Generation of a Design Flood-Event Scenario for a Mountain River with Intense Sediment Transport

International directives encourage the incorporation of sediment transport analyses into flood risk assessment, in recognition of the significant role played by sediment in flood hazard. However, examples of risk analysis frameworks incorporating the effect of sediment transport are still not widespread in the literature, resulting in a lack of clear guidelines. This manuscript considers a study site in the Italian Alps and presents a hydro-morphologic model for generation of flood scenarios towards hazard assessment. The analysis is concentrated on a design flood event with 100-year return period, for which an outflowing discharge is computed as a result of the river modeling. However, it is also argued how suitable model input parameter values can be obtained from analyses of river flows in a yearly duration curve. Modeling tools are discussed with respect to their capabilities and limitations. The results of the analysis are site-specific, but the proposed methodology can be exported to other hydro-graphic basins

Monitoring riverbank erosion in mountain catchments using terrestrial laser scanning

Sediment yield is a key factor in river basins management due to the various and adverse consequences that erosion and sediment transport in rivers may have on the environment. Although various contributions can be found in the literature about sediment yield modeling and bank erosion monitoring, the link between weather conditions, river flow rate and bank erosion remains scarcely known. Thus, a basin scale assessment of sediment yield due to riverbank erosion is an objective hard to be reached. In order to enhance the current knowledge in this field, a monitoring method based on high resolution 3D model reconstruction of riverbanks, surveyed by multi-temporal terrestrial laser scanning, was applied to four banks in Val Tartano, Northern Italy. Six data acquisitions over one year were taken, with the aim to better understand the erosion processes and their triggering factors by means of more frequent observations compared to usual annual campaigns. The objective of the research is to address three key questions concerning bank erosion: "how" erosion happens, "when" during the year and "how much" sediment is eroded. The method proved to be effective and able to measure both eroded and deposited volume in the surveyed area. Finally an attempt to extrapolate basin scale volume for bank erosion is presented

geoelectrical characterization and monitoring of slopes on a rainfall triggered landslide simulator

Abstract In this paper, we present the results of time-lapse electrical resistivity tomography (ERT) monitoring of rainfall-triggered shallow landslides reproduced on a laboratory-scale physical model. The main objective of our experiments was to monitor rainwater infiltration through landslide body in order to improve our understanding of the precursors of failure. Time-domain reflectometry (TDR) data were also acquired to obtain the volumetric water content. Knowing the porosity, water saturation was calculated from the volumetric water content and we could calibrate Archie's equation to calculate water saturation maps from inverted resistivity values. Time-lapse ERT images proved to be effective in monitoring the hydrogeological conditions of the slope as well as in detecting the development of fracture zones before collapse. We performed eight laboratory tests and the results show that the landslide body becomes unstable at zones where the water saturation exceeds 45%. It was also observed that instability could occur at the boundaries between areas with different water saturations. Our study shows that time-lapse ERT technique can be employed to monitor the hydrogeological conditions of landslide bodies and the monitoring strategy could be extended to field-scale applications in areas prone to the development of shallow landslides

Sperimentazione alla scala di laboratorio per il monitoraggio di frane indotte da precipitazioni con misure geoelettriche time-lapse

Secondo l’Inventario dei Fenomeni Franosi d’Italia (IFFI), al 2016 le frane censite in Italia sono 614.799, interessano un’area pari al 7.5% del territorio nazionale e il 70.5% dei Comuni italiani. Le frane indotte da precipitazioni, inoltre, per la loro evoluzione veloce, sono una grave minaccia per l’incolumità della popolazione, dei beni e delle infrastrutture del territorio che, in assenza di un sistema di allerta adeguato non possono essere salvaguardati. Lo studio e il monitoraggio di fenomeni franosi può essere realizzato a diverse scale e con diverse tecnologie, ma negli ultimi decenni le metodologie geofisiche sono state largamente utilizzate per questo scopo, grazie alla peculiarità di essere non invasive e di poter rilevare la variazione di parametri fisici in un volume di terreno. Per quanto riguarda le frane superficiali, analizzate in questo studio, uno dei fattori predisponenti per l’attivazione è l’apporto precipitativo, che va a determinare variazioni nel contenuto d’acqua del suolo e nella pressione interstiziale. Diversi ricercatori hanno constatato l’utilità di misure geoelettriche per la valutazione del contenuto idrico nel corpo di frane superficiali (Perrone et al., 2008; De Bari et al., 2011; Ravindran e Prabhu., 2012) e in alcuni casi è stato predisposto un sistema di monitoraggio in continuo (Supper et al., 2008; Kuras et al., 2009; Hilbich et al., 2011). L’obiettivo di questo studio è quello di valutare, partendo dalla sperimentazione di laboratorio, l’applicabilità di un monitoraggio geoelettrico nel riconoscimento di un livello soglia di contenuto d’acqua per l’instaurarsi dell’instabilità di una frana superficiale

