impact of small reservoirs and dugouts in the ghana portion of the black volta basin on hydrology...
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by J. Atulley, S. Nii Oda and F. Annor Presented at the Final Volta Basin Development Challenge Science Workshop, September 2013TRANSCRIPT
Joan A. Atulley 1,, Samuel Nii Odai 1 and Frank Annor 1,2
Main message Despite the important role agriculture play in the livelihood of most rural populace, the majority still rely on rainfed farming. Meanwhile, uni-modal rainfall pattern of SSA makes rain-fed agriculture unreliable. Hence, small reservoirs provides the opportunity to store water for dry season irrigation, livestock watering, aquaculture and domestic purposes among others. Non the less, developing more reservoirs upstream beyond a certain threshold may pose significant adverse effect on hydrology and users downstream (Bartley et al., 2002).
Conclusions (lessons & Recommendations for defined stakeholder)
Pictures
CGIAR Challenge Program on Water and Food P.O. Box 2075,127 Sunil Mawatha Pelawatta, Battaramulla, Sri Lanka T: +94 11 288 0143 F: +94 11 278 4083 E: [email protected]
www.cgiar.org www.waterandfood.org This document is licensed for use under a Creative Commons Attribution –Non commercial-Share Alike 3.0 Unported License August 2013
June 2013
Purpose
Findings
About CPWF The CGIAR Challenge Program on Water and Food was launched in 2002. CPWF aims to increase the resilience of social and ecological systems through better water management for food production (crops, fisheries and livestock). CPWF currently works in six river basins globally: Andes, Ganges, Limpopo, Mekong, Nile and Volta. CPWF is a member of the CGIAR Water, Land and Ecosystems Research Program. The program focuses on the three critical issues of water scarcity, land degradation and ecosystem services, as well as sustainable natural resource management. CGIAR is a global agriculture research partnership for a food secure future. Its science is carried out by the 15 research centers who are members of the CGIAR Consortium in collaboration with hundreds of partner organizations.
Method
The purpose of this study is to explore the impact of small reservoirs and dugouts in the Ghana portion of the Black Volta basin on hydrology and water allocation in the Basin
field visits
Data Acquisition
Scenarios Development
introduced key assumptions
Secondary
Data
Satellite Imagery
WEAP Calibration
Interviews/ observation Irrigation
water Livestock
water
Hydro-meteological
data
Reservoirs’ location GPS
Cord.
• There is no significant impact on water quantity flowing downstream from upstream catchments Nwokuy, Samandeni, Goere & Boromo)
• About 55.6Bm3 of water flow downstream untapped sustaining aquatic ecosystem services, biodiversity and groundwater recharge
• It is possible to develop up to 350 SR by 2040 without significant impact on current flow regimes, assuming current rainfall patterns persist. On this basis, we recommend 5 reservoirs be constructed annually to expand livestock production and dry season irrigation
•48% of reservoirs in the UWR are silted, broken or seeping
• Concerns on water quality impacts are not addressed
Cat. No. Dap. 11
Nou. 58
Von. 16
Bui 4
Bam 1
Total 90
Bamboi Livestock Bui Livestock Dapola Livestock Noumbiel Livestock Vonkoro Livestock
Unmet DemandScenario: Reference, Monthly Average
January February March April May June July August October December
Cub
ic M
eter
6,500
6,000
5,500
5,000
4,500
4,000
3,500
3,000
2,500
2,000
1,500
1,000
500
0
3* growth rate 5* growth rate Reference
Unmet DemandSelected Demand Sites (3/33), Monthly Average
January February April May June July August October December
Th
ou
san
d C
ub
ic M
ete
r
55
50
45
40
35
30
25
20
15
10
5
0
Bamboi small reservoir1Bui small reservoir1 Dapola Small Rreservoir1Noumbiel Small Reservoir1Vonkoro Small Reservoir1
Demand Site Coverage (% of requirement met)Scenario: Reference, Monthly Average
January M arch A pril M ay June July A ugust October D ecem ber
Per
cent
100.099.899.699.499.299.098.898.698.498.298.097.897.697.497.297.096.8
52.4
32.4
8.3 6.9
0
10
20
30
40
50
60
Perc
enta
ge o
f res
ervo
irs
State of reservoirs
State of reservoirs in the Upper West Region •Good - silt occupies ≤ 25 % designed volume & good embankment •Silted- ≥ 50 % filed with silt.
Seepage – Water leaks out from dam wall Broken – embankment is broken
Impact of Small Reservoirs and Dugouts in the Ghana portion of the Black Volta basin on hydrology and water allocation in
the Basin
0
500
1000
1500
2000
2500
1950 1960 1970 1980 1990 2000 2010
Flo
ws
(cm
s)
Year
September flows for Bui (1951-2010)
Infiltration
Full Supply Level of
Bui
Total vol. of
reservoirs
6.3 Mm3
225Mm3
12.7 Bm3
Runoff downstream
55.6Bm3
68.5 Bm3 Runoff
Rainfall
Small reservoirs’ contribution to decline river flow
Unmet Water requirements
Available surface water
1
3
2
• L-Bamboi records hihest unmet demand for Jan. & Feb.
• I-Highest unmet demand recorde in March & April (peak of dry season
• S-96.8% coverage for April