International Journal of Civil Engineering and Technology (IJCIET)
Volume 10, Issue 04, April 2019, pp. 260–267, Article ID: IJCIET_10_04_027
Available online at http://www.iaeme.com/ijmet/issues.asp?JType=IJCIET&VType=10&IType=4
ISSN Print: 0976-6308 and ISSN Online: 0976-6316
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ENERGY DISSIPATION AND DISCHARGE
COEFFICIENT OVER STEPPED GABION AND
BUTTRESS GABION SPILLWAY
Gamal M. Abdel Aal, Maha R. Fahmy, Eman Aly Elnikhely and Eslam El-Tohamy
Staff members, Water and Water Structures Engineering Department,
Faculty of Engineering, Zagazig University, Egypt.
ABSTRACT
Gabions are economic structure widely used in small head works to avoid the
effect of large potential energy. The aim of this paper is to study the Energy
Dissipation and Discharge Coefficient over Stepped Gabion spillway and a suggested
new gabion style. This new style was suggested to enlarge the max head of gabions
depending on buttress wall technology. This structure was named as Buttress Gabion
spillway. The dimensional analysis was used to correlate the different parameters
affecting the studied phenomena. It was found that using of large particle increases
energy dissipation and coefficient of discharge. Also as the number of buttress walls
increases the energy dissipation coefficient of discharge decreases.
Key words: Energy dissipation, Experimental, Theoretical, Gabion, Buttress,
Discharge Coefficient walls, spillway
Cite this Article: Gamal M. Abdel Aal, Maha R. Fahmy, Eman Aly Elnikhely and
Eslam El-Tohamy, Energy Dissipation and Discharge Coefficient over Stepped
Gabion and Buttress Gabion Spillway, International Journal of Civil Engineering and
Technology 10(4), 2019, pp. 260–267.
http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=10&IType=4
1. INTRODUCTION
"Rocks in its natural form is the most abundant and economical material in hydraulic
engineering practice. Rocks have been used in dam construction, river engineering works,
river intakes etc. Gabions are hexagonal mesh boxes filled with small sizes of
stone(photo.1,2). The Gabions retains the advantages of rock fill in its flexibility and
permeability so that water pressure is minimized. The wire mesh container can act intension.
Nowadays, the gabion is used for hydraulic engineering works such as revetments, channel
linings, weirs, groins and energy dissipation structures"(Stephenson, 1979). One application
of gabion is for constructing the stepped spillways. In this structure, the kinetic energy of flow
is dissipated, as water flows downstream. Flow through the rock mixes with the flow over the
crest, resulting in energy dissipation by Jet impingement as well as due to friction loss
through the rock fill. In addition, the energy is dissipated as flow cascade from one step to
another.Many researchers interested in this type of structure as, (Stephenson, 1979),(Agostini,
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Energy Dissipation and Discharge Coefficient over Stepped Gabion and Buttress Gabion Spillway
Bizzarri, Masetti, & Papetti, 1987), (Peyras, Royet, & Degoutte, 1992),(KELLS, 1994),
(Shafai-Bejestan & Kazemi-Nasaban, 2011),(Salmasi, Chamani, & Zadeh, 2012), (Vicari,
2014),(G Zhang & Chanson, 2014),(Gangfu Zhang & Chanson, 2016),(Vashisth, 2017)
Figure 1 "some gabions models"[Ref.1]
Figure 2 "Gabion stepped spillway used to reduce water velocity and to collect sediments in mountain
valley (left), and gabion structure in a retaining wall for slope stability (right) on Onebne-Ali
mountain, north of Tabriz (IRAN) "[Ref.1]
In this study the effect of changing the particle size was compared. Also the effect of
slices in the flow direction was studied to show the effect of structure supports that would be
used in high head gabions.
This idea is amerge between gabion spillway and buttress wall structure system."A
buttress dam or hollow dam is a dam with a solid, water-tight upstream side that is supported
at intervals on the downstream side by a series of buttresses or supports. The dam wall may be
straight or curved. Most buttress dams are made of reinforced concrete and are heavy. Water
pushes against the dam, but the buttresses are inflexible and prevent the dam from falling
over. Buttress dams of slab concrete construction became popular in the United States in the
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Gamal M. Abdel Aal, Maha R. Fahmy, Eman Aly Elnikhely and Eslam El-Tohamy
early 20th Century with the patented process of Norwegian-American". As an example Yate
Dam Spillway in New Caledonia, France photo.3&4
Figure 3 https://en.wikipedia.org/wiki/Buttress_dam date: 31/1/2019
Figure 4 Yate Dam Spillway New Caledonia, Francehttps://www.canva.com/photos/tag/spillway/ date:
31/1/2019 the limitation of gabion head can be solved by enhancing its upstream wall by buttress. This method
may be structurally useful but with effects on energy dissipation. So this study will cover this side and show the
effects.
