River management in Japan －With focus on river levee－

January 2009 Masahiro Atsumi River Bureau, Ministry of Land, Infrastructure, Transport and Tourism, Japan Objectives of river management

Article 1 of the River Law

◆Prevent damages during floods and high water ◆Use rivers properly ◆Maintain the normal functions of running water ◆Improve and protect river environment Classes of rivers and river managers

Sections other then the designated sections of Class A river (managed by the Minister) Designated section of Class A river (managed The river manager is specified by the governor) for each river by the River Law and administers the river on the basis of the authority.

Class A river Class B river Details of the rivers in Japan (as of April 30, 2007)

Number of river systems Total length of the rivers Manager Note Class A river Minister of Land, The designated sections (77,262 km) 109 ８７，８３４ｋｍ Infrastructure and are administered by prefectural systems Transport governors. Class B river 2,726 Prefectural governor systems ３５，８５８ｋｍ Actual activities of river management

Normal time ◆Daily patrol of the river ◆Maintaining and controlling river administration facilities (levee, sluices, etc.) ◆Management of the river space ◆Control of running water in the river

During floods ◆Patrolling the river during floods ◆Draining behind levee ◆Flood fighting Importance of levee management

Major cities in Japan spread in areas below the design high water levels. Once the levee breaks, serious inundation occurs. Levee management is one of the most important flood control activities in Japan.

●Tokyo and the Edogawa, Arakawa and Sumidagawa Rivers

Tokyo Kitahama Line Musashino Line National Highway No. 6 Elevation (m) Shin-sakagawa River Obagawa River Joban Line Nakagawa River Nakagawa Edogawa River Edogawa Sakagawa River Arakawa River Arakawa Ayasegawa River Sumidagawa River

Arakawa Adachi Katsushika Misato Matsudo Kita Ward Ward Ward Ward City City

●New York Empire State Building Central Park Central Long Island CityLong Island UN Headquarters UN Calvary CemeteryCalvary Long Island Long Island railway New Jersey Turnpike Jersey New Turnpike Jersey New East River Hudson River Hackensack River Hackensack Ridgewood Manhattan Island Long Island West New West York Wood Ridge Functions and shapes of river levee

Cabinet Order Concerning Structural Standards for River Administration Facilities, etc. (1976 #)

Required function: Ensure safety against ordinary actions of running water not exceeding the design high water level as one body with revetment, spur dykes, etc.

Required configuration: Secure the specified levee height, crown width and slope inclination

Crown width: To be determined Free board: To be determined based on flow based on flow

Slope inclination: Not exceeding 50% Materials: Soil in principle Levee is a structure of a long history

Most levees have been repetitively reinforced by increasing the height and/or width, etc.

a) Improvement project (1911) b) Reinforcement project (1949) c) Revised improvement project (1949) d) New revised improvement project (1980) Historical changes in the cross section of the levee along the Edo River Construction methods have differed depending on era.

The construction methods of levees (for filling and compacting earth, etc.) have varied reflecting the technological and economical capabilities of the age.

Early 20th century (Tone River) 1940’s (Watarase River)

Today’s construction methods (Benching and roller compaction using tire rollers for expanding the width of the levee) Complicated soil composition

Levee has mainly used the soil produced at the site and other materials that have varied by project.

Sand gravel [Inland] [Riverside]

Silt with clay

Sand with gravel Sand gravel Silt with fine sand

Clayey silt Medium fine sand Sand and gravel (brown) Example of soils constituting levee bank

The bank has a complicated constitution of gravels, sand, clay, silt, etc. Complicated foundation ground

Most plains in Japan are alluvial plains, which were formed by sediment accumulation during floods of rivers. The majority of river levees are constructed on old river courses, and thus the foundation ground is complicated.

