Natural Hazards https://doi.org/10.1007/s11069-018-3398-5 ORIGINAL PAPER

A historical geomorphological approach to flood hazard management along the shore of an alpine lake (northern Italy) F. Luino1 • A. Belloni2 • L. Turconi1 • F. Faccini3 • A. Mantovani1 P. Fassi4 • F. Marincioni5 • G. Caldiroli2

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Received: 17 March 2018 / Accepted: 8 June 2018  Springer Nature B.V. 2018

Abstract A project to develop a flood hazard management plan along the east shore of Lago Maggiore was carried out. Several municipal territories along a coastal stretch have been analysed, identifying the rate of water rise and the limits of the submerged areas. This study discusses the overall methodological approach and presents the results for Porto Valtravaglia, as a significant case study. The first step was a detailed analysis of historical events to locate the most frequently damaged sites. Thousands of historical documents on past floods were collected, selected and validated, to map the most vulnerable sites. The second step was a morphological analysis of the studied coastal stretch. Multi-temporal aerial snap-shots were used and field surveys were conducted to verify the reliability of the historical data and to identify the critical hydraulic conditions along the shore. The third step was a review of the general urban development plans of the 17 studied municipalities. Aerophotogrammetric and cadastral maps were used to evidence and define the eight classes of land use destinations. In addition, the floodable areas were divided into three vulnerability and exposure categories considering different peculiarities of social and working life. Finally, using GIS spatial analysis tools, these data were compiled into risk maps and wielded as the municipal emergency plans’ baseline scenarios. For each studied municipality was hypothesised the alarm thresholds upon which were activated the flood emergency procedures. Keywords Lacustrine floods
Historical geomorphology
Emergency plans
Lago Maggiore
Northern Italy

1 Introduction Floods are the most widespread natural events affecting people and infrastructures worldwide (Luino 2016). Every year, there are many floods in populated areas all over the world causing the death of thousands of people and destroying crops, facilities, and & F. Luino [email protected] Extended author information available on the last page of the article

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infrastructure. More than 20 million people worldwide are affected by floods annually, and this number could increase to 54 million by 2030 due to climate change and socioeconomic development (WRI 2015). Within Europe, Italy ranks highest in the variety of geohydrological hazards: these processes claim victims and cause damage amounting to billions of Euros every year (Canuti et al. 2001). Historical research has shown that 11,000 landslides and 5400 floods have occurred in the last 80 years. The costs for these processes are extremely high. In the period 1980–2000, the Italian government has paid 42.4 billion Euros, that is, 5.7 million Euros per day (Luino 2005). Lombardy is the most important region of Italy, not only from an economic point of view: it has a surface of 23,844 km2 and occupies the middle part of the Po plain. Milan is its chief town with over than 3 million inhabitants. This region is historically vulnerable to both riverine and lacustrine floods. According to a recent research of the Italian National System for Environmental Protection-ISPRA (ISPRA 2015), in Lombardy, 80.8% of the towns are exposed to high level of geohydrological hazard; as a matter of fact, landslides, debris flows, and floods, caused numerous casualties and heavy losses of infrastructures, over the past few decades (1983, 1987, 1988, 1992, 1993, 1994, 1997, 2000, 2002 and 2014) (Cancelli and Nova 1985; Ceriani et al. 1992; Govi and Turitto 1994a; Govi et al. 2002; Tropeano et al. 2006; Luino and Turconi 2017). Despite a seeming increase in event frequency, the most significant impacts are evenly distributed over time (Luino 2005). On the contrary, the rate of damage of these events is constantly increasing (Luino et al. 2014). Inappropriate land use policies, especially the post-WW2, played a more important role, letting the urban expansion occupy floodplains (Luino et al. 2012) and areas vulnerable to debris flows and landslides. The recognition of flood-prone areas has been, and still is, an ongoing debate within the scientific community both in Italy (Caroni et al. 1990; Govi and Turitto 1994b; Dutto 1994; Giacomelli et al. 1998; Oliveri et al. 1998; Sole and D’Angelo 1999; De Martino et al. 2000; Luino et al. 2002b; Aronica et al. 2002; Aureli et al. 2006; Castellarin et al. 2011; Faccini et al. 2015; Luino et al. 2016) and worldwide (Oya 1971; Wolman 1971; Waananen et al. 1977; Tag-Eldeen and Nilsson 1979; Leroi 1996; Faisal et al. 1999; Bates and De Roo 2000; Sharma and Priya 2001; Horritt and Bates 2002; Hardmeyer and Spencer 2007; Pappenberger et al. 2007; Gilles et al. 2012; Okoye and Ojeh 2015). Nowadays, technical and scientific public bodies develop multi-disciplinary analysis to detect flood-prone areas (Disse and Engel 2001), draw up emergency management plans, and provide guidelines for revising the existing urban plans or informing the design of future ones. With this study, we contribute to the process of enhancing safety for the people and assets located along the lake shore. A multi-disciplinary approach formed by a historical investigation and a geomorphological study superimposed on an updated land use and planning map will facilitate the definition and visualizing flood-prone areas along the lake shores. If properly used, this information will help reducing future flood damage on the existing urban areas and possibly limit the proliferation of new buildings over inundable areas.

