Flash flooding in Spain: geomorphological approaches supporting flood frequency analysis, and the implications for the design of structures

Conventional methods for the estimation of flood frequency are generally based on the statistical analysis of data series resulting from the measurement of water levels at specific locations, which are translated into discharges (m³/s) using standard stage/discharge relationships. Subsequently, these gauged flows are used to identify the largest flood event experienced by a river or catchment, and to produce growth curves used in the estimation of the return periods of specific flood events, as well as in the calculation of discharges for specific required design events (e.g. return period 1 in 100 year). In areas where gauging data records are scarce, and/or the data series are short or interrupted, geomorphological interpretation of the physical environment, dating of fluvial deposits and flooding episodes and hydraulic reconstruction of past flood events can be used as complementary tools aiding conventional hydrological and flood frequency analysis methods. This paper will discuss the undertaking of this approach in the Guadalope Catchment in northeast Spain. It will examine the findings in relation to the inadequate design of existing structures such as dams, spillways, canals and reservoirs, and will also look at the potential risks associated with flooding at present.