The state of Karnataka extends roughly from 11°.35' North latitude to 18°.30' North latitude and 74°.5' East longitudes to 78°.35' East longitudes. Karnataka’s total land area is 1.91.791 sq km. As per 2011 census, the state’s population is 6.11 crore persons out of which 3.11 crore are males and 3.0 crore are females (sex ratio of the state is 968 and density per sq. km is 319). It is 5.05% of all India population of 1.21 billion

Most of the large tanks were built by rulers, chieftains, rich merchants, or religious men as charity works in the distant past. They are often called sagara or lakes. The Shantisagara tank near Channagiri (Shimoga) for example, has a water spread of 41 sq km and the Watadahosahalli tank near Gudibanda (Kolar) irrigates nearly 1,000 hectares. Such large tanks are, however, only few in number and more than 90 per cent are small units with less than 40 hectares ayacuts, 16,400 have an ayacut of less than four hectares each.

Figure 2

The performance of tank irrigation is not satisfactory in recent years. At one time, this was a main source of irrigation in the state. In the past, tanks were managed by rural communities as a community resource. Unfortunately, in recent years, they are neglected and their maintenance has been considerably deteriorated.(Ministry of water resource report-2018)

Figure 3

Tanks had the largest area under irrigation (44.25 per cent of net irrigated area) in 1956-57 and canals came a distant second with 22.50 per cent. The decline in tank irrigated area is attributable mainly to the reduction in their storage capacity as most tanks have silted up and their weirs, some of which are very old, have collapsed for want of repairs. The funds granted by the government for tank maintenance are grossly inadequate and the irrigation users also do not come forward to share the cost or work, thus allowing an enormous potential worth scores of major schemes, to go to waste-a major failure of the Karnataka state, (extract from the irrigation report 2003-04)

Over 70 per cent of the 3,524 minor irrigation tanks in Karnataka have gone dry due to poor monsoon rains. Minor irrigation tanks play a vital role in the State's food grain production and cover a total ayacut area of 4.19 lakhlhectares. According to Karnataka minor irrigation department statistics, at the end of two south-west monsoon months of monsoon rains, 28 per cent of the tanks have storage capacity of 30 per cent to 50 per cent of their capacity. Only one per cent of the tanks had storage of more than 50 per cent.

It is one of the traditional methods of irrigation practiced since ancient times in almost all the districts of the state. Tank irrigation has shown sharp decline over the last 50 years from 44.25% in 1956 to only 6.17% in 2019. Even the spatio-temporal patterns of tank irrigation have undergone phenomenal change in the state over a period of 6 decades. The below table gives a clear picture of changing pattern of tank irrigation.

Figure 4

In 1956, tank irrigation was extensively found in almost all the districts of the state except Bidar and Bijapur districts. Bangalore, Kolar, Tumkur, Hassan, Chitradurga, Shimoga, Dharwad and Uttar Kannada districts practiced tank irrigation with their full potential. In 1976, there were 7 districts under the category of less than 10% showing a declining trend. In 2019, except Shimoga, all the districts of the state lost area under tank irrigation drastically.

The sustained and pervasive decline of area under tank irrigation is a pointer to a great contention of the present study. As a source of irrigation, tanks compare unfavorably with canals, both in respect of productivity and stability gains. While the land productivity gains are found to be quite modest, the agricultural stability gains turn out to be rather precarious. Land was an abundant resource in ancient times; hence large tanks were built by native kings, but now, land is quite a scare resource. Moreover, tanks submerge fertile, cultivable and more useful land when compared to dams which are usually constructed on hilly regions (Pandey 1979). It is because of the present high value of land on one hand and high density of population on the other hand that the tank beds have been extensively encroached upon by both tank beneficiary farmers and settlers on the fore shore side of tanks.

The main reason for this decline is silting of tanks, failure of monsoon, encroachment of tank area, poor maintenance etc. In Bangalore urban districts, the major reason for vanishing of tanks is speedy growth of urbanisation. Many residential layouts growing like mushrooms have swallowed large tank areas in recent years. According to many town planning experts, frequent inundation of waters during monsoon in Bangalore city is due to construction of houses on the encroached tank area.

Embanked tanks are an integral part of the rural landscape of Karnataka. They formed till recently, an extremely important irrigation source in the state. In spite of a decline in their number in recent years, Karnataka still has about 36,000 tanks, their ayacut size varying from a few to over 500 hectares

The main reasons for this decline are

Silting of tanks

Failure of monsoon

Encroachment of tank area

Poor maintenance

Too many tube wells.

Lack of proper policy by the government

Rain water harvesting policy should be adopted. Periodic desilting of tanks should be taken. Encroached area should be regained through strict and stringent government policy. Tanks should be well connected to major canals of river valley project

Suitable adjustments in the cropping patterns and improvements in irrigation techniques can bring about a lot of efficiency and save substantial loss of tank water.

There is need to effect these changes, particularly in the irrigation of paddy and sugarcane, which crops with only about 12 per cent of the total cropped area consume more than 40 per cent of irrigation water. They require 3-4 times the water needed for irrigating crops like jowar, ragi,maize and other oil seeds. Scientific policy should be evolved for drilling tube wells. Rejuvenation and renovation of tanks should become the immediate concern for the government.