Flood Generation and Classification of a Semi-Arid Intermittent Flow Watershed: Evrotas River Ourania Tzoraki a , David Cooper B , Thomas Kjeldsen C , Nikolaos P
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This article was downloaded by: [Cyprus University Of Technology ], [Ourania Tzoraki] On: 21 March 2013, At: 07:28 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK International Journal of River Basin Management Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/trbm20 Flood generation and classification of a semi-arid intermittent flow watershed: Evrotas river Ourania Tzoraki a , David Cooper b , Thomas Kjeldsen c , Nikolaos P. Nikolaidis d , Christos Gamvroudis e , Jochen Froebrich f , Erik Querner g , Francesc Gallart h & Nikolaos Karalemas i a Technical University of Crete (TUC), Chania, Greece b Centre for Ecology and Hydrology (CEH), Bangor, United Kingdom c Centre for Ecology and Hydrology (CEH), Wallingford, United Kingdom d Technical University of Crete (TUC), Chania, Greece e Technical University of Crete (TUC), Chania, Greece f Centre for Water and Climate (CWK), Alterra, Wageningen, The Netherlands g Centre for Water and Climate (CWK), Alterra, Wageningen, The Netherlands h Institute of Environmental Assessment and Water Research (IDAEA), CSIC, Barcelona, Spain i Faculty of Geology, University of Athens, Greece To cite this article: Ourania Tzoraki , David Cooper , Thomas Kjeldsen , Nikolaos P. Nikolaidis , Christos Gamvroudis , Jochen Froebrich , Erik Querner , Francesc Gallart & Nikolaos Karalemas (2013): Flood generation and classification of a semi-arid intermittent flow watershed: Evrotas river, International Journal of River Basin Management, 11:1, 77-92 To link to this article: http://dx.doi.org/10.1080/15715124.2013.768623 PLEASE SCROLL DOWN FOR ARTICLE Full terms and conditions of use: http://www.tandfonline.com/page/terms-and-conditions This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae, and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand, or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material. Intl. J. River Basin Management Vol. 11, No. 1 (March 2013), pp. 77–92 # 2013 International Association for Hydro-Environment Engineering and Research Research paper Flood generation and classification of a semi-arid intermittent flow watershed: Evrotas river OURANIA TZORAKI, Technical University of Crete (TUC), Chania, Greece. Email: [email protected] DAVID COOPER, Centre for Ecology and Hydrology (CEH), Bangor, United Kingdom. THOMAS KJELDSEN, Centre for Ecology and Hydrology (CEH), Wallingford, United Kingdom. NIKOLAOS P. NIKOLAIDIS, Technical University of Crete (TUC), Chania, Greece. CHRISTOS GAMVROUDIS, Technical University of Crete (TUC), Chania, Greece. JOCHEN FROEBRICH, Centre for Water and Climate (CWK), Alterra, Wageningen, The Netherlands. ERIK QUERNER, Centre for Water and Climate (CWK), Alterra, Wageningen, The Netherlands. FRANCESC GALLART, Institute of Environmental Assessment and Water Research (IDAEA), CSIC, Barcelona, Spain. NIKOLAOS KARALEMAS, Faculty of Geology, University of Athens, Greece. ABSTRACT Hourly water level measurements were used to investigate the flood characteristics of a semi-arid river in Greece, the Evrotas. Flood events are analysed with respect to flood magnitude and occurrence and the performance of Curve Number approach over a period of 2007–2011. A distributed model, Soil and Water Assessment Tool, is used to simulate the historic floods (1970–2010) from the available rainfall data, and the performance of the model assessed. A new flood classification method was suggested the Peaks-Duration Over Threshold method that defines three flood types: ‘usual’, ‘ecologi- cal’ and ‘hazardous’. We classify the basin according to the flood type for the most serious past simulated flood events. The proportion of hazardous floods in the main stream is estimated to be 5–7% with a lower figure in tributaries. Flood Status Frequency Graphs and radar plots are used to show the seasonality of simulated floods. In the Evrotas, the seasonality pattern of hazardous flood is in agreement with other studies in Greece and differs from other major European floods. The classification in terms of flood types in combination with flood type seasonality is identified as an important tool in flood management and restoration. Keywords: Temporary streams; floods; river basin; SWAT model; flood seasonality; flood type; Greece Downloaded by [Cyprus University Of Technology ], [Ourania Tzoraki] at 07:28 21 March 2013 1 