An integrated study for the evaluation of natural and anthropogenic causes of flooding in small catchments based on geomorphological and meteorological data and modeling techniques: The case of the Xerias torrent (Corinth, Greece)

This study investigates the natural (hydro-meteorological and geomorphological) and anthropogenic factors responsible for flooding events in the ungauged Xerias torrent drainage basin, which is located in northeastern Peloponnesus, Greece. The study focuses on the analysis of the meteorological and hydrological processes of the most severe flooding event of the torrent, which happened on January 11th and 12th, 1997. The combined effects of spatially-varied precipitation and catchment characteristics on surface runoff were examined for this flash-flood event. The major meteorological feature of this event is associated with the passage of a cyclonic system accompanied by a cold front. 176 mm of rainfall in 10 hours was recorded at the meteorological station closest to the flooded area, demonstrating the severity of the event. In order to investigate the development and evolution of this cyclonic system, a numerical simulation was performed using a non-hydrostatic limited area atmospheric model on a very fine spatiotemporal resolution. Detailed atmospheric and soil parameters derived from the atmospheric simulation were imported into an integrated Geographical Information System (GIS) for further hydrological analysis and estimation of hydrographs throughout the catchment area. Additionally, the quantitative geomorphological characteristics of the Xerias torrent drainage basin were estimated and studied. The hierarchical drainage by stream order was investigated and the longitudinal profiles, as well as the stream power diagrams of the main stream and seven of its major tributaries, were constructed and analysed. The estimated maximum discharge for the outlet was similar to 610 m(3)/sec at almost 21:00 (12/12/1997), while this value for Solomos (9 km upstream from the river mouth) and Soussana (13.6 km upstream from the mouth) were estimated as similar to 540 m(3)/sec and similar to 410 m(3)/sec, respectively. Among the most important natural flood causes are extreme rainfall and the geomorphological characteristics of the drainage network. These features include irregularities in the number of channels that drain directly into streams of higher order, as well as the high bifurcation ratio values between the fourth and the fifth order streams and high channel gradients in the upper reaches of the tributaries. A crucial flood factor is also human interference, expressed by artificial confinement of the channels and the construction of inefficient bridges and pipes to facilitate the discharge.