2. EXPERIMENTAL SETUP
Experimental work was carried out in the Hydraulic and water Engineering Laboratory of the
Faculty of Engineering, Zagazig University, Egypt. The used flume is 30 cm width, 46.8 cm
depth with an overall length of about 15.6 m. The flume is equipped with a tailgate to control
the tail water depth. A pump lifts the water from a tank to the flume inlet. The water runs
through the flume working section then returns back to the tank in a closed circle. The
discharge was measured by a pre-calibrated orifice meter installed in the feeding pipe line.
The used stepped spillway model is made from metal covered with metal narrow mesh
with 28 cm height and 7 steppes 7cm horizontal and 4 cm vertical each as shown in photo 5.
Different particle size (D=2.36mm, 5mm, 10mm, 14mm, 20mm and 28mm) were tested under
the same flow conditions.
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Energy Dissipation and Discharge Coefficient over Stepped Gabion and Buttress Gabion Spillway
Figure 5 Gabion experimental model
As shown in (photo.6) wooden strips used to simulate the buttress walls that may be used
to increase the gabion height. The cases studied were three cases with 2, 3 and 4 slices using
the same particle diameter 20 mm.
Figure 6 Slices experimental model
3. DIMENSIONAL ANALYSIS
Using the principals of the dimensional analysis, the different variables affecting the energy
dissipation through the spillway could be formulated in the following dimensionless equation:
ΔE
B
D
 f (Fup, B ,
)
E up
Bs h s
CD  f (
BB D Yc
,
, )
Bs h s hs
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Gamal M. Abdel Aal, Maha R. Fahmy, Eman Aly Elnikhely and Eslam El-Tohamy
Where
D is the particle size,hs is the spillway upstream depth, Yc is the critical water depth, Bs is the
spillway width , BB is the total slices width ,CD is the coefficient of discharge and Fup is the up
stream Froude number
5. ANALYSIS OF EXPERIMENTAL RESULTS
The different flow characteristics were analyzed as a function of the inflow Froude number
.Such as the energy loss, jump length, tail water depth.
5.1. Effect of different particle size on relative energy loss
Fig.(7) represents the relationship between relative energy loss ∆E/Eup versus upstream
Froude number Fup for different relative particle diameter D/h. For the same particle size, the
relative energy loss decreases as Froude number increases. The results obtained from
experimental test reveals that the relative energy loss increased with increasing the relative
particle diameter. The relative energy loss increased with increasing the relative particle
diameter. This is may be due to that the large particle size helps in draining water. So, for
design purpose, the use of gabion spillway with larger relative particle diameter can be
considered to reach the maximum energy dissipation rate.
solid
D\hstep=0.13
D\hstep=0.35
D\hstep=0.70
Linear (D\hstep=0.06)
Linear (D\hstep=0.25)
0.900
ΔΕ\ΕUP
0.800
D\hstep=0.06
D\hstep=0.25
D\hstep=0.50
Linear (solid)
Linear (D\hstep=0.13)
Linear (D\hstep=0.35)
0.700
0.600
0.500
0.030
Figure 7 Relations between
0.060
FUP
0.090
and
FUP
E Eup for different particle sizes.
5.3. Effect of different particle size on coefficient of discharge
The coefficient of discharge indicates the ability of structure to pass the flow under a certain
head. For the same head, the larger discharge means the larger C d. the water head on the crest
“h” was measured to study this factor. Fig. 8 shows the relationship between relative head
“h/Yup” and Cd. in this relation as the relative head increases the coefficient of discharge
increases for the same particle diameter. On the other hand the increase in the diameter
increases the coefficient of discharge for the same relative head.
