ICG2022-21

A discussion about the possible cause-effect links between some socioeconomic drivers and changes in geomorphic processes is presented. Different types of physical impacts, including geomorphic effects on land subsidence, denudation or frequency of geomorphic-related disasters, show global spatial distributions very similar to Gross Domestic Product (GDP) density, an indicator of the intensity of human pressure on the environment. The intensity of the indicated impacts has increased in recent times, particularly after mid-twentieth century.

            Data and estimates are presented showing that direct plus indirect “human erosion” is currently 1-2 orders of magnitude greater than purely natural one, and growing. Whereas GDP, as an indicator of per capita potential to modify the environment, has tripled in just over half a century, per capita human transfer of earth materials has increased tenfold. The frequency of disasters related to geomorphic processes has also been amplified about tenfold in less than a century. This increase is much greater than the one of other types of “natural” disasters.

            The changes observed in geomorphic processes appear to respond to land surface modification, to a great extent linked to urban and infrastructure development. The growing intensity of these stressors appears to have a global impact at least as great as that of climate, on the geomorphic changes described which seem to be one of the characteristics of the Anthropocene.

How to cite: Remondo, J., Cendrero, A., Forte, L. M., Beylich, A. A., and Cienciala, P.: An Anthropocene, human-driven geomorphic change not determined by climate?, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-643, https://doi.org/10.5194/icg2022-643, 2022.

The increasing scientific interest in urban geomorphological survey and mapping is recently demonstrated by the number of case studies which can be found in literature. It is due to the support the discipline brings to the knowledge of the effects of urban growth on geomorphological processes and landforms and vice versa, and to the analysis of urban geological risks. In addition, the dissemination of cultural geoheritage in urban areas represents an effective communication tool, both for the landscape historical evolution storytelling and the knowledge of anthropogenic impact on urban sustainability.

This work highlights the contribution to the discipline of the working group on Urban Geomorphology within the Italian Association of Physical Geography and Geomorphology (AIGeo), considering the importance of urban geomorphological analysis in Europe and in Italy especially, where the cities were founded in historical times, expanded in the Middle Ages and progressively entered a period of uncontrolled urban sprawl in the 20th century.

Examples from several Italian urban areas are presented: Rome, Milan, Palermo, Genoa, Venice, Perugia, Rimini, Cagliari, Pescara, Pesaro, Pozzuoli (Naples), Potenza, Fano, Benevento, Chieti, Senigallia, Vasto, Sulmona, together with two international experiences in collaboration: Patras (Greece) and São João da Barra (Rio de Janeiro, Brazil).

The geomorphological survey was performed in all the cities involved in this work, moreover each one is representative for geomorphological applications:

Mapping – research groups in Rome, Palermo, Genova, Naples, Rimini and Cagliari, published the geomorphological map of the city.

Risk analyses – it is the main application of urban geomorphological studies here reported. The studies allowed in the different cities the assessment of the hydrogeological risk conditions (e.g. Benevento, Patras and many other cities), linked to the progressive valley filling of pre-urbanization rivers flowing; the landslides, floods and flash floods occurrence, the last two also related to the sewerage system efficiency (e.g. Milan); the analysis of hazards related to rockfalls, sinkholes, coastal (sea level rise, erosion, interventions in the watershed system upstream the city, e.g. São João da Barra) and anthropic processes; the geomorphological approach for seismic hazard analysis (e.g. Sulmona); the bradyseismic phenomena management.

Paleomorphology and Historical Landscape reconstruction –  the studies are characterized by different kind of data collection and processing: database of borehole stratigraphies, which allowed the reconstruction of buried paleomorphologies (e.g. Potenza); preurbanization morphological setting of the historical city centers ; historical and recent evolution of drainage networks; environmental transformations of canals and salt marshes, also in relation to historical river diversions (e.g. Venice); historical changes of the shoreline and of the rivers' mouths, determining the urban architectural cities' evolution (i.e. Pesaro).

Urban Geoheritage - The urban environment is a perfect laboratory for opening the scientific topics to a broad audience, our studies represent a tool to communicate the cities anthropogenic landscape evolution and the related impacts.  Most of the cities here listed experienced geoheritage inventory and valorisation based on geomorphological survey. In example a geological exhibition was organized in the city of Perugia using interactive tools, laboratories and trekking tours, other examples are the geotourist itineraries in Rome.

