Windhoek Namibia: A Case Study in Water

Supply in an Arid Environment

Petrus du Pisani City of Windhoek

Why Drink Waste Water?

• When there are no alternatives, the choice becomes easy

• Why is there no choice? • Surviving and growing on limited

Natural resources is possible• TheWindhoek experience might

benefit those facing reduced supplies due to Climate Change

Scope of Presentation

• History and supply imperatives• Potable Reclamation• Water Demand Management• Semi Purified Irrigation• Artificial Aquifer Recharge• Aquifer Protection• Conclusions

• No CC strategies in place• Several models, mostly indicate:

Larger part of Southern Africa hotter with less rainfall

• More droughts & floods - less run-off & natural groundwater recharge

• Slight change in temperature implies major reduction in run-off (10% to 20%+)

Climate Change

Temperature & Rainfall Change

Von Bach Dam Inflow (Main supply source)

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Rainy Season

Inflo

w in

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Inflow Median

Finding Water in Namib

Fish river flood 2005

Location of Namibia and Perennial Rivers in Africa

Namibia / Windhoek• Area 825 000 km²• Population 2 000 000• GDP per Capita (2002) U$ 2 284 • Average rainfall mm 250 • Average evaporation3700 mm • Windhoek Capital City• 300 000 inhabitants @ 5% per year

History of Water Supply

• Settlement at Hot springs 1840 • 1911 Well field development • 1933 Avis Dam, capacity 2,4Mm³• First mention of reuse in 1954• By 1957 , aquifer overused by 57%• 1958 Goreangab Dam & plant• Groundwater still main source

Water Supply Imperatives

• Annual rainfall of 360 mm• Annual evaporation of 3400mm• Groundwater over exploited• Closest Perennial river 750 km• Yields from 2 dams low• Known existing sources mostly

harnessed

Hydrological cycle14

%

83%

1%2%

100%

Potable Reclamation

• Early 1960’s first Pilot plants • By 1968, scientists confident that

water could be produced that was fit and safe to drink.

• 1968, Goreangab plant converted• Potable reuse accepted as part of

supply strategy

Potable Reclamation

• Initial capacity 4300 m³ / day• 1969 and 1992 4 x Process

upgrades• 1996 Ultimate Capacity of 7500m³• City Consumption 60 000m³ p/d• Okavango option unaffordable

Other Supply Initiatives

• ’78 to ‘93 Govt built 3 surface dams on ephemeral rivers safe yield 17 M m³

• Independence 1990 High Influx • 1995 Eastern National water carrier• 1990 to 2000, 3 seasons >average inflow• Major droughts in 1986, 1991, 1996

EXISTING PIPELINES

CANALDAMS

PROPOSED PIPELINE

Extended Potable Reclamation

•1996: decision to extend to 35%•Construction New 21 Mld Goreangab Plant started 1999•Upgraded process train•Blending ratio fixed to 35% max•Plant completed 2002•Currently producing 16 Mld, 25%•20 Yr quality based O&M Contract•Waste water reliable resource

New Goreangab Process Train

PAC, ACIDOZONEPOLYMER

KMnO4NaOH

H2O2

FeCl3FeCl3

RAPID SAND FILTRATION

DISSOLVED AIR FLOTATION

COAGULATION / FLOCCULATION

OZONATION

ULTRAFILTRATION

CHLORINE /NaOH

CHLORINE /NaOH

BLENDING &DISTRIBUTION

CHLORINATION / STABILISATION

BIOLOGICAL & GRANULAR ACTIVATED CARBON

FILTRATION / ADSORPTION

BAC

BAC

GAC

GAC

GAC

GAC

New Goreangab Plant completed in 2002

Short History Of Wastewater

Water Demand ManagementCity of Windhoek - Water Supply and Demand

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ater

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in M

m3

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50,000

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latio

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Total WC Lower likely Likely Upper Likely Low Middle High Total supply Population

