Catering to the rising water demand in Greater Colombo Area

Greater Colombo (GC) area has been experiencing some massive all round development in almost every sphere involving housing, building, road, commercial and industrial activities coupled with a huge population growth during the past two to three decades, and naturally exerting demand for corresponding increase in public utility services and infrastructure.

Consequently, the demand for pipe borne water supply too has increased manifold. Studies carried out in the late 1990s indicated that the water demand in the GC area increased at a rate of around 32000 m3/Day (7.0 m.g.d) annually. The GC area is supplied with water from three treatment plants: 1) Labugama reservoir, 2) Kalatuwawa reservoir and, 3) Ambatale - Kelani River.

GC area is faced with a severe water shortage as is evidenced from regular public complaints. The NWS&DB has to keep looking up to Kelani River as the only reliable source to meet these water demands. Already when rains fail to come down in time in the catchment areas of Kelani river, NWS&DB is faced with difficulty of providing a reasonably satisfactory water supply. People living in elevated areas are severely affected.

Water users are advised to use water sparingly so that those in elevated areas will receive at least a small quantity in the middle of the night. Supply restrictions cause hardship to many. Plights of such affected people are regularly highlighted by all news media.

There are some locations where pipelines have been laid but not connected to the system because of the shortage of useable water in the river for abstraction; thus, depriving households in the vicinity of these pipelines the opportunity of deriving any benefit.

A project is already being implemented to provide water supply to Towns North of Colombo encompassing the rapidly developing southwest area of Gampaha district at a cost of circa Rs. 3.0 billion. Work on the distribution system is nearing completion, Thus it will be an utter waste of funds if such a scheme completed proves incapable of operating to the expected capacity.

Plans are being made to provide a treatment plant of 200,000 m3/day (44 m.g.d) capacity in the right bank of Kelani River (with provision for further expansion) along with a separate intake to meet the GC future water demand, because the prevailing arrangement of feeding from Ambatale intake has been unsatisfactory.

It seems that implementing the right bank project will not solve these burning issues because there are serious doubts about the feasibility of abstracting the expected quantity of water from the river considering the prevailing situation.

The NWS and DB in consultation with the Ministry in charge has been looking at ways of continuing to abstract optimum quantity of water from Kelani River at comparatively low costs. From about 1992 studies have been conducted engaging both foreign and local consultants about the possibility of abstracting more water from the Kelani.

After extensive studies carried out over several years it was finally decided to construct a permanent salinity barrier in the river just downstream of Ambatale with appropriate protection to prevent collapsing of the banks and also without hindering the movement of boats.

NWS and DB has already spent millions of both local and foreign funds for the study, design and tender documentation. Necessary approvals have been obtained from both government agencies and local authorities. This project can be further evaluated in relation to cost-benefit aspects. Any delays can enlarge the water shortage gap which would further increase the cost of investment.

It is not advisable to continue with temporary barricading of the river with sand bags. Such devices cause additional damage to the riverbanks and the public and private property in the vicinity, leading to unnecessary environmental destruction and considerable economic losses. The riverbed around Ambatale is about 5 m below Mean Sea Level.

This proposed salinity barrier consists of a RCC structure and an inflatable rubber tube dam of 1.5 m height fixed on to its crest. The crest level of the RCC structure will be 0.5 m below MSL.

During low flows this rubber tube dam can be inflated creating a water pond with the overflow level at 1.0 m above MSL, at the same time preventing salinity intrusion towards upstream of it. During high flows this inflated rubber tube dam could be deflated allowing normal flow in the river.

The benefits of having a permanent salinity barrier would be numerous:

* Avoiding intrusion of salinity into raw water pump houses and the treatment plant

* Making more water available for abstraction

* Increasing the depth of the fresh water level upstream of the salinity barrier

* Increasing the availability of fresh water for treatment plants

* Increasing the efficiency of raw water pumps

* Improving the reliability of Greater Colombo water supply system

* Reducing the cost of production of potable water from Kelani River

* Avoiding bringing expensive Kaluganga water to Colombo District

* Providing water demand of south western part of Gampaha District from proposed Kelani River right bank treatment plant

* Preventing erosion of Kelani River embankments in Ambatale area

* Maximizing the proper usage of available fresh water in Kelani River during drought periods

* Possibility of controlling sand extraction close to the upstream of the barrier.

At present, the effluent from Biyagama Investment Promotion Zone is released to Kelani River upstream of the present water intake. Action should be taken to divert this effluent to downstream of the proposed Salinity Barrier to utilize total flow of the river during low flows. It must be noted that this cost is negligible compared to the advantages of having the barrier.

Greater Colombo area is growing in all directions and so is the demand for services and what is economically advantageous has to be given priority. No development could be planned without having adequate water supply.

To improve the water supply to Greater Colombo area and to satisfy the needs the most urgent projects identified after years of study by experts and evaluation by several committees appointed by the subject Ministry and the Board have to be implemented. Some of the important projects are:

1. Construction of the permanent salinity barrier down stream of Ambatale as explained above;

2. Construction of intake and treatment plant in the right bank of Kelani River to serve the areas in the towns North of Colombo;

3. Construction of a new ground reservoir in Kolonnawa;

4. Laying of a pumping main of adequate capacity from Ambatale to this new reservoir at Kolonnawa along with appropriate high head pumps

5. Laying of transmission pipelines of adequate capacity from new reservoir at Kolonnawa to Colombo city and Kelanitissa power plant complex

In 1998 the NWS and DB identified and land suitable for a large ground reservoir in Kolonnawa area (item 3 above). This land has since been purchased by the NWS and DB. The proposal is to construct a reservoir of suitable capacity so that water could be fed from this reservoir to areas east of Baseline road with a view to improving water supply to Colombo.

Presently water supply to these areas is provided from Maligakanda and Jubilee reservoirs, but the proposed arrangement will relieve Maligakanda and Jubilee reservoirs to carry more water to serve areas closer to these reservoirs.

Thus the presently affected high elevated areas such as Wolfendhal and Hulftsdorf could be served better. Jubilee reservoir will have increased capacity to serve presently affected Wellawatte area via the jubilee - Maharagam - Dehiwala - Wellawatte pipe network. In addition, CEB's requirements of additional water for Kelanitissa power plant complex could be conveniently supplied from the proposed Kolonnawa reservoir.

These are plans developed after careful study over a long period of time. It is the responsibility of those with authority to arrange timely implementation of the proposals so that the public will receive better service within a short period of time.

If some others have better proposals let them be made known, so that the rate-payers in Greater Colombo will have some hope of receiving a reasonably satisfactory water supply service within the next two to three years.

(Past and Present Senior Executive Officers' Association of the NWS and DB)