How to cite: Pica, A. and the AIGeo working group on Urban Geomorphology: The urban geomorphological survey and mapping as a support to risk assessment and communication tools, through the enhancement of the geological heritage., 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-310, https://doi.org/10.5194/icg2022-310, 2022.

Urban development in the interior of South Africa is historically centred around mining development such as gold, uranium and platinum-group metals and can only be sustained by amongst other, providing a reliable constant supply of potable water for human use and industrial development alike. Therefore, several water transfer schemes were initiated since the 1970’s to pump water from the well watered eastern parts of South Africa and the Kingdom of Lesotho to the drier central industrial and mining hubs of the Pretoria Witwatersrand Vereeniging urban complex in the Gauteng province, and the Rustenburg mining hub in the North-West province. Furthermore, post-apartheid era progress was made to provide access to improved water supply to previously marginalised communities in urban areas – many of which has grown significantly in recent years as people move to urban areas in search of employment opportunities.

These urban developments have not only extensively transformed land cover resulting in changed runoff characteristics of catchments and watercourses but has also in altered the flow regimes of these watercourses. Notably ephemeral and seasonal streams and wetlands started to receive a copious supply of nutrient rich water from aging water infrastructure: leaking pipelines, overflowing or inefficient water treatment plants and uncontrolled release of industrial and effluent waste into streams. Consequently, streamflow increased, resulting in erosion of channels, and desiccation of wetlands in lowering base levels. The oversupply of sediment has resulted in new wetlands further downstream in the landscape. Moreover, the steady supply of nutrients and sediment allowed vegetation species such as Phragmites and Typha to expand and dominate valley bottom systems. Consequently, the footprint of these anthropogeomorphological wetlands has expanded as a positive feedback loop ensued with an increase of surface roughness, diffused water flow, sediment trapping and nutrient cycling. Although these natural processes now interact to form wetlands which clearly provide valuable ecosystem services in an urban environment it remains to be seen if these systems will be self-sustaining if the anthropogenic hydrological drivers are altered with future urban change.

The change in volume and nature of water released from different catchments greatly influences wetlands in affected catchments. South African case studies that will be shared include the effluent affected areas of Rietvlei, Soutpanspruit, and Colbyn, wetlands in Gauteng province; the water transfer scheme affected area of Liebenberg spruit; and the potable water leak wetland of Kgaswane Mountain reserve, North West province.

Keywords:  Urban sprawl, water supply, anthropogeomorphological wetland

How to cite: Grundling, R., Beckedahl, H., and Loubser, M.: Urban Anthropogeomorphological Wetlands – South African Case Studies, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-618, https://doi.org/10.5194/icg2022-618, 2022.

Um relevo de região é o resultado de diferentes processos que ocorrem no subsolo no tempo e no espaço. O tempo de evolução da modelagem de superfícies, que até então era extremamente geológica, começa a apresentar uma forte influência humana, provocando, assim, rápidas mudanças na dinâmica natural. Nesse contexto, o objetivo desta pesquisa foi analisar as feições antrópicas nas encostas da região nordeste de Ouro Preto - MG, agravadas pela ocupação urbana não planejada. A área de estudo é caracterizada por uma região montanhosa com declividades íngremes composta por quartizitos, filitos, itabiritos e mármores, que é suscetível a movimentos de massa. Tal região foi cenário de intensa exploração de ouro, principalmente no século XVIII. Durante o trabalho de campo, em maio de 2019, foram registradas antigas minas, cavidades, poços subterrâneos e ruínas. A participação da comunidade na identificação do enfraquecimento tornou-se essencial para compreender e encontrar fenômenos antrópicos. Os dados quali-quantitativos foram compilados pelo método SWIFT. As características deixadas pelo garimpo conseguiram manter-se preservadas na região estudada devido ao longo período em que essas paisagens estiveram praticamente desabitadas devido ao esgotamento das jazidas. No entanto, esta ocupação durante o período de exploração do ouro provocou alterações no curso d'água subterrâneo, prejudicando a estabilidade das encostas o que levou a graves consequências que puderam ser observadas após o período de chuvas intensas de dezembro de 2021 a janeiro de 2022. As características deixadas pelo garimpo conseguiram manter-se preservadas na região estudada devido ao longo período em que essas paisagens estiveram praticamente desabitadas devido ao esgotamento das jazidas. No entanto, esta ocupação durante o período de exploração do ouro provocou alterações no curso d'água subterrâneo, prejudicando a estabilidade das encostas o que levou a graves consequências que puderam ser observadas após o período de chuvas intensas de dezembro de 2021 a janeiro de 2022. As características deixadas pelo garimpo conseguiram manter-se preservadas na região estudada devido ao longo período em que essas paisagens estiveram praticamente desabitadas devido ao esgotamento das jazidas. No entanto, esta ocupação durante o período de exploração do ouro provocou alterações no curso d'água subterrâneo, prejudicando a estabilidade das encostas o que levou a graves consequências que puderam ser observadas após o período de chuvas intensas de dezembro de 2021 a janeiro de 2022.

