It indicates how discharge, occupied channel width, channel depth, and average load quantity increase downstream, and other properties such as load particle size, channel bed roughness, and gradient as characteristics that decrease.
The text explains that as water flows through a channel, the amount of flow (discharge), the width and depth of the channel, and the volume of material carried in the flow increase downstream. Conversely, characteristics like particle size, bed roughness, and the slope of the channel decrease.