Large woody debris are trees, that are deliberately placed in a river channel, to increase its structural diversity through their influence on the flow conditions.
Between 3rd and 4th kilometer of the Mulde River (project site: Jagdbrücke Pelze) 3-4 tree trunks were anchored to the river bed. Their installation was coordinated by the research teams and aimed at preventing some of them from drifting freely. In case of the others, the chosen form of attachment to the river bed allowed buoyancy. In the area where the trees were located, the natural bank structures were restored by dismantling stone packs at length of approximately 30 m.
Three further tree trunks were anchored securely between 11th and 13th river kilometer (project site: Törten). No changes to the river banks were applied on this site, as the research team used it to observe impacts of the river on an unrestored section of the river bank.
North from Retzau, a section of the river bank was secured by a stone embankment.
From the current perspective, this measure of flood control is not necessary, as the floodplain lays among meadows and forests, far from buildings, whose protection would justify containment of the natural shifts of the river bank.
The stone embankment was removed from the river banks on a section of approximately 500m. The water can now freely erode the floodplain and shape the river banks. Sand martins found their new home in the exposed river banks.
Over the course of several years, the river Mulde will move its bed into the adjacent meadows. This process will slow down only, when the river will reach the forest edge, as plant roots bind soil together. Some of the trees on the forest edge will plummet into the river and form the natural large woody debris.
Approximately 2 km before the confluence with the Elbe river, a left-sided side channel was re-connected to the Mulde river. It is believed that the existing connection with the side channel was blocked by people many decades ago. Exactly at the same spot, a new opening of the side channel was created. During the medium water level, it connects the side channel with the river Mulde. When the water level is high enough, water can flow through the channel, to the river Elbe.
To connect the channel, an opening, approxiamtely 80 m long had to be dredged. The excavated soil was transported north from the connection, where it was used to create a hill, on which animals can find shelter during a flood. This, so called, „wildlife-rescue-hill” is necessary, as reconnecting the side channel created a closed island, from which wild animals cannot easily escape when the water level is high.
Hardwood floodplain forests develop on areas located near to rivers, however not flooded regularly. Hardwood trees, especially the common oak, adorn the landscape. Contrastingly, the riparian softwood trees can be found directly at the river bank. Only trees, that can withstand frequent and prolonged flooding can survive there.
It is likely, that north from the reconnected side channel, the natural development of a hardwood forest will be supported. For this purpose, numerous seedlings and seeds will be distributed on an area of approximately 4 ha. The planting sites will be fenced and selected plants will be additionally protected from damage caused by feeding herbivores. The exact location of the planting sites has not yet been determined.
In addition to the actual improvements of the river state, the project aims at raising awareness of the general public about the unique wild riparian landscape of the Mulde river. For this purpose, several Mulde-river days will be organized. Display boards, a digital nature guide, geocaching and regular tours should incent a discussion about the floodplains of the Mulde river. The changes occurring in the Mulde river will be further illustrated by a long-term observations and by public presentations of their results.
