Secchia River Research Articles

A Bayesian network approach for multi-sectoral flood damage assessment and multi-scenario analysis

Extreme weather and climate related events, from river flooding to droughts and tropical cyclones, are likely to become both more severe and more frequent in the coming decades, and the damages caused by these events will be felt across all sectors of society. In the face of this threat, policy- and decision-makers are increasingly calling for new approaches and tools to support risk management and climate adaptation pathways that can capture the full extent of the impacts. In this frame, a GIS-based Bayesian Network (BN) approach is presented for the capturing and modelling of multi-sectoral flooding damages against future ‘what-if’ scenarios. Building on a risk-based conceptual framework, the BN model was trained and validated by exploiting data collected from the 2014 Secchia River flooding event, as well as other contextual variables. Moreover, a novel approach to defining the structure of the BN was performed, reconfiguring the model according to expert judgment and data-based validation. The model showed a good predictive capacity for damages in the agricultural, industrial and residential sectors, predicting the severity of damages with a classification accuracy of about 60% for each of these assessment endpoints. ‘What-if’ scenario analysis was performed to understand the potential impacts of future changes in i) land use patterns and ii) increasing flood depths resulting from more severe flood events. The output of the model showed a rising probability of experiencing high monetary damages under both scenarios. In spite of constraints within the case study dataset, the results of the appraisal show good promise, and together with the designed BN model itself represent a valuable support for disaster risk management and reduction actions against extreme river flooding events, enabling better informed decision making.

Estimation of levee breach discharge hydrographs: comparison of inverse approaches

ABSTRACT In this paper, we present a methodology to estimate the flow hydrograph through a levee breach in an inverse framework. The procedure requires a forward model of the river reach, water levels recorded in a gauging station downstream or upstream of the failure site and an optimization method; there is no need to model either the flood-prone area outside the river or the breach evolution. In particular, we compare the results of a novel optimization method, the ensemble smoother with multiple data assimilation (ES-MDA), with those of the Bayesian geostatistical approach (BGA). The methods are applied to the real case of the breach that occurred on the Secchia River in Northern Italy in January 2014. The two optimization methods lead to similar results, but ES-MDA requires a number of runs of the forward model about 10 times lower than that needed by BGA, saving significant computational time.

Failure Probability Analysis of Levees Affected by Mammal Bioerosion

AbstractMammal bioerosion is an emergent threat to the functionality of levees. In the present paper, the problem of assessing the failure probability of levees affected by mammal bioerosion is addressed. A fully bivariate description of peak flow discharge and flood duration is combined with a deterministic unsteady seepage flow model to obtain a suitable model of variably disturbed levee response to the observed natural variability of floods. Monte Carlo analysis is also implemented to evaluate the epistemic uncertainty connected to the description of the river system. The obtained model is tested with respect to a real‐world levee located along the Secchia River in northern Italy, which underwent a disastrous failure caused by mammal bioerosion in 2014. The convex linear combination of two Archimedean copulas is found to fit the empirical dependence structure between peak flow discharge and flood duration. The reliability of the unsteady seepage flow model is tested against detailed numerical simulations of the seepage occurring through the levee body. A limit state function is obtained by comparing the maximum extent of the seepage front to the distance between the den end and the riverside levee slope, and the corresponding levee safety and failure regions are delimited. Results obtained from the developed model reveal a significant impact of mammal dens located near the levee crest in terms of failure probability and related return period. This impact is consistent with failures observed in the study area.

Levee Breaching: A New Extension to the LISFLOOD-FP Model

Levee failures due to floods often cause considerable economic damage and life losses in inundated dike-protected areas, and significantly change flood hazard upstream and downstream the breach location during the event. We present a new extension for the LISFLOOD-FP hydrodynamic model which allows levee breaching along embankments in fully two-dimensional (2D) mode. Our extension allows for breach simulations in 2D structured grid hydrodynamic models at different scales and for different hydraulic loads in a computationally efficient manner. A series of tests performed on synthetic and historic events of different scale and magnitude show that the breaching module is numerically stable and reliable. We simulated breaches on synthetic terrain using unsteady flow as an upstream boundary condition and compared the outcomes with an identical setup of a full-momentum 2D solver. The synthetic tests showed that differences in the maximum flow through the breach between the two models were less than 1%, while for a small-scale flood event on the Secchia River (Italy), it was underestimated by 7% compared to a reference study. A large scale extreme event simulation on the Po River (Italy) resulted in 83% accuracy (critical success index).

