1. Evaluation of the effect of the disaster prevention technique using coastal farmlands Kiri H. and H. Tanji National Institute for Rural Engineering National Agriculture and Food Research Organization (NARO) 1

2. The Great East Japan Earthquake Tsunami Inundation Run-up Local time : 14:46 March 11, 2011 Magnitude : 9.0 The rupture area : 450 km x 200km Stricken coast : 1,300 km Inundated area : over 400km 2 2 Joint survey group

3. Seawall and Coastal Dikes 3

4. Drainage facilities and farmlands 4

5. To prevent huge tsunami disasters What should we do? Committee for Technical Investigation on Countermeasures for Earthquakes and Tsunamis Based on the Lessons Learned from the Earthquake The Central Disaster Management Council 5 The tsunami disaster in this scale is not a just once experience. It repeat in 600 to 1,000 years.

6. Basic principles for Tsunami countermeasures Return period 100~150 yr Not include the tsunami in 2011 Construct coastal protection facilities and breakwaters For the future tsunami countermeasures … require the assumption of two levels of tsunamis. Possible Largest ( Level 2 ) Tsunamis Frequent ( Level 1 ) Return period >1,000 yr Comprehensive disaster management measures Focus on the evacuation of local residents 6

7. The Disaster-prevention farmland 7 Moving settlements near the coast to hilltops. Readjusting large farms in the lowland area along the coast. Permitting flooding of farmland in the case of a tsunami or a storm surge exceeding the planned height. Having the function of a second dike assigned to inland roads and protecting property and human lives in evacuation space. Concept

8. Evaluation by a Hydraulic Model Test 8

9. Hydraulic Models Normal farmland Disaster-prevention farmland 9

10. Offshore wave 10

11. Nearshore wave 11

12. Tsunami run-up velocity ~Normal farmlands~ Average 10.5 m/s Front speed Coast < Inland 12

13. Tsunami run-up velocity ~Disaster-prevention farmland~ Average 5.9 m/s Average 10.5 m/s Normal farmland Energy dissipated ! 13

14. Inundation depth ~Short wavelength~ 14

15. Inundation depth ~Long wavelength~ 15

16. Conclusions 16 The effect of coastal farmland for flood prevention technique was evaluated by hydraulic model test. The disaster prevention technique using coastal farmlands dissipates the energy of tsunami run-up. The result of the hydraulic model test indicated that coastal farmlands decrease tsunami run-up for two minutes. The effect of the disaster-prevention farmland at a model coast is also confirmed by a numerical simulation.