Geography Reference
In-Depth Information
fire, landslides, wood parasites (including beavers), sickness, competition within
the phytocoenosis, aging, and human activity (Stevens 1997 ). The impacts of wood
on the flow of water can be divided into morphological (erosion-accumulative
processes, transport of wooden debris, basin stability), biological (position and
species diversity, oxidisation of water), hydraulic (roughness of the basin, flow
direction, flow dissipation) and the circulation of particles (food for animals,
collection of mineral sediments, spiraling of nutrients) (M ´ˇ ka and Krej ˇ´ 2006b ).
Wood is removed naturally in three ways: washing away, covering by sediments and
decomposition. Most LWD is washed away during floods, when the energy of the
flow is much higher and often washes away entire trees for significant distances. A
fallen tree on the gibbous bank can be moved to the alluvial bank due to lateral erosion
of the basin, where it is buried by sediments. The decomposition of wood is slower in
water than in dry conditions. Even so, wood also often removed by decomposition,
but it is more commonly washed away down the stream before it decomposes.
The Kenicka Accumulation and Woody Debris
Another unique feature of the study area is the K´nick´ accumulation, which is one
of the largest accumulations of woody debris in the country. It is located north of the
former isthmus of the meander. Its age is unknown. Authors (M ´ˇ ka and Krej ˇ´
2006a ) specify that “in 2000, there were only five trees lying diagonally in the basin
of the river. Additional material was gradually caught by these key trees.” The most
important sources of LWD were the withdrawal of the adjacent banks due to
narrowing of the isthmus. Smaller pieces of wood and woody debris from the
course are captured by large trunks. The accumulation is stabilised on several
gravel-sand deposits.
In the autumn of 2011, the accumulation consisted of four parts with different
characteristics. The north part consisted of several trunks that have captured
medium sized and small pieces of wood as well as large amounts of plastic trash.
This part was the highest of the four, and it is higher than the left bank. The central
part is the largest and was formed by large and long trunks of different ages that
accumulated in a group perpendicular to the flow. This part is the biggest obstacle to
flow during the highest water levels. The south part of the accumulation consists of
long trunks at different orientations that are separated because most of the flow
occurred through this part. A part consisting of SWD (small woody debris) formed
directly adjacent to the south bank of the river. SWD was carried by floods and
remained on the land after the water subsided. Before the isthmus ruptured, the
accumulation divided the flow into three parts: a main part that was directed around
the accumulation along the right bank of the river and then crossed the part of the
accumulation that consisted of long trunks without woody debris; a middle part (the
weakest) where water flowed under the main parts of the accumulation and then
merged with the main flow; and the third part where water flowed north along the
main part and crossed the accumulation where medium size and incomplete trunks
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