Search

In mountain environments, landslide sediment supply is one of the main factors that can affect fluvial morphodynamics. In settings underlain by clay-rich lithologies, where earthflows are the dominant agents of hillslope sediment transfer, limited quantitative information is available on the contribution of these processes to the sediment budget. This is a critical aspect both for addressing basic scientific questions on landscape evolution, as well for tackling more applied issues on river sediment management.This study focuses on the mountain portion of the Sillaro River basin (138 km2), a fluvial system underlain by argillites and siltstones of the Ligurian domain, Northern Apennines (Italy). Here, earthflows are the most common landslide type. Through the compilation of a multi-temporal earthflow inventory (1954-2019), we aim to: (i) characterize earthflow source-to-sink sedimentary pathways, with special reference to sediment delivery to ephemeral and perennial streams; (ii) explore possible litho-topographic controls on earthflow size, frequency and recurrence; (iii) examine historical trend of earthflow activity in relation to rainfall variability and land use changes. Finally, the high and extended temporal resolution of the inventory, will offer the opportunity to test how relevant information could complement the existing inventory of the Emilia-Romagna region, for evaluating earthflow hazard and risk potential.Data collection entailed inspection of 12 sequential aerial photo sets (1954, 1969, 1976, 1988, 1996, 2000, 2006, 2008, 2011, 2014, 2016, and 2018), through which earthflows were classified and mapped in GIS environment. This remotely-based activities were complemented by confirmatory field visits on a subset of most recent events. Overall, we have mapped a total of 506 earthflows, which collectively extend over an area of 4.1 km2.Preliminary results show that earthflow size (i.e., total disturbed area) ranges from 400 m2 to 98000 m2, with frequencies peaking around 10000 m2. In terms of source-to-sink pathways, we find that earthflows chiefly tend to deliver sediment to ephemeral gully channels (61%) and perennial tributaries (25%). Whereas, 5% of the events remain on the slopes, and another 5% are buffered by roads and similar anthropogenic barriers. Only a very limited proportion of earthflows (4%) makes it directly to the Sillaro River main stem.This work, as part of the projects BEDFLOW and BEFLOW PLUS, is partially funded by Fondazione Cassa di Risparmio in Bologna.

In dolomitic headwater catchments, intense rainstorms of short duration produce runoff discharges that often trigger debris flows on the scree slopes at the base of rock cliffs. In order to measure these discharges, we placed a measuring facility at the outlet (elevation 1770 m a.s.l.) of a small, rocky headwater catchment (area ∼ 0.032 km2, average slope ∼ 320%) located in the Venetian Dolomites (North Eastern Italian Alps). The facility consists of an approximately rectangular basin, ending with a sharp-crested weir. Six runoff events were recorded in the period 2011-2014, providing a unique opportunity for characterizing the hydrological response of the catchment. The measured hydrographs display impulsive shapes, with an abrupt raise up to the peak, followed by a rapidly decreasing tail, until a nearly constant plateau is eventually reached. This behavior can be simulated by means of a distributed hydrological model if the excess rainfall is determined accurately. We show that using the Soil Conservation Service Curve-Number (SCS-CN) method and assuming a constant routing velocity invariably results in an underestimated peak flow and a delayed peak time. A satisfactory prediction of the impulsive hydrograph shape including peak value and timing is obtained only by combining the SCS-CN procedure with a simplified version of the Horton equation, and simulating runoff routing along the channel network through a matched diffusivity kinematic wave model. The robustness of the proposed methodology is tested through a comparison between simulated and observed timings of runoff or debris flow occurrence in two neighboring alpine basins. This article is protected by copyright. All rights reserved.

