Oil spill trajectory modelling of Chennai coast, east coast of India

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1 INCHOE (Proceedings) 5-7 Feb. Goa, India 9-99 Oil spill trajectory modelling of Chennai coast, east coast of India R. Mohan* 1, R.S. Kankara and R. Venkatachalapathy 3 1 -Department of Physics, Annamalai University, Annamalai Nagar-. Tamil Nadu, India. rethinamohan@gmail.com - Scientist-F, Ministry of Earth Sciences, ICMAM-PD, NIOT Campus, Pallikaranai, Chennai-, Tamil Nadu, India. kankara@icmam.gov.in 3 - Professor, Faculty of Marine Sciences, CAS-MB, Annamalai University, Parangipettai- 5, Tamil Nadu, India. venkatr5@rediffmail.com ABSTRACT Mohan, R., Kankara, R.S. and Venkatachalapathy, D.,. Oil spill trajectory modelling of Chennai coast, east coast of India, Proceedings of the Fifth Indian National Conference on Harbour and Ocean Engineering (INCHOE), 5-7 Feb., CSIR-NIO, Goa, India. Computational modeling play a vital role in order to prepare the impact of an oil spill and preparedness for contingency plan. Oil spill trajectory modeling attempt was made at Chennai coast. The Chennai coast is one of the high risks area for oil spill due to its exposure to oil related activities i.e. oil refinery, sub-sea pipeline, port and harbor, economical importance and close to tanker routes. Number of ships/tankers is being handled at Chennai port. These have increased the risk of oil spill in the coastal waters. Numerical model was setup to investigate the potential risk of an accidental oil spill along Chennai coast. The two probable spill scenarios, one for Fuel oil leak ( m 3 ) for hours at off Marina and other for 5 m 3 of crude (Bombay High) oil for instantaneous spill at anchorage area (off port) were considered. Current and wind are two main factor for oil transport. Therefore, a hydrodynamic model was setup and calibrated using measured water level and current data. The calibrated model was used to generate the circulation pattern over the year required for generating monthly oil spill trajectory. The oil spill was simulated for hours duration for each month/season considering prevailing current and monthly mean wind condition. The model simulation revealed that the spilled oil had tendency to move towards south-west direction to reach sandy shore less than hours after the spill was occurred in the ocean during NE monsoon. The results for both leak and instantaneous spill indicate that spilled oil will not move towards the marina beach during SW monsoon. More than % of the diesel and 5% of crude oil will be evaporated within h of oil spill. Based on the results, a suitable cleanup and contingency plan can be devised to mitigate the adverse impacts arising due to diesel spill in the study area. ADDITIONAL INDEX WORDS: Numerical Model; diesel and crude oil spill; MIKE; Chennai coast. INTRODUCTION The main source of oil pollution in oceans is from shipping and maritime activities. Nearly half of the world production of oil has been transported by the sea route(clark, 199). More than three million metric tons of oil contaminates the sea every year. Operational or accidental release of oil into the sea has caused harmful effects on marine environment and marine life, making oil spills a matter of international concern and global issue. Indian coastline extends to about 5 kms on the mainland and to about kms along two groups of islands. The Arabian Sea and the Bay of Bengal have been estimated to annually receive around 5x and x t/y petroleum respectively from routine discharges from oil tankers and other ships (Hinrichsen, 9). The majority of ships sailing from the Persian Gulf to Japan and China transports oil through the Indian Exclusive Economic Zone (EEZ). The port sector handles a large volume of oil, and many numbers of new oil industries are being set up in the coastal zone. Seagoing transport of oil poses the risk of oil spills that may occur due to accidents, grounding of ships, tankers, etc., which would cause extensive damage to the marine ecosystem and the living resources. Since the preventive measures can not eliminate the risk of oil spills in marine waters, it is necessary for effective and suitable mitigating measures to know about the fate of an oil spill on marine water and its impact on the marine resources. The numerical modeling approach has emerged as a useful tool to simulate the scenarios and address the issue of oil dispersion in the case of a spill. Computer models provide a valuable support to make predictions about the trajectory and fate of spilled oil in marine environment. Several oil spill models have been used in the past three decades based on transport and weathering processes (Kankara and Subramanian, 7; Kolluru et al., 199; Mackay et al., 19; Naidu et al., 13; Tkalich et al., 3; Vethamony et al., 7) In the present study, an attempt has been made to investigate the potential risk of an accidental oil spill along Chennai coast. STUDY AREA The Chennai coast is one of the high risk areas for oil spill due to its exposure to oil related activities i.e. oil refinery, subsea pipeline, port and harbour, economical importance and close to tanker routes. Number of ships/tankers is being handled at Chennai port. These have increased the risk of oil spill in the coastal waters. The past two decades, four oil spills incidents are reported in Chennai coastal water i.e. during August 199, November 199 and 1995 and January (Bluewaters., ). It shows the potential risks of oil spills Proceedings of the Fifth Indian National Conference on Harbour and Ocean Engineering (INCHOE) 9

