Flood design recipes vs. reality: can predictions for ungauged basins be trusted?

Abstract

Abstract. Despite the great scientific and technological advances in flood hydrology, everyday engineering practices still follow simplistic approaches that are easy to formally implement in ungauged areas. In general, these "recipes" have been developed many decades ago, based on field data from typically few experimental catchments. However, many of them have been neither updated nor validated across all hydroclimatic and geomorphological conditions. This has an obvious impact on the quality and reliability of hydrological studies, and, consequently, on the safety and cost of the related flood protection works. Preliminary results, based on historical flood data from Cyprus and Greece, indicate that a substantial revision of many aspects of flood engineering procedures is required, including the regionalization formulas as well as the modelling concepts themselves. In order to provide a consistent design framework and to ensure realistic predictions of the flood risk (a key issue of the 2007/60/EU Directive) in ungauged basins, it is necessary to rethink the current engineering practices. In this vein, the collection of reliable hydrological data would be essential for re-evaluating the existing "recipes", taking into account local peculiarities, and for updating the modelling methodologies as needed.

Hydrological response characteristics of Mediterranean catchments at different time scales: a meta-analysis

“…Nevertheless, this is not true for all Mediterranean catchments. A recent study by Efstratiadis et al (2014), who analysed several flood events in small catchments in Greece and Cyprus, highlighted that the key component of flood runoff is interflow, not overland flow. The authors also demonstrated that the initial soil moisture conditions drastically influence the basin response (which is a common conclusion of all studies in the Mediterranean).…”

Predicting the ungauged basin: model validation and realism assessment

“…This left the hydrological community with a wide range of methods that can improve the reliability of predictions in ungauged basins, but the lack of model validation methods in real case studies hinders a widespread use of these models. This is also expressed by Efstratiadis et al (2014), who discussed model realism in truly ungauged case studies. They concluded that flood design and modeling in ungauged basins is more than "blind application of recipes, " and one should carefully assess to what extent modeling results can be trusted.…”

“…Within these 10 years, the hydrological community developed a wide variety of new data acquisition techniques and approaches for hydrological modeling, to allow better estimations of model uncertainty and hydrological behavior in ungauged catchments. Although this resulted in a set of new tools and methods it remains difficult to put PUB into practice (Efstratiadis et al, 2014). We believe that this is strongly related to the fact that clear validation methods in PUB are still missing and are therefore omitted in many cases.…”

A curve number approach to formulate hydrological response units within distributed hydrological modelling

“…The above formula has been extracted and validated according to average CN-values obtained from the analysis of numerous flood events in a number of experimental river basins in Greece and Cyprus (Efstratiadis et al, 2014b). The minimum value of CN parameter is 28, while the maximum is 100.…”