自然災害科学 J. JSNDS 37 特別号 93 -105（2018 ）Experimental Study on the
Performance of Slope-crested
Groynes in Erodible Meandering
Channels of Diﬀerent Sinuosity
Saroj KARKI1, Hajime NAKAGAWA2, Kenji KAWAIKE3 and Masakazu HASHIMOTO4

Experimental Study on the Performance of Slope-crested
Groynes in Erodible Meandering Channels
of Different Sinuosity
Saroj KARKI1, Hajime NAKAGAWA2,
3
Kenji KAWAIKE and Masakazu HASHIMOTO4
Abstract
Riverbank erosion is a vital issue in the management and restoration of rivers, especiallyin alluvial meandering channels because of their unique channel morpho-dynamics. Various
countermeasures are thus implemented to minimize riverbank erosion and maintain stablechannel sections of meandering channels. This study analyzes the performance of modified
impermeable groynes with sloped crests as a countermeasure for bank erosion. Experiments
were conducted in erodible meandering channels of two different sinuosities to evaluate theperformance of the proposed countermeasures under varying sinuosity as well as analyze theoverall morphological evolution of the channel. The results show that the low sinuosity (LS)channel was more prone to erosion compared to the higher sinuosity (HS) channel. Channel
sinuosity also affected the overall channel morphological evolution with the LS channel
showing more distinct characteristics of a meandering channel forming point bar and pooland rifﬂe sequences. The proposed countermeasure showed slightly better performance in thecase of the LS channel. Although the presence of the proposed groynes did not signiﬁcantly
deﬂect the high-velocity core towards the channel center, the velocity near the bank region was
signiﬁcantly reduced.
Key words：Meandering channel, Sinuosity, Bank erosion, Groyne.
123Doctoral Student, Dept. of Civil and Ear th Resources
Engineering, Kyoto University, Japan
Prof., Disaster Prevention Research Institute (DPRI),
Kyoto University, Japan

4

93

Assoc. Prof., DPRI, Kyoto University, Japan
Asst. Prof., IRIDeS, Tohoku University, Japan

94

Experimental Study on the Performance of Slope-crested Groynes in Erodible Meandering Channels of Different Sinuosity

1. INTRODUCTION

yan et al., 2010; Teraguchi et al., 2011; Cunningham

It is important to protect river banks from ero-and Lyn, 2016), groynes are still one of the mostsion, particularly in meandering channels, in orderwidely implemented countermeasures for bankto maintain the stable dimensions, patterns andprotection especially in natural bends or meander-

profile of a river (Bhuiyan et al., 2010). Based on

ing channels (Teraguchi, 2011). Groynes help toprevious studies as well as observation in naturalprotect the riverbank from erosion by deflecting

channels, erosion occurs at the outer bank forming

high-velocity flow away from the banks to thedeep pools and deposition occurs at the inner bankchannel center (Uijttewaal, 2005; Dehghani et al.,forming a point bar (Struiksma et al., 1985; Hickin2013). However, rectangular impermeable groynes

and Nanson, 1984). Erosion-deposition induced

can cause increased flow velocity and result in in-channel migration in meandering rivers causes thecreased erosion on the opposite bank, high turbu-

loss of hundreds of hectares of mainland floodplain

lence and vorticity behind the structures and highand agriculture, affecting the livelihood of millions

scour near the tip of structures (Zhang and Nak-of people around the world. Such phenomena haveagawa, 2009; Karki et al., 2018; Zhang et al., 2009;

inspired the search for different bank protection

Dehghani et al., 2013). Figure 1 shows time series

countermeasures to improve outer bank stability

images of the impact of rectangular impermeable

and minimize erosion (Cunningham and L yn,

groynes on the erosion-deposition process in the2016). Although bank protection countermeasuresbend of an alluvial river. Due to the deposition

such as submerged vanes, bendway weirs, stream

induced by the groyne field, a significant portion

barbs, bank-attached vanes, bandal like structures,of land has been reclaimed on the adjacent bank.

etc. have been tested (Jamieson et al., 2013; Bhui-

However, nearly the same amount of land has beenFig. 1 Time series images of the channel planform evolution after implementation of a groyne. (Google
Earth, 2018)

95

自然災害科学 J. JSNDS 37 特別号（2018 ）lost to erosion on the opposite bank. In order toto the effect of sinuosity in sine-generated (SG)minimize such adverse impacts, the shape andmeandering channels have been conducted toorientation of the structures have been modified

understand the flow dynamics and channel mor-by changing the shape of the tip of the groynes

phological evolution (Da Silva et al., 2006; Xu and(L-head, T-head, round head, etc.), varying the an-

Bai, 2012). However, studies considering the effectgle of inclination, adjusting the permeability of theof channel sinuosity on the performance of bankstructure, and changing the slope of the crest ofprotection countermeasures have not been tested.

groynes.

