Whether for irrigation, power generation, drinking, manufacturing, or recreation, water is one of our most critical resources. Visual Image interpretation can be used in a variety of ways to help monitor the quality, quantity, and geographic distribution of this resource and also deciphering ground water with help from aerial photograph.
Sediment pollution is often clearly depicted on aerial and space images. Materials that form films on the water surface, such as oil films, can also be detected through the use of aerial and satellite images. Normal colours or ultraviolet aerial photography is often employed for the detection of oil films on water.
Thick oil slicks have a distinct brown or black colour. Thinner oil sheens and oil rainbows have a characteristic silvery sheen or iridescent colour banding but do not have a distinct brown or black colour.
Jharkhand State now a days is affected with ground water scarcity forcing the people to depend on the surface water like lakes, rivers etc. which are polluted like Damodar river and Suwarnrekha river. Damodar river flowing through coal fields is affected with sediment pollution carrying coal mining wastes leading to lowering of water level from November to June.
In this paper, we are concerned principally with the use of visual image interpretation in water pollution detection, and deciphering of groundwater with special reference to Jharkhand State of India.
Water pollution is any physical or chemical change in water that can adversely affect organisms. It is a global problem, affecting both the industrialized and the developing nations. It is harmful to humans, animals, to desire able aquatic life or otherwise causes significant departures from the normal activities of various living communities in or near the bodies of the water.
All naturally occurring water contains some impurities. Water is considered polluted when the presence of impurities is sufficient to limit its use for a given domestic and /or industrial purpose. Not all pollutants are the result of human activity. Natural sources of pollution include such things as minerals leached from soil and decaying vegetation. When dealing with water pollution, it is appropriate to consider two types of sources: point and non point. Point sources are highly localized, such as industrial outfalls. Non-point sources, such as fertilizer and sediment runoff from agricultural fields, mining wastes, have large and dispersed source areas.
It is rarely possible to make a positive identification of the type and concentration of a pollutant by visual image interpretation alone ( Lillesand and Kiefer,2000). However, it is possible to use visual image interpretation to identify the point at which a discharge reaches a body of water and to determine the general dispersion characteristics of its plume. In some instances, such a s the case of sediment suspended in water, it is possible to make valid observations about sediment concentrations using quantitative radiometry coupled with the laboratory analysis of selective water samples. Sediment pollution is often clearly depicted on aerial and space images.
According to Verner (1977) the detection of pollutants in water is more complex because the light attenuation characteristics of water limit detection of below-surface pollutants to the visible and near-visible portions of the spectrum. Even for surface pollutants, detection is often difficult, because the characteristic scattering or reflection of sunlight by pollutants is a function of the state of surface roughness as well as the angle of incident and reflected sunlight. Also, many dissolved chemicals have no spectral signature detectable through remote analysis. On the other hand, there are classes of pollutants that may be detected when water surface conditions and sun angle permit. These are particulates, algae, petroleum products, and thermal anomalies.
Materials that form films on the water surface, such as oil films, can also be detected through the use of aerial and satellite images. Oil enters the world’s water bodies from a variety of sources including natural seeps, municipal and industrial waste discharges, urban runoff, and refinery and shipping losses and accidents. Thick oil slicks have a distinct brown and black colour. Thinner oil sheens and oil rainbows have a characteristic silvery sheen or iridescent colour banding but do not have a distinct brown and black colour (Lillesand and Kiefer,2000).
Direct human interventions over the years have lead to reduction in groundwater recharge. These include deforestation, destruction of local water systems (including traditional water systems, e.g. ponds, tanks, lakes, wetlands and so on). Deforestation also leads to change in river flow regime in the affected area that also affects the recharge in the given area.
There are larger and indirect human interventions that has also affected the groundwater recharge systems, including urbanization, concretization of more and more land, the those factors that lead to global warming also contribute in reduction in groundwater levels as evapo-transpiration needs are higher when temperatures go up, leading to more groundwater use.
Mining also leads to destruction of groundwater recharge systems in the mined areas. In fact mining areas (like Jharkhand) groundwater is many times unnecessarily pumped out to the near by rivers so that mining becomes possible.
A knowledge of groundwater location is important for both water supply and pollution control analysis. Groundwater is one of the most important source of water. Almost 85% of the rural water supply in India is dependent on groundwater (Ministry of rural Development, government of India). Remote sensing plays a vital role in delineating potential areas of groundwater occurrence for detailed exploration, thus reducing the cost and time involved in groundwater exploration. Potential groundwater areas cannot be seen on satellite images directly. The clue to the groundwater search is the fact that sub-surface geological elements forming aquifers have almost invariable surface expressions, which can be detected by remote sensing techniques (Joseph,2005). Satellite data provide information about geomorphic features, structures, land uses and rock types (in a few cases) indicating the presence of groundwater. Some selected landforms and structural features that are indicators for potential groundwater zones are valley fills, palaeochannels, alluvial fans, dykes, interdunal depression etc.