Water tunnels in mountain areas: Assessing the erosional activity with GPR

Hydrogeological risk assessment regarding mountain rivers (both alpine and pre-alpine) must entail careful geological and hydraulic analyses about the interaction between water flow and man-made structures. This is not limited to dams and check-dams, but also include concrete tunnels that are often built to channel water flow into the underground in densely populated urban areas. Mountain streams generally feature small concentration time and significant solid transport that may pose a serious threat to the population. More in details, solid transport can cause diverse issues, including major alterations in the water flow regime, flooding and, in the worst cases, severe damages to structures. In this work we present a case study concerning the investigation of a concrete lined water tunnel located in the pre-alpine area in the North of Italy. We performed geophysical analysis by means of the Ground Penetrating Radar (GPR), a high-frequency electromagnetic technique able to investigate concrete structures in a non-destructive manner and with a good resolution. Our aim is to identify the erosional activity beneath the tunnel floor caused by water flow and the associated solid transport. The outcomes of this study can identify the damaged tunnel segments where repair interventions are most urgent

Geological Assessment and Physical Model of Complex Landslides: Integration of Different Techniques

Complex landslides usually need to be investigated in depth in order to understand the geological setting that led to their formation and influenced their development. The knowledge of the landslide structure and history is the key point to understand potential future development and evolutions. Classical geological tools and campaigns can only give a partial insight and integration of different survey techniques arises as a crucial point to improve knowledge and overcome traditional techniques\u2019 shortcomings. Here, the Torrioni di Rialba (Italy) case study is presented. A vertical 135 m-high rock cliff in Abbadia Lariana, Northern Italy, is suspected to be potentially unstable, although no information about the geological setting is available. Although the landslide has not shown activity evidences in the last decade a possible collapse threatens a narrow corridor of extreme importance. The urge to better understand landslide causes led to start a broad campaign of surveys. Geological investigations were conducted along with geophysical surveys, namely seismic tomography and several electrical soundings, to give an insight in the inner slope structure and were calibrated drilling two boreholes on the slope. An accurate Lidar survey of the area as well as lake bathymetry near the landslide spot allowed for precise geometry assessment of the area to correctly locate information gathered. In this work the weak and strong points of each choice is debated in order to highlight uncertainty in the decisional process and to define good practice and caveats. The entire work, which took four years, due to economical and logistic limitations is critically reviewed and the better choices are underlined

Monitoring bedload sediment transport in a pre-Alpine river: an experimental method

Sediment transport in Alpine and pre-Alpine zones is an essential part of the broad field encompassing hydro-geological instabilities, with particular significance during high intensity rainfall events. This study describes an experimental method for the characterization of the dynamics of this phenomenon at a small spatial and temporal resolution. A set of Radio Frequency IDentificator (RFID) equipped pebbles has been tracked for a period of 6 months and their propagation along the stream has been recorded after each rainfall event. A descriptive database has been devised in order to explore the mobility of the single grains with respect to their geometrical characteristics, their mass as well as the influence of the precipitation intensity on the monitored river reach. Preliminary results indicate the strong correlation of sediment mobility to river discharge and suggest the influence of initial position in terms of morphological characteristics on the sediment mobility

RFID-Aided Sediment Transport Monitoring\u2014Laboratory and Preliminary Field Test Results

Although often disregarded during natural hazard evaluation, sediment transport phenomena could represent a matter of major significance when dealing with hydro-geological instabilities with possible adverse impacts on river basin management, structural integrity of hydraulic structures, and public safety. Under conditions of high precipitation and consequent propagation of flood waves, the phenomenon is severely intensified, especially in Alpine and pre-Alpine areas, characterized by relatively high slopes and intense sediment supply from the upstream valleys. This study investigates the application of RFID (Radio-Frequency IDentification) transponders (also referred to as tags) as a qualitative and quantitative sediment transport monitoring tool. Preliminary laboratory and field tests have been carried out on both transponders and transponder-equipped pebbles under various conditions of the surrounding environment such as burial and water depth in order to evaluate the performance of the technology. Results of the laboratory experiments indicate that the detection distance depends on the orientation of the tag itself and therefore insertion of two or even 3 tags in a single pebble according to its axes is necessary in order to ensure higher recovery rates. Further, characteristic grain size curves have been used to identify 90 RFID-equipped and painted grains divided in several size classes and used in a first field experiment. The groups have been deployed at predefined locations characterized by similar granulometry and flow conditions. Two recovery campaigns have been since carried out, with the former some 15 h after a relatively intensified rainfall event and the latter two days later. A relatively high recovery rate has been recorded (72% during the first and 78% during the second campaign) to a distance of up to 50 m downstream of the initial deployment point. Despite some limitations, the technology appears to yield promising insights in the more detailed understanding of sediment transport