At the time the International Commission on Large Dams was formed in 1930, the world dam inventory numbered 2500 between 15m and 30m high, of which 80% were embankment dams, and 500 more than 30m high, of which 70% were masonry or concrete structures, a few being more than 100m high. Ninety per cent of these dams were found in Japan, Europe and the USA. There were about one hundred reported failures.
More than 40,000 new dams qualifying as ‘large’ dams on ICOLD criteria have been built since 1930, 35,000 of them between 1950 and 1980, 25,000 of the latter in the non-industrialised countries. More than 30,000 are less than 30m high (90% embankment structures), 8000 are 30-100m high (80% embankment dams), and 500 more than 100m high (mostly concrete dams). The aggregate reservoir capacity of these 40,000 dams is one hundred times greater than for pre-1930’s dams but the failure rate for dams more than 30m high is ten times less than for their equivalent pre-1930’s counterparts (the gain in safety is less for smaller dams).
ICOLD has been instrumental in advancing and disseminating information on modern dam design and construction methods and improving safety since its foundation in 1930 through its Annual Meetings and three-yearly Congresses, and has been issuing Bulletins on relevant subjects for twenty years. While originally focusing on engineering issues and, over the last thirty years, on reservoir siltation problems, the question of cost savings has more recently led to the setting up of two technical committees, which have issued some ten Bulletins.
The Committee on Technology of Dam Construction produced Bulletin 63 in 1988 on new construction methods conducive to savings on construction with potential impacts on design. An enlarged Bulletin 73 entitled Savings in Dam Construction (1989) estimated that the average cost saving on new dams might amount to 20%. It examines the decision-making process, the impact of contract specifications on costs, completion times, the effect of component cost estimates on project development, and the cost impact of relationships between the parties as embodied in the project contracts.
Component costs and contractual relationships were dealt with more fully in two further Bulletins which appeared in 1992. Bulletin 83 Cost Impact on Future Dam Design noted how slowly dam engineering was progressing compared with the rapid changes in techniques and costs in plant and materials. It traces the relative changes in the cost of the various components of a dam project in order to identify logical (if not probable) future trends in the choice of dam type and the appearance of new types of dams. It gives full weight to the influence of widely-differing economic conditions in different countries.
Bulletin 85 entitled Owners, Consultants and Contractors: How to Improve Relationships deals with a subject which is not often discussed yet has considerable repercussions on the final project cost. Drawing on a wide body of experience, it presents a critique of frequent cases in which inefficient procedures, ill-defined responsibilities, and poor on-site relationships may lead to serious delays and substantial extra costs that are frequently harmful to all parties involved. The authors suggest practical strategies for improvement, remarking that most unjustified extra cost is borne sooner or later by the owner.
Bulletin 89 Dam Construction Sites: Accident Prevention dealing, as it title suggests, with accidents to workmen, would not appear to be relevant to the cost saving issue. Yet studies conducted on many projects throughout the world have shown that effective accident prevention also has a favourable effect on construction cost. Besides much practical advice and the conclusion that there is room for much improvement in safety at work, Bulletin 89 notes that such accidents account for many more injuries and deaths than failures of completed dams and that the risk is dependent on the volume and type ofwork involved. The risk is highest on mechanised jobsites in countries with low labour costs where a large labour force works side by side with heavy machinery. Most future dams will be built under such conditions.
In 1991, ICOLD formed a Committee on Cost of Dams to identify opportunities for savings in all areas of dam design, construction and operation with special reference to safety. The membership of twenty includes representatives from dam owners, government agencies, consultants and construction companies with a large contingent from the non-industrialised nations.
This Committee, like the Committee on Technology of Dam Construction, faces some difficult tasks. It is not easy to make meaningful cost comparisons when dams are all ‘one-off structures of very different sizes in a wide spectrum of different economic contexts. ln addition, ICOLD technical committees are usually engaged on start-of-the-art reports, and reaching any consensus on how current practice can and should be improved demands much effort and time. Lastly, the importance attaching to safety in the search for ways of reducing costs requires very thorough analysis of accidents on the basis of dam and reservoir type and construction methods, using work by other committees. Yet such analyses may throw new light on widely-held preconceptions.
ICOLD Bulletin 110 Impact on Cost of Rules, Criteria, Specifications and Contractual Issues considers a wide range of potential savings in design, contract writing and regulatory requirements. It also discusses changes in dam design and foreseeable future trends.
Other reports deal with more specific subjects. Bulletin 108 Cost of Temporary and Permanent Flood Control in Dams discusses cost factors involved with standard spillways, practical problems with gates, control of river floods during construction of the dam, and unconventional spillway control devices like labyrinth sills, fusegates and inflatable weirs.
Bulletin 109 Dams Less than 30m High deals with the 35,000 large dams 10-30m in height and the 100,000 small dams in the 10-15-metre range impounding reservoirs of one million cubic metres or more. Seventy-five per cent are found in the non-industrialised countries and were mostly built without heavy constructional plant, a factor which was hitherto largely overlooked in ICOLD’s work.
Dams less than 30m high account for only a minor proportion of total investment in dams but have been the cause of most accidents. Bulletin 109 puts forward practical ways of enhancing safety for some types, improving operational efficiency, and reducing the cost of new dams in this category.
A Bulletin currently nearing completion deals with gravity dams. Gravity dams were not a popular choice over the period 1960-1985 but may have a bright future before them. Economical roller compacted concrete may lead to new dam designs that are cheaper to build and suitable for a wider range of foundations. Rising labour costs in non-industrialised countries are causing manual fill placement to be supplanted by more economical RCC (or masonry). The modern concept of designing dams for very rare flood events is favourable to gravity dams. No concrete gravity dam built since 1930 has collapsed.
Future concrete gravity dams may be designed very differently from earlier ones. A forthcoming Bulletin will analyse the excellent cost/efficiency ratio of non-structural details, maintenance, inspection, operating staff training, instrumentation, warning systems and efficient management. It is felt this will be an extremely valuable report but drafting it is complicated by the very wide variety of different cases to be examined.
Another planned Bulletin discusses BOT contracts as means of financing new construction and encouraging greater economies. It will deal chiefly with practical considerations for more widespread use of this formula.
Studies conducted by ICOLD over the last ten years call for some more general remarks. Many design criteria and common preconceptions should be reviewed or abandoned. Standard tendering procedures current today, which favour consultants and contractors submitting the lowest estimates, do not encourage the most economical engineering designs and the final project cost is frequently higher than it need be.
The extra costs that theoretically enhance safety are frequently unjustified in actual practice, more specifically when embodied in overdetailed specifications liable to distract attention from the more important points, especially at smaller dams.
In future, the greatest safety risk from dams will probably lie in the construction period, due to accidents at congested construction sites with an abundant workforce, and inappropriate flood management practices during subsequent operation. Risks of dam failure may be very substantially mitigated with low-cost engineered safeguards and non-structural approaches. Designers and contractors could make substantial contributions if encouraged or permitted by suitable procedures and contract relationships, but it is not their job to do extra unpaid work when they are underpaid by the employer.
Most dams built in recent years have been either moderately-sized structures in non-industrialised countries with abundant use of cheap labour, or higher dams in the industrialised countries where labour rates are high, built with the minimum workforce. In future, there will be fewer new dams but they will be larger in size and built in the emerging economies with steadily-rising labour costs. This situation may lead to optimised dam designs that differ widely from what we are familiar with today. Since dams will probably weigh heavily on these nations’ economies, cost savings will be a vitally important goal.