Sustainability may best be defined as the 'capacity for continuance into the long-term future'. Anything that can go on being done on an indefinite basis is sustainable. Anything that cannot go on being done indefinitely is unsustainable. Found on http://www.encyclo.co.uk/local/20468
The degree to which flood and coastal defence solutions avoid tying future generations into flexible and/or expensive options for defence. This will usually include consideration of inter-relationships with other defences and likely developments and processes within a catchment or coastal cell.
Found on http://www.encyclo.co.uk/local/20493