4.3.2 Case 3: Tributary Response
Tributary responses to the change in rainfall pattern depend largely on
their position. Individual tributaries experience changes in erosional
efficiency proportional to their change in rainfall. Changes to both
quantities are always different from those of the trunk river at their
confluence (Figure 2a inset). Additionally, tributaries also respond to
changing boundary conditions related to adjustment of the trunk river.
These signals are often conflicting. For example , enhanced incision
along the trunk river downstream from xsc causes
tributaries there to experience a relative increase in the rate of
base-level fall. Alone, this should promote steepening, but higher
erosional efficiency (higher rainfall) counteracts steepening. The net
effect of this competition plays out differently as a function of
tributary position as 1) the discrepancy between the local rainfall
conditions experienced by tributaries and the upstream averaged rainfall
experienced by the trunk profile narrows upstream (Figure 2a inset), 2)
the transient base level signal (i.e., trunk knickpoint) changes shape
as it sweeps upstream, and 3) the duration of transient adjustment
increases upstream.