LACUNA STRATIGRAFICA TRA LE FORMAZIONI DI RANZANO E DI ANTOGNOLA NELLE ZONE DI ROTEGLIA E MONTEBARANZONE (APPENNINO REGGIANO E MODENESE)

The Monte Piano — Blsmantova sequence (Middle Eocene — Late Miocene) in the Northern Apenmnes represents a new sedimentary cycle after the tectonic phase of the Early—Middle Eocene. This phase principally affected the structural Units of Ligurian domain. This sedimentary sequence (the postorogenic Ligurian Sequence), shows evidence of the progression of the Apennine orogenesis mainly through the development of unconformities of regional extension. In fact, this new sedimentary cycle began after the definitive closure of the Ligurian ocean (Oceanic stage) and sedimentation continued durIng the subsequent development of a collisional margin (Ensialic stage) between the European and African Adriatic plates.
 The stratigraphic and structural features of the Apenmne margin between Tresinaro Valley and Lavino Valley are described brteflv in this paper. Moreover, the contact between the Ranzano Formation and the Antognola Formation, parts of the postorogenic Ligurian Sequence, is discussed in terms of the micropaleontologica] data obtained from three stratigraphical sections situated In the lower valley of the Secchia River. The contact coincides with an unconformity that is marked by a biostratigraphical hiatus.
 In fact, foraminifera] associations indicate that the top of the Ranzano Formation is attributable to Zone PI 8 (Lower Oligocene) and that the base of the Antognola Formation is already attributable to Zone P 21 (Upper Oligocene). There was no evidence of the presence of Zone PI 9/20. The chronological range of the hiatus is estimated as 2.4 to 1 0 Ma, depending upon the chronological scale adopted and the exact position of the "top" of the Ranzano Formation and the base of the Antognola Formation.
 On the basis of the stratigraphic relations existing among the various units of the postorogenic Ligurian Sequence outcropping in the studied area and on the basis of the data collected on the contact between the Ranzano Formation and Antognola Formation, it is clear that the hiatus is attributable to submarine erosion of a part of the turbiditic deposits of the Ranzano Formation, which are affected by pronounced tectono—sedimentary phenomena. The tectonic movements developed in the Ligurian domain in a per10d preceding the deposition of the Antognola Formation. They are thus contemporary with the beginning of the deposition of the Macigno in the Tuscan paleogeographical domain.

Contribution of water geochemistry and isotopes (δ18O, δ2H, 3H, 87Sr/86Sr and δ11B) to the study of groundwater flow properties and underlying bedrock structures of a deep landslide

A comprehensive understanding of bedrock lithology and groundwater circulation is necessary to identify areas prone to landslide initiation and reactivation. This necessity is particularly required in the case of outcroppings of weak rocks such as gypsum that, due to their high solubility and low mechanical strength, can promote slope deformation with the development of caves and collapses. In the Upper Secchia River Valley, where gypsum outcrops extensively and is covered by landslide deposits, an accurate identification of the gypsum outcrops and their distribution is needed to reduce the damage to urbanized slopes. In this paper, a hydrologic and geochemical approach is used in the Montecagno landslide to identify the origin, flow paths and transit time of groundwater circulating inside the landslide body and to identify gypsum deposits and their distribution in the bedrock. The results of groundwater-level monitoring, δ18O-δ2H and 3H isotope analyses and FLOWPC modelling suggest a local and recent origin of the groundwater hosted in shallow flow paths inside the landslide. Chemical and isotope (87Sr/86Sr, δ11B) analyses offer evidence of the presence inside the landslide of small blocks of gypsum that, due to their dimensions, probably have a minor influence on landslide stability. This research demonstrates that the methodology used can provide satisfactory information about bedrock structures and their hydrological aspects.

