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Journal of Civil Engineering and Materials Application
Journal home page: http://jcema.ccom
Received: 26 February 2018 • Accepted: 27 April 2018
Research
doi: 10.22034/JCEMA.2018.91992
Experimental Study on the Effect of Single Spur-dike
with Slope Sides on Local Scour Pattern
Hamed Haghnazar1*, Behnoush Hashemzadeh Ansar2, Farzin Asadzadeh3, Seyed Ali Akbar Salehi Neyshabouri4
1
Department of Civil Engineering, Islamic Azad University of Shahr-e-Qods, Tehran, Iran
2
Department of Civil Engineering, Shomal University, Amol, Iran
3
Department of Civil Engineering, Tarbiat Modares University, Tehran, Iran
4
Water Engineering Research Institute, Tarbiat Modares University, Tehran, Iran
*Correspondence should be addressed to Hamed Haghnazar, Department of Civil Engineering, Islamic Azad University of Shahr-e-Qods,
Tehran, Iran; Tel: +989128451247; Fax: +9888853153; Email: haghnazarh@gmail.com.
ABSTRACT
Constructing the spur-dikes is one the most efficient methods for protecting river banks. The spur-dike in the flow path leads
to local scour around this structure. Scour around the spur-dike is one the major problems that might endanger the stability
of the structure. Therefore, estimating the scour around this structure based on the flow condition and geometry of the spurdike is highly important. The experiment was conducted in laboratory flume 6m long, 0.45 m width and 0.45 m deep and with
median diameter of particle size 1.48 mm and the maximum local scour around the direct upright and trapezoidal spur-dike
(with slope side) and the effect of Froude number and spur-dike side slope on geometry of local scour are investigated.
According to the results, by increasing the Froude number and spur-dike side slope, the maximum scour depth and hole
dimension of scour is increased, also sedimentation length is increased but its height is decreased and the amount of bed
changes toward downstream is increased.
Key words: Spur-dike, Slope side, Scour, Froude number.
Copyright © 2018 Hamed Haghnazar et al. This is an open access paper distributed under the Creative Commons Attribution License.
Journal of Civil Engineering and Materials Application is published by Raika Pajuhesh Pars; Journal p-ISSN xxxx-xxxx; Journal e-ISSN 2588-2880.
1. INTRODUCTION
T
he spur-dikes are deflector structure that are
developed from the river banks towards the flow
center and leads to deviation and directs the flow
from the banks towards the river centerline. This flow
deviation creates rotating area with severe turbulence
around the spur-dike. Hydraulic process of this matter
expands the scour hole around the spur-dike and bed
material sedimentation in downstream and the river bank.
While the scour is considered as a serious hazard for the
spur-dike and consequently for the river, sedimentation in
downstream river banks is a natural solution for protecting
the river banks. The spur-dike in flow path causes local
scour around this structure. The spur-dike increases the
local flow velocity and its turbulence and creates vortexes
that impose extra erosion forces around the structure bed.
Many researches have investigated the scour around the
spur-dike. Kuhnle et al. (1999) via their studies on the
maximum depth of the scour hole concluded that in
shallow flow, the maximum scour depth occurs in spur-
dike nose and by increasing the flow it moves towards the
center of the channel (1). Ghodsian and Tehrani (2001)
conducted a research on investigation of position and
length of the spur-dike on its scour in 90O bend. The results
showed that the maximum scour depth of the first half of
the bed is less than that of the second half bend. Opposite
of the maximum scour depth, dimensions of the scour hole
increases by moving the spur-dike from the first half of the
bed to its second half (2). Nagy (2004, 2005) by studying
the spur-dike angle with the bank and Froude number for
submerged and non-submerged spur-dike in direct channel,
reached to the conclusion that the scour increases by
raising the Froude number and also the scour for 90⁰ is
more than other angels. On the other hand, the maximum
scour depth, width and volume of the hole for nonsubmerged spur-dike is more than that of submerged (3, 4).
Ardeshir et al. (2005) conducted a research in a laboratory
flume on spur-dike series and reported that the most
appropriate length for subsidiary spur-dike is 0.66 to 0.77
of the first spur-dike length. Also as the first spur-dike
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diverts the flow towards the other side bank, the maximum
scour occurs in the second spur-dike (5). Also Nasrollahi et
al. (2008) studied the effect of flow depth on where the
maximum scour depth occurs. They concluded that by
increasing the flow depth, the maximum scour depth
location moves towards the center of the spur-dike (6).
