Dr. Shrikant D Limaye.

Project Leader, UNESCO-IGCP Project 523:”GROWNET”Director, Ground Water Institute,2050 Sadashiv Peth, Poona 411 030, INDIA

Phone: +91 20 2433 1262; Phone/Fax: +91 20 2433 3535; E-mail: limaye@vsnl.com

 

Abstract: Augmentation of recharge to ground water through percolation tanks is closely related to the survival of about 15 million farmers and an equal number of cattle, living in the semi-arid basaltic plateau in western India. Here the Monsoon rains are restricted to a few rainy days between June and September. It is therefore, necessary to harvest the monsoon runoff into small percolation Tanks in mini- catchments, by constructing earthen bunds on small streams and allowing the stored water in the Tanks to percolate and recharge the ground water body. The residence time of water in the mini-catchments is thus increased and it is possible for the farmers to dig wells and give supportive irrigation to the crops in their small farm plots. The efficiency of the percolation Tanks is hampered by the silt, which accumulates in the tank bed, year after year. It is therefore, necessary for the beneficiary farmers to remove silt the tank bed when the tank dries in the summer season. Soil conservation practices should also be followed in the watershed of a percolation tank in order to reduce the silt coming into the tank. NGOs have an important role to play in this field.  Recharge augmentation through watershed management & construction of percolation tanks is one of the ‘best practices’ included in the UNESCO-IGCP Project no.523: GROWNET, for which the Author is Project Leader.

 

1       Introduction

The International Geoscience Program (IGCP- formerly known as International Geological Correlation Program) is a joint endeavor of UNESCO and IGUS (International Union of Geological Sciences) and operates in about 150 countries, involving several thousands of scientists. It provides a multinational platform for scientists from all disciplines related to earth sciences to exchange knowledge and methodology on a multitude of geological problems of global importance. Recently, in concomitance to the change in name, the IGCP has started encouraging projects related to practical applications of geology, especially of hydrogeology.

In 2005, out of 17 projects approved by IGCP, three projects are related to ground water development. Amongst these, the Author is convening Project no. 523, titled as “Grownet – Ground water network for best practices in ground water management in low-income countries”. Although many ground water development projects do not function in an ideal or sustainable fashion, even in the developed countries, ‘best practices’ are sometimes observed as isolated and scattered methodologies adopted in different phases in different projects. In ground water development projects for promoting irrigated agriculture and/or providing drinking water supply in backward, rural areas, best practices may thus occur in exploration, assessment, institutional financing, digging/drilling of wells, pumping, utilization, marketing of agro-products, recovery of loans, monitoring, watershed management, recharge augmentation, encouraging participation of beneficiaries and in fostering women’s role. Studying such best practices and posting them on a common ‘website’ on the Internet is the purpose of “Grownet”.

Out of the several types of best practices in ground water management mentioned above, the two, which relate closely with the Theme of this Conference are: (a) Watershed management for soil and water conservation leading to increased natural recharge and (b) Recharge augmentation through artificial processes. Out of about 500,000 sq kms of basaltic area in India, about 30% falls in the semi-arid zone. Recharge augmentation has become a crucial issue in this semi-arid basaltic terrain due to over-exploitation of the resource. The change in overexploited and critical areas in India, between 1984-85 and 1992-93 represents a growth of 5.5% per year. If this rate continues, such areas would double after every 12.5 years. (World Bank-1998.) Concerted efforts from various players are therefore, necessary for recharge augmentation so as to control over-exploitation.

2       Watershed Management For Increasing Natural Recharge

The World Meteorological Organization has warned that due to natural and anthropogenic causes, the climatic pattern in near future would have more extremes, causing frequent flash floods in some areas and severe droughts in other areas of the same country or the state. During the last Monsoon season in India, the west coast area experienced ravaging floods while in the eastern portion of the same State of Maharashtra the meager rainfall resulted in near-drought conditions in many Districts. Several villages had to be supplied with drinking water in Tankers. Ironically, in the countrywide average, excess and deficit precipitation would get balanced to show that the Monsoons have been normal. Any model on climate will not be able to predict the daily or weekly amount of rainfall over a given area.

Under these circumstances, there is a need to create a buffer, a cushion or a resilient interface to absorb the shocks of the climatic changes and to provide some insurance for the water managers. A watershed, subdivided into mini-watersheds of first order streams, which are properly managed for soil and water conservation, provides such a resilient interface. The soil surface with its cover of grass, bushes and trees, properly tilled farms with contour bunds, farm ponds, check-bunds on small streams or gullies, and contour trenches on hill slopes, are the meeting points of climate on one side and hydrology/hydrogeology on the other.

In low rainfall areas proper management of mini-watersheds promotes recharge to ground water, thereby increasing the residence time of water in the watersheds. In the form of surface runoff, rainwater flows out of a watershed in just a few days. But when recharged to ground water reservoir, it stays for a few years. The frequency of droughts is higher in semi-arid areas and ground water assumes unique importance in providing drinking water supply in drought years. In high rainfall areas, a degraded watershed gives rise to an evil stream having sharp-peaked, narrow-based hydrograph, while a well-managed watershed generates a beneficial stream with a gentle- peaked, broad-based hydrograph. ‘Best Practices’ in the low-income countries to be verified and evaluated under the ‘Grownet’ project, will be selected from land-use planning and watershed management programs, promoted by the Government with active participation of local people and NGOs.  The dissemination of these best practices from Grownet website on the Internet, will result in their duplication elsewhere. Planners and policy-makers in low income countries will also be made aware of the importance of NGOs in ensuring people’s participation in watershed management programs.

