Eco-System Based Beach Erosion Control By Berm Nourishment
Combined With Buried Sand Tube
Shinji Sato, Professor, D.E.

Yuuichi Okamura

Civil Engineering Department, The University of Tokyo

Miyazaki Office of River & National Highway,
The Ministry of Land, Infrastructure & Transport

Keisuke Murakami, Professor Ph.D.

Shin Hashimoto, D.E.

Civil Engineering Department, Miyazaki University

Engineer, Token Consultant, Co. Ltd.

Coastal Erosion at Miyazaki Coast

2/24

 20km beach Ooyodo River and Hitotsuse River severe erosion since 1985

MiyazakiCoastal Erosion at Miyazaki Coast

3/24Jetties
1967-1985

southwardtransport ?

Miyazaki Port
1982-2005

Coastal Erosion at Miyazaki Coast

4/24

 structures alone cannot mitigate erosion
SumiyoshiAkaeAoshima

Coastal Erosion at Miyazaki Coast sea turtle

5/24
 surfing reluctance against
concrete structures
No moreconcrete!

TL intensities of Feldspar particles (Sato et al., ICCE 2010)6/24
Mimigawa
River
Tsuno
RiverTL

Omaru
River

nourishment

Hitotsuse
River

OoyodoRiver

NanukiRiversouthwardtransport ?

 southward transport sand supply from rivers

Mimigawa
RiverIshinami

Tsuno
Harbour

Jetties
1967-1985

Kawaminami
HarbourOmaru

Jetty this study

Hitotsuse Ishizaki

Miyazaki Miyazaki
Airport
PortOoyodo

Aoshimasediment volume (x 104 m3)

Sediment budget: southward transport ~ 200x103 m3/yr

7/24

200 x103 m3/yr

Tsuno
HarbourMimigawa
1983 1988 1993 1998 2003 2008
River 2013 2018
IshinamiRiver

Kawaminami
Harbour

Omaru
River

Miyazaki Miyazaki
AirportJetty this study Port

Hitotsuse Ishizaki
RiverRiverOoyodo
RiverAoshima

Wave Data at Miyazaki Port

8/24

( Data: Miyazaki Prefecture )normal to the shoreline

1992-2002
all waves
全波高データH1/3 >1m
波高1m以上H1/3 >2m
波高2m以上波高3m以上H1/3 >3m
波高4m以上H1/3 >4m

2
1.5
1

waves from northwaves from south
waves by typhoons

waves
in winter

0.5

angle 方位(N基準)from north (degree) contribution by typhoons ?

164

154

144

134

124

114

104

94

84

74

64

54

44

034

energy flux (%)
wave
エネルギーフラックス比(%)

2.5

Consensus building

9/24

Erosion control plan (2011)10/24

 structures (3 groins) nourishment
this study
 buried sand tube

Jetties at Hitotsuse
River mouthnorthburied sand tubes
L=1,600mburied sand tubes
L=1,100m
groin L=50m
ＰＡ

groin L=150m

ＩＣsouthgroin L=300m

Erosion on unprotected beachOct 11, 201411/24

Oct 13, 2014
Jetties at Hitotsuse
River mouthburied sand tubes
L=1,600mburied sand tubes
L=1,100m
groin L=50m
ＰＡ

groin L=150m

ＩＣgroin L=300m

Impact of typhoon waves on long-term erosion ?

12/24

Coastal Road
northBuried sand tubes (2013-)

13/24

Ooida Beach
2008

W > 18m

4m (m aintenance road )dune erosion

CenterDun e

2012
T.P.+ 7m
Extrem e sw ashw ave heig ht

nourishment
2015
re-nourishment

2016

ScarpBermn ourish m en tT.P.+ 4m
Tem p oral d esig ncrow n heig ht

Stormcon d ition

Fill b ysoil

sand tube

T.P.+ 1m
Found ation p rotection(asp halt m at) ag ainst scouring

Norm alcon d ition

Buried sand tubes (2013-)

14/24
2013

Sand tubes buried by nourishment

15/24

Five typhoons affected Miyazaki in July-October 2014

16/24

Northward currents generated by typhoon storms
(m)

T1408

T1412

T1418 T1419

T1411
St. A

17/24
(s)

T1/3

H1/3
H1/3
(m)
St. Bu(cm/s)
no dataTide at Miyazaki Port(m)(m)June 2014
St. B(m)Longshore sand transport model

18/24

Kraus et al. (1982, ICCE)
Sand volume(x 103m3)
500

north

3.8 × 104 2
𝑄=𝐻𝑏 ⋅ 𝑉𝛾tan𝛽
390

280

as large as long-term annual
southward transport ~ -200 x 103 m3

240

290

250

100

-40-250-240

south-260-500

Northward sand transport by five typhoons~ 760 x 103 m3

Northward sand transport >105m3 by five typhoons

19/24(m)June 2014
St. B

Dec 2014+60(m)
+140

St. B

-580

-100

Change in nearshore sand volume (x103m3)
Hitotsuse
RiverErosion control by buried sand tubes20/24

Nourishment
only ※写真は1419号通過後の10月22日撮影
埋設護岸未設置区間

Nourishment+ Buried
sand tube
埋設護岸設置区間※写真は1419号通過後の10月31日撮影

10

標

標高(海抜) T.P.m

天然砂丘(浜崖) 養浜sand tube
サンドパック

高目標汀線位置(目標浜幅50m)(T.P.m)9

H26.06(埋設護岸設置後)
June 2014
H26.10(1419号通過後)
October 2014

8天然砂丘
7 (浜崖)

天然砂丘
(浜崖)

養浜

H26.06(埋設護岸設置後)
June 2014
H26.10(1419号通過後)
October 2014

天然砂丘
(浜崖) 養浜

養浜

65

目標汀線位置(目標浜幅50m)

4sand
サンドパック
tube
321

大炊田海岸
No.O50-1-2010

2030

4050607080-40-30-20-100102030

40

50

60

7080

浜幅基線からの沖向き距離 (m)

浜幅基線からの沖向き距離 (m)(m)

June 2014
St. B

Buried sand tubes exposed by typhoon storms
2017

21/24

Buried sand tubes exposed by typhoon storms

22/24

Oct 11, 20142017

Oct 13, 2014

Sea turtle laying eggs on nourished bermmark of sea
turtle lay-eggs

bermnourishment

23/24
2017

exposed sandtubes

Sea turtle laying eggs on nourished bermmark of sea
turtle lay-eggs

bermnourishment
mark of sea
turtle lay-eggs

24/24
2017

exposed sandtubesExposed sand tubes buried by re-nourishment

re-nourishment

dune erosion

exposedsand tube

25/24

Summary

26/24

Eco-System Based Beach Erosion Control By Berm
Nourishment Combined With Buried Sand Tube
1. The northward longshore sand transport due to a single
typhoon storm was found to be as large as the annual
southward longshore sand transport, thus causing rapid
dune erosion.
2. Eco-system based control works, berm nourishment withburied sand tubes, appeared effective to mitigate dune
erosion with minimum impact on eco-systems.