Nat. Hazards Earth Syst. Sci., 12, 2329–2346, 2012 www.nat-hazards-earth-syst-sci.net/12/2329/2012/ Natural Hazards doi:10.5194/nhess-12-2329-2012 and Earth © Author(s) 2012. CC Attribution 3.0 License. System Sciences

Uncorrected land-use planning highlighted by flooding: the Alba case study (Piedmont, Italy)

F. Luino, L. Turconi, C. Petrea, and G. Nigrelli Consiglio Nazionale delle Ricerche, Istituto di Ricerca per la Protezione Idrogeologica, Strada delle Cacce 73, 10135 Torino, Italy

Correspondence to: F. Luino ([email protected])

Received: 19 March 2012 – Revised: 22 May 2012 – Accepted: 8 June 2012 – Published: 24 July 2012

Abstract. Alba is a town of over 30 000 inhabitants located This study shows that the historic floods and their dynam- along the Tanaro River (Piedmont, northwestern Italy) and ics have not been duly considered in the land-use planning of is famous for its wine and white truffles. Many important Alba. The zones that were most heavily damaged in the 1994 industries and companies are based in Alba, including the flood were those that were frequently affected in the past and famous confectionery group Ferrero. sites of more recent urbanisation. Despite recurrent severe The town suffered considerably from a flood that occurred flooding of the Tanaro River and its tributaries, areas along on 5–6 November 1994. Forty-eight percent of the urban area the riverbed and its paleochannels have been increasingly was inundated, causing severe damage and killing nine peo- used for infrastructure and building (e.g., roads, a munici- ple. After the flood, the Alba area was analysed in detail to pal dump, a prison, natural aggregate plants, a nomad camp), determine the reasons for its vulnerability. which has often interfered with the natural spread of the Information on serious floods in this area since 1800 was floodwaters. Since the 1994 flood, many remedial projects gathered from official records, state technical office reports, have been completed along the Tanaro and its tributaries, in- unpublished documents in the municipal archives, and arti- cluding levees, bank protection, concrete walls and floodway cles published in local and national newspapers. Maps, plans channels. In spite of these costly projects, some areas remain and aerial photographs (since 1954) were examined to recon- at high risk for flooding. struct Alba’s urban development over the last two centuries The method used, which considered historical data, river and the planform changes of the Tanaro River. corridors identified by hydraulic calculations, geomorpho- The results were compared with the effects of the Novem- logical aspects and land-use planning, can indicate with good ber 1994 flood, which was mapped from aerial photographs accuracy flood-prone areas and in consequence to be an use- taken immediately after the flood, field surveys and eyewit- ful tool for the coherent planning of urban expansion and the ness reports. mitigation of flood risk. The territory of Alba was subdivided into six categories: residential; public service; industrial, commercial and hotels; sports areas, utilities and standards (public gardens, parks, athletics grounds, private and public sport clubs); aggregate 1 Introduction plants and dumps; and agriculture and riverine strip. The six categories were then grouped into three classes with differ- Flood plains have consistently been attractive locations for ent flooding-vulnerability levels according to various param- urban development because of level ground, fertile soil, good eters. Using GIS, the three river corridors along the Tanaro sun exposure, ease of access and plentiful water. Human use identified by the Autorita` di Bacino del Fiume Po were over- has been constant and extensive, and growing urban pres- laid on the three classes to produce a final map of the risk sures are causing additional development. The flood risk has areas. not been adequately considered, and the use of flood plains has often resulted in loss from floods or in the expense of adequate protection (Waananen et al., 1977). The increase in

Published by Copernicus Publications on behalf of the European Geosciences Union. 2330 F. Luino et al.: The Alba case study (Piedmont, Italy)

flood damage in the last decades has generally been caused (Smith, 1994; Du Plessis and Viljoen, 1999; Loaiciga,´ 2001; by the human settlement of flood plains, which increases ex- Messner and Meyer, 2006; Brody et al., 2008; Jonkman et posed property and population within flood-prone areas. al., 2008; Luino et al., 2012). In the last 25 yr, insurance The detection of areas that are potentially subject to flood- companies have shown interest in this field and various pa- ing has been one of the most frequent debates among the pers and reports have been published (Arnell, 1987; Smith, scientific community in Italy during the last decades (Caroni 1994; FEMA, 1997; Munich Re, 1997; Glaschen et al., 1998; et al., 1990; Govi and Turitto, 1994; Dutto, 1994; Giacomelli Blanchard-Boehm et al., 2001; Kron, 2009; Bhattamishra, et al., 1998; Maraga and Turitto, 1998; Oliveri et al., 1998; 2010). It is important to be able to estimate the likelihood Sole and D’Angelo, 1999; De Martino et al., 2000; Luino et and the social, economic and environmental consequences al., 2002a; Aronica et al., 2002; Aureli et al., 2006; Castel- of a disaster (Van der Sande, 2001; Queensland Govern- larin et al., 2011) and internationally (Oya, 1971; Wolman, ment, 2002; Liu and Liu, 2002; FEMA, 2003; United Na- 1971; Newson, 1975; Waananen et al., 1977; Dunne and tions, 2006). Leopold, 1978; Tag-Eldeen and Nilsson, 1979; Mayer and In Italy, the increasing vulnerability of land along water- Nash, 1987; Leroi, 1996; Faisal et al., 1999; Tucci and Vil- courses is mainly due to intensive urbanisation, which has ac- lanueva, 1999; Bates and De Roo, 2000; Sharma and Priya, celerated since the 1960s. Urban development has not been 2001; Berg, 2002; Horritt and Bates, 2002; Sinnakaudan et controlled by careful land management that considers nat- al., 2003; Hardmeyer and Spencer, 2007; Pappenberg et al., ural threats. Useful information about historic floods (e.g., 2007; Gilles et al., 2012). flooded areas, flow velocity, erosion processes, damage) has The identification of areas prone to severe floods can rarely been taken into account. For this reason, local bod- be approached by different methods. Some authors have ies (e.g., interregional authorities, regional and provincial ad- used specific criteria, including historical (Luino, 2002; Tro- ministrations, and municipalities) must now address socio- peano and Turconi, 2004; Coeur and Lang, 2008), geomor- economic difficulties. phological (Maraga, 1986; Baker et al., 1987; Fernandez- In 1989, the Italian government passed an environmental Lavado et al., 2007; Benito and Hudson, 2010), hydrologic- protection law (Law 183/89) that created several “Autorita` hydraulic (Dawson and Wilby, 1999; Brych et al., 2002; di Bacino” (Basin Authorities). They are mixed state and Diez-Herrero et al., 2009; Musall et al., 2011), and remote- regional organisations responsible for hydrographic basins. sensing methods (Jain et al., 2005; Hui et al., 2008). Other The Basin Authorities consider the hydrographic basins uni- authors have combined methods, which can yield better re- tary systems for the purposes of land and subsoil conser- sults because the technique can compensate for the lim- vation, water reclamation, water-resource management and itations of individual methods. Notable results have been environmental protection, regardless of administrative divi- achieved, for example, by combining historical and geomor- sions. This legislative innovation in the conservation sector phological methods (Luino et al., 2002b) or geomorpho- is a result of the famous “Commissione De Marchi” that cre- logical and hydrological methods (Chen and Simons, 1986; ated the conditions for broad, integrated solutions to land- Townsend and Walsh, 1998; Lastra et al., 2008; Lelievre` et management problems on the basin scale after the severe al., 2008; Chouari, 2009; Ballard et al., 2011) or by an ap- flood that hit Florence in November 1966. proach based on historical-hydrogeomorphological reconsti- The objective of the Basin Authorities was to overcome tution and hydrological-hydraulic modelling (Santos et al., the institutional divisions that prevent unified and integrated 2011). planning for the major European basins. The Authorities co- In the last decades, GIS (Geographical Information Sys- ordinate planning among the institutions involved in the con- tems) and LiDAR (Laser Imaging Detection and Ranging) servation, use and control of resources in accordance with so- have been important tools in spatial processing. GIS uses cial, economic and environmental sustainable development. a series of software tools to capture, store, extract, trans- The Basin Authorities introduced, for example, the con- form and display real-world spatial data (Burrough, 1986), cept of a “river corridor”, which is defined as “the area of whereas LiDAR is an optical remote-sensing technology for land (and water) affecting and/or affected by a river” (Gar- creating high-resolution digital models of the earth’s surface. diner, 1991), an important concept for geomorphologists that LiDAR is particularly useful because the ongoing construc- had not previously been defined by clear regulation. tion of levees, dikes, roads, railway embankments and build- For each watercourse of a main hydrographic network, ings constantly changes the land’s appearance. river corridors are identified as follows: (1) the limits of Regardless of the method, the quality of the results ob- the riverbed and flood-prone areas with respect to large tained is always dependent on the assessment of the natural floods; (2) the conditions of the defense system, including world. Only after a flood can a model be re-calibrated and levees, bank protection, flood-control works, and floodways; inadequacies improved. (3) riverbed morphology and geometry; and (4) type of land The demarcation of flood-prone areas has been requested use in the valley bottom. by local citizens, industries and organisations, as well as The Po River Basin Authority, which is responsible for state and regional bodies responsible for disaster prevention the Tanaro River, classifies the river corridors as follows:

