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Promoting conjunctive use of surface and groundwater: A case study from a major irrigation system

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Presented by IWMI's Lal Muthuwatta (Regional Researcher – Hydrological Modeling & Remote Sensing) to a group of European Union (EU) delegations in Asia at a discussion on 'Using research on agriculture climate and water to support sustainable food systems', held at IWMI Headquarters in Colombo, Sri Lanka, on June 8, 2016.

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Promoting conjunctive use of surface and groundwater: A case study from a major irrigation system

  1. 1. Promoting conjunctive use of surface and groundwater: A case study from major irrigation system L.P. Muthuwatta, H, Manthrithilake, W. Premachandra, E.N.S.Silva
  2. 2. Mahaweli System H • Settlement for 19,656 farmer families and 8,557 non-farmer families. • Total land is 51,232 ha from which 25,365 ha are fed by canal water and nearly 7,800 ha of land are rain fed. • Period between May and September is characterized by low and erratic rainfall and the crop water requirement is supplemented by irrigation water.• Located in the North central province of Sri Lanka. • Primarily designed for paddy production .
  3. 3. Water Management Issues • System H often experiences water shortages. • However, large volumes of return flows regularly overflows the down stream Rajangana Tank. • Though large number of Agro-wells exist, only handful of farmers prosper through groundwater use, which is informal. • Mahaweli water managers consider 40% of the water issued as losses
  4. 4. Objective To estimate the potential of conjunctive use of surface and ground water in system H of the Mahaweli Development Program in order to improve the agricultural production as well as the livelihood of the farmers.
  5. 5. Agro-well Irrigation • Some farmers use water from the agro-wells to irrigate their fields to cultivate high value crops. • Project identified and surveyed 4,746 agro wells within System H. • Data on well location , construction quality, water depths, ownership, cultivated area etc., were collected.
  6. 6. Observations • OFCs - Big Onion, Cabbage, Bitter goat, Tomato, Soya, Banana, Water melon, Snake goat. • These crops are cultivated vastly in Yala ( April - Sept) and part of irrigation water comes from Agro-wells . • Farmers use fuel or solar energy to pump water for irrigation of these crops.
  7. 7. • Irrigation methods include manual methods, sprinklers and drip irrigation. • Agro-wells are mostly replenished with canal water that seeps through the soil. • Farmers who installed sprinkler systems in their fields use 27% less water and earn more profits compared to those use traditional methods. Observations
  8. 8. RBMC area
  9. 9. 0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00 80.00 90.00 EPPAWALA MAHAILUPPALLAMA NOCHCHIYAGAMA THALAWA THAMBUTTEGAMA CI(%) Cropping Intensity for Yala Season Block CI CV EPPAWALA 22.9 0.49 MAHAILUPPALLAMA 47.2 0.49 NOCHCHIYAGAMA 44.3 0.64 THALAWA 54.6 0.47 THAMBUTTEGAMA 51.1 0.56
  10. 10. OFC Cultivation- GW + SW Block Cultivated Area (ha) Total Area (ha) No. of Wells EPPAWALA 131.0 570.6 664 MAHAILUPPALLAMA 42.5 90.0 89 NOCHCHIYAGAMA 318.1 717.3 809 THALAWA 552.1 1011.7 1097 THAMBUTTEGAMA 355.7 697.1 789 Total 1399 3087 3448
  11. 11. CI % Number of farms % 10-50 2226 65 50-80 455 13 80-100 767 22 About 1022 ha are having low CI ( 10- 50%) while depth to GW level is low (0 - 0.5 m. It will require about 7 mcm of water to achieve 100% CI in these areas.
  12. 12. Water balance – RBMC – 2014 - Yala In flow From Kalawewa 118.1 mcm Rainfall 79.1 mcm GW use 8.9 mcm Diversions Nachchaduwa – 16.23 mcm Tissawewa – 0.55 mcm Total - 16.78 mcm ET 101.7 mcm Balance 87.6 mcm
  13. 13. Agro-well Irrigation During Yala • Area – 1.5 acres of big onion. • Initial investment for the watering system – LKR 399,000.00. • Cost for land preparation, fertilizer and harvesting - LKR 197,000.00 • Net profit – LKR 1,054,000.00.
  14. 14. Crop Water Source Irrigation interval (days) Cost/ac (LKR) Net Income/ac (LKR) Paddy Canal 33,000.00 43,860.00 Cauliflower Agro-well 3-5 121,000.00 151,000.00 Snake gourd Agro-well, Canal 5 285,000.00 480,000.00 Chilies Agro-well, Canal 3-5 110,000.00 358,000.00 Tomato Agro-well, Canal 3-5 98,000.00 167,000.00 Soya Agro-well, Canal 8-10 43,000.00 257,000.00 Banana Agro-well, Canal 8-10 85,000.00 365,000.00 Cost vs. Income
  15. 15. Cost vs. Income 0.0 500.0 1,000.0 1,500.0 2,000.0 2,500.0 3,000.0 3,500.0 Paddy Cauliflower Snake gourd Chilies Tomato Soya Banana $ Crop Cost/ac Net Income/ac
  16. 16. • Water balance indicates that a large volume of water leaves the system as base flow. • Significant potential exists to improve water availability by tapping portion of this water during Yala season. • Small portion of this water (10%< )can increase CI to 100% in 1022 hectares. Use of water from the agro-wells have already helped some farmers to achieve 100% CI during Yala season. • OFC cultivation in the Yala season provides more profits to the farmers. Conclusions

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