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.

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. 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. 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. 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. 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.

7. 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.

8. • 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

9. RBMC area

10. 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

11. 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

12. 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.

13. 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

14. 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.

15. 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

16. 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

17. • 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