The Mühlgraben is a 2nd order water body in the urban area of Erfurt and an important main watercourse for the district of Gispersleben. Below the crossing of the Gera by the Road of Nations, at km 16 of the Gera, the Mühlgraben is diverted by the Gera to flow back to the Kiliani park at km 15 of the Gera. The lines of the Mühlgraben were predominantly straight in the existing structure, the largely deepened sole was mostly built in, as were the banks. The continuity in several areas was especially for juvenile fish.
The aim of the water restoration on behalf of the city of Erfurt was to integrate the water into the Nördliche Geraaue recreational area with a view to the Federal Garden Show 2021 in Erfurt, to implement measures to improve the structure, to preserve existing valuable biotope structures and to establish continuity in order to achieve good ecological status in accordance with the EU WFD. Tractebel Hydroprojekt GmbH was commissioned by the City of Erfurt with the basic services for work phases 1 to 9 in accordance with HOAI for the scope of services for engineering structures and open-air facilities, the landscape conservation accompanying plan with integrated species protection technical contribution and the preliminary EIA inspection, the hydraulic proof on the 2D model, the local construction supervision and the ecological construction supervision.
During the planning phase, the longitudinal gradient of the Mühlgraben was changed in several sections by elevation or deepening in such a way that the requirement for longitudinal continuity in both directions was met. Smaller variations of the longitudinal gradient in the watercourse also ensure structural diversity. With the help of an approx. 50 m long bottom glide in bar-pool construction, it was possible for fish to migrate through even the steeper sections.
In two areas, the Mühlgraben was moved away from directly adjoining private properties in order to upgrade the lines and moved into the surrounding park. Bottom and bank structures were largely removed and additional structures installed (vegetation rollers, fish shelters, small groynes to initiate water dynamics, etc.). Steep banks were partially flattened to allow the water to be experienced, and the banks were planted with trees and shrubs suitable for the location, as well as meadows and high shrub meadows. The old trees were preserved as far as possible. For the kingfisher as an inhabitant of torrent slope slides, a kingfisher wall was built in the cut-off lake to compensate.
The construction work started in September 2018 is expected to be completed in April 2019 with the planting of the trees. Until the end of 2021 the monitoring of the development care of the plantation will still take place.
Franka Ludwig, Christian Klaua – Weimar