Case study of Jharkhand State:
Jharkhand meaning “forest tract” is the ancient name given, as a whole, to the forested upland geographically known as the Chotanagpur plateau forming the north-eastern portion of the peninsular plateau of India. It is a region of great unevenness consisting of a succession of plateaus, hills and valleys drained by several large rivers such as the Damodar, Subernarekha, Barakar etc.
On the basis of physiographic consideration, this plateau can be further sub-divided into the Ranchi and Hazaribag plateau.
The Chotanagpur plateau as a whole represents a denuded old land surface constituted of granitic rocks with associated metamorphic and basic igneous rocks as also two linear stretches of Gondwana rocks having coal basins running east-west in Hazaribag, Palamau and Dhanbad districts and north-south in Santhal Parganas districts, demarcated by faults on either sides.
The plateau has a number of drainages flowing almost in all directions. The northerly flowing rivers are the Son, North Koel, Punpun, Phalgu etc. Amongst the easterly flowing rivers, the Ajoy, Barakar, Damodar and Subernarekha are by far the most important ones. The southerly flowing rivers are the Sankh, south Koel etc. ( Central Ground Water Board Report 1976-1985).
A major part of the Jharkhand State are covered by yellow to reddish and medium light coloured catenary soils (Mahadevan, 2002). In the Netharhat Plateau of Palamau districts and the Rajmahal Plateau, soils derived from basaltic flows are black and heavy and develop wide cracks when dry and swell when wet.
Deciphering surface water pollution from Aerial photographs:-
Large scale mining operations and rapid urbanisation has adversely affected the surface water quality in Jharkhand State. Liquid effluents from coal handling plants, colliery workshops, and mine sites and suspended solids from coal washeries and mine wastes have caused serious water pollution in the region, adversely affecting fish and aquatic life. Damodar and Subernarekha valley are the cradle of industrialization in Chotanagpur plateau region. Damodar is the most polluted amongst Indian rivers. About 130 million litre of industrial effluents and 65 million litre of untreated domestic water finds way to Damodar drainage system every day.
The release of different toxic metals like arsenic, mercury, chromium, nickel etc. from the coals and mine spoil heaps in Damodar and its tributaries have caused severe damage to water quality ( Priyadarshi 2004 ,Priyadarshi 1999).
Sediment pollution is a tedious problem in major rivers of the Jharkhand. Sediments make the rivers, streams, channels and reservoirs to overflow. They also change the flow rates and depth of water systems( Sharma and Kaur, 1994). Sediment pollution is clearly depicted in Damodar river in above figures. In both figures silt laden Damodar river is seen passing through Coal fields of Jharkhand State. It has not only narrowed the river bed and flow but also posing threat to the existence of the river. Source of the sediments in this river are soils and remains of coal mine wastes deposited along the river sides which are washed away from the land by rain waters and surface runoff. These sediments may be the carrier of different trace elements like arsenic (already present), lead, nickel, chromium etc. as the coals of these areas contain above mention elements (Priyadarshi,2004; Geological Survey of India,1982). It may affect fish population by blanketing fish nests and food supplies. It may also reduce the sunlight available to green aquatic plants.
Phosphorus is often regarded as the main culprit in cases of eutrophication in lakes subjected to point source pollution from sewage. The concentration of algae and the trophic state of lakes correspond well to phosphorus levels in water.
State is occupied by hard rocks belonging mostly to Archaeans and Palaeo-Mesozoics (including Gondwanas), and these hard rocks bear groundwater only in their weathered top portion which rarely exceeds 10 metres. Joints and cracks in hard rocks also contain groundwater (Geological Survey of India, 1974).
Sediment pollution is clearly depicted in the Damodar river flowing through the coalfield area. The aerial photographs helped us to identify potential areas of groundwater where detailed geophysical surveys can be carried to confirm availability of water. It has also helped in concentrating the field in selected areas where greater potential of groundwater may exist. It has also helped us to identify the sites where the check dams can be built to recharge the groundwater.
· Central Ground Water Board Ministry of Water Resources, Government of India (1976-1985). Monitoring of ground water from hydrogeological and chemical data of national hydrograph network stations in Bihar. Series “D”, No.8 Calcutta.
· Geological Survey of India (1974). Geology and mineral resources of states of India, part V-Bihar, No.30.
· Geological Survey of India Bulletins (1982). Trace elements studies in the major tertiary and gondwana coalfields of India, no.49 pp.66.
· Joseph, G. (2005). Fundamentals of Remote Sensing (2nd ed.). University Press, Hyderabad.
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· Priyadarshi, N. (1999). Trace metal concentration in Damodar river of Bachra area of North Karanpura Bihar. In book “Environmental crisis and protective measures with special reference to the Chotanagpur region of Bihar”, edited by Sahay,U. and Bhagat, L.N. Jawaharlal Nehru College, Chakradharpur, Jharkhand, pp.49-55.
· Priyadarshi, N. (2004). Distribution of arsenic in Permian coals of North Karanpura coalfield, Jharkhand. Jr. Geol. Soc. India, vol.63, pp. 533-536.
· Sharma,B.K. and Kaur, H. (1994). Water pollution. Goel publishing house, Meerut.