Downstream impacts of the melamchi inter basin water transfer plan (miwtp) under current and future climate change projections

Water for a food-secure world

P. Gurung and L. Bharati

International Water Management Institute (IWMI), Lalitpur, Nepal

Downstream impacts of the Melamchi Inter-basin Water Transfer Plan (MIWTP) under current and

future climate change projections


Background

Melamchi Water Supply Project (MWSP):

1973 (Identified) 1998 (Implemented)

2008 (Planned to Complete) 2015 (Extend to Complete)

Demand of local people, political circumstances and challenges to engage

private sector partner is major barrier to complete project

Drinking Water Demand of Kathmandu: 220 MLD

Water available in Kathmandu Valley: 90 MLD (Dry Season)

130 MLD (Wet Season)

In addition, downstream hydrological impacts is another issue

(Project has set minimum downstream release nearly 35 MLD)


Objective of the Study

1. Use of distributed hydrological model developed for entire Koshi basin

to look hydrological impacts of the MIWTP until the outlet of the Koshi

basin at Chatara

2. To evaluate impact of climate change on downstream hydrology under

current and future climate scenario

3. To quantify impact of water transfer on agricultural command area of

Melamchi river (289 hectare) under current and future climate scenario


Model used for the Study

Soil Water Assessment Tool (SWAT) Model:

- Physically based semi-distributed hydrological model

- To simulate water quantity, sedimentation and water quality

- Developed by Department of Agriculture of USA

Soil, Water and Salt Balance (BUDGET) Model:

- Field based model

- To simulate crop water requirement (CWR) and prepare irrigation

schedule

- Developed by faculty of applied bioscience and engineering, Katholieke

Universiteite Leuven of BELGIUM


Study River Reach

Ü1

8

6

2

4

3

5

14

9

32

17

51

7

16

78 73

11

18

10

75

12

45

34

27

13

5762

65

58

56

15

38

5560

72

23

71

30

61

53

54

36

6967

44

66

42

35

59 64

40

74

70

19

47

43

4137

68

31

7679

28

48

77

29

39

22

20

46 5249

63

25

50

33

262421

0 60 12030 km

Model developed for Koshi basin is divided into 79 sub-basins (Outlet Chatara)


Study River Reach

Ü

!(

!(

!(!(

!(

!(

!(

!(

!(

!(!(

!(

!(

!(

!(

!(

!(!(

!(

!(

!(

!(

!(

!(

#*

#*

#*

#*

#*

#*#*

#*

#*

#*

#*

#*

#*

#*#*

78

55

72

61

67

42

35

7679

48

77

22252421

4300

4000

2223

2222

2221

14191406

1404

1325

1324

1307

1303

13011220

1213

1212

1206

1115

1108

11031062

1022

1006

285885

695690

684

681

670652

650647

630

620

668.5

627.5

604.5

0 60 12030 km

LEGEND

#* Flow Station

!( Climate Station

River Netwroks

Melamchi River (Stage-I)

Yangri River (Stage-II)

Larke River (Stage-III)

Study River Reach

Koshi River Basin

Country Boundary

Ü

INDIAINDIA

NEPAL

CHINA

INDIA

Downstream impact of MWSP is carried out for 11 among 79 sub-basins of Koshi basin


Study River Area

78

55

72

61

67

42

35

7679

48

77

22

24

2125

2225

35

24

21

Study River Reach

Water Transfer Location

In this study, the study river reach starts from sub-basin 35 and ends at sub-basin 79

Water Transfer Location

(I) (II) (III)


Climate Change Projection Scenario

Global Circulation Model:- Downscaled using MarkSim Weather Generator (http://gismap.ciat.cgiar.org/MarkSimGCM/)- Average of CNRM-CM3, CSIRO-Mk3.5, ECHam5, and MIROC3.2- AR4-SRES: BL, A2 and B1- Period: 2000s (1971-2000) for BL

2030s (2016-2045) for A2 and B12050s (2036-2065) for A2 and B1

- Variable: Rainfall, Temperature (Max & Min), Solar Radiation

Statistical Downscaled:- AR4-SRES: BL, A1B, A2 and B1- Period: (1971-2000) for BL

