Downstream Hydrological Impacts of the Melamchi Inter-basin Water Transfer Plan (MIWTP)
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Transcript of 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)
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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
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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
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Method
78
55
72
61
67
42
35
7679
48
77
2224
21
25
2225
35
24
21
Study River Reach
Water Transfer Location
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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
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Result and Discussion
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
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15.71
18.06
0
10
20
30
40
50
60
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
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
Result and Discussion
Mean Monthly Flow Available at MWSPs Headwork in Melamchi River :
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Result and Discussion
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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Result and Discussion
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
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Result and Discussion
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 !!!
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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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Additional Information and Further Work
1
10
100
1000
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
WaterDepth[mm]
CWR [Change in Cropping Pattern]
CWR [Present Cropping Pattern]
80% Dependable Rainfall
Impact of MIWTP on Agricultural Command Area of Melamchi River:
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
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Additional Information and Further Work
Impact of MIWTP on Agricultural Command Area of Melamchi River:
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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Additional Information and Further Work
Impact of MIWTP on Agricultural Command Area of Melamchi River:
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)