To clarify the reason of this phenomena Darcy low had some answers. It is a simple
relation between the unit discharge “q” and the hydraulic slop “∆h/L” with the hydraulic
conductivity “K” as the equation constant factor as follows:
q=K*∆h/L
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Energy Dissipation and Discharge Coefficient over Stepped Gabion and Buttress Gabion Spillway
For constant K and L, as ∆h increases the discharge though the porous media increases so
for the same diameter as the relative head increases the pressure head increases, the part of
flow through the structure increases so the total discharge and coefficient of discharge
increases.
0.850
0.800
Cd
0.750
0.700
0.650
0.600
0.550
0.500
0.120
D=2.35mm
0.170
0.270 h/Yup 0.320
0.220
D=5mm
D=10mm
Figure 8 Relations between h / YUP and CD
D=20mm
D=28mm
.
for different particle sizes.
5.1. Gabion data comparison
To verify the experimental results it was compared with the results studied by Ayush(2017).
Four stepped spillway models were made from wood with a slope of 1:1. The height and
length of the model were taken 20 cm and the width was taken 24.5cm. Each step had an
equal height and length of 5cm. A sample of aggregate which passed through 12.75mm sieve
and retained on 4.75 mm sieve was used to model the gabion core, these aggregate were filled
in the model which is hollow at the center. Those results were compared with the results
obtained in our study as shown in fig.12.
By comparison it was clear that the results of relative energy loss were close to each
other. The different in the models dimension affect the results of upstream energy (Eup& EO)
and clearly shown in fig.9.
35.000
33.000
E up
31.000
29.000
27.000
25.000
5.000
D=2.35
6.000
D=5mm
7.000 Q L\S 8.000
D= 10mm
D=14 mm
9.000
D=20 mm
10.000
Ayush(2017)
Figure 9 Relations between Q and Eup for different particle sizes and Ayush (2017).
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Gamal M. Abdel Aal, Maha R. Fahmy, Eman Aly Elnikhely and Eslam El-Tohamy
Fig.9 shows that the results of relative energy loss ofAyush (2017) are very near to our
results, which is because of the dimensionless ratio E Eup that canceled the dimension
difference action between this study and Ayush (2017).
5.3. Effect of the longitudinal slices
By studying its effect fig.10 it was found that the energy dissipation decreases as the number
of slices increase, where the relative widths are as shown in table.
No. of slices "n"
relative width "BB/Bs"
zero
zero
2
0.10
3
0.15
4
0.20
This effect is because the structure changed from full porous to partially solid and as
showed previously the solid structure dissipate less energy than the gabions.
D/hst=0.50&B/Bs=0.00
D/hst=0.50&B/Bs=0.15
Linear (D/hst=0.50&B/Bs=0.00)
Linear (D/hst=0.50&B/Bs=0.15)
D/hst=0.50&B/Bs=0.10
D/hst=0.50&B/Bs=0.20
Linear (D/hst=0.50&B/Bs=0.10)
Linear (D/hst=0.50&B/Bs=0.20)
0.75
0.70
ΔΕ\Εup
0.65
0.60
0.55
0.50
0.04
0.06
Figure 10 Relations between
0.08
Fup
0.10
FUP and E Eup for different width ratios.
D/hst=0.50&B/Bs=0.00
D/hst=0.50&B/Bs=0.15
Linear (D/hst=0.50&B/Bs=0.00)
D/hst=0.50&B/Bs=0.10
D/hst=0.50&B/Bs=0.20
Linear (D/hst=0.50&B/Bs=0.10)
0.85
0.80
CD
0.75
0.70
0.65
0.60
0.55
0.50
0.17
0.21
0.23 h/Yup 0.25
0.27
Figure 11 Relations between h / YUP and CD
for different width ratios.
0.19
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Energy Dissipation and Discharge Coefficient over Stepped Gabion and Buttress Gabion Spillway
Fig.11 shows the relation between relative head “h/Yup” and Cd. in this relation as the
relative head increases the coefficient of discharge increases for the same case. On the other
hand the increase in the slices number increases the coefficient of discharge for the same
relative head.
6. CONCLUSIONS
From the results of the present study, the following conclusions can be introduced.
1- The large particle size increased energy dissipation for the same Froude number.
2- The large particle size increased the coefficient of discharge for the same relative head.
3-The increase in the relative width BB/Bs decreases the coefficient of discharge for the same
relative head.
4-The increase in the relative width BB/Bs decreases the energy dissipation for the same
Froude number.
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