Nat. Hazards Earth Syst. Sci., 12, 2329–2346, 2012 www.nat-hazards-earth-syst-sci.net/12/2329/2012/ F. Luino et al.: The Alba case study (Piedmont, Italy) 2331

channel A, for ordinary floods; channel B, for 200-yr return Fig. 1 – Map of the Tanaro basin with the period floods; and channel C, for catastrophic 500-yr return isohyetal (mm) pattern for November 2-6, 1994. In the upper-left corner is a period floods (Autorita` di Bacino del Fiume Po, 1997). The meteorological map of the conditions method of defining these river corridors uses three criteria, prevailing just before the catastrophic event (November 4, 1994, 12:00 p.m., 850 hydrodynamic, geomorphological and ecological, to identify hPa) (from the European Meteorological Bulletin of the Deutscher Wetterdienst, three strips of different amplitudes. The goal of the “River modified). Corridor Plan” is to plan resource use within the fluvial re- gion to preserve the correct operation of fluvial processes (hydraulic, geomorphological and ecological) in accordance with human requirements and existing use (Baruffi et al., 2005). The regulation of activities within the corridors has prevented uncontrolled urban development along the river and other human action that has threatened the natural bal- ance of watercourses in the recent past (Passino, 1996). Following the severe floods of 1992, 1993 and 1994, the Fig. 1. Map of the Tanaro basin with the isohyetal (mm) pattern for 2–62.2. NovemberThe Alba flood 1994. In the upper-left corner is a meteorological Piedmont Regional Administration, in collaboration with re- On November 5, 1994, beginning in midday, the first floods occurred along the Riddone stream and gional professional associations, adopted regulatory guide- mapCanale of thedel conditionsMussotto, severely prevailing flooding just beforethe Socchi the catastrophicand Mussotto eventquarters. At the same time, the Cherasca lines and standards that must be observed during the draft- (4stream November inundated 1994, part 24:00 of the LT, Bonomo 850 hPa) quarter. (from The the Tallo Europeanria’s floodwaters Meteo- overflowed on the right bank near ing of geological studies in support of planning instruments. rologicalthe stream’s Bulletin mouth, of ran the Deutschertoward the Wetterdienst,town and, togeth modified).er with the Canale di Roddi waters, flooded several buildings in Le Basse quarter before striking the Piave and Vivaro quarters. During a second phase, the Circular 7/LAP/1996 and Technical Note/1999 identify the Talloria floodwaters reached the famous Ferrero plant at 5:30-6:00 p.m., filling the plant’s yards and guidelines as a regional standard for the implementation of buildings to a height of 60-70 cm. In the Piave quarter at the foot of the hill, basement flats and ground floors the “check of hydraulic and hydrological compatibility with were flooded (20-40 cm) by the runoff coming from the saturated slopes or by the malfunctioning of the sewage system. the future planning instruments with the conditions of insta- persistentIn the following wide depression hours, the Tanaro over inundation northwestern reached Europe its paroxysmal pro- phase (Fig. 2). The severe overflow bility...”. ducedand the heavy violent rains passage over of the alarge waters portion over the ofground Piedmont left deep (Fig. scour 1). erosions on the left bank at the river’s Despite these efforts, recent field surveys have found new Theconfluence highest with intensities,the Talloria stream, 35–40 near mm the h −sand-and-1 withgravel a peak separating of plant, and on the right bank. The residential and commercial construction along watercourses, 55floodwaters mm h−1 spread(Cairo into Montenotte the Socchi area raingauge), between 11:00 occurred and 12:00 during p.m. Similar severe processes affected the right bank, where the old levee broke and the waters cut deep scour erosions as they flowed around the large particularly in mountain areas where municipal administra- theblockage night created of 4 by November. the municipal Precipitation dump. extended north to tions manage the streams within their municipalities as they the regionThe floodwaters of Asti spreading and the out Langhe on the Topino hills, whereplain we rainre dammed gauges by the embankment of the Asti-Cuneo see fit. In this unregulated land management, the complai- recordedhighway, where an intensity they reached of 5.6 over m in 200 height mm (Fig. day −3).1 ,After with the a embankment peak gave way to the waters along the lower stretch, the−1 flood struck Alba. At 10:30 p.m., violent waves burst into the Ferrero company plant, sance of engineers and geologists has proved decisive. These ofdemolishing 264.6 mm its day externalat wall the and Levice inundating station. all of the On bu 6ildings November to a height of 2.80-3 m. Between 12:00 p.m. freelancers are paid by the municipalities and have largely theand rainfall 1:00 a.m. intensity on November dropped 6, the water over in the the lower Tanaro zones basin of the in Vivaro the quarter was approximately 3.25 m worked to satisfy municipality demands, constantly attempt- earlydeep. hours of the morning, while the most intensive rainfall ing to bypass land restrictions through legislative chicanery hit northwestMeanwhile, Piedmonton the left bank, following the Tanaro a SE-NW waters overfl direction.owed the In railway an embankment to join the Riddone waters, reaching the Mussotto quarter (Fig. 4). Part of the Tanaro flow sought to return to the riverbed but that seeks amnesty for the infringement of local building reg- areawas withdammed an by average the highway annual embankment, rainfall ofraising approximately the water level 850– to 3.6 meters. The stretch of the Tanaro − ulations and variations of the land-use plan instead of observ- 1100valley mm, bottom rainfall between of the approximately confluence of the 200–230 Talloria and mm Cherasca day 1 wasstreams was flooded by a single expanse ing the existing laws. recordedof water 2.5 by km numerous in width, on rain average. gauges. 3 −1 −2 Finally, in 2007, the European Community adopted Direc- Unusual river discharges peaked at 7.3 m s km tive 2007/60/EC. “The aim of this Directive is to establish (Luino, 1999). Extensive river flooding caused serious losses a framework for the assessment and management of flood in 38 urbanised areas: the percentages of flooded urban sur- risks, aiming at the reduction of the adverse consequences faces were between 10 % and 90 % and averaged 30 %–50 %, for human health, the environment, cultural heritage and eco- with water elevations reaching approximately 1 m and maxi- nomic activity associated with floods in the Community” mum values of 2.5–3 m. The Tanaro also flooded Alba, Asti (Directive 2007/60/EC). With this directive, an improvement and Alessandria, important towns with more than 30 000 in- in land management and a decrease in errors in land-use plan- habitants (Luino et al., 1996). Locally, buildings increased ning can be anticipated. their hydraulic levels, creating momentary barriers (e.g., 4 walls, doors, fences). The forces created by the floodwaters caused many buildings to suddenly collapse, which witnesses 2 The 5–6 November 1994 event and the Alba flood heard as booms and crashes. The collapsing buildings caused small surges that increased the floodwater’s level at a rate of 2.1 Meteorological conditions approximately 10 cm min−1. The effect of this event was catastrophic: it left 44 dead The flood of 5–6 November 1994 was one of the most dis- and 2000 homeless and killed thousands of animals. Kilo- astrous in the Tanaro river basin in the last two centuries. metres of roads and railways were washed out, stranding During this period, only one comparable flood occurred, hospitals and schools. Electrical power was cut, and hun- in May 1879. During the first week of November 1994, a dreds of factories were crippled. The total damage to publicly www.nat-hazards-earth-syst-sci.net/12/2329/2012/ Nat. Hazards Earth Syst. Sci., 12, 2329–2346, 2012 2332 F. Luino et al.: The Alba case study (Piedmont, Italy)

Fig. 2 - November 5-6, 1994 flooding in the Alba area. Fig. 2. 5–6 November 1994 flooding in the Alba area.

