HYDRODYNAMICS BALANCE OF THE SKAWA RIVER WITHIN ...

HYDRODYNAMICS BALANCE OF THE SKAWA RIVER
WITHIN THE INFLUENCE OF THE BACK WATER
OF THE SWINNA POREBA WATER RESERVOIR
Wojciech Bartnik*, Kazimierz Banasik**, Leszek Ksiazek*,
Artur Radecki-Pawlik*, Andrzej Struzynski*
*Department of Water Engineering, Faculty of Environmental Engineering and Land
Surveying, Agricultural University of Cracow, 30-059 Cracow, Al. Mickiewicza 24-28,
Poland
** Department of Hydraulic Engineering and Environmental Recultivation, Faculty of
Engineering and Environmental Science, Warsaw Agricultural University, 02-787
Warsaw, Nowoursynowska 166, Poland
The influence of backwater reach of the Swinna Poreba Reservoir (which is under construction at
the moment) on the hydrodynamic balance of the Skawa River is analyzed along a paper. This
process is possible when employing the CCHE2D model from University of Mississippi. CCHE2D
is a hydraulics software, which predicts river bed changes calculated along measurement
river/stream region. The methodology of the research includes: geodesy survey along the river
within influence of backwater of the Swinna Poreba Reservoir as well as the geodesy survey of the
Swinna Poreba water reservoir terrain (31 cross section), granulometry of river bed measured using
freeze-sample method from river bed cover (armoring layer) and layers below it (45 samples),
gravel bars granulometry (4 gravel bars) and geometry and finally grain shapes. On the basis of
obtained data the state-of-the-art CCHE2D software will be used to model the hydrodynamics
balance. To compare obtained results from CCHE2D model the additional ARMOUR software
(developed at the Agricultural University of Cracow) is used. The prognosis of hydrodynamic
balance of the river bed is always additionally more difficult due to very flat grains in the bed
surface, which are present in the Skawa River.
KEY WORDS: hydrodynamic balance, mountain river, computer modeling, back water influence
1. INTRODUCTION
The existing of any hydraulic structure within a river channel inevitably changes
and/or at least has its influence on the river hydrodynamics of water flow. Especially the
influence of water reservoir, which dams-up millions of cubic meters of water must
imprint in river behavior and fluvial processes in a catchment. This is because the

important aspect of fluvial processes is the hydrodynamics of river flow with which
sediment transport and river, channel formation and transient changes are interrelated.
Since river flow is an open-channel flow, principles and equations in nonprismatic openchannel
hydraulics are generally employed in river hydraulics. An important task in river
hydraulics is to determine the free surface (especially after interfering in to river channel
by building any hydraulics construction) so other hydraulics parameters such as hydraulic
radius, velocity, shear stresses, flow resistance parameter, roughness and energy gradient
may also be obtained.
If one understands that dynamics is a branch of physical science (and a subdivision
of mechanics) that is concerned with moving bodies and the physical factors that affects
the motion (e.g. force, mass, momentum and energy) [Thomas and Goudie 2000] and on
the other hand prefix hydro- denoting water, hydrodynamics will be the study of forces,
energy, pressure etc. of water (in some cases of liquid) in motion [Uvarov and Isaacs
1986]. Thus, by building the dam across the river we change hydrodynamics of water.
The interplay between the resultant of hydrodynamics forces on a particle and of its
weight represents the physical mechanism of the sediment in motion [Graf 1980] the
water reservoir built up in the river channel influenced also the sediment transport. The
problem is though that we still do not have quite good recognition and knowledge of
forces and their effects on the sediment and riverbed changes when interfering in to river
system. Today many sophisticated computer models capable of working with many
different scenarios could help us predict hydrodynamics changes within water channel of
the river after constructing hydraulic structures or building water reservoir.
In the present paper the influence of backwater reach of the Swinna Poreba Water
Reservoir (which is at the moment under construction – the building site is in the
Southern part of Poland in Polish Carpathians, the earth-dam is nearly finished as well as
many concrete parts of the dam) on hydrodynamic balance of the Skawa River is
analyzed. Employing the CCHE2D model from University of Mississippi does this
prediction. The CCHE2D is a sophisticated hydraulics model, which predicts river
hydraulics and sediment transport parameters calculated along chosen river/stream
region. On the basis of obtained data from the field the state-of-the-art CCHE2D
software is used to model the hydrodynamics balance.
2. MATERIALS AND METHODS
2.1. RESEARCH CATCHMENT
The investigated site situated close to Sucha Beskidzka municipality and Zembrzyce
village is within a rich of back water from the Swinna Poreba Water Reservoir, which at
the moment is under construction. The basic parameters of the planned water reservoir
are gathered in Table 1.
The bedload characteristics were done using of two methods. The first was a sieving
method and the second was an in situ freezing sample method. The average value of bed
mean diameter in research region equals 0.078 m and d 50 = 0.066 m. Within 1055
measured grains 59% were ellipsoids, 38% - disks and rods and 3% - spheres.

