Geoscience Reference
In-Depth Information
The headstreams of the river are located at an altitude of 1,420 m a.s.l. The area of
the Białka catchment is 229.9 km
2
with a length of 41 km. It flows into the artificial
reservoir Czorsztyn at an altitude of 529 m a.s.l. The mean annual flow is about
5m
3
s
1
, whereas spring floodwaters reach the flows of about 500 m
3
s
1
.Inthe
analyzed, mouth part, the Białka is a braided river with usually one to three arms. The
presentedmaterial covers 2.5 kmof the river from its mouth. A 1-mhigh concrete step
is situated at a distance of 360m from the river mouth. The width of the cross-sections
of the measured riverbed at this mouth section fluctuates from 75 to 255 m. The river
bottom slope at this section is 1.04%on the average, which causes the river to become
inaccessible at above 60-70 cm flow depth. The bottom ordinates for individual arms
in the same cross-section may differ by more than 10 cm. The bedload is mostly
composed of granite grains with diameters reaching more than 50 cm.
3 Measuring Methods
The measurements before the floodwater (m-1) were conducted on 12-14 May
2010, and after floodwater (m-2) on 1-2 July 2010. Geodetic measurements of the
bankfull channel and measurements of bed material granulation were carried out.
3.1 Surveying Measurements
The measurements of the riverbed in the m-1 measurement cycle were conducted
using scattered points condensed in selected cross-sections, whereas during m-2
measurements, we focused on making the cross-sections. In this way, m-1 measure-
ments in situ were carried out at 1,019 measurement points, whereas during m-2
measurements 470 pickets were marked. The data accumulated prior to floodwater
occurrence made it possible to prepare 25 cross-sections used in the process of
computer modeling (Fig.
1
). The measurements conducted after the floodwater
passage enabled a comparison of the bottom configuration changes. The analyses
were performed in six cross-sections: the first was situated 10 m upstream from the
river step (340 m upstream from the Białka mouth), the second was 111 m upstream
from cross-section I, the sixth was 50 m upstream from the road bridge on the
border of D˛bno and Frydman villages (700 m upstream from the Białka mouth),
the third was 300 m upstream from the bridge, the fourth was 315 m, and the fifth
was 390 m upstream from the bridge.
3.2 Granulometric Measurements
Because of the character of the river hydraulics, a photographic method of measur-
ing the dimension and shape of the grains was chosen to determine the bedload
granulation. Application of the photographic method has been possible because the