Comparing 2D capabilities of HEC-RAS and LISFLOOD-FP on complex topography

ABSTRACT This study evaluates and compares two-dimensional (2D) numerical models of different complexities by testing them on a floodplain inundation event that occurred on the Secchia River (Italy). We test 2D capabilities of LISFLOOD-FP and HEC-RAS (5.0.3), implemented using various grid sizes (25–100 m) based on 1-m DEM resolution. As expected, the best results were shown by the higher-resolution grids (25 m) for both models, which is justified by the complex terrain of the area. However, the coarser resolution simulations (50 and 100 m) performed virtually identically compared to the high-resolution simulations. Nevertheless, the spatial distribution of flood characteristics varies: the 50 and 100 m results of LISFLOOD-FP and HEC-RAS misestimated flood extent and water depth in selected control areas (built-up zones). We suggest that the specific terrain of the area can cause ambiguities in large-scale modelling, while providing plausible results in terms of the overall model performance.

Dealing with sediment transport in flood risk management

Flooding events are rising across European watercourses because of changing climatic conditions and anthropogenic pressure. To deal with these events, the European Floods Directive requires the development of flood risk management plans regularly updated every 6 years, where areas affected by flood risk and relative management strategies should be identified. Along the Directive, sediment transport and morphological changes in freshwater environments like rivers are only marginally considered, leading to a possibly wrong estimate of the impact of floods in the case of watercourses in which sediment transport represents a fundamental component. Using the Secchia River in Italy as a case study, the paper compares two numerical simulations performed with the freeware iRIC suite, imposing the same boundary conditions but comparing fixed and mobile bed. The obtained results pinpoint the importance of considering sediment transport in drawing flooding scenarios for alluvial sandy rivers. As suggested by this example, for the incoming revisions of the flood risk management plans, forecasted by 2021, water managers should account for the dynamic behaviour of surface watercourses, considering sediments not only as a driver of pollutants but also as a key aspect that shapes the environment and should be considered in modelling future scenarios and drawing associated management strategies.

Evidence of late-Holocene mud-volcanic eruptions in the Modena foothills (northern Italy)

Among natural hazards, mud volcanoes can damage property and infrastructures and affect hillslope evolution at different spatial and temporal scales. The results of 10-year-long multidisciplinary investigations performed on a Roman-age archaeological site, La Rovina di Montegibbio, are presented, showing a peculiar example of mutual interplay between human settlement and geological forcing in the mud-volcanic environment. The site (350 m a.s.l.) lies at the termination of the upper Secchia River catchment, near the town of Sassuolo (Modena Province). Here, a 4-km-long mud volcano belt borders the Apennines chain front, comprising one of the most prominent mud volcanoes of Italy ( Salsa di Montegibbio), and the still-active chain hinge tectonics gives origin to gas and oil seeps. Based on geological, geoarchaeological, palaeobotanical, geochemical, geophysical records and analytical data, we unravel the onset, the evolution and the abandonment of the settlement in relation to the existence of a previously unknown mud volcano, belonging to the larger Montegibbio mud volcano system. The damages affecting the Roman-age buildings record the ground deformations in the context of mud volcano tectonics. In particular, the pattern of faults set buried under the archaeological site is shown and compared with that of the main mud volcano conduit. At least two Roman-age eruptive episodes have been recorded, whose ejected muds are geochemically characterized. The first recorded eruption must be regarded as the reason for the initial location and function of the sacred ancient settlement. The final site abandonment was because of subsequent severe ground deformations affecting the hillslope as a consequence of mud volcano activity.

Development and assessment of uni- and multivariable flood loss models for Emilia-Romagna (Italy)

Abstract. Flood loss models are one important source of uncertainty in flood risk assessments. Many countries experience sparseness or absence of comprehensive high-quality flood loss data, which is often rooted in a lack of protocols and reference procedures for compiling loss datasets after flood events. Such data are an important reference for developing and validating flood loss models. We consider the Secchia River flood event of January 2014, when a sudden levee breach caused the inundation of nearly 52 km2 in northern Italy. After this event local authorities collected a comprehensive flood loss dataset of affected private households including building footprints and structures and damages to buildings and contents. The dataset was enriched with further information compiled by us, including economic building values, maximum water depths, velocities and flood durations for each building. By analyzing this dataset we tackle the problem of flood damage estimation in Emilia-Romagna (Italy) by identifying empirical uni- and multivariable loss models for residential buildings and contents. The accuracy of the proposed models is compared with that of several flood damage models reported in the literature, providing additional insights into the transferability of the models among different contexts. Our results show that (1) even simple univariable damage models based on local data are significantly more accurate than literature models derived for different contexts; (2) multivariable models that consider several explanatory variables outperform univariable models, which use only water depth. However, multivariable models can only be effectively developed and applied if sufficient and detailed information is available.