The mean value of shape factor SF=0.38 confirm the grains of the sector of The Skawa
River are flat. For bedload transport characteristics in Wang formula the Shields stresses
of f 1 = 0.045 for d i /d m ≥0.6 and f 2 = 0.03 for d i /d m

effects of bed form, channel geometry, sediment size and vegetation, etc. into this
coefficient. But for detailed near field simulation/verification with experimental data, the
first approach is physically sound and thus worth adopting if roughness parameter is
available.
It is important that when loose bed and bank are considered (with or without sediment in
motion), the roughness height and Manning’s n used for calculating shear stress should
include both bed material grain size and bed form roughness effects. These two
parameters representing bed resistance to the flow can be converted from each other
using Strickler’s formula.
The bed load transport formula developed by van Rijn is adopted, where the critical shear
stress is calculated according Yalin’s suggestion, which modified the Shields curve.
The shear stress τ in this formula is evaluated from
τ = γ ( u / C
' ) 2
(1)
'
where: C = .8ln(12h
/3d
)
7
90
The model takes into consideration bedload motion affected by transversal slope and
bedload motion affected by secondary flow. The critical shear stress obtained from flat
bed assumptions has to be corrected according to the slope angles in the streamwise and
transversal direction. Furthermore, natural river channels usually have curved
meandering patterns. When water flows along a curved channel with varying curvatures,
secondary current would occur due to the centrifugal force; bed load always tends to
move towards to the inner bank of the channel systematically making the channel more
and more curved.
The calculations of bedload transport for mountain rivers can be executed using
SEDTRA module where 3 equations are applied:
0.01 - 0.15 mm - Laursen,
0.15 - 2.0 mm - Yang,
> 2.0 mm - Meyer-Peter and Muller (MPM).
The first step to start simulations is creating a mesh. The mesh is generated base on
survey measurements. There are several methods to interpolate the interior nodes and bed
elevation and smoothing created mesh. The equations used for smoothing mesh include
Poisson equation, Variational Laplace equations and Laplacian method (Zhang and Jia,
2002).
3. RESULTS
Using the CCHE2D model a simulations were done for discharges Q=35, 112 and
205 m 3·s -1 for reservoir water level 304.56, 306.50, 307.80 and 309.60 m a.s.l.
The Fig. 1 presents water surface for discharges Q=35, 112 and 205 m 3·s -1 for reservoir
water level 304.56 m a.s.l. The average slope of water level for discharge Q=112 m 3·s -1 is
equal to 3.5‰ and for Q=205 m 3·s -1 respectively 3.7‰. One can predict that average
slope of water level for discharges greater than simulated tends to reach a slope of the
whole Skawa River valley - 4.1‰.

Cross-section XIV-XIV
Fig. 1. Simulated water surface level (WSL) for the reservoir water level 304.56 m a.s.l.
In the Fig. 2 there is calculated a reservoir water surface level for water discharge Q=35
m 3·s -1 . At this flow conditions the back-water region is rather small and moves up and
down along a distance about 1.5 km, depending on the water reservoir water level. For
any other higher flow rate that distance is longer.
Fig. 2. Simulated water surface for discharge Q=35 m 3·s -1 and different reservoir water level

Cross-section XIV-XIV
Fig. 3. Calculated WSL for different discharges and the reservoir water level 309.60 m a.s.l.
Water surface levels (WSL) as a result of CCHE2D simulations are presented in the
Fig.3. The simulations were run for discharges Q=35, 112 and 205 m 3·s -1 and normal
reservoir water level equal to 309.60 m a.s.l. At this WSL selected cross-section XIV-
XIV are located within back-water of the Swinna Poreba reservoir. Also, the back-water
region for bankfull is about 0.5 km.
Calculated shear stresses τ o and critical one τ cr in cross-section XIV-XIV
Table 2
Run
Critical shear
stress
τ cr [N·m -2 ]
Shear stress at
the … point
τ o [N·m -2 ]
Max τ within XIV-
XIV cross-section
τ max [N·m -2 ]
Water
discharge
Q [m 3·s -1 ]
WSL
[m a.s.l.]
D01 57.63 98.27 304.56
D02 59.47 70.85 306.50
D03 57.60 68.83
205
307.80
D04 9.45 20.79
309.60
D09 44.59 49.20 304.56
D10 37.35 41.07 306.50
D11 37.18 41.34
112
307.80
D12 0.52 16.38
309.60
D17 17.19 17.51 304.56
D18 17.18 18.28 306.50
D19 12.21 13.96
35
307.80
D20
0.81 1.87
309.60
for dm=0.078 m τcr = 37 N·m -2
for dm=0.14m (armoured
leyer) τcr = 70 N·m -2

As a criterion of incipient motion of bedload transport very often shear stress is used.
Tab. 2 presents calculated critical shear stresses τ cr shear stresses τ o for different
discharges and water surface level as a result of water reservoir changes. At the selected
region - along cross-sections XIV-XIV – shear stresses were read from the CCHE2D
data probes. For instance runs D01-D04 are executed for a discharge 205 m 3·s -1 and
respectively reservoir water levels were set up into 304.56, 306.50, 307.80,
309.60 m a.s.l.
There is a strong influence of reservoir water level in selected cross-section on incipient
of motion of sediment. Critical shear stresses calculated using ARMOUR software along
cross-section XIV-XIV for armoured bed equal to 70 N·m -2 (Bartnik et al. 2004) and
there are reach or exceed for discharge Q=205 m 3·s -1 and reservoir water surface less then
normal one (309.60 m a.s.l.). For another cases the initial conditions of bedload transport
are not reached.
A deposition takes place when τ o

ACKNOWLEDGEMENT
The project was realized in the cooperation of Agricultural University of Cracow and
University of Mississippi under the research program USPTTP02 CAU.
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