Polski
Science, Issue 17/2025
How restoration is improving the condition of mountain rivers in southern Poland
Dec
Many of Poland’s mountain rivers have been heavily transformed in recent decades – regulations, channel straightening, vegetation removal and intensive gravel mining have led to disruption and even loss of natural processes. The study by Dr. Pawel Mikus from the Institute of Nature Conservation of the Polish Academy of Sciences summarizes various techniques for revitalization and restoration of Carpathian rivers in terms of their effectiveness in the short and long term.
Methods of restoration activities on a regional scale
The study, published November 20, 2025 in the journal
The two main streams of activity are:
- Passive methods – involving the restoration of natural processes, such as restoring erosion processes, restoring multicorridors, increasing the amount of dead plant debris in the riverbed;
- Active methods – requiring the construction or reconstruction of elements of the riverbed, including the lowering of thresholds, the construction of fish ladders, artificial rapids or the reactivation of severed branches.
The author stresses that large, comprehensive restoration projects are quite rare in Poland, mainly due to the enormous costs. However, the importance of small, scattered initiatives led by NGOs, anglers or local communities should not be underestimated. Their strength lies in their numbers and long-term commitment.
Black Dunajec: when nature takes over the reins
The study examines in detail the history of the Black Dunajec River as an example of spontaneous self-renaturalization. In the 1970s. The riverbed was deepened and straightened, increasing the gradient from 0.0054 to 0.0081 m/m and lowering the bottom by about 2.3 m. Three natural streams with a total area of 69.6 m² were replaced by one channel with an area of 160.5 m², or 2.3 times larger.
The impact? The minimum and average annual water level dropped by more than 2.1 meters, and the maximum by 1.95 meters. The riverbed stopped flooding the floodplain, and soils in the newly created fields quickly became dry.
After forty years, the river began to spontaneously recover its former structure. Gravel banks up to 1.5 meters high and new low flow levels appeared. Although the water level rose by 0.35 m (for minimum levels) and 0.58 m (for average levels), it was still up to 1.8 m lower than before regulation. So you can see that a natural recovery is possible, but it takes decades.
Renaturalization of Carpathian rivers in practice: experiences from various projects
The return of rivers to their natural form can generally be accelerated. Research shows that both passive and active measures have significant effects if they are carried out at the right scale and analyzed over the long term.
Dr. Mikus lists the basic passive forms of restoration:
- Erosion corridors allow the river to shape the channel on its own. Studies on the Biala confirm that this is an effective method of improving hydromorphology.
- Multi-stream restoration on the Rab River led to the widening of the channel and the creation of islands after 30- and 35-year return flows between 2011 and 2017. The islands have increased the species diversity of the coastal zone.
- Coarse plant debris (large woody debris) improves habitat conditions and natural sediment retention – used on the Biała, Raba and Black Dunajec, among others.
Very promising results, according to the author, also come from active restoration methods:
- Lowering thresholds and weirs (e.g., Krzczonowka and Trzebunka) – replacing high barriers with near-natural block ramps effectively traps debris, raises the bottom of the riverbed, and improves ecological conditions, especially where there is a lack of riparian forest that allows natural wood blockages to form.
- The fish ladders allow fish migration, although they do not solve the problem of debris deficit.
- The reactivation of the cut-off branches on the Black Dunajec River cost about €9,000, almost seven times less than the planned traditional regulation (about €60,000). The measure increased the diversity of fish and invertebrates and reversed the direction of erosion.
- Artificial rap ids have proved durable – the structures in the Beaver from 2013-2014 survived nine years and major floods, restoring the river’s spawning functions.
Why are the effects sometimes short-lived?
The author notes that improvements in river hydromorphology after restoration do not always stand the test of time. Failures, however, are not solely due to implementation errors. The problem is usually too narrow an approach – measures often cover only the riverbed and ignore the river valley. Without room for the current to migrate, the river quickly loses the effects of restoration.
Other problems include:
- Lack of long-term monitoring;
- unpredictability of fluvial processes – the example of the Black Dunajec River shows that a change in the main current can create new threats as early as 2 km below the intervention site;
- additional risks, such as the release of heavy metals and chemicals from eroded banks and the retention of macroplastics in multicorridor structures.
Conclusion: renaturalization makes sense if we think broadly
The study clearly indicates that restoration, especially when conducted at the scale of the entire river corridor, can effectively reverse hydromorphological degradation. Passive methods produce the most durable results, while active interventions support the process where nature cannot cope alone.
The success of restoration depends largely on broad cooperation between scientists, authorities and local communities. The author also recommends replacing spot measures with broader planning, based on the natural or possibly undisturbed conditions of a given watercourse. Above all, a long perspective is important – rivers need time to recover.
pic. main: MarcinZ83/Pixabay
Source:
Mikus, P. Renaturalization Drives Hydromorphological Recovery in Degraded Gravel-Bed Streams in Poland. Water 2025, 17, 3315. https://doi.org/10.3390/w17223315
