Workshop
Japan and the Netherlands
Climate Adaptation and Resilience
Oct 31, 2019. Tokyo,

Erosion of River Delta Coastlines dueto Climate Change

Hitoshi Tanaka
Senior Director, International Activities Center (IAC), JSCE
Prof. Dr.Eng., Tohoku University, Sendai, Japan

Cua Dai Beach, Vietnam
Dec 12, 2015

1. Recent flood disaster in Japan induced
by Typhoon No.19 (Typhoon Hagibis)
2. Erosion of River Delta Coastlines due toClimate Change

Breaching of river embankment

Class A

Sendai
Breaching

Yoshida R.
（MLIT)

Chikuma R.

（MLIT)(the Asahi Shimbun)

Yoshida R.

Class ASendai
Breaching

BreachingDrainage tunnel（MLIT)

Cornelis Johannes van Doorn(1837-1906)
Stayed in Japan from 1872-1880

van Doorn’s technical reportfor the drainage system

https://www.midorinet-fukushima.jp/

JSCE Civil Engineering
HeritageDelta Formation and Deformation

LAND

Accretion

Dam
ErosionNile River delta, Egypt
OCEAN

Accretion

Thu Bon River delta, Vietnam

Two mechanisms of beach erosion(1) Intercept of longshore sediment movement by coastal structureLongshore
sediment
movement

Shinnecock Inlet, New York

Wave incidenceerosion
Longshore
sediment
movement

accretion

Two mechanisms of beach erosion(2) Reduction of sediment supply from a river basin
Cua Dai River mouth, Vietnam

Cua Dai River mouth, Vietnam
ErosionRiver Sediment supply
Reduction of River
Sediment supplyErosion

Beach Erosion by Sea Level Rise
IPCC AR5 (2014)
average from2081 to 2100

Mean water level rise(average from 2081 to 2100)
WorstScenario

Best
Scenario

Scenario

From:

Water level rise

Shoreline Retreat Theory
Equilibrium beach profiles (EBP) ( Bruun, 1962,1988)

h = Ay 2 / 3(1)h : water depth, A : scale parameter, y : horizontal distance from the shoreline

Dean’s theory (1977)
1. Wave energy dissipation per unit water volume.
2. Wave energy dissipation per unit surface area.
3. Uniform average longshore shear stress across the surf zone.

 24
D* A=25 ρg g κ 

2/3(2)

Shoreline Retreat Theory
Bruun’s rule (1962) : Response of beach profile to sea level rise
R∞ = SL*
h* + B

R∞h*

L*
Shoreline retreat due to sea level rise.

4020002040

Sea-level Rise (m)
6080
100

Relationship between sea level rise and area oferoded sandy coast (Mimura et al., 1994).
0IwateMiyagi
Akita
Yamagata
Fukushima
Ibaraki
Chiba
Tokyo
Kanagawa
NiigataToyamaIshikawa
Fukui
Shizuoka
Aichi
MieKyoto
OsakaHyogo
Wakayama
Tottori
Shimane
Okayama
Hiroshima
Yamaguchi
Tokushima
KagawaEhime
Kochi
Fukuoka
Saga
Nagasaki
Kumamoto
Oita
MiyazakiKagoshima
Okinawa

60

Erosion Ratio (%)

80

Hokkaido
AomoriArea of Erosion (%)

Future Shoreline Retreat in Japan
100

10080

60

4020120

Erosion ratio of sandy coast in each prefecture(prediction for 30.6cm sea level rise)(Mimura et al., 1994).

Delta Coastline Erosion in VietnamImportance of Beach Erosion in Vietnam

PM Nguyen Xuan
Phuc’s visit toJapan in 2017

(Yomiuri Online, June 6, 2017)

Similarity between Japan and Vietnam
Cuspate shape shoreline due topredominant sediment supply fromthe river basin
Beach erosion in the vicinity ofthe river mouth

Tenryu R. (Japan)

020km

Thu Bon R.
Vietnam020km

Erosion of Tenryu River Delta
Location of dams

Large numberof dams
⇒Reductionof sedimentsupply to thesea

Feb 7, 1976

⇒BeacherosionDamRivermouth

March 15, 2014

Beach erosion in the adjacent sandy coastCountermeasures

2015/1
2

Cua Dai BeachVietnam

Structural measure- detached breakwater- artificial reef
- groindetached breakwater(Arahama Coast, Sendai)Non-structural measure- increasing sediment discharge- beach nourishment

groin(Yamamoto Coast, Miyagi)Beach Nourishment in Rikuzen Takata, Japan“Miracle pine",a lone pinetree thatstood as asymbol ofhope.

Pre-tsunami
Jul. 23, 2010

Post-tsunami
Mar 14, 2011

Restoration of Rikuzen Takata
Pine tree plantation
Beachnourishment+12.5m AMSL+3m AMSLBeach Nourishment PlanRegion 1Region 3

Region 2

Length: 700m
Length: 650m
Beach width: 30m-60m Beach width: 60m

Length: 400m
Beach width: 30m-60m
Groin
Groin

Groin

Groin

Beach Nourishment Project

Iwate Prefectural Government (Aug, 2016)

Iwate Nippo (May 28, 2017)

Thank you for your kindattention!