The rôle of the land discussed in this paper is that which determines, from any specific precipitation period, the stream-channel inflow, which will result directly therefrom, and which will occur during or immediately following that period. Stream-channel inflow of normal ground water, from the water table, is not discussed in detail. This paper recognizes that this “role” is not a matter peculiarly related to “flood” periods, but that the land effect during flood periods is merely a special case of its effect during any ·period of precipitation.