and 1024 samples are taken (512 seconds) and stored in internal RAM. It has a range of 0-690 kPa with an accuracy of 210 Pa and a resolution of 7 Pa. Currents Variation of current speed and direction were continuously measured for a period of 14 days at 2 locations, i.e. 7 days at each location. The details of measurement locations, viz., Stns. C1 and C2 are shown in Fig. 6 and Table 1. The current speed and direction were recorded at 20 minute interval close to water surface. Aanderaa RCM 7 Self-Recording Current Meters manufactured by Aanderaa Instruments, Norway were used for current measurements. They are the self-recording type and used in the sea to obtain the vector averaged current speed and direction. The measurable speed range is 2 to 295 cm/s with an accuracy of + 1 cm/s. The current direction is measured with a resolution of 0.35o and accuracy of + 5o. The Clock is of Quartz crystal having an accuracy of better than + 2 s/day. Littoral Drift Based on the ship reported wave
data, the longshore sediment transport rate at the study region
was estimated using the following equation (Shore Protection Manual,
CERC, US Army, 1975). Where, Q = longshore sediment
transport rate in m3/year, Salinity and Temperature A self-recording conductivity-temperature-depth instrument manufactured by Aanderaa Instruments, Norway was installed at stns. C1 and C2 as indicated in Fig. 6. The measurements were made 2 m below the sea surface. The time series profiles on salinity/temperature variation were collected at 20 minute interval. Dispersion Fluorescent tracer Rhodamine-B was used to conduct the dispersion experiment at nearshore. The concentrated dye solution was prepared and released at 700 m distance from the shoreline along the proposed corridor of the outfall (Fig. 6). The experiment was conducted during a relatively calm sea condition, which prevailed on 8.9.2005. The dye patch was allowed to spread without any external disturbance and the extent of spread was measured using DGPS. The dye samples were collected along and across the spread of the dye patch. The collected samples were analyzed using Spectrophotometer. Based on the analysis of the dye samples and the spread of the dye patch, the dispersion characteristics of the coastal region were estimated. Bathymetry The nearshore region proposed for laying intake and outfall pipelines as shown in Fig. 7. was surveyed in August 2005. Echosounder: ODOM HYDROTRAC Survey Echosounder manufactured by ODOM Hydrographic Systems, USA was used for carrying out the bathymetry. The unit is a single frequency echosounder with a standard transducer having the frequency of 200 kHz. It measures the depth ranging between 0 and 200 m with the accuracy of 0.01 m and a resolution of 0.01 m. The system works on 9 - 18 VDC or on 220 VAC. The horizontal positioning was
carried out using the GBR21 and GPS12XL DGPS Beacon Receiver manufactured
by Garmin Limited., USA. It is a 12 channel GPS receiver with
an integrated Beacon receiver. The system provides accuracy close
to 1 m. It has two programmable RS422 serial ports with NMEA output.
The system can be powered with 12/24 VDC. It updates at 5 Hz with
a differential speed of 0.2 km/hr. The Beacon receiver works in
the frequency range of 283.5 - 325 kHz with a channel spacing
of 500 Hz. For the present surveys, the DGPS Beacon Transmitter
operated at Pondicherry at 315 kHz was interfaced. The nearshore upto 3 km into the sea, i.e. the proposed corridor for laying the intake and outfall pipelines as shown in Fig. 7 was surveyed to understand the geological structure beneath the seabed. CAP 6600 Chirp II Acoustic Sub-Bottom Profiler manufactured by BENTHOS, INC., USA was used for carrying out the shallow seismic survey. It is a fully integrated dual channel, single frequency sonar system. The system uses advanced Chirp technology to produce high resolution sub-bottom profiles of both the shallow layers (layer 1 and layer 2). Side scan sonar survey The nearshore upto 3 km into the sea, i.e. the proposed corridor for laying the intake and outfall pipelines as shown in Fig. 7. was surveyed to understand the geology of the top of seafloor. The Side Scan Sonar model SS-340
manufactured by Odom Hydrographic System Inc., USA was used. It
operates on the central frequency of 340 kHz. It employs the latest
in Microelectronic Technology to provide sonar image that one
fully corrected for slant range, and amplitude providing a plan
view map of the seafloors topographical features. It also maintains
a high quality and high resolution image. The acoustics, signal
processing, and graphic recording are consistent. Water samples were collected at 9 stations along 3 transects covering approximately 30 km2 of the coastal region (Fig. 6). The details of the sampling locations are also presented in Table 1. Samples were collected at surface, mid depth and bottom using Niskin water sampler. Sampling was carried out at 3 stations along transect 1 (W13, W14 and W15), 3 stations along transect 2 (W7, W9 and W11) and 3 stations along transect 3 (W16, W17 and W18). While the transect 2 was planned along the proposed pipeline corridor, transects 1 and 3 lie 2.5 km at north and south respectively. Samples for Dissolved Oxygen
(DO) was collected in DO bottles (125 ml capacity) soon after
the sampler was recovered. The bottles were rinsed with the water
sample. The end of the nozzle tube was inserted into the sample
bottom and filled till 100 ml and the water was allowed to overflow
from the bottle to ensure that no bubble is trapped is carried
out in the bottle. To the brimful DO bottles 1 ml of Winkler A
(manganese chloride) and 1 ml Winkler B (alkaline KI) were added.