(2001-2100) for A1B, A2 and B1- Variable: Rainfall, Temperature (Max & Min), Solar Radiation,

Relative Humidity and Wind Speed


35

48

61

55

67

72

78

77

76

79

42

24

21

Melamchi

Sapta Koshi

Sun Koshi

Rosi

Tama Koshi

Likhu

Dudh Koshi

Arun and Tamor

Water Supply

to

Kathmandu Valley

Stage-II&III: Water Transfer

1.97 m3/s [62.1 MCM]

Stage-I: Water Transfer

1.97 m3/s [62.1 MCM]

Indrawati 22

25

Larke

Yangri

Melamchi Inter-basin Water Transfer Plan (MIWTP)[Conceptual Plan for Modeling]

Conceptual Methods

Stage I: Sub-basin 24 [170 MLD]

Stage II: Sub-basin 25 [85 MLD]

Stage III: Sub-basin 22 [85 MLD]

Order of the sub-basins as per flow direction

The rivers flow intoStudy River Reach

Impact of MWSPoccur in 11 sub-basins


Monthly Available Water at Headwork of MWSP:

0

50

100

150

200

250

300

350

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Mo

nth

ly F

low

Vo

lum

e [M

CM

]

Larke River

Yangri River

Melamchi River

Total Water Transfer Plan

More than 80% of the total annual river flow occurrs within June to October

Result of Current Scenario


Downstream Impact on River Reach of Koshi Basin:

0.5

1.3

0.6

0.8

0.7

3.9

4.8

77

0.50.2

1.4

0.5

0

12

1.6

3.6

1.6

2.5

1.6

12.7

15.5

1.30.6

4.1

1.3

0 201836 Ü

0.2

2

0.6

0.3

0.4

0.3

2.5

34

0.20.1

0.7

0.2

6

0LEGEND

Dry Season Average Outflow Reduction [%]

Wet Season Average Outflow Reduction [%]

Annual Average Outflow Reduction [%]

0 50 10025 km

Annual Reduction: Stage I : 12%

Stage II : 7%

Stage III : 7%

Wet Season Reduction: Stage I : 6%

Stage II : 4%

Stage III : 3%

Dry Season Reduction: Stage I : 36%

Stage II : 18%

Stage III : 20%

Reduction at Chatara:

Annual : 0.2%

Wet : 0.1%

Dry : 0.6%

Result of Current Scenario


Current Flow [MCM] CC Projected Range of Flow [MCM]

(1976-2005) 2030s 2050s

Before MWSP:

Melamchi river 499 312 - 347 316 - 359

Yangri river 443 306 - 336 306 - 340

Larke river 448 302 - 342 299 - 349

After MWSP:

Melamchi river 437 250 - 285 253 - 297

Yangri river 412 275 - 305 275 - 309

Larke river 417 271 - 311 268 - 318

Annual Available Water at Headwork of MWSP:

Result of CC Scenario


Range of Change in Annual Projected Flow at Headwork of MWSP:



Range of Change in Wet Season Projected Flow at Headwork of MWSP:



Range of Change in Dry Season Projected Flow at Headwork of MWSP:



Average Change and Standard Deviation [±µ,(±σ)] in Projected Flow (2030s):

Annual Change: Stage I : -29% (±2%)

Stage II : -29% (±3%)

Stage III : -37% (±1%)

Wet Season Change: Stage I : -33% (±2%)

Stage II : -33% (±3%)

Stage III : -42% (±1%)

Dry Season Change: Stage I : -16% (±4%)

Stage II : -13% (±5%)

Stage III : -19% (±3%)

Change at Chatara:

Annual : - 8% (±25%)

Wet : -15% (±22%)

Dry : +18% (±37%)



16 (60)

9 (52)

10 (54)

7 (51)

6 (50)

6 (45)

1 (36)

0 (48)

14 (58)42 (58)

15 (59)

LEGEND

Dry season average change in projected flow [%]

Wet season average change in projected flow [%]

Annual average change in projected flow [%]

0 50 10025 km

Ü

-11 (42)