2 Oil spill trajectory modelling along Chennai coast. A major spill may occur during normal operations, illegal oil releases like bilge water releases, tank washing, etc. These are created oil pollution threatens for coastal environment, tourist beaches and affect unfavorably the economic, ecological and biological life. The shortest time for the oil to reach the shoreline was identified through the numerical model simulation of the trajectory model as well as to estimate weathering process under the specified hydrodynamic and meteorological conditions. The study area is located between the longitudes of E and E and the latitudes of 5 N and N coast of 3 km long coastal stretch from Tiruvottiyur to Neelankarai. The coastal stretch containing fishing harbour, Chennai port, Adyar and Coovum river mouth, Marina & Besant nagar beach, Astalakshmi temple, Santhome church are located along the coast in study area (Figure 1). The coastline orientation is about in Northern part and in Southern side (Kankara et al., 11). Figure 1. Chennai coastal region MATERIAL AND METHODS A numerical modeling technique is applied for simulating spatial and temporal patterns of an oil spill under given environmental conditions. The numerical modeling approach has been emerged as a useful tool to simulate various scenarios of likely oil spills to understand the fate and behavior of oil for given scenerio. Two modelling packages i.e. MIKE-1 and ADIOS were used to simulate the oil spill in Chennai coast. MIKE-1 was used to generate the oil trajectory and to track the path of spilled oil under prevailing hydrodynamic and meteorological conditions. The two modules, namely MIKE1-HD for generating the hydrodynamics and Spill Analysis (SA) for spreading and dispersion analysis of hydrocarbons in marine environments, were used. The oil spill module MIKE 1 (SA) applies a Lagrangian discrete parcel method to predict the trajectory of spilled oil and estimate the fate and behavior of oil spills based on complex algorithmsdhi. (7). In the model, the oil is represented by a large ensemble of marked particles. The movement of each particle is affected by the Physio-chemical processes. Once the parcels are released in the water body, their discrete path and mass are followed and recorded as a function of time relative to the reference grid system. The details of depth-averaged two-dimensional hydrodynamic model are described Kankara et al. (11), were used to link oil spill module and to provide the data for the water movement in the study area. The weathering model ADIOS (Automated Data Inquiry for Oil Spills) predicts the changes in oil characteristics that may occur over time, under the influence of a variety of environmental conditions. ADIOS uses mathematical equations and information from the database to predict changes over time in the density, viscosity and water content of an oil or product, the rates at which it evaporates from the sea surface and disperses into the water, and the rate at which an oil-inwater emulsion may be formed Lehr et al. (1997). It was designed to make use of as little information as possible, and to use information that can quickly be estimated or obtained in the field, such as wind speeds, wave heights, water temperature, and salinity or density, the type and amount of oil or product spilled, and the rate and duration of the spill Lehr et al. (). Accordingly different oil spill scenarios were considered at specific period and trajectories of oil spill were studied for two different locations along Chennai coast. The fundamental of actual spill scenario with the information of oil type, volume of spill, release duration and release location, climatic condition are tabulated (Table 1). A hypothetical accidental spill of diesel and crude oil was used in this study. The results of the trajectory and fate model calculation determine both travel times and location of shoreline oiling, together with slick volume and amounts evaporated, dispersed and emulsified over time. Table 1. Details of scenarios considered in present study. Spill site with coordinates off Marina beach (.31917, 13.) Off Chennai port (.9, ) Channel ( , ) Spill