2024 International Seminar organized by REDD-plus and ForestDRR Research and Development Center (FFPRI)International Expansion of Disaster Prevention and Mitigation
Technologies Through Forests

Feasibility of the Japanese Forest-based
Disaster Risk Reduction (F-DRR)
Techniques in Vietnam
ベトナムにおける日本のF-DRR技術の適用可能性
Takashi Okamoto (FFPRI)
岡本隆（森林総合研究所）

Today’s Topics

本日の内容 Forest-based Disaster Risk Reduction (F-DRR) andJapanese traditional techniques: “Chisan”
森林を活用した防災・減災（F-DRR）と日本の治山事業

 Scientific field survey in a mountainous watershed inVietnam to determine the causes of sediment discharge
ベトナム山地流域の土砂流出要因に関する科学的調査

 Adapting F-DRR (Chisan) techniques to Vietnam
ベトナムへの日本のF-DRR（治山）技術の適用性

2Forest-based Disaster Risk Reduction (F-DRR) F-DRRとはEco-DRR (Ecosystem-based Disaster Risk Reduction) is the idea of reducing

disaster impacts on humans and property by utilizing ecosystems as
natural buffers, in conjunction with risk-aware land use practices.

生態系を自然の緩衝材として活用し、リスクを考慮した土地利用の実践と組み合わせることで、人間や財産への災害の影響を軽減するという考え方。

ForestLakes and Marshes

Focusing on thefunctions of forests
Rivers andFloodplains

F-DRR

Forest-based Disaster Risk Reduction

Coral Reefs

Examples of Ecosystems with DRR Functions(partially modified from Nakamura, 2023)

Root systems

Forest soils

3Chisan: Japanese Traditional Strategy for F-DRR 日本の治山

What is Chisan?
Chisan is a Japanese traditional
forest conservation strategy for FDRR. It maximizes disasterprevention and mitigation throughforest management. This helps toprotect lives and property fromsediment-related disasters, sustain
water resources, and improve ourliving environment.
治山は、F-DRRのための日本の伝統的な森林保全政策である。森林の適切な維持造成を通じて防災・減災を最大化することで、土砂災害から人命と財産を守り、水資源を維持し、生活環境を改善する。

Multifunctional Roles of Forests


Sediment-related Disaster Prevention
Water Resource Cultivation
Climate Change Mitigation
Timber Production

Biodiversity Conservation
Promotion of Culture and Tourism Industry

Chisan Techniques: Effective inDeveloping Countries
 Cost-efficient Forests' Multiple Benefits

4Natural Disasters in Vietnam

ベトナムの地理と自然災害

Vietnam, like Japan, is prone to natural disasters. The northwesternpart, with its mountainous terrain rising over 2,500 meters, frequently
experiences sediment-related disasters.

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Joint Research Initiatives with Vietnam

ベトナムとの共同研究

 Joint research with the Vietnamese Academy of Forest Sciences (VAFS) since2020.
 The mountainous watershed in Mu Cang Chai, Yen Bai Province, NorthwestVietnam.
 Scientific evidence on sediment disasters and the forest functions for DRR.

Mu Cang Chai

© 森林総合研究所

Research Watershed in Northwest Vietnam (Mu Cang Chai District)

Area: about 200 km²
Elevation: 970-2000 m
Precipitation: 1730mm/year

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Joint Research Initiatives with Vietnam

ベトナムとの共同研究

Mu Cang Chai, Yen Bai Province, Northwest Vietnam.

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Landslides in Mountainous Slopes

山地斜面で発生した表層崩壊

Shallow landslides, with a sliding surface depth of less than 1 meter,
were more frequent in degraded forests and abandoned fields on
the steep slopes. In contrast, there were fewer landslides in wellmaintained terraced rice paddies.

