Manual of beaver management within the ... - DANUBEPARKS

Manual of beaver management within the Danube river basin8.4 Dam building activitiesBeavers build dams whenever the water level in their habitat is too low or if thefluctuations are too much to keep the entry to their den continuously below the watersurface. They also build dams for easier access food sources farther away from wateror to transport food easier on the water. In a cultural landscape, beavers very often donot have to build “real” dams. It might be enough to block man-made “bottlenecks” asculverts or pipes.In the cultivated landscape, areas flooded by beaver ponds become inoperable toagricultural use and forestry, and even the use of non-flooded areas can be indirectlyaffected, e.g. when access routs are flooded.Impacts of beaver dams can reach way beyond the areas flooded due to associatedrise in ground tables. Even in areas farther away, land use can be impacted, cropgrowth can be impeded, or commercially valuable tree species might die off.Water-soaked river banks are more likely to break down, and paths, roads and railwaysalong damed areas can be threatened. Beaver dams can also lead to backflow intodrainage pipes and sewage treatment plants, thus influencing their function.In fish hatcheries beaver dams can block of fresh water inflow. Blocked outflows in fishhatcheries and sewage plants can yield to water running over the dams and washingthem off. Blocking of outflow structures in fish hatcheries can impede harvesting.Only in very intensively man-changed creeks and ditches beaver dams can impede fishmigration, as in this cases by-pass channels can not form.Photo No. 33.: Beaver flooding caused by a dam in a private forest55