The stopper is then inserted and the bottle shaken vigorously
for about 1 minute to bring each molecule of dissolved oxygen
in contact with manganese (II) hydroxide. After fixation of oxygen,
the precipitate was allowed to settle. The DO bottles were kept
in dark and transported to the laboratory for analysis. Water samples for salinity, total suspended solids, nutrients, trace metals and phenolic compounds were stored in PVC bottles directly from the water sampler, after rinsing the same with the water sample. The samples were then transported to the laboratory in an ice box. Water samples for Petroleum hydrocarbons were collected separately in 5 litre glass bottles. The sample for Phenol was collected in a pre cleaned 1 litre plastic container. Method of analysis Temperature: Temperature was noted immediately after the water sampler was retrieved using a graduated centigrade thermometer, which was graduated from 0 to 5°C with 0.1 °C accuracy up to 50°C. pH: pH was measured immediately
after collection of water samples using a portable digital pH
meter (Hanna Instruments, model RI 02895) having an accuracy of
? 0.2 pH. The instrument was calibrated using standard pH buffer. Dissolved Oxygen (DO): Dissolved Oxygen content of the water samples were analysed by Winkler’s method. The precipitate of manganese (II) hydroxide is dissolved by acidification (50% HCl), liberating the manganese (III) ions, which reacts with iodide ions previously added to water sample together with potassium hydroxide. The iodine ions liberated by oxidation of iodine ions was titrated against sodium thiosulphate. The end point of the titration (blue? colourless) is indicated by using starch as an indicator. Biochemical Oxygen Demand (BOD): BOD was determined by the same procedure (Winkler method) as that for DO, after 5 days of incubation at 20°C in a BOD incubator. The difference in the amount of oxygen on the 1st and 5th day gave the measure of Biochemical Oxygen Demand. Turbidity: Turbidity was measured by the Nephelometric method after calibrating the Nephelometer using known dilutions of standard prepared from hydrazine sulfate and hexamethylene tetramine in distilled water. Ammonia-Nitrogen (NH3-N): This
nutrient was estimated by following method suggested by Grasshoff
etal (1983). Ammonia from the seawater sample reacts in moderately
alkaline solution with hypochlorite to monochloramine, which in
the presence of phenol, trisodium citrate buffer and excess hypochlorite
and gives indophenol blue. The reaction temperature of 37 - 40°C
was used for the estimation of ammonia-nitrogen. The concentration
was measured spectrophotometrically at 630 nm to obtain NH3-N. Nitrate-Nitrogen (NO3-N): It was determined using the method given by Parson et al (1984). Nitrate in the sea water was quantitatively reduced to nitrite by running the sample through a column containing cadmium filings coated with metallic copper. The nitrite produced is diazotised with sulfanilamide and coupled with N-(1-naphthyl)-ethylenediamine to form a pink coloured azo dye, which was measured spectrophotometrically at 543 NM. Nitrate values were corrected for nitrite in the sample. Inorganic Phosphate (PO4-P): It was determined by following the procedure of Parsons et. al., (1984). In this method the seawater sample was allowed to react with a composite reagent containing molybdic acid, ascorbic acid and trivalent antimony. The resulting phosphomolybdate complex is reduced to give a blue colour solution, which was measured using in spectrophotometer at 880 nm. Total Suspended Solids (TSS): The TSS of seawater samples was determined by filtering a known volume (500 ml) of seawater sample through pre-weighed 4.5 cm Whatman GF/C glass microfibre filter paper. Filtration was carried out under controlled vacuum source. The filter papers were then dried (40°C) till a constant weight was obtained. The difference between the final and initial weight of the filter paper resulted in the estimation of TSS from the water samples. Phenols: Phenols in seawater (500 ml) was converted to yellow coloured antipyrine complex by adding 4 –amino antipyrine. The complex was extracted in chloroform (25 ml) and the absorption was measured at 460 nm using phenols as a standard. Petroleum Hydrocarbons (PHC): Water sample (5 litre) was extracted with HPLC grade n-hexane. The organic layer was separated and dried over anhydrous sodium sulfate. The fluorescence of the extract was measured using Fluorometer with calibration using Saudi Arabian Crude Oil. Cadmium and Lead: Known volume of sample was acidified to pH 2.0 using HCL. APDC (Ammonium Pyrrolidine Dithiocarbamate) was added and sample shaken well for complete mixing. Known volume of MIBK (Methyl Isobutyl Ketone) was added to the sample followed by thorough mixing. Metals’ forming a yellow ring over the sample was separated and this extract was kept for further