Oil Spill Management

Oil Spill Management

By: Staff Reporter
The threat for oil spill demands preparedness to protect sensitive habitats. Modelling is a useful aid for appropriate decisions to minimise damage.
Pollution

The bulk of the world’s oil is transported through sea and about seventy percent of India’s demand for crude oil is being imported via the oceanic route. Also many nations depend on oil imported from West Asia which passes through Indian Exclusive Economic Zone (EEZ). As a consequence, there is a constant risk of oil spills along ship routes, near oil handling facilities and ports. So far, 66 spill incidents have been reported in the Indian waters during the last twenty years (1988-2007), though most were minor.

The threat for oil spill demands preparedness to protect sensitive habitats and marine national parks along Indian coast such as Kachchh, Mumbai, Malvan, Goa, Mangalore, Kerala, Mannar, Kakinada, Haldia and Sundarban etc. However, the Gulf of Kachchh (GoK) is a priority region due to its strategic proximity to the Persian Gulf and its ecologically rich habitat. Although declared as the Marine National Park and Marine National Sanctuary, GoK is the hub of oil handling agencies catering to a present capacity of 78 MMT of crude oil against a total Indian import of 128 MT for 2007. Any possible incidence of collision of oil tanker in the GoK is bound to result in extensive damage to fish, corals, mangroves, and other inter tidal flora and fauna and the marine ecological system in the region. Proper understanding of the physical and chemical properties of crude oils and how they behave on the sea surface is crucial for activating appropriate spill control and clean up procedures.

 

Causes of oil spill

Spills happen due to bad weather (hurricanes, storms, and earthquakes), intentional acts of violence (like war, vandals or dumping) and human mistakes. Oil spills may be grouped into two categories like ‘operational’ and ‘accidental’. Spills from oil tankers worldwide, indicate that over 90 per cent are operational spills involving small quantities (<7 tonnes) during routine procedures such as loading, discharging and bunkering in ports or at oil terminals. Accidental causes such as collisions and groundings generally give rise to much larger spills, with nearly 84 percent of the incidents involving quantities in excess of 700 tonnes.

 

Oil spill in marine environment

There is several hundred type of crude oil depending upon their origin, physical and chemical properties. The physical properties which affect the behaviour and persistence of an oil spilled at sea are specific gravity, distillation characteristics, viscosity and pour point. All are dependent on chemical composition (e.g. the amount of asphaltenes, resins and waxes) of the oil. The transport of spilled oil however is not only governed by oil properties but also hydrodynamics, meteorological and environmental conditions. When the oil spill occurs on the sea surface, it spreads to form a thin film called oil slick.

The composition of slick changes from the time of the spill. Light (low molecular weight) fractions evaporate, water soluble components dissolve, and immiscible components become emulsified and dispersed in the water column as small droplets. The formation of an oil-in-water emulsion depends upon turbulence, but usually occurs within days to weeks after the initial spill. It forms thick pancakes on the water and intractable sticky masses if it comes ashore. After considerable time this disintegrates into lumps of tar. In some circumstances, the oil droplets may become attached to sediment particles in the water column and move towards seabed where oil gets buried leading to bacterial degradation, a much slower process. Although the individual processes causing these changes act simultaneously, but their relative importance varies with time.

 

Factors influencing oil spill

Oil Spill Modeling is a complex process, influenced by many factors, such as oil properties- surface tension, specific gravity, temperature, spreading, advection – waves, winds and current, and weathering. General environmental factors affecting oil spill weathering are water and air temperature, sea state and wind speed. Type of release, solar radiation, air temperature, water characteristics and sediment load are also important to some extent. High temperatures and wind speeds increase evaporation, which decreases the toxicity of the remaining oil. Temperature also influences the rate of microbial degradation. Computer models are able to consider temporal and spatial changes in these parameters for a given domain over a period. Oil moves at approximately 3.5 percent of wind velocity and at the surface current velocity.

 

Estimating the spill volume

It is very difficult to procure accurate information about oil quantity and its type. Therefore, to run the model initially, the quantity of spilled oil can be computed by visual observations. Subsequently the model can be updated using more precise information about oil quantity to generate the oil trajectory.

geographical features

Oil spill modelling

Computer models are able to make predictions to generate the likelihood of sensitive resources being threatened and associated time scales, using required data. Modelling exercise provides a clear idea about oil movement and will enhance the decision making strategy for necessary response. However, it is essential that the operator understands various limitations, such as water currents and inherent difficulties in predicting some oil fate processes. Modelling is only a predictive tool and cannot readily replace the need to monitor a spill physically in the event of an actual incident. This can be effectively verified from visual observations or remote sensing applications.