The current study investigated the performance

Various experimental studies have examinedthe effect of groynes on the flow field, local scour,of slope crested impermeable groynes in erodible
meandering channels of two different sinuosities.

sediment transport, channel evolution, etc. However, most of those studies on countermeasures
such as groynes have been performed in straight

2. EXPERIMENTAL SET-UP
2. 1

Meandering Channel Preparation

channels (Zhang and Nakagawa, 2009; Yossef and

The experimental works discussed in the cur-Vriend, 2010; Uijttewaal, 2005). Even in cases ofrent study were conducted in Ujigawa Open Lab-

meandering channels, most of the previous stud-

orator y under the Disaster Prevention Researchies considered either a fixed bed and fixed bankInstitute (DPRI), Kyoto University. The schematic(FBFB) or an erodible bed and fixed bank (EBFB)

layout of the experimental flume as illustrated inchannels (Giri et. al., 2003; Giri and Shimizu,

Fig. 2 consists of a fixed bed inlet and outlet chan-2004). Moreover, such experiments focused onlynel 50 cm and 100 cm in length, respectively. The

on a single channel bend or meandering channel

main channel includes a 400 cm long and 200 cm

with single sinuosity. Since meandering channels

wide erodible bed filled with non-uniform (Dmean＝have various characteristics (sinuosity, amplitude,

0.72 mm, σ＝(d84/d16)0.5＝1.38 and specific gravity

deflection angle, ratio of radius of curvature to the＝1.41) and non-cohesive sediment up to a thick-channel width (R/B), etc.), the effectiveness ofness of 20 cm from the bottom. The sine-generated

countermeasures cannot be fully evaluated undercurve (SGC) defined by Eq. (1) was used to delin-a single sinuosity channel as it can be affected byeate the meandering channels within the erodible

dominant channel characteristics. Studies related

boundary. The main parameters determining the

Fig. 2 Schematic layout of the two experimental channels used in the study (units in centimeters)

96

Experimental Study on the Performance of Slope-crested Groynes in Erodible Meandering Channels of Different Sinuosity

SGC are channel-wise wavelength (M) and maxi-

were generalized and a total of four experiments

mum deflection angle (ω) (Langbein and Leopold,

were selected for this study, i.e. two experiments

1966).

for each type of meandering channel. For each(1)where s is the channel-wise length and φ ismeandering channel, one experiment without any
countermeasures and another experiment withcountermeasures were performed. The four casesin this study were a high sinuosity channel without

the local deflection angle.
By integrating Eq. (1) in the X- and Y-direc-

groynes (HS-NG) and with groynes (HS-G), andtion, valley-wise wavelength (λ) and amplitude

a low sinuosity channel without groynes (LS-NG)(A) were obtained. In this experiment, two SG

and with groynes (LS-G). The experimental flow

channels were prepared whose different parameterconditions are presented in Table 2.

values are listed in Table 1.

The experimental flow was partially governed

To prepare an erodible meandering channel,

by the size of the channel as well as non-cohesive

first, the channel bed was compacted and levelled,

sediments used for making the erodible channel.

then bank materials around were filled and com-

Preparing a larger channel would have been ex-pacted around a prefabricated wooden channel.

tremely difficult. Also, due to the non-cohesive sed-Two separate prefabricated wooden channels

iments, the selection of a higher discharge would

following a SGC were constructed to prepare ex-have resulted in high and rapid erosion forcing

perimental meandering channels of two different

us to shorten the experimental time. A discharge

sinuosities. The same type of sediment was used

was chosen that transpor ts sediment but doesin the bed as well as in the bank. After the bank

not overtop the banks of the designed channel.

materials were compacted and levelled, the prefab-

Experiments were conducted under clear water

ricated channel was carefully removed to obtain

conditions for a duration of 40 minutes (mins). In

the designed rectangular experimental channel

the cases of experiments with countermeasures,

having an initial width of 20 cm and depth of 5 cm.

