UNCOTROLLED GROUNDWATER EXPLOITATION FROM VULNERABLE
AQUIFER OF ADDIS ABABA, ETHIOPIA
Tamiru Alemayehu (PhD) Dept. Earth Sciences
Addis Ababa University, Ethiopia [email protected]
Location
General
Addis Ababa was established as the capital city of Ethiopia in 1886 (119 years old)
Currently hosts around 4 million residents.
First water supply: Springs & Dug wells
Second supply: Surface water
Third supply: Surface + Groundwater
Current supply shortfall:
25%of the population
Rate of urban increase
7 km2/yr (37km2 in 1970 to 230.4km2 in 1999)
Municipal Water Resource
Water demand is continuously increasing
The effective recharge is 200mm (Eastern), 150mm (Western) and 64mm (central &
Southern) part of the city
Gefersa 30,000 m3 per day
Legedadi 150,000 m3 per day.
Dire dam supply 42,000 m3 per day for Legedadi center
Tot: 222,000 m3 per day
More than 600 Operational boreholes are found in the city
Some Bore holes
Three major aquifers
1. Shallow aquifers: made of weathered volcanic rocks and alluvial sediments along the river valleys.
2. Deep aquifers: made of fractured volcanic rocks that tap fresh ground water derived from regional recharge and circulation.
3. Thermal aquifer: that is located at depth greater than 300m in the central part of the city (Filwoha aquifer).
Groundwater flow
Filwoha fault
Fanta Fault
Groundwater abstraction
Well spacing: Average distance 50m
The abstraction from the main municipal wells (Akaki well field) 30,000 m3/day and from other municipal well is 10,221 m3/day (sub total= 40,222m3/day).
Other private wells tap as much as 49,986.67m3/day
Total abstraction is 90,208m3/day :: Again this is not yet sufficient
Impact on water table
2018.50 2018.60 2018.70 2018.80 2018.90 2019.00 2019.10 2019.20 2019.30 2019.40 2019.50 2019.60 2019.70
Nov- 2001
Nov- 2001
Dec- 2001
Dec- 2001
Jan-2002 Feb- 2002
Mar- 2002
Mar- 2002
Apr-2002 Apr-2002
Observation time Head
Intrinsic vulnerability of the aquifer
Bacteria in groundwater
E. Coli ranges from 3 to 89 bacteria/100ml derived from domestic sewage both in
springs, dug wells and boreholes
Bacteria travel time
To the depth of 50 m below surface
with hydraulic conductivity of 340m/day
2:30-4:00 hours
Primary protection zone:
2000m
Conclusion
Main water supply aquifer of the city lies on medium to highly vulnerable zone
No aquifer management regulations are set
Due to domestic and industrial waste
contamination, most of the wells are tapping contaminated water.
Due to recent climate changes (excessive heat and low rainfall in the Horn of Africa)
Effective recharge to water supply aquifers is progressively decreasing.
Private owners are not treating the groundwater, and are in risk zones
The Municipal authority should:
1. Fix minimum well spacing based on the cone of interference ,
2. Control the usage i.e industry, agriculture, business etc.
3. Control the quality as the users confuse the sources of the waterborne disease
(Municipal supplies are treated and disinfected)
Therefore, priority should be given to municipal authority to fulfill the public supply.
