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The Effect of Global Warming in Safeguarding
Water Supply in Arid Regions
Ben van der MerweEnvironmental Engineering Services
Contents
• Climate Change ????• Water supply sources• Water Demand Management• Unconventional Sources • Security of Supply• Water supply threads• Conclusions
Rainfall and Evaporation
CountryRainfall Range
(mm/a)
AverageRainfall(mm/a)
PotentialEvaporation
Range(mm/a)
Total Surface Runoff
(mm) (km2)
Angola 25 – 1,600 800 1,300 – 2,600 104 130.0
Botswana 250 – 650 400 2,600 – 3,700 0.6 0.35
Lesotho 500 – 2,000 700 1,800 – 2,100 136 4.13
Malawi 700 – 2,800 1,000 1,800 – 2,000 60 7.06
Mozambique 350 – 2,000 1,100 1,100 – 2,000 275 220.0
Namibia 10 – 700 250 2,600 – 3,700 1.5 1.24
South Africa 50 – 3,000 500 1,100 – 3,000 39 47.45
Swaziland 500 – 1,500 800 2,000 – 2,200 111 1.94
Tanzania 300 – 1,600 750 1,100 – 2,000 78 74.0
Zambia 700 – 1,200 800 2,000 – 2,500 133 100.0
Zimbabwe 350 – 1,000 700 2,000 – 2,600 34 13.1
Change in Biomass (Climate Change??)
2030??
Possible Effects of Climate Change • Intergovernmental Panel on Climate Change (1.5 Max 20C)
• Scandinavia & Arctic Circle 300 C (Permafrost)• Namibia: Increased evaporation rates i.e. from surface
reservoirs (10 to 13%)• Heat wave days increase with 20 to 48 days• More frequent droughts with an estimated decline of
20% on the average rainfall in the CAN by 2050?? • Increased maximum temperatures (2 to 2.70 C) result in
stronger winds • Groundwater recharge down with up to 70%• Erratic periods with more intense rainfall with a possible
increase in flooding in some parts
Effect of Climate Change (IWA)
Central Area of Namibia
Conventional Water Supplies
Schematic Representation of the Dam Basin CharacteristicsConjunctive use of surface and groundwater to curb evaporation
Von Bach Dam (48.6 Mm³) 1970Swakoppoort Dam (63.5 Mm³) 1977Omatako Dam (43.5 Mm³) was completed in 1982Several Aquifers north & central area
CONVENTIONAL SOURCES (CONJUNCTIVE USE)•Three dam system 16 Mm3/a (average)•Ground water Karst 2.8+ Mm3/a (Drought)•Windhoek boreholes 0.5-1.73 Mm3/a (5.5 Drought)WDM: 20%+ reduction since 1995
UNCONVENTIONAL WATER SOURCESPotable Reuse (1968) 6 (7.6) Mm3/aFuture Target 50% of total water productionWMARS (19 Mm3/a) 1.73+ up to 11.5 Mm3/aDual Pipe System 1.3 Mm3/a
Available Water Sources
Water Demand Management Approach
Strategies for Bulk Supply, Urban, Rural, Livestock, Irrigation, Mining & Tourism
Water Regulator: Evaluate Tariffs
Set targets for PI’s
Access to services
Urban performance indicators based on population served and water use
Effect of WDM in Windhoek
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roje
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s i
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m3/a
ENWC Low ENWC Likely ENWC High
CAWMP Low CAWMP Middle CAWMP High
TSA Low TSA Likely TSA High
WCE NWRMR PRODUCTION
REPAYMENT PERIOD 8 MONTHS THROUGH BULK SUPPLY SAVINGSSpot leakage on Google Earth
Location Average Night Flow
(litres/h)
Median Night Flow
(litres/h)
Maximum Night Flow (litres/h)
Augustinium High School 12 294 14 088
14 624(N$ 3.4 m)
Centaurus High School 107 55
551(N$ 127 00)
Cohen Building 146 0.0494
(N$ 133 620)
Windhoek Prison 23 998 24 201
27 512(N$ 6.4 m)
Government Buildings in Windhoek
Do Nothing Alternative?
Integrated Water Resource
Management Plan
Windhoek Water Supply Sources
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Calender Year
An
nu
al P
rod
uc
tio
n in
Mm
3 /a
Boreholes Reclaimed Surface Water Irrigation
Windhoek Aquifer Hydrogeological Set-up
Aquifer Compartments(74 Mm3 250 m slice)
11.7 Mm3
33.6 Mm3
5.3 Mm3
10.2 Mm3
Total: 89.11 Mm3
Best Estimate: Future Storage Abstraction Potential
0 Mm3
6.9 Mm3
3.8 Mm3
7.2 Mm3
10.4 Mm3
7 km
Scheme or Water Source kWh/m3 Remarks
Weighted Average up to Reservoirs
NGWRP up to Windhoek Reservoirs 1.40 Excluding plant power requirement of 0.95 kWh/m3
Gammams Advance Reclamation up to Windhoek Reservoirs
0.76 Excluding plant power requirement of 1.5 kWh/m3
Von Bach up to Windhoek Reservoirs
3.01 Excluding plant power requirement of 0.2 kWh/m3
Weighted average WMARS injection
2.83 Blend NWRP, Von Bach & New Gammams Reclamation
Weighted average WMARS abstraction
1.07 Abstraction up Windhoek reservoirs
Weighted average of injection and abstraction up to Windhoek Reservoirs
2.93 Based on average abstraction until 2030 (15 years) less natural recharge to determine injection volume
Desalination Coast-Windhoek up to Windhoek Reservoirs
11.28 Excluding treatment plant energy of 3 kWh/m3
Okavango River to Windhoek up to Windhoek Reservoirs
4.91 Excluding Von Bach WTP energy requirement estimated at 0.2 kWh/m3
Power Requirements
Results of the Modelling Green Climate Fund(95% Security of supply)
Blue Green Algae Swakoppoort
Incentive for Maximize Reuse in Windhoek to 50%+ of supply (No effluent)Require dedicated source for aquifer recharge
Chemical Water Quality Swakoppoort Dam
Conclusion
In arid countries implementation of WDM and the utilisation of unconventional sources in
combination with conventional resources can improve security of supply in shorter term
and can realise major savings in capital costs and energy in the long term
References
• City of Windhoek & NamWater for updated information
• IWRM Reports
• Okavango link report
• Various WMARS reports
Thank you for listening
Drilling of Inclined Probe Boreholes
Install Casing in a Production Borehole
