The influence of geological–morphological and land use settings on shallow landslides in the Pogliaschina T. basin (northern Apennines, Italy)

Abstract

On 25 October 2011, the eastern Liguria (Vara Valley and Cinque Terre area) and northwestern Tuscany (Magra Valley) were affected by an extreme rainstorm (almost 600 mm/24 h) that caused floods, thousands of shallow landslides, 13 casualties and damage to villages and infrastructure. This study aims at analysing the main features of the 25 October 2011 shallow landslides occurred in the Pogliaschina Torrent basin (25 km2 wide, Vara Valley), in order to investigate the influence of specific predisposing factors (land use, geological and structural setting, plan and profile curvature, slope angle and aspect) on landslide occurrence. For this purpose, both a landslide inventory map and a geology map (scale 1:10,000) were prepared.\ud In addition, a database including the main geological, geomorphological, structural and land use features of the landslide source areas was implemented. The relationship between landslide source areas and the main predisposing factors was evaluated through spatial and statistical analysis

Comment on ‘The influence of geological–morphological and land-use settings on shallow landslides in the Pogliaschina T. basin (northern Apennines, Italy)’ by Bartelletti et al. (2017)

“…Model results show a satisfactory agreement with post-flood field estimates, with peak discharge within the uncertainty range of field estimations in four out of the six sub-basins. The representation of event precipitation featuring the lowest rainfall heights in the southern sector of the Pogliaschina basin ( Figure 3 of Bartelletti et al, 2017) does not agree with extreme runoff response arising from post-flood estimates of peak discharge, which were corroborated by hydrological modelling implemented at the wider scale of the Magra River basin .…”

“…In the Pogliaschina basin, a striking difference between the rainfall distribution presented in Figure 3 of Bartelletti et al (2017) and that of Figure 1 is the rainfall amount in the southernmost sector of the basin. In the isohyet map of Bartelletti et al (2017) this sector received the lowest rainfall amounts, whereas very high rainfall rates arise from the integrated analysis of rain gauges and weather radar data (Figure 1).…”

“…Within the context of their study on the landslides triggered by the rainstorm of 25 October 2011 in the Poglischina Torrent basin (northern Apennines, Italy), Bartelletti, Giannecchini, D'Amato Avanzi, Galanti, and Mazzali (2017) present isohyet maps of event rainfall that are also used for interpreting the occurrence of landslides in different sectors of the basin. The spatial distribution of event rainfall ( Figure 2 in Bartelletti et al, 2017) is characterized by 'islands' of high (e.g.…”

“…The spatial distribution of event rainfall ( Figure 2 in Bartelletti et al, 2017) is characterized by 'islands' of high (e.g. Brugnato and Calice al Cornoviglio -Molunghi) or low (e.g.…”

“…Bartelletti et al (2017) ascribe the low ratio of landslide area to the formation area of the Macigno to 'the relatively less intense rainfall that hit the area where this formation crops out'. Based on the analysis of rainfall and resulting discharge, this comment argues that the isohyet map indicating less intense rainfall in the southern sector of the Pogliaschina basin does not provide a satisfactory representation of rainfall distribution for the rainstorm of 25 October 2011.…”