plentiful supply of fresh water without extremes such as drought and severe flooding [2m]. Drainage also impacts on population density and distribution as areas near a river are more densely populated than areas without freshwater [2m]. Rivers provide rich, fertile alluvium for intense agricultural activity, as well as transport and drinking water [2m]. Some of the most densely populated parts of the world are located in river valleys, e.g. River Nile in Egypt [*2m].