Foto: Vojta Herout, www.nafotime.cz
Revitalization of the Millrun in Semily
For the local community, the Ostrov park (“Island Park”) in the centre of Semily is a popular place to relax and go for walks. However, the millrun that borders it on one side was a disgrace until recently. People had to pass a clogged and smelly riverbed, overgrown with vegetation. The retaining walls were crumbling, which increased the risk of floods. Even animals that encountered too many barriers did not do well there.
The revitalization helped the millrun, the park and the natural environment The water was given space so that the riverbed could cope both with drought and floods. The millrun and its banks became part of the park. Children and adults are now able to discover the life in and around the water. It has also become a safe place for the children to play with and in the water. The European crayfish are back, and the locals hope that the brook lamprey will follow.
The Adaptation Journey
The positive impact
The revitalization of the millrun has significantly increased the level of flood protection. Thanks to its varied morphology and ponds, the millrun also retains water in the urban landscape and allows people access to water on hot days. The whole Ostrov park eliminates the effect of the urban heat island. Thanks to the revitalized watercourse, the local microclimate is even more pleasant. In addition, the modifications support the biodiversity of the site.
How does it work?
It is now a protected area, which is part of the Natura 2000 sites. The revitalization of the millrun had to take this into consideration, and it had to be spread over two years.
The condition of 380 trees was checked on both banks and about a quarter of them had to be cut down. Most of them were small self-seeded trees and shrubs. However, it was necessary to cut down some mature trees as well due to their poor condition. Wetland and riparian plants were planted and the numbers of the newly planted trees were limited to make the space more permeable and airier. Stumps left on the edges of the banks now serve as shelter for fish and there are new birdhouses on the trees for small bird species.
The terrain of the millrun has been newly shaped. The formerly narrow muddy riverbed was widened and has a less steep profile. It also slightly meanders within the confines of the limited space. The sediments, which clogged the stream, were dug out and taken to agricultural land. Thanks to the changes, 7 side pools were created. The transverse object in the riverbed, protecting the engineering networks, was an obstacle for migrating animals. It could not be moved and is now more permeable since the modification. After being crushed, the old embankment walls were used to strengthen the banks and the raised riverbed, where water reaches only during flooding - so-called berms. There is now a pleasant and safe access to water, which is widely used by schools and kindergartens.
Almost half a kilometre of the riverbed of the millrun around the Ostrov Park hadn’t been maintained for a long time. A large part of it was clogged with stinking sediments, in places it was filled up with soil and was overgrown with self-seeded vegetation. There were also crumbling retaining walls in the technically modified part of the millrun. In addition, the transverse step, in the millrun for utility networks, was a migration barrier in the habitat of specially protected animal species. All these problems affected runoff problems and increased flood risk.
Operation and maintenance
This project was only recently completed. The cost of maintenance is expected to be below 20 thousand crowns per year and will be mainly about maintaining the flow and cleaning.
Why was the measure chosen?
The transverse object in the riverbed protecting the utility networks could have been moved. However, such a relocation would be too costly and would not be an eligible cost for the subsidy programme. Therefore, the object was only modified to make it more permeable.
The contractor changed the planned gravel bench along the millrun to one made with reinforced concrete. Although a more natural solution would have been more appropriate in terms of flow, it would have been too expensive to change it. However, the bench is now widely used by playing children as it is.
Obstacles and challenges
It was not easy to combine all the measures so that the result was accepted by the local community, and, at the same time so that it was as close as possible to the natural state of the stream. All this was at a relatively high cost, which can often be perceived negatively by the public.
A search for a mutual agreement between the contractor and the authors of the project brought challenges. It was obvious that the contractor saw the project from a more technical point of view without showing the necessary understanding for nature-friendly solutions.
Compliance with all the requirements of the nature protection authorities associated with specially protected species was also complicated.
Operation and maintenance
An unexpected problem occurred because of the behaviour of people who were still throwing the remains of biowaste and sometimes some other waste into the upper parts of the millrun, causing issues lower down the stream in the revitalized part of the millrun.
The frequent use by schools and kindergartens in the summer is positive. They come here to swim, play with fishing nets or float toy boats on the water. They learn to play in the natural environment and to love nature.
How much did it cost?
The cost of the project was 16 million crowns.
The city received 11 million crowns from the Operational Programme Environment. The remaining funds came from the town budget.
Due to the nature of the project, the return of the investment cannot be estimated.
With regular maintenance, a service life of many decades can be expected.
The project has an anti-flood effect and at the same time generates the need for maintenance costs. The costs could, though, be balanced out.
Revitalization of water elements Urban greenery Flood control measures Floods and torrential rainfall