for the first 20 mins, the channel was allowed to

The same procedure was repeated to prepare both

adjust to the flow conditions. The flow was thentypes of channels.

stopped, the countermeasures were installed along
the pre-determined locations along the outer bank

2. 2

Experimental Methods

and then the flow was resumed for the next 20

A series of experiments were conducted undermins. In both cases, a constant discharge of 0.95 l/

two different channels to ensure that the results

s was supplied by a pump to the upstream storagetank through which water gradually entered theTable 1 Parameters of Experimental Channels
Parameter (cm)

Table 2

Experimental Flow Conditions

Channel-LS

Channel-HS

Width (B)20

20

Flow Variable

Value

Radius of Curvature (R)2545Discharge (l/s)

0.95

R/B Ratio

1.25

2.25

Mean Flow Depth (cm)2.86

Amplitude (A)3080Mean Velocity (cm/s)

Meander Length (L)

120

270

Channel Slope

Valley Wavelength (λ)

100

200

Shear Velocity (cm/s)

Sinuosity (K＝L/λ)

1.2

1.35

Froude Number

0.31

Angle of Deflection (ω)

450

600

Reynolds Number

5322

16.6
1 :5501.99

97

自然災害科学 J. JSNDS 37 特別号（2018 ）channel inlet. The target area for the study in theof flow. The dimensions and a schematic layout ofcase of both channels is shown in Fig. 2.

the groynes are shown in Fig. 3.

Various parameters of the flow and channel,

The position of the groynes along the outernamely: surface velocity distribution, water-levelbank is shown in Fig. 4 for both channels. Groynes

at particular locations and bed topography wereare placed starting from upstream of the apex tomeasured every 20 mins during the experiments.

the crossover or the point of inflection along the

For the determination of the surface flow field,

outer bank. Accordingly, due to the difference inpolyvinyl chloride (PVC) particles having a meanchannel length, the number of groynes in each type

diameter of 50 μm were used as trace particles

of channel varied from one to another. The groynes

while the analysis was performed using MATLAB

from upstream up to the apex were inclined at 1200

software. Channel topography was measured using

to the upstream bank in order to ensure a smootha laser displacement sensor.

flow approach towards the downstream groynes
whereas the groynes downstream of the apex were

2. 3

Arrangement of Groynes

placed at right angles to the bankline. During theGroynes modified for the present studies
consisted of a triangular portion inclined from thebank top towards the channel and a rectangularportion inserted inside the banks to prevent theflow outflanking around the structures. Comparedto the rectangular groynes, the sloping crest fromthe bank towards the channel caused minimum
flow constriction, less turbulence and safe passage

Fig. 3 Schematic layout and geometr y of thegroynesFig. 4 Position of the groynes and the change in the channel bed elevation between time, t＝20 mins and t＝0mins for cases HS-G and LS-G.

98

Experimental Study on the Performance of Slope-crested Groynes in Erodible Meandering Channels of Different Sinuosity

initial channel adjustment period, the pattern, location and the extent of the bank erosion varied from

3. RESULTS AND DISCUSSION
3. 1

Morphological Evolution of the Channel

one channel to another as shown by the change

The morphology of a meandering channel

in channel elevation (dZ＝Z 20 mins-Z0 mins) between

continuously evolves due to the interaction of flow,t＝20 mins and t＝0 mins in Fig. 4. Due to thissediment transport and channel planform. Figure

non-uniformity in the bank erosion process, the5 (a-d) shows the difference (dZ＝Z40 mins-Z0 mins) in

positioning of the groynes was also affected. The

channel elevation between the end (t＝40 mins)bank erosion process after the implementation ofand the start (t＝0 mins) of the experiment for all

groynes is discussed in the next section.

cases (the flow is from the left to the right). The
black dashed line in the figure represents the original bankline (t＝0 mins) while the red dashed line
indicates the bankline at the end of the 20-minuteFig. 5 (a-d): Change in the channel bed elevation between the final (t＝40 mins) and the initial (t＝0 mins)
time for all experiment cases.

