London - Dams have delivered major benefits to more than 140 countries but have exacted a high price in human hardship and environmental damage, experts said yesterday. "If you do not do your homework you are going to end up with a lot of unanticipated or unexpected costs, be they financial, political or environmental," Mr Achim Steiner, the secretary-general of the World Commission on Dams (WCD), said. A new report by the commission, an independent body whose sponsors include the World Bank, is the first assessment of the world's dams.