Aynalem T. Tsegaw and Knut Alfredsen Comparison of continous time rainfall-runoff model, event based model and statistical methods to estimate floods at ungauged rural small catchments Aynalem T. Tsegaw and Knut Alfredsen (Tel.: [+47] 73592409 and Fax: [+47] 735 91298); E-mail addresses: aynalem.t.tasachew@ntnu.no, knut.alfredsen@ntnu.no 2. Back ground of estimation methods 2.1 Rational and Statistical methods Advantages Based on simple assumptions and simple to use Uses the observed data for analysis Disadvantages Contains parameters which are dificult to estimate (e.x. runoff coefficient) Do not consider antecedent moisture condition Based on stationarity assumption Based on questionable assumptions (ex.P200 = Q200) 2.2 Continous time rainfall-runoff model –DDD Incorporates the moisture and ground condition prior to flood producing preci. event Able to include the contribution of ground water Produces hydrographs(not only peak flood) Disadvantages /challenges Lack of availability of high spatial resolution of geographical data Lack of availability of high spatial and temporal resolution of hydro-meteorological data 3. Methodology used 3.1 Ungauged rural small catchments ( < = 50km2)- Regionalization of DDD Have short response times (few hours or even sub-hourly ) It is difficult to setup hydrological models Model parameters need to be transfered from gauged catchments 3.2 Distance distribution dynamics(DDD) model parameters-Regionalized hourly Multiple regression, physical similarity and combined methods 4. Results 4.1 Regionalization methods Multiple regression is best of all the three regionalization methods tested Physical similarity performed the poorest 4.2 Flood estimation methods Objectives: 1. 1 To compare flood estimation methods Event based model- Rational formula Statistical method – NIFS formula Continous time rainfall-runoff model –DDD 1.2 To select appropriate mthod to study: Impacts of future landuse changes Impacts of future climate changes 200years, 1 hr duration precipitatin 23.4mm/hr Case1. August 2013 when: The subsurface is 32.2% saturated No snow mel Case2. August 2013 when: The subsurface is 100% saturated No snow melt Case3. May 2013 when: The subsurface is 100% saturated There is snow melt Rational NIFS formula DDD 3.96 1.79 1.15 3.96 1.79 1.83 3.96 1.79 2.77 Small rural ungauged catchment (1.5km2)-used for case study 5. Conclusion Continuous rainfall-runoff hydrological models have the potential in studying flood risk management in small rural ungauged catchments under future land use and climate with better understanding of the hydrology leading up to the flood event. Acknowledgements We acknowledge the Research Council of Norway in funding the research work under the project www.klima2050.no