京都大学防災研究所年報 第 56 号 B 平成 25 年 6 月
Annuals of Disas. Prev. Res. Inst., Kyoto Univ., No. 56 B, 2013

Laboratory Study of Bed Variation due to the Installation of Spur Dykes withDifferent Head Shapes
Amir Reza MANSOORI (1), Hajime NAKAGAWA, Kenji KAWAIKE, and Hao ZHANG(1) Graduate School of Engineering, Kyoto University
SynopsisBased on the shapes of the spur dykes in the plan, different kinds of spur dykes can berecognized: “Straight shape or I-type”, “T-type”, “L-type” and etc. So far a goodnumber of works have been devoted to the study of the “straight” shape spur dykes,
mainly aimed at investigating the flow structures around them. On the other hand, there
are some limited researches and knowledge about the study of sediment transport
around spur dykes with different shapes of head, especially when they are arranged in aseries. In this study, the bed variation around two types of spur dykes with different
shapes of head was investigated using experimental works. The equilibrium of bed
variation in both spur dykes was shown and the differences and similarities of thepattern of scour hole were investigated.
Keywords: Spur Dyke, Groyne, Sediment Transport, Bed Variation, T-type, I-type1.

Introduction

Spur dyke is one of the main transverse
hydraulic structures installed in the streams toprevent the bank erosion and improve navigationroutes in rivers. Recently it is also used to provide
better environment for the stream species which are
in need of a diverse bed with various range ofhydrodynamic, topographic and biologic conditions
in rivers.
Based on the shapes of the spur dykes in theplan, different kinds of spur dykes can berecognized: “Straight shape or I-type”, “T-type”,“L-type” and etc. Spur dykes are rarely installed
individually in the streams, but usually in series.
So far the considerable works have been
dedicated to the study of the “single straight” shapespur dykes, mainly aimed at investigating the flow
structures around them. On the other hand, there aresome limited researches and knowledge about thestudy of sediment transport around spur dykes withdifferent shapes of head, especially when they arearranged in a series. In 1964, Linder et al conducteda set of experiments to find the optimum
combination of a series of L-shape spur dykes in aleft bank of a reach of Missouri River in the U.S. In
2009, Vaghefi and Ghodsian studied flow field
scouring around a single T-shape spur dyke in a 90
degree bend. In 2010, Kadota et. al. conducted aseries of experiments in which they studiedhydrodynamic of flow around an individual T andL- shape spur dykes.
To sum up, so far the researches about spurdykes have mainly focused on the study of straightspur dykes and even in the few researches aboutother shapes of spur dykes, the most cases wereindividual spur dyke (not series). In other word,
there is still an extensive debate on how to optimize
the spur dyke shape and their spacing in a series ofspur dykes in order to increase their functionality― 497 ―

specifically when it is needed to design
nature-friendly spur dykes and to improve thebio-diversity of living environment of riverine biota
and fauna by applying this kind of hydraulicstructures inside the streams.
In this study, the formation of scour hole around
two types of spur dykes with different shapes ofhead was investigated using experimental works.
Two case studies were considered: a simple seriesof straight spur dykes and a simple series of spurdykes with T-head shape. The equilibrium of bed
variation in both spur dykes was shown and thedifferences and similarities of the pattern of scour
hole were investigated. Finally, an in-depth
discussion about the formation of the scour holeand the deposition area around these types of spurdykes was studied in order to evaluate theperformance of the special geometrical features ofT-head shape spur dykes (its wing) to the formationand extension of scour hole toward the downstream.
The importance of this study can be highlighted
regarding the fact that controlling bank erosion,
better navigation and/or improving biodiversity arebeing directly affected by the shapes of thesestructures and accordingly on the basis of theprimary objectives of the application of spur dykes,
using a series of T-type would be an advantage
compared to common designs.

Table 1 shows hydraulic conditions used foreach different case in the experiments

2.

Table 1 hydraulic conditions used for each different
case in the experiments

Laboratory experiments

3.

Experimental procedure

Each experimental case was carried out for 4
hours, which is the time necessary to reach thedynamic equilibrium condition based on previous
test experiments. Measurement of discharge wasdone by a V-notch weir and a point gauge. The
water surface level for each hydraulic condition wasregulated by a steel gate positioned at thedownstream end of experimental flume. The
deformed bed levels in the movable bed area were
measured using a laser displacement sensor (Model:LK-2500) after the flume was completely drainedout.
4.

