Presentation from

2015 World Water Week in Stockholm www.worldwaterweek.org

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World Water Week 2015 Stockholm

The impact of floods and droughts on groundwater resources: the Namibia case study, The Cuvelai- Etosha Basin (CEB), Namibia

Authors: Quinger, M.1 ; Ihemba, S2; Amakali, M 2 ; Lohe, C.1; Christelis G.3 *1 Bundesanstalt für Geowissenschaften und Rohstoffe - BGR Germany *2 Ministry of Agriculture Water and Forestry – Namibia *3 CHR Consult – Namibia

Key aspects of this presentation 1. Are large scale groundwater mapping projects useful? 2. Can a strategic groundwater exploration program help to mitigate existing or imminent water shortages: Example Northern Namibia 3. Conclusions / points for discussion

Hydrogeological Map of Namibia

Precipitation

Potential Evaporation

Study Area Cuvelai- Etoscha Basin (CEB)

Current water supply of northern CEB

Climate Change: Floods and Droughts

Climate change in Northern Namibia is a fact!

In the past 6 years: • 4 exceptional floods • 2012/2013 dryest year since 1980

Situation  45% of Namibian population in the CEB  out of those, about 80% are supplied by a pipeline network that receives water from Angola  25% relies on partly poor groundwater resources  The dry year in 2012/13 demonstrated the high vulnerability of the current supply: many boreholes and dugwells fell dry  As a reaction, numerous “drought relief” boreholes were drilled without proper planning into the same resource, worsening future problems

Steps from groundwater investigation to management 1. 2. 3. 4.

Desktop Study (2006) Hydrocensus / Sampling campaign (2007- 2011) Geophysical Investigations (1999, 2007 -2009) Drilling of boreholes, Hydrogeological and Geophysical tests, Hydrochemical sampling campaign (2009 – 2013) 5. Monitoring, Protection Guidelines (2011 – 2016) 6. Evaluate and disseminate information, elaborate abstraction volumes (2011 – continuous)

Geophysical investigation (TEM)

Investigations on Groundwater Resources in the CEB 

Intense geophysical surveys (TEM)



In total 36 boreholes were drilled in Phase I and II of the project and installed with data loggers



The first 400m cored borehole in the Kalahari-Deposits.



Pump-tests and hydraulic tests evaluated.



Long term Pump test Eenhana conducted. First wellfield drilled with capacity of > 100 m3/h.



On the job-training with more than 40 hydrogeologists from GeoDiv and students



7 Groundwater Sampling campaigns in the Ohangwena Region were conducted for general composition, rare earth elements, stabile isotopes, radio isotopes (C-14), Fluoride Studies



Cooperation with Unam, IAEA, Sasscal established

Oshana perched aquifer

unsaturated zone Ohangwena I upper (often saline) aquifer ~140-200 m Depth

overburden

aquifer

aquitard

confining layer

hydraulic exchange

!

aquiclude aquitard

deeper seated, fresh water aquifer

?

aquifer

Ohangwena II sustainable yield ~250-350 m Depth

aquitard

Recharge Principle (not to scale) N

S

Recharge Border Nam - Ang

Abstraction

Perched Hydraulic Head

Ohangwena I

Impermeable Layer

Ohangwena II

Namibia

Angola

From discovery to Sustainable usage

Key Figures KOH II Parameter

Values presented in 2013

Current Status Values

Area covered Namibia

2500 km²

5170 km²

Stored volume

5 billion m³

20 billion m³

Actual recharge 2011/2012

???

635,000m³

Potential recharge

???

???

Average depth to top of aquifer

250 m

235 m (189 – 331)

Average thickness

60

65 m (33 – 97)

Average rest water level below ground

20 m

17 m (9 – 29)

Average Transmisivity

???

74 m²/day (5 – 240)

Average specific yield per m draw down

???

1,4 m³/h (0.28 – 5.29)

Basis for resource protection • Assessment of current status • Establishing of modern GW monitoring network • Vulnerabilty and Risk Assessment • Protection measures: Delineation of protection zones, abstraction licenses etc. • Legal framework • Law enforcement vs stakeholder participation

Extent of KOH II Aquifer

GROWAS II Modules

GROWAS II monitoring data

Planningtool Vulnerability Map

Products: -

Vulnerability Map of Groundwater Resources in the CEB

-

Risk Assessment / Hazardous sites

-

Main technical Report

-

Simple manual on how to use the map

-

Update of GROWAS database

-

GIS Hydrochemistry CEB

-

Guideline GW Protection zones

Conclusion •

The „hidden treasure“ groundwater is still widely under- utilized and poorly managed due to a lack of awareness. The global and regional overview maps serve as an „eye-opener“ for politicians and water users.

•

Improved groundwater management is one of the best adaptation measure to climate change in arid areas. Especially Africa‘s GW- potential is by far not fully utilized.

•

The protection and sustainable use of resources requires careful monitoring, a sound legal framework and very close cooperation with all stakeholders.

•

The investigation approaches especially in developing countries need to be re- considered! Only strategic, large scale exploration programs can deliver the basis for sustainable management.

Thank you for your attention!