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2 Study area: the eastern bank of the Lago Maggiore Lago Maggiore, the second largest lake (210 km2) of Italy, lies at the foot of the Alps, bordering the Italian Regions of Piedmont to the West and Lombardy to the East and Switzerland to the North (Fig. 1). The Swiss territory houses just its extreme northern end (42.6 km2). The lake’s large catchment basin (6598 km2) includes the valleys of the Ticino and Toce Rivers (the principal tributaries), and the Maggia and the Tresa torrents. It also receives water from the lakes of Lugano, Orta, Varese and Mergozzo. The Ticino River is its only outlet from Lago Maggiore at Sesto Calende (close to the Miorina Dam) and then after 110 km flows into the Po River near the town of Pavia. This study analyses the Lombardy shore (highlighted with an azure line in Fig. 1), comprising 17 municipal territories along a coastal stretch of about 56 km. In this paper, by way of example, are shown maps and tables of suggested emergency procedures only for one of the town studied, the urban area of Porto Valtravaglia. The little town is here analysed both because morphologically it is suitable to be analysed properly to an analysis of the hydraulic risk, and because it suffered serious damage during the flood of October 2000 and finally since, in the oldest part of the town, it is possible to find a marble plaque indicating the height reached by the floodwaters during the greatest flood of October 1868 (see box in Fig. 9).

Fig. 1 Map of Lago Maggiore with the 17 studied municipalities (red dots) along the Lombard shore. A = 460858.92N 85118.41E, B = 45454336.75N 83610.29E. Source: Google Earth

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3 Study about lacustrine flooding Lacustrine flooding mechanisms are not as widely studied as are those of river flooding. The available scientific literature shows a decidedly higher number of articles dealing with river floods. Most likely, this is due to river floods being a more frequent occurrence and often with sudden onset causing victims and large damage. Lake floods, on the other hand, have slow onset allowing people to escape and almost completely save their movable property. Among the papers dealing with lacustrine floods, some tackle the phenomena from a climate change perspective (Gilli et al. 2013), or provide geomorphic evidence and analysis of historical fluctuations (Atwood 1994). While others provide forecast of future flooding by analyzing precipitation, evaporation, inflow and water levels (Vecchia 2008). Insurance companies have also supported studies to assess the economic impacts of lacustrine floods (Wang et al. 2011; Grahn and Nyberg 2014). Many studies point to the rising of the lakes not being caused by natural processes, but being the consequences of dam and levee’s construction or bad watershed management (Shankman and Liang 2003; Shankman et al. 2006; Tucci 2006; Wang et al. 2015). The cost of lacustrine flood mitigation is also greatly studied (Cummings et al. 2012; Zheng et al. 2014; Gulbin 2017), along with the consequent socio-environmental impacts (Arago´n-Durand 2007). Vulnerability of lifelines along lake shores has been studied and appropriate protective actions proposed (Keith 2008). Overall, it can be said that lacustrine flood hazard is studied through uncertainty propagation of the rainstorm control model (Fu et al. 2013), and by geological–geomorphological studies aimed at comprehending the local lake watershed system, to help designing flood control structures to protect the exposed urban area (Ferrario et al. 2015).