Introduction Lanen et al. 2007). In an area where water limitation is a major concern, a priority for river basin managers is to estimate and Many catastrophic flood events causing serious damage and improve the retention of rainwater in the catchment while also threatening human life are recorded each year in the Mediterra- controlling the effect of floods. This requires improved under- nean area. In the future under projected climate change, an standing of the flood generating processes for the successful increase in flood frequency and magnitude is expected (Van design of the flood relief and related schemes. Catchment Received 2 October 2012. Accepted 17 January 2013. ISSN 1571-5124 print/ISSN 1814-2060 online http://dx.doi.org/10.1080/15715124.2013.768623 http://www.tandfonline.com 77 78 Ourania Tzoraki et al. characteristics including topography (elevation, area, slope, and the CN method captures poorly the temporal runoff dynamic drainage density), spatial variation of soil types, geological of monsoonal climates and areas dominated by complex hydro- substrate, and vegetation density all play a role in determining geology (White et al. 2011). Also in karstic basins, floods are catchment hydrology in semi-arid catchments (Belmonte and initiated only if a rainfall threshold is exceeded (Kourgialas Beltra´n 2001, Marchi et al. 2010), and the magnitude and et al. 2010), supporting the assumption that the local geology occurrence of floods. is a key factor in flood generation process. The authors identified In Mediterranean rivers, the hydrological regime is character- three flash flood classes depending on antecedent soil moisture ized by flash floods (Vivoni et al. 2006), fluctuations in conditions (Kourgialas et al. 2010). A modified CN equation floodplain inundation (Tockner et al. 2000), spring baseflow in the SWAT model gave satisfactory streamflow predictions of (Rimmer and Salingar 2006) and periods where there is no Ethiopian and Catskill Mountains river basins (White et al. flow (Nikolopoulos and Anagnostou 2011). The behaviour of 2011). Physical properties of the soil are affected by rainfall such rivers is difficult to study and predict (Gallart et al. 2008, events enhancing runoff velocity, transport capacity and redu- Kirkby et al. 2011) due to limited flow data, difficulties in instru- cing the lag time of a flash flood event (Fohrer et al. 1999, Kour- ment installation and operation in such environments (Tzoraki gialas et al. 2011). et al. 2007, Kourgialas et al. 2010, Moraetis et al. 2010), and We analyse flood events with respect to flood magnitude and insufficient precipitation measurement in an area where rainfall occurrence and the performance of CN approach to flood simu- is highly variable in time and space. Post-event analysis of 25 lation in the Evrotas catchment, Greece using high frequency example floods (Marchi et al. 2010), strengthened the belief available flow data of the period 2007–2011. The SWAT distrib- that available methodologies for flood prediction are highly uted rainfall–runoff model is calibrated and validated on data uncertain and new approaches should be developed for flood over the period 2000–2011. The model is then used with precipi- analysis. Flood events in perennial rivers have been studied by tation data from 1970 to 2000 to generate a historic flow record Gaume et al. (2009) with a view to creating an atlas of over this period. We delineate homogenous regions according extreme flash floods across Europe. They observed a strong to flood classes for the most serious past simulated flood seasonality to flood occurrence, revealing different forcing events, identifying the areas of high flood risk. Finally, we mechanisms in each region. assign flood classes frequency and location of occurrence. The estimation of flood distribution characteristics is ideally based on a long-term flow record. However, such a record is 1.1 Catchment characteristics often not available; in which case flood estimates can be derived using a model based on precipitation records as drivers Our study catchment, the Evrotas, like many rivers in the Med- and catchment characteristics as response moderators. The use iterranean region, is a temporary river with intermittent flow in of such a model introduces additional uncertainty into flood the main stream and many tributaries. The basin (Figure 1) is characterization because of uncertainty in the drivers and mod- located in the south-eastern Peloponnese (Greece) covering erators themselves, and in the relationship