Change over time is certain. Just what that change will be is the only thing that is uncertain. But whatever they are, these changes will surely impact the physical,
biological, and social dimensions of water resource systems. An essential aspect in the planning, design, and management of sustainable water resource systems is the anticipation of change: changes in the natural system due to geomorphologic processes, changes in the engineered components due to aging, changes in the demands or desires due to a changing society, and even changes in the supply of water, possibly due to a changing climate.