impact of small reservoirs and dugouts in the ghana portion of the black volta basin on hydrology...

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: cpwfsecretariat@cgiar.org

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