Falling water table in a tube-well block: recharge ponds or more free power?
Kansabati block has 14,200 ha of cultivated land. Between 2006 and 2024, energised tube wells rose from 210 to 1,120, and boro paddy area rose from 900 ha to 3,600 ha. Rainfall shows no significant trend (mean 1,180 mm; the 2022 drought gave 780 mm). Pre-monsoon water level in the state observation-well network fell from 7.8 m below ground level in 2006 to 21.5 m in 2024, and 38% of sampled wells now yield under 300 L/min. Two habitations report wells dry by February, and women walk 1.8 km to a single deep well. Farmers pay a flat electricity tariff, so pumping cost does not change with volume. The irrigation department proposes lining 18 km of canal; the agriculture department proposes free power for another 500 shallow wells. A consultant suggests 25 recharge ponds of 0.4 ha each for ₹6.5 crore. The district has ₹7 crore.
1. Using the data given, distinguish between a drought-driven shortage and long-term over-extraction. State what can and cannot be concluded, and what additional data you would request before approving any scheme.
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Diagnosis. Rainfall has no significant trend, so the 2022 drought cannot explain a 13.7 m fall in pre-monsoon water levels over 18 years. The decline is persistent and coincides with a 5.3-fold increase in tube wells and a fourfold increase in boro paddy. Boro paddy is grown in the dry season, when recharge is minimal and dependence on stored groundwater is highest. A flat tariff means the marginal cost of pumping extra water is zero, so there is no economic signal to conserve. This pattern points to long-term over-extraction, with drought acting as an amplifier rather than the cause.
What cannot be concluded. Water-level data alone do not show whether the aquifer is being dewatered or whether a local cone of depression has simply deepened. They also do not show whether storage loss is permanent. We lack aquifer geometry, specific yield, actual pump hours, and water-quality trends.
Additional data needed: at least 10 years of monthly hydrographs from clustered observation wells; pump-hour or energy-consumption records for a sample of wells; seasonal crop-area maps; pumping-test values of transmissivity and storativity; arsenic and fluoride testing; and a seasonal water balance. Without these, any recharge estimate is only a guess.
2. The district has ₹7 crore. Compare canal lining, free power for 500 new wells, and 25 recharge ponds on effectiveness, speed, equity and risk. Recommend a funded package with justification.
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Free power for 500 new wells should be rejected. It lowers the marginal cost of extraction, adds capacity in an already stressed aquifer, and favours farmers who can afford land, wells and pumps. It is a classic maladaptation: it may raise output for one or two seasons while accelerating the water-level decline.
Canal lining can reduce seepage, but seepage also recharges the aquifer in some reaches. Lining 18 km without a seepage study may reduce local recharge and transfer water downstream. It is worth funding only after measurement, and it does not address demand.
Recharge ponds are locally useful but small. Assuming 1 m of monsoon water captured over 10 ha, the 25 ponds store roughly 0.1 million cubic metres, whereas boro paddy over 3,600 ha may use of the order of 30 million cubic metres. Ponds can raise village well levels and provide drinking-water security, but they cannot offset unchecked extraction.
Recommended package within ₹7 crore: ₹2.0 crore for 12 pilot ponds in the most depleted villages; ₹1.0 crore for metering 300 wells and energy audits; ₹1.5 crore for crop diversification, direct-seeded rice and extension; ₹1.0 crore for canal lining only after a seepage study; ₹0.5 crore for monitoring; and a ₹1.0 crore reserve. Couple this with a notified block where new irrigation wells require permission. This mixes supply-side recharge with demand management and protects smallholders and drinking-water users.
3. Design a three-year monitoring plan to show whether the package is working. Name variables, frequency, sampling design and a decision rule.
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Design: three clusters of four observation wells each, located up-gradient, mid-gradient and near the recharge ponds, plus two rain gauges. Record water level monthly and continuously in six wells with data loggers. Measure rainfall daily, crop area each season by ground survey and satellite imagery, and pump hours on 50 metered wells monthly. Test arsenic, nitrate and TDS quarterly. Record pond water levels after each monsoon and sediment accumulation annually. Track energy sales as a proxy for pumping.
Quality control: calibrate loggers against a manual tape every quarter; use blank and duplicate water samples; store data with a named custodian.
Decision rule: compare pre-monsoon levels with the 2024 baseline. If the decline continues at more than 0.5 m per year, tighten extraction controls and expand recharge. If the decline falls below 0.2 m per year and metered pump hours fall by at least 15%, scale up the package. If water levels stabilise but arsenic rises above 0.01 mg/L, issue a drinking-water advisory and investigate. Report publicly every six months.