70th SWCS International Annual Conference July 26-29, 2015 Greensboro, NC

1. Assessing the groundwater resources and estimating
future demand for irrigation in three districts of Nepal
Presenter:
Romulus O. Okwany, PhD.
Acknowledgement:
Birendra Yadav
UNESCO-IHE

2. Presentation Outline
• Background
• Problem statement
• Research objectives
• Research questions
• Study Area
• Methodology
• Results
• Conclusions and Recommendations

3. Background
• Nepal is located between Himalayan mountains and
Gangetic plain.
• Endowed with water resources.
• Nepal Terai has significant groundwater but only 10
% has been developed.
• Agriculture contributes 32 % in GDP.
• Nepal Terai (23 %), produces 56% of the national
cereal production.
• Almost all cultivated land is irrigable: 1,356,000 ha
out of 1,359,000 ha.
• But still only about 40 % is irrigated and very low
year round irrigation facility.
Livelihood and
Subsistence
Farming

4. Research Questions
 What are the potential water
resources and its availability for the
long term use for Rabi crops
irrigation in the study area?
 What is the groundwater recharge
rate?
 What is the irrigation water
requirement in different seasons for
the existing cropping pattern?
 What is the possible irrigation
potential of the available water
resources verses demand?
Research Objectives
Overall objective:
Evaluate temporal and spatial variation of
water availability and irrigation potential
for rabi crops
Specific objectives
• Assess potentials of groundwater
and pond water sources.
• Determine Irrigation requirements
of common grown crops.
• Project irrigation area based on the
water assessment and irrigation
requirements.
• Determine sustainable levels of rabi
crop irrigation.

5. Study Area

6. Methodology

7. Results
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JAN
FEB
MAR
APR
MAY
JUN
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AUG
SEP
OCT
NOV
DEC
GroundwaterTabledepthBGS(m)
MonthlyPrecipitationandPET(mm)
Sunsari District
Avg. Rainfall Avg. ET Avg. WT 0.0
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JAN
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DEC
GroundwaterTabledepthBGS(m)
MonthlyPrecipitationandPET(mm)
Saptari District
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JAN
FEB
MAR
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SEP
OCT
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DEC
GroundwaterTableDepthBGS(m)
MonthlyPrecipitation&PET(mm)
Dhanusha District
Average Monthly Rainfall, PET and Water Table

9. • MWLF is difference of the
deepest WT in May and
shallowest WT in
September (2000-2010).
•Higher Fluctuation
indicates water table is
lower in the May and
Higher in September.
•Filling in Monsoon and
evacuating in dry season.
Maximum Water Table
Fluctuation

10. 6.6
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2004 2005 2006 2007 2008 2009 2010
WaterTableBGS(m)
Years
Water Table Recovery
GWT Godam Rajbiraj
Water Table Recovery in High Groundwater Fluctuation Area
Although MWLF > 5m but maximum inter-annual variation is about 1 m.
Indicates replenishment of groundwater use by rainwater.

11. Annual Recharge Estimation Using Surfer and WTF Method
Name of
Districts
Surfer Annual
Recharge
(mm/yr)
WTF Annual
Recharge
(mm/yr)
Average
Annual
Recharge
(mm/yr)
Average
Annual
Rainfall
(mm/yr)
Recharge as %
of Rainfall
Sunsari 141 135 138 2163 6%
Saptari 161 169 165 1749 9%
Dhanusha 119 132 126 1624 8%
Result Accuracy
• Results from Surfer and WTF shows close results.
• Recharge study area 143 mm/yr is very close national internal ground
water recharge of 145 mm/yr (Margat and Van der Gun, 2013).
0
50
100
150
200
250
300
350
2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010
Sunsari District
Surfer WTF
Average Annual Groundwater Recharge and Rainfall

12. Pond Water Source
Districts No. of Permanent
Ponds
No. of Temporary
Ponds
Potential annual volume
for use ( MCM)
Sunsari 707 576 1.55
Saptari 1848 996 7.00
Dhanusha 1956 902 4.82

13. Total Annual Available Water for Use
Gross irrigation requirements of common crops
Gross Irrigation Requirement (mm)
Crops Paddy Wheat Pulses/Oilseeds Winter Vegetable Maize
Sunsari 186 150 110 115 48
Saptari 350 245 151 154 125
Dhanusha 327 169 122 187 72
Districts Groundwater
Volume (MCM)
Pond water
Volume (MCM)
Total Annual Water
Availability (MCM)
Sunsari 158 2 160
Saptari 205 7 212
Dhanusha 146 5 151

14. District
Non irrigated area (ha)
Irrigation requirement Volume based on current use
form groundwater (MCM)
Total
Available
water
(MCM)
Summer
Volume Winter Volume Spring
Volume
Total
Volume
(MCM)
Summer Winter Summer Winter (Rabi Crop) Spring
Sunsari 7768 41398 8 50 12 70 160
Saptari 21151 50137 21 60 15 96 212
Dhanusha 32655 60994 33 73 18 124 151
District
Non irrigated area (ha)
Gross Irrigation requirement Volume based on CWR
(MCM)
Total
Available
water
(MCM)
Summer
Volume Winter Volume Spring
Volume
Total
Volume
(MCM)
Summer Winter Summer Winter (Rabi Crop) Spring
Sunsari 7768 41398 17 79 20 116 160
Saptari 21151 50137 100 99 25 224 212
Dhanusha 32655 60994 135 89 44 268 151
Irrigation requirement and Available Water

15. Districts Agriculture
Demand
(MCM)
Domestic
use (MCM)
Industry and
cattle use
(MCM)
Total
Demand
(MCM)
Water
Availability
(MCM)
Sunsari 116 11 3 130 162
Saptari 224 10 4 238 212
Dhanusha 268 11 3 282 151
Total Water Demand and Availability
0
50
100
150
200
250
300
Sunsari Saptari Dhanusha
Volume(MCM)
Water Availability, Use and Demand
Water available Present WU Present Application Rate Total Demand

16. • Potential water sources for Rabi crop can be Groundwater and Pond water.
• Potential annual water sources available for use was found 160, 212 and
151 MCM for Sunsari, Saptari and Dhanusha districts respectively.
• Average annual groundwater recharge of 138, 165 and 146 mm/yr was
found Sunsari, Saptari and Dhanusha districts respectively.
• Total irrigation volume requirement for all seasons are 116, 224 and 268
MCM for Sunsari, Saptari and Dhanusha districts respectively.
• Significantly high water availability than Rabi crop demand indicates that
available water can be used sustainably for Rabi crops.
• For Summer season, it is possible to irrigate all non irrigated agricultural land
in Sunsari whereas only 97 % and 11 % of non irrigated area in Saptari and
Dhanusha districts respectively.

17. Recommendations
• Utilizations of available water by facilitating the farmers or group is necessary to raise
production and productivity in the study area.
• Development and Management of Temporary ponds to increase the water availability
as well as recharge.
• Conjunctive use of groundwater for sustainability and to minimize the cost of
irrigation.
• Adoption of proper irrigation methods to minimize the losses of water.
• Important to know base flow for groundwater balance.
• WRA is an important for better planning and sustainable development.
Recommendations and Future Research
Future Research
• More comprehensive study on spatial specific yield.
• Economics of groundwater use.

18. Thank You!
Contact Information:
Romulus O. Okwany
Email: r.okwany@cigar.org
Skype: @Romulus_Okwany
https://np.linkedin.com/pub/romulus-okwany/1a/472/466
Australian Center for International Agricultural Research (ACIAR)
Research program on Water, Land and Ecosystems (WLE)