The existing stock of hydroelectric projects, particularly in the developed world, is ageing. Rehabilitation (or refurbishment) of such facilities is becoming increasingly important in older, industrialised locations such as Europe and North America. But why is rehabilitation more effective than the construction of new facilities? Rehabilitation of an existing hydroelectric plant is more cost-effective, perhaps by a factor of three to six, than new construction. Certainly, considering the time taken to obtain planning approval, a given increment of power can be made available more quickly from a rehabilitation project than from a new one. Furthermore, the environmental factor works to the advantage of rehabilitation just as it is a potential obstacle to the construction of a new plant — communities appear to be keen to hold on to an installation that not only provides clean power but also employment and the possibility of secondary activities on and in the reservoir.

Rehabilitation is of particular relevance to hydroelectric projects as opposed to other forms of power production, quite simply because the life expectancy of the components is so different. Dams and major civil works for example may confidently be expected to last over 100 years given good design, construction and maintenance. Some indeed would assert that their life is unlimited, and the international-commission-on-large-dams (ICOLD) is attempting to make this true by improving the quality of the rehabilitation of civil works that is required from time to time.

Experience suggests that the most serious impediment to the satisfactory performance of hydroelectric plants in developing countries is financial stringency. Of particular importance is a shortage of capital for the purchase of spare parts and for rehabilitation, and a lack of technical training and support for professional staff running the plants. Hence the underlying reasons for the rapid deterioration and poor performance of hydroelectric plant so often observed in these parts of the world are primarily non-technical.

There can be little doubt that these are among the important drivers in making the rehabilitation of ageing plant, and institutional strengthening, of particular importance in countries, such as those in Eastern Europe, where money is in short supply. There is a specific role here for funding agencies.

Rehabilitation projects are particularly difficult to manage, to cost and programme. Detailed activity before the decision to invest in rehabilitation will pay dividends. A feasibility study is an essential preliminary and in justification of this, it is revealing to link the level of funds committed to a rehabilitation project to the quality of the estimate of the final cost.

The table below has been helpful in demonstrating how rapidly, and at what proportionately low level of expense, it is possible to increase confidence in the final cost of the project. The feasibility study gives considerable confidence to the decision makers at the modest expense of less than 5% of the project.

Too often the scope of the rehabilitation is chosen from too narrow a perspective. As with other construction activity, the economic optimum solution to the range of alternative rehabilitation proposals is being sought. The feasibility study should be carried out by a multi-discipline team capable of thinking widely and deeply. Among the particular factors to be considered in the feasibility study are the following:

•Advances in component design which allow replacement with more efficient equipment.

•The changing requirements of the power system may require the characteristics of the scheme to change.

•The scheme itself could lend itself to design changes that enhance its value to the power system.

The benefits of rehabilitation derive from the reduced cost of maintenance and also from the increased reliable output of the plant. The output will improve for at least four reasons: •The decline in output from the effects of ageing has been made good.

•The plant will have greater efficiency, of the order of 2% or so is not uncommon.

•The plant has a higher availability.

•The plant may have been modified to produce more power.

Practical matters that require the detailed attention of the manager of the rehabilitation project include the prequalification of tenderers. This is an important consideration, underlying the importance of the highly developed technical and management skills needed by the contractor. Too often the temptation is to use a local firm with little expertise at an apparently low cost.

ICOLD is active in the field of rehabilitation of dams and their appurtenant works. The Committee on Rehabilitation of Dams was established in 1994 and will produce its Bulletin in 2000. The source of information ICOLD has used is a database comprising recent examples of rehabilitation projects throughout the world, and the Commission has been keen to identify innovative solutions. It will also seek to identify state-of-the-art dam rehabilitation and provide a reference for practising engineers concerned with the design, planning or construction of rehabilitation works for dams and the structures associated with them.

The Bulletin will also deal with the management of rehabilitation projects and refer to the instrumentation and monitoring of ageing dams, encouraging a better understanding of the research needed to define the fundamental processes involved in ageing and its amelioration.