BEAVER-DECEIVERS
Installation of a beaver deceiver in the municipality of Puconci
At the beginning of February 2024, we installed the sixth “beaver-deceiver” on the Logojca brook, near the settlement of Predanovci (municipality of Puconci), where the surrounding agricultural land was flooded due to the higher water level behind the beaver dam. We used two sewage pipes 7.5 m long and 315 mm in diameter. We installed an iron cage on one side of the pipe and thus prevented possible clogging with driftwood.
First, we made a small hole in the dam by hand, so that the water level dropped a little. The pipes were installed in the dam, and an iron cage was attached to the bottom of the riverbed to keep it submerged. At the end, the pipes were manually covered with branches and mud, so that the dam was similar to the condition before the intervention. Before the intervention, the water depth behind the dam in the river bed was around 1.8 m in the deepest part. With the insertion of the flow tube, the water level dropped by at least 30-40 cm. The water depth therefore still suits the beaver, but the land is no longer flooded during normal water levels.
Before installing the beaver barrier, we obtained permission from the Slovenian Ministry of Natural Resources and Spatial Planning.
Installation of a beaver deceiver in the municipality of Lendava
On October 13th 2023, Lutra Institute team installed a flow pipe, i.e. “beaver deceiver” within the beaver dam constructed across one of the Mura river side channels (Stara Mura). Its purpose was to reduce the flooding of the surrounding agricultural areas. We solved a similar case nearby (also on one of the side channels of the Mura River) in April. In this instance, a double layered ribbed polyethylene pipe was inserted into the dam. The pipe measured 9 m in length and 315 mm in diameter. To prevent beaver from clogging one end of the pipe, one side had a metal cage (75 cm in height, 140 cm in diameter) attached to it. To prevent the plastic pipe from resurfacing, it was punctured on several places along its whole length to enable captured air within it to leave.
Next step was to create a gap within the beaver dam, big enough to insert the prepared pipe with the cage at its one end. The gap had to be about the size of the pipes’ diameter.
The purpose of our intervention was not to remove the dam or to disturb the beaver, but to lower the water level to such an extent that flooding no longer occurred and for the water level to remain high enough for the beaver. To interact with the protected beaver structure (dam) legally, we obtained in advance permission from the Ministry of Natural Resources and Spatial Planning.
The water depth behind the dam before the intervention was approximately 1.6 m measured at its deepest part. With the insertion of the flow pipe, the water level dropped to about 20-30 cm. After the intervention, we monitored the situation daily and found out that the agricultural land was no longer flooded.
Installation of a beaver deceiver in the municipality of Črenšovci
To prevent flooding of the surrounding forest areas, a beaver-deceiver was installed on 24th of April 2023 within a beaver dam created across one of the Mura River side channels at the Municipality of Črenšovci.
A double layered ribbed polyethylene pipe was used and inserted into the beaver dam, measuring 9 m in length and 315 mm in diameter. A metal wired cage was installed at one end of the pipe to prevent beaver from clogging it. The cage measured 105 cm in height and 140 cm in diameter. Small holes were drilled into the pipe, along its whole length, as this is standard procedure to prevent the pipe from re-surfacing due to trapped air. The pipe was weighted down to the bottom of the stream bed with two concrete bricks, as was also the metal cage. The whole construction was covered up carefully with sticks and mud in order to camouflage it within the surrounding area.
The water depth was lowered approximately 30 to 40 cm. Before the procedure, the water depth measured about 1,7 m at its deepest part. The area was afterwards monitored daily and was noticed, that the forest area was not flooded anymore. Camera traps were also installed to monitor the situation further. Immediately after the carried-out procedure, the beavers were recorded repairing the dam at the incision place, where the pipe was inserted. This beaver activity was recorded nightly; however, its intensity dropped after a couple of days and was observed only a couple of times a night.
Beaver-deceiver installation in the Municipality of Podčetrtek
On Friday, 25th of March 2022, we headed again to Kozjanski park, this time to Ribnik brook near Lastnič settlement, where the intention was to install two beaver-deceivers into two consecutive beaver dams. Ribnik Brook is a tributary to Sotla river, which flows not far from the settlement along the Croatian border.