4 Materials and methodological approach In the last two decades, the Istituto di Ricerca per la Protezione Idrogeologica (IRPI) of the Consiglio Nazionale delle Ricerche (CNR) located in Turin has studied several areas of Lombardy using a multi-disciplinary approach (historical, morphological and land use/town planning) with the goal to identify flood-prone areas along some important watercourses to inform the revision of the existing urban and emergency plans (Luino et al. 1999, 2002a, b; Lumbroso et al. 2011). Building on these prior studies, the CNR-IRPI has applied the same multi-disciplinary approach to the analysis of flood risk along the Lago Maggiore shores. This study comprises: (1) historical investigation of past flooding data, (2) geomorphological study, (3) land use and urban planning analysis. The resulting maps were joined through GIS software to create a risk map which was used to revise and update municipal emergency plans. Historical investigations are becoming increasingly important for a correct prediction and prevention of future floods. It is, therefore, essential to search, select and analyse all the documents describing past floods and their effects (Benito et al. 2004; Kadetova and Radziminovich 2014). For this study, the gathering of historical documentation about past flood events, was carried out in different places: (a) Italian national technical office archives, searching for unpublished reports on past inundations. Useful pieces of information were collected about flood dynamics and timing, discharges, hydrometric levels, flooded areas, water depths in the towns, number of victims and economic damage; (b) municipal libraries, searching for

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papers, technical and historical books about Lago Maggiore; (c) newspaper and magazines archives, searching for local articles about flood events; (d) municipal archives and registry of the 17 villages examined, searching for reports and other documents detailing the city or village councils’ activities. At the end of the research, more than 400 old documents dealing with past floods, going back to the 17th–18th centuries, were collected. A morphological study was carried out along the whole shore, with a particular detail for the urbanized areas. For this study, different maps have been consulted and used since the end of the 18th century: maps of the Theresian Cadastral realized at the mid-eighteenth century, maps of the Lombard–Venetian Kingdom Stabile cadastre (1841) and the maps of the Istituto Geografico Militare Italiano from 1880. For the last few decades, a good historical scientific support has been provided by aerial photographs taken in the years 1954, 1968 and 1978, black and white or colour, at different scale. The analysis of the old maps and the photointerpretation of snap-shots highlighted the natural and anthropic changes of the coastline. The reliability of the evidence from the aerial photographs was verified through field surveys along the shore. During the surveys, all buildings, roads, bridges, bank protections and protecting walls located along the coast were photo-documented and their maintenance status and conditions were described. Also the mouth of the streams crossing the urban areas was considered: their critical hydraulic conditions along the shore were indicated. With the aim of acquiring the existing status of the built environment and verifying areas for future building expansions, a territorial and urban analysis was carried out for all the municipalities along the coast. In a first phase of the work, after having collected the necessary maps in the Municipal Technical Offices, the urban planning instruments in force (that is mainly the general urban development plan) were analysed and subsequently a grouping was carried out for the different areas. The collected maps refer to the municipal land use plans or their general variations: they are cadastral maps, aerophotogrammetric maps at 1:2000 and 1:5000 scale. Their use can help to identify the critical areas from a hydraulic point of view, to forbid the construction of new buildings and hence, to limit the increase of new risk situations along the coast. For each municipal territory, a careful and updated analysis was carried out of the urbanized areas. The different land uses have been highlighted based on importance of the buildings and of the activities carried out inside: residential, tourist, public services, commercial/industrial, sports, agricultural, etc. Then these categories have been merged. In the study, another important factor has been considered, in fact, the categories are not subject to the same degree of vulnerability. It was, therefore, important to attribute to these categories several levels of vulnerability according to different parameters: (a) presence or concentration of people over a 24-h period or during particular hours of the day; (b) presence of machineries or properties; (c) presence of social–recreational activities and/ or loss of profit due to damage to the agricultural zones; (d) presence of environmentally attractive areas. This result was reported on the Regional Technical Map (scale 1:10,000), supplemented by the information drawn from recent aerial photogrammetric shots. It is also necessary to emphasize how often the lack of homogeneous and updated reference cartography created numerous problems during field surveys and in the drafting of summary maps.

