Many dams are multipurpose, providing two or more of these benefits. Numerous large dams have been built during the past 50 years, numerous land areas have disappeared under the surface of these lakes, and the larger the dam, the larger the lake and the larger the potential problems, ' noted the company.

Hydroconsult says a large dam is defined as one higher than 15m. There are more than 40,000 large dams worldwide, over 300 of them defined as 'major dams' - which meet one of a number of criteria on height (at least 150m), dam volume and reservoir volume.

'The major problem with dams and reservoirs is siltation, ' said the company, which is closely related to deforestation and soil erosion. Siltation is generally considered as the most common problem because it largely determines the lifetime of a hydropower or water resource project.

Hydroconsult says it believes that in the next 10-15 years, 50 per cent of dams could become obsolete due to siltation. This would eliminate 10 per cent of the world's power supply.

'Overtopping causes 40 per cent of disasters involving power dams, and this will increase, ' said the company, noting that increased siltation created a threat of flooding, and induced seismic activity.

To help tackle the problem, Hydroconsult is offering a range of services to dam operators, including integrity surveys using ROVs; hydrographical and topographical surveys;

geophysical and geotechnical surveys; seismographic impact assessment; dredging and silt treatment proposals; silt disposal/usage proposals;

infrastructural studies and proposals; and financing assistance.