Mountains and hills Plateau To Natural levee r d ive 現a r y’ cou河s Old sand bar r 道 se Alluvial land Raised-bed river section Sand dune Old river course Crescentic levee lake Flood plain Wetland Old wetland Reclaimed land Old river course Raised land Cliff Levee under direct control (design section) Today’s levee Levee under direct control (tentative section Other levees

Site where there was once a levee Landform classification map Revetment (Tone River, as an example) Contour line Engineering design and checking of levee

July 2002 Design Guideline for Rive Levee ・ New levees shall be checked for safety when designing. ・ Existing levees shall be checked for safety.

(Performances required to levee) ・ Resisting seepage ○ Safe against sliding failure ○ Safe against piping failure ・ Resisting erosion ○ Safe against direct erosion (of the riverside slope and toe surfaces) ○ Safe against lateral erosion (erosion and scouring of flood plain) ・ Resisting earthquake ○ Safe against secondary damage (by preventing outflow of river water accompanying levee deformation) Example of a burst in levee caused by seepage and overflow combined ①

Point of burst

×

Maruyama River

Maruyama River October 2004 Example of a burst in levee caused by seepage and overflow combined ②

Maruyama River

Maruyama River October 2004 Flow of checking safety against seepage

● ● 1. Setting continuous sections Classifying sectionsofsimilarshapesand soilcharacteristics Classifying weakpoints Extracting Information used 4. Modeling levee ● ・River・河道特性 channel properties ・Flooded・洪水氾濫区域 area safetybycalculations Checking Outputアウトプット Information used ・・ボーリング調査結果（原則3本）Boring survey (three, in principle) ・Sections・堤防の断面形状が同一の区間 of similar bank cross sections ・・土質試験（C、φ、ρSoil test (C, φ, ρ, etc.) 等） ・・透水試験Permeability test, etc. etc.. Outputアウトプット ・Calculation model for checking safety 2. Classifying continuous sections ・安全性照査実施のための計算モデル

Information used ・Levee・堤防の高さ height ・Conditions・背後地の状況 of the hinterland 5. Checking safety ・Soil・堤体・基礎地盤の土質 of the bank and foundation ground ・Year・築堤年代 of construction, etc. etc.. ・Saturated・飽和・不飽和浸透流計算 and unsaturated seepage flow Outputアウトプット analysis・円弧すべり計算 ・ Sections・堤防の持つ構造的・土質的特性が of similar structural and soil ・Circularアウトプット arc method properties 同様の区間 Outputs・堤体の浸透に対する安全性 ・Safety of the levee against seepage ・Safety・基礎地盤のパイピングに対する安全性 of the foundation ground against piping 3. Selecting cross section to check

Information・被災履歴 used ・Flood history ・地形上のウィークポイント etc.. ・Topographical weak points, etc. Outputアウトプット ・Cross・細分区間における安全性照査断面 section to be checked for each class (Cross （求められる機能（この場合は浸透） section most likely to be prone to damageに対して最も厳しい条件であると (seepage in this case)) 思われる箇所） Investigation on seepage (① Soil survey)

[Riverside] 〔堤外側〕 [Landside]〔堤内側〕 g ririnngg ring ring ding BoBo Bo Bo g un ndin So Sou

5m

5m

Standard標準貫入試験 penetration test Field現場透水試験 permeability test 砂質土 基 砂質土 Soil乱した試料の土質試験 test of disturbed specimen 堤 Sandy soil ground Sandy soil 礎 Sampling乱さない状態での力学試験用試料の採取 and soil test of undisturbed specimen 地 forと土質試験（粘性土） dynamic test (clayey soil) Bank 体 粘性土Clayey soil 盤 粘性土Clayey soil Sampling乱した状態での力学試験用試料の採取と and soil test of disturbed specimen for土質試験（砂質土、礫質土） dynamic test (sandy soil, gravelly soil) Foundation Survey across levee (Example) Investigation on seepage (② Checking safety)

Sliding failure ● Assessment based on the safety factor calculated by the saturated and unsaturated seepage flow analysis plus the circular arc method Ｆｓ≧１．２×α１×α２ （Riverside slope） α１：Coefficient of the bank history (1.0, 1.1, 1.2 Complicated # larger value) α２：Coefficient of the foundation ground (1.0, 1.1 With dangerous landform # larger value)

