Examples of Forest Regeneration in Slovakia

examples of best practices in restoration of erosion gullies, logging roads and other damaged areas at risk of flooding.

Autor: Ing. Pavol Suty

Translated by: Peter Bujnak

Technical University of Zvolen, Faculty of Forestry

 

DESCRIPTION OF THE FOREST LANDSCAPE

Forest landscapes, especially flysch zones are impacted by considerable deforestation due to large scale commercial forestry activity and development. Timber harvesting with heavy machinery has created a large number of approach roads not only in sloping terrain but also in and along streams. In the case of Slovakia, growth in timber harvesting is not accompanied by adequate construction of suitable forestry roads, as such retrieving timber from forests is accompanied by the formation of large erosion gullies and increased destruction of the natural eco-system. These erosion gullies rapidly drain water from the forests, remove the subsoil and sedimentation as well as carry off logging debris. This result is regarded as the degradation of the landscape which causes flooding during intense precipitation.

All the negative aspects within the forested landscape increase the outflow of water from a territory and lead to its gradual dehydration. This process is the cause of flooding and loss of water in Slovakia and is applicable to many other countries and regions around the world. Such a country is akin to being diseased and requires treatment. Treatment consists of the revitalization of commercial forestry landscapes in order to restore the eco-system and reduce the risks of flooding and drought. Effective revitalization is focused on micro-basin restoration in elevated terrains situated above municipalities where the intensity of flood damages can be averted. Flooding intensity and frequency provides us with insights into what direction to look to in order to mitigate these anthropogenic processes. For centuries, man has been interfering in the natural processes of an ecosystem through intense landuse alterations, now we have something to learn from this and gain new experiences.

ELEMENTS CONTRIBUTING TO FLOOD RISKS

  • A large quantity of water that causes damage by volume and strength
  • Kinetic energy of water during intense precipitation carries soil, gravel, stones, wood and small debris causing clogging of bridges, streams and other water channels and gullies
  • Layers of humus and mud carried away from the forest by excess water run-off

EXAMPLES OF DAMAGED FORESTS

 

Two overused and unmaintained logging roads meet with a large erosion gully running through them.

Erosion gully forming on an unmaintained logging road.

 

 

A hiking trail turns into a stream during rain with no diversion throughs in place, water leaves the forest.

 

EXAMPLES OF ENVIRONMENTAL MAINTENANCE FROM THE PAST

Our ancestors, to the best of their knowledge, took care of the earth responsibly. In addition to the gentler processing of agricultural lands and a more sensitive approach to forestry, they maintained water balance by building various water retention measures such as brick check dams, wooden cascades, riffles, wooden catchment areas for fish, vegetative bank reinforcements of rivers and streams and other measures. In the Kysuce area situated in north central Slovakia, we have found a number of such old structures, especially wooden ones, which serve their purpose of water retention for decades to this day. According to the description by the locals, the oldest wooden dam - approx. 2 m high - is located in the village of Radôstka, in the Hulák district. This relatively large check dam was built in the 1950’s and is still functioning without any required maintenance.

 

Wooden check dam in the village of Radôstka,

Hulák district was built in the 1950’s and still

Functions to this day.

 

Wooden cascade in the village of Vysoka

nad Kysucou built in the 1940’s.

 

Wooden cascades in the village of Vysoká nad Kysucou have been protecting the bridge downstream against flood waves since its inception. Fish catchments built decades ago for trout breeding are scattered throughout the Kysuce area and have survived large floods.

 

IMPLEMENTED WATER RETENTION MEASURES

STONE CHECK DAMS

Oščadnica – Masonry stone dam with a capacity of 30,000m3 of water retention with an expected life expectancy of 100+ years

 

Krivany – dispersed stone check dam

 

Lačnovský potok – Dispersed stone check dam

 

Stara Bystrica - masonry stone dam with outflow pipe

 

Kriviansky potok – stone check dam

 

LAYERED CHECK DAMS

Vyšné Vane- layered check dam with a membrane

 

Nová Bystrica- Check dam with Willow weaving

 

Krasňany – layered check dam

 

Krasňany – layered check dam

 

Dunajov – Check dam slowing snow melt in the spring

 

Hlohovec – check dam in eroded gully

 

Check dam after heavier rainfall

 

