Geomorphological origin of recession curves

We identify a previously undetected link between the river network morphology and key recession curves properties through a conceptual‐physical model of the drainage process of the riparian unconfined aquifer. We show that the power‐law exponent, α , of − dQ / dt vs. Q curves is related to the power‐law exponent of N ( l ) vs. G ( l ) curves (which we show to be connected to Hack's law), where l is the downstream distance from the channel heads, N ( l ) is the number of channel reaches exactly located at a distance l from their channel head, and G ( l ) is the total length of the network located at a distance greater or equal to l from channel heads. Using Digital Terrain Models and daily discharge observations from 67 US basins we find that geomorphologic α estimates match well the values obtained from recession curves analyses. Finally, we argue that the link between recession flows and network morphology points to an important role of low‐flow discharges in shaping the channel network.