Hydrograph estimation at upstream ungauged sections on the Secchia River (Italy) by means of a parallel Bayesian inverse methodology

In this work, we present a reverse flow routing procedure, which allows estimating discharge hydrographs at upstream ungauged stations by means of information available at downstream monitored sites. The reverse routing problem is solved adopting a Bayesian Geostatistical Approach (BGA). In order to capture the complex hydrodynamic field typical of many real cases of rivers including large floodable areas, meanwhile overcoming the computational time limitations, we adopted as forward model a selfdeveloped 2D-SWE parallel numerical model (PARFLOOD) that allows achieving ratio of physical to computational time of about 500-1000. To exploit the computational capabilities of modern GPU cluster, a parallel procedure to estimate the Jacobian matrix required by the BGA approach has been implemented. The inflow hydrograph in a river reach with several meanders and floodplains has been estimated in “only” 13 hours using a HPC cluster with 10 P100 Nvidia GPUs.

Carbon, oxygen and strontium isotopic constraints on fluid sources, temperatures and biogeochemical processes during the formation of seep carbonates - Secchia River site, Northern Apennines

Understanding authigenic seep carbonate formation provides clues for hydrocarbon exploration and insights into contributions to gas budgets of marine environments and the atmosphere. Seep carbonates discovered in the outcropping succession along the Secchia riverbanks (near Modena, Italy) belong to the Argille Azzurre Formation of Early Pleistocene age deposited in an upper shelf environment overlying the Miocene foredeep successions, which include hydrocarbon fields. The fluid migration from the hydrocarbon fields, up to the surface, is presently active on land and started in the marine succession during the Late Miocene.Authigenic globular carbonate concretions and carbonate chimneys are interspersed along the strata throughout the section. A comprehensive geochemical characterisation of the carbonates has been carried out to understand the processes leading to their formation. The carbonate concretions are the record of past hydrocarbon vents linked to the Miocene petroleum system of the Northern Apennines. The samples are composed of >50% microcrystalline dolomite. The δ13C signatures identify two groups in the samples according to different type of formation processes. Globular concretions have positive values that suggest an influence of CO2 associated to secondary methanogenesis due to microbial degradation of higher hydrocarbons. The analysed chimney, with negative δ13C values, is interpreted as former conduit where carbonate precipitation is promoted by Anaerobic Oxidation of Methane coupled with Sulfate Reduction. The δ18O range, coupled with 87/86Sr signatures, indicate that the contribution of deep connate water from the Miocene reservoirs is up to 23% during the formation of the globular concretions. The connate water occurrence is also documented by higher ambient temperatures. The different isotope signatures in seep carbonates result from the relative contribution of the recognised gas and water components, linked to different plumbing systems and fluid supply from a well-defined hydrocarbon field. The seep carbonate characteristics have enlightened variations in biogeochemical processes, which can be rarely quantified in ancient and present-day marine environments.

Investigation of the influence of animal burrowing on the failure of the levee of San Matteo along the Secchia river

Animal burrowing can greatly influence the water pressures in a flood protection embankment and thereby be a cause of breaching of flood defences. However, little guidance and literature is available on this subject. This paper investigates the contribution of badgers, porcupines and foxes to the failure of the levee of San Matteo (Modena, Italy) on 19th January 2014. The proposed method evaluates their influence on the water pressures in the embankment during rainfall and a high water tide. The influence of the burrowing is assessed through a transient FEM flow analysis. Starting from the documented entrances situated in the vadose zone, different scenarios for the internal distribution of tunnels and chambers are proposed. The most likely representative network for the loss of stability of the dike is assessed.