owned property alone was estimated at US$ 14 billion, equal erosions on the left bank at the river’s confluence with the to 1.2 % of the gross Italian national product in 1994. Talloria stream, near the sand-and-gravel separating plant, and on the right bank. The floodwaters spread into the Socchi 2.2 The Alba flood area between 23:00 and 24:00 LT. Similar severe processes affected the right bank, where the old levee broke and the wa- On 5 November 1994, beginning in midday, the first floods ters cut deep scour erosions as they flowed around the large occurred along the Riddone stream and Canale del Mus- blockage created by the municipal dump. sotto, severely flooding the Socchi and Mussotto quarters. The floodwaters spreading out on the Topino plain were At the same time, the Cherasca stream inundated part of dammed by the embankment of the Asti-Cuneo highway, the Bonomo quarter. The Talloria’s floodwaters overflowed where they reached 5.6 m in height (Fig. 3). After the em- on the right bank near the stream’s mouth, ran toward the bankment gave way to the waters along the lower stretch, town and, together with the Canale di Roddi waters, flooded the flood struck Alba. At 22:30 LT, violent waves burst into Fig. 3 – November 6, 1994, 1:00 p.m. The Tanaro River is Fig. 4 – The Mussotto quarter, close to the highway (W in Fig. 2). several buildingsstill swollen. in Le The Basse effects quarter of the flooding before are striking evident. the In the Pi- The theneighboring Ferrero Asti-Cuneo company plant,embankment, demolishing acting as itsa externaldam, wall and ave and Vivaroforeground, quarters. the Duringlink road aof secondthe Asti-Cuneo phase, highway the Tallo- has retainedinundating the Tanaro allfloodwaters, of the buildingswhich reached to the a second height floor of of 2.80–3 m. Be- been stripped by the violence of the waters. On the left, along the houses (red arrow). In the center, a fire department rescue boat ria floodwatersthe reachedhighway embankment, the famous is Ferrerothe site where plant the at 17:30–deepest is intween action. 24:00 and 01:00 LT on 6 November, the water in the 18:00 LT, fillingfloodwaters the plant’s (5.60 m) yards were and measured buildings (X in toFig. a height2). In the of lower zones of the Vivaro quarter was approximately 3.25 m 60–70 cm. Inbackground the Piave is quartera thick poplar at the forest foot recently of the planted hill, base-in a deep. natural area along the Tanaro. ment flats and ground floors were flooded (20–40 cm) by the Meanwhile, on the left bank, the Tanaro waters overflowed runoff coming from the saturated slopes or by the malfunc- the railway embankment to join the Riddone waters,5 reaching tioning of the sewage system. the Mussotto quarter (Fig. 4). Part of the Tanaro flow sought In the following hours, the Tanaro inundation reached its to return to the riverbed but was dammed by the highway paroxysmal phase (Fig. 2). The severe overflow and the vi- embankment, raising the water level to 3.6 m. The stretch of olent passage of the waters over the ground left deep scour

Nat. Hazards Earth Syst. Sci., 12, 2329–2346, 2012 www.nat-hazards-earth-syst-sci.net/12/2329/2012/ Fig. 2 -Fig. November 2 - November 5-6, 19945-6, 1994 flooding flooding in the in theAlba Alba area. area.

F. Luino et al.: The Alba case study (Piedmont, Italy) 2333

Fig. 3 – November 6, 1994, 1:00 p.m. The Tanaro River is Fig. 4 – The Mussotto quarter, close to the highway (W in Fig. 2). still swollen. The effects of the flooding are evident. In the TheFig. 4.neighboringThe Mussotto Asti-Cuneo quarter, closeemba tonkment, the highway acting (W as in a Fig. dam, 2). Fig. 3 – November 6, 1994, 1:00 p.m. The Tanaro River is Fig.The 4 neighbouring– The Mussotto Asti-Cuneo quarter, embankment,close to the highway acting as (W a dam, in Fig. re- 2). Fig. 3.foreground,6 November the 1994,link road 13:00 of LT. the The Asti-Cuneo Tanaro River highway is still has retained the Tanaro floodwaters, which reached the second floor of still swollen. The effects of the flooding are evident. In the Thetained neighboring the Tanaro floodwaters,Asti-Cuneo whichemba reachednkment, the acting second as floor a ofdam, swollen.been The stripped effects by of thethe floodingviolence areof the evident. waters. In On the the foreground, left, along the houses (red arrow). In the center, a fire department rescue boat foreground, the link road of the Asti-Cuneo highway has retainedthe houses the (redTanaro arrow). floodwaters, In the centre, which a fire reached department the second rescue boatfloor of the linkthe road highway of the Asti-Cuneoembankment, highway is the has site been where stripped the bydeepest the is in action. been strippedfloodwaters by the (5.60 violence m) were of themeasured waters. (X On in the Fig. left, 2). along In the theis inhouses action. (red arrow). In the center, a fire department rescue boat violence of the waters. On the left, along the highway embankment, the highwaybackground embankment, is a thick poplaris the forestsite whererecently the planted deepest in a is in action. is the site where the deepest floodwaters (5.60 m) were measured (X floodwatersnatural (5.60 area along m) werethe Tanaro. measured (X in Fig. 2). In the in Fig. 2). In the background is a thick poplar forest recently planted background is a thick poplar forest recently planted in a in a natural area along the Tanaro. natural area along the Tanaro. produced works that devastated the existing city fabric. In5 1848, a long road bridge across the Tanaro River was built, and this bridge was widened in 1865 to accommodate the 5 the Tanaro valley bottom between the confluence of the Tal- new Alessandria-Cavallermaggiore railway line. However, loria and Cherasca streams was flooded by a single expanse Alba’s large-scale expansion did not begin until just after the of water 2.5 km in width, on average. Second World War. The growth of important companies (Fer- rero in confectionery, Miroglio in textiles and Mondo Rubber in sport flooring) attracted more people to the area, leading 3 The history of Alba: urban development and land to a need for housing and infrastructure. transformation A comparison between the different editions of the of- ficial cartography (IGM = Military Geographic Institute) at Historical studies have shown that a prehistoric settlement of the 1:25 000 scale with the most recent Regional Technical Alba was probably located on the right bank of the Tanaro Map at the 1:10 000 scale allows a detailed analysis of Alba’s River, where the waters could flow freely on the valley bot- planimetric development since 1852 (Fig. 5). The compari- tom unhindered by man-made structures. Evidence of a large son shows that the urban expansion was modest and uneven flood was discovered in a stratum of alluvial deposits, inter- until the 1930s and primarily affected the sector east of the calated with strata containing archeological findings. The in- historic core (the left bank of the Cherasca stream). habitants moved their settlement to higher ground slightly to The development that has characterised the post-war pe- the south along the left bank of the Cherasca stream, where riod, particularly the recent decades, and relates to the pro- the first Roman camp (“castrum”) subsequently arose. The cess of industrialisation in the area has occurred mainly along city of Alba became a well-known settlement of the Roman the Corso Piave (toward the SW) and Corso Langhe (toward Empire, called Alba Pompeia. the S). The highest concentration of new housing and in- The chief characteristic of the city’s historic core is the dustrial districts has occurred near the Tanaro, both on the pseudo-octagon, which was originally bounded by walls built left (Mussotto quarter) and right banks (Vivaro quarter), al- for defensive purposes. In the Middle Ages, Alba became though these quarters have often been hit by floods in the a thriving commune, and the town walls were later rein- past. Recent important structures and infrastructures built in forced and protected by a deep moat. The town’s appearance the Tanaro valley bottom are the aggregate plants, the mu- changed little until the first part of the 19th century, when nicipal dump, the Asti-Cuneo highway, the prison and the demolition of the walls began (Cavallari Murat, 1975). nomad camp. In 1829, the first efforts in modern town planning began, The analysis of the planform changes of the Tanaro River, with three goals: to pave the streets; to mitigate the traf- derived from the same cartographic comparison mentioned fic of carts, carriages and people; and to improve the gen- above, shows a simplification of the riverbed (Fig. 6). In the eral appearance of the town. Modernisation and development past, the riverbed was characterised by several channels that

www.nat-hazards-earth-syst-sci.net/12/2329/2012/ Nat. Hazards Earth Syst. Sci., 12, 2329–2346, 2012 water-gauge station (3,277 km² basin), located 12 km upstream of Pollenzo and in operation since 1882 (Perrone, 1916). The data, recorded since 1890 with an interruption from 1950 to 1959 (Ufficio Idrografico e Mareografico per il Bacino del Po, Sezione di Torino), facilitated the identification of floods with water levels higher than 2.50 m (the height of an ordinary flood) for subsequent investigations. In addition, publications and technical reports written mainly by the Regional Offices of the State and collected in the CNR-IRPI’s archives in Turin were consulted. Similar documents collected in Alba’s public library and municipal archive as well as articles from national and local newspapers, particularly the local "La Gazzetta d’Alba" founded in 1882, were also examined. This investigation located information about the effects and damage caused by the floods measured by the 2334Pollenzo water gauge and floods that occurred prior to F.the Luino Pollenzo et al.:observations The Alba and case during study their (Piedmont, Italy) interruption.

Fig. 5 - Urban development of Alba, reconstructed from historical maps with all place names cited in the paper. Fig. 5. Urban development of Alba, reconstructed from historical maps with all place names cited in the paper.