How to cite: Félix Andrade Silva, C., Pacheco de Moura Pereira, M., Amorim Machado, H., and Rodrigues Silva, J.: Anthropogenic Landform Features in the Auriferous Region of Ouro Preto-MG-Brazil, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-342, https://doi.org/10.5194/icg2022-342, 2022.

In Brazil, urbanization and industrialization processes were intensified from the 1930s onwards, in order to meet global economic demands that required an industrialized and modernized country. Soon after the capital transference to Brasília, the then State of Guanabara, ruled by Negrão Lima (1965-1971), expanded its urban fabric to the West Zone, considered as a rural area of ​​the Sertão Carioca, at the time. Thus, urbanist Lúcio Costa produced the first territorial plan for the Baixada de Jacarepaguá, in which he included the neighborhood of Recreio dos Bandeirantes. The landscape changes, including the geomorphological aspects, were striking and such transformations provoke studies of urban geomorphology and its anthropogenic effects.

Anthropogenic geomorphology’s studies are marked by the speed of human action on the earth-system, in a historical time scale: “the time that is made” (SUERTEGARAY and NUNES, 2001). Therefore, such studies, associated with this branch, such as urban geomorphology allow managers to analyze the problems arising from urbanization, since they analyze the change in natural dynamics, products of the peculiar way in which urbanization processes take place in “developing countries”. From the moment that there is occupation and intense use of the soil, the (re)organization of the natural environment starts to present strong anthropogenic influences, which act, even, as geomorphological and, consequently, environmental agents.

The present research work has as its main objective to evaluate geomorphological features alteration, caused by the urbanization process in the neighborhood of Recreio dos Bandeirantes. To this end, specific objectives are defined: to present the changes in geomorphological processes resulting from human action and to identify the impacts on geomorphology, resulting from this urbanization dynamic.

The methodology of the research work starts from a historical reconstruction of the most recent process of urbanization in the study area (2009 to 2021), through the use of retrospective geomorphological cartography, via the use of Google Earth images and aerial photographs of that period, allowing comparative analysis between pre-urban geomorphology (RODRIGUES, 2010) and current geomorphology (period of consolidated urbanization). The cartographic products were used in the visual analysis of landscape changes over historical time and cumulative to the bibliographic research, regarding the area's urbanization plans and fieldwork.

The most prominent changes in satellite images’ historical series clearly reveal the transformations of geomorphological features of coastal formations in the region, such as eradication of dunes, channeling of swamps and lagoons and channel straightening, especially by urban agents, which in this context, are also exogenous geomorphological agents.

         As developments, studies on the evolution of the neighborhood and on the consequences of changes in landforms and their consequent environmental impacts are still oriented. Finally, the role of the State, supposedly regulating in this context, is also questioned.

How to cite: Silva Furtado, A. P., Brito da Frota Filho, A., Lopes da Silva, S. E., Motta de Freitas, M., and Teixeira Guerra, A. J.: Relief changes generated by the urbanization process: urban geomorphology case studyin the neighborhood Recreio dos Bandeirantes - Rio Janeiro (RJ).., 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-357, https://doi.org/10.5194/icg2022-357, 2022.