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5 Results Historical research highlighted that over the period 1826–2017, the Lago Maggiore coast was affected by at least 148 damaging floods (Fig. 2). In terms of monthly distribution, October–November appears to be the months recording the highest number of damageprovoking events (47% of the total). The systematic measurements of the Lago Maggiore water level date back to 1829, with the installation of the Sesto Calende hydrometric station on the Lombardy shore (see Fig. 1). Another historic hydrometric station from which we gathered data is the Pallanza hydrometer (Cantoni 1869), located on the opposite shore of the lake, in Piedmont (see Fig. 1). Data from the Sesto Calende station are pivotal for any hydrometric series analysis because it records the main changes occurred in the structure of the Ticino riverbed as it exits Lago Maggiore. The most severe inundation recorded, occurred on 3 and 4 October 1868 (Fig. 3): all towns and villages along the studied shore were heavily flooded. Water levels reached the maximum height ever recorded. At Sesto Calende, waters rose to 6.94 m (199.81 m a.s.l.) above the level zero of staff gauge (located at 192.87 m a.s.l.). This height was 2.32 m higher than the second historical level, reached on 17 October 2000. The rate of water rise was also carefully studied, as this is a very important information upon which drew new emergency management plans (Krausmann et al. 2011) (Fig. 4). During the October 1868 floods, the Sesto Calende hydrometric station recorded a

Fig. 2 Lago Maggiore flood events affecting the Lombard shore, from 1826 to 2017 (compiled into a 25-year period). This chart considers only the 148 top levels that reached or exceeded 2 m above the level zero of the Sesto Calende’s staff gauge, located at 192.87 m a.s.l. Inset, monthly distribution: October (red) and November (orange) are the months with the highest number of floods (together reach 47.1% of the total). No floods occurred in January, February, March and December

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Fig. 3 An antique print of the 1868 flood depicting the main square of Sesto Calende. The colour thumbnail image at the top left displays the present situation: the ‘‘Albergo Tre Re’’ Hotel is clearly identifiable (yellow asterisk), even if slightly modified. In the thumbnail’s background, indicated with a red arrow is the Lago Maggiore; the red oval pinpoint is the location of the marble plaque shown in Fig. 4

Fig. 4 Sesto Calende: a photo shooted a few meters from the lake during the November 2002 flood (see shore road and pathway inundate). The marble plaque indicates the heights and dates of the main flood events occurred from 1705 to 2000

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maximum rising rate of 16.3 cm/h; this was twice as much the values recorded during the previous month (September 1868), when over a period of 24 h, the maximum rising rate value was 7.3 cm/h. As a matter of fact, the exceptional flood of October 1868 caused an erosion of the Miorina threshold (channel outlet), essentially altering the scale of lake flooding. The erosional change occurred is comparable to a general lowering of the lake bottom of about 30–36 cm (De Marchi 1950; Baccarini 1973). Another important event that greatly affected the outflow of Lago Maggiore was the construction of the mobile barrier of the Miorina Dam, toward the end of 1942. As a consequence, to perform comparisons between homogeneous series of hydrometric measurements, the flood level’s series taken before or after the construction of such dam must be examined separately. All statistical considerations aimed at informing the revision of the existing urban and emergency plans should only consider data of the lake flood events that occurred after 1943. In the period 1943–2017, 54 flood events exceeding the 2.13 m mark at the Sesto Calende staff gauge (located at 192.87 m a.s.l.), corresponding to the level 195.00 m a.s.l. at which begins the inundation in some of the coastal municipalities on the Lombard shores. Unlike riverine floods, lacustrine floods can last many days. During this period, as it often happens during lacustrine flood events, the lake has several altimetric fluctuations during the same event: for this analysis, only the maximum level reached in each flood was considered, corresponding also to the maximum annual. The 54 flood events cited have thus reduced to 31 (Fig. 5). Thirteen of these events reached or exceeded the level of 196.00 m, while only two inundations exceeded the level of 197.00 m (September 1993 and October 2000). The maximum of 197.49 m a.s.l. was registered on October 2000 (historical maximum since the construction of the Miorina Dam).