The Montevecchio landslide is an active earthflow in the province of Forli-Cesena (Northern Apennines of Italy). In the last few years, this landslide reactivated several times. In order to investigate the landslide dynamics, two monitoring systems were installed by combining 3 permanent GPS stations (to measure landslide movement) and 4 geophones (to evaluate surface-wave velocity). In this paper we present the monitoring data collected during the last reactivation of the landslide (24th – 25th of May 2015). The geophones data show a clear relationship between surface-wave velocity (Vr) and displacement rate. In particular, a decrease of Vr value was observed just before an increase of velocity, while higher Vr values were detected when the landslide was slowing down. Moreover, a pressure sensor, buried at low depth beside the geophones, showed an increase in pore water pressure before the failure in correspondence of the critical rainfall event, and while the displacement rate increased the pore water pressure had a positive value (above the ground level), probably due to the undrained compression of the landslide material.

Surface mapping, GPS surveys, T-Lidar surveys, boreholes, seismic profiles, and HVSR measurements were used to study the mechanisms of sediment transport along the Mount Pizzuto earth flow in southern Italy. The earth flow has several kinematic zones, with transitional areas marked by changing structural styles, from compressional structures (thrusts) upslope to extensional structures (normal faults) downslope. We relate sediment discharge at these transitional zones to internal strain. The results suggest that during surge events, flow acceleration starts within the head and propagates downslope inducing a cascade effect between kinematic zones. During surge events, the average sediment discharge is nearly constant, and a change from sliding to flowing allows propagation of movement towards the toe. During slow movement, kinematic zones are independent and sediment discharge varies along the flow. In general, the velocity profile and the structural style are controlled by the basal slip surface. The implications are: i) sediment discharge is not constant but is a function of the earth flow activity, ii) during surge, earth flow material behaves similar to an incompressible fluid, and iii) the distribution of surface structures can provide information about the geometry of the slip surface and the velocity profile. Additionally, earth flows with a well-defined neck seem to be more likely to surge with respect to those without. © 2017 Elsevier B.V.

We used GPS surveys, boreholes, seismic profiles and field observations to investigate the cross sectional geometry, kinematics and sediment discharge of the Mount Pizzuto earth flow in southern Italy. This earth flow is characterized by several kinematic zones, characterized by an area of stretching with normal faults upslope and an area of shortening with thrust faults downslope. Our results indicate that: (i) during surging episodes, earth flow acceleration propagate from the head toward the toe with constant sediment discharge inducing a cascade effect between consecutive kinematic zones, (ii) change in mechanical behavior of the material might occur due to the presence of a well-defined neck influencing movement propagation, (iii) during ordinary movements, sediment discharge varies along the flow and the activity of kinematic zones seems to be independent from each other. Implications are that it is not correct to consider sediment discharge as constant but rather as a function of the earth flow activity.

Landscape evolution in active mountain chains can be dominated by gravitational slope movements. This is observed in a large portion of the Reno river catchment, Apennines, Italy, where weak rocks, such as clayshales, are subject to earthflows that control hillslope morphology and supply sediments to the channel network. In this paper, we evaluate the sediment flux generated by earthflows and compare it with Holocene-averaged deposition rates to assess the contribution of mass movements to landscape evolution. Present-day hillslope sediment flux is estimated by combining measured displacement rates (72 inclinometers) and spatial attributes of earthflows and historical frequency of reactivations. Averaged sediment yield (~ 1.6 x 10 3 t/km 2 /yr) compares well with similar studies on earthflow-dominated landscapes, despite notable differences in methodology. In the study area, the connectivity between hillslopes and the stream network is well developed and no significant sediment sinks influence the sediment transport processes. We document best estimates of regional sediment fluxes and related uncertainties, based on available data. Coarse limestone fragments, present in the clayshales, are used as a natural sediment tracer to allow a comparison with sedimentation rates taking place at the mouth of the intramontane catchment. Here, available borehole logs, 14 C datings and stratigraphic correlations of the alluvial fan are used to obtain an estimate of the deposition that took place during Holocene times. Taking also into account the role of solute transport, sedimentation rates are compared to earthflow sediment production rates. Results show a good agreement and demonstrate that earthflows are the primary mass wasting process in these weak rock lithologies. We document best estimates of regional sediment fluxes and related uncertainties. Present earthflow sediment production outpaces Holocene-averaged sedimentation rates by a factor of two. The gap between sediment production and deposition can be partly justified by uncertainties associated with our estimates and by time-scale differences. With this respect, the dynamic equilibrium between erosion and deposition, is likely affected by intra-Holocene oscillations at a short time scale (10 to 1 ky) attributable to climate variability. Terraced deposits documenting sedimentary episodes would also support such interpretation.

