FLOOD DISASTER AND SAFE EVACUATION IN DRAINAGE AREA WITH SMALL RIVERSYukimi WAKAYAMA, Taisuke ISHIGAKI
Civil, Environmental and Applied Systems Engineering, Graduate School of Science and Engineering, Kansai University
INTRODUCTION
The frequency of fluvial floods has been lower than before due to flood control, but the frequency of pluvial
floods becomes higher in drainage area with small rivers. To mitigate damages of such floods, it is important
to strengthen not only the structural measures but also nonstructural measures. In this paper, the difficulty ofevacuation and the time to start evacuation are discussed when pluvial and fluvial flooding occur
simultaneously.

2. FLOOD SIMULATION
Fig.5 shows the results of the flood analysis. In this paper, the results for levee break point 1 are shown. t=0(h)is just before the fluvial flood occurs. The result at t=0(h) in Fig.5 (a) indicates that pluvial flooding occurred
before fluvial flooding started. Residents in flooded areas need to evacuate early because floodwaters canreach the second floor.

1. SIMULATION MODEL
Fig.1 shows the study area. In this area, pluvial floods caused by flooding of small rivers have frequently
occurred. Flood in study area is calculated using InfoWorksICM. Fig.2 shows the structure of calculation model.
<Drainage system>
Rainfall

Sewerage pipes

3. SAFE EVACUATION
Small rivers

Pumping stations

Main river (Yura river)Fig.1 Study area(Fukuchiyama City, Kyoto Prefecture, Japan)

Fig.2 Calculation model structure of InfoWorksICM

Fig.5 The results of the flood analysis

The time when the specific force per unit width becomes larger than 0.080(m3/m) is defined as theevacuation difficulty time (Asai et al.(2010)). The evacuation start time for each community association area
was revealed using the shortest route search tool of GIS.
One-third of the people who need evacuation will have the difficulty immediately after the peak of rainfall(Fig.6). Pluvial flood has already occurred just before fluvial flood occurs, and about half of those who need toevacuate are already having the difficulty. Also the road shown in Fig.7[a] is difficult to evacuate before fluvial
flooding occurs, even though most of the inundation depth less than 0.5m as shown in Fig.5(a).

Fig.3 shows the results of the calculation of pluvial flooding in 2014. Verification of the model anddetermination of coefficients were done by using the data of the pluvial flooding that occurred in 2014. The
accuracy of the inspection range compared with actually depth is MAE=0.21(m), RMSE=0.28(m), and R=0.55.
The flood discharge was calculated by using the River Planning Simulator Runoff Analysis System of the Japan
Institute of Country-ology and Engineering. Yura River basin was divided with reference to Takasao et al.
(1988). The coefficient was calibrated using rainfall data at the time of Typhoon 2013. In this study, theextended rainfall of Typhoon 18, 2013, of which total rainfall is 494mm for two days, are used as the extreme
condition. The conveyance discharge at Fukuchiyama is 6,500 m3/s. Fig.4 shows the extreme rainfall
hyetograph, and the conveyance discharge hydrograph.
Fig.6 Number of people who can evacuate at each time

Fig.7 Evacuation time of road and evacuation start time

10000

Rainfall intensity
discharge

Discharge (m3/s)

8000

Conveyance discharge
6000
4000
2000
0-30Fig.3 Results of the calculation of pluvial flood in 2014.

-20-10010Time(h)2030010203040506070809010040Fig.4 The extreme rainfall hyetograph and hydrograph

Rainfall intensity(mm/h)

CONCLUTIONSIn this study, safe evacuation was investigated by using inundation analysis results during pluvial and fluvial
floods. The impact of pluvial flooding must be taken seriously because pluvial flooding before fluvial flood
occurred were serious.

REFERENCES
 Takasao, T., Takara, K., Mitani, Y., and Fueta, T. (1988) Real-time calibration of rainfall measured by a radarfor flood runoff forecasting, DPRI Annuals, Disaster Prevention Research Institute, Kyoto University, No.31 B2, pp. 1-14. (in Japanese) Asai et al. (2010): SAFETY ANALYSIS OF EVACUATION ROUTES CONSIDERING ELDERLY PERSONS DURING
UNDERGROUND FLOODING, Journal of Hydroscience and Hydraulic Engineering, Vol.28, No.2 November,
15-21.
CONTACT Yukimi WAKAYAMA, Graduate student, Kansai University, Japan (k669675@kansai-u.ac.jp)