1994-Water demand management

1992-1998 drought

Demand Management Measures

•Permanent Rising Block tariff0-6 m³ p/m N$ 6.276-36 m³ p/m N$ 10.43> 36 m³ p/m N$19.21

•Private Pools covered when not in use•Low water use plumbing mandatory•No automatic flushing urinals•Garden watering hours•Hose pipe bans when required• Water intensive industry not promoted

Semi Purified irrigation• Dual pipeline length 75 km versus

approximately 1 800 km water lines. • Replaced 5.8% (2005) of potable supply

with filtered sewage effluent • Unrestricted irrigation landscaping,

sports fields & parks • Treatment train: Secondary sewage,

coagulation, flocculation, DAF, sand

filtration and chlorination.

Landscaping & Sports fields

Windhoek Country ClubWindhoek Country Club

Artificial Aquifer Recharge

•Ground water from springs and shallow wells was reason for Windhoek location• Vast volume of water est to be KMm³•Natural recharge average 1,73 Mm³•Aquifer over exploited by 20Mm³•High evaporation from dams 3400 mm/a•If water can be replenished, high abstraction possible : up to 2 year supply•Since 2006, deep abstraction and injection holes up to 470 metres

Ground Water Contribution

Aquifer Recharge PotentialDisplay by Dr. Ricky Murray of the CSIR

Typical Recharge Station

Carbon filters & Chlorine Contact

Conjunctive Use of Water Sources

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Year

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harg

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Boreholes Surface waterReclaimed AR Abstraction Irrigation AR Injection

Production from sources until 2006

Future AR Scenarios

Water Supply per Source (Conventional versus Unconventional)

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Ann

ual v

olum

e in

Mm3 /a

nnum

2005 2011 2014 2019Year

Boreholes Surface waterReclaimed AR Abstraction Irrigation AR Injection

4.6%

7.2%

49.8%

25.8%

6.4%

21.6%

27.1%

31.3% of Demand

6.3%

26.6%

6.9%

10.3%

34.3%

9%

65.2%

2%

5.8%

15.4%

74.1%

Augmentation Alternatives

Tsumeb & Karst III

N$ 310 mil

Okavango Schemes

N$ 1642 mil

Windhoek MAR

N$ 216 mil

Adjusted 2007 cost estimates

Aquifer Protection Initiatives

STUDIES REVEALED:• High recharge potential• Extremely high rates of

groundwater movement• Highly fractured and jointed

geology• High pollution potential

Aquifer Vulnerability Study

• 1998 vulnerability study• Risk based approach after

Rosen and Legrand• Assessed pollutant travel

potential• Produced vulnerability map

Aquifer Vulnerability Map

Aquifer protection

• Existing Development included industrial area in aquifer area

• Approved planning included 17 000 residential plots

• Enabling legislation lacking• Protection built into town

planning scheme• Replanned for 7000 plots

Town Planning Approach

• Designed to control land use• Southern area defined as

conservation zoning• Prohibited uses defined for

existing developments

Development Limitation Line

Town Planning Provisions• CONSENT USES• Municipal purposes and public

infrastructure, hotel or other accommodation establishment designed to promote environmental conservation with adequate provisions that ensure no groundwater pollution will occur, park, playground, pasture land and associated agricultural building but excluding any concentration of domesticated animals, …….

Town Planning Provisions• PROHIBITED USES• No noxious industrial buildings may be

erected, no noxious activities may be undertaken and no hazardous substances may be stored in combined quantities exceeding 200 litres on land located South of the Southern edges of Academia, Windhoek, Olympia and Klein Windhoek Townships

Conclusions

• Windhoek has no specific plans for CC• All Planning decisions are based on

availability of water• Existing water sources optimised• Unconventional sources Maximised• PROTECT , OPTIMISE , REDUCE

DEMAND , REUSE MAXIMALLY• Climate Change - Attitude Change

Visit our website at

www.windhoekcc.org.na