Evidence of an emerging levee failure mechanism causing disastrous floods in Italy

AbstractA levee failure occurred along the Secchia River, Northern Italy, on 19 January 2014, resulting in flood damage in excess of $500 million. In response to this failure, immediate surveillance of other levees in the region led to the identification of a second breach developing on the neighboring Panaro River, where rapid mitigation efforts were successful in averting a full levee failure. The paired breach events that occurred along the Secchia and Panaro Rivers provided an excellent window on an emerging levee failure mechanism. In the Secchia River, by combining the information content of photographs taken from helicopters in the early stage of breach development and 10 cm resolution aerial photographs taken in 2010 and 2012, animal burrows were found to exist in the precise levee location where the breach originated. In the Panaro River, internal erosion was observed to occur at a location where a crested porcupine den was known to exist and this erosion led to the collapse of the levee top. This paper uses detailed numerical modeling of rainfall, river flow, and variably saturated flow in the levee to explore the hydraulic and geotechnical mechanisms that were triggered along the Secchia and Panaro Rivers by activities of burrowing animals leading to levee failures. As habitats become more fragmented and constrained along river corridors, it is possible that this failure mechanism could become more prevalent and, therefore, will demand greater attention in both the design and maintenance of earthen hydraulic structures as well as in wildlife management.

Simulation of the January 2014 flood on the Secchia River using a fast and high-resolution 2D parallel shallow-water numerical scheme

The capability of a GPU-parallelized numerical scheme to produce accurate and fast simulations of floodings induced by levee breaches in large domains, adopting high-resolution digital terrain maps, is investigated. The good predictive skills of the presented 2D shallow-water model were proven with regard to the inundation caused by a levee breach that occurred on the Secchia River, Italy, in January 2014. The numerical computations were carried out on a domain of about 180 km2 adopting a Cartesian grid of approximately 7.2 M cells with size 5 m. The results of the simulation were validated against several field data and observations, including a high-resolution synthetic aperture radar image. A ratio of simulation to physical times of about 1/15 was achieved; this kind of simulation tool opens up new perspectives in the devising and implementing of flood event management strategies for civil protection purposes and with the aim of minimizing the economic loss.

Impacts of Land Cover and Climate Changes on Peak Floods Probability Distribution Function

Climate and land cover are the main regulators of discharge formation. We combined here 5 alternative land cover case with 2 different precipitation scenarios. Land cover scenarios are: (a) present land cover according to CORINE 2006 maps, (b) ICES scenario at 2050, (c) IMAGE scenario at 2050, (d) cementification scenario C1 and (e) cementification scenario C2. The ICES and IMAGE scenarios are based on consideration of economy and population growth, cementification scenarios 1 and 2 are intended as exemplificative what-if scenarios for urbanization of rural areas. Precipitation is modelled as (a) the observed one and (b) increasing of 10% the average value. Peak flood probability distributions are analytically for each of the 10 land cover-climate combinations. The case study is the Secchia river basin in Emilia Romagna region. Results show that in absence of changes in the precipitation regime, the peak flood associated to low return period (

Inferring the flood frequency distribution for an ungauged basin using a spatially distributed rainfall-runoff model

Abstract. The estimation of the peak river flow for ungauged river sections is a topical issue in applied hydrology. Spatially distributed rainfall-runoff models can be a useful tool to this end, since they are potentially able to simulate the river flow at any location of the watershed drainage network. However, it is not fully clear to what extent these models can provide reliable simulations over a wide range of spatial scales. This issue is investigated here by applying a spatially distributed, continuous simulation rainfall-runoff model to infer the flood frequency distribution of the Riarbero River. This is an ungauged mountain creek located in northern Italy, whose drainage area is 17 km2. The hydrological model is first calibrated by using a 1-year record of hourly meteorological data and river flows observed at the outlet of the 1294 km2 wide Secchia River basin, of which the Riarbero is a tributary. The model is then validated by performing a 100-year long simulation of synthetic river flow data, which allowed us to compare the simulated and observed flood frequency distributions at the Secchia River outlet and the internal cross river section of Cavola Bridge, where the basin area is 337 km2. Finally, another simulation of hourly river flows was performed by referring to the outlet of the Riarbero River, therefore allowing us to estimate the related flood frequency distribution. The results were validated by using estimates of peak river flow obtained by applying hydrological similarity principles and a regional method. The results show that the flood flow estimated through the application of the distributed model is consistent with the estimate provided by the regional procedure as well as the behaviors of the river banks. Conversely, the method based on hydrological similarity delivers an estimate that seems to be not as reliable. The analysis highlights interesting perspectives for the application of spatially distributed models to ungauged catchments.