All of the floods selected for study are shown in figure 7. In addition to the floods that reached a high were often separatedhydrometric by large height vegetated (m > 3.60), islands. floods On without the 1991 hydromet4ric references Historical or analysiswith low asvalues a tool were for considered evaluating vulnerable map, the riverbedaccording appears to damage reduced documentation. to a single narrow channel areas In Table I, these floods are listed chronologically with a summary of the information collected on each flood, without islands.including watercourse name, effects and damage, and the affected quarter (see Fig. 6). DocumentationSome relatinggeneral conclusions to the hydraulic can be drawn defense based works on an analysisIn recentof the pattern decades, obtained. historical research has become increas- along the river was examined (Destefanis, 1928; Ministry ingly important. Determining what occurred in a specific of Public Works,- For Royal the floods Corps that of occurred Engineers before of the Cuneo, Pollenzo un- water areagauge instation the pastwas in is use, essential an assessment for the of prediction gravity of risk sce- published). Thecan documentation be made only based reveals on thatthe descriptive the river’s information sim- avnarios,ailable particularlyand without the on ability a valley to verify floor. the Given levels its location on reached by the watercourse. In the case of the May 1879 flood, which equaled and surpassed the previous plification was induced by the numerous and repeated reme- the flood-prone Tanaro with three hazardous tributaries and dial works along the banks since the end of the 19th century. many channels, Alba has a long, well-documented7 history of These interventions were performed to create new farmland floods. and, in recent decades, to permit aggregate extraction along For this reason, after the 1994 flood, a thorough analysis the Tanaro’s active riverbed. of the Tanaro’s floods over the last two centuries was per- The defense works, mainly groins and gabions, were prin- formed. The research began with the reading of the long se- cipally designed to restrain the mainstream current and min- ries of observations made at the Pollenzo water-gauge station imize the serious threat of riverbank erosion, which is par- (3277 km2 basin), located 12 km upstream of Pollenzo and ticularly stressful in the bends close to the Socchi and Sarda in operation since 1882 (Perrone, 1916). The data, recorded farms on the left and the Topino and Topinotto farms on the since 1890 with an interruption from 1950 to 1959 (Ufficio right. In addition, repeated repairs were made on the levees Idrografico e Mareografico per il Bacino del Po, Sezione di at the Topino bend on the right and, between 1848 and 1850, Torino), facilitated the identification of floods with water lev- further downstream on both banks of the river to convey the els higher than 2.50 m (the height of an ordinary flood) for Tanaro flow under Alba’s main bridge. subsequent investigations. In addition, publications and technical reports written mainly by the Regional Offices of the State and collected in the CNR-IRPI’s archives in Turin were consulted. Similar documents collected in Alba’s public library and municipal

Nat. Hazards Earth Syst. Sci., 12, 2329–2346, 2012 www.nat-hazards-earth-syst-sci.net/12/2329/2012/ highest levels at the Asti and Alessandria water gauges, respectively (Luino et al., 1996), we can say that in the Alba area, the flood was exceptional. The large and detailed quantity of data collected has facilitated the confident identification of the affected sectors. In addition, the data have enabled a comparison of the extent and destructiveness of this flood with the flood of November 1994. Information about floods that occurred before 1879, although significant, is scarce and less detailed. Only rarely can references be found to specific areas of land. However, in some cases, the type of information available has permitted the determination of the "width" of river flooding, even in the absence of detailed information. For the October 1846 flood, for example, the severity of the effects on the Tanaro Valley emerged in several documents. The flooding in the Alba area is described as follows: "... exceptional flood never seen for the Tanaro River occurred in the month of October just expired, and particularly in those most grievously occurred in the period 1-5 and then in the period 16-20... The fury of the waters invaded, broke, dragged everything from F. Luino et al.: Thethe Alba Alba town case till study almost (Piedmont, to the edge of Italy) the opposite hill, so that the Valley of the Tanaro resembled to a 2335 narrow sea, dominated by a current" (Prandi, unpublished).

Fig. 6 - Planform changes of the Tanaro riverbed during the period 1852-2006 from historical maps. Letters in gray circles indicate Fig. 6. PlanformAlba’s changes different of the quarters. Tanaro riverbed during the period 1852–2006 from historical maps. Letters in gray circles indicate Alba’s different quarters.

- For the flood levels measured at the Pollenzo water gauge, a high hydrometric level does not always correspond to reports of damage. In the period between the beginning of measurement (1890) and the archive as well asSecond articles World from War, national 20 floods and reached local newspa-heights greater than gauges,3.60 m. However, respectively damage (Luino documentation et al., 1996), is we can say pers, particularlyavailable the local for “La only Gazzetta four floods, d’Alba” which probably founded indicates in that fewthat structures in the Alba and infrastructures area, the flood were was present exceptional. The 1882, were also examined.in the flooded areas. For the flood of November 1962, little largedamage and was detailed reported, quantity most likely of databecause collected of has facili- This investigationthe remedial located work information along the riverbed about theafter effects the destruction wroughttated theby the confident four major identification floods of 1948-1951. of the affected sectors. and damage causedIn contrast, by the damage floods measuredreports exist by for the the Pollenzo floods of April 1941In and addition, October the1942, data which have were enabled characterized a comparison of the by modest floodwater heights. It should be noted that the documentation relates mainly to localized water gauge andflooding floods thatand occurredthe disruption prior or to destruction the Pollenzo of bank protection.extent Finally, and destructiveness for the November of this 1968 flood and with the flood of observations and during their interruption. November 1994. Information about floods that occurred All of the floods selected for study are shown in Fig. 7. In before 1879, although significant, is scarce8 and less de- addition to the floods that reached a high hydrometric height tailed. Only rarely can references be found to specific (m > 3.60), floods without hydrometric references or with areas of land. However, in some cases, the type of infor- low values were considered according to damage documen- mation available has permitted the determination of the tation. “width” of river flooding, even in the absence of detailed In Table 1, these floods are listed chronologically with a information. For the October 1846 flood, for example, summary of the information collected on each flood, includ- the severity of the effects on the Tanaro Valley emerged ing watercourse name, effects and damage, and the affected in several documents. The flooding in the Alba area is quarter (see Fig. 6). described as follows: “... exceptional flood never seen Some general conclusions can be drawn based on an anal- for the Tanaro River occurred in the month of October ysis of the pattern obtained. just expired, and particularly in those most grievously occurred in the period 1–5 and then in the period 16– – For the floods that occurred before the Pollenzo wa- 20... The fury of the waters invaded, broke, dragged ev- ter gauge station was in use, an assessment of grav- erything from the Alba town till almost to the edge of ity can be made only based on the descriptive infor- the opposite hill, so that the Valley of the Tanaro resem- mation available and without the ability to verify the bled to a narrow sea, dominated by a current” (Prandi, levels reached by the watercourse. In the case of the unpublished). May 1879 flood, which equaled and surpassed the pre- vious highest levels at the Asti and Alessandria water www.nat-hazards-earth-syst-sci.net/12/2329/2012/ Nat. Hazards Earth Syst. Sci., 12, 2329–2346, 2012 2336 F. Luino et al.: The Alba case study (Piedmont, Italy)

Table 1. Main effects and damage caused by floods of the Tanaro and its tributaries in different areas of Alba during the period 1801–2000.

Date of the flood Damaged areas Watercourse Effects – Damage (see Fig. 6) May 1817 A – C TANARO Overflows, Floods – Road network 26 Oct 1829 A – C TANARO Overflows – Buildings, bridges, road network on the right 2 Oct 1846 B TANARO Large Inundations – Bank protection, pontoon bridge, road network 20 Oct 1851 B TANARO Overflows, Bank Erosion – Road network, municipal Cherasca bridges 21 Oct 1857 F TANARO Bank protection 18 Oct 1872 A – C TANARO Overflows, Floods, Bank erosion – Channels, buildings, factories 4 Dec 1872 A – C TANARO Overflows, Bank erosion – Bank protection 28 May 1879 A – B – C – D TANARO, Talloria, Large inundations, Floods, Bank erosion – Bank F–H Cherasca protection, buildings, road network, railway, municipal waterworks 23 May 1893 A – B – D – E – F TANARO Overflows, Floods, Bank Erosion – Buildings, road network 4 Jun 1900 A – B – E – G TANARO Large inundations, Floods, Bank erosion – Railway and road bridge, road network, bank protection, power stations 16 May 1926 A – G TANARO Large inundations, Floods, Bank erosion – Buildings, Talloria road network Cherasca 10 May 1936 D – G TANARO Overflows, Floods, Bank erosion – Bank protection, buildings, road network 7 Apr 1941 A – F TANARO Overflows, Bank erosion – Bank protection 28 Oct 1942 B TANARO Overflows, Erosion left bank – Bank protection 15 May 1948 A – B – D – E – F TANARO Overflows, Floods, Bank erosion – Bank protection, buildings 4 and 12 Sep 1948 A – B – C – D – E – F – TANARO Estese inondazioni, Floods, Bank Erosion – Bank H–K Cherasca, protection, building, road network, bridges, municipal L–M Misureto, waterworks, factories Talloria 3 May 1949 A – C TANARO Overflows, Bank erosion, Riverbed Enlargement – Bank protection 10 Nov 1951 A – B – E TANARO Bank erosion – Bank protection 8 Nov 1962 A – B TANARO Overflows, Bank erosion – Bank protection 2 Nov 1968 H – L – M Cherasca, Overflows, Bank erosion – Bank protection, bridges, Misureto railway 18 Sep 1973 B – D – E Riddone, Overflows, Floods, Bank erosion – Bank protection, Canale del Mussotto buildings 5–6 Nov 1994 A – B – C – D – E – F – TANARO, Riddone, Very large inundations, Floods, Bank erosion – Bank G Talloria, protection, buildings, road network, factories, railway H–K Cherasca