duration *Predominant Mean Wind Effect Water depth (m) Type of oil Diesel Fuel Oil Spill volume (m 3 ) Crude Oil 5 hours Heavy Fuel Oil SW monsoon NE monsoon (I) Hydrodynamic simulation Climatic Scenarios SW and NE monsoon SW and NE monsoon Spill type Continuous Instantaneous 5 Monthly Instantaneous Wind Consideration Predominant Mean Wind speed and Wind direction * Predominant Mean Wind speed and Wind direction * Monthly Wind speed and Wind direction Wind Speed =. m/s: Wind Direction = 33 degree Wind Speed =. m/s: Wind Direction = 7 degree RESULTS The simulations of hydrodynamic model was calibrated and validated with the observed data and was used in the oil spill simulations. A typical plot of water surface elevation, current Proceedings of the Fifth Indian National Conference on Harbour and Ocean Engineering (INCHOE) 95

3 Mohan et al. speed and direction during NE monsoon condition are shown in figure. The length of the arrows shows the current direction and speed in the region. It was observed that the flow is towards southern direction. The model computed surface elevation are well comparable with field data and are grossly comparable for U and V velocity components to the overall period. The model computed surface elevation and V velocity component are highly correlated with observed data for.9 and.7 and moderate for U component (.1). The relative mean absolute error (RMAE) and index of agreement (IoAd) was. and.9 for surface elevation and.7 and.7 for U component and. and.5 for V component Kankara et al. (11). This hydrodynamic model along with monthly mean wind data was used to simulate monthly oil spill scenarios which are very useful for contingency plan. (II) Oil spill Simulations (a) Scenario-I (Oil spill at off Marina beach) In this case, the source location of spilled oil was selected off Marina beach over the duration of hours, m 3 of diesel fuel oil of accidential spill (continuous) at a depth of m. The predominant mean wind speed of. and. m/s and mean wind direction of 3 and 7 during SW and NE monsoon respectively were taken to run the model. During SW monsoon, the direction of spilled oil movement was noticed parallel to the shore towards north-north-east direction. The movement of the oil slicks and flow direction on the water surface was influenced by uni-directional coastal current and wind. During SW monsoon, spilled oil does not reach the coast. The oil in the water column runs up to hours from the time of initial spill and pass away from the model domain during SW monsoon (Figure 3a). Similarly, during NE monsoon, the slick movement was noticed towards the southwest direction (Figure 3b). The spilled oil reaches the shore within 3 hours after the spill and may affect the coastal reagion of marina beach. The. cm size of oil slick affected the shore and and migrated around a length of 1 km. (b) Scenario-II (Oil spill at anchorage area (off port)) The effect of wind force on the instantaneous spilled oil concentration on the surface area is examined. The oil spill simulation was carried out for hours, with a volume of 5 m 3 for crude oil at a depth of m along the specified spill site (anchorage area (off port)). The model was run to predict the movement of oil in both SW and NE season with predominant mean wind effect like scenario-i. The movement of oil spill was monitored after hours from the initial time. It was found that, the oil spill was moving towards north-north-east and south-south-west direction during SW and NE monsoon season respectively (Figure a&b). During the SW monsoon, the spilled oil crosses away from the model domain whereas, the oil dispersed in the water column over a period of time in NE monsoon. From the results it was found that there is no impact in the near-shore region, which may be due to the direction of tidal current and occurance of oil spill away from the coast. Figure. Synoptic view of current vector plot for NE monsoon 1 a) b) /11/ :: Scale 1: 1// :: Scale 1:1139 Figure 3. Simulated trajectory of diesel oil spill at off Marina with predominant wind effects during a) SW and b) NE monsoon Proceedings of the Fifth Indian National Conference on Harbour and Ocean Engineering (INCHOE) 9