Statistical and deterministic methods are widely used in geographic information system based landslide susceptibility mapping. This paper compares the predictive capability of three different models, namely the Weight of Evidence, the Fuzzy Logic and SHALSTAB, for producing shallow earth slide susceptibility maps, to be included as informative layers in land use planning at a local level. The test site is an area of about 450 km2 in the northern Apennines of Italy where, in April 2004, rainfall combined with snowmelt triggered hundreds of shallow earth slides that damaged roads and other infrastructure. An inventory of the landslides triggered by the event was obtained from interpretation of aerial photos dating back to May 2004. The pre-existence of mapped landslides was then checked using earlier aerial photo coverage. All the predictive models were run on the same set of geo-environmental causal factors: soil type, soil thickness, land cover, possibility of deep drainage through the bedrock, slope angle, and upslope contributing area. Model performance was assessed using a threshold-independent approach (the ROC plot). Results show that global accuracy is as high as 0.77 for both statistical models, while it is only 0.56 for SHALSTAB. Besides the limited quality of input data over large areas, the relatively poorer performance of the deterministic model maybe also due to the simplified assumptions behind the hydrological component (steady-state slope parallel flow), which can be considered unsuitable for describing the hydrologic behavior of clay slopes, that are widespread in the study area.

A method proposed for delineating lahar-hazard zones in volcanic valleys is adapted to debris flows. The original method is based on two predictive equations that relate the lahar volume to the cross-sectional inundated area and to the planimetric inundated area. These predictive equations were derived by combining a scaling analysis of lahar kinematics with the statistical analysis of data for 27 historical lahars. This paper tests the applicability of this approach to debris flow fans. Forty debris flow basins in the Italian Alps were surveyed, and data on 27 historical debris flow events were collected in the field or by means of aerial-photo analysis. Collected data reveal that the flow area ( A ) and the planimetric area ( B ) of a debris flow are linearly correlated to the debris flow volume ( V ) on a logarithmic scale, with high statistical significance. Moreover, the computed regression equations are very similar to those obtained from other published datasets on debris flows, leading to the global fitting equations A = 0.08 V 2 / 3 and B = 17 V 2 / 3 . These predictive equations are then implemented in an automated code (DFLOWZ) that delineates the inundated area on a debris flow fan on the basis of a user-specified debris flow volume, taking the statistical uncertainty in the prediction into account. DFLOWZ is simple reproducible, and it can handle both confined and unconfined flow. The model is tested against 10 historical debris flow events, providing a satisfactory agreement between observed and computed inundated areas. In spite of the limitations due to DEM accuracy and statistical uncertainty of the regression parameters, test results show that the method can be useful for practical applications.

We present an automated time series analysis of InSAR data for the characterization of ground subsidence induced by longwall mining at Metropolitan mine (New South Wales, Australia). The dataset derives from SqueeSAR™ processing of two Envisat radar data stacks of 44 images acquired from the ascending orbit and 43 from a descending orbit, acquired on a 35-day repeat interval in the period June 2006 to September 2010. Automated time series classification was carried out with PSTime, a specifically designed software that employs a sequence of statistical tests to classify the time series into the six different classes: uncorrelated, linear, quadratic, bilinear, discontinuous without constant velocity and discontinuous with change in velocity. Results highlight a cluster of bilinear trends with acceleration at the front of longwall panel progression and a cluster of bilinear trends with deceleration at the back. Linear trends are found at the centre of the subsidence bowl while outside most trends are uncorrelated. This picture is consistent with the evidence of acceleration in deformation trend when mining is approaching and a deceleration after extraction is completed and an essentially constant while mining takes place just underneath a specific point. Thus, time series analysis proved to be valuable for subsidence dynamics characterization, constraining in space and time the patterns of deformation trend in mining applications.