analysis of trace metals (Cd and Pb) using AAS (Model- HITACHI-Z-7000, Polarized Zeeman Atomic Absorption Spectrophotometer, Graphite Furnace, Tube type covet). Samples were analysed with standards NOAA and BCSS-1 and chemical standards Lead Nitrate and Zinc chloride for different trace metals. Mercury: Seawater samples for the determination of mercury was transferred from Niskin sampler to acid washed bottles and acidified to a pH below 2 by adding 0.1 N hydrochloric acid which was previously tested for traces of mercury. Pre-concentration of mercury in seawater was achieved by complexing with dithiozone at pH below 2. The complex was extracted in carbon tetrachloride and back extracted in 5 M hydrochloric acid. The acid extract was shaken with sodium nitrite to decompose the dithizone and revert mercury to the aqueous phase. Excess of nitrite was reduced to hydroxylamine hydrochloride. Inorganic mercury compounds in the final solution was reduced to the elemental mercury with stannous chloride and measured by cold vapor Atomic Absorption Spectroscopy. 6.2.3. Sediment characteristics Method of collection Seabed sediment samples were collected at all 9 water sampling locations (Fig. 6). Seabed sediments were collected using Vanveen grab, whereas shore sediments were collected using handheld shovel. After collection, the scooped sample was transferred to polythene bags, labeled and stored under refrigerated conditions. On reaching the laboratory the sediment samples were thawed, oven dried at 40?C and ground to a fine powder. Method of analysis Size distribution: The sediment samples were dried and sieved. The fractions retained in each mesh size were weighed. Total nitrogen: Total nitrogen from the sediment sample was estimated by extracting the sediment with an extracting reagent (CuSO4 and silver sulfate) and shaking the experimental flask for 15 minutes. Later Ca(OH)2 and MgCl2 was added and the contents filtered through Whatman filter paper. A known volume (5 ml) of the filtrate was used for total nitrate estimation similar to the process used for water samples (reduction by passing through a cadmium column). Total Phosphorus: Total Phosphorus of the sediments was estimated by initially digesting the sediment samples in sulfuric acid for 30 minutes to oxidize phosphorus to phosphate. After filtration, a known volume of the filtrate was allowed to react with ammonium molybdate and reduced using ascorbic acid to form a blue coloured complex which was measured at 880nm using a spectrophotometer. Total Organic Carbon: TOC was determined by Wet oxidation method. The sample was added with potassium dichromate followed by Sulfuric acid and after cooling by adding distilled water a drops of diphenylamine indicator and pellets of sodium fluoride was added, and sample was titrated against Ferrous ammonium sulfate. Cadmium and Lead: Sediment sub-samples were collected and sealed in plastic bags and frozen till the analyses were carried out at the shore laboratory. These were thawed and dried in oven at 40°C. The dried sediment was then finely ground and digested with hydrofluoric acid in a pre cleaned acid washed Teflon beaker. During this process the silica volatized as silicon tetrafluoride. This was followed by treatment with nitric and perchloric acid to destroy the organic matter. The residue after the evaporation of acids was dissolved in dilute hydrochloric acid. The metals were determined on a graphite furnace Atomic Absorption Spectrophotometer, calibrated with suitable standards digested similarly and measured at recommended wavelengths. Mercury: Sediment samples were oven-dried at 40°C and crushed to fine powder. About 0.5 gm aliquot of the sample was transferred into 300 ml BOD bottles (in duplicate). 5 ml of Milli Q water and 5 ml Aqua Regia were added and mixed with the sample. The samples were heated for 2 minutes in a water bath at 90°C. On cooling 20 ml of Milli Q water and 15 ml of KMnO4 solutions were added to each. After thorough mixing, the samples were again heated in the water bath for 30 minutes at 90°C. On cooling 6 ml of sodium chloride- Hydroxylamine hydrochloride reagent was added to each bottle to reduce the excess permanganate and the final volume was made up to 75 ml. Blanks and standards were also digested similarly. Mercury compounds in the final solution were reduced to elemental mercury with 5 ml of 20% stannous chloride and measured by cold vapor Atomic Absorption Spectrophotometer at 253.7 nm. Primary Productivity: Primary
Production was estimated at all 9 locations where water samples
were collected (Fig. 6). From the water sampler, the samples were
immediately transferred to 125 ml Dissolved Oxygen (DO) bottles
(two light bottles and one dark bottle). One light bottle containing
sample was fixed with Winkler A and Winkler B for analysis of
initial oxygen content. The other light bottle and dark bottle
