Rivers and streams are a seasonal phenomena. Every year their water is replenished by melting snow and spring rains.
As the year progresses the water level gradually fades away as its source is depleted. This dramatically alters the shape of the landscape around it, as the water covers less of the shore.
Such a recurrence is clearly a phenomenon in terms of its clockwork (the changing of seasons) frameworks (the consistency of the change and the directed flow of the river) and things (the water, the shore and the river itself.)