Mining is an essential activity in our society, as it provides the materials and metals essential to support our current life level and development. However, it also produces a high environmental impact wherever it occurs. The environmental impact of mining on landscape systems is well recognized. Surface mining imposes severe ecological effects on the land because alteration affects vegetation, soils, bedrock and landforms-landscapes. Surface hydrology and groundwater levels and flow paths are also changed. The science of geomorphology, which deals with the study of earth’s landforms and the surface processes by which they are shaped, provides a useful framework both for an understanding of the environmental effects of surface mining, including changes in erosion–sedimentation processes and soil properties and for designing the most appropriate strategies for landscape reconstruction. Methods for landscape reconstruction based on geomorphic science have been developed and advanced in recent decades. New technologies have developed alongside the recognition of the environmental impact and resultant societal expectation of a rehabilitated and integrated post-mining system. A post-mining landscape requires physical stability (and, if present, chemical stability). Australia, United States, Canada, Chile and the European Union, among others, have mine regulations requiring physical and chemical stability and non-polluting post-mining landforms for mine closure. Physical stability can be guaranteed by expert Geomorphic Landform Design (GLD) and Landscape Evolution Modelling (LEM). In this framework, we describe the combination of GLD tools (GeoFluv – Natural Regrade and Talus Royal) with a LEM method (SIBERIA), and with Acid Mine Drainage (AMD) stabilization measures where they are needed. All that at the LIFE RIBERMINE project (https://liferibermine.com/en/homepage_en/), at two locations of the Iberian Peninsula (an ancient pyrite mine at Lousal, Portugal; and an abandoned kaolin mine at Peñalén, Spain). In conjunction, LIFE RIBERMINE is the first mine rehabilitation project, globally, which combines the GeoFluv – Natural Regrade (for geomorphic landform design of unconsolidated sandy waste dumps) and Talus Royal (for landform design of hard-rock residual highwalls). And within the European Union, it is the first mine closure project combining GeoFluv-Natural Regrade GLD with: (a) AMD chemical stabilization measures; and, (b) landscape evolution modelling to evaluate erosional stability of post-mining landform designs. This contribution describes the design and implementation of the referred methods, demonstrating that the science of geomorphology can have a key contribution to solve critical environmental problems derived from one of our most needed economic activities (mining).

How to cite: Sánchez, R., Martín Duque, J. F., Tejedor, M., Martins, M., Pereira, A. M., Madureira Pinto, A. M., Rodrigues de Sancho Relvas, J. M., Hancock, G. R., Martín Moreno, C., and de la Villa Albares, J.: Geomorphic Landform Design and Landscape Evolution Modelling for Mine Rehabilitation in Portugal and Spain (LIFE RIBERMINE PROJECT), 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-732, https://doi.org/10.5194/icg2022-732, 2022.

The geomorphological map of Rome city centre, first published in 2016, is one of the most representative case studies for urban geomorphology, due to the widespread anthropogenic changes to landscape caused by human activities over the city’s millenarian history.

The today topographical and hydrographic setting is therefore the result of both natural and anthropogenic processes, which have occurred and intertwined over time. In particular, the most relevant human interventions affect the hydrographic network in the eastern area of the city, where it firstly arose and developed and where resource abundance and at the same time water management and supply needs were more relevant.

Before significant land-use changes had started since the roman time, this area was drained by the most important left tributaries of the Tiber River, such as the Aniene River, the main watercourses of the city, the Nodicus-Aqua Mariana stream, the Almone River, the Grotta Perfetta and the Vallerano streams. Their courses became culverted or were diverted. Emblematic is the example of the Nodicus valley, standing between Aventino and Palatino historical hills, and the Rivo Aqua Mariana artificially streaming into the Nodicus drainage basin since the 1122 a.D. diversion, which probably restored the original Nodicus hydrographic system.

This work aims at presenting the first relevant results towards the reconstruction of the main topographic transformations on the Tevere River hydrographic left area by analysing the current drainage network and its anthropogenic modifications. The methodological approach consists of multidisciplinary bibliographic research supported by multitemporal geomorphological and topographical analyses. The results of this work are summarized in the map of the changes to the hydrographic network.

How to cite: Vergari, F., Pica, A., Schiavella, S., Luberti, G. M., and Del Monte, M.: Multitemporal analyses of anthropogenic changes to the drainage network in urban areas: a case study in Rome (Italy), 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-280, https://doi.org/10.5194/icg2022-280, 2022.