with sample were kept in a bucket containing same water sample
for 6 hours to allow photosynthesis and respiration. After 6 hours
the samples were fixed with Winkler A and Winkler B, and later
the DO was analyzed in the laboratory. The increase in dissolved
oxygen of water as a result of photosynthesis was measured in
the light bottle, simultaneously the decrease in oxygen content
in the dark bottle was measured to estimate the respiration alone
in the same sample of water. From the DO values the amount of
organic carbon synthesized during photosynthesis was calculated. Zooplankton: Zooplankton samples were collected at 5 locations viz., station W14 along transect 1, station W7, W9 and W11 along transect 2 and station W17 along transect 3 (Fig. 6). Zooplankton net (300 micron) was towed 0.5 m below water surface for 10 minutes and the collected samples were immediately preserved in 5% formalin. The preserved zooplankton samples were transferred into sedimentation chamber for settlement. After settlement, 1 ml aliquot of sample was taken for quantitative population analysis. Depending upon the biomass concentration, sub samples were taken to study the whole species diversity. Organisms were counted and identified upto genus level under a microscope using standard identification key counting chamber. The biomass values of zooplankton were calculated from the displacement volume of water. Macro Benthos: Seabed sediment samples for macro benthos were collected using Van Veen grab sampler at 9 locations where the water samples were collected (Fig. 6). The intertidal benthos samples were collected at three stations (B1, B2 and B3) as shown in Fig. 6. The benthic organisms were separated by sieving through 500 micron mesh and preserved using formaldehyde with rose bengal. The samples were sorted and identified upto groups/Genera level using stereo zoom microscope. The wet weight was taken to calculate the biomass of benthic organisms. Microbiology: The microbiological samples were collected at 9 locations where water samples were collected (Fig. 6). Samples were collected in sterilized bottles and preserved for analysis. Pour plate method was used to culture the microorganisms. The agar media used for analysis were: Nutrient agar, MacConkey agar, M.FC agar, Thiosulphate Citrate Bile Sucrose agar, Xylose Lysine Deoxycholate agar, M. Enterococcus agar and Cetrimide agar. Plates were incubated at 37oC except for total viable bacterial count, for which the plates were incubated at room temperature (28oC). After 3 days, the organisms were counted and identified based on their colour characteristics. Fisheries: The information on fisheries and their potential were collected from local fishing villages and from the Department of Fisheries, Govt. of Tamilnadu. Coastal vegetation and Seaweeds:
The shore plants over the sand dunes and seaweeds were collected
and Herbarium was prepared for further identification in the laboratory.
Wind The month wise distribution of wind speed and direction are shown in Table 2. It is observed that during April, May, June and December wind speeds were around 10 -11 knots and during the remaining months wind speeds were varying between 7 and 9 knots. During April to September, the morning wind mostly prevailed from SW and W, and during November to February, it mostly prevailed from NW. The wind patterns during morning hours and evening hours show the influence of land-sea breeze system in this region. During the days of depressions and cyclones, the wind speed commonly exceeds 50 kmph. Storm The tracks of cyclones which have crossed the coast near Chennai (within 150 km on either side) during 1877 to 1990 are presented in Table 3. It indicates that totally 58 storms had occurred within 300 km off the project region. The occurrence of storms in this region are more frequent in November (23) and in October (19). Among them about 37 number of storms had crossed the coast within 300 km distance during 1877 to 1990. Currents The variation of current speed and direction measured at stn. C1 (1000 m into sea), and stn. C2 (2000 m into sea) are shown in Figs. 8 and 9 respectively. At stn. C1 (1000 m from shore),
the current speed persisted between 0.02 and 0.30 m/s. The current
direction remained unidirectional towards 350o consistently during
the measurement period. At stn. C2 (2000 m from shore), the current
speed persisted between 0.02 and 0.20 m/s. The current direction
remained unidirectional towards 350o consistently during the measurement
period. The earlier study shows that the tidal effects on currents are relatively of small order compared to the contribution from the wind. By the onset of northeast monsoon (i.e. from mid October to mid March) the currents set in towards south, During the rest of the year, i.e. in southwest monsoon and fair weather period, the coastal currents turn towards north consistently. |
||||||