In Northern Apennines, landslides involving weak rocks such as clay shales are widespread and often cause damage to public infrastructure and private properties. These landslides, mostly classifiable as earthflows, generally exhibit continuous slow movements, with temporary increases of velocity controlled both by groundwater and rainfall regime. Although the relationship between precipitation, groundwater flow and displacement rate is evident, its quantitative description remains problematic. We use piezometric and slope movement continuous monitoring to investigate the groundwater flow system in the vicinity of the contact between clay shales and overlying more permeable units, where the village of Lizzano in Belvedere is located. Our aim is to describe the groundwater flow and its relation to slope deformation in order to simulate the effect of possible drainage measures both on piezometric levels and expected displacement rates. Timing and magnitude of piezometric responses at different depths are related to observed deformations and used to calibrate a transient 3D groundwater flow model. Groundwater modeling validates the conceptual hydrogeological scheme and allows simulation of the impact of surface and deep drainages on piezometric levels. Results indicate that horizontal drains are more effective than infiltration reduction measures, both in terms of drawdown and time effectiveness of action. Simulated hydraulic heads are then used to produce a probabilistic prediction of the expected displacement rates by means of an empirical method. In the case of Lizzano in Belvedere, according to our results, the lowering of hydraulic heads operated by horizontal drains can reduce the velocity of slope movements from centimeters per year to millimeters per year.

A debris flow event occurred in June 1997 in the Dolomites (Eastern Alps, Italy). The phenomenon was directly observed in the field and recorded by a video camera near its initiation area. The debris flow originated shortly after an intense rainstorm (25 mm in 30 min) whose runoff mobilised the loose coarse debris that filled the bottom of the channel in its upper part. The analysis of the steep headwater basin indicates a very short concentration time (9–14 min) that fits the quick hydrological response observed in the field. The debris flow mobilisation was not contemporaneous with the arrival of the peak water discharge in the initiation area probably due to the time required for the saturation of the highly conductive channel-bed material. Channel cross-section measurements taken along the flow channel indicate debris flow peak velocity and discharge ranging from 3.1 to 9.0 m/s and from 23 to 71 m3/s, respectively. Samples collected immediately after deposition were used to determine the water content and bulk density of the material. Channel scouring, fines enrichment and transported volume increase testify erosion and entrainment of material along the flow channel. Field estimates of the rheological properties based on open channel flow of Bingham fluid indicate a yield strength of 5000±400 Pa and relatively low viscosity (60–326 Pa s), probably due to a high percentage of fines (approx. 30%).

This paper illustrates research addressing the subject of the earthquake-induced surface effects by means of a multidisciplinary approach: tectonics, neotectonics, seismology, geology, hydrogeology, geomorphology, soil/rock mechanics have been considered. The research is aimed to verify in areas affected by earthquake-triggered landslides a methodology for the identification of potentially unstable areas. The research was organized according to regional and local scale studies. In order to better emphasise the complexity of the relationships between all the parameters affecting the stability conditions of rock slopes in static and dynamic conditions a new integrated approach, Rock Engineering Systems (RES), was applied in the Northern Apennines. In the paper, the different phases of the research are described in detail and an example of the application of RES method in a sample area is reported. A significant aspect of the study can be seen in its attempt to overcome the exclusively qualitative aspects of research into the relationship between earthquakes and induced surface effects, and to advance the idea of beginning a process by which this interaction can be quantified.

