Geoscience Reference
In-Depth Information
Computer simulation did not illustrate the occurrence of riverbed processes
in horizontal pattern. Despite activating the module enabling modeling fast bed
changes with unsteady flow, both simulated erosion and bed material accumulation
processes were of vertical character and did not cause a disappearance or formation
of new forks. No distinct processes of side erosion were observed.
The causes of modeling errors might be: the application of 2D model containing
only the module generalizing vertical water velocities distribution as logarithmic
one, limiting the number of nodes to over 40,000, application of the formula for
computing bed material transport not calibrated for diameters exceeding 12.8 cm,
and occurrence in nature of areas of increased flow roughness which caused
oversize grains or wood debris. The presented model did not consider the existing
transport of suspended load.
5.3 Bedload Transport
Results of bedload transport at the moment of peak floodwater passing obtained
from CCHE2D program were compared in cross-section VI with the results of
computations conducted using TRANS program. The modeled bedload transport
in the individual nodes was added up giving the result of transport in the whole
cross-section equal to 27.18 kg s
1
. Transport computed using TRANS program
was converted into the 1 m of the transportation zone width yielding the result
of 4.69 kg m
1
s
1
. The value converted into the model transportation zone width
in both existing flow streams of 15 m gives the results of 70 kg s
1
.The
transportation zones determined on the basis of the cross-section after floodwater
together have a similar width (16 m) but are slightly differently situated. The
model, despite the fact that the deepest part of the cross-section is on the right,
quite correctly points to the occurrence of more intensive transport in the river
channel axis, about 10 m from the left bank. Analysis of cross-section VI
indicates that the left transportation zone should be situated 40 m to the right in
the area of eroded bank. The critical depth for the Białka bedload was computed
as 0.78 m.
6 Conclusions
An analysis of flows for the many-year period (1995-2004) demonstrates that
the interpreted floodwater may appear twice in 15 years. This has been confirmed
by the age of the bush vegetation covering gravel bars in the area of the Białka
riverbed.
Floodwaters may appear in spring or in summer.
Bedload starts to move during floodwater and rapid changes occur in the
horizontal and vertical pattern of the watercourse. Prior to the 2010 floodwater,
