The PRA Team:

The phenomenon of interactive effect of wells, also known as well interference, refers to the groundwater nexus between wells. Here, among accidentally connected wells, withdrawal of groundwater from one well will result in reduction of groundwater yield and water level in the other. In practice, it is likely that there may be either one well to one well interaction, or one well to many wells multiple interactive effects. The interference phenomena are obscure; to the extent that one or more wells may be causing the problem, it is proper to study the predicament faced by farmers due to ‘cumulative’ well interference, since it is difficult to discern the effect of a specific well on another well. By ‘cumulative’ we mean the sum total effect of over-pumping of ground water from several (types and numbers of) wells resulting in the reduction of yield and water levels in the surrounding wells. The National Geophysical Research Laboratory, Hyderabad, conducted thousands of pump tests and recorded the discharge and water levels for wells with different interwell spacings. They concluded that the isolation distance between (i) open well to open well should be 82 metres; and (ii) open well to dug-cum-borewell or borewell should be 250 metres, to avoid the problem of interference. Hence, wells which  are spaced below the threshold isolation limits prescribed are likely  to be more affected from interference than those wells which pass this threshold.

Why study interference?

The well interference problem poses serious threats to sustainability and equity in well irrigation. A large farmer who can afford to dig, drill, or deepen many irrigation wells can seriously hamper the irrigation prospects of neighbouring small farmers irrigating with one or two wells. In the long run, the small farmer may be forced to shift his/her operations to dryland agriculture. There is a clear equity issue here. When the process of withdrawal of groundwater without regard to recharge efforts goes unabated, the resource itself may become unsustainable, clearly reducing the economic life of the well, which underscores the sustainability issue.

Statistical and PRA approaches In this note we provide a combination of statistical and PRA approaches for selecting farmers to study and analyse the equity issues involved due to interference of irrigation wells. It is to be noted that either statistical or PRA approaches singularly cannot provide efficient study guidelines for the choice of the study taluks, villages, and farmers. The statistical approach provides the first step is sampling for choosing the taluks and villages; the PRA approach is the second and final step for choosing the farmers from among the villages selected for studying well interference problems, both the approaches running complementary to one another.

Why statistical approach is necessary to identify the taluks/villages suffering from interactive effect(s) of well(s) At the taluk/village level, it is difficult to have a list of taluks/villages which suffer from well failure due to interactive effect(s) of well(s). Hence, we need to generate a realistic index which uses the available secondary sources of information. We developed five different indices, each providing a proxy for locating the taluk/village having well failure due to interactive effect(s) of well(s), and chose one of the five indices which best reflected the problem. The chosen index is: the number of irrigation pumpsets per million cubic feet of utilisable groundwater for irrigation in a taluk (or village)(1) . This index reflects the dependency of a number of wells on a unit of groundwater for irrigation. Hence, the taluk or village with the highest number of wells per unit of groundwater reflects high well interference problems compared to a taluk which has the lowest number of wells per unit of groundwater. For a comparison of the well interference problems in the most affected and the least affected taluk, we have chosen the taluk with the highest number of wells per unit of groundwater in each agro-climatic zone of Karnataka state. The details of the statistical approach used are provided in Appendix 1.

Why PRA approach is necessary to study the interactive effect(s) of well(s) within a selected village or a portion of the village

The secondary source of information to locate well failure(s) largely due to well interference (by one well to another well) or cumulative well interference (by one well to many well or by many wells to one well, or among many wells themselves) is not available with the Department of Agriculture or Department of Mines and Geology, or any other source. The only recourse to such a vital information is through PRA mapping of closely spaced or densely located wells with respect to: (i) year of drilling of wells, (ii) inter-well distance, (iii) depth of wells, (iv) water yield, (v) method of locating groundwater in well, and many other variables which contribute to interference. Hence, after choosing the taluk and the village using the statistical approach already highlighted, locating closely spaced wells through a base map of all wells in the village or a portion of the village aids in identification of pockets of density of wells in a village or its portion. The location of wells in the village and their mapping can be done only by the farmers of the selected village. In addition, mapping of items (i) through (v) listed above cannot be done singularly but by the cumulative efforts of the farmers. Hence the PRA mapping is sine-quo-non to the study of well failure due to interactive effects of wells.

