Downstream Hydrological Impacts of the Melamchi Inter-basin Water Transfer Plan (MIWTP)

8/6/2019 Downstream Hydrological Impacts of the Melamchi Inter-basin Water Transfer Plan (MIWTP)

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P. Gurung and L. Bharati

International Water Management Institute (IWMI), Lalitpur, Nepal

Downstream Hydrological Impacts of the Melamchi

Inter-basin Water Transfer Plan (MIWTP)


2/20

Introduction

Melamchi Water Supply Project (MWSP): 1973 (Identified)

1998 (Implemented)2008 (Planned to Complete)

2015 (Extend to Complete)

Drinking Water Demand of Kathmandu: 220 MLD

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

130 MLD (Wet Season)

Demand of local people, political circumstances and challenges to engage

private sector partner is major barrier to complete project

Till 2008, project has paid Rs. 880 million as a cash compensation to local

In addition, downstream hydrological impacts is another issue


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Introduction

Project has set minimum downstream release: nearly 35 MLD

At present , Water in Melamchi River Basin is using for :

Irrigation and Water Supply,

MHP Generation and operating Water Mills

Consumed by Forest and Vegetation

Few studies are carried out to account water focused on Indrawati Basin

Use of distributed hydrological model developed for entire Koshi basin to lookhydrological impacts of the MWSP until the outlet of the Koshi basin at

Chatara


4/20

Soil Water Assessment Tool (SWAT) Model:Physically based semi-distributed hydrological model

Water quantity, sedimentation and water quality

Developed by Department of Agriculture, USA

SWAT model developed for Koshi basin is divided into 79 sub-basins (Outlet Chatara)[Developed under Storage Project in Koshi basin of IMWI Nepal]

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

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

Method


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Method

18

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

2624

21

0 60 12030 km


6/20


7/20

Method

78

55

72

61

67

42

35

7679

48

77

2224

21

25

2225

35

24

21

Study River Reach

Water Transfer Location


8/20

Method

Model Calibration and Validation:

Plot of observed versus simulated flow at Koshi basin outlet, Chatara

Calibration and validation is carried out for 15 flow stations within Koshi basin

Calibration Period (1996 2000) and validation period (2001-2005)


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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 Transfer1.97 m3/s [62.1 MCM]

Stage-I:Water Transfer1.97 m

3/s [62.1 MCM]

Indrawati22

25

Larke

Yangri

Melamchi Inter-basin Water

Transfer Plan (MIWTP)[Conceptual Plan for Modeling]

Method

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 flowdirection

The rivers flow intoStudy River Reach

Impact of MWSPon 11 sub-basins


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0

10

20

30

40

50

60

70

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

Flow[m3/s]

Percentage of Exceedence

Stage I - Melamchi River

Stage II - Yangri River

Stage III - Larke River

Water Transfer Plan

Result and Discussion

Simulated Water Availability in Headwork of MWSP:

Downstream flow release at driest month:

Stage I: 13% of the river flow of that month

Stage II: 57% of the river flow of that month

Stage III: 57% of the river flow of that month


11/20


Simulated Water Availability in Headwork of MWSP:

0

50

100

150

200

250

300

350

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

MonthlyFlowV

olume[MCM]

Larke River

Yangri River

Melamchi River

Total Water Transfer Plan

Annual Simulated Flow :

Melamchi: 499 MCM

Yangri: 443 MCM

Larke: 448 MCM

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


12/20

15.71

18.06

0

10

20

30

40

50

60


MeanMonthly

Flow[m3/s]

SWAT Simulated Bhattarai et al., 2002

Annual Mean, SWAT Simulated Annual Mean, Bhattarai et al., 2002

R = 0.99

0

20

40

60

0 20 40 60

SW

ATSimulated

Bhattarai et al., 2002

Flows

Bisector

NSE = 0.93


Mean Monthly Flow Available at MWSPs Headwork in Melamchi River :


13/20


Impact of MIWTP along Downstream 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

02018

36

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%


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Water Balances at the Sub-basins in Study River Reach:

-4000

-2000

0

2000

4000

21 24 25 22 35 42 48 55 61 67 72 78 77 76 79AnnualAv

erageWaterBalance[mm]

Sub-basin Number

Precipitation Actual ET Surface Runoff Percolation Soil Water Content Return Flow Lateral Flow

Highest annual precipitation occur at sub-basin 35 (3355 mm) and lowest at 55 & 61 (1028 mm)

All hydrological component is following the trend of precipitation

Decreasing trend is observed in all hydrological component further towards outlet of basin outlet


15/20


Water Balances at the Sub-basins in Study River Reach:

Sub-basin Number Area, km2 Rainfall, mm Actual ET, mm Net Water Yield, mm21 & 24 148 2072 603 1454

25 110 2072 603 145022 114 2072 614 144435 424 3355 735 258442 432 2088 750 131148 213 2088 707 135355 751 1028 537 48761 558 1028 534 49067 468 1926 696 120872 700 1798 645 113278 1393 1872 731 111977 205 1498 580 89776 231 1180 629 54379 231 1040 658 381

Simulated annual average water balance at sub-basins in study river reach


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Conclusion

In past study, detail quantification of the impacts in downstream sub-basins have notbeen done, hence this study help to fill this gap

In this study, flow reduction is quantified in all three stages at sub-basin level

Result of the study shows that the MIWTP has considerable hydrological impacts on thesub-basin that is immediately downstream of the transfer points but not furtherdownstream towards the basin outlet

All the hydrological components are following the trend of precipitation occurred in thesub-basin and in average these trends are in decreasing order

THANK YOU !!!


17/20

Additional Information and Further Work

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

Type1 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

Present Cropping Pattern andCalendar in Melamchi RiverCommand Area

Possible Change in Cropping

Pattern and Calendar inMelamchi River CommandArea

Impact of MIWTP on Agricultural Command Area of Melamchi River:


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1

10

100

1000


WaterDepth[mm]

CWR [Change in Cropping Pattern]

CWR [Present Cropping Pattern]

80% Dependable Rainfall


Rainfall versus crop water requirement (CWR) in present and possible change in cropping pattern

BUDGET model, developed by KU Leuven, is used to obtain CWR


19/20



Gross irrigation requirement (GIR) in dry season (Jan-May, Nov-Dec) and driest month (Apr)

1

10

100

1000

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

WaterVolume[MC

M]

Overall Efficiency

GIR [Present Copping Pattern]

GIR [Change in Copping Pattern]

Stream Flow in Dry Season (At Present)

Stream Flow in Dry Season (After MWSP)

Stream Flow in April (At Present)

Stream Flow in April (After MWSP)


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GIR in change in command area at 40% irrigation efficiency in dry season and driest month

167%, 9.43

29%, 4.57

104%, 9.43

-1%, 4.57

1

10

100

-50% 0% 50% 100% 150% 200% 250% 300%

WaterVolume[MCM

]

Change in Agricultural Command Area

GIR at 40% Overall Irrigation Efficiency [Present Cropping Pattern]

GIR at 40% Overall Irrigation Efficiency [Change in Cropping Pattern]

Stream Flow in Dry Season (At Present)

Stream Flow in Dry Season (After MWSP)

Stream Flow in April (At Present)

Stream Flow in April (After MWSP)

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Downstream Hydrological Impacts of the Melamchi Inter-basin Water Transfer Plan (MIWTP)

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