1. 4 th International Symposium on Flood Defence Generation of Severe Flood Scenarios by Stochastic Rainfall in Combination with a Rainfall Runoff Model U. Petry, Y. Hundecha, M. Pahlow, A. Schumann Institute of Hydrology, Water Resources Management and Environmental Engineering, Ruhr-University Bochum, Germany 1

2. 4 th International Symposium on Flood Defence Generation of Severe Flood Scenarios by Stochastic Rainfall in Combination with a Rainfall Runoff Model 2 Contents introduction concepts of the different models the case study evaluation of hydrological risk conclusion

3. 4 th International Symposium on Flood Defence Generation of Severe Flood Scenarios by Stochastic Rainfall in Combination with a Rainfall Runoff Model 3 Motivation objective: evaluation of efficiency of flood protection measures (reservoir) safety approach:  one single parameter (peak probability) for hydrological risk assessment  no detail information about conditions for system failure  uncertainty in the applied level of protection risk based approach:  considering different features of flood events (spatial distribution)  conditional probabilities for system failure  requires broad data base generating flood scenarios by stochastic rainfall in combination with a rainfall runoff model

4. 4 th International Symposium on Flood Defence Generation of Severe Flood Scenarios by Stochastic Rainfall in Combination with a Rainfall Runoff Model 4 Approach of generating extreme flood events stochastic rainfall model 1. Generation daily time series of rainfall disaggregation model hourly time series of rainfall rainfall runoff model hourly time series of flow 2. Disaggregation3. Simulation

5. 4 th International Symposium on Flood Defence Generation of Severe Flood Scenarios by Stochastic Rainfall in Combination with a Rainfall Runoff Model 5 Contents introduction concepts of the different models the case study evaluation of hydrological risk conclusion / discussion

6. 4 th International Symposium on Flood Defence Generation of Severe Flood Scenarios by Stochastic Rainfall in Combination with a Rainfall Runoff Model 6 The stochastic rainfall model combination of multivariate autoregressive model and mixture of Gamma / Pareto distribution function (Hundecha et al., 2008) objectives:  reproduction of the statistical properties of the historical rainfall at each site  maintenance of the historical spatial correlation structure

7. 4 th International Symposium on Flood Defence Generation of Severe Flood Scenarios by Stochastic Rainfall in Combination with a Rainfall Runoff Model 7 The disaggregation models combination of an univariate and a multivariate rainfall model in a disaggregation framework (Koutsoyiannis et al., 2003) univariate model (Hyetos):  generating a synthetic rainfall series at one location multivariate model (MuDRain):  considering the temporal statistics and the spatial correlation between the stations work flow of disaggregation: Hyetos temporal disaggregation at reference station spatial-temporal disaggregation at all other stations generating daily rainfall at multiple locations MuDRain

8. 4 th International Symposium on Flood Defence Generation of Severe Flood Scenarios by Stochastic Rainfall in Combination with a Rainfall Runoff Model 8 The rainfall runoff model proven conceptual model NASIM (Hydrotec, Germany) allows short-, middle- and long-term simulations (flexible increment for in- / output) simulation of important hydrological processes (e.g. retention, snow melting, rainfall, runoff formation, flood routing) implementation of a reservoir model (operation rules)

9. 4 th International Symposium on Flood Defence Generation of Severe Flood Scenarios by Stochastic Rainfall in Combination with a Rainfall Runoff Model 9 Contents introduction concepts of the different models the case study evaluation of hydrological risk conclusion / discussion

10. 4 th International Symposium on Flood Defence Generation of Severe Flood Scenarios by Stochastic Rainfall in Combination with a Rainfall Runoff Model 10 The Wupper catchment (813 km²)

11. 4 th International Symposium on Flood Defence Generation of Severe Flood Scenarios by Stochastic Rainfall in Combination with a Rainfall Runoff Model 11 Results of rainfall disaggregation MuDRain (statistics based on hourly time steps) sample station 1sample station 2 mean variance

12. 4 th International Symposium on Flood Defence Generation of Severe Flood Scenarios by Stochastic Rainfall in Combination with a Rainfall Runoff Model 12 Results of rainfall disaggregation MuDRain (maxima based on hourly time steps) sample station 1sample station 2 annual 1-hour-maxima precipitation annual 3-hour-maxima precipitation

13. 4 th International Symposium on Flood Defence Generation of Severe Flood Scenarios by Stochastic Rainfall in Combination with a Rainfall Runoff Model 13 Results of rainfall runoff simulation (probabilities based on hourly time steps) Annual maxima of discharge peaks at gauge Kluserbrücke with Wupper reservoir

14. 4 th International Symposium on Flood Defence Generation of Severe Flood Scenarios by Stochastic Rainfall in Combination with a Rainfall Runoff Model 14 Results of rainfall runoff simulation (probabilities based on hourly time steps) Annual maxima of discharge peaks at gauge Kluserbrücke with Wupper reservoir

15. 4 th International Symposium on Flood Defence Generation of Severe Flood Scenarios by Stochastic Rainfall in Combination with a Rainfall Runoff Model Contents introduction concepts of the different models the case study evaluation of hydrological risk conclusion / discussion 15