Fazli et al. (2008) also investigated the laboratory changes
of scour and how the scour hole is formed around the
direct spur-dike in diverse position of 90⁰ bend and
concluded that as the spur-dike approaches to the end of
the bend the scour increases (7). Zhang and Nakagava
(2009) investigated an experimental and numerical study to
simulate the flow pattern and bed alternation in presence of
permeable and impermeable spur-dike. These experiments
have been conducted in direct flume 8 m long, 0.4 m wide
and 0.4 m deep in clear water condition. This research
showed that permeability has an important effect on flow
pattern and bed changes. Results showed that in a
permeable spur-dike due to the flow separation and
formation of vortexes, the scour occurs between the shafts
while in impermeable scour due to flow separation and
formation of horseshoe vortexes, scour occurs behind the
spur-dike (8). Masjedi et al, (2011) conducted a laboratory
research on a scour around L-shaped spur-dike in 180⁰
bend in clear water condition. They performed their tests
by Fr=0.23, 0.25 and 0.35. The spur-dike with the length
of 10, 15, 20 and 25 percent of channel width were settled
in 30⁰, 45⁰, 60⁰ and 90⁰ in bend. The obtained results
showed that the depth of scour increases by passage of
time. The scour depth increases by raising Froude number.
Increasing the length of spur-dike raises the maximum
depth of the scour (9). Teraguchi et al, (2011) used a
laboratory model for investigation of turbulent flow and
bed changes around permeable and impermeable spurdikes. Results of the tests showed that the maximum scour
depth in impermeable spur-dike nose is more than that of
permeable spur-dike (10). Osman and Negmaldin (2012)
investigated the effect of constriction on permeable and
impermeable spur-dikes series via laboratory model.
Results of these tests showed that the scour depth around
the impermeable spur-dike with 60% is 2.6 times more
than the scour depth around spur-dike with 80%
constriction and this ratio is 3 times more for the
permeable spur-dike in the same condition (11). Van Den
Heever (2013) by conducting a laboratory research
investigated the erosion and sedimentation and hydraulic
flow of a laboratory model of rivers in South Africa. In this
study, the variables were: length, distance and angle of
locating spur-dikes. Their research showed a slow velocity
area between the spur-dikes in which the sedimentation
occurs. By increasing the distance between the spur-dikes,
the flow velocity between them increases and this matter
lead to changes the sedimentation pattern between the
spur-dikes (12). By considering the studies of the previous
researches, it is found that few number of researches have
been done on the shape and geometry of the structure,
scour hole expansion and scour pattern around spur-dikes.
One practical and economical method is to construct spurdike by using Rip Rap and therefor the spur-dikes are often
built in trapezoidal shaped. In this research, the maximum
of local scour in erodible bed around direct upright and
trapezoidal (with slope sides) spur-dike were studied. By
doing this research for different side slopes and also
diverse hydraulic condition, besides comparing the result
of upright spur-dike, the effect of side slopes on the
erosion around the spur-dike can be found out.
2. MATERIALS AND METHODS
The experiments were conducted in a laboratory flume 6 m
long, 0.45 m wide and 0.45 m deep in the hydraulic
laboratory of Tarbiat Modares University. The walls and
the bottom of the channel are made of glass which is 10
mm thick. The bed material is sand with d50=1.48 mm. The
Channel’s characteristics have been shown in Figure 1.
Figure 1. Laboratory equipment and channels
The utilized spur-dikes in the experiments are impermeable
and made of Plexiglas. In this research four spur-dikes
have been used which are 10 cm length, 5 cm width, 42
cm deep and the side slope are 90⁰, 85⁰, 80 and 75⁰.
Utilized spur-dikes are shown in Figure 2.