Large reactivated landslides in weak rock masses: a case study from the Northern Apennines (Italy)

This case study paper is about a large rotational rock and earth slide—earth flow located in the Secchia River Valley, in the Northern Apennines of Italy, that has displayed multiple reactivation phases between 2002 and 2004. The main geological constraints of the mass movement are related to the overlap of flysch rock masses over clayey complexes that allows rock slides to take place in the source area. The disarrangement and weathering of rock masses following slope movements causes large amount of fine-grained debris to be accumulated on the slope and mobilised by earth sliding and flowing. Analysis of rainfall data at the onset of reactivation events has proved that they occurred after periods with cumulated values higher than the averages of the last 30 years. The quantification of the morphological modifications induced by these reactivations has been made possible by comparing pre- and post-event digital elevation models. Depletion and accumulation has been in the range of 30 m in different parts of the slope. In particular, an advancement of the landslide toe of more than 400 m, which caused a 30-m thick landslide tip to deposit, has been clearly seen. Monitoring data regarding subsurface movements and surface tension crack widening (tension cracks so large as to be properly described at trenches) has shown that sliding surfaces as deep as 43 m exist in the upper part of the landslide, while the accumulation lobe has moved by sliding and flowing over surfaces as deep as some 10 m. Velocities of cm/day have been recorded in the deep surfaces and in widening trenches of the source area, while the advancement of the accumulation lobe has been estimated as having velocities of up to 10 m/day. Groundwater in the landslide body has been observed at depths of 5–15 m in the upper areas, while it is estimated as being at the ground level in the toe. On this basis, it is concluded that the landslide still has a high potential for further development, both in the upper landslide zone and in the toe area.

Investigation and monitoring in support of the structural mitigation of large slow moving landslides: an example from Ca' Lita (Northern Apennines, Reggio Emilia, Italy)

Abstract. The Ca' Lita landslide is a large and deep-seated mass movement located in the Secchia River Valley, in the sector of the Northern Apennines falling into Reggio Emilia Province, about 70 km west of Bologna (Northern Italy). It consists of a composite landslide system that affects Cretaceous to Eocene flysch rock masses and chaotic complexes. Many of the components making up the landslide system have resumed activity between 2002 and 2004, and are now threatening some hamlets and an important road serving the upper watershed area of River Secchia, where many villages and key industrial facilities are located. This paper presents the analysis and the quantification of displacement rates and depths of the mass movements, based on geological and geomorphological surveys, differential DEM analysis, interpretation of underground stratigraphic and monitoring data collected during the investigation campaign that has been undertaken in order to design cost-effective mitigation structures, and that has been conducted with the joint collaboration between public offices and research institutes.

Sensitivity of the peak flows to the spatial variability of the soil infiltration capacity for different climatic scenarios

The use of distributed rainfall-runoff models in applied hydrology has been widely increased in the latter years. One of the main advantages that these model possess with respect to their lumped-parameters counterpart is the possibility to account for the spatial variability of the local runoff production. However, the application of these models is often limited by the large amount of data required, which are quite difficult to obtain. A possible way out for reducing the data requirements of distributed models is to neglect the spatial variability of the soil infiltration process by lumping the correspondent model parameters at the basin scale. This might be a reasonable assumption if one is interested in modelling those situations where the spatial variability of infiltration is expected to exert a marginal effect on the river discharge. Accordingly, the present study is aimed at verifying the effects of the spatial variability of the soil infiltration parameters on the flood flows modelled by a distributed model, for different climatic scenarios. The analysis is carried out referring to the case study of the Secchia River basin, located in northern Italy.