Water Supply System, Abuja

Water Supply System for the Federal Capital City

Abuja Nigeria

1. Current Situation – Water Demand

The  water  supply  system  for  the  City  of  Abuja  has  been  designed  in  modules following the planned increase of the city’s population. According to this master plan, the population of Abuja and the capacity of the water supply system would develop as follows:

The City has grown much faster than foreseen in the master plan. This is mainly because areas previously not envisaged in the master plan are now supplied. These areas  include  Gwagwalada,  Kubwa,  Karu,  Nyanyan,  Karmo,  Idu  and  others. Presently, the population living in the FCT has been estimated at 6 million (2 million urban; 4 million peri-urban+ rural). The population actually served by the FCT water supply system is estimated with approx. 2 million. The population in peri-urban and rural areas is supplied by decentralized systems (hand-pumps with boreholes).

During dry season, the demand outstrips the capacity to supply, therefore shortages in particular in high altitude supply areas (Maitama, parts of Wuse 1&2, Asokoro) occur. Some areas which have been designed as low water consumption areas (e.g. Maitama), have now turned into high water consumption areas.

Assuming that an urban population of 2 million with an estimated consumption of 120 liters per capita per day and a peri-urban and rural population of 4,0 million with an estimated consumption of 80 liters per capita per day have to be served (see table below), the total domestic demand would be 560.000 m³/day. The industrial demand is estimated to be 22.000 m³/day. The total water demand will result in 582.000 m³/day. Assuming that the actual network losses are approx. 20 %, the total demand will be 698.400 m³/day (8,1 m³/s).

Table: Actual Water Demand calculation in F.C.T.

2. Current Situation – Water Production

Currently the main water source for the city of Abuja is the Usuma Dam and treatment works. The dam is located within the higher altitude of the territory within a well protected environment free from domestic or industrial pollution. The dam reservoir has a maximum capacity of 100 million cubic meters. The hight of the main dam is 45 meters. Two pipelines with a diameter of 1,500 mm transport  raw water from the dam intake to the treatment plants by gravity.

There are two water treatment plants, each with a capacity of 1,35 m3/s. The first plant came into operation in 1987 and the second in the year 2000. The treatment process includes the following (standard) steps:

    Aeration    Coagulation    Flocculation    Rapid Filtration    Final Disinfection    Neutralisation

In addition to the main treatment plant from Usuma Dam, a water treatment plant with a capacity of 0,083 m³/s supplies the area of Gwagwalada. Raw water is caught at a weir impoundment on the Usuma river. The total installed capacity therefore is 2,783 m³/s. A laboratory is responsible for quality control analysis on the physical, chemical and biological properties of the water. The quality control unit is also responsible for the process of water treatment (chemical dosing).

3. Current Situation – Water Storage and Distribution

The masterplan scheduled a total of 10 storage tanks (ST) for both stages. At present, four of the planned storage tanks (ST 2,3,4,5) located on the north/west edge of the city, are already in place. Storage tank 1 and 6 are now proposed to complete stage I. Storage tank 7,8,9,10 are scheduled for a further extension (stage II).

The existing situation shows that additional distribution systems are necessary to cope with the demand of the fast growing city. Treated water is transported to two storage tanks at the outskirts of the city through a 41 km steel pipeline (diam. 1,500 mm) by gravity. Several storage tanks have been constructed to distribute water to the subsequent supply areas:

* numbers do not correspond to numeration of master plan

The distribution network has been designed as closed loop, each taking its source from the storage tanks at the periphery of the city. In addition to the main distribution system, Gwagwalada water supply system (including 2 tanks) is fed from an independent treatment plant (see above). The F.C.T. has an estimated number of  800  rural communities with an average population of 1,500 each (total: 1,2 million inhabit.). The rural population is mainly supplied by hand-pump operated boreholes which are currently under rehabilitation.

4. Current Situation – Operation and Maintenance

Metering of  water is a  key element  to demand management and  improving the revenue  situation  of  water  companies.  The  board  is  currently  embarking  on residential metering and is fostering pre-paid systems (e.g. smart token meters). The water tariff for private consumers is approx. 100 Naira (€ 0,8) per m3. The population of peri-urban and rural areas is often supplied by private water vendors who by water from the city supply system at a rate of 250 Naira / m³ and sell it at 1000 Naira / m³ to the households. Preventive maintenance is not a common practice in many Nigerian water companies. However, the importance of regular maintenance has been recognized and the staff is supported by various training courses to improve their skills. Comparing the water demand of 8,1 m³/s (698.400 m³/day) with the actual installed capacity of 2,78 m³/s the present water supply deficiency is evident, even if part of the population is supplied with hand-pumps from additional boreholes.

The strategy to meet the demand therefore is  to increase the installed capacity (proposed: 8,1 m³/s), to reduce per capita consumption (down to 120 lcpd for urban population) by demand management programme and metering, to expand the distribution and storage system to non supplied areas or areas with insufficient water quality. In order to increase the available quantity of water, the construction works of the River Gurara Dam and intake and the conveyance line from River Gurara to Usuma Dam are under way. By 2006, sufficient raw water is available at Lower Usuma Dam to operate the next stage of the water supply system. The capacity of the new raw water supply from Gurara will be 12,6 m³/sec., which is well in excess of the need for the stage 1 (phase 1-4) of the water supply system.