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Figure 2. A schematic view of the utilized spur-dike in the experiments
In order to find a relationship between the effective factors
on the scour around the spur-dikes, a dimensional analysis
was conducted on the influential parameters. The
independent and effective variables are: Channel width (B),
channel longitudinal slope (s0), spur-dike length (L), the
angle of spur-dike with wall (β), the spur-dike height (H),
the spur-dike width (b), the side slope of the spur-dike (z),
the average flow velocity before the spur-dike (U), the
flow depth in upstream (h), the average diameter of the bed
material (d50), the standard deviation in distribution of the
particle size (σg), submerged density of the bed material
(ϒs), water mass density (ρ), sediments mass density (ρs),
acceleration of gravity (g), kinematic viscosity (ν). By
selection of maximum scour depth (dse) as the dependent
variable, the following relation is obtained:
dse=f (B, S0, L, β, H, b, Z, U, h, d50, s, g, , ,s, , g,)
(1)
The general form of the above mentioned relation by
using Π-Buckingham Method could be written as follow:
𝑑𝑠𝑒
ℎ
𝐵
𝐿
𝐻 𝑏
= 𝑓( ℎ , 𝑆0, ℎ,𝜃, 𝐿 , ℎ, 𝑍,
(2)
ℎ 𝜌
𝑈ℎ 𝜌 𝑈2
, , ,𝜎 , ,
)
𝑔ℎ 𝑑50 𝜌𝑠 𝑔 ∆𝛾𝑠𝑑50
𝑈
𝐻 𝜌
dimensional parameters of 𝑆0, 𝜃, 𝐿 , 𝜌𝑠, 𝜎𝑔, are removed.
Consequently by combining, the following dimensionless
parameters are considered as follow for investigation of the
variable effect on the scour around the spur-dike with slope
side:
𝑑𝑠𝑒
ℎ
= 𝑓( 𝐹𝑟, 𝑅𝑒, 𝑍)
(3)
Due to the turbulence of the flow, the effect of Reynolds
number can be ignored and ultimately the following
equation is obtained:
𝑑𝑠𝑒
ℎ
= 𝑓( 𝐹𝑟,𝑍)
(4)
Discharge is constant for all the experiments in 15 l/s, and
once the channel width and the flow depth is known, U can
be calculated. In this way U/Uc is determined. Three flow
depths were considered for the experiments and
consequently the ratio of U/Uc was obtained. Table 1
shows the flow condition in the experiments. By
considering the three Froude number and four slope sides
for the spur-dike, twelve experiments were conducted.
Due to the channel slope, the angle of spur-dike with the
wall, Fluid, length and depth of spur-dike are constant, the
h (m)
0.11
0.12
0.13
Table 1. Froude number and flow depths in the experiments
U (m/s)
Uc (m/s)
U/Uc
0.303
0.355
0.85
0.278
0.367
0.76
0.256
0.377
0.68
At the beginning of the experiments, large amount of scour
could be seen around the spur-dikes and gradually by
passage of time the erosion process slowed and finally
after a while it was balanced. In this research Ettema
criteria was used. Ettema (1980) considered the relative
Fr
0.29
0.26
0.23
balance time for the scour hole in experiments equal to the
time that the scour depth changes in each 4 hours be less
than 1 mm (13). In Figure 3, the balance time of one of the
test can be seen. Based on the figure and the calculation,
24 hours has been considered as the balance time.
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Figure 3. The balance time of scour
In these experiments, after the channel drainage, changes
in the bed around the spur-dikes after the scour and
sedimentation were measured by a laser meter.
Longitudinal grids for measuring have been irregular in a
way that in the areas with more bed changes, smaller
gridding is selected and in the areas where the topography
was flatter, bigger gridding was used. The minimum and
maximum distance between the longitudinal grids along
the channel were respectively 2 cm and 10 cm. The
distance between measured points in latitudinal grids was
1.5 cm.
3. RESULTS AND DISCUSSION
In this research, different parameters of scour geometry
were studied. The defined parameters are: upstream length
of scour hole (a), downstream length of the scour hole (b),
scour hole width (c), maximum scour depth (ds) (Figure 4).
Figure 4. The scour hole dimension
In order to investigate the effect of the spur-dike slope
sides on the maximum scour depth, the scour hole width
and the scour hole upstream and downstream length, above
mentioned experiments were conducted in U/Uc=0.68, 0.78
and 0.85. In Figure 5 the effect of slope on these
parameters can be seen. According to Figure 5 (a), by
increasing the spur-dike side slope from 75⁰ to 90⁰, the
maximum scour depth increases. Since by increasing the
spur-dike side slope, vortex power in upstream of spurdike increases and this increase eases the material erosion
of the spur-dike upstream and also the capacity of sediment
transport inside the scour hole increases. In addition, the
maximum scour depth occurs in upstream of spur-dike
nose. In Figure 5 (b), changes of the downstream length of
scour hole have been shown. By decreasing the spur-dike
side slope, the downstream length of the spur- dike hole is
also decreased because by reducing the spur-dike side
slope, the spur-dike width is increased and the vortex is
formed and moved from the upstream of spur-dike nose,
should pass a long distance for sediment transport from
spur-dike to downstream and this matter leads to reduction
of sediment transport power to downstream and
consequently decrease the downstream length of scour hole.
