Deltas are environmental and economic hot spots, occupy about 1% of the global land surface, are home to some 500 million people and often are vibrant ecosystems. Deltas pose great challenges, whether marine or lacustrine as regions of purely natural conditions or regions of intense human activity set in the context of complex and often rapidly changing natural environments. Physically they are complex systems, the end-products of catchment processes involving water supply, sediment delivery and water quality &ndash elements that are fast changing over time as a result both of human influences and change in climatic drivers. Tides, waves, sea level changes, storm surges, tsunamis and littoral currents all impact. The contributions result from a joint symposium of the International Associations of Hydrological Sciences (IAHS) and Physical Sciences of the Ocean (IAPSO).
