The potential of in-channel large woody debris in transforming discharge hydrographs in headwater areas (Ore Mountains, Southeastern Germany)

Large woody debris (LWD) is a natural component of watercourses. To prevent flood-related damage caused by LWD, trunks and big branches are removed from the channels during maintenance work, thus accelerating runoff and intensifying incision. However, the impact of in-channel LWD on flood waves is not adequately known. This project shows the results of experiments on the potential of LWD as an in-channel roughness element. LWD was installed and secured in a 282 m long channel of a first-order stream. Artificial flood waves with a return period of 3.5 years were generated, and the retention effect of the LWD was monitored. Results show a significant delaying of the flood wave progression and a distinctive shift of flow volume from high to low runoff coefficients, but only a low attenuation of peak discharge. The authors conclude that LWD plays an important role as an in-channel roughness element to decelerate runoff and increase water retention in the channel.