Degraded forests

Abandoned fields

Rainfall at the time of the disaster is unknown (under investigation)

Shallow landslides caused by heavy rainfall
near Mu Cang Chai district in August 2023

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Sediment-related Disasters in Mu Can Chai ムーカンチャイ地区の土砂災害 9
表層崩壊

ShallowLandslide

地すべり

Deep-seatedLandslide

フラッシュフラッド

土砂流出Flash Flood

Sediment Discharge Field surveys for four types of sediment disasters toobtain scientific evidence Focusing on erosion and sediment discharge in thispresentation

Field Surveys in Vietnam to Obtain Scientific Evidence
科学的根拠を得るためのベトナムでの現地調査

1. Monitoring of river water levels and turbidity
河川水位・濁度の長期観測

2. Infiltration capacity testing
地表面の浸透能測定

3. Multi-point sampling of sediment discharge
流出土砂の多点サンプリング

10Monitoring of river water levels and turbidity 河川水位・濁度の長期観測 11
 Quantitative data have been obtained showing an increase in water level andturbidity during rainfall. These will be utilized in future analyses.

Water level

Nam Kim river

Turbidity
Turbidity
Water temperature

Sensors for water level
Monitoring results of the riverin the research site for 8 months(Feb.2023 to Sep. 2023)

Infiltration capacity 地表面の浸透能
 Forest land has a high infiltration capacity over 100 mm/h, preventing surface
erosion under normal rain.
 Walking path and valley filled embankment have lower capacities under 10mm/h, making them prone to surface erosion in stronger rains.

Equipment for infiltration
capacity testing

Relationship betweenland cover and infiltration
capacity of the ground

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Multi-point Sampling of Sediment Discharge 流出土砂量のサンプリング13
 River water was sampled at many points in thewatershed and the amount of sediment contained
was measured in the laboratory.
 For flow rate estimation, the river width and thedistribution of depth and velocity were measured.

Water sampling and measurement at many points in the watershed

River water sampled

Where is the Source of Sediment Discharge? 土砂流出はどこから？ 14Results
 Substantial sediment discharge(6,896 g/m3) is observed from alarge artificial embankment.
 In this watershed, human-induced
land modifications significantlyimpact sediment discharge.

© 森林総合研究所

Suspended sediment concentration in thewatershed surveyed on Sep. 13, 2023, which
experienced a daily rainfall of 20mm.

The large artificial
embankment

Challenges in Adapting ‘CHISAN’ Techniques to Vietnam
ベトナムへの治山技術の導入における課題

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 Abandonment of cultivated slopes leads to devastated lands, increasing the risk ofdisasters."
 Restoring these lands to forests is key to reducing disaster risks, with great
potential in 'Chisan', Japanese forest-based disaster risk reduction techniques.

cultivated slope

abandoned cultivation
Gabions for road protection

Slopes Along the Roadsides in Vietnam

Challenges in Adapting ‘CHISAN’ Techniques to Vietnam
ベトナムへの治山技術の導入における課題

 One of the ‘CHISAN’ techniques, Horizontal Step Works, stabilizes slopes
using logs and makes a good foundation for forest growth.
 Compared to concrete structures like Check Dams or Retaining Walls, it issignificantly lower in cost and requires less technical expertise.

Horizontal Step Works

筋工

Use of thinning logs in horizontal step works for theprevention of sheet erosion and forest growth enhancement.

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Challenges in Adapting ‘CHISAN’ Techniques to Vietnam
ベトナムへの治山技術の導入における課題

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 It is crucial to explore methods for implementing ‘CHISAN’ techniquesthat consider both the social and economic circumstances and theneeds of the local residents.

Corn cultivation is being carriedout in the landslide area

Devastated slope from landslide activity

KEY TAKEAWAYS
本日のポイント

Adapting Japan’s Chisan (F-DRR)

techniques to developing countries
requires understanding local sedimentdisasters with scientific evidence.

Effective implementation demands

matching scientific methods with local
needs in developing countries.

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Thank you for your kind attention.