4 Oil spill trajectory modelling 1 a) b) WS= m/s 1 WD=5 WD=7 WD=7 July August September WS=3 m/s 1 WD=5 WD= WD= // 1:: Scale 1:1139 1/5/ 1:: Scale 1:1139 Figure. Simulated trajectory of instantaneous spilled oil at anchorage area (off port) with predominant wind effects during a) SW and b) NE monsoon. October November December Figure. Monthly scenarios of spill for the duration of every hours during July to December. (c) Scenario-III (Simulation of monthly oil spill thickness and trajectories of hypothetical spill location of shipping channel) The effect of the monthly mean wind force at the instantaneously spilled oil concentration on the surface area is examined. For a specified spill site (shipping channel), the simulation was carried out for hours of the oil spill and observation was made for every hours about the volume of 5 m 3 for heavy fuel oil. The model has been run for predicting the total concentration of oil spilled with the varying wind speed and direction. After hours from beginning, the release of spilled oil was monitored. It was found that the oil spill reached the shore for the wind direction of E and SE. Chennai port and Royapuram fishing harbor areas are affected by this movement of spill during February, March, April and May. The movement of spilled oil was noticed towards SW direction during the month of October, November, December and January and may affect Marina beach and Coovum. From June to September, spill movement was observed towards NNE direction and oil found floating in water column. 1 1 WD=5 WS=.5 m/s WD=135 WD=9 WS=.5 m/s WD=135 WS= m/s WD=135 January February March WS=.5 m/s WD=7 The movement of the spilled oil particle was found which is due to uni-directional tidal current flow with the influence of wind also. The overall simulation results reveal that the surface oil thickness varied between and. cm (Figure 5 and ). These studies provids very valuable information of actual situation of an oil spill at the Chennai coast. (III) Simulation of Weathering Process As a second stage of simulation, the weathering conditions were analysed using ADIOS. The model has been run for the SW monsoon environmental conditions such as water temperature ( C), wind speed (. m/s), wind direction (3 ), current speed and direction (. m/s & ), wave height (. m) and salinity (3 ppt). Preplanning for a selection of oil can provide an excellent guidance during a weathering process and the m 3 volume of oil was selected from the model database. The oil mass balance was computed for Fuel oil no. (Diesel) and evaporation, vertical dispersion is simulated to yield estimates of the total volume of oil remaining. It was found that the model over forecasts about leaked oil for 15-% was lost due to evaporation during the early hours and -5% was vertically dispersed in the water column within 15 hours out of hours of duration (Figure 7). From the Figure, the model has been run for the NE monsoon environmental conditions such as water temperature ( C), wind speed (. m/s), wind direction (7 ), current speed and direction (. m/s & ), wave height (. m) and salinity (3 ppt). The 5 m 3 volumes of crude oil were selected from the model database. The simulation result reveals that % was lost due to evaporation during the early hours and 7-% was vertically dispersed in the water column more than hours of duration. April May June Figure 5. Monthly scenarios of spill for the duration of every hours during January to June. Proceedings of the Fifth Indian National Conference on Harbour and Ocean Engineering (INCHOE) 97

5 Oil viscosity (cst) Mohan et al. Figure 9 show the change in oil viscosity. As can be see, the viscosity of oil changes significantly with evaporation. If about % oil evaporates, their viscosities increase more than and times for diesel and crude oil respectively. DISCUSSION Figure 7. The fate of m 3 volume of diesel fuel oil leakage Figure. The fate of 5 m 3 volumes of instantaneous crude oil spill 1 Jun 7 Jun Jun 9 Jun a) Jun 11 The overall simulation results reveal that the surface oil concentration was varied between.5 and.3 cm for diesel fuel oil whereas, 5 and cm for crude oil. The movement of the spilled oil particle was found which is due to unidirectional tidal current flow with also the wind. From the findings, during SW monsoon the spilled oil at off Marina not reaching the shoreline does not mean that it will not pollute the water. The minimal impact was found along the shoreline for oil spilled at off Marina beach which may affect biological activities at near-shore region during SW monsoon. During NE monsoon, the oil patches reaches the shoreline and impacts were found to be high on Marina beach. Generally, the impact of spill is high along Marina beach which is nearest to Chennai port. The movement of spilled oil off port was noticed towards south-south-west direction during SW monsoon whereas, north-north-east during NE monsoon season. There is no impact in near-shore region and oil in the water column. However, the oil dispersion in the water column increased considerably with time due to the increase in density of oil and the variation of viscosity. The shoreline of Chennai and their area of operation are very sensitive due to the sandy beach, port activities, settlements, etc. The highest percentage of evaporation and lowest dispersion were noticed in the diesel oil due to its low viscosity. The results shows that the evaporation process was very fast at the initial stage of spill and slowed down subsequently. The results revealed that the priorities should be