-4 (50)

-25 (30)

-25 (35)

-25 (31)

-10 (39)

-14 (34)

11 (46)-13 (42)

-10 (47)

-12 (42)

-6 (45)

-1 (51)

-19 (34)

-19 (38)

-7 (40)

-20 (35)

-12 (34)

-8 (45)18 (48)

-8 (48)

-7 (45)

-9 (3)-18 (3)-12 (5)

-15 (5)

-39 (3)-30 (3)

-31 (3)

-26 (2)

-35 (3)-27 (3)

-28 (3)

-23 (2)

Annual Change: Stage I : -28% (±3%)

Stage II : -27% (±3%)

Stage III : -35% (±3%)

Wet Season Change: Stage I : -31% (±3%)

Stage II : -30% (±3%)

Stage III : -39% (±3%)

Dry Season Change: Stage I : -15% (±5%)

Stage II : -12% (±5%)

Stage III : -18% (±3%)

Change at Chatara:

Annual : +18% (±48%)

Wet : +11% (±46%)

Dry : +42% (±58%)


Average Change and Standard Deviation [±µ,(±σ)] in Projected Flow (2050s):


Crop

Type 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2

Paddy 101 150 1 27

Wheat 74 135 30 16

Maize 289 125 1 3

Millet 188 105 16 28

Barley 4 120 15 16

Pulses 47 100 25 16

Oilseed 52 110 4 16

Potato 62 130 9 1

Vegetable 50 105 28 16

MayIrrigated Area [ha]

Cropping Length [Day]

Jan Feb Mar Apr DecJun Jul Aug Sep Oct Nov

Crop

Type 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2 1 2

Early Paddy 161 90 25 22

Main Paddy 289 105 25 7

Wheat 74 120 15 16

Maize 128 105 1 13

Vegetable 215 180 8 11

MayIrrigated Area [ha]

Cropping Length [Day]

Jan Feb Mar Apr DecJun Jul Aug Sep Oct Nov

Existing Cropping Pattern and Calendar

Source: - Field investigation - District Ag. statistics

Possible Change in Cropping Pattern and Calendar

Source: - Field investigation - Proposing by DoI

Cropping Pattern and Calendar of Melamchi River Command Area:

Result – Crop Water Requirement


Rainfall vs Crop Water Requirement (CWR) in present and change in cropping pattern scenario


Crop Water Requirement (CWR) of Melamchi River Command Area:

1

10

100

1000

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Wat

er D

epth

[m

m]

CWR [Change in Cropping Pattern]

CWR [Present Cropping Pattern]

80% Dependable Rainfall

Irrigation Requirement – Change in cropping pattern

scenario

Irrigation Requirement – Present cropping pattern

scenario


Comparative plot of water availability and gross irrigation requirement (GIR) in driest month


Impact of MIWTP on Melamchi River Command Area in Current Climate Scenario:



Impact of MIWTP on Melamchi River Command Area in Current Climate Scenario:

Comparative plot of water availability and GIR at 40% overall efficiency in driest month

Intensive Water Use Scenario


Impact of MIWTP on Melamchi River Command Area in CC Scenario (2030s):





Impact of MIWTP on Melamchi River Command Area in CC Scenario (2050s):





Conclusion

In past, detail quantification of the impacts in downstream sub-basins have not been done, hence this study help to fill this gap

In this study, flow reduction is quantified in all three stages at sub-basin level under current and future climate projection scenario

In the current scenario, MIWTP will decrease annual water availability by less than 12% on the sub-basin that is immediately downstream of the transfer points but not further downstream towards the basin outlet, the water availability will decrease by 0.2%

THANK YOU !!!

Average climate change result shows that no water stress problem will occur in Melamchi river command area under current and future scenario

Under intense water use scenario, the Melamchi river command area can increase;< 2.2 times of the present area at current climate scenario (< 636 hectare)< 1.4 times of the present area at 2030s climate scenario (< 405 hectare)< 2.0 times of the present area at 2050s climate scenario (< 578 hectare)

Education

Downstream impacts of the melamchi inter basin water transfer plan (miwtp) under current and future climate change projections