Clay-shales largely outcrop in the Northern Apennines of Italy, where they are associated with frequent and widespread landslide activity. The paper presents the results of monitoring activities carried out in two field-sites and focused on the hydrology of clay-shales prone to landsliding. In the monitored slopes, the water table is close to the ground surface throughout the year, with seasonal fluctuations of tens of centimetres to a couple of metres. Shallow weathered soils, or clay cover, and unaltered material exhibit a much different behaviour. Although responses to single rainfalls are clearly identifiable as pressure pulses in the clay cover, they are never observed in the underlying parental clay-shales where downward gradients indicate recharge and only long-term seasonal fluctuations are recorded. Short-term variations of pressure head in the clay cover are ruled by downward propagation of a pressure wave in saturated conditions. More than 400 pore-pressure responses collected in the two sites are analysed in terms of lag time, rate and amount of pressure increase and timing of pressure peaking. It emerges that the linear diffusion theory can satisfactorily explain the observed behaviour. In deeper unaltered material, the barometric effect influences the measures similarly to what is observed in confined aquifers. After its removal, the corrected data exhibit regular seasonal fluctuations which are used to estimate the diffusivity of the material based on phase-lag and attenuation of the downward propagating long-term periodic pulse. Copyright © 2011 John Wiley & Sons, Ltd.

Empirical mobility relationships can be used for delineating debris flow inundated areas. A database of documented events in alpine mountain catchments of northeastern Italy is used to test the model DFlowz ( Berti and Simoni, 2007 ). We back-analyzed 25 DF events, ranging in volume from 3000 to 350,000 m 3 , with the support of high resolution topographic information derived from LiDAR. The analysis makes use of an objective methodology for evaluating the accuracy of the predictions and involves the calibration of the model based on factors describing the uncertainty associated with the empirical relationships. Results indicate that the model is capable of reproducing the observed behavior with a maximum uncertainty of a factor of 3. The most relevant source of error lies in the estimation of the deposited volumes which affects the results of back-calculation and is mainly responsible also for the scatter associated with the empirical mobility relationships. On the contrary, the influence of different flow properties on the depositional process appears to play a minor role as the mutual relations between the three main scaling parameters (volume, inundated area, and cross-sectional area) are respected in the vast majority of cases and calibrated mobility coefficients show no significant relationship with the angle of reach of the deposit.

Debris flow initiation by channel bed mobilization is a common process in high mountainous areas. Initiation is more likely to occur at the outlet of small, steeply sloping basins where concentrated overland flow feeds an ephemeral channel incised in slope deposits. Such geological conditions are typical of the Dolomite region (Italian Alps), which is characterized by widespread debris flow activity triggered by severe summer thunderstorms. Real-time data and field observations for one of these catchments (Acquabona catchment, Belluno, Italian Alps) were used to characterize the hydrological response of the initiation area to rainfalls of varying intensity and duration. The observed behaviour was then reproduced by means of a simple hydrological model, based on the kinematic wave assumption, to simulate the generation of channel runoff. The model is capable of predicting the observed hydrological response for a wide range of rainfall impulses, thus providing a physical basis for the understanding of the debris flow triggering threshold.

In 1997 a field monitoring system was installed in Acquabona Creek in the Dolomites (Eastern Italian Alps) to observe the hydrologic conditions for debris flow occurrence and some dynamic properties of debris flow. The monitoring system consists of three remote stations: an upper one located at the head of a deeply-incised channel and two others located downstream. The system is equipped with sensors for measuring rainfall, pore pressures in the mobile channel bottom, ground vibrations, debris flow depth, total normal stress and fluid pore-pressure at the base of the flow. Two video cameras record events at the upper channel station and one video is installed at the lowermost station. During summer 1998, three debris flows (volumes from less than 1000 m3 up to 9000 m3) occurred at Acquabona. The following results were obtained from a preliminary analysis of the data: 1) All of the flows were triggered by rainfalls of less than 1 hour duration, with peak rainfall intensities ranging from 4.8 to 14.7 mm / 10 minute. 2) Debris flows initiated in several reaches of the channel, including the head of the talus slope. 3) The initial surges of the mature flows had a higher solid concentration and a lower velocity (up to 4 m/s) than succeeding, more dilute surges (more than 7 m/s). 4) Total normal stress and pore fluid pressures measured at the base of the flow. (mean depth about 1.1 m) were similar (about 15 kPa), indicating a completely liquefied flow. 5) Peak flows entrained debris at a rate of about 6 m 3/m of channel length and channel bed scouring was proportional to the local slope gradient and was still evident in the lower channel where the slope was 7°.