16. 4 th International Symposium on Flood Defence Generation of Severe Flood Scenarios by Stochastic Rainfall in Combination with a Rainfall Runoff Model evaluation of hydrological risk 16 evaluation of hydrological risk according to local stages of flood warning (discharge at gauge Kluserbrücke)  up to 80 m³ s -1  no flood conditions  80 to 150 m³ s -1  severe flood conditions  more than 150 m³ s -1  critical flood conditions

17. 4 th International Symposium on Flood Defence Generation of Severe Flood Scenarios by Stochastic Rainfall in Combination with a Rainfall Runoff Model evaluation of hydrological risk 17 simulated annual maxima discharge at gauge Kluserbrücke

18. 4 th International Symposium on Flood Defence Generation of Severe Flood Scenarios by Stochastic Rainfall in Combination with a Rainfall Runoff Model evaluation of hydrological risk 18 separating events with peak < 80 m³ s -1 at gauge Kluserbrücke without reservoir simulated annual maxima discharge at gauge Kluserbrücke

19. 4 th International Symposium on Flood Defence Generation of Severe Flood Scenarios by Stochastic Rainfall in Combination with a Rainfall Runoff Model evaluation of hydrological risk 19 evaluation of hydrological risk according to local stages of flood warning  up to 80 m³ s -1  no flood conditions  80 to 150 m³ s -1  severe flood conditions  more than 150 m³ s -1  critical flood conditions evaluation of the efficiency of the Wupper reservoir  reduction of discharge peak at gauge Kluserbrücke  up to 80 m³ s -1  reservoir efficient  80 to 150 m³ s -1  reservoir less efficient  more than 150 m³ s -1  reservoir inefficient reasons for different efficiency levels (flood conditions)  available flood control storage, inflow to reservoir, spatial distribution of discharge

20. 4 th International Symposium on Flood Defence Generation of Severe Flood Scenarios by Stochastic Rainfall in Combination with a Rainfall Runoff Model evaluation of hydrological risk (available flood control storage, inflow to reservoir) 20 reservoir inefficient reservoir less efficient reservoir efficient

21. 4 th International Symposium on Flood Defence Generation of Severe Flood Scenarios by Stochastic Rainfall in Combination with a Rainfall Runoff Model evaluation of hydrological risk (available flood control storage, inflow to reservoir) 21 flood control storage filled up to 50 % flood control storage filled more than 50 % thresholds for classification  10 m³ s -1  60 m³ s -1  100 m³ s -1 thresholds for classification  40 m³ s -1  60 m³ s -1  100 m³ s -1

22. 4 th International Symposium on Flood Defence Generation of Severe Flood Scenarios by Stochastic Rainfall in Combination with a Rainfall Runoff Model evaluation of hydrological risk (depth of runoff) 22 storage filled up to 50 %, inflow < 10 m³ s -1 threshold for classification  200 mm

23. 4 th International Symposium on Flood Defence Generation of Severe Flood Scenarios by Stochastic Rainfall in Combination with a Rainfall Runoff Model evaluation of hydrological risk (total number of events) 23 discharge at gauge unaffected by reservoir simulated runoff filling of flood control storage evaluation of reservoir efficiency ≤ 80 m³ s -1 inflow to reservoir > 80 m³ s -1 339 661 more than 50 % up to 50 % 198 463 7 depth of runoff downstream < 10 m³ s -1 10-60 m³ s -1 60-100 m³ s -1 20 110 130 147 < 200 mm  200 mm less efficient inefficient efficient less efficient inefficient 173 46 127 < 100 mm  100 mm 6 < 125 mm  125 mm > 100 m³ s -1 13 efficient 113 34 < 50 mm  50 mm

24. 4 th International Symposium on Flood Defence Generation of Severe Flood Scenarios by Stochastic Rainfall in Combination with a Rainfall Runoff Model evaluation of hydrological risk (probabilities) 24 discharge at gauge unaffected by reservoir simulated runoff filling of flood control storage evaluation of reservoir efficiency ≤ 80 m³ s -1 inflow to reservoir > 80 m³ s -1 0.34 0.66 more than 50 % up to 50 % 0.30 0.70 0.54 depth of runoff downstream < 10 m³ s -1 10-60 m³ s -1 60-100 m³ s -1 0.15 0.85 0.28 0.32 < 200 mm  200 mm less efficient inefficient efficient less efficient inefficient 0.37 0.27 0.73 < 100 mm  100 mm 0.46 < 125 mm  125 mm > 100 m³ s -1 0.03 less efficient efficient 0.77 0.23 < 50 mm  50 mm (0.27) (0.07) starting point

25. 4 th International Symposium on Flood Defence Generation of Severe Flood Scenarios by Stochastic Rainfall in Combination with a Rainfall Runoff Model Conclusion objective: risk-based approach for evaluation of flood protection measures combination of stochastic rainfall model, disaggregation model and rainfall runoff model  good agreement of historical and simulated rainfall and runoff  broad data base of flood events allow consideration of (probabilities of) differentiated flood characteristic evaluation of risk (efficiency) for different conditions by conditional probabilities 25 further steps:  simulate longer time series to get better data base for extreme floods  different criteria for evaluation of efficiency (e.g. reduction of flood damage)

26. 4 th International Symposium on Flood Defence Generation of Severe Flood Scenarios by Stochastic Rainfall in Combination with a Rainfall Runoff Model Thanks to German Ministry for Education and Research (BMBF) / RIMAX the water board of the Wupper catchment the German Weather Service 26... and the audience for its attention !!! contact: uwe.petry@rub.de