In mountain rivers, sediment from landslides or debris flows can
alluviate portions or even full reaches of bedrock channel beds,
influencing bedrock river incision rates. Various landscape evolution
models have been developed to account for the coevolution of alluvial
cover and sediment-flux-dependent bedrock incision. Despite the
commonality of their aims, one major difference between these models is
the way they account for and conserve sediment. We combine two of the
most widely used sediment conservation schemes, an Exner-type scheme and
an erosion-deposition scheme, with the saltation-abrasion model for
bedrock incision to simulate the coevolution of sediment transport and
bedrock incision in a mixed bedrock-alluvial river. We compare models
incorporating each of these schemes and perform numerical simulations to
explore the transient evolution of bedrock incision rates in response to
changes in sediment input. Our results show that the time required for
bedrock incision rates to reach a time-invariant value in response to
changes in sediment supply is over an order of magnitude faster using
the Exner-type scheme than the erosion-deposition scheme. These
different response times lead to significantly different time-averaged
bedrock incision rates, particularly when the sediment supply is
periodic. We explore the implications of different model predictions for
modeling mixed bedrock-alluvial rivers where sediment is inevitably
delivered to rivers episodically during specific tectonic and climatic
events.