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.