Numerous urban centres developed along rivers because of the resources that they provide. Consequently, many of the world’s rivers are impacted by urbanization. Thus, complex and two-way interactions have established between rivers and cities, resulting in potential benefits or damage in both directions. Focusing on fluvial geomorphological processes, the consistent presence of vulnerable elements close to the riverbed generally results in severe geo-hydrological risk conditions.

Based on multi-temporal comparison of historical maps and present-day aerial images, geomorphological survey, boreholes data analysis, high-resolution topographic data investigation, and archival document collection and review, this contribute aims to illustrate in detail the geomorphological changes associated with urban sprawl that has affected the lower Bisagno and Polcevera rivers since the first half of the 19th century.

From the 10th century to 1815 the urban development of Genova was limited to the hills surrounding the so-called Porto Antico Bay, which correspond to the present-day historical centre. From the 19th century onwards, Genova has developed over the Bisagno and Polcevera valleys, Est and West of the Porto Antico Bay, respectively. The cultivated narrow and elongated alluvial-coastal plains close to the seaside were progressively turned into industrial and residential areas. Meanwhile, the Polcevera and Bisagno lower reaches experienced relevant narrowing, simplification of landforms and complete channelization. The downstream-most section of the Bisagno River was culverted in the 1930s; at the mouth of the Polcevera, a progradation of the coastline to the sea occurred, completely due to the filling of the seaside to realize flat surfaces for industrial activities. Nowadays, the surface behind bank protections overall corresponds to made ground or landscaped ground and no pristine landforms are recognizable. Minor tributaries were squeezed, diverted, channelized, and culverted. In conclusion, the anthropogenic interventions completely reshaped the early-nineteenth-century landscape leading to the current geomorphological setting.

This research is framed in a larger project concerning (i) the quantitative analysis of urban river morphological dynamics at medium- and short-term temporal scales and (ii) the geomorphological evolution of the waterfront of Genova, which aims to support proper management of urban areas and geo-hydrological risk mitigation within a city of historical and cultural value that is very prone to flash floods.

How to cite: Mandarino, A., Brandolini, P., Terrone, M., and Faccini, F.: Medium-term geomorphological changes along rivers in urban areas: the lower Bisagno and Polcevera Valleys in Genova city (Italy), 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-531, https://doi.org/10.5194/icg2022-531, 2022.

In the surroundings of São Pedro valley, in the village of São Pedro de Moel, several episodes of gully erosion of dune sands have occurred in recent decades, with relevant occurrences in 2002, 2016, 2017 and 2021. 

The São Pedro valley has an unusual geomorphology caused by the presence of a hidden karst spring creating a short water line with a length of only 475m until it reaches the sea at the São Pedro de Moel beach. The upstream zone of the São Pedro valley presents a singular shape similar to an elongated horseshoe, due to the soil erosion, by the action of the permanent karst spring.

The inclination of the valley slopes varies between around 30°, exceptionally reaching 50º in the most abrupt areas when the vegetation supports the dune sands, and a minimum of about 10° in the flattest areas of the slopes.  

The stratigraphic sequence of the São Pedro valley consists of Toarcian limestone at the base, overlapped by undifferentiated Plio-Pleistocene soil, covered by dunes and dune sands, locally overlapped by road fills essentially built with dune sands. 

The gentle slope of the ground to the west, towards the sea, in the surroundings of the valley, together with the low permeability streets paving, favors the surface runoff to the west, until reaching the alignment of the São Pedro valley. At this point the runoff waters, are redirected and strat to flow north, according to the alignment of the initial section of the São Pedro valley. 

The generality of the gully erosions mentioned before resulted from the occurrence of episodes of intense precipitation that concentrate quantities of water above the normal. By analyzing the last erosive process, it was confirmed that the beginning of the gully erosion occurs when the water overturns the crest of the slope, flowing along the higher inclination, perpendicular to the face of the slope, until the bottom of the São Pedro valley. The erosive process develops very quickly, and last a few tens of minutes. The absence of storm drainage systems in the streets at the crest of the São Pedro valley aggravate the erosive phenomenon, allowing the concentration of surface runoff water, increasing the erosion processes.  

