Geomorphology plays an important role in hydrological processes, as it largely controls a catchment’s hydrologic response. Study of morphometric characteristics becomes even more significant in ungauged basins, especially when systematic hydrological data are scarce. A very well suited tool for accurate quantification of these characteristics is GIS software and especially ArcHydro model. In this work, four catchments in Greece, with rich flooding history are studied in terms of flood hazard spatial distribution. ArcHydro is used for rapid computation of catchment and sub-catchment characteristics. Based on these computations and with the aid of the time-area method, instantaneous unit hydrographs are developed in numerous locations across each catchment. Subsequently, peak discharge values extracted from these hydrographs, are interpolated across each catchment to visualize the runoff pattern, highlighting the areas where there is an inherent tendency for higher peak flow rates. In this way, the method allows the detection of locations where higher peak discharge creates a higher flood hazard potential. Results of the method are compared with historical floods damages for verification purposes, showing good correlation with the resulting flood hazard zonation.

The drainage basin of the Mediterranean Sea, accounting for some 4,184 10³ km² (including the R. Nile), is larger than that of the Black Sea (2,320 10³ km²). Estimates of the annual water load for the Mediterranean and Black Sea rivers are 550 km³ and 395 km³, respectively. According to these figures, the corresponding values of annual water yield 130 m³/km² (Med) and 170 m³/km² (Black) show that Black Sea Rivers have a larger water capacity. In the case of the Black Sea, the large river systems (>10,000 km²) drain 87% of its catchment supplying the 60% of its freshwater load. In contrast, the medium and small (<10,000 km²) Mediterranean Sea rivers, although they drain 16% of its watershed, supply almost 70% of its water load. The impact of river damming has already reduced the freshwater fluxes by 40% for the Mediterranean and <10% for the Black Sea.

This study deals with the evaluation of flash flood hazard in the ungauged Diakoniaris torrent drainage basin which is a fifth order stream located in northwestern Peloponnese. Diakoniaris drains an area of 27.83 km² and discharges into the Gulf of Patras. Its lower reaches flow through the city of Patras and has suffered from intense human interferences due to increased urbanization during the last decades. For the purposes of the study the quantitative geomorphological characteristics of the basin were estimated and studied focusing on the investigation of the hierarchical drainage by stream order. The longitudinal profiles as well as the stream power diagrams of the main stream channel and its major tributaries were constructed and analyzed. A routing model based on runoff travel time was created within GIS environment in order to estimate the discharge at the outlet of the basin for an assumed extreme rainfall event.

Flooding is one of the most important types of disasters in southern Greece with many victims and extended damages over the last century. The increase in population together with the augmented pressure for urban expansion has increased flood risk during the last decades considerably across southern Europe. Peloponnese is not an exception in this regime, recording a significant amount of flood events and casualties. In this work, a catalogue of flooding phenomena during the period 1896-2010 in Peloponnese has been compiled based on numerous sources. Based on this record the temporal and spatial distribution of flood events and victims was examined. In total, 102 events were identified, causing 57 human casualties and inflicting extensive damage across the study area. Results showed seasonality patterns with more events clustering in November. They also showed that urban and coastal environments tend to present higher flood recurrence rates than mountainous and rural areas. An increasing trend in reported flood event numbers and casualties during the last decades was discovered. Moreover, spatial patterns were identified highlighting areas with higher flood recurrence rates across the region studied.

The increase in urban population and the continuous pressure for cities’ expansion along with the increase in urban flooding phenomena in Greece and worldwide, stress the need for enhancement of flood risk mitigation efforts. West Athens urban area, in Greece, experienced a significant population clustering since the 1950s leading, in some occasions, to a poorly-planned development, even in areas with imminent flood risk. An issue becomes apparent, taking into account the rich flooding record, the extended damages in property and infrastructure and the 76 flood victims during the last century in the area. In this work, flood hazard is assessed in 10 municipalities of West Athens, with the application of a GIS-based methodology that exploits catchment morphometric characteristics to delineate flood hazard zones. Historical flood events are reconstructed to provide better understanding of the flooding problem in the area. Finally flood hazard was studied in conjunction with vulnerability to estimate flood risk spatial distribution. The results showed that areas around Fleva and Eschatia torrent, especially Mpournazi, parts of Ilion and Kamatero and some parts of Peristeri presented the highest flood hazard and risk values. Additionally, moderate flood risk appeared in several mountain torrents in west parts of Petroupoli and Peristeri.