Fig. 5 Lago Maggiore’s floods: maximum water levels reached over the period 1943–2017 measured at the Sesto Calende hydrometric station. The red line indicates the height of 195.00 m a.s.l., to which inundation begins in some of the coastal municipalities on the Lombard shores

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All gathered instrumental data and information (newspaper articles, flood maps, photographs, and interviews with local residents) were verified and analysed to draw a historical map of all damaged sites along the shore. In Fig. 6, as methodological output example, the hazard map of the small town called Porto Valtravaglia is shown. For each municipality, the limit of the inundated areas recorded during the severe event of the October 2000, the maximum inundation since October 1868, and considered the ‘‘flood of reference’’, and set as the current flood marker (blue line in Fig. 6). Concurrently, reports about past flood events were entered into a catalogue file and associated with a symbol linked to the map. The symbols differ in form and colour to show exact or approximate location of the damaged sites (structure, infrastructure, stretch, etc.). A red dot denotes a record referring to an exact location for the damaged site. A yellow triangle, situated at the midpoint of a bank or a damaged road, indicates that the record has no clear reference to repair or consolidation works. A green square next to the name of the village means that the record contains only general information of the flooded area. This kind of map was done for each studied municipality of the coast. The morphological study was based on the analysis of the old maps and multi-temporal aerial photographs integrated by morphological surveys, which allowed identification of evidence for all the sites critically exposed to inundation, e.g. low-lying areas, unstable walls, bridges with insufficient spans, covered channels and other features that could create severe problems for the public safety. The most important tributaries had also their final stretch analysed, to highlight the built-up sectors that are mostly exposed to backwater phenomena.

Fig. 6 Porto Valtravaglia hazard map. Sites damaged by flood events registered over the last 100 years (1907, 1977, 1981, 1983, 1986, 1987, 1993, 2000 and 2002) are highlighted with different symbols: the labels refer to the event code (alphanumeric in ascending order) related to a single historical report. The blue line delineates the limit reached by the flood waters during the 2000 flood event. The big red circle marks the areas flooded multiple times (almost nine times), while the blue circles pinpoint the hydraulic critical sites (mainly bridges with insufficient span). Within the red circle is located the wharf of Porto Valtravaglia, named ‘‘scalo’’

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The production of the land use maps for the areas near the shore required an in-depth study of the 17 municipalities. The urban planning mosaic is generally composed of eight categories defined by their principal functions: (A) residential settlement: existing and anticipated residential areas; (B) hotel/residences and tourist facilities: residences, hotels, health resorts, etc.; (C) public services areas: municipal buildings, garrisons, schools, hospitals, churches, dumping areas and storage platforms, etc.; (D) sport areas, utilities and standards: public gardens, parks, athletics grounds, private and public sport clubs, etc. All areas occupied by roads, railways and cemeteries were marked in the same colour; (E) industrial and handicraft areas: existing and anticipated industrial, craft and commercial buildings; (F) agricultural areas: sheds, stables, and other old farming buildings; (G) woods: forests, grassland, pastures; (H) lake areas/beaches: natural areas along the lake defined as flood-safeguard zones. Only five of these eight categories are present in the Porto Valtravaglia urban area (Fig. 7). The final step, the result of all the analyses previously developed, concerned the production of a ‘‘risk map’’. Each of the eight land use categories was assigned an index according to the following vulnerability parameters: (i) presence/concentration of people over the 24-h period and in particular hours of the day; (ii) presence of machineries or properties; (iii) presence of social–recreational and agricultural areas; (iv) presence of environmentally attractive areas. Indeed, to define the risk level of the studied shores, analysis was also performed to evaluate the construction characteristics and structural behaviour of exposed buildings. The vulnerable buildings were assessed in terms of expected damage (Luino et al. 2014; Glas et al. 2017), also considering the related costs of any improvement or restructuring measures envisaged for flood mitigation. Joining the hazard map (see Fig. 6), defining the maximum heights reached by the floodwaters along the lake shore, with the urban planning map (see Fig. 7) enriched with these further information, a simplified risk map was obtained (Fig. 8). Three classes of

Fig. 7 Urban planning map of Porto Valtravaglia municipal area: the land use planning categories are indicated by different colours

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Fig. 8 Porto Valtravaglia’s final map indicating the shore areas with different flood risk levels

different flood risk levels were defined: HIGH level (comprising the A–C land use categories); MEDIUM level (D–F), and LOW level (G and H).