To solve this recurrent problem, punctual stabilization works were initially carried out, but proved to be inefficient. Recently, stabilization work more expensive, more elaborated but more effective were used, using a surface protection of the slope with a Reno mattress, complemented with the construction of surface drainage systems in the streets, with capacity to drain the storm waters and properly route those exceptional flows. 

This case study allows to verify that to obtain good urban performance, geomorphology, geology, hydrology, hydrogeology and engineering must be considered in a complementary approach.

How to cite: Quinta-Ferreira, M.: Gully erosion episodes in the São Pedro valley at São Pedro de Moel, Portugal, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-615, https://doi.org/10.5194/icg2022-615, 2022.

Large urban gullies (UGs) cause major infrastructural damages and often claim casualties in many tropical cities of the Global South. Nonetheless, our insight into this new type of geo-hydrological hazard remains limited to some case studies and the overall impacts remain poorly quantified. Here, we aim to bridge this gap by making a first assessment of the number of persons affected by urban gullies at the scale of the Democratic Republic of Congo (DRC). We used Google Earth imagery in combination with local news sources and earlier research to identify 25 cities in DRC where UG occur at a significant scale (at least ten UGs). This list is likely exhaustive. Next, for each of these cities, we used Google Earth imagery and other high resolution satellite images to map all visible UG, evaluate their expansion rate and inventorize detectable damages to houses and roads. In total, >2,000 UGs were mapped across the 25 affected cities.  Overall, the problem of UGs in DRC is especially acute in the cities of Kinshasa, Mbujimayi, Kikwit, Tshikapa and Kananga. Over 90% of these gullies were active during the observation period (typically from 2002 to 2020). 
Next, we assessed the total number of persons that are directly affected, as well as the number of persons currently at risk. Using available high resolution population density data and taking into account the current position of urban gullies, we estimate that around 68,700 people were directly displaced due the formation and expansion of UGs over the last 15 years. This corresponds to an average of ca. 4,300 persons per year. By considering the population that lives in the direct vicinity (<100 m) of an UG, we estimate that around 1.3 million people in D.R. Congo are currently at risk and/or experience significant impacts because of UGs (e.g. reduced land value, problems with trafficability, stress). This number has doubled over the past 10 years (2010-2020) and will likely continue to increase as a result of urban expansion and climate change.  
Overall, this research shows that urban gullying is a very serious problem in the Democratic Republic of Congo, but likely also in many other countries of the Global South. More research is needed to better understand this processes and, ultimately, to prevent and mitigate its impacts. The results and the database of this study provide an important step towards this.

How to cite: Ilombe Mawe, G., Lutete Landu, E., Makanzu Imwangana, F., Nzolang, C., Michellier, C., Poesen, J., Bielders, C., Dewitte, O., Hubert-Ferrari, A., and Vanmaercke, M.: Quantifying the direct impacts and risks of large urban gullies in the Democratic Republic of Congo, 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-145, https://doi.org/10.5194/icg2022-145, 2022.

