Assessing the groundwater resources and estimating future demand for irrigation in three districts of Nepal

Presenter:Romulus O. Okwany, PhD.

Acknowledgement:Birendra YadavUNESCO-IHE

Presentation Outline

• Background• Problem statement• Research objectives• Research questions• Study Area• Methodology• Results• Conclusions and Recommendations

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

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.

Study Area

Methodology

Results

JANMAR

MAY JUL

SEP

NOV0

100

200

300

400

500

600 0.00.51.01.52.02.53.03.54.04.55.0

Sunsari DistrictAvg. Rainfall Avg. ET Avg. WT

Mon

thly

Pre

cipi

tatio

n an

d PE

T (m

m)

Gro

undw

ater

Tab

le d

epth

BG

S (m

)JAN

MARMAY JU

LSE

PNOV

0

100

200

300

400

500

600 0.00.51.01.52.02.53.03.54.04.55.0

Saptari District

Mon

thly

Pre

cipi

tatio

n an

d PE

T (m

m) G

roundwater Table depth BG

S (m)

JAN FE

BM

ARAPR

MAY

JUN JU

LAUG

SEP

OCTNOV

DEC0

100

200

300

400

500

600 0.00.51.01.52.02.53.03.54.04.55.0

Dhanusha District

Mon

thly

Pre

cipi

tati

on &

PET

(mm

) Groundw

ater Table Depth BG

S (m)

Average Monthly Rainfall, PET and Water Table

• 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

2004 2005 2006 2007 2008 2009 20106.6

6.8

7.0

7.2

7.4

7.6

7.8

8.0

8.2

8.4

8.6Water Table Recovery

GWT Godam Rajbiraj

Years

Wat

er T

able

BGS

(m)

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.

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).

2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 20100

50

100

150

200

250

300

350 Sunsari District

Surfer WTF

Average Annual Groundwater Recharge and Rainfall

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

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

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

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

Sunsari Saptari Dhanusha0

50

100

150

200

250

300

Water Availability, Use and Demand Water available Present WU Present Application Rate Total Demand

Volu

me

(MCM

)

• 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.

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.

Thank You!

Contact Information:Romulus O. Okwany

Email: r.okwany@cigar.orgSkype: @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)