Nat. Hazards Earth Syst. Sci., 12, 2329–2346, 2012 www.nat-hazards-earth-syst-sci.net/12/2329/2012/ September 1973 floods, the reported damage is not attributed to Tanaro floods but to those of the Tanaro’s F. Luino et al.: Themajor Alba tributaries. case study (Piedmont, Italy) 2337

Fig. 7 – Tanaro floods during the period 1801-2000 with related hydrometric heights (m above gauge datum equivalent to 183.86 m Fig. 7. Tanaro floodsa.s.l.) during measured the at periodthe Pollenzo 1801–2000 station. Floods with causing related damage hydrometric in the Alba heightsarea are indicated (m above in red. gauge Floods datum without equivalent hydrometric to 183.86 m a.s.l.) measured at the Pollenzovalues are station.labeled “without Floods overflowing” causing (n damageo damage) in or the“with Alba overflowing” area are (damage). indicated in red. Floods without hydrometric values are labelled “without overflowing”Tab. I - Main effects (no damage)and damage orcaused “with by floods overflowing” of the Tanaro (damage). and its tributaries in different areas of Alba during the period 1801- 2000. Date of the flood Damaged Watercourse EFFECTS – Damage areas – For the flood levels measured(see Fig. at 6) the Pollenzo wa- already severely damaged. For this reason, and because ter gauge, a high1817/May hydrometric A - level C does TANARO not always OVERFLOWS, FLOODSof the – short Road intervalnetwork of time between the two floods, the correspond to1829/Oct./26 reports of damage. A - C In the TANARO period OVERFLOWS be- – Buildings,damage bridges, caused road is notnetwork treated on the separately right in the historical tween the beginning1846/Oct./02 of measurement B (1890) TANARO and LARGE the INUNDATIONSdocuments, – Bank and protection, the two pontoon floods bridge, have road been considered a network Second World1851/Oct./20 War, 20 floods reachedB heightsTANARO greaterOVERFLOWS, BANKsingle EROSION flood. - Road network, municipal than 3.60 m. However, damage documentationCherasca is avail-bridges able for only four1857/Oct./21 floods, which F probably TANARO indicates Bank that protection– Over the 200 yr investigated, the distribution of the rele- 1872/Oct./18 A - C TANARO OVERFLOWS, FLOODS,vant floods BANK is EROSION homogeneous – Channels, (9 cases buildings, inthe 19th century few structures and infrastructures were present infactories the flooded areas.1872/Dec./04 For the flood of A - NovemberC TANARO 1962, littleOVERFLOWS, BANKand 12EROSION in the – 20th Bank century),protection although the severity of the damage was1879/May/28 reported, most A - likelyB – C – becauseD TANARO, of theLARGE re- INUNDATIONS,floods differed.FLOODS, TheBANK tendency EROSION of floods- Bank to occur in au- F – H Talloria, protection, buildings,tumn road (overnetwork, 50 railway, % of themunicipal floods) waterworks is apparent. medial work along the riverbed after theCherasca destruction wrought by the four major floods of 1948–1951. In con- 1893/May/23 A - B – D - E TANARO OVERFLOWS,– FLOODS,On the basisBANK ofEROSION the collected – Buildings, information, road we can say trast, damage reports exist for the- F floods of April 1941network that among the floods considered, the floods of 1846, and October 1942,1900/June/04 which were A - B - characterised E - G TANARO by mod- LARGE INUNDATIONS, FLOODS, BANK EROSION – Railway and road bridge, road1879, network, 1900, bank 1926, protection, 1948 power and stations 1994 are particularly im- est floodwater heights. It should be noted that the doc- 1926/May/16 A - G TANARO LARGE INUNDATIONS,portant FLOODS, because BANK of the EROSION extent - ofBuildings, the territory affected umentation relates mainly to localised floodingTalloria androad the network and the severity of damage. As mentioned above, the disruption or destruction of bank protection.Cherasca Finally, for 1936/May/10 D - G TANARO OVERFLOWS, FLOODS,area involved BANK canEROSION be determined - Bank protection, only if the historical the November 1968 and September 1973 floods, the re- buildings, road networkdocumentation provides detailed information on the af- ported damage is not attributed to Tanaro floods but to fected locations (e.g., the names of farms, quarters, and those of the Tanaro’s major tributaries. roads). On the basis of such specific9 information, Ta- ble 2 presents the 12 sectors into which the study area – During the flood of 4 September 1948, a large number of has been divided (see Fig. 3), listed in descending order municipal sectors were affected because of violent ero- by number of floods. sion and floods of the Cherasca, Talloria and Misureto streams in addition to the extensive Tanaro flooding (see The historical records show that the Topino-Topinotto Table 1). On 12 September 1948, a new Tanaro flood farmhouses (A) were inundated at least 15 times between struck most of the area that had been affected in the 1801 and 2000. Due to its position on the right bank of a previous week. Despite the new flood’s modest height large left bend of the Tanaro River, this site is subject to the (2.70 m), the flood is mentioned in the sources because natural spreading of floodwaters. In some years (1846, 1872, it swept away structures and infrastructure that were 1879, 1893, 1948), the waters rose 50 to 75 cm. During the www.nat-hazards-earth-syst-sci.net/12/2329/2012/ Nat. Hazards Earth Syst. Sci., 12, 2329–2346, 2012 2338 F. Luino et al.: The Alba case study (Piedmont, Italy)

Fig. 8 – Urban planning mosaic map of the Alba municipal area. Different colors represent the categories of land use. Fig. 8. Urban planning mosaic map of the Alba municipal area. Different colours represent the categories of land use.

Table 2. Areas of theThese Alba regionsix categories that have have suffered been repeated unified Floods. into three classes with different flooding vulnerability levels (exposure to flood hazard) according to the following parameters: a) the presence of a concentration of people over 24 hours or at particular hours of the day; b) the presence of machinery or private property; c) Areas Damaged locality Date of the flood the occurrence of social-recreational activities and/or loss from damage to agricultural zones; and d) the (see Fig. 3) presence of environmentally valuable areas. Residential and public-service areas form LEVEL 1 (highest); Aindustrial, commercial Topino-Topinotto and hotel areas zone form LEVEL 2; and 1817–1829–1872–1872–1879–1893–1900–1926– sports, greenery and agriculture form LEVEL 3 (lowest). 1941–1948–1948–1949-1951–1962–1994 As mentioned in the introduction, the Po River Basin Authority introduced the concept of river corridors: B Paruzza-Socchi zone 1846–1851–1879–1893–1900–1942–1948–1948– it used hydrodynamic, geomorphological and ecological criteria with the aim to identify three strips of 1951–1962–1973–1994 different amplitudes (Fig. 9). CUsing a simple risk Vivaro matrix quarter/Cemetery facilitates a correlation 1829–1872–1872–1879–1948–1949–1994between the hazards of the three river corridors, Ddefined by the Po River Mussotto Basin SW/Mogliasso/VaccheriaAuthority, and the exposure 1879–1893–1936–1948–1948–1973–1994 level of the land-use classes (Fig. 10). In the case of Alba, the superimposition of the river corridors on the urban planning mosaic map can Ehighlight the areas with Sarda the farm/Mussottohighest risk levels NE quarter along the Tanaro 1893–1900–1948–1948–1951–1973–1994 valley bottom (Fig. 11). FThe aggregate plants Ferrero/Courthouse and the nomad camp are located 1879–1893–1941–1948–1948–1994 in river corridor A (red in Fig. 9), close to the GTanaro riverbed, both Le on Basse the left quarter bank. The locations are high 1900–1926–1936–1994 risk. River corridor B (green in Fig. 9) includes farms and roads as well as the municipal dump, which was partially destroyed during the 1994 inundation Hbut is still operative Bonomo(although quarter the dump should be shut 1879–1948–1968–1994 down mainly because of the pollution risk). In Kaddition, the Vivaro Piavequarter quarter contains residential buildings, 1948–1994 with nearby 2- and 3-story houses and a large group of council houses (bungalows and terraced houses) inhabited by Ferrero employees. These houses L Corso Langhe quarter 1948–1968 were inundated till 1.70 m in height during the 1994 event. M Moretta quarter 1948–1968 N Old town – 12

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Fig. 9 – Alba: subdivision of the Tanaro valley bottom in three different river corridors. A = ordinary floodplain, B = 200-year return Fig. 9. Alba: subdivisionperiod floodplain, of the C = Tanaro 500-year valley return bottomperiod floodplain. in three In different the lower-right rivercorridors. corner the general A = ordinary outline for floodplain, defining river B = corr200-yridors return period floodplain, C =adopted500-yr by return the Basin period Authorities floodplain. (Autorità In di the Bacino lower-right del Fiume corner Po, 1997). the general outline for defining river corridors adopted by the Basin

Authorities (Autorita` di Bacino del Fiume Po, 1997).