Figure 5 (c), by increasing the spur-dike sides slope in all
conditions, upstream length of the scour hole increases
because by increasing the scour hole depth, material
collapse from the hole side increases and this matter leads
to growth of scour hole length in upstream. In Figure 5 (d)
by increasing the spur-dike side slope, the scour hole width
increases and this is caused by the scour depth growth due
to the slope increase.
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(a)
(b)
(c)
(d)
Figure 5. The scour hole parameters change in diverse spur-dike sides slope: a) the maximum scour depth, b) the scour hole downstream length, c)
the scour hole upstream length, d) the scour hole width
In Figure 6, longitudinal profile in 10% of the channel
width for Fr=0.26 has been shown. As it is seen, by
increasing the spur-dike side slope, the scour depth in
upstream and downstream of the spur-dike is increased.
Also by increasing the spur-dike sides’ slope, bed change
and migration towards downstream becomes more.
Figure 6. Longitudinal profile in 10% of the channel width for Fr=0.26
In Figure 7, the bed topography for Fr=0.26 has been
shown. According to the results, the maximum scour
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occurs in the upstream of spur-dike nose. Also after the
scour hole around the spur-dike, sedimentation is formed
and after that, a scour hole is shaped as well while the
extracted material from this hole formed sedimentation in
downstream. Regarding the hole dimensions the first scour
hole (around the spur-dike) is bigger than the second one
and also the first sedimentation is bigger than that of the
second one in every respect. According to the figure, the
first sedimentation is formed near the spur-dike wall and
the highest part of this sedimentation is close to the spurdike adjacent wall. By increasing the spur-dike side slope,
dimension of the scour hole around spur- dike also
increases. Consequently, dimension of the sedimentation is
increased and it is divided into two parts. By decreasing
spur-dike side slope from 90O towards 75O migration and
alternation of the bed towards the downstream of spur-dike
is decreased.
(b)
(a)
(d)
(c)
Figure 7. Bed topography changes for Fr=0.26 a) spur-dike with 75⁰ side slope, b) spur-dike with 80⁰ side slope, c) spur-dike with 85⁰ side slope, d)
spur-dike with 90⁰ side slope (flow is from right to left)
In Fig.8 The effect of the Froude number on downstream
length of the scour hole, maximum scour hole width and
upstream length of the scour hole are seen. These
experiments were conducted in four modes of spur-dike
sides’ slope. As it is shown in Figure 8 (a), by increasing
Froude number, the maximum scour depth in scour with
different slope always increases and it is caused by
increase of the flow velocity. By increasing the Froude
number in a constant side slope, downward flow and
horseshoe vortex work more appropriately in order to
increase the maximum scour depth. In Figure 8 (b), the
upstream length changes of scour hole in diverse slopes
and three Froude number are seen. According to this figure,
for all slopes of the spur-dike by increasing the Froude
number, upstream length of scour hole is increased. When
the Froude number of the flow in constant discharge
increases, by increasing the flow velocity and decreasing
the flow depth and increasing the downstream flow power,
before the spur-dike bigger vortex formed. Therefore, the
flow effect on the spur-dike upstream bed expands to
farther areas. On the other hand, the upstream hole length
depends on the scour in the hole center so that the
materials collapsed from the hole wall and transferred to
the downstream with the channel main flow due to the
vortex caused by pressure difference. Therefore, it brings
about many changes of the scour hole upstream length
compared to the Froude number. In Figure 8 (c) the effect
of Froude number on alternations of the scour hole
downstream length in different slopes of the spur-dike has
been shown. By increasing the Froude number, the
downstream length of the scour hole is increased, because
by increasing the Froude number, sediment transport
power is increased. In the spur-dikes with steeper slopes,
this parameter alternation is more than Froude number. In
Figure 8 (d), in lower Froude numbers, due to the low
speed of the flow in the spur-dike upstream, the local effect
of the flow on the width of the scour hole is little. By
increasing the Froude number, the flow speed is increased
and its depth is decreased and this matter increases the
effects of velocity on the width of the scour hole and
consequently by increasing the Froude number of the flow,
the width of the scour hole is increased.
