The Aswan high dam, for example, is often cited as a cautionary example, a quixotic construction that now reduces the mighty Nile to a dribble before it trickles to the sea, leaving behind an explosion of water hyacinth, outbreaks of bilharzia, polluted irrigation channels and a build-up of sediment inland that would otherwise compensate for coastal erosion from Egypt to Lebanon.

ECONOMIST: Small projects often give better returns