given to protect the area due to spilled oil along the Chennai coast as Marina beach, Chennai port, Fishing harbor, Coovum and Adyar river mouth, Elliot beach. These studies provides very valuable information for the consideration of the actual situation of an oil spill at the Chennai coast. If the spill occurred in this region, it may affect not only in terms of human life and the environment but also for coastal economies. This analysis provides valuable information that the oil remediation using dispersant or application of booms will be effective in the initial phase of spill. The residual oil, along with dispersed and dissolved components, would be a threat to a coastal and marine environment because either it would hit the coast or disperse in the water column over a period of time. Analysis of the oil transport, weathering, and computed oil thickness provides a way to investigate the environmental risks to the marine ecosystem due to a spill. 1 Jan Jan 5 Jan Jan 7 b) Jan Figure 9. The change in oil viscosity of a) Diesel and b) Crude oil CONCLUSIONS The monthly simulation of a hypothetical accidental oil spill showed that, the movements of oil mainly rely on the combined effect of tidal current and wind. In SW monsoon, the spill moves towards north-north-east direction while it moves south-south-west during NE monsoon. During NE monsoon season, the spilled oil has prolonged contact shoreline. The results shows that the spill occurred in nearshore region will reach the shoreline within to 3 hours depending on wind speed and direction. The oil mass balance was computed with hours of simulation for diesel and crude oil with their different volume. It was found that % of diesel oil was lost due to evaporation and -5% was vertically dispersed in the water column within 15 hours out of hours Proceedings of the Fifth Indian National Conference on Harbour and Ocean Engineering (INCHOE) 9

6 Oil spill trajectory modelling of duration. The % crude oil was evaporated and 7-% was dispersed in water column. The results are useful for both industry and government agencies, which require specific information at the planning stage or to respond to a spill incident. ACKNOWLEDGMENTS Tkalich, P., Huda, K. and Hoong Gin, K.Y., 3. A multiphase oil spill model. Journal of Hydraulic Research, 1(): Vethamony, P. et al., 7. Trajectory of an oil spill off goa, eastern arabian sea: Field observations and simulations. Environmental Pollution, (): 3-. The authors wish to express their sincere thanks to Dr. Sailesh R. Nayak, Secretary, Ministry of Earth Sciences, and Dr.M. Atmanand, Director, ICMAM-PD, Chennai and Dr. B.R. Subramanian, Former Director, ICMAM-Project Directorate, for their constant encouragement and for providing the requisite facilities for carrying out this work. The authors gratefully acknowledge Dr. T. Balasubramanian, Former Director, Faculty of Marine Science, Centre of Advanced Study in Marine Biology, Annamalai University, Parangipettai, and his team for their valuable support during the field campaign. REFERENCES Bluewaters.,. Blue waters : Newsletter on marine environment security. Blue waters : newsletter on marine environment security. Clark, R.B., 199. Marine pollution. Oxford University Press, New York. DHI., 7. Scientific documentation, mike 1 oil spill module, dhi water and environment. Horsholm, denmark: Dhi software. Hinrichsen, D., 9. Our common seas : Coasts in crisis / don hinrichsen. [electronic resource]. Sterling, VA Earthscan, International Institute for Environment and Development. Kankara, R.S., Mohan, R. and Venkatachalapathy, R., 11. Hydrodynamic modelling of chennai coast from a coastal zone management perspective. Journal of Coastal Research: Kankara, R.S. and Subramanian, B.R., 7. Oil spill sensitivity analysis and risk assessment for gulf of kachchh, india, using integrated modeling. Journal of Coastal Research: Kolluru, V., Spaulding, M.L. and Anderson, E., 199. A three dimensional subsurface oil dispersion model using a particle based approach. ARCTIC AND MARINE OILSPILL PROGRAM TECHNICAL SEMINAR, p.^pp.. Lehr, W., Jones, R., Evans, M., Simecek-Beatty, D. and Overstreet, R.,. Revisions of the adios oil spill model. Environmental Modelling and Software with Environment Data News, 17(): Lehr, W., Overstreet, R., Jones, R., Eclipse, L. and Simecek- Beatty, D., The next generation in oil weathering modeling. International Oil Spill Conference Proceedings, 1997(1): Mackay, D., Paterson, S. and Trudel, K., 19. Mathematical model of oil spill behavior. Environment Canada. Naidu, V.S., Sukumaran, S., Dubbewar, O. and Reddy, G.S., 13. Operational forecast of oil spill trajectory and assessment of impacts on intertidal macrobenthos in the dahanu region, west coast of india. Journal of Coastal Research: Proceedings of the Fifth Indian National Conference on Harbour and Ocean Engineering (INCHOE) 99