Flood Control and Related Technology in Japan

Transcription

1 Flood Control and Related Technology in Japan Countermeasures against Urban Flooding Kingo Saeki, Deputy Director General Japan Sewage Works Association 1

2 Contents 1. Current Status of Sewerage in Japan 2. Current Status of Flood Damage 3. Current Status of Flood Control Measures 4. Current Technology for Flood Control 5. Flood Control in the Future 2

3 1. Current Status of Sewerage in Japan Percentage of population accessible to sewerage in Japan Sewerage construction accelerated in the 1960s. Percentage of sewered population: 75.8% Percentage of accessiblity to sanitary system: 87.6% (as of end March 2012) Percentage of Population( % ) 99.4% 98.9% 91.8% 90.9% 85.2% 82.7% 86.7% 74.6% 80.2% 60.5% Percentage of Access to Sanitary System Percentage of Sewered Population 73.9% 48.0% Privately owned sewerage Agricultural community Sewerage Onsite System Public Sewerage System Population of Municipality (Unit: Thousand) more than less than 5 3

4 Current Status of Sewerage in Japan (2) Expected Roles of Sewerage (1) Collect sanitary sewage and stormwater with Sewer Networks. (2) Properly treat sanitary sewage and safely drain stormwater with WWTPs, pumping stations, etc. (3) Recycle by-products without harming the environment and by converting them useful for people s life and social activities. (Treatment/utilization: Recycling facilities, etc.) Sewerage Service must achieve the above three roles. Symbiosis Stormwater Environment Water Resources Energy Symbiosis Recycle People s life Social activities Sanitary sewage Sewerage Artery Water Resources Energy Recycle Store Infiltrate Drain Vein Purify Regenerate 4

5 Change in the Amount of Damage Caused by Flood Change in the flood damage pattern The amount of flood damage has been increasing with the rapid urbanization since the 1960s while reducing fatalities. Damage (billion yen) Fatality (persons) 5

6 Concept of Urban Flooding Infiltration Before Urbanization In Urban cities, Strom water is drained to rivers and seas by way of sewerage. However, the Intensity of rainfall exceed design intensity of sewer, floods occur. Also, when level of receiving water become higher than planned water level, the sewer cannot drain runoff leading to flooding. Urban Flood River Flood Source: Ministry of Land, Infrastructure, transport and Tourism of Japan After Urbanization 平成 11 年 (1999)6 月博多駅博多口 6

7 2. Current Status of Flood Damage Causes of flood damage in Japan Since the 1960s, urban areas have expanded and land use has been advanced rapidly. As compared with urbanization, the construction of flood control facilities by river and sewerage system has been slower. Development in watershed has increased runoff resulting in shorter time of concentration. The capacity of old sewerage facilities is insufficient now. The frequency of intense rainfall has increased. Change in land use in Nerima, Suburb City, Tokyo Around 1960 Around 2010 Frequency of over the design rainfall events The frequency shows an increasing trend over the last 30 years. Runoff 50% Infiltration 50% Runoff 75% Infiltration 25% 7

8 Current Status of Flood Damage (2) Urban Flood Flooding in urban areas is increasing all over the world Damages to private assets and urban infrastructures Fatal accidents by flooding in underground spaces and underpasses September 2000 Flood due to torrential rains in Tokai Region (Nagoya City) July 2003 Underground flood in Fukuoka City September 2009 Hitachi City, Ibaraki Prefecture 8

9 Current Status of Flood Damage (3) Storm water drainage by sewerage It is a basic role of sewerage systems to drain stormwater in urban areas In order to protect people s lives and properties from urban floods, structural and non structural measures are taken. Demarcation of River and Sewerage Damage Ratio of Urban Flood Protection of Overflows from Channels Nationwide Rest including River Flood 52%, 1.3 trillion yen Urban Flood 48% 1.2 trillion yen Drainage of storm water to Public Waters To the river or sea Tokyo Rest including River Flood 22%, 22 billion yen Urban Flood 78% 48 billion yen 9

10 3. Current Status of Flood Control Promotion of comprehensive flood control measures Flood control measures are promoted with a combination of structural measures and self-help efforts. The former includes the improvement of sewers and pumping stations. The latter includes the provision of rainfall information to help private companies, residents, and the community to take disaster precautions. Structural measures Self-help efforts 10