Stará Bystrica – check dam made of Willows

 

RAINWATER DIVERSION THROUGHS

Nová Bystrica – rainwater diversion trough on logging road

 

Krivany – rainwater diversion trough

 

Dunajov – construction of a diversion trough on a logging road

 

 

CASCADES

 Krasňany – Wooden cascade check dams

 

Krivany – palisade with membrane

 

Dunajov – combined check dam made of stone and wood

 

Palisade check dam with membrane

 

Simple palisade check dam

 

During heavy rainfall, run-off is slowed down

 

 

SMALL RESERVOIRS

Hranovica – small catchment reservoir built above a Roma settlement

 

Reservoir comprised of a wooden check dam at its edge

 

Nižné Vane - reservoir for forest fire fighting built along a forest road

 

Stará Bystrica – small retention reservoir for peak flow control

 

Hlohovec – check dam made of wood and stones

 

Diversion throughs, seepage pits and soaking belts are also a key part of the revitalization of micro-territories. Most of these measures use wood as their main structural element.

Retention Swale

 

Retention swale with infiltration pit

 

STABILITY AND DURABILITY OF CHECK DAMS AND OTHER RETENTION MEASURES

The main element of a stable and durable check dam is its proper construction. The transverse wooden logs should be layered with branches and pulp (fascines) along the profile of the corridor. It is important to reinforce the edges of the logs and fascines with stones and soil to ensure their stability.

Another important static element is the embedding of cross-cuts in between the transverse logs and fascines on the slope spanning a height of 1 to 1.5 m within the space between the dam walls. This space should not exceed the combined diameter of the logs used so that these cross cuts are firmly in place (20-30 cm).

The entire transverse and cross-sectional structure is stabilized by wooden steaks 8-12 cm in diameter which are hammered into the bed of the corridor until they cannot be wedged. These three elements are interconnected by nails of appropriate size. If using coniferous timber, then it is vital to remove the bark from the logs and steaks.

The stability and strength of the check dam is augmented after a first rainfall because sedimentation settles in and around the structure and loose space is filled in.

Assuming the inaccessibility of the terrain, all work is done manually. By the check dam, the cross-sectional logs are not inserted into excavated grooves but are secured on the slope. Fascines are secured using copper wire 2-3 mm in thickness.

 

 

CONSIDERATIONS FOR DESIGN AND IMPLEMENTATION OF CHECK DAMS

  • Synergy with forestry and agricultural landscape
  • Placement of check dam in the narrowest profile of the corridor and directly against the current while simultaneously ensuring that the retention area achieve its maximum size
  • Individual check dams should not affect the effectiveness of other individual check dams
  • Co-operation with stream managers and landowners is absolutely essential
  • It is necessary to take into full consideration the historical value and uses of the water basin
  • Incorporate nature conservation values and knowledge during entire design and implementation process

MISTAKES TO BE AVOIDED DURING THE IMPLEMENTATION

  • Improper embedding of cross-sectional logs into the slope
  • Insufficient width and length of transverse logs and fascines of the check dam
  • Improper laying of the base log (log should be placed just below the corridor surface)
  • Insertion of thick nails near the edges of the logs (results in split wood)
  • Poorly inserted wooden steaks
  • Angle of check dam leaning downstream of current

 

STATE OF CHECK DAMS 7 YEARS AFTER IMPLEMENTATION

Čadca, part Rieka – 2018 during floods within the region

 

 

 

Dunajov - diversion through fulfilling its purpose of diverting water back into the forest even though it is worn down (left) and fish catchment pond (right).

 

Dunajov - dispersed stone check dam – downstream side above and upstream side below

 

 

  

Catchment pond for fish (left) and channel for fish (right)

 

  

Collection of check dams along a gully and a washed out check dam

 

  

Sludge pits for capturing sedimentation

 

  

Rehabilitated stream bed (left) and dispersed rock check dam that also acts as a bridge (right)

 

Lodno - layered check dam filled with mud and rocks

 

  

Layered check dam filled with sedimentation gradually restores the ravine (left) and cascades consisting of wooden check dams (right)

 

Poorly built fascines resulted in them being washed out

Check dam with a retention capacity of roughly 150m3

 

Foundational transverse log was set too high

 

Check dam with a 130m3 retention capacity