The current climatic changes due to the greenhouse effect impose new demands on old dams. The impact of el Niño may be a relevant example. Existing spillway structures may need to be re-evaluated and new or modified spillways may be needed. Clogging of spillways with floating debris during major floods is another issue, which may need increased attention.

Suitable safety requirements and methods of evaluation vary depending on the access to historical data and the consequences of inadequate spillway or storage capacity for water whether it is for domestic or industrial use or for irrigation and navigation. Sediment handling may be critical in some parts of the world and simultaneously the diminished sediment transport downstream of dams may lead to erosion and depletion of agricultural lands. In cold climates ice and frazil formation may be equally critical.

We have been engaged in these questions over the last 35 years in Africa (Zambia, Tanzania), South and Central America (Argentina, Peru, Jamaica), Europe (Sweden, Latvia, Iceland) and in Asia (India, Vietnam, Indonesia) and designed some very large spillways both in terms of capacity and head.