Introduction
The rate at which we deplete and degrade our fresh aquatic resources poses a great threat to our future life support system. The rise in human population exploits more of natural resources and this is met through the growth of industries specifically chemicals and petrochemicals, urbanisation, deforestation and intensive agricultural practices. The industries and urban sprawl discharge the waste into river. The deforestation process itself aggravates the sedimentation transport into the streams. And the use of chemicals in the crops for better production contaminates ground water through percolation, and rivers and lakes through surface run-off. All these sporadic degrading activities have lead to gradual deterioration in the quality of surface and subsurface water. The loss of quality is causing health hazards and death of human, livestock and death of aquatic lives, crop failure and loss of aesthetics. Keeping in view the importance of good water quality, the Central Pollution Control Board (CPCB), in 1976, initiated a series of integrated river basin studies all over the country. CPCB in collaboration with the State Pollution Control Boards (SPCB) established the Water Quality Monitoring (WQM) network in the country. The CPCB has identified river stretches all over the country, which have been polluted to the maximum extent. The Krishna river, which is one such polluted rivers of the country, flows in the states of Maharashtra, Karnataka and Andhra Pradesh. The present study is taken up for the monitoring, identification and suggesting preliminary measures of water pollution control in the Satara-Sangli stretch (stretch-I) of the Krishna basin in Maharashtra with the help of Geographic Information System (GIS). The stretch-I, also known as the country's sugar-belt, has been identified by CPCB and MPCB (Maharashtra Pollution Control Board) for the restoration of water quality under the National River Action Plan (NRAP).
Satara - Sangli Stretch
General
The Satara-Sangli stretch of the Krishna river in Maharashtra is known as the sugar belt of the country. The Krishna river flows with a southeasterly trend in Maharashtra, traversing a distance of 280 kms from Mahabaleshwar through Satara to Sangli [latitudes 160 00' N - 180 00' N, longitudes 730 30' E - 750 00' E, altitude 150-600 m] on a rocky area. The river is met by river Koyna, about 137 kms away from its source. Numerous seasonal tributaries dissect the basin giving rise to a dendritic pattern of drainage with a medium drainage density. The total geographical area of the Krishna basin in Satara is 10,816 km2 (4%) and that of Sangli is 8,572 km2 (3.2%). The districts of Satara and Sangli experience a warm-humid climate with an annual average precipitation between 600-800 mm. Eighty percent of the rainfall in the Krishna basin is influenced by the south-west monsoon giving rise to heavy rainfall on the west coast of the western ghats. The mean temperature varies between 22.5 - 25 0C. Usually, the geological formations consisting of Deccan traps are rich in basalt and dolomite type rocks. The soils in the basin are in-situ in nature and a major portion comprises mainly of medium black cotton (b.c) soils. These b.c. soils are the weathered derivations of the Deccan Basalts. Extensive bleaching and weathering of b.c. soils has given rise to red loamy and lateritic soils.
Landuse/ Landcover
Krishna basin covers a non-arable land area of 53010 km2 out of which 22.4% falls in Maharashtra. In Satara 2.1% of the reporting area is non-arable land while the same is 3.3% in Sangli. Forest land accounts for 1583 km2 (15.1%) in Satara and 488 km2 (5.6%) in Sangli. The total cultivable land in these two districts of the Krishna basin is 13,844 km2 that is 65.3% in Satara and 81.5% in Sangli. The districts of Satara and Sangli exhibit substantially wooded tropical evergreen forest. About 75% of the total forest cover is dominated by teak species. The common varieties of teak found in this category are Tectona grandis, Terminalia torrentosa, Adina, Laemnea and Cleistanthus collinus. Amongst all types of landuses, agriculture is dominant in Krishna basin with over 50% total land actually under cultivation. Table 1 shows that 86% and 83% of the cultivable land is actually under plough in the districts of Satara and Sangli. The intensity of cultivation is more clearly indicated by the average number of crops grown in a year given by gross sown area divided by the net sown area which equals to 1.10. The extent of irrigation applied for crops in Satara and Sangli is 16.9% and 11.1% respectively. The major crops grown in this area are cereals, pulses, jowar and sugarcane. Irrigation is done mainly using stream diversions or canals (42%) and ground water source (58%). About 21% of gross sown area is irrigated.
Fertiliser and Pesticide Consumption
To get higher yields in the cultivated land, farmers apply more and more of chemical fertilizers. Table 2 shows the fertilizer consumption in the districts of Satara and Sangli since 1980. The total chemical fertilizer consumption in Satara and Sangli during 1995-96 was 50390 and 83153 tonnes. With intensification of agriculture, particularly since introduction of higher yielding but low pest-resistant varieties of crops, the use of pesticides and biocides has been increasing steadily. The total pesticide consumption in Maharashtra is 711 MT/Year, of which 7% is consumed in Satara and 6.4% in Sangli. In these two basin districts organo-chlorine share is the highest. The application rate per hectare is about 0.09.
Water Consumption and Effluent Discharge
The state of Maharashtra is ranked first in terms of industrial investment in the country. Major industrial sectors are in power, fertiliser, sugar and cement industries. In satara and Sangli fifteen medium to large size sugar industries are located. There are many liquor factories located along the stretch-I. The quantity of water that is consumed for domestic, industrial and irrigation uses are respectively 66, 18 and 3366 MCM. Correspondingly, the amount of effluent that is being discharged from urban, industrial and irrigation are 29, 14 and 673 MCM. From the sugar factories and its surrounding domestic locations about 13400 and 1525 cubic meter of effluents are being discharged everyday.
A Framework for Monitoring Water Quality in GIS
River water quality monitoring is the process of regular study of parameters related to river water. It helps determining the quality trend and hence the threshold values for the restoration of water quality to its normal. Different factors those affect the water quality are physical, chemical and socio-economic parameters of the river basin. A detailed monitoring framework is shown in the figure 1. The present case study is followed up as per this framework. Using GIS, the database on pollution load, the relationship between pollution load with population, fertiliser consumption and factory location, and the river zonation have been assessed and graphically presented. The techniques of river zonation has been reviewed and modified. The prime objectives of using GIS over traditional methods are :
- Effective storage and analysis system for spatial and temporal databases such as maps on geology, geomorphology, soils, landuses and attributes on meteorology, population, water quality etc.,
- Spatial analysis on depicting the source-pollutant relationship,
- Graphical presentations, visual impacts and spatial distribution of graphical outputs on water quality changes, pollution load and relationship with sources and
- Management of river basins by generating buffer zones on the basis of water quality criteria.