Modelling headwater channel response and suspended sediment yield to in-channel large wood using the Caesar-Lisflood landscape evolution model.

Forest management activities have the potential to significantly modify large wood loads in riparian areas, and thus the availability of material for recruitment into the stream channel, hence it is important that forest management practices take account of the role wood supplied from riparian areas play in the development of channel structure and sediment retention capacity. In this study the cellular landscape and river reach process model CAESAR LISFLOOD (C-L) was used to simulate the effect of in-channel obstructions created by large wood on the distribution of erosion and deposition within a small headwater channel and suspended sediment yield at the catchment outlet. The process model was parameterised and calibrated against an observed discharge and suspended sediment record. Following calibration, 12 discharge and large wood obstruction scenarios were carried out to model erosion and suspended sediment transport over a timber harvesting cycle. The inclusion of obstructions into the model runs to simulate in-channel LW pieces substantially reduced suspended sediment yields in all three discharge scenarios and increased sediment storage along the channel. The modelled location of channel bed degradation and aggradation generally coincided with the pattern of sediment storage along the channel bed demonstrating that C_L was predicting the pattern of erosion and deposition in the channel reasonably well. Modelled erosion rates were extremely low for the respective discharge and large wood model scenarios, with the highest rates ranging from 0.02 t ha−1 year−1 to 0.1 t ha−1 year−1 for the no large wood model over the 22-year period. These findings reinforce the importance of maintaining sufficient volume of standing wood in buffer strips alongside small headwater channels to ensure ongoing recruitment of large wood to the channel network in forests managed for timber production. [ABSTRACT FROM AUTHOR]