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criterion of similarity was applied to calculate the appropriate forces occurring both
in nature and in the model (Cunge and Ackers
1987
; Novak and
ˇ
´
belka
1981
;
Vischer and Hager
1998
). For the studied phenomenon, also a certain contribution
comes from a viscous force. To limit the influence of viscous force to minimum, the
same kind of flow in the model as that in nature had to be assured. According to
input data, under the conditions of computational discharges passage, the condi-
tions of turbulent flow occur; therefore, it is required that the turbulent flow, with
relatively great Reynolds number, should also occur in the model (Novak and
ˇ
´
belka
1981
). Under model conditions and at variable discharges, the Reynolds
numbers from
Re
35,000 for discharge
Q
0
:
1
%
were obtained. Hence, it was inferred that the phenomenon modeled was signifi-
cantly affected by the gravity force.
In maintaining the similarity of phenomena observed both in model and in
nature, the design of model with appropriate roughness seems to be of prime
importance. According to input data, all elements of external outlet installation
are made of concrete, hence roughness coefficient
n
is equal to 0.020. Because the
model scale is
¼
15,000 for discharge
Q
0.5%
to
Re
¼
1.8493 (Machajski
2009
), the
resultant roughness coefficient of the material that should be used for essential
details of the model outlet installations should be equal to:
a
l
¼
40, therefore, after counting
a
n
¼
n
N
a
n
¼
0
:
020
n
M
¼
8493
¼
0
:
01081
1
:
This equation proves that elements of outlet installation should be made of a
very smooth material, for example, Plexiglass
®
or Vinidur
®
.
The aim of changes introduced into the model was to check a possibility of
capacity ability improvement of spillway, that is, to reconstruct or to build some
elements that were not present on the object earlier and to correct the height
configuration of flume bottom. First, the investigations were carried out for the
existing state to confirm a consistence of a discharge curve currently valid for
spillway with the calculated one - Change I (Fig.
5
).
A significant change introduced into the model consisted in setting a constant
width of flume - Change II (Fig.
6
). The aim of Change III was to correct the height
configuration of flume bottom, that is, its lowering by about 1.50 m (Fig.
6
). Change
IV concerned the checking of an impact of dividing pillar and steering walls
on the conditions of water flow through side channel spillway (Fig.
6
). The last
Change V consisted in the deepening of flume bottom by about 2.50 m (Fig.
7
).
6 Hydraulic Characteristics of Spillway
The spillway characteristic was determined for discharges ranging from 0.0 to
400 m
3
s
1
and for damming up level varying from 309.30 m asl (spillway crest
elevation) to 312.00 m asl (elevation of dam crest from upstream). During
