Thursday, March 15, 2012

Groundwater Awareness Week: Marathi Movies And Upland Farmers Of The Deccan

Geology and Livelihoods # 13

It is groundwater awareness week in the United States. What a great idea.. and why restrict it to national boundaries? Here is a story from India.

The video is from the Marathi language movie Tingya, set in the Deccan basalts of Maharashtra. In the short clip you can see a river valley. The boy - whose name is Tingya - starts running up a slope and keeps going until he reaches his house which is at a considerable altitude. Here, his family lives and farms a small plot of land.

The boy is very much attached to the family work animal, a bull named Chitangya. One day, at the crucial time of preparing the field for harvest, Chitangya falls ill. He can't work anymore and the family is forced to sell him for meat. Tingya protests vehemently and invokes the incomparable logic of children - " The neighbors grandmother has been lying sick and useless for months. Why don't they send her to be cut up for meat!?"

These are the lives of marginal farmers eking out a living on slopes and high plateaus of the Deccan. Groundwater is not mentioned in the movie but the lives of these communities is sustained by the monsoon and whatever groundwater is available. 

I have seen these situations up close. An example from near Pune.

The river is the main source of water in the valley. Fields are irrigated by lifting water from the river or from constructed holding tanks. Groundwater is also used but often is a secondary source, used for domestic consumption and for minor irrigation.  Up on the slopes and plateaus, the situation is different. Post monsoon, the only source of water is groundwater, tapped either through shallow dug wells, or channeling water seeping out of springs to holding tanks. Local irrigation networks move this water to the fields.

The structure of the lava flows control the location of groundwater and springs. Here is a schematic of the topography and geology. The steep slopes are exaggerated. The distance from the river to Tingya's home would be a few kilometers and the altitude difference a few hundred feet:

The lava pile is composed of alternating vesicular flows and compact flows. Lava when it erupts has volatiles and gases trapped in it and this results in the solidified basalt having a vesicular (cell or sac like structures which are empty or are filled with secondary minerals) texture. They also  have extensive sheet joints i.e. cracks which are parallel to the body of the flow and through which water can flow. The cracks may have originated as cooling cracks as the lava cooled and contracted or as cracks that form when the overburden was removed due to erosion. Prolonged weathering of the rock mass due to movement of water accentuates these cracks into larger openings. Compact flows, as the name suggests are denser and have sub-vertical joints and fractures, possibly of cooling or tectonic origin.

Vesicular flows and compact flows together form an aquifer unit like the one in the schematic below.


Rain that falls on the plateaus and slopes infiltrates through cracks. It gets stored mostly in the vesicular and sheet-jointed type of lava flow. Dug wells tap this sheet jointed unit for maximum benefit. Sheet joints of these flows when exposed along slopes are the locations of the best springs.

Tingya's family likely gets by using this type of water arrangement, a combination of dug wells and springs. Dug wells are expensive to excavate and poor families rely mainly on springs. There is sometimes a third option. And that is to pay lowland farmers to lift water from the streams or holding ponds to irrigate fields higher on the slopes. This does not come cheap though. It may cost up to several thousand rupees to irrigate an acre of wheat or vegetables. Most marginal farmers won't be able to afford this additional water source. Some families opt for a fourth option. Members migrate to cities to work in the dry season, returning to their fields in the monsoon. Many stay on permanently in the cities, supplementing family agricultural income.

These farmers need help in the form of groundwater management advice. Groundwater extraction sustains these people. But to manage this resource the key questions would be - a) how much water does the aquifer hold?  b) how much water can be extracted sustainably?  c) how much and how quickly can the aquifer be recharged, either naturally or through artificial methods?  For that, a thorough geological understanding of the aquifer is needed. Such geological expertise is not always available to farmers. Some work is being done to redress the situation. For example, much of the geology in this post is based on a field trip I took some years ago with ACWADAM , a NGO focusing on understanding the hydrogeology of the Deccan lava flows.

Tingya's family pull through their crises in the end. Chitangya fetches a decent price. They buy another animal who gives birth to a calf. Tingya sees in that calf Chitangya reborn. The cycle of life continues. Other families may not be that lucky. The story could easily end differently for them.  Monsoons may fail. Unplanned water extraction may leave wells dry. The hard basalt may become unrelenting.

Disaster then is often just one illness away. 

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