 

Mathematical Models

As per the Allocation of Business Rules 1961, Ministry of Earth Sciences (MoES) is responsible for coordination and regulatory measures for prevention, conservation and protection of the ocean. Accordingly, Ministry has taken up a R&D programme to understand the movement of oil in marine environment and identifying the resources at risk using two mathematical models of different level of complexity. One is a generic model, developed to predict the movement of oil and its fate in the Indian Ocean. The other is habitat specific model for detailed trajectory and impact analysis on marine resources. The generic model uses GNOME (Generalized NOAA Oil Spill Modelling Environment) computer code for tracking of oil spills from offshore to coastal areas of India. The model is based on wind speed, wind velocity, sea current, etc., with 60 to 18 km resolution. GNOME is capable of running in hind and forecast mode using diffusion, forecasted winds and forecasted regional currents for ocean state. The model also considers uncertainty parameter which can be decided based upon the data quality being used for the model.

 

Geographic information system

A GIS is useful in handling spatially referenced data which can hold information at any scale – with data from all sources residing together, including satellite images, air photos and standard cartographic products. These advantages should be exploited with careful use of data, respecting issues of common data scales and data quality. Information on bathymetry, circulation pattern, movement of oil, oil concentration and thickness, quantity of dispersed oil etc., may be incorporated in the maps. Also details about ecologically sensitive areas such as coral reefs, seagrass beds, mangroves, salt pans, mudflats, beaches and nature of shoreline, wildlife protected areas and fishing activities may be layered. Details of the areas of greatest sensitivity such as feeding and breeding areas, locations, which are important for threatened or endangered species, near shore shallow water fishing areas, should be gathered. Among socio-economic features, data on ports, harbours, jetties, boat ramps; industrial facilities, for example water intake system for power stations and desalination plants, coastal mining, and salt evaporation lagoons; recreational resources such as amenity beaches, bathing enclosures, water sport and game-fishing areas; and sites of cultural, historical or scenic significance, on or close to the shore, may be incorporated in the GIS application.

 

Use of GIS in Estimation

An operational GIS based information system was used to predict the comprehensive movement and fate of spilled oil in the Gulf of Kachchh, to explore different strategies to respond to an oil spill and quantify its impact on resources. To analyse the impact of an oil spill on marine organisms and resources, a model output was generated in terms of track of oil, oil thickness, area of dispersal and dissolved material. The model outputs were converted into a GIS compatible format. The results were then analysed using Arc-View to identify the resources that were ‘hit’ for a given scenario. The time exposition maps were prepared and overlaid on the resource map to quantify the resources at risk,

 

NATIONAL OIL SPILL DISASTER MANAGEMENT PLAN

The country has a National Oil Spill Management Programme since 1980 to protect coastal and
marine areas against spill damages. The Ministry of Home Affairs is the nodal Ministry for crisis management and the Coast Guard is the coordinating agency for combating spill pollution in maritime zones. The use of booms and skimmers to recover floating oil and dispersants to enhance natural dispersion are established methods of responding to oil spills. Response strategies to a spill are decided based upon the aerial/visual observations, quantification of floating oil, assessment of potential threat, protection of sensitive resources, shoreline clean up etc.

The spill management programme was reviewed in May 2005 wherein the MoES was entrusted with the additional responsibility of providing scientific support in monitoring and detection of oil pollution and spills, predicting its movement towards Indian shores and assessment of extent of damage along with existing responsibility of scientific monitoring of oil pollution through Coastal Ocean Monitoring and Prediction System (COMAPS) Programme.

The Ministry has taken up a project on ‘Oil Spill Modelling’ during XI plan period under COMAPS Programme. 18 priority areas to be placed in a model are Dwarka, Mumbai, Dhanu, Goa, Mangalore, Cochin, Neendakara, Vizhinjam, Kavaratti, Kanyakumari, Gulf of Mannar, Chennai, Pulicat, Kakinada, Visakhapatnam, Paradip, Hooghly and Sundarban to understand movement of oil in a marine environment and identifying the resources at risk. The GIS based Oil Spill Tracking System works as a useful aid to meet a number of requirements for oil spill responders and planners to take appropriate decisions to minimise the environmental and economic damage to the shoreline.

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