The Krishna Basin India
The Krishna Basin is India’s fourth largest river basin and covers 258,948 km2 of southern India, traversing the states of Karnataka (113,271 km2), Andhra Pradesh (76,252 km2) and Maharashtra (69,425 km2). (See figure 1.)
The basin is relatively flat, except for the Western Ghats and some forested hills in the center and northeast. It lies mostly on granites and basalts with limited groundwater potential, with some deep alluvium in the delta with high groundwater potential.
The basin is home to some 74.2 millions inhabitants. The population density is 287 inh/km²—with people concentrated in the irrigated areas and metropolitan urban centres. The lowest densities are recorded in the southwest and centre of the basin in Karnataka state (Deccan plateau). Some 68% of the population lives in rural areas and are dependent on agriculture for their livelihoods.
The basin’s climate is largely semi-arid, but there is a narrow north-south strip along the Western Ghats that is humid, a dry-sub humid area in the Krishna Delta, and it is arid in the rain-shadow east of the Western Ghats.
Annual rainfall averages ~800mm but ranges from below 300mm in the northwest, to ~1000mm in the delta, to a maximum of over 2000mm in the Western Ghats. About 90% of the rainfall is received during the monsoon months of May to October. Potential evapotranspiration varies spatially over the basin and is highest in the south and the east while lowest records are registered in the northwest. Evapotranspiration exceeds precipitation in all but three months of the year during the peak of the monsoon (July, August, and September), which makes irrigation necessary during the other periods of the year—notably in the east, and the northwest of the basin. The basin has been divided into 12 sub-basins for the hydrological study: Upper Krishna, Middle Krishna, Ghataprabha, Malaprabha, Upper Bhima, Lower Bhima, Lower Kishna, Tungabhadra, Vedavati, Musi, Palleru and Munnaru
Most of the area in the basin lies on crystalline and basaltic rocks whereas soil is generally shallow clayey with some areas of gravelly clay and loamy. Soil type in western part is Entisols and Vertisols (black soil) whereas Alfisols (red soils) in south and east. Krishna causes a high degree of erosion in monsoon season. It takes fertile soil from upstream areas of Maharastra and Karnataka and deposits in delta regions. Soils on an average are deeper in valley bottoms and also deep in Andhra Pradesh.
Diversified cropping pattern persists in the Krishna basin. Principal crops, which are being cultivated are: rice, sorghum, corn, sugarcane, millet, cotton, groundnut, and variety of horticultural crops. The total cultivable area in the basin is about 203,000 Km2, which is equivalent to 77% of the total geographical area of the basin. About 47,200 km2 have irrigation potential. Moreover, the basin has a total hydropower potential of 2,997 MW at 60% load factor.
Existing and forecasted uses and concerns
The total storage capacity of major reservoirs larger than 200 MCM is 42,910 MCM. In total, the storage capacity of major and medium reservoirs in the basin have almost reached the total water yield. Therefore, the basin is nearly completely closed. Discharge at the Vijaywada gauging station has drastically reduced since 1960. The average yield at this gauging station during 1901-1960 was about 6500 m3/sec in the month of August. It has come down to about 100 m3/sec in 2000-04. Moreover, the basin is not only closed at the mouth of sea but discharge has been substantially reduced also at sub-basin level. For instance, discharge from the Upper Bhima river has declined from an average of 8,816 MCM in 1970-80 to 3,615 MCM during 1994-2004, reflecting the upstream development in the sub-basin. T
he closing of the basin has resulted in an additional 36,000 MCM of water being evaporated to the atmosphere every year. This has changed the atmosphere, including increased humidity and decreased temperature in areas of extensive irrigation development.
Domestic and industrial demand has also increased with increasing population in the basin resulting in competition among different demand sectors. The massive developments proposed by each state provoked conflict between them for their water rights. To resolve conflict among three states, the Krishna tribunal was formed in 1969. The tribunal assessed the water in each sub-basin and allocated water based on “equitable apportionment” in 1976. Importantly, KWDT (Krishna Water Dispute Tribunal) allocated 11,740 MCM of surplus water from Upper Krishna to Lower Krishna that has 12,740 MCM water deficits.
Despite the lack of additional water supplies, development of both surface and groundwater continues, primarily for irrigation. Water extractions for agriculture, industrial, and domestic uses continue to grow to support one of the fastest developing regions of peninsular India. As the three states share the shrinking water resource, basin closure has aggravated interstate water conflicts.
Rapid urbanization in the basin also makes demands on water supplies. Hyderabad city, for example, now has 7 million people and consumes 380 million m3 of water annually. Much of the urban water supply returns to the local Musi River as wastewater and is used for irrigation, which has important consequences for human health, soil salinity and the environment. The downstream state, Andhra Pradesh, has experienced a shift in land use while Karnataka and Maharashtra, which lie further upstream, have large dry regions and want to continue developing their water resources to maintain their agricultural growth and reduce poverty. Furthermore, crop yields in the basin still average less than half their potential, presenting opportunities to improve water productivity.