Topographical change is a good indicator of not only the stability of substrate but also the stability of ecological circulation on a tidal flat ecosystem. Thus, prediction of topographical change becomes an important technology for managing natural and constructed tidal flat. To reveal the basic feature of tidal flat topographical change, series of field observations were conducted at Banzu natural tidal flat in Tokyo Bay, Japan and Nishiura constructed tidal flat in Mikawa Bay, Japan.
　In the natural tidal flat, the macro-scale topography is conserved for long time, while small-scale topographical fluctuations were varied by the time and space. On the other hand, in the constructed tidal flat, successive development of sand bar was observed as a result of transitional phase after the completion of the construction.
　Current, water depth and suspended sediment (SS) concentration were measured on the natural tidal flat for study SS transportation processes that is controlling topographical change. The SS flux could be separated as a fraction of tidally induced oscillating flux and wind driven flow that has unidirectional flux. It was suggested as the SS flux by wind driven flow had a significant contribution for the bottom topographical change.
　Some features of micro-topography which appeared in the tidal flat (sand ripple, small creeks web and sand wave) are also introduced.