99

自然災害科学 J. JSNDS 37 特別号（2018 ）experiment, just at the time of implementation of

However, the LS channel had a shorter channel

the groynes. Positive values in the figure signify

flow path and low R/B ratio, which caused rapid

deposition while negative values indicate erosion.

flow transition and resulted in higher erosion in

In both channels, at the beginning of the experi-

the LS-NG case. In the HS-NG case, maximum ero-ment, the erosion at the bank toe caused the banksion occurred near the point of inflection or cross-materials to fail as a block mass, which was trans-over region whereas in the case of LS-NG, channel

ported by the flow. In the later stages, the bankerosion occurred near the apex of the inner bend

slope adjusted to the flow conditions and thus mass

and gradually shifted in the upstream direction.

failure did not occur. However, due to excess near-

The extent of erosion or channel expansion had anbank shear stress, fluvial erosion continued at spe-

effect on the direction of the flow approach, which

cific locations along the channel banks resulting inin turn dictated the performance of the groynes.

the widening of the channel. The erosion rate was

The erosion and channel evolution pattern in thehigher in the case of LS-NG compared to that ofcase of LS-NG were more uniform and predictable

HS-NG. In the cases of the high sinuosity channel

as compared to the HS-NG case. The bed forms(HS-NG and HS-G), the characteristic features ofincluding the point bar tended to migrate down-a meandering channel such as a pool and riffle

stream in both channels.

sequence did not distinctly develop as compared toWith the installation of groynes, the erosion

the cases of the low sinuosity channel (LS-NG andnear the outer bank apex was controlled in bothLS-G). This difference could be attributed to thethe HS and LS channels. The erosion at the down-

unequal erosion in the HS and LS channel. Since

stream of the apex was also greatly reduced in theno sediment was supplied externally, all the trans-

case of LS-G but slightly higher erosion occurred

port of sediment must occur from the bed and thein HS-G. Within the field of the groynes, erosion

bank materials. Accordingly, the higher erosion in

was minimized, however, it continued on the down-

the LS-channel resulted in more transport of sed-stream end after exiting the groynes field. The

iment to develop deep pools and the subsequent

size of the deep pools as well as the scours at the

point bar on the opposite bank. The growth of theouter bank in the case of LS-G were also reduced

point bar and the consequent migration of deep

to some extent as compared to those in the LS-NG

pools towards the outer bank resulted in higher

case. Although scour at the tip of the groynes was

erosion in the cases of LS-NG and LS-G. However,observed in one or two groynes, the overall scourin the case of HS-NG and HS-G, the size of theat the tip of the groynes was not so significant.

deep pools, as well as the point bar, were compara-

Considerable erosion occurred in the space be-tively smaller and there was less overall erosion.

tween the groynes in the case of HS-G compared to

The ratio of the radius of cur vature (R) of

that of the LS-G. The deep pools in the case of LS-G

the channel centerline to the channel width (W),caused the incoming flow velocity to be more mod-which signifies the sharpness or the tightness oferate and thus reduced the turbulence whereas

the channel curve is an important parameter con-in the case of HS-G, the approach on the groynes

trolling the channel erosion and migration (Hickinoccurred with higher velocity thereby causing

and Nanson, 1975) in meandering channels. The

more recirculation behind the groynes. This angle

HS channel, due to the longer flow path and highof approach might also be influenced by the deflec-

value of the R/B ratio, had smooth flow transition

tion angle of the meandering channel since the HS

and thus less erosion occurred in the HS-NG case.

channel had a deflection angle of 600 compared to100

Experimental Study on the Performance of Slope-crested Groynes in Erodible Meandering Channels of Different Sinuosity

the 450 of the LS channel.

channel centerline as well as along the initial rightbankline between time t＝40 mins to t＝20 mins, i.e.

3. 2

Erosion-deposition Pattern

after the implementation of groynes. Channel ero-

The erosion-deposition pattern of the channelsion is represented by negative values while depo-

was analyzed in order to determine the sedimentsition is given by positive values. The comparison

transport behavior of the channel. Figure 6 depicts

between the LS-NG and LS-G (Fig. 7(a)) shows

the temporal change in the erosion-deposition vol-that the presence of groynes caused degradation

ume for all cases of the experiment.