The present paper examines the maximum flow rate and soil erosion of the watershed of the Dadia stream. The use of empiric forms took place, in order to calculate the maximum flow rate, while the volume of soil erosion was estimated by the Universal Soil Loss Equation (USLE) and the modified Gavrilovič method. The methods above classified the sub-basins and the TopRunDF Model was applied to the most important watershed of all. The TopRunDF is a simulation model based on GIS, developed by Scheild and Rickenmann (2009) and predicts the repository and the amount of sediment deposition on the torrential fan. An extensive use of GIS took also place, for the simulation parameters to be defined and for the model to be wholly depicted.

In August 2009 a wildfire in northeast Attica, in Greece, burned approximately 187 square km of forest and agricultural land, inducing significant damages in properties and infrastructure. The fire extended in 19 hydrological basins affecting substantially the hydrological processes in the area and raising significant questions about changes in their flood risk regime. In this work, possible changes in peak discharge and the total runoff volume after intense rainfall, due to the wildfire effects in Charadros and Rapentosa catchments in Marathonas, Greece, are investigated. The results showed that peak discharge resulting from the 50-year return period design storm will be increased between 13.8% and 19.8% in Rapentosa and Charadros. Peak flow rate resulting from the 100-year design storm will increase between 11.4% and 16.7% in the two basins. Total runoff volume presents an increase of 9.5% to 16.7% in the two catchments depending on the storm scenario. Furthermore, it is shown that a new probability regime has been introduced, as discharges connected with storms with annual probability of 1%, before the fire, will now require storms of 1.6% annual probability of occurring in Charadros and 1.3% in Rapentosa.

The geoenvironmental setting is a determinative factor in catchments’ response during heavy precipitation events. In this work, the flash flood of 2008 in Potamoula (Aetoloakarnania, Greece) is investigated in terms of hydrologic and geomorphologic features. The study area is a relatively small, partly forested, rural catchment situated in western Greece with steep mountainous topography and with flysch being the prevailing lithology. In 2nd of October 2008 a storm of high intensity (measured up to 280 mm in 24 hours) produced noteworthy quantities of runoff which inundated the lower parts of the small valley, inflicting damage to a significant number of structures and killing two people. Field investigations were carried out to record the extent and characteristics of damage, the physical attributes of flooding such as the peak discharge, the geomorphic effects and the geological factors affecting the local hydrology. The results were investigated in comparison with geomorphological and geological evidence showing that this event, although extreme, corresponded very well to the geological record of the area. Finally, runoff response of the catchment was assessed with respect to the geology of the basin.

Three approaches have been used to analyze the hydrograph of Inountas River basin in two reaches. Flow in each reach was estimated by combining the water level records with monthly field flow measurements. Base-flow separation has been accomplished by using the SWAT (Soil and Water Assessment Tool) baseflow filter program. The fraction of water yield contributed by baseflow was estimated between 0.76-0.62 for Kladas reach and 0.79-0.70 for Vassaras reach respectively. Flow duration curve for each reach was constructed from daily flow data. The flow-probability relationship, Q₅₀ for Vassaras reach had a value of 0.164 and for Kladas 0.198. The ratio Q₉₀/Q₅₀ for Vassaras reach was 0.689 indicating that 68.9% of Vassaras stream flow was contributed from groundwater storage. The calculated recession factors were for Kladas reach 0.024 (10/04/2010- 04/06/2010) and for Vassaras reach 0.009 (20/03/2010-27/05/2010) and 0.005 (09/07/2010-11/10/2010).

In order to research soil moisture of a limestone peak forest plain in Laibin, Guangxi Province, the investigation had chosen three lands, a maize field covered by mulching film, a common maize field and a set-aside land, from March, 2006 to April, 2007, measuring soil moisture content and potential at the depths ranging from 0-450 cm in profiles by neutron probe and tensionmeter. The results showed that the content of soil moisture in aeration zone varied intensely at depth of 10 cm, and attenuate at 100 cm and 450 cm. On the other hand, soil moisture content and dynamic variation presented seasonal features, Between Mar. and April, 2006, the mean soil moisture content was 36.7 %, which was the biggest value in that year. In this period, it was general higher and increased progressively. From May to August, the mean was 34.1%, and both maximum and minimum appeared during this time. From September to November, the mean was 32.6%, mainly showed a trend of decreasing gradually. From December 2006 to February the next year, the mean was 31.4%, which was the lowest value in that year. The ZEP of soil moisture in aeration zone existed 338 days during one year. Depth of ZEP, from November 2006 to February 2007, was 170cm, and less than 100cm in the other months. In all observation time, transpiration of soil moisture was 865.66mm, accounting for 88.5%. And infiltration was 145. 47mm, taking up 11.5%.The field capacity was 30.3%.