Post on 06-Mar-2018
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)
7.56.712.514.4
0102030405060708090
100110120
1970
/71
1972
/73
1974
/75
1976
/77
1978
/79
1980
/81
1982
/83
1984
/85
1986
/87
1988
/89
1990
/91
1992
/93
1994
/95
1996
/97
1998
/99
2000
/200
1
2002
/200
3
2004
/200
5
2006
/200
7
Rainy Season
Inflo
w in
Mm
3 /ann
um
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
0
5
10
15
20
25
30
35
40
45
50
1980
1985
1990
1995
2000
2005
Ann
ual W
ater
Dem
and
in M
m3
0
50,000
100,000
150,000
200,000
250,000
300,000
350,000
Popu
latio
n
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$19.21
•Private Pools covered when not in use•Low water use plumbing mandatory•No automatic flushing urinals•Garden watering hours•Hose pipe bans when required• Water intensive industry not promoted
Semi Purified irrigation• Dual pipeline length 75 km versus
approximately 1 800 km water lines. • Replaced 5.8% (2005) of potable supply
with filtered sewage effluent • Unrestricted irrigation landscaping,
sports fields & parks • Treatment train: Secondary sewage,
coagulation, flocculation, DAF, sand
filtration and chlorination.
Landscaping & Sports fields
Windhoek Country ClubWindhoek Country Club
Artificial Aquifer Recharge
•Ground water from springs and shallow wells was reason for Windhoek location• Vast volume of water est to be KMm³•Natural recharge average 1,73 Mm³•Aquifer over exploited by 20Mm³•High evaporation from dams 3400 mm/a•If water can be replenished, high abstraction possible : up to 2 year supply•Since 2006, deep abstraction and injection holes up to 470 metres
Ground Water Contribution
Aquifer Recharge PotentialDisplay by Dr. Ricky Murray of the CSIR
Typical Recharge Station
Carbon filters & Chlorine Contact
Conjunctive Use of Water Sources
02468
1012141618202224262830323436
1950
1953
1956
1959
1962
1965
1968
1971
1974
1977
1980
1983
1986
1989
1992
1995
1998
2001
2004
2007
2010
2013
2016
2019
Year
Ann
ual U
se &
Rec
harg
e in
Mm
3
Boreholes Surface waterReclaimed AR Abstraction Irrigation AR Injection
Production from sources until 2006
Future AR Scenarios
Water Supply per Source (Conventional versus Unconventional)
02468
10121416182022242628303234
Ann
ual v
olum
e in
Mm3 /a
nnum
2005 2011 2014 2019Year
Boreholes Surface waterReclaimed AR Abstraction Irrigation AR Injection
4.6%
7.2%
49.8%
25.8%
6.4%
21.6%
27.1%
31.3% of Demand
6.3%
26.6%
6.9%
10.3%
34.3%
9%
65.2%
2%
5.8%
15.4%
74.1%
Augmentation Alternatives
Tsumeb & Karst III
N$ 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