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(b)
(a)
(c)
(d)
Figure 8. The scour hole parameters changes with different Froude number a) maximum scour depth, b) the scour hole downstream length, c) the
scour hole upstream length, d) the scour hole width
In Figure 9 and Figure 10, longitudinal profile in 10% of
the channel width for the spur-dike with 80 and 90 slopes
has been shown. As it is seen, by increasing Froude
number, the scour depth flow in upstream and downstream
of the spur-dike is increased and by increasing the Froude
number length of the first sedimentation is increased.
Figure 9. Longitudinal profile in 10% of the channel width for the spur-dike with 90 side slope
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Figure 10. Longitudinal profile in 10% of the channel width for the spur-dike with 80 side slope
In Figure 11 and Figure 12 the bed topography for two
spur-dikes with 75 and 90 side slope has been shown.
According to the figure it can be concluded that by
increasing the Froude number, the maximum scour depth
and dimensions of the scour hole is increased. In addition,
length of the sedimentation after the spur-dike is increased.
By increasing the Froude number, expansion of the bed
surface changes towards downstream increases and the
height of the sedimentary hill decreases.
(a)
(b)
(c)
Figure 11. Bed topography changes for 90 spur-dike, a) Fr = 0.29, b) Fr=0.26, c) Fr=0.23
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J. Civil Eng. Mater.App. 2018 (June); 2 (2): 111-120
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(b)
(a)
(c)
Figure 12. Bed topography changes for 75 spur-dike, a) Fr = 0.29, b) Fr=0.26, c) Fr=0.23
On the whole it can be concluded that in direct spur-dikes
with the slope sides in different Froude numbers, by
increasing the Froude number and when the spur-dikes
side slope gets steeper, the maximum scour depth and
dimension of scour hole is increased. Also by increasing
Froude number and the spur-dike sides slope, the
sedimentation length is increased but its height decreases
and expansion of bed changes towards downstream
increases.
4. CONCLUSION
In this study, the maximum of local scour around the direct
upright spur-dikes and trapezoidal spur-dike (with slope
sides) have been studied and the effect of Froude number
and the spur-dike side slope on the scour geometry
provided. Results show:
1. By increasing the spur-dike side slope from 75 to 90
degree, the maximum scour is increased because by
increasing the spur-dike slope, the vortex power in spurdike upstream is increased and the sediment transport
power in the scour hole is increased.
2. By decreasing the spur-dike sides’ slope, also the scour
hole downstream length decreases because by decreasing
the spur-dike side slope, its width increases and it leads to
the vortex energy reduction and it caused the reduction of
the sediment transport power to downstream.
3. By increasing the spur-dike sides slope in all forms, the
upstream length of the scour hole increases, because by
increasing the scour hole depth, the material collapse from
the hole wall is increased.
4. By increasing the scour side slope, the scour hole width
increases and it leads to the scour depth increase due to
slope increased.
5. By increasing Froude number the maximum scour depth
in spur-dike with different slopes continuously increases
and its main reason is increase of the flow velocity.
6. For all the spur-dike sides slope, by increasing the
Froude number the scour hole upstream length increases
because by increasing the flow velocity the downward
flow power and the vortexes close to the spur-dike
increases.
7. By increasing the Froude number, the downstream
length of the scour hole is increased because by increasing
the Froude number, the sediment transport power is
increased. In the spur-dike with steeper slope, this
parameter changes is more than that of Froude number.
8. In lower Froude numbers due to low velocity of the flow
in upstream of spur-dike, the local effects of the flow on
the scour width is little. By increasing the Froude number,
the flow velocity increases and it leads to the scour hole
width increase.
FUNDING/SUPPORT
Not mentioned any Funding/Support by authors.
ACKNOWLEDGMENT
Not mentioned any acknowledgment by authors.
AUTHORS CONTRIBUTION
This work was carried out in collaboration among all authors.
CONFLICT OF INTEREST
The author (s) declared no potential conflicts of interests with respect
to the authorship and/or publication of this paper.
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