along the right bank due to local scouring particu-

The erosion-deposition volume between thelarly downstream of the apex. However, along the

successive time periods was calculated based onchannel centerline as shown in Fig. 7(b), the chan-

the change in measured bed elevation at different

nel was continuously aggraded due to the trans-

time periods. The erosion, as well as deposition vol-port of eroded sediment from the bank towards theume, was higher in the first 20 mins for all cases ascenter. In the case of the HS channel, the channel

the channel underwent rapid adjustment under theaggradation-degradation pattern changed little

given flow conditions. Although the volume waseven in the presence of groynes. Along the rightslightly different even for the same type of channel,bank, slight deposition occurred upstream of thethe overall initial channel adjustment behavior wasapex and slight degradation was seen just near thesimilar. After the implementation of groynes, theapex region (Fig. 7(c)). A similar pattern of eleva-erosion and deposition volume were significantly

tion change was also observed along the channel

reduced in the case of LS-G as compared to that ofcenterline as shown in Fig. 7(d).

LS-NG. This suggests that the groynes effectively
reduced the erosion and enhanced channel trans-

3. 3

Surface Velocity Distribution

port capacity. However, in the case of HS-G, theThe continuous change in the channel

erosion-deposition volume changed little compared

planform as well as the channel bed due to ero-to that of the HS-NG case. This might suggest thatsion-deposition phenomena largely af fects thethe channel adjustment process was still active in

distribution of velocity in both the longitudinal as

the HS channel.

well as transverse direction. Conversely, velocity

Figure 7 (a-d) shows the change in the chan-

distribution dictates the channel morphologicalnel elevation (dZ＝Z40 mins-Z20 mins) along the initial

evolution. In fact, these phenomena proceed simul-

Fig. 6

Temporal change in the erosion-deposition volume for different experiment cases.

自然災害科学 J. JSNDS 37 特別号（2018 ）101

Fig. 7 (a-d): Difference in the elevation between t＝40 mins and t＝20 mins along the original channel
centerline and along the original right bankline.

102

Experimental Study on the Performance of Slope-crested Groynes in Erodible Meandering Channels of Different Sinuosity

taneously. Surface velocity distribution obtained by

8 c and d).

the PIV technique was analyzed to determine how

During the initial 20 mins where the channel

the morphological evolution process is related toadjustment process was dominant, the velocity

the velocity distribution in the channel. Figure 8

distribution within the channel was nearly uniform.

shows the distribution of the surface velocity be-

After the channel adjusted to the given flow condi-

fore implementing the groynes (first 20 mins) andtions by undergoing morphological changes, theafter implementing the groynes (next 20 mins) in

distribution of velocity also tends to be non-uni-

the cases of HS-G (Fig. 8 a and b) and LS-G (Fig.

form. Due to the longer flow path as well as theFig. 8 (a-d): Velocity distribution along the channel before (first 20 mins) and after (last 20 mins)
implementation of the groynes.

103

自然災害科学 J. JSNDS 37 特別号（2018 ）R/B ratio, smooth flow transition occurred in theextending from upstream of the outer bank apex toHS-G case. Consequently, the velocity was more or

the inner bend apex was observed (Fig. 8(d)).

less uniformly distributed across the channel sec-

Similarly, Fig. 9 (a and b), shows the stream-tion as well as along the channel as shown in Fig.

lines and velocity near the groynes area in the8(a). However, the velocity was slightly high at thecase of HS-G and LS-G, respectively. For HS-G,

point of inflection between the two apices becausea stagnant zone did not develop upstream of theof which higher erosion was obser ved aroundapex. However, in the space between the groynes

those areas. Similarly, in the case of LS-G, before

downstream of the apex, strong recirculation flow

the implementation of groynes, the high velocity

was observed, which resulted in higher erosion in

was concentrated near the apex of the inner bend

that region. Similarly, the flow deflection aroundas shown in Fig. 8(c), which caused higher erosion

the groynes was slightly higher in the case of thearound that region. The transverse velocity compo-

HS channel. This was mainly because of the direc-

nent in the case of the LS channel was higher be-tion of the approach flow towards the groynes. In

cause of which more bed load transport occurred

the case of HS-G, the erosion in the previous bend

forming deep pools near the outer bank and point(X＝150-200 cm) in Fig. 5(b) was minimum due

bar near the inner bend. After the implementation

to which the flow smoothly approached towardsof the groynes, the near bank velocity was signifi-

the initial groynes. However, in the case of LS-G,

cantly reduced in both LS-G and HS-G (Fig. 8 (bdue to higher erosion in the preceding bend (Xand d)). However, apart from the slight deflection＝175-200 cm) in Fig. 5(d), the flow of approacharound the groynes region, no noticeable change

was towards the end groynes and further down-in velocity distribution within the channel was ob-

stream. Consequently, less flow deflection, as wellserved. Velocity around the groynes was reduced

as higher erosion downstream of the groynes, wasbut it tends to increase after exiting the groynes

observed.

