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Dr. Emmanuel Obuobie Surface Water Division WRI Conference Room, 15.07.2014 Groundwater Futures in Sub-Saharan Africa (Grofutures)

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Presentation on theme: "Dr. Emmanuel Obuobie Surface Water Division WRI Conference Room, 15.07.2014 Groundwater Futures in Sub-Saharan Africa (Grofutures)"— Presentation transcript:

1 Dr. Emmanuel Obuobie Surface Water Division WRI Conference Room, Groundwater Futures in Sub-Saharan Africa (Grofutures)

2  Project Duration: 1 year ( )  Project Locations: Ghana, Tanzania, Ethiopia, & Uganda  Implementing Partners: WRI, Addis Abba University, IWMI, Sokoine University of Agriculture, University College London, University of Sussex, Overseas Development Institute, International Development Study, IGRAC Project Basics

3  WRI Project Team: E. Obuobie, C. Asante-Sasu, & F. Oblim  Project Status: Ongoing, Catalyst phase - 70% completed Project Basics Cont’d  Main Objective: To develop scientific basis and tools to guide the management and sustainable use of groundwater to help meet increased agricultural, domestic and industrial water demands, and to protect vital groundwater discharges that sustain vital ecosystem services

4 Current and future water demands/supply in the Atankwidi basin & role of groundwater

5 Project Area River Basin: Atankwidi (275 km 2 ) Admin: Upper East Region (northeastern Ghana) Districts: Bongo, Bolga, Kasena Nankana (E+W)

6 Monthly mean temperature and rainfall at Navrongo ( ) (Martin, 2006) Characteristics of basins Cont’d

7 Basin covers 6 villages in Ghana – Kandiga, sirigu, Yuwa, Zoko, parts of sumbrungu and Mirigu Population was 45,841 in 2010 (GSS, 2012) – 47% males & 53% females Settlement is largely rural (90% rural, 10% urban)

8 Current water demands (2010) Average per capital requirement for domestic use: 11.7 m 3 /c/year (90% of population – 30 l/c/d; 10% of population – 50 l/c/d) – figures from (MWH, 1998, cited in Agodzo, 2003) Industrial use: assumed to be about half of domestic use – 6 m 3 /c/year Total per capital water requirement for domestic/industrial uses is 17.7 m 3 /year Basin population in 2010: 45,841 Total water requirement for domestic/industrial uses in 2010 was 811,386 m 3 Domestic & Industry – Atankwidi Basin

9 Current water demands (2010) Total land area under irrigation in the dry season: 387 ha (2008 figure – Barry et al., 2010) Main irrigated crop: Tomato– water requirement of 604 mm or 6,040 m 3 /ha in northern Ghana (Agodzo et al., 2003) Assuming water requirement is fully met, and irrigation efficiency of 0.7, irrigation requirement in the basin would be 3,272,472 m 3 ( km 3 ) Irrigated agriculture - Atankwidi

10 Current water demands (2010) Domestic and industrial demand = 811,386 m 3 Irrigation water requirement = 3,272,472 m 3 Total current water requirement = 4,083,858 m 3 Total water demand- Atankwidi

11 Future water demands (2025) Average per capital requirement for domestic use in 2025 is 15 m 3 /c/year (80% of population – 35 l/c/d; 20% of population – 65 l/c/d: Agodzo et al., 2003) Industrial use: assumed to be half of domestic use – 7.5 m 3 /c/year Total per capital water requirement for domestic/industrial uses will be 22.5 m 3 /c/year Basin population in 2025: 54,016 (growth rate of basin region: 1.1 % - GSS, 2012) Total water requirement for domestic/industrial uses in 2025 will be 1,215,360 m 3 Domestic & Industry – Atankwidi Basin

12 Future water demands (2025) Current (2010) irrigation water demand = 3,272,472 m 3 ( km 3 ) Two scenarios are considered for 2025: – Sc1: Increasing irrigation water demand by population growth between 2010 and 2025; and – Sc2: increasing irrigation water demand by doubling cropping intensity (from 1 to 2) Basin population growth rate is assumed to be same as the census growth rate for the Upper East Region (1.1 % - GSS, 2012) Irrigated agriculture - Atankwidi

13 Future water demands (2025) cont’d Basin population: 45,841 (2010 estimated at growth rate of 1.1%) & 54,016 (2025) – Population Growth between 2025 & 2010 = 17.8 % Irrigation demand for 2025 – Sc1: 3,861,517 m 3 ( km 3 ) – Sc2: 6,544,944 m 3 ( km 3 ) Irrigated agriculture - Atankwidi

14 Future water demands (2025) cont’d Total water demand in 2025 under irrigation scenario 1: 5,076,877 m 3 Total water demand in 2025 under irrigation scenario 2: 7,760,304 m 3 Total water demand- Atankwidi

15 Basin Water Resources Rainfall Stream/river flow Groundwater

16 Basin Water Resources Cont’d Mean annual rainfall ( ) = 990 mm (0.990 m) Basin catchment area = 275 km 2 Rainwater in the catchment = 273 Mm 3 (0.273 km 3 ) Rainfall – Atankwidi

17 Basin Water Resources Cont’d Runoff at basin outlet – Atankwidi Estimated based on Budyko’s model (Budyko, 1974)  Runoff = Precipitation - Evaporation Basin mean annual evaporation = 844 mm (estimated from FAO New_LocClim) Basin annual runoff = 152 mm (15.2% of annual rainfall) Runoff volume (surface water) = 42 Mm 3 (0.042 km 3 ) There is no information on surface water usage. Groundwater is used mainly.

18 Basin Water Resources Cont’d Groundwater– Atankwidi (Martin, 2006) Groundwater abstraction structures:  Boreholes with hand pumps = 120 (2002)  Hand dug wells (HDW) = 224 (November 2002); 40% modern wells and 60% traditional wells. Traditional wells: 135  Built by community or family  Depth ranges from 1.5m - 14m (averaged 6 m) below ground  Constructed more than 25 years ago; some in the 1920s  Groundwater abstraction is done manually  About 70% of wells dry up during dry season

19 Basin Water Resources Cont’d Groundwater– Atankwidi Modern wells:  Built with external support (government, NGOs)  Depth: 6m – 18m (averaged 10m)  Relatively recent, about 10 years ago  A third of modern HDW are equipped with hand pumps  40% of wells dry up in the dry season

20 Basin Water Resources Cont’d Groundwater – Atankwidi Location of boreholes and hand dug wells in Atankwidi basin in Ghana (Martin, 2006)

21 Basin Water Resources Cont’d Groundwater – Atankwidi Key assumptions for computation:  HDW were used averagely 4 hours per day (high end)  Withdrawal rate for HDWs was assumed to be 0.5 m3/h (equiv. of 2 buckets/minute – a bucket is about 4 liters)  Due to drying up of HDWs, period of usage was fixed at 10.5 months for modern HDWs and 9 months for traditional HDWs  Boreholes were used averagely 10 hours per day  Boreholes pumps were mostly Afridev/Indian Mark II with pump rates of 0.6 – 1.7 m 3 /h; assumed average pumping rate of 1 m 3 /h

22 Basin Water Resources Cont’d Groundwater– Atankwidi Groundwater abstracted as proxy for supply:  Annual total abstraction = 594,000 m 3  Annual abstraction via HDW = 167,000 m 3 (28%)  Annual abstraction via boreholes = 427,000 m 3 (72%) Potential available groundwater (based on recharge):  Mean annual basin recharge = 6% of rainfall (990 mm)  Assume 3% of recharge is available for use; leaving the other 3% to environmental flow and other uses  Potential available groundwater = 8,167,500 m 3 (8.17 Mm 3 )

23 Basin Water Demands/Supply _SC12025_SC2 Demands4,083,8585,076,8777,760,304 Supply50,167,500 (Total) 8,167,500 (GW-R) 594,000 (GW-Ab)

24 Thank you


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