The flood pulse concept explains how the periodic inundation and drought (flood pulse) control the lateral exchange of water, nutrients and organisms between the main river channel (or lake) and the connected floodplain. The annual flood pulse is the most important aspect and the most biologically productive feature of a river's ecosystem. describing the movement, distribution and quality of water in river ecosystems and the dynamic interaction in the transition zone between water and land (aquatic/terrestrial transition zones - ATTZ). It contrasts with previous ecological theories which considered floods to be catastrophic events.