Anna Roccati

Applied geomorphological map of the Portofino Municipal Territory (Italy)

Abstract Please click here to download the map associated with this article. Here we present an applied geomorphological map at a scale of 1:5,000 of the Portofino territory (Italy). The map was compiled by combining available geological and hydrogeological information with a new geomorphological field survey and data derived from geotechnical studies carried out for town planning and building purposes. Portofino is one of the most well known old town centres; its territory is entirely included in the Park of the same name created in 1935. This charming village is located at the mouth of Fondaco Stream. Although the catchment has a limited size—its highest altitude is just over 200 m a.s.l.—the watercourse drainage culverts built in the late 19th century cause hazards caused by gravity, owing water and wave action. We used the following methods: a) bibliographic and map research of scienti-c papers; b) a geological field survey, preceded by photo interpretation; c) stratigraphic and geotechnical data collection where building sites are located; and d) laboratory tests to determine rock strength. This paper presents an example of geocartography that could be applied to land planning in areas with high landscape value but threatened by geomorphological hazards.

Engineering geological map of the Chiavari city area (Liguria, Italy)

An engineering geological map at a scale of 1:10,000 of the Chiavari city area (Northern Italy) – a major tourist and economic attraction of the Ligurian East Riviera – is presented in this paper. The municipality land shows an excellent geomorphological case-study of the well-known Ligurian coast: a floodplain, fairly wide and inhabited, formed by several floods of the two main rivers, a hill hinterland, reasonably inhabited, developed in marly limestones and sandy shales flysch and the coast – featuring cliffs and narrow pebbly beaches – deeply modified. This map was compiled by combining available geological data with a new engineering geomorphological field survey and including geotechnical data which were obtained from studies carried out for town planning and building purposes. On the basis of the critical review of the available lithostratigraphic data from drilling, as well as geotechnical and geophysical analyses carried out between 1981 and 2010 on the municipality land, an engineering geological map was compiled. Nine engineering geological units were established, based on their physical characterizations and geomechanical properties. This paper presents an example of geocartography that could be applied to urban land planning for housing and construction of technical works; it also represents the base for geological hazard evaluation.

Geo-hiking map of Mt. Penna and Mt. Aiona area (Aveto Natural Park, Italy)

This work presents a geo-hiking map of Mt. Penna and Mt. Aiona area (Aveto Natural Park, Italy), an original and useful tool in the Earth science mapping field. Aveto Park is one of the best known Italian protected areas; it is located in the Ligurian Apennines and belongs to the Ophiolitic Protected Areas Coordination (‘C.A.P.O.’) and to the European Ecological Network Nature 2000. The Park area is crossed by more than 500 km of paths and trails where hikers, climbers and mountain lovers walk every year. The geo-hiking map was compiled by combining available geological and geomorphological bibliographic data with a field survey and basic information derived from hiking and tourist maps. The main stages used for production of the map are as follows: (a) bibliographic and map research of scientific papers; (b) a geological and geomorphological field survey; (c) trail and route data from tourist park maps; (d) research of geotouristic elements of interest. This work shows an example of geocartography research that really contributes to the implementations of documents and maps useful in the hiking tourism field. The main map is complemented with a natural hazard map; increasing tourism during the whole year in areas with geomorphological hazards results in a relationship between the human element, natural processes and hazard phenomena.

A tool for the automatic calculation of rainfall thresholds for landslide occurrence

Abstract Empirical rainfall thresholds are commonly used to forecast landslide occurrence in wide areas. Thresholds are affected by several uncertainties related to the rainfall and the landslide information accuracy, the reconstruction of the rainfall responsible for the failure, and the method to calculate the thresholds. This limits the use of the thresholds in landslide early warning systems. To face the problem, we developed a comprehensive tool, CTRL–T ( C alculation of T hresholds for R ainfall-induced L andslides− T ool) that automatically and objectively reconstructs rainfall events and the triggering conditions responsible for the failure, and calculates rainfall thresholds at different exceedance probabilities. CTRL−T uses a set of adjustable parameters to account for different morphological and climatic settings. We tested CTRL−T in Liguria region (Italy), which is highly prone to landslides. We expect CTRL−T has an impact on the definition of rainfall thresholds in Italy, and elsewhere, and on the reduction of the risk posed by rainfall-induced landslides.

The geological layout of Landscape Master Plan: an example from Liguria (Italy)

After more than 25 years since the first studies, the Landscape Master Plan of Liguria has contributed to maintaining the cultural and natural landscape. The current plan is made by three descriptive layouts and related regulations: the settlement and botanical settings represent the features of the landscape linked to buildings and vegetation. The geomorphological layout shows only the regulations, without any reference to Earth surface processes and landforms. This research suggests a methodology aiming at providing the plan with an engineering geologic suitable layout with the other settings. We propose eight geomorphological landscape units: all of them are connected with Earth surface dynamic factors, including man-made landforms and geodiversity values. A double key to the interpretation of this geo-map is suggested. The capital letters corresponding to regulations are maintained; we have inserted a new label linked to the geomorphological landscape unit. This updating may be integrated in the review processes of the Landscape Master Plan already started by Regional Authority.

Rainfall events with shallow landslides in the Entella catchment (Liguria, Northern Italy)

In recent decades, the Entella River basin, in the Liguria Apennines, northern Italy, was hit by numerous intense rainfall events that triggered shallow landslides and earth flows, causing casualties and extensive damage. We analyzed landslide information obtained from different sources and rainfall data recorded in the period 2002–2016 by rain gauges scattered throughout the catchment, to identify the event rainfall duration, D (in h), and rainfall intensity, I (in mm h−1), that presumably caused the landslide events. Rainfall-induced landslides affected the whole catchment area, but were most frequent and abundant in the central part, where the three most severe events hit on 23–24 November 2002, 21–22 October 2013 and 10–11 November 2014. Examining the timing and location of the slope failures, we found that the rainfall-induced landslides occurred primarily at the same time or within 6 h from the maximum peak rainfall intensity, and at or near the geographical location where the rainfall intensity was largest. Failures involved mainly forested and natural surfaces, and secondarily cultivated and terraced slopes, with different levels of maintenance. Man-made structures frequently characterize the landslide source areas. Adopting a frequentist approach, we define the event rainfall intensity–event duration (ID) threshold for the possible initiation of shallow landslides and hyperconcentrated flows in the Entella River basin. The threshold is lower than most of the curves proposed in the literature for similar mountain catchments, local areas and single regions in Italy. The result suggests a high susceptibility to rainfallinduced shallow landslides of the Entella catchment due to its high-relief topography, geological and geomorphological settings, meteorological and rainfall conditions, and human interference. Analysis of the antecedent rainfall conditions for different periods, from 3 to 15 days, revealed that the antecedent rainfall did not play a significant role in the initiation of landslides in the Entella catchment. We expect that our findings will be useful in regional to local landslides early warning systems, and for land planning aimed at reducing landslide risk in the study area.