Forestation of degraded watersheds with grasses, bushes and trees is the first step in watershed development. It is however, necessary to exercise caution regarding the choice of species of deep-rooted trees for forestation in semi-arid regions in basaltic terrain. There have been instances when the plantation of eucalyptus trees in semi-arid watersheds actually decreased the recharge from rainfall due to high rates of transpiration by eucalyptus. In semi-arid regions, eucalyptus may virtually prevent recharge from rainfall. Many times, local species of hardy trees and bushes with very low water requirement are more suitable.

3       Artificial Recharge Augmentation

Activities for artificial recharge augmentation in semi-arid regions in basaltic terrain of western India are undertaken during the Monsoon rainy season (June – September). A few of them also continue during the following dry winter season (October to February), using the stream-flow in winter season or the stored runoff water in percolation tank, as the source of water for recharge. These activities are more site-specific compared to watershed development activities, which are spread over the whole watershed. In the semi-arid basaltic region, percolation tanks are in vogue for the past three decades and are dealt with separately in the next section. Some of the non-conventional means of artificial recharge augmentation being recently introduced are as follows:

To blast several bore wells around a low yielding dug well in summer season and create an artificially fractured aquifer, which eventually gets recharged during Monsoon rains.

To arrest the natural outflow of ground water by putting underground barriers of clay or corrugated PVC sheets across the bed of a stream. The increased level of water table causes influent seepage. 

To dig a percolation pit around a dug well or a bore well.

To pump runoff water in winter season from a stream, back into the dug wells away from stream bank.

To catch roof-water during the rainy season, pass it through sand filter and put it in a bore well or dug well. And lastly,

To remove clay and silt from the beds of old tanks in villages, so as to increase their capacity and foster better infiltration.

To use old stone quarries in water divide region for rainwater storage and pump the stored water into dug wells for recharge.

4       Artificial Recharge by Percolation     Tanks

In order to achieve artificial recharge on a much larger scale, construction of percolation tanks is a widely practised technique in semi-arid basaltic terrain.  Due to the high evaporation rates of surface water in the summer months, storage in ground water reservoir is a preferred method in this region. In order to augment ground water storage, runoff water in several seasonal streams in a large watershed is impounded by constructing earthen bunds across the streams. Percolation Tanks are formed during the Monsoon season, behind such bunds, collecting runoff water from catchments ranging between 10 to 50 sq. kms. This water percolates during the four months of the winter season (October-February) and by the beginning of summer the tank becomes dry. Once the runoff water collected in the tank percolates to join the phreatic water table, its residence time in the stream valley changes from a few days to a few years. Drought years are frequent in the semi-arid region. It is, therefore, important to collect runoff whenever available, allow it to percolate and recharge the ground water reservoir, so that in the dry season, people, crops, and cattle may depend upon ground water available in dug wells and bored wells. Sustainability of these percolation Tanks assumes unique importance on this background. At places, where the quality of ground water is impaired due to high salinity or high fluorides, it is possible to locate the drinking water well of a village on the downstream side of the percolation tank. Here, the quality of ground water gets improved due to the percolation of good quality runoff water from the tank.  An important socio-economic factor, favoring construction of percolation Tanks in the drought-prone, semi-arid region is that during a drought year construction of an earthen bund across a stream gives employment to about 1,000 to 1,200 men and women, for 6 to 8 months. Therefore, Government departments take up these constructions as a part of  ‘drought-relief’ programs. They are useful for providing employment to the villagers and farmers, who have no other work on the farm due to drought conditions. The payment to the construction laborers is made partly in cash and partly in food-grains. 

Sustainable management of such percolation tanks is closely related to the survival of about 15 million farmers and an equal number of cattle, living in the semi-arid basaltic plateau in western India. However, the silt accumulating in the tank bed, year after year, hampers the efficiency of a percolation tank. The beneficiary farmers have to de-silt the tank-bed when the tank dries in the summer season, in order to maintain the storage volume of the reservoir and also the rate of vertical infiltration. (Limaye & Limaye, 1986). NGOs have an important role to play in this field and have come up with some of the best practices in maintenance of tanks and in active participation of the local people. 

5       Conclusions

1. A well-managed watershed not only provides a resilient interface for absorbing variations in climatic pattern but also promotes ground water recharge.

2. In semi-arid basaltic terrain in India, augmentation of recharge by natural and artificial techniques during and after the Monsoon rains has a direct influence on providing irrigational and drinking water supply to millions of farmers, thereby reducing their hardship.

3.Construction and maintenance of percolation tanks is of unique importance in augmenting dry-season recharge and in helping the survival of poor farmers.

4. In an international conference such as this, the IGCP Project no 523 (GROWNET) aims at bringing together hydrogeologists having experience in best practices in ground water development in low-income countries and seek their cooperation for posting these practices on the Website, for global dissemination.

 

6       References

[1]      Limaye S.D and Limaye D.G (1986) Ground water management under stress conditions in small sub-basins. In Proceedings of the International Conference on Ground Water Systems Under Stress, Brisbane, Australia, Australian Water Resources Council Series no.13, P 277-282.

[2]      World Bank 1998 India- Water Resources Management Sector Review, Ground Water Regulation and Management  Report, Rural Development Unit, World Bank South Asia Region. Page 11.