Center of the slip circle Measured value Calculated value (Unit: hour)

Water level (m) Vertical line Time (hr) Center of gravity

Slip circle Seepage flow analysis Circular arc method Present state of safety inspection along the rivers under the jurisdiction of the national government

○ Of the entire levee of about 10,000 km, 8,800 km has been inspected for safety by the end of March 2008. ○ About 3,500 km was found to be insufficient in safety against seepage. ○ Inspection of the remaining 1,400 km will b completed by the end of fiscal 2009.

An example of publishing sections requiring countermeasures (Yahagigawa River)

Not inspected yet 1367km Inspected and 14% require countermeasures 3,554km Prior section 35% measures Inspected and require 要対策箇所 n requiring Section tio no countermeasures ec s ing ior uir 5,206km Pr eq n r 所 s tio策箇ure ec対 as 51% S 要 me Inspection completed g irin qu所 n re箇 ctgio対 策 res equSierin要 asu ectio対n策 r 箇所 me S 要 es measur Percentage of levee sections inspected for safety Safety安全性照査基準以上 standards against seepage satisfied (As of the end of March 2008) Safety安全性照査基準未満 standards not satisfied Executing reinforcing measures

●A three-year priority project started in 2007 to reinforce the 48 km sections that were found to be especially unsafe and have a history of damage.

●The other sections will be reinforced by patrolling during floods and monitoring damage, and careful flood-fighting activities will be carried out.

After completing safety inspection by the end of fiscal 2009, a full-scale reinforcement project will be executed by selecting sections of top priority based on safety, history of damage, population in estimated flooded areas, and the conditions of the hinterland. Flow of executing works for reinforcing levee

Checking safety

No

Deciding sections to reinforce

Nominating candidates of reinforcement method (Selecting effective methods for securing the required safety)

Comparing the candidates of reinforcement method (Comparing the costs and social and natural impacts, etc.)

Deciding the reinforcement method

Executing the reinforcement work Standard reinforcement methods (against seepage)

■断面拡Impervious 大工法 material Widening of the cross section (Widening) 難透水性材料 透水性材料 Pervious material ・ The hydraulic gradient is reduced by elongating the seepage route. ・ The safety of slopes against sliding is improved by reducing the Basic sectional form inclination. 基本断面形状 Wetting surface Drain method before reinforcement ・ Filter material The discharge of water penetrated into the bank is accelerated by replacing the toe of the inland slope by highly permeable materials. Drain Wetting surface after ・ Rises in the wetting surface are controlled, and the drops in the shear reinforcement strength of the bank are prevented. Water channel at ・ The stability of the slopes is improved by replacing the toes by drain the food of the bank materials of large shear strength. Lining Wetting surface before Coating of the riverside slope (Soil, impermeable reinforcement ・ The riverside slope is coated by impervious material (either soil or membrane, etc.) Wetting surface after reinforcement artificial material) to prevent the river water from penetrating into the bank, rain water from seeping from the crown, and the shear strength of the bank from dropping. Example of seepage control

Example of widening (Tone River)

ＨＷＬ La 1:5 ndside1 rside :7 Rive

Lining表のり面被覆＋ドレーン工法による対策事例（木津川） the riverside slope + drain method

Impervious遮水シート sheet

Gabion mat

Material for preventing soil draw-out吸出し防止材

ドレーンDrain 遮水矢板Impervious sheet pile Prevention of Serious Damage by Super levee

○High standard levee (super levee) is being constructed along the six major rivers in the Tokyo and Kinki Metropolitan areas, where levee break is estimated to cause very serious damages. ○Super levee is much wider than ordinary levee expanding wide under cities, and １）Does not break even when water overtops, ２）Does not break even when water seeps, and ３）Is strong against earthquakes. ○Landuse in river zones has been strictly regulated by the River Law. The Law was revised in 1991 stipulating the zone from the top of the slope to the toe of the landside slope of super levee to be a special zone, enabling the top of super levee to be used as ordinary land.

