The influence of sediment cover variability on long-term river incision rates: An example from the Peikang River, central Taiwan

This study explores the hypothesis that the relative frequency of rock exposure in the bed of an incising channel can have a first-order impact on the long-term average erosion rate. The 1999 Chi-Chi earthquake in central Taiwan generated thousands of landslides along the middle reach of the Peikang River. Sediment from these landslides produced widespread aggradation, such that much of the river's bed remains shielded from active bedrock incision. We present data that constrain the spatial and temporal variability of sediment cover for the Peikang River. Because the river is undergoing spatially variable Holocene bedrock incision (1-10 mm/yr), it offers a unique natural experiment to test the influence of intermittent sedimentation on long-term incision rates. Published electrical resistivity surveys at seven locations along the river reveal median sediment depth values ranging from 1.9 to 11.5 m. The sediment depth correlates inversely with long-term incision rate and sediment transport capacity. We interpret this as an indication that the frequency of bedrock exposure exerts a major influence on incision along the Peikang River.