Land subsides in groundwater guzzling UP districts

Land subsides in groundwater guzzling UP districts [1]

Central Uttar Pradesh (up) is quite literally on shaky ground. Land subsidence has been reported from several districts of the region, including Fatehpur, Farrukhabad, Kannauj and Unnao. Alarmingly, the culprit is neither seismic nor mining activity, but excessive groundwater extraction. This despite these districts lying in the Gangetic plain and supporting several rivers. At the root of the paradox lies the inequitable distribution of water.

The most recent cases of land cracking have been reported from Fatehpur's Khakreru and Pur Buzurg villages. But it was in mid-1995 that land subsidence was first detected in villages located in Kannauj and Farrukhabad districts (see table: The extent of land subsidence).

The extent of land subsidence
Village	District	Date	Land-cracking dimensions
Khakreru (Mazra Kanpurwa)	Fatehpur	July 30, 2002	48 metres (m) long, 15 centimetres (cm) wide and 1.5 m deep
Pur Buzurg	Fatehpur	July 20, 2002	45 m long, 50 cm wide and 0.6 m to 1.5m deep
Roti Chauraha	Fatehpur
Nadesia	Kannauj	August 1, 1995	100 m long, 40 cm wide
Rasulpur	Farrukhabad	July 18, 1995	300m long
Nagla Lachhiram	Farrukhabad	June 28, 1995	9 m long, 5m wide and 1.5-2m deep
Nagla Umrai	Farrukhabad	June 27, 1995	200m long, 15cm wide
Sources: 1) Anon 2002, State Ground Water Department, Lucknow, mimeo 2) C S Agarwal 2002, Hydrology Journal, State Groundwater Department, Lucknow, March.

A team comprising hydrologists and geophysicists of the state and central groundwater departments promptly visited the affected areas after the latest occurrence also. It was headed by C S Agarwal, senior hydrogeologist in the State Groundwater Department, Lucknow, and S A H Rizvi, joint director, Groundwater Division, Kanpur. The group has confirmed that earthquakes are not behind the phenomenon since the region does not fall in a shifting tectonic plate zone. It has further found that "overdrafting of water from the shallow first aquifers through cavity wells from a more or less uniform depth of 30 metres (m) to 40 m has led to ground subsidence and cracking'. Agarwal says: "The discharge from cavity-type wells is about 3000-4000 gallons per hour.'

Strangely, though the experts' observations were made more than six months ago, no damage control exercise has been undertaken to date.
Deep impact Cavity wells are dug where a layer of fine sand lies below hard clay strata. Such a formation has poor permeability. Significantly, Farrukhabad, Kannauj and Fatehpur districts belong to the central part of the Gangetic alluvial plain. This region consists of sandy, clayey and kankar (lime and clay mix) formations.

In these places, normal boring techniques using screen pipes proves inadequate. To ensure a good discharge, a hole is made in the aquifer and a casing pipe is lowered in till the sandy subsoil. While the base of the casing pipe is sealed in tubewells, it is left open for pumping out water in a cavity-type well. In addition a cavity is formed around the base of the bored-in pipe by pumping in compressed air to facilitate subsequent water extraction.

Over a period, the cavity takes on a convex shape. As adjoining wells grow wider, they coalesce and form a hollow shaft. The dry overburdened layer gets saturated due to rain and the underlying cavity collapses as the pressure of the top layers increases.

"The wells were also giving out sand prior to subsidence,' points out B B Trivedi, scientist in the Central Ground Water Board (cgwb), northern region, Lucknow.

Drained resources
In Farrukhabad, government tubewells cater to approximately 4.3 per cent of the total land under cultivation while a whopping 86 per cent is taken care of by private tubewells. The situation is quite similar in Fatehpur. About 6.32 per cent is covered by government tubewells and 60 per cent by private tubewells. In short, a near-complete dependence on groundwater sources.

Sure enough, Farrukhabad's pre-monsoon groundwater level data shows a declining trend from 1984 to 1995, when land subsidence surfaced in the region. Water dipped to 10.81 m below ground level in 1995 from 5.69 m in 1984 in Nawabganj, from 15.45 m in 1984 to 16.35 m below ground level in 1995 in Kamalganj, and from 15.65 m in 1984 to 18.58 m below ground level in 1995 at some places in Kannauj.

Census surveys conducted by the up minor irrigation works and the district-wise statistical review clearly show a significant increase in the number of tubewells and borewells from 1995 to 2002. This implies that the groundwater level would have further plummeted during these seven years.

According to the survey of 1995, the total number of wells that were dug and bored in Farrukhabad district stood at about 3380, while there were approximately 9499 electric tubewells. The 2002 survey reveals that about 28 new deep tubewells were installed in Farrukhabad since 1995, despite this area being declared a "dark zone' (where 85-100 per cent of the available groundwater is extracted). In Fatehpur, too, a 20 per cent and 850 per cent increase has been recorded in the number of electric tubewells and deep tubewells, respectively.

Sowing trouble
Apart from the dense network of borewells and tubewells in the two districts, the cropping pattern of the region is also responsible for the fall in groundwater level. "I cultivate mainly wheat, sugarcane and paddy but other farmers also grow potatoes, chana and rye,' says Avesh Kumar, a farmer of Manawa village in Fatehpur.

The crops that are grown in the district include wheat, paddy, sugarcane and potato

Publication Date:

30/03/2003

Author(s): Sutapa Ghosh [2]

Source: Down to Earth [3]

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