6 Emergency planning in the Lago Maggiore area Emergency management within the study area had to consider two distinct governmental jurisdictions. The northern segment of the lake shore, from the Swiss border to Laveno (Fig. 1), is under the jurisdiction of the ‘‘Valli del Verbano Mountain Community’’ (a territorial association of mountain and foothill municipalities). This intermediate government body was required by the Lombardy Regional Law no. 16 of 22/5/2005 (Unified Text about Civil Protection), to, inter-alia, develop and coordinate an emergency plan for all the municipalities included in its jurisdiction. The southern segment of the shore, stretching from Laveno down to Sesto Calende (Fig. 1), is not included in the Mountain Community, and the emergency plans have been drafted independently by each individual municipalities. To guarantee the coordination among the various emergency plans, the Regional Government of Lombardy ordered its civil protection technicians to harmonize the alert and emergency management procedures in such area. This study contributed to this goal providing alert thresholds, extension and limits of the previously inundated areas around Lago Maggiore. The worst case flooding scenario was again defined as the maximum extension of the area flooded during the event of October 2000, the most important event of the twentieth century, not only for Porto Valtravaglia (Fig. 9), but for all the small towns along the shore. To prepare an emergency scenario map, the authors have considered: the hazard analysis map (with the boundaries of the expected inundation based on the 2000 flood) and

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Fig. 9 October 2000: Dock square and ticket office of Porto Valtravaglia (photo Luino F.). In the small photograph, the marble plaque shows the height of the floodwaters during the 1868 event, 2.32 m higher than the 2000 event level

Table 1 Important thresholds for Porto Valtravaglia Alert codes

Altitude (m a.s.l.)

Pre-alert

195.12

Spatial reference

Estimated time from the beginning of the flood in the lowest point (increasing rates of 5–10–15 cm/h)

Laveno

0

Place Caduti del Lavoro Alert

195.40

Porto Valtravaglia

From 2.00 to 6.00 h

Dock and piers Emergency

195.60

Porto Valtravaglia

From 3.20 to 10.00 h

Provincial Route 69

the infrastructures analysis map, with the critical evaluation of the vulnerable buildings including the strategic infrastructures (useful for emergency management operations). The emergency scenario map layouts the infrastructures likely to be damaged and the possible consequences on the population. These scenarios are defined on the basis of spatial exposure and vulnerability data as well as past events. The definition of an ‘‘emergency scenario’’ contributes to the definition of the possible areas likely to be hit by the next extreme event, thus providing important information, such as the location and extent of the most flooded area, the structures (including strategic ones) that may be involved, the functionality (more or less compromised) of the transport networks involved, the routes of communication and the distribution lines, as well as the expected losses in terms of human lives, injuries, homelessness, collapsed and damaged buildings along with the corresponding economic damages. All events with obvious repercussions on civil protection activities, both in terms of planning and actual emergency response. In the

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Natural Hazards Table 2 Specific flood emergency procedures in Porto Valtravaglia Urban system

Place

Expected damages

Response actions

Scenario 1/phase 1—level of water rise to 195–196 m a.s.l Town centre

Dock, Ronchetti Square, Borgato Street, houses along the northward shores

Residential buildings: Expected basement flooding Public services: Flooding in the ferries ticket office, Dock and Market square

Interruption of navigation Services and public market. Rising of wharfs and moorings

Commercial—tourist structures: Flooding in the service station Road network

Dock Square, Ronchetti Square

Flooding of the provincial route 69

Coordinated action of the Municipal and Provincial government: road closure and diversions: D1, D2, B1, B2, B3

Lifelines

Market Square

Interruption of electrical supplying on the lake front

Shut down electrical network (point T1)

Critic points

Muceno—bottleneck on Provincial Route 31

Traffic jam (this is the only alternative to Route 69)

Road signals detouring traffic.

Scenario 2/phase 2—level of water rise to 196–197.5 m a.s.l. Population

Borgato Street, lake shore

Town centre

Dock Square, Ronchetti Square, Borgato Street, Mazzini Street, houses along the coast northward

Road network

Lifelines

Preparing evacuation of disabled people (zone E1) and boat delivering supplies at isolates home (zone I1) Residential buildings: Flooding in the basements and lower floors

Preparing for: Footbridges in zones P1, P2 Sand sacks in zones S1, S2

Commercial—tourism structures: Flooding of lower floors of shops, banks, hotel, restaurants, newspapers kiosk, pharmacy Public services: Flooding in the basements of the town hall and the post office

