This document summarizes a study on hydrological modeling of boundary conditions for flash floods. It discusses what flash floods are and provides examples of earlier cases from the UK, US, and Hungary. It then describes the pilot area being studied, instrumentation used to measure boundary conditions like rainfall and soil moisture, and data analysis methods. The results showed precipitation is crucial but soil properties also important. Time of concentration and differences between watersheds were also factors. The document concludes the modeling software was suitable and consideration of boundary conditions through detailed data collection is necessary to understand flash flood events.

1. Hydrologycal modeling of
boundary conditions of flash
floods
Peter Hegedüs
University of Pécs, Hungary
YWP 2012 May 16-18, Sofia

2. Introduction
• What is a flash floods?
• What are the earlier cases?
• Why are we dealing with kind of floods?
• How can we measure boundary
conditions?
• What are the main goals of our study?

3. Generation of flash floods
• Increasing weather extremities
• Intensity of rainfall events are growing
• Rapid runoff according to relief
• Short concentration time

4. Earlier examples
• Boscastle (UK) 2004
• Rapid City (South-Dakota, USA)
1972
• Mátrakeresztes (Hungary, 2005)
Economic & Infrastructural damages
Private property losses
Life losses

5. Major property damages
• ~140m3/s peak discharge
• 100 houses damaged
Boscastle (UK)

6. Rapid city: dam breach

7. Pilot area properties
Bükkösd Stream’s watershed in SW
Hungary
• Small low-mountainous & hilly region
• Quite high relief
• 7 major flood events from the earlier
decades
• Relatively representative area (1.7 km 2 )

10. Measurement instruments
• Rain gauges
with EM-50 loggers
(Decagon Devices Inc.)
• 5-TM TDR-type
soil moisture sensors
• Stream gauges
http://ttk.pte.hu/kornyezettudomany/baross/galeria_kepek/decagon.JPG

11. Gauges indicated on orthophotos

12. Data analysis
• HEC-HMS 3.4 hydrologic modeling
program (Davis, USA)
• Arc GIS 9.2
• AGROTOPO soil database
• CLC land cover

13. Results
• Precipitation is crucial, however soil
properties are very important
• Time of concentration is also considerable
• Flood occurance in late spring, summer

14. Soil moisture
• Monthly averages (May, June) usually
between 12.1 – 19.8 % (VWC)
• Major differences

15. Time of concentration
• Peak discharge & precipitation values needed
• Intensity can be variable between a short range
of area
• More rapid concentration on tributary streams

16. Simulation of the flood event in
2010 May
• Numerous data
needed: water
content, canopy
cover, stream
discharge etc.
• Western and
eastern
watershed
differences

17. Conclusions
• HEC-HMS is suitable for modeling
• Plethora of data – consideration of
boundary condition analysis is necessary
• Rainfall intensity greatly varies –
secondary effect problems
• VWC & soil saturation calculation must be
cautious – software sensibility

18. Acknowledgement
The present study was funded by the “TÁMOP
4.2.1.B-10/2/KONV-2010-0002” Scolarship
(Developing competitiveness of universities in
the South Transdanubian Region)

19. Thank you for your attention!