Fig. 10 – A risk matrix with three different classes that identify the areas exposed to flooding: green (low degree of damage) to red (high 1879 and 1893 floods, farmers had to be rescued from theirdegree of leastdamage). seven times before the 1994 event, the area was flooded isolated farmhouses by rowboats. not only by the Tanaro, but also by the Riddone. In 1994, For many years, this area remained undeveloped because the Riddone flowed partially underground through Mussotto it was known to be particularly prone to flooding. Despite the inside a small channel. Now, a large bypass has been built awareness of the hazard, the municipal dump was established that carries the Riddone around the quarter and reaches the here at the end of the 1970s. Some years later, a large prison Tanaro across non-urban areas to the north. During the 1994 was built 700 m to the south, just behind the main levee. flood, both the Vivaro and Sarda-Mussotto quarters were in- During the November 1994 flood, the Topino-Topinotto zone undated. In the lowest sites, the waters reached 3.6 m. flooded. The waters deeply eroded the municipal dump, tak- ing tons of refuse with them, and the overflow of water de- stroyed the 40 to 50 cm levee surrounding the prison yard. 5 Land-use planning analysis Another example is the Vivaro quarter (C) on the right bank of the Tanaro River, a low area that has been flooded Studies of flood-prone areas have been conducted for years seven times over the last two centuries. In September 1948, without considering land use. However, land-use analysis the Talloria flood caused casualties, destroyed houses and is an important step in assessing vulnerability, risk and ex- roads, and invaded the new Ferrero facility. In the lowest pected damage: land-use regulation is a prerogative granted sites, muddy deposits were recorded one meter above the by the state to local governments. Although case law and ground. Today, the Vivaro quarter is one of the town’s most planning legislation differ from state to state, general legal populous quarters and the site of the Ferrero manufacturing principles pertain to all efforts to control land13 use and de- plant. velopment (Waananen et al., 1977). A land-use plan is a key A final example is the Sarda-Mussotto quarter (D and E). component of a comprehensive plan that includes objectives, Situated on the left bank of the Tanaro River, the quarter policies, and proposals for the type, pattern, and intensity of has expanded considerably along the railway and the road land use in a planning area. The goal of land-use planning to Turin over the last 50 yr. Historical records report that at in floodplains is to reduce the expected flood damage and www.nat-hazards-earth-syst-sci.net/12/2329/2012/ Nat. Hazards Earth Syst. Sci., 12, 2329–2346, 2012

Fig. 9 – Alba: subdivision of the Tanaro valley bottom in three different river corridors. A = ordinary floodplain, B = 200-year return period floodplain, C = 500-year return period floodplain. In the lower-right corner the general outline for defining river corridors adopted by the Basin Authorities (Autorità di Bacino del Fiume Po, 1997).

2340 F. Luino et al.: The Alba case study (Piedmont, Italy)

6. AgricultureFig. 10 – andA risk riverine matrix strip with (dark yellow).three different In these ar-classes that identify the eas,areas old exposed farms can to be flooding: renovated andgreen the (low building degree volume of damage) to red (high slightlydegree expanded.of damage).

These six categories have been unified into three classes with different flooding vulnerability levels (exposure to flood hazard) according to the following parameters: (a) the pres- ence of a concentration of people over 24 h or at particu- lar hours of the day; (b) the presence of machinery or pri- vate property; (c) the occurrence of social-recreational ac- tivities and/or loss from damage to agricultural zones; and (d) the presence of environmentally valuable areas. Residen- tial and public-service areas form LEVEL 1 (highest); indus- trial, commercial and hotel areas form LEVEL 2; and sports, greenery and agriculture form LEVEL 3 (lowest). As mentioned in the introduction, the Po River Basin Au- thority introduced the concept of river corridors: it used hy- drodynamic, geomorphological and ecological criteria with the aim to identify three strips of different amplitudes Fig. 10. A risk matrix with three different classes that identify the (Fig. 9). areas exposed to flooding: green (low degree of damage) to red Using a simple risk matrix facilitates a correlation between (high degree of damage). the hazards of the three river corridors, defined by the Po River Basin Authority, and the exposure level of the land-use classes (Fig. 10). the risk of development in the floodplain by following less In the case of Alba, the superimposition of the river cor- flood-hazardous building practices. To reach this goal, the ridors on the urban planning mosaic map can highlight the various land-use options within floodplains must be analysed areas with the highest risk levels along the Tanaro valley bot- (Du Plessis and Viljoen, 1999). tom (Fig. 11). Alba’s land-use plan was approved just before the 1994 The aggregate plants and the nomad camp are located in 13 inundation. A new plan was established only in 2011. The river corridor A (red in Fig. 9), close to the Tanaro riverbed, new plan takes into account the effects and damage of the both on the left bank. The locations are high risk. River cor- 1994 flood. However, the plan mainly considers the remedial ridor B (green in Fig. 9) includes farms and roads as well works accomplished during these seventeen years. as the municipal dump, which was partially destroyed during An analysis of the new land-use plan was performed for the 1994 inundation, but is still operative (although the dump the Alba region. The analysis covers both existing built-up should be shut down mainly because of the pollution risk). areas and future land use while taking into account the plan- In addition, the Vivaro quarter contains residential buildings, ning laws currently in force. Available aerophotogrammetric with nearby 2- and 3-story houses and a large group of coun- and cadastral maps were collected to draw an urban zoning cil houses (bungalows and terraced houses) inhabited by Fer- map. The territory was subdivided into 6 categories (Fig. 8): rero employees. These houses were inundated till 1.70 m in height during the 1994 event. 1. Residential areas (red): existing and planned. River corridor C contains large residential areas, the court- 2. Public service areas (light blue): areas for municipal house, the Ferrero plants, other industrial and commercial buildings, schools, hospitals, barracks, churches, park- areas, hotels, and scattered farms (Topino and Topinotto, ing areas, storage platforms, purification plants, ceme- zone A in Fig. 6; the Mogliasso-Vaccheria area, zone D in teries, etc. Fig. 6). Farms dot the entire Tanaro floodplain: their grain silos, barns and the new additions built by owners who have 3. Industrial, commercial and hotel areas (violet): exist- not considered the consequences are consistently exposed to ing and planned industrial, trade and handicraft ac- risk. However, flood risk is low in the agricultural areas. tivities, commercial buildings, structures and buildings Because of building density, river corridor C has a medium used mainly during the holiday season. inundation risk, particularly in the Mussotto quarter (E in 4. Sports, utilities and standards area (green): sport fields Fig. 6). This quarter is characterised by 3- and 4-story blocks and clubs, athletic grounds, public gardens and parks. of flats. Many houses have ground-level garages. Some garages are underground, as are most cellars. All ground 5. Aggregate plants and dumps (brown). floors are permanently occupied.

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Fig. 11 – Final map in which areas with different flood-risk levels have been identified with different colors. Fig. 11. Final map in which areas with different flood-risk levels have been identified with different colours.