Placing of sand sacks in zone S3

Provincial Route 69: Lucchini Boulevard (the stretch bordering with Brezzo di Bedero), Dock Square, Ronchetti Square

General flooding and traffic disruption

Road closure at point B5 and B3

Battisti Street, Ronchetti Street, Mazzini Street

General flooding of the road network

Borgato Street, lake shore

Possible damages to the sewer system

Preparing for school closure

Road closure at point B4

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Fig. 10 Extract of the emergency scenario map for Porto Valtravaglia (town centre)

former, the information allows to identify and describe the potential impact to organize the human resources, the materials to be used and their allocation. In the latter, the information on the evolving event provides a timely description of the ongoing impact, thus informing the decision on which supporting activities pursue for overcoming the emergency. Using historical data, three emergency thresholds have been defined for each municipality, assessing different rates of water rise (5–10–15 cm/h). To each threshold was linked the estimated flooded areas. Table 1 shows the alert levels and their spatial references, while Table 2 details the emergency procedures. This information along with a detailed town-planning analysis allowed highlighting the critical situations existing in the various municipal territories. Figure 10 represents an excerpt of the coordinated emergency scenario map in the municipality of Porto Valtravaglia: operative indications, such as escape routes, blocks on the road network, buildings to be evacuated are shown. Unfortunately the urban area of Porto Valtravaglia is very low, and indeed the town has been flooded several times, even after minor meteorological events.

7 Discussion and conclusions Despite the numerous and frequent flooding of Lago Maggiore (Luino et al. 2005), urban development of its shores continues unabated. Future development policies should avoid the phenomenon referred to as the ‘‘safe development paradox’’ (Stevens et al. 2010). Indeed, the lake shores have been undermined by intensive and unorganised urbanization since the 1950s (Luino et al. 2012). In such densely inhabited areas, risk mitigation is no longer deferrable and should be implemented through: (i) in-depth analysis of the territorial hazards (Karmakar et al. 2010; Cuya-Antonio and Antonio 2017), (ii) empowerment and

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accountability of the residents; (iii) compulsory flood insurance. The historical geomorphological approach to flood risk reduction proposed in this paper is a valid method to identify flood-prone areas. Particularly, this method can be useful not only to formulate guidelines for future urban development, but also to outline risk scenarios for developing or updating emergency plans (Frigerio et al. 2013). The second and third aspects are more problematic in Italy. The empowerment and accountability of citizens in terms disaster reduction require a profound cultural change. Who is responsible for flood risk and who should pay for its mitigation are still unsettled questions. Quite often the responsibilities for the creation of risk lie both in the public and private sectors (poor planning and building speculation), yet the costs to repair past errors are expected to be paid off by the government. Namely, the feast tab (nefarious urban development of these last 80 years or so) is expected to be split among both attendees and non-attendees, i.e. among the entire national community. For this reason, the idea of developing a flood insurance programme (Kron 2005, 2009; Priest et al. 2005; Luino et al. 2009; Surminski et al. 2015) to distribute the cost of flood mitigation only among those who expose themselves to flood hazard, possibly to make them more responsible during future choices, is being resisted. Until this cultural change happens, the practical solution is to keep enhancing flood hazard and flood risk assessment methodologies and fostering emergency planning and management to reduce the loss of lives and infrastructures.

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Affiliations F. Luino1 • A. Belloni2 • L. Turconi1 • F. Faccini3 • A. Mantovani1 P. Fassi4 • F. Marincioni5 • G. Caldiroli2

•

1

Consiglio Nazionale delle Ricerche, Istituto di Ricerca per la Protezione Idrogeologica (CNRIRPI), Strada delle Cacce 73, 10135 Turin, Italy

2

Regione Lombardia, Direzione Generale, Sicurezza, Protezione Civile e Immigrazione, Piazza Lombardia 1, 20100 Milan, Italy

3

DISTAV – University of Genoa, Corso Europa 26, 16145 Genoa, Italy

4

Regione Lombardia, Protezione Civile, Coordinamento Service Tecnico H24, Sala Operativa, 20100 Milan, Italy

5

Department of Life and Environmental Sciences, Universita’ Politecnica delle Marche, Via Brecce Bianche 12, SNC, 60131 Ancona, Italy

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