Results and discussions

Figure 2 shows the bed deformation of theseries of spur dykes with T-head shapes and I-head
shape with different opening length (1L, 2L, 3L,and 5L, in which L is the length of the groyne). In
T-head spur dykes, the opening ration is from thedownstream tip of one spur dyke to the mostupstream tip of the next sour dyke in the series.
Comparing the different open ratio between theseThe experiments were done in a straight flumewith of Ujigawa Open Laboratory, Disaster
Prevention Research Institute, Kyoto University,
Japan with 12.0m-long, 0.8m-wide and 0.28m-deep.
Figure 1 shows a schematic view of the flume. Thebottom and the sidewall of the flume were made ofmetal sheets with smooth roughness. The length (L)of spur dykes was 0.01m and they were installed ina recession area of channel with sand, located 5
meter from upstream of the channel.
A calibrated V-notch weir, fitted at the inlet ofthe flume, was used to measure the inflow
discharge. The equipments for the measurements
are fixed on the carriage which can move throughthe flume in the longitudinal direction. The spurdykes used during the experiments were made by
Plexiglas plates with 1cm thickness.

― 498 ―

Flow Condition
Discharge (Q) (m3/s)
Channel Slope

0.02001/800

Channel width (B) (cm)80.00

Flow depth (hw) (m)Flow Velocity (m/s)

0.067
0.37

Shear Velocity (u* ) (m/s)

0.028

Sediment No

3.00

Sediment (d50) (mm)1.78sg1.18

Sediment Density (g/cm3)
B/hw

2.65
11.94

Re25000

Fr0.20u*/u*c0.86

8.0 mFixed bed

Movable area

Fixed bed

0.8 m

FlowYX

5.0 m

50 cm
10 cm

10 cm

Figure 1. Schematic view of the experimental set up
two head shapes, firstly shows the considerable
effect of the head shape on the bed changes.
In all Opening Ratio (OR), the overall pattern ofthe bed is different. In OR=1 and 2, in the series ofT-head shape spur dykes , the presence of the wingof the spur dykes, made a sort of uniform patternalongside of the embayments. While in I-type thechanges has been formed right away from the banksof the channel. In OL=1, in the first embayment of
the groyne a very limited point bar has been formed.
By arising the OL to 2, this point bar has started to
moved to upstream and near the center of theembayment. By increasing the OL to 3 and form,
but the location of this point bar has been fixed andinstead, the volume and dimensions of it has been
started to expanding. This trend in I-type, but has asignificant different. Comparing different OL in
I-shape head shows a lag in similar behavior
compared to the series of T-shape spur dykes. Inother words, While in T-shape spur dykes, theformation of point bar in the first embayment wasstarted from OL=1 and then moved to the upstream
at OL=2 and expanding from OL=3, in I-shape spurdyke this trend has been observed from OL=2
(instead of OL=1). The first implication of thisdifference, highlight the less effect of the opening
spaces in the interface of embayment and main
channel on the formation of channel bed inside theembayment. Simply speaking, regardless ofopening spaces in the interface of embayment andmain channel, the distance between the boy of spurdyke has particular and clear affect on the pattern ofbed changes in the series. Comparing the second
embayment in these two different series, but shows

the crucial rule of the head shape on the pattern ofthe bed inside and in front of embayments. In
T-head spur dykes, before OL=3, there is no
significant changes inside the embayment and it isjust after OL=3 in which a visible point bar wasformed between second and third spur dyke. Whilein I-type, the formation of point bar was started
from OL=1. The third embayment in the series ofspur dyke can be considered as a region in which
there was enough length after the first spur dyke inseries to form a uniform flow in front of theembayments. In this particular embayment, inT-head spur dykes, till OL=3 the presence of thewing caused the uniform area alongside theembayment. It was just after OL=3 (OL=5), in
which by increasing the OL, the flow had enoughspaced to intrude to the embayment and the wingsof the spur dykes were not able to prevent theformation of the point bar. In I-shape spur dykes,
this trend is somehow similar but with a lag in OL.
The first result of this comparison highlights theparticular rule of the wing in the control ofsediment transport in the first and second
embayments. These two embayments are those one
in which the uniformity of flow has not still been
formed. On the contrary, in the third embayment inwhich there was enough length for the uniformity of
the flow after the installation of the first spur dykes
in the upstream, this rule was sort of faded.
In OL=5, but since the spaces between spurdykes was too high, so that the effect of the head
shape has been rather local, the general pattern ofthe bed changes inside the embayments andalongside the interface between the embayments― 499 ―