The city of Benevento is located in an intramontane Plio-Pleistocene basin of the Campanian Apennines (Southern Italy), at the confluence of the Calore and Sabato Rivers. Most of the city lies on different orders of terraces, while the more recent settlements are located on summits and flanks of hilly relieves. The terraces, as confirmed by both literature and field surveys, have an alluvial origin and a lower Pleistocene to upper Pleistocene age. The substratum of these terraces mainly consists of conglomerates with sandy intercalations. There are also limited outcrops of silty-clayey sequences with sandy-gravelly intercalations, interpreted as results of fluvio-lacustrine sedimentary episodes. The scarps between the different orders were probably smoothed artificially over time, also using the rubble produced by earthquakes, which are still intense in this area. On the slopes that border the recent alluvial plain, landslides are frequent, especially on north-facing slopes. The most recent alluvial terraces are not older than Holocene. The substratum of these terraces consists of gravels and sands with interbedded tephras and paleosols. Currently, the main fluvial landforms are the single‐thread channels with small‐sized bars and fluvial islands of the Calore and Sabato Rivers. The geomorphological analysis, based on GIS-based comparisons of historical maps and aerial photos from different dates and supported by field data, also shows several inactive fluvial landforms, such as abandoned channels, degraded fluvial scarps and summits of river terraces, together with an intense channel narrowing. Probably, the first stable settlements of Benevento, dated back to the Archaic and Classical age, were located on the floodplains of the Sabato and Calore rivers. This allowed the exploitation of water for agro-pastoral purposes. When there was the need to organize more structured settlements, also protected from both frequent floods and military attacks, the population moved upward to the middle-upper Pleistocene aged alluvial terraces. The first settlement was probably built in the 5th century B.C. and subsequently expanded during the Roman and, then, Longobard ages. The water supply in the most elevated areas was made by a series of artificial canals built along the southern slopes of the surveyed area, prepared with suitable terracing. On the northern side, in a recently restored monumental complex dated back to the VI-VII century, the effects of a series of catastrophic events (i.e., floods and earthquakes) that affected this area can be recognized in the materials preserved there. For centuries, a clear subdivision in the land use was maintained. Namely, rural areas were located on the plain and surrounding slopes, while residential areas were located on the most elevated terraces. However, during the twentieth century, a transformation gradually occurred due to a significant demographic increase. The urban environment quickly occupied large agricultural areas, despite the fact that these areas were subject to frequent flooding, which caused extensive damage and even fatalities. In order to protect them, therefore, impressive bank works were carried out on the rivers, but in other cases the lack of care of farmers still makes difficult any recovery and mitigation intervention.

How to cite: Valente, A., Cusano, A., Magliulo, P., and Russo, F.: Fluvial landforms as a constrain to urban development of Benevento (southern Italy), 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-473, https://doi.org/10.5194/icg2022-473, 2022.

The city of São Paulo in Brazil is the largest urban agglomeration in the world outside Asia. The urbanization process has developed extensively and with a high density of construction in areas of high drainage density of this tropical environment, including over natural floodplains and low terraces, which has made flooding the most prevalent type of risk. Historically, the containment of such events involves the implementation of artificial channels and the construction of artificial storage structures, which have proven to be insufficient, since the episodes of floods with great impacts on the population are repeated annually. Apart from intense tropical rains and increasing impermeabilization, studies suggest that the loss of natural flood-dampening capacity exerted by floodplains is critical to the extent of flood events. In order to evaluate this factor in the occurrence of floods observed in recent years, a highly urbanized sample basin was selected and high-resolution airborne Lidar data was obtained. Differentiating the points, it was possible to classify the surface elements, isolating the terrain, vegetation, buildings and suspended structures such as bridges and transmission lines. The delimitation of the floodplain’s natural extension was carried out through stereoscopic restitution, using aerial photos from the pre-urbanization period, also supported by the terrain model obtained by classified Lidar. As a result, a GIS terrain modeling stage was carried out, in which different water level heights were tested to completely fill the floodplain. This process was undertaken by subdividing the original floodplain surface into blocks, so that this hypothetical water surface could be adjusted to the existing slope between the different sections. Obtaining the volume of water needed to completely fill the natural floodplain, it was then possible to obtain the volume occupied by buildings within this simulated area. Likewise, it was possible to run the same simulation for floods with different heights, from 0.5 to 6.5 meters above the bankfull stage (value identified as the threshold for complete filling of the floodplain). This analysis showed that the average storage volume lost due to the presence of buildings decreases as the water level is raised in the simulated events (in terms of cubic meters lost per meter of water column). This allows us to identify that one of the most immediate effects of the presence of buildings on the floodplain is the widening of floodspreads in events of lesser magnitude. When testing the complete filling of the floodplain, the volume occupied by the buildings corresponds to 25% of the volume of water that could be stored by its natural morphology. This volume of lost storage exceeds by 22 times the capacity planned by public authorities for the installation of artificial storage structures. Furthermore, considering a recent high-magnitude flood event (5 meters above bankfull stage) the lost storage volume exceeds the projected capacity by 17 times. Thus, it is considered that the structural engineering measures, already applied and planned, would be insufficient and impractical to compensate the loss of this environmental service naturally provided by the floodplain.

How to cite: Simas, I., Rodrigues, C., and Hooke, J.: High resolution modelling of floodplain water storage capacity loss in a highly urbanized tropical catchment and its implications for flood management., 10th International Conference on Geