Dr. Emmanuel ObuobieSurface Water Division

WRI Conference Room, 15.07.2014

Groundwater Futures in Sub-Saharan Africa (Grofutures)

Project Duration: 1 year (2013-2014)

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

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

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

Project Area • River Basin: Atankwidi (275 km2)• Admin: Upper East Region (northeastern Ghana)• Districts: Bongo, Bolga, Kasena Nankana (E+W)

Monthly mean temperature and rainfall at Navrongo (1961-2001) (Martin, 2006)

Characteristics of basins Cont’d

Characteristics of basins Cont’d• 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)

Current water demands (2010)

• Average per capital requirement for domestic use: 11.7 m3/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 m3/c/year

• Total per capital water requirement for domestic/industrial uses is 17.7 m3/year

• Basin population in 2010: 45,841 • Total water requirement for domestic/industrial uses in

2010 was 811,386 m3

Domestic & Industry – Atankwidi Basin

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 m3/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 m3 (0.0032 km3)

Irrigated agriculture - Atankwidi

Current water demands (2010)

• Domestic and industrial demand = 811,386 m3

• Irrigation water requirement = 3,272,472 m3

• Total current water requirement = 4,083,858 m3

Total water demand- Atankwidi

Future water demands (2025)

• Average per capital requirement for domestic use in 2025 is 15 m3/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 m3/c/year

• Total per capital water requirement for domestic/industrial uses will be 22.5 m3/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 m3

Domestic & Industry – Atankwidi Basin

Future water demands (2025)

• Current (2010) irrigation water demand = 3,272,472 m3 (0.0032 km3)

• 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

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 m3 (0.0038 km3)– Sc2: 6,544,944 m3 (0.0065 km3)

Irrigated agriculture - Atankwidi

Future water demands (2025) cont’d

• Total water demand in 2025 under irrigation scenario 1: 5,076,877 m3

• Total water demand in 2025 under irrigation scenario 2: 7,760,304 m3

Total water demand- Atankwidi

Basin Water Resources

• Rainfall• Stream/river flow• Groundwater

Basin Water Resources Cont’d

• Mean annual rainfall (1961-2001) = 990 mm (0.990 m)• Basin catchment area = 275 km2

• Rainwater in the catchment = 273 Mm3 (0.273 km3)

Rainfall – Atankwidi

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 Mm3 (0.042 km3)• There is no information on surface water usage.

Groundwater is used mainly.

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

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

Basin Water Resources Cont’d

Groundwater – Atankwidi

Location of boreholes and hand dug wells in

Atankwidi basin in Ghana (Martin, 2006)

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 m3/h; assumed average pumping rate of 1 m3/h

Basin Water Resources Cont’d

Groundwater– Atankwidi • Groundwater abstracted as proxy for supply:

Annual total abstraction = 594,000 m3 Annual abstraction via HDW = 167,000 m3 (28%) Annual abstraction via boreholes = 427,000 m3 (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 m3 (8.17 Mm3)

Basin Water Demands/Supply2010 2025_SC1 2025_SC2

Demands 4,083,858 5,076,877 7,760,304

Supply 50,167,500 (Total)8,167,500 (GW-R)594,000 (GW-Ab)

Thank you