The beaver built three consecutive dams as well as several side channels which lead to beaver huts. The area is therefore a typical and highly educational flooded beaver habitat.
Similarly, as it happened with Buča brook, the surrounding agricultural land is flooded. The agricultural fields are extending into the area belonging to the banks of the brook. As we already reported previously, these areas are protected through the Water Act and should not be tempered with. If the vegetation belts along the water courses are left intact, the land owner protects his own property, as the chances of erosion and flooding are lessened. beaver damage is also minimised, as the beaver has more food to feed on and can use it as building material as well. By having enough food, the beaver will less likely feed on the crops. The dense wooded vegetation also works as a filter, which prevents nutrients from fertilisers and pesticides from entering the water course as well as the underground water used as drinking water.
The process of installing the pipes into the beaver dams at Ribnik brook took a bit longer, as two separate involvements were needed. The task was excellently carried out by Kozjansko Regional Park employees.
During the summer, when the corn crops are ripe, the beaver feeds on them. We advised the tenant farmer to protect the corn field with an electrical fence, which needs to be raised from the ground between 15 to 25 cm.
Installation of a beaver deceiver in the municipality of Kozje
In April 2023, we installed a beaver-deceiver into a beaver dam at Buča brook at Kozjansko Regional Park to regulate the overflowing banks. It is the second case of similar practice carried out in Slovenia (we already reported on a beaver deceiver at Žerjavinski brook). The reason for the experiment was to stop the flooding of the neighbouring agricultural fields, however, we also noticed that the fields were extending too far into the area belonging to the watercourse. Unfortunately, this practice is quite common in Slovenia, despite the banks being protected through the Slovenian Water Act (exceptions to this legislation are written under article 37). Because of the common practice and not following the legislation, the consequences are seen in increase overflow of banks and flooding the fields/houses in the area.
Because of the low terrain, the area outside of the banks got flooded, therefore, we decided to install a beaver-deceiver into the beaver dam. With this practice, we ensure undisturbed water flow through the beaver dam, consequently decreasing the water levels and preventing the flooding.
As part of the Life Beaver project, we have allocated funds for a limited number of such interventions. We financed the material for the work through the project, but the practice was carried out by the Kozjansko Regional Park employees. Approximately, six hours were needed, to create a hole into the beaver dam and to install two 6 m long drainage pipes of 40 cm diameter, the ends of which were fitted with an iron mesh. The iron mesh prevents the beavers from clogging the edge of the pipe. The beavers instinctively respond to the sound of water flow and would clog any leaks they can find as part of the dam repairment.
The pipe is set up in such a way as to regulate the water level above the beaver dam, but we ensured sufficient water level for the beaver to swim as well as to reach the neighbouring trees, which it is using for building material. The pipe running through the beaver dam was covered up partly with branches and twigs, but the rest was left for the beaver to finish covering up.
The intervention was carried out in a single day and a camera was set up in the vicinity of the beaver-deceiver, to monitor the beaver activity in the area.
Installation of a beaver deceiver in the Žerjavinski potok (brook)
In the beginning of June 2021, we collaborated with the Institute of the Republic of Slovenia for Nature Conservation (ZRSVN Novo mesto) and installed for the first time a »beaver deceiver«, which is a method for regulating water levels increased due to beaver dams.
A local construction company (CGP) installed a 15 m long pipe into the bank next to the Žerjavinski brook near Otočec and created a water flow past the beaver dam.
As part of the ongoing monitoring of the installed beaver deceiver at Žerjavinski brook, we had a look at the functionality of the flooding solution during the winter.
In spring and summer time, we did not record any flooding. However, in winter time, the brook flooded part of the surrounding meadow as well as the passage over the brook. The passage is made as a culvert and is meant to be used by heavy farm machinery to reach the agricultural fields. The passage is on a lower terrain, as is the beaver dam, and the water consequently overflows. The whole of the culvert passage needs to be raised and stabilised with extra gravel.
We noticed that all three of the beaver dams, following each other along the brook before Krka confluence, are in good condition. There was also some freshly chewed wood piled on top of the beaver dams, so the beaver hut is clearly in use. We continue to monitor the events along the brook with the help of our trap cameras.