Opening
60

60

Length40

40

20

20

1L050
-11.0 -10.0 -9.0 -8.0 -7.0

2L-6.0-5.0-4.0 -3.0 -2.0 -1.5

150
-0.0

0.0

0.5

0

200
1.0

1.5

2.0

3.0

50

[cm]

4.0

60

40

40

20

20050
-11.0 -10.0 -9.0 -8.0

100
-7.0

-6.0

-5.0 -4.0 -3.0 -0.0

150
0.0

0.5

1.0

2.0

3.0

[cm] -11.0 -10.0 -9.0

4.0

60

60

40

40

20

20

0050
-11.0 -10.0 -9.0 -8.0 -7.0

100
-6.0

-5.0

-4.0 -3.0 -2.0 -1.5

150
-0.0

0.0

0.5

1.0

1.5

2.0

3.0

[cm]

4.0

-5.0 -4.0 -3.0 -2.0

-5.0

-4.0 -3.0 -2.0 -1.5

60

40

40

20

20

0.0

0.5

-1.0

-0.0

0.0

-6.0

-5.0

200

1.0

1.5

2.0

3.0

4.0

1.0

1.5

2.0

3.0

150

200

0.5

100

-11.0 -10.0 -9.0 -8.0 -7.0

60

-0.0

100

-8.0 -7.0 -6.0

50

200

150

-6.050200
1.5

100-11.0 -10.0 -9.0 -8.0 -7.0

60

0

3L

100

4.0

150

-4.0 -3.0 -2.0 -1.5

-0.0

0.0

0.5

200
1.0

1.5

2.0

3.0

4.0

5L0

50
-11.0 -10.0 -9.0 -8.0 -7.0

100
-6.0

-5.0

-4.0 -3.0 -2.0 -1.5

150
-0.0

0.0

0.5

0

200
1.0

1.5

2.0

3.0

4.0

[cm]

-11.0 -10.0 -9.0

50
-8.0

100
-7.0

-6.0

-5.0

-4.0

-3.0

-2.0

150
-1.5

-1.0

-0.0

0.0

0.5

200
1.0

1.5

2.0

3.0

4.0



Figure 2 Bed changes in the series of spur dyke with different shapes and different opening length (OL)
Right: I-shape head spur dykes
Left: T-shape head spur dykes
and main channel is rather similar in T-type andI-type.
5.

Conclusions

In this paper, it was tried to compare the effect ofhead shapes of spur dykes on the general pattern of
bed changes inside the embayments and alongside
the interface between the embayments and main
channel. It was shown that till the OL=5, thepresence of the wing in T-shape spur dyke hassignificant effect, specifically in the first andsecond embayments. In third embayment in theseries, the rule of the wing was rather less and was

to form a uniform pattern alongside the interfacesof the embayment and main channel. In OL greaterthan 3, since the flow has enough space to intrude
to the embayment completely, the rule of head
shape on the general pattern of bed variation inside
the embayment was rather local and limited.
References
Linder, W. (1964): Laboratory Investigation of
L-Head Channel Control Structures, TechnicalReport.
Kadota, A., Suzuki, K., & Kojima, E (2010).: Flow
Visualization of mean and coherent flow
structures around T-type and L-type groynes,
River Flow 2010.

― 500 ―

Kandasamy J K, Melville B W (1998): Maximum
local scour depth at bridge piers and abutments,
Jornal of Hydraulic Research, Vol. 36: 183–197.
Vaghefi, M., & Ghodsian, M. (2009): Experimental
study on the effect of a T-shaped sour dike
length on scour in a 90 channel bend, The― 501 ―

Arabian Journal for Science and Engineering,34(2), 337-348.
(Received June 11, 2013)