River corridor C contains large residential areas, the courthouse, the Ferrero plants, other industrial and commercial areas, hotels, and scattered farms (Topino aandnd Topinotto, the commercial zone A developmentin figure 6; the of Mogliasso- former farmlands began Vaccheria area, zone D in figure 6). Farms dot the entireto Tanaro expand. floodplain: The development their grain silos, occurred barns withoutand the taking into ac- new additions built by owners who have not considered the consequences are consistently exposed to risk. However, flood risk is low in the agricultural areas. count that the newly developed areas were seriously flooded Because of building density, river corridor C has a mediumduring inundation four floods risk, inparticularly 1948–1949. in the Between Mussotto 1952 and 1993, quarter (E in figure 6). This quarter is characterized by only3- and one 4-story Tanaro blocks flood of (1962)flats. Many and twohouses tributary have floods (1968 ground-level garages. Some garages are underground, as areand most 1973) cellars. caused All damage.ground floors During are thepermanently roughly 40 yr of undis- occupied. turbed co-existence with their river, the town’s inhabitants

developed a feeling of living in safety, which led to develop- 6. Discussion of the data ment in hazardous areas. One example is the Topino-Topinotto area (A in Fig. 6), Since 1852, Alba has increased over tenfold in area (froma zone 40 on hectares the right to bank475 hectares) subject toby thegradually natural expansion of incorporating outlying farms and villages into an urbanizedTanaro center for floodwaters manufacturing whose and hazardousnessagriculture. Growth had been demon- rates in urbanization and population increased quickly after 1950, when local industry and the commercial development of former farmlands began to expand. The strateddevelopment by recurrent occurred floods.without taking This knowledgeinto account is confirmed in Fig. 12. Urban development of Alba measured from maps of 1852, a report by Cuneo civil engineers (Ministry of Public Works, 1880, 1933, 1965,that 1991 the newly (in red), developed compared areas with were percentage seriously of flood the ed during four floods in 1948-1949. Between 1952 and 1993, only one Tanaro flood (1962) and two tributary floodsOffice (1968 of Civil and 1973) Engineering, caused damage. unpublished) During the in which the crit- urban area would have been flooded in those years by an event sim- roughly 40 years of undisturbed co-existence with their river, the town’s inhabitants developed a feeling of ilar to that of November 1994 (in blue). ical situation was noted: “Upstream of the city of Alba, at a living in safety, which led to development in hazardous areas.distance of just more than one kilometre, on the right bank, One example is the Topino-Topinotto area (A in figure 6),there a zone is a placeon the that,right frombank subject an hydraulic to the natural point of view, has al- expansion of Tanaro floodwaters whose hazardousness had been demonstrated by recurrent floods. This ways been a cause of grave concern for the inhabitants. In this 6 Discussion of the data area, called Topino, is found a large bend, where14 the mass of water acquires a relevant velocity in consequence of a natu- Since 1852, Alba has increased over tenfold in area (from ral shoot of the riverbed, in the stretch immediately preceding 40 hectares to 475 hectares) by gradually incorporating out- the bend...”. lying farms and villages into an urbanised centre for manu- For over a century, the local population had avoided build- facturing and agriculture. Growth rates in urbanisation and ing in the most vulnerable area of sector A. In the 1970s, this population increased quickly after 1950, when local industry www.nat-hazards-earth-syst-sci.net/12/2329/2012/ Nat. Hazards Earth Syst. Sci., 12, 2329–2346, 2012 2342 F. Luino et al.: The Alba case study (Piedmont, Italy) area became the site of a municipal solid-waste landfill. The The negative role played in November 1994 by the road feasibility study for the municipal dump was accompanied network, particularly the Asti-Cuneo motorway, which was by a geological report that stated, “The area was absolutely completed in the early 1980s, should also be emphasised. out of Tanaro floodings”. However, on 5–6 November 1994, As mentioned in Sect. 3, on both sides of the Tanaro, the the great heap was eroded and swept away by floodwaters, structure represented an impediment to the natural spread of with serious consequences for health and hygiene. floodwaters, locally favouring the accumulation of water vol- Superficiality and ignorance of the looming hazard in sec- umes that flowed violently once past the obstacle. tor A has also allowed the construction of a prison in the im- This scenario was particularly evident on the Tanaro’s mediate vicinity of the levee facing the Topino farm. During right bank approximately one kilometre upstream from the the 1994 flood, the floodwaters overtopped and demolished bridge on the highway (see Fig. 4). At the end of the last cen- the levee (see Fig. 2) and inundated the land occupied by the tury, the waters here demolished a levee and inundated the prison with 50–60 cm of water. plain of the river (see Fig. 3). The water retained by the road In Alba, one factor that has increased the town’s vulnera- embankment rose more than 5 m above ground level before bility to flooding is the selection criteria for the development passing the lowest point of the barrier (Fig. 14) and inun- of newly urbanised areas. In a retrospective projection of a dating the village of Vivaro. Again, tragic consequences oc- 1994-type flood, a comparison of historical with present-day curred. The flood current reached the Ferrero industrial area, city maps shows that the flooded urbanised areas would have already inundated by the waters of the Talloria, and collapsed totaled 4.2 % in 1852, 9.4 % in 1880, 10.7 % in 1933, 25.4 % the plant’s eastern perimeter wall, crushing two people. in 1954, and 48.4 % in 1994 (Fig. 12). In the Alba area, an Although in the final map (Fig. 11) the derivable risk posed identifiable hazard is the river’s tendency to reoccupy the his- by the tributaries has not been considered, it is important to toric riverbed, whether it was originally abandoned naturally note that areas C, D, E and K in Fig. 2 are crossed by dan- or artificially precluded. gerous streams and channels that have caused severe damage During the 1994 flood, for example, on the left bank, in in 1994 and in the more distant past. After the 1994 flood, front of the confluence with the Talloria stream (southern many remedial works were built along the Tanaro and its sector B), the bank was extensively eroded. The floodwaters tributaries. In some locations, the banks have been protected first demolished the defense just erected to prevent overflows by large boulders to prevent erosion. Specific projects devel- and then flowed on the ground, digging deep furrows where oped for the Talloria, Cherasca and Riddone streams include the river ran before 1954. On the right bank, similar violent the removal of vegetation and detritus from the stream beds, processes occurred just downstream from the Topino levee, an intervention that must be considered unusual. If all works and water reclaimed the riverbed of 1875 (the area where the are taken into account, the flood risk has been reduced con- municipal dump was established, as mentioned above). siderably around Alba. On the left bank, near the Sarda farm, the road embank- To limit the violence of fluvial processes and contain the ment intersects with an old Tanaro bend, which was still ac- damage such processes can cause, structural and nonstruc- tive in 1933 (see Fig. 6). During the 1994 flood, floodwa- tural interventions must be made in the entire river basin. ters overflowed the embankment, stripping away 100 m of the upper part and drowning two people who had been driv- ing along the road just as the waves reached it (Fig. 13). 7 Conclusions The tendency of the Tanaro to reoccupy the abandoned riverbeds is confirmed by numerous documents relating to To defend inhabited areas against the effects of the river’s the rehabilitation and widening of damaged bank defenses, natural processes, which often turn catastrophic because they particularly the deep bank erosions near the Socchi and Sarda are unforeseen, new fluvial areas must be adequately sur- farms on the left and the Topino and Topinotto farms on the veyed before they can be developed. right. For most floods, the present banks and wall-protection sys- During the September 1948 flood, for example, the deep tems provide sufficient safety for inhabitants because the sys- erosion of the Socchi bend produced remarkable instabili- tems can control the fluvial processes and limit their effects. ties: “... The serious situation ... is significantly enhanced for However, in an extreme event, the speed and violence of the widening of the bend erosion, which now is only 40 m the processes overwhelm all defenses. The 1994 Alba flood from the provincial road Alba-Bra and from the railroad. Be- serves as a classic example of a population caught unpre- sides considerable land, two houses have also been removed” pared. (Consorzio Idraulico di 3a categoria, unpublished). The analysis has shown the most important natural and At four bends, repairs had repeatedly been necessary not man-made reasons why the town was vulnerable to the rav- only as a result of serious floods but even after ordinary ages of the flood. Although the disaster was exceptional, the floods to counteract the erosive effect exerted laterally by the flood’s main natural cause was the Tanaro’s tendency to re- river currents to regain the ancient, artificially closed chan- appropriate its paleochannels, where the floodwaters run with nel. particular violence. Therefore, it is necessary to identify the