PRA approach to choose the study area within a village and interact with farmers For the purpose of developing the PRA techniques necessary to understand the perceptions of farmers, water diviners, and others involved in groundwater irrigation, the Bhattarahalli village in Kolar taluk, Karnataka State, India, was selected. Since this was more in the nature of a training programme for the UAS team in the use of PRA techniques, the village was selected at random by MYRADA out of many villages in the taluk that have a large number of irrigation borewells. The information diffusion on groundwater exploration is by ‘word of mouth’ among farmers in the absence of agricultural extension efforts. The local water diviners play a crucial role in the diffusion of information. It is debatable whether the farmers get the right information on groundwater exploration from their peers and local diviners. Hence, it was also necessary to understand the perception of occurrence and movement of groundwater by local water diviners (water witches), since they provided (as we later found out) 60% of the groundwater location points and wield great influence with regard to groundwater exploration.

The local diviners were asked to figure the underground water system. Their perception is reflected in the following diagram:

Diagram 1

The local diviners were asked to explain (i) direction of movement of  groundwater, (ii) method used in water divining, and (iii) the hydro-geological formations. It appeared that each diviner’s perception was distinctly different from the others. We could discern the following methods of divining groundwater from their answers :

1. Y-shaped tree stem (the stick should be lean and wet)
2. Plumb ball method :

i) magnifying lens and thick copper wire tied to a thread.
ii) magnifying lens and precious stone tied to a thread.
iii) magnifying lens and metal watch tied to a thread.

3. Dehusked coconut.
4. Young boy feeling giddy at the point where groundwater is located.
5. Asking boon from god in a temple.
6. North-east geomancy (deva moole).
7. Anjana method (witchcraft)
8. Head torch method.
9. Where the following are located : termite hill, Calotropis gigantica var.albiflora.
10. Geophysical survey.

Only a few of the above methods were mentioned by the local diviners and the remaining were obtained during informal interactions with the local diviners of other areas. The ‘Y’ stick and ‘Plumb bob’ were the more often adopted local divining methods. One diviner opined that the groundwater availability increases as we move from south to north in the area where the PRA was conducted. The diviner mentioned that normal groundwater yielding fractures could be cited at three distinct depths : 75 feet, 145 feet, and 185 feet. This was ratified by the geologist also. Some of the local diviners mentioned that groundwater would be flowing in a canal beneath the rocks underground (as shown in the underground water transect). This highlighted the misconceptions farmers have with regard to groundwater occurrence. Infact, the size of the fractures in the rocks of hardrock areas is limited to around 5 millimetres where groundwater would be flowing. The hardrock system cannot support the existence of underground canals. Some others mentioned that rainfall is the only source for underground water. They also mentioned that a good volume of groundwater can be traced to intersections of north-south and east-west directions on the ground. They believe that groundwater exists only in fractures and gaps. The groundwater joins a river at some place during its flow.

One of the local diviners who was acknowledged by the geologist as a person with a better understanding of groundwater than the other local diviners, suggested that both ‘local’ and geo-physical methods be used in locating groundwater; ‘local’ method to locate the point for drilling and geo-physical method to estimate the depth and yield. The geologist agreed with few of the opinions of the local diviners and the geologist was taken to a farmer’s field. The ‘Plumb Bob’ local diviner and the geologist interacted in divining a well point. Incidentally the ‘Plumb Bob’ diviner’s location was ratified by the geologist, but he attributed the success of the local diviner to a chance factor.

PRA MAPPING

Understanding the situation of failed wells from the perspective of farmers is crucial since they are the ultimate field decision makers and investors for coping with the well interference problems. The farmers’ perception of failure may be entirely different from the technical definition of well failure. For instance, according to NABARD, a dug well or dug-cum-bore well is considered a failed well if it yields below 5000 gallons per day in rabi season, and a borewell is considered failed if it yields below 1000 gallons per hour. The farmers’ perception of failure may be different from the technical definition, as the technical definition of well failure is a sort of overall average and discounts the coping mechanisms adopted by farmers to use whatever available scarce groundwater.

The well failure in our study is defined as :

i) well that dries up because of new well(s) coming in (but not because of decline in rainfall).
ii) well that loses a large degree of its yield because of new well(s) coming in (but not because of decline in rainfall), and 
iii) well that is deepened because of new well(s) coming in.

In order to obtain field impressions of well interference in Bhattarahalli village, we conducted PRA exercises and developed maps of {1} year of drilling of wells, {2} interwell distance, {3} water yield, {4} depth of wells, and {5} method of locating groundwater in well. We have a limitation in our study. In our maps, we were unable to obtain information on items {1} to {5} above for all the wells in the village, as all the well-owning farmers could not be present for various reasons. This PRA was our first attempt to get ourselves acquainted in several PRA techniques. Accordingly, we have mapped the data only for the wells for which information was available.

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