After reading this article you will learn about water harvesting and recycling in India.
In India, the first major attempt to harvest water in earth-cum-masonry dam was initiated prior to 150 A.D. near “Girinagara” in drought prone Kathiawar district of Gujarat.
Major efforts in harvesting water resources in Deccan plateau were made through tanks or ponds, mostly of embankment type to harvest monsoon rain and distribute it to the fields below. In 1876, there were more than 33,000 tanks in Madras Presidency with irrigation potential of approximately 100 acres in each case.
The National Commission on Agriculture in 1971 assessed that it may not be possible to provide irrigation to more than 40% of cultivable land area in India even with utilisation of all available water resources in the form of major and medium river valley project schemes. The remaining 60% of land area shall remain dependent on available monsoon rains as source of water for crops.
Recent studies have shown that the crop production can be increased substantially by providing one or two life-saving irrigation in times of moisture stresses of crops by harvesting surplus water flowing out as runoff during monsoon periods (Table 11.2). This calls for development of water harvesting and recycling techniques which could be adopted in small watersheds.
The annual precipitation in the Indian sub-continent has been assessed as 1223 million ha- m of which about 553 million ha-m is last as surface flow (Table 11.2), 406 million ha-m as evaporation or evapotranspiration and remaining 264 million ha-m is retained either as soil water or recharge to ground water.
The runoff water results into floods which has caused loss of more than Rs. 6,000 crores in the last two decades.
The major river valley projects for storage of irrigation water are in the resource regions (i), (iii) and (iv), and for diversion irrigation in the regions (ii) and (v).
The monsoon rain, generally occurs in the form of high intensity short duration storms inducing high surface runoff and flash floods. If such surplus water occurring in one or few phases during monsoon months is stored in ponds and reservoirs and recycled for crop use, the possibility of large scale crop failure can be greatly avoided.
Depending upon the size of the watershed contributing to runoff, and site where water can be stored with minimum losses, the surface runoff harvesting programme can be practiced effectively.
In designing runoff harvesting structures at DVC, an average runoff of 45 to 50% in cases of upland catchment was assumed by Hakim (1952). He opined that storage or water spread areas may be assumed between 1/6th to1/8th of the catchment with tentative water depth of 3 m in the ponded area.
The use of farm ponds (Fig. 11.1) for ensuring rabi crops for rainfed agriculture has been found economical in Dehradun region. About 15 ha-cm/ha/annum of runoff can be harvested from the agricultural watershed of 15.02 ha under normal terracing and brush wood forest conditions. The farm pond is quite effective in reducing flood hazards.
Contour bunding, with adjustments to fit the field boundary bunds, is being routinely implemented in almost all parts of India. Contour bunding, in contrast to watershed management, employs distinctly different concepts of water conservation and management.
In contour bunding, runoff may flow in a concentrated manner, causing erosion between bunds. The runoff collects at the bund and is forced to flow across one or more small watersheds and then is finally disposed of in roadside drains or gully.
In the graded (150 cm) beds and furrows system developed at ICRISAT centre for cropped watersheds, excess water is allowed to flow slowly through small furrows to grassed drainage ways and is then safely conducted to a tank and/or outlet (Fig. 11.2).
The velocity of flow of water is controlled by the direction and slope of the furrows. These beds and furrows provide considerable protection against soil erosion throughout the year as they form a permanent land feature.
Experience at ICRISAT showed that this system controls runoff and erosion and facilitates infiltration of water into the soil uniformly over the watershed area. The system provides opportunity for surface water collection in the tanks and groundwater recharge for wells which can then provide water year-round for domestic use as well as supplemental irrigations.
Results at ICRISAT centre indicate that the optimum slopes for the bed-and-furrow system are 0.3 to 0.6% on alfisols (red soils) and 0.4 to 0.8% on vertisols (black cotton soils).