Nat. Hazards Earth Syst. Sci., 12, 2329–2346, 2012 www.nat-hazards-earth-syst-sci.net/12/2329/2012/ away 100 m of the upper part and drowning two people who had been driving along the road just as the waves reached it (Fig. 13). The tendencyaway 100 ofm ofthe the Tanaro upper topart reoccupy and drowning the aba twondoned people riverbedswho had beenis confirmed driving along by numerousthe road just documents as the relatingwaves to thereached rehabilitation it (Fig. 13). and widening of damaged bank defenses, particularly the deep bank erosions near theThe Socchi tendency and of Sarda the Tanarofarms onto thereoccupy left a ndthe the aba Topinondoned and riverbeds Topinotto is confirmed farms on bythe numerous right. documents Duringrelating the September to the rehabilitation 1948 flood, and forwide example,ning of damagedthe deep bank erosion defenses, of the par Socchiticularly bend the deepproduced bank remarkableerosions near the Socchi and Sarda farms on the left and the Topino and Topinotto farms on the right. instabilities: "... The serious situation ... is significantly enhanced for the widening of the bend erosion, During the September 1948 flood, for example, the deep erosion of the Socchi bend produced remarkable whichinstabilities: now is only "... 40 The meters serious from situation the provincial ... is significan road Alba-Bratly enhanced and forfrom the the widening railroad. of Besides the bend considerable erosion, land, whichtwo houses now is have only also40 meters been removed”from the provincial (Consorzio road Idraulico Alba-Bra di and 3ª categoria,from the railroad. unpublished). Besides considerable At fourland, bends, two houses repairs have had also repeatedly been removed” been (Consnecessaryorzio notIdraulico only dias 3ª a categoria,result of unpublished).serious floods but even after ordinaryAt fourfloods bends, to counteract repairs had the repeatedly erosive beeneffect necessary exerted notlaterally only asby a theresult river of currentserious sfloods to regain but even the ancient,after artificiallyordinary closed floods channel. to counteract the erosive effect exerted laterally by the river currents to regain the ancient, The negativeartificially role closed played channel. in November 1994 by the road network, particularly the Asti-Cuneo motorway, whichThe was negative completed role playedin the earlyin November 1980s, 1994should by also the robead emphasized. network, particularly As mentioned the Asti-Cuneo in chapter motorway, 3, on both sides whichof the was Tanaro, completed the structure in the early represented 1980s, should an impedi also bement emphasized. to the natural As mentioned spread inof chapterfloodwaters, 3, on bothlocally favoringsides the of accumulation the Tanaro, the of structurewater volumes represented that flowedan impedi violentlyment to oncethe natural past the spread obstacle. of floodwaters, locally This scenariofavoring thewas accumulation particularly of evidentwater volumes on the that Tanaro flowed’s violentlyright bank once approximately past the obstacle. one kilometer upstream from Thisthe bridge scenario on wasthe particularlyhighway (see evident Figure on 4). the At Tanaro the end’s right of the bank last approximately century, the watersone kilometer here demolished upstream a from the bridge on the highway (see Figure 4). At the end of the last century, the waters here demolished a levee and inundated the plain of the river (see Fig . 3). The water retained by the road embankment rose levee and inundated the plain of the river (see Fig . 3). The water retained by the road embankment rose more morethan than5 m above5 m above ground ground level level be forebefore passing passing the the lowest lowest pointpoint of the barrierbarrier (Fig. (Fig. 14) 14) and and inundating inundating the the villagevillage of Vivaro. of Vivaro. Again, Again, tragic tragic consequences consequences occurred. occurred. The The flood flood current reachedreached the the Ferrero Ferrero industrial industrial area, area, alreadyalready inundated inundated by theby thewaters waters of ofthe the Talloria, Talloria, an and dcollapsed collapsed thethe plant’s easterneastern perimeter perimeter wall, wall, crushing crushing twoF. Luino people.two et people. al.: The Alba case study (Piedmont, Italy) 2343

Fig. 14. A large failure caused by the undercutting floodwaters Fig. 13 – Tanaro floodwaters swept away cars on the Asti- Fig. 14 – A large failure caused by the undercutting floodwaters blocked the Asti-Cuneo Highway. In the background, the light sub- Fig. 13.13Cuneo Tanaro– Tanaro link floodwaters road, floodwaters causing swept two swept away deaths carsaway (Y on in thecars Fig. Asti-Cuneo on 2). the Asti- link Fig.blocked 14 – theA largeAsti-Cuneo failure Highway. caused byIn thethe undercuttingbackground, thefloodwaters light road, causing two deaths (Y in Fig. 2). subsidencesidence of theof the highway highway where where the th waterse waters overflowed overflowed (K (K in in Fig. Fig. 2) Cuneo link road, causing two deaths (Y in Fig. 2). blocked the Asti-Cuneo Highway. In the background, the light 2)left left a largea large accumulation accumulatio ofn of uprooted uprooted trees. trees. subsidence of the highway where the waters overflowed (K in Fig.

2) left a large accumulation of uprooted trees. Although in the final map (Figure 11) the derivable risk posed by the tributaries has not been considered, it is old riverbeds,important which to note are oftenthat areas easily C, recognisable D, E and byK in mor- figure retrieved3 are crossed quickly. by Thedangerous data belong streams in the and public channels domain that and phological evidence on the ground’s surface, even where Althoughhave incaused the final severe map damage (Figure in 199411) the and derivable in the more risk distantshould posed past. be by available Afterthe tributaries the to 1994 the cadastral flood,has not many register been remedial considered, and at theworks citi- it is the evidence is partially effaced by mining, farming and importantwere tobuilt note along that the areas Tanaro C, D,and E its and tributaries. K in figure In some 3zens’ are locations, crossed disposal. bythe dangerousbanks have streamsbeen protected and channels by large that havewidespread caused poplar severe plantings. damage To in precisely 1994 and identify in the and more date distantThe past. inhabitants After the must 1994 be warned flood, aboutmany impending remedial haz-works the paleochannels,boulders to oldprevent maps areerosion. indispensable. Specific projects developed for the Talloria, Cherasca and Riddone streams were includebuilt along the removal the Tanaro of vegetation and its andtributaries. detritus fromIn some theards stlocations,ream in the beds, areas the an where interventionbanks they have live. that Abeen civil-defense must protected be considered plan by must large At a minimum, the following local measures are neces- prepare the inhabitants by staging regular flood response bouldersunusual. to prevent If all works erosion. are taken Specific into account, projects the deve floodloped risk hasfor beenthe reducedTalloria, considerably Cherasca andaround Riddone Alba. streams sary: (a) the encouragement in a suitable area upstream of drills. The people’s safety must be ensured by a tool that includeTo thelimit removal the violence of vegetation of fluvial and processes detritus and from contain the sttheream damage beds, such an interventionprocesses can that cause, must structural be considered and the rolling process of the natural subsidence of floodwaters can identify areas at different risks, develop an escape plan, unusual.to reducenonstructural theIf all flow works rates interventions are to the taken bridge mustinto and account,be increase made in the the out-flood entire risk andriver has select basin. been strategic reduced sites considerably for emergency around evacuation Alba. and safe Toflow limit capacity the ofviolence the riverbed of fluvial in the urbanprocesses stretch; and (b) contain the shelter.the damage Discouraging such processes development can on cause, floodplains structural may be and nonstructuralequipping of the interventions embankment ofmust the be Asti-Cuneo made in Highway the entire riverachieved basin. through billsticking of old photographs and histor- with fornices7. Conclusions to allow the natural outflow of floodwaters and ical data, public-information programs, warning signs, tax- prevent the formation of a reservoir that could overlap the assessment practices, financing policies, and public-utility To defend inhabited areas against the effects of the river’s natural processes, which often turn catastrophic 7.highway Conclusions and violently release water; (c) the removal from extension policies. Flood insurance requirements and costs the riverbedbecause and they its immediateare unforeseen, vicinity new every fluvial obstacle areas to themust bemay ade constitutequately surveyed an additional before important they can deterrent. be developed. free flow of floodwaters, particularly the disused processing Toplants defend (especially inhabited the one areas immediately against upstream the effects of the of high- the river’s natural processes, which often turn catastrophic16 becauseway bridge), they the are indigenous unforeseen, tall trees new and fluvial the thick areas plantings must be adeAcknowledgements.quately surveyedThe Authors before wouldthey can like tobe thankdeveloped. the col- of poplars; (d) the imposition of severe construction limits in leagues Ornella Turitto and Chiara Giorgia Cirio for their help and the areas severely damaged in November 1994. useful suggestions. 16 The current condition of the Tanaro floodplain is the prod- Edited by: D. Castaldini uct of town-planning choices made in response to the need Reviewed by: two anonymous referees for space, but without fluvial-hazard evaluation and despite the many relevant documents available. The summary provided here should be used to review the References recent modifications to the town layout. The summary con- stitutes an indispensable starting point for the identification Arnell, N. W.: Flood insurance and floodplain management, in: of land zones with different risk levels that require different “Flood hazard management”, edited by: Handmer, J., Geo planning restrictions. Books, Norwich, UK, 117–133, 1987. The current zoning regulations must not only guide de- Aronica, G., Bates, P. D., and Horritt, M. S.: Assessing the uncer- tainty in distributed model predictions using observed binary pat- cisions about where future urbanisation is most suitable but tern information within GLUE, Hydrol. Process., 16, 2001–2016, must also establish criteria for determining the reconstruction 2002. of buildings and infrastructure that were damaged by flood- Aureli, F., Mignosa, P., Ziveri, C., and Maranzoni, A.: Fully-2D and ing or that played a negative role during floods. The collected quasi-2D modelling of flooding scenarios due to embankment information should be managed by a data bank and linked to failure, river flow, Taylor and Francis Group, London, ISBN:0- a GIS so the sites can be located and the stored information 415-40815-6, 2006. www.nat-hazards-earth-syst-sci.net/12/2329/2012/ Nat. Hazards Earth Syst. Sci., 12, 2329–2346, 2012 2344 F. Luino et al.: The Alba case study (Piedmont, Italy)

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