field as shown in Fig. 8 (b and d). Some previous
studies (Karki et al., 2018) on straight rectangulargroynes showed a higher flow deflection, which

4. CONCLUSIONS AND RECOMMENDATIONS

resulted in higher bank erosion on the opposite

We examined the evolution of flow and chang-bank. In the case of LS-G, a stagnant or dead zone

es in sediment transport and channel morphology

Fig. 9(a-b): Streamlines and velocity around the groynes: (a) HS-G (b) LS-G

104

Experimental Study on the Performance of Slope-crested Groynes in Erodible Meandering Channels of Different Sinuosity

in erodible meandering channels of two different

case of the LS channel. However, further exper-

sinuosities. Modified groynes with a sloped crest

iments, as well as numerical simulations under

extending from the bank towards the channel were

varying flow conditions and different orientations

introduced as a bank protection countermeasure.

of groynes, are necessary for better understanding

The effect of the groynes on the evolution of flowof the mechanism.

and morphology as well as the effect of the channel

ACKNOWLEDGEMENT

sinuosity on the performance of the groynes wereanalyzed. The initial channel adjustment processThis research was supported by the JST/JICA

was similar in both channels but the erosion-depo-

SATREPS program on disaster prevention/mitiga-

sition pattern was different. Maximum erosion oc-tion measures against floods and storm surges incurred near the inner bend apex in the LS channel

Bangladesh (PI: Dr. Hajime Nakagawa). The firstwhereas in the case of the HS channel, maximum

author would like to thank the reviewers for theirerosion occurred near the point of inflection or thecomments to help improve the manuscript and also

crossover region. The low sinuous channel was

the Government of Japan for the MEXT scholar-

characterized by the formation of distinct pool-bar

ship.

sequences due to higher erosion whereas thosefeatures were relatively less distinct in the high sin-

REFERENCES

uous channel. In terms of the bank erosion, again

Bhuiyan, F., Hey, Richard D. and Wormleaton, Peter R.:
Bank-attached vanes for bank erosion control andrestoration of river meanders, Journal of Hydraulic Engineering, ASCE, Vol. 136, No. 9, pp. 583-

the LS channel was observed to be more prone toerosion under the no groynes case and thus resulted in a uniform widening of the channel. However,in the HS channel, localized bank erosion occurredat some specific points. This suggests that thebank erosion behavior is more difficult to predictin the HS channel, which could ultimately dictate
our choice of countermeasures and where to locate
them. However, in our experiments, the locationsof the groynes were pre-decided. The implementation of a series of groynes influenced the local
flow, sediment transport and bank erosion near
the structures. Bank erosion was reduced in bothtypes of channel, however, the erosion in between
the groynes continued mainly due to recirculation
flow and was higher in the HS channel. Although
the deflection of high velocity towards the channel
center was not significant, the velocity near thebank decreased considerably. After the flow extended beyond the groynes, the velocity increased
in both channels. The performance of the proposed
countermeasures varied under different sinuosity
channels with a slightly better performance in the596, 2010.
Cunningham, R.S. and L yn, D.A.: Laborator y studyof bendway weirs as a bank erosion countermeasure, Journal of Hydraulic Engineering, ASCE,
Vol. 142, No. 6, pp. 1-21, 2016.
Da Silva, A.M.A., El-Tahawy, T. and Tape, William
D.: Variation of flow pattern with sinuosity insine-generated meandering streams, Journal of
Hydraulic Engineering, ASCE, Vol. 132, No. 10,
pp. 1003-1014, 2006.
Dehghani, A.A., Azamathulla, H.Md., Hashemi Najafi,
S.S. and Ayyoubzaeh, S.A.: Local scouring aroundL-head groynes, Journal of Hydrology, Vol. 504, pp.
125-131, 2013.
Giri, S., Shimizu, Y. and Fujita, M.: Flow characteristics in a mildly meandering channel with &without river training structures, Annual Journalof Hydraulic Engineering, JSCE, Vol. 47, pp. 835840, 2003.
Giri, S. and Shimizu, Y.: Observation on bed variation
in a meandering like flume with river training
structures, Annual Journal of Hydraulic Engineering, JSCE, Vol. 48, pp. 1069-1074, 2004.

