2 research outputs found
On the propagation of diel signals in river networks using analytic solutions of flow equations
Several authors have reported diel oscillations in streamflow records and
have hypothesized that these oscillations are linked to evapotranspiration
cycles in the watershed. The timing of oscillations in rivers, however, lags
behind those of temperature and evapotranspiration in hillslopes. Two
hypotheses have been put forth to explain the magnitude and timing of diel
streamflow oscillations during low-flow conditions. The first suggests that
delays between the peaks and troughs of streamflow and daily
evapotranspiration are due to processes occurring in the soil as water moves
toward the channels in the river network. The second posits that they are due
to the propagation of the signal through the channels as water makes its way
to the outlet of the basin. In this paper, we design and implement a
theoretical model to test these hypotheses. We impose a baseflow signal
entering the river network and use a linear transport equation to represent
flow along the network. We develop analytic streamflow solutions for the case
of uniform velocities in space over all river links. We then use our analytic
solution to simulate streamflows along a self-similar river network for
different flow velocities. Our results show that the amplitude and time delay
of the streamflow solution are heavily influenced by transport in the river
network. Moreover, our equations show that the geomorphology and topology of
the river network play important roles in determining how amplitude and
signal delay are reflected in streamflow signals. Finally, we have tested our
theoretical formulation in the Dry Creek Experimental Watershed, where
oscillations are clearly observed in streamflow records. We find that our
solution produces streamflow values and fluctuations that are similar to
those observed in the summer of 2011