Geography Reference
In-Depth Information
were caught. Live vegetation grows in the top parts of the accumulation. The
accumulation is 40
40 m in size, and the height ranges from 1.5 m below the
right bank up to 1.5 m above the bank.
A large amount of woody debris was caught near a large fallen tree perpendic-
ular to the basin in the meander between profiles 14 and 15. This unstable accu-
mulation (further transport of material is prevented by this tree) will be eliminated
in May. Other woody debris was caught downstream by fallen trees near the former
isthmus and formed several small accumulations of wood that were mostly caught
by one piece of LWD (large woody debris). Pieces that were washed away were
replaced by eight trees from the former isthmus; three were full-grown and several
tens of metres high, while the rest were between 5 and 15 m high. The total volume
of woody debris in this area has not changed significantly except for the removal of
part of the Kenick´ accumulation. Other observed phenomena include the washing
away of a tree that had been cut down by a beaver from a gully of the meander near
profile No. 11 and its capture in the accumulation with trash as well as a change of
orientation of a tree near profile No. 13 that had fallen perpendicular to the basin
and had been rotated to the downstream direction due to flow of water.
Further Development of the Locality
The further development of the meander after its rupture is described by M
´ˇ
ka and
Krej
ˇ´
(
2006a
). The authors based their description on the assumption that the
isthmus ruptured at its narrowest point. They expected that a passageway in the
isthmus at least 25 m wide would develop rapidly, but this has not happened yet. At
the beginning of May, the passageway was only 17.5 m wide. One possible reason
is the rapid decline of the flood waters after the rupture, so the river did not have
enough energy to widen the passageway. Further erosion is prevented by trees and
their roots that have fallen into the river basin. The tree trunks (located in the water
perpendicular to the flow) cause deep erosion, prevent lateral erosion, and generate
the extreme depth of the former isthmus. This deepening is also supported by the
presence of a pool at the bottom of the isthmus, which indicates that the level of the
river bottom will decrease due to backward erosion. The rate of erosion will depend
on the frequency and strength of future floods. The K´nick´ accumulation has
already started to block the inlet of the meander, where the flow of the water is
presently much weaker (in some places, the water is almost stagnant). In the future,
it will completely block the inlet. Most of the assumptions of this study were
confirmed two months after the rupture of the isthmus, but the future configuration
will depend on further development and its speed. The current configuration
indicates that a future meander zone that forms from the potential meanders
shown on the map will be even longer. It is possible that new meanders will also
affect the lower part of the K´nick´ branch, which would become a basin if it is
exposed to the regular flow of water. However, this is only a hypothesis of what
may occur in the future.