105

自然災害科学 J. JSNDS 37 特別号（2018 ）Hickin, E.J. and Nanson, G.C.: The character of channel migration on the Beatton River, Northeast
British Columbia, Canada, Geological Society
America Bulletin, Vol. 86, pp. 487-49, 1975.
Hickin, E.J. and Nanson, G.C.: Lateral migration rates
of river bends, Journal of Hydraulic Engineering,
ASCE, Vol. 110, No. 11, pp. 1557-1567, 1984.
Jamieson, E.C., Rennie, C.D. and Townsend, R.D.: 3D
flow and sediment dynamics in a laboratory channel bend with and without stream barbs, Journalof Hydraulic Engineering, ASCE, Vol. 139, No. 2,
pp. 154-166, 2013.
Karki, S., Hasegawa, Y., Hashimoto, M., Nakagawa,H. and Kawaike, K.: Short-term evolution of flow
& morphology in an erodible meandering channel with & without groynes, Annual Journal of
Hydraulic Engineering, JSCE, Vol. 74, No. 4, pp.
1147-1152, 2018.
Langbein, W.B. and Leopold, L.B.: River Meanders-Theor y of minimum variance, Geological
Survey Professional Paper, Vol. 422-H, pp. H1H15, 1966.
Struiksma, N., Olesen, K.W., Flokstra, C. and Vriend,
H.J.DE.: Bed deformation in curved alluvial channels, Journal of Hydraulic Research, Vol. 23, No. 1,
pp. 57-79, 1985.
Teraguchi, H.: Study on hydraulic and morphologicalcharacteristics of river channel with groynes
structures, PhD Thesis, Kyoto University, 2011.

要

Teraguchi, H., Nakagawa, H., Kawaike, K., Baba, Y.,
and Zhang, H.: Effects of hydraulic structures onriver morphological processes, Int. J. of Sed. Res.,
Vol. 26, No. 3, pp. 283-303, 2011.
Uijttewaal, Wim S.J.: Effects of groynes on the flow in
groynes fields: Laboratory experiments, Journalof Hydraulic Engineering, ASCE, Vol. 131, No. 9,
pp. 782-791, 2005.
Xu, D. and Bai, Y.: Experimental study on the bed topography evolution in alluvial meandering rivers
with various sinuousnesses, J. Hydro-environment
Research, Vol. 7, pp. 92-102, 2012.
Yossef, M. and Vriend, H.D.: Sediment exchange between a river and its groyne fields: mobile-bed
experiment, Journal of Hydraulic Engineering,
ASCE, Vol. 136, No. 9, pp. 610-625, 2010.
Zhang, H. and Nakagawa, H.: Characteristics of local
flow and bed deformation at impermeable andpermeable spur dykes, Annual Journal of Hydraulic Engineering, JSCE, Vol. 53, pp. 145-150, 2009.
Zhang, H., Nakagawa, H., Kawaike, K. and Baba, Y.:
Experiment and simulation of turbulent flow in local scour around spur dyke, Int. J. Sed. Res., Vol.
24, No. 1, pp. 33-45, 2009.
（投 稿 受 理：平成30年 4 月 6 日
訂正稿受理：平成30年 7 月 4 日）

旨

河岸侵食は河川管理のために重要な課題の一つであり，特に沖積蛇行河川ではその地形動力学的な特徴から，重要度が高い。そのため，侵食の最小化や流路の安定化のために，様々な対策が取られている。本研究では斜形不透過型水制の河岸侵食に対する低減効果を分析した。水路実験は，蛇行度の異なる 2 種類の侵食可能蛇行流路を用いて行った。本研究の目的は，提案する対策の様々な蛇行度における性能を評価することと，流路全体の形態学的な流路の発達を分析することである。結果より，低蛇行度の方が，高蛇行度よりも侵食し易い傾向があることを示した。また，蛇行度は流路全体の形態学的な流路の発達に影響しており，低蛇行度の場合で独特な点状砂州，瀬ー淵シーケンスの形成が見られた。提案された対策は低蛇行度の場合で良好な性能を示しており，河岸近傍の流速の低減効果が確認されたが，水はね効果もまた低減されることがわかった。