The next phase of the Abuja water supply system shall include –      the water treatment plant with a capacity of 5,32 m³/sec.,-      storage tank no. 1 with a capacity of 30,000 m³,-      storage tank no. 6 with a capacity of 40,000 m³ and the-      associated trunk lineso diameter 1,500 mm, length 15.460 km o diameter 1,400 mm, length 60.280 km o diameter 1,000 mm, length 10.190 km. The installed capacity of 8,1 m³/s would allow to supply a population of: –      2 million urban population (with 120 lcpd) and 4 million rural and peri-urban (with 80 lcpd). Depending on the success of the demand management program and the water losses in the system, the new capacity will be sufficient to meet the demand of  6 million people and will thus almost triple the existing capacity.

6. Alternative Water Resources

Due to the urgent need to provide adequate water supply for the people of Abuja, the focus of this project is solely on the implementation of an additional water treatment plant and the necessary supply lines. For the later development of the water supply system for the Federal Capital Territory, additional concepts may be valuable. We may raise some issues which might be covered during our project development: A major principle in urban water supply is to exploit several water resources in order to improve sustainability and reliability of the water supply system. Toxic pollution or extreme draught might limit the use of surface water and might cause extreme water scarcity. Alternatively or additionally to the proposed treatment of surface water (dams and reservoirs) by flocculation, in addition to the foreseen extension and rehabilitation, we propose to assess the possibilities to exploit : groundwater from boreholes and wells; and ground water from bank filtration groundwater from artificial recharge.

7. Hydrological Considerations

Abuja is located on the Southwestern foothills of Jos Mountains, watershed hydrology is characterised by predominantly surface drainage through several tributaries to river Niger and river Benue (river Gurara etc.). Groundwater recharge is provided by direct water infiltration from the surface deriving from some more than 1000 mm precipitation during one rainy period per year. Numbers of groundwater recharge are not available.

Groundwater from boreholes and wells

Based on the rough knowledge of the geological situation, we assume that Quaternary sediments in the river basins contain mostly fine sediments, the actual porosity is estimated with some 10%. That means   that   an   efficient   groundwater extraction can be provided particularly by numerous vertical filter wells. Generally spoken, groundwater exploitation under natural conditions will anyway stay within a limited frame.

Groundwater from bank filtration

According to the sedimentation of fine sandy and silty material a high suspension in river water is expected during the rainy season thus effecting a high degree of colmatation along the river bed. This situation has to be tested since there exists no information on the relation between groundwater and the related surface drainage system.

Groundwater from artificial recharge

Boundary conditions for artificial recharge are given by the fact that groundwater recharge occurs only during the rainy period, while 6 to 8 months per year are considered as arid months with a negative climatic water balance. Consequently a significant draw down of groundwater level is obvious. Artificial groundwater recharge could fill up this gap for a proper groundwater utilisation during the whole year. All current limitations lead to the conclusion that key  technology  for  a  sophisticated  water resources management in semiarid areas includes the artificial recharge of surface and ground water to  balance  the changing  availability  of underground water. Surface storage is limited by the geological features and evaporation inducing high  losses  from  the  open  reservoirs.  Since artificial recharge is depending on local and regional geological and hydrogeological conditions we have to distinguish between two systems:

a)  Autochtone recharge:

Recharge into the same system; a part of the surplus water from the rainy season is pumped back into the recharge area taking into account the turnover time of underground water in the natural aquifer. For the actual case this option will probably have to be neglected because of the geological situation.

b)  Allochtone recharge:

Recharge into a separate system; surplus water is transported to another aquifer with a reasonable storage capacity – indication of recharge mechanism and underground storage – study of physical processes in the aquifer, especially from the effects of storm events with gradual modifications for both aquifer systems – groundwater  modelling  of  the  allochtone  aquifer  in  order  to  recognise infiltration processes – selection  of  proper  kinds  for  infiltration  (punctual  at  the  surface,  punctual through injection boreholes, linear by infiltration drainages, areal by infiltration ponds)

Alternative Water Resources – Remarks

Presently, there is a lack of combined application and synoptic view for better understanding of mass and solute transport processes. Therefore, the methods described above are usually applied separately, although a combination might lead to considerable synergies. Certainly a comparison between water supply from surface and from groundwater has to be carried out. There is no doubt that the combination of both, surface and groundwater supply provides the greatest benefit for the population to be served with drinkable water: Groundwater, in the actual case also artificially recharged, does not need any treatment, when the delineation of protection zones is well defined. Nevertheless a monitoring network for groundwater quality control has to be established. For artificial recharge the large rivers shall not be used, since they are in general considerably polluted. Small rivers with a well defined catchment area where the use  of  the  land  can  be  regulated  may  serve  the purpose. In many cases, water supply has become much cheaper by decreasing treatment costs. A typical case has been our project in Curitiba/Brazil, a town of 2 million inhabitants. Originally all the water supply was covered by treated surface water with a price of about 1 USD per m³. Nowadays after introducing groundwater extraction in the vicinity of the town (up to 40 km) the township is charging 63 US cents for 1m³ of water. Austria  has  a  long  tradition  in  applying  these technologies and gained very positive experience. The technology  has  not  only  been  used  successfully  in Europe, but is also recommended for African countries like in Kigali/Rwanda, where the World Bank and the Austrian government opted for this innovative solution. Other projects  in  Syria,  Iran  and  Bolivia  are  in  a  phase  of  pre-feasibility  under  the supervision of Austrian experts.

ICCF International Consultant, Austria (c) 2004