High standard levee

Constructing a city and high standard levee as one body

Height of levee（h） Special area for high standard embankment 30h (about 30 times of the height of the levee) River zone Need of super levee

During an unexpectedly large- During an unexpectedly long and During a great earthquake, the soft scale flood, water overtops and large-scale flood, water seeps and ground may liquefy, causing may break the levee. may break the levee. serious damage to city structures at the site.

●Ordinary levee ●Ordinary levee ●Ordinary levee

●Super levee ●Super levee ●Super levee

Overtopping water flows slowly on Even when water seeps in the The levee is strong against the levee and does not break the levee during a long and large-scale liquefaction because the soft levee. flood, the levee does not break ground is improved when because it is wide. necessary and the slope is gentle. Examples of super levee construction

Super levee along the Arakawa River (Tokyo)

Before construction After construction Close-range view

Super levee along the Yodo River (Osaka)

Before construction After construction Close-range view Example of super levee construction (Tama River, Tokyo)

Location 栃木県 茨城県

群馬県

荒 川

埼玉県 利根川 Shimomaruko District 江戸川 千葉県 東京都 Tama River 東京湾 神奈川県 太平洋

Photographed on April 1, 2007 Monitoring levee

Besides visual monitoring, some levees are monitored using measuring instruments.

[Seepage] Water gauges in the bank 【堤外】[Riverside] [Landside]【堤内】

▽ H.W.L.

River water gauge Bank堤体

Foundation基礎地盤 ground Ground water level gauge

[Erosion] Monitoring the surface velocity ▽ H.W.L. Foot 根固工protection River water gauge 護岸工Revetment 張芝Sodding

Erosion sensor Scouring sensor Spiral up of designing technologies using the results of monitoring

Detecting damages and abnormalities during floods by monitoring levee

Ensuring the safety of levee Investigating the causes by taking measures and assessing

Improving design methods, etc. Number of breaks per year for each decade after 1945

250 230 Total: 678 breaks (from the data of the national and prefectural governments) 200

150 107 112 100 ８９ 79 61 50

0 ４５～５４ ５５～６４ ６５～７４ ７５～８４ ８５～９４ ９５～

Reference: Actual states of breaking of dykes WWII (2002, River Improvement and Management Division) Elaborating technologies for controlling levee (by constructing a risk management system)

“Simulation of emergency measures during breaking of levee” started in fiscal 2007 in all Offices of River.

○Collecting knowledge on emergency ○Flow of emergency measure simulation measures during breaking of levee

1. Understanding the properties in all The knowledge on emergency measures sections of the river

during breaking of levee collected by the 2. Assuming the point and scale of breaking national government is summarized. 3. Understanding various conditions

3-2. Conditions of materials, Rough coffering 3-1. machines and equipment Conditions of the site 3-2-1. 3-2-2. 3-2-3. Conditions of Operation Transportation stationing capacity route

5. Investigating operation plan

6. Assessment and analysis

Kokaigawa River Secondary →：Flow of the river coffering →：Flow of the flood water Simulation completed Revising Elaborating technologies for controlling levee (by constructing a levee investigation system)

[Society of the research of levee] The society was established in 2008 aiming to always maintain river levees reliable by 1) developing levee technologies, 2) acting as a center of technologies, and 3) promoting education and training.

[Headquarters] Collecting technological information in levee and giving directions and advice to solve issues Preparing technical standards

Extracting issues Giving directions and advice

[Regional Development Sharing the summarized Bureau, etc.] Reflecting the obtained knowledge in technological information Giving directions and advice technical standards, projects, etc. to River Offices Investigating issues

Extracting issues Giving directions and advice

[River Office A] [River Office B] [River Office X] Constructing and Constructing and Constructing and maintaining levee maintaining levee maintaining levee