11 Flood Control Measures (Technology for Structural Measures 1) Measures through the improvement of flood control facilities, structural measures Improvement of storm sewer and pumping station for draining storm water safely Improvement of storage facilities to compensate for limited sewer capacity in the downstream Improvement of stormwater infiltration facilities to reduce storm water runoff from the surface Construction of storage sewer using a large-diameter tunneling shield WadaYayoi Trunk Sewer, Tokyo 8.5 m in diameter Example of a new tunneling technology + boring Construction using two TBMs from one drive shaft to two reception shafts 11

12 Flood Control Measures (Technology for Structural Measures 2) Storm sewer constructed using a longdistance and curve pipe jacking Pipe jacking to avoid underground obstacles obstacle and to follow winding road alignment High durability drop shaft for large flow Inflow structure from collector to storage sewer while preventing vibration, noise, and structural damage Ventilation tower Shaft Dia. 14 m Height 58 m Source: Alpha Civil Engineering Inc. website 12

13 Flood Control Measures (Technology for Structural Measures 3) Effective and Efficient Operation of Pumping Stations To rationalize operation, water levels of sewer and receiving rivers are monitored. Operational standby pumps are installed to deal with a rapid stormwater inflow. Pump operation using water level info Optical fiber water level sensor Installation of an optical fiber water level gauge in the sewer Pumping station 13

14 Flood Control Measures (Technology for Structural Measures 4) Operational Standby Pump An operational standby pump can operate at full speed regardless of water level. The pump can be ready with the delivery valve full open prior to stormwater inflow and drain water promptly in response to surge. 14

15 Flood Control (Technology for Structural Measures 4) Stormwater Storage / Infiltration Facilities Improvement of stormwater storage facilities to compensate for the sewer capacity shortage in the downstream of network Improvement of stormwater infiltration facilities to reduce stormwater runoff These facilities are sometimes constructed due to discharge limit to the river or for recharging ground water in case of infiltration facilities. Storm water reservoir constructed under a baseball park Storage 15,000 m 3 Irrigation use 1,000 m 3 Storm water storage tank using recycled plastics Storage 10,000 m m high The circular area at the center is the stormwater reservoir. (Hiroshima City) (Musashino City) 15

16 Flood Control (Technology for Non- Structural Measures 1) Measures to caution private companies, residents, and the community for self-help efforts Provision of rainfall information Development and public release of a flood risk map Information on the water level of trunk sewers Provision of rainfall information In order to assist with flood prevention activities and evacuation actions, real-time rainfall information using the radar rainfall gauge system is provided on the web. It was created for sewerage maintenance and management use. (Tokyo) (For Tokyo Metropolitan Government official website) (For mobile phones) 16

17 Flood Control Measures (Technology for Non- Structural Measures 2) Development and public release of a flood risk map A flood map is developed and released to the public to inform citizens of the flood hazard caused by intense rainfall exceeding the design level of river channel. (Legend: Flood depth) 17

18 Flood Control (Technology for Non Structural Measures 3) Provision of information on the water level of trunk sewers Information is provided to citizens on the water level of shallow trunk sewers converted from rivers in order to be utilized for flood prevention activities. They are prone to overflows. Example of the display of the information on the water level inside trunk sewers (Nakano City) Installation of an electrical bulletin board (Nakano City: Momozono-kawa trunk sewer) 18

19 Flood Control (Technology for Self Help Measures) Countermeasures voluntarily taken by residents (Self-help efforts) Promotion of self-help disaster response Runoff reduction in private property Examples of flood mitigation by citizens Flood Barrier to Protect Basement Stormwater infiltration cleanout Stormwater infiltration trench 19

20 5. Flood Control Measures in the Future (1) Shift to the human oriented target setting It is necessary to shift the target of flood control measures from the conventional rainfall intensity or natural parameter to the human oriented target. Targets should be set from the human perspective with the characteristics of flooding in the relevant area taken into consideration. (2) Planned implementation of structural measures, strengthening of nonstructural measures, and promotion of self-help efforts While strengthening structural measures as planned, it is also necessary to promote self-help efforts by residents in order to minimize the damage. In order to lead to effective self-help efforts, it is important to take non-structural measures, such as providing information. (3) Prioritizing the area Instead of promoting structural measures at the same pace for all areas, it is necessary to determine the areas on which investment should be prioritized. Then, the areas should have intensive investment by setting a deadline. (4) Technology development for effective utilization of existing facilities Networking of the existing facilities by installing interceptors, and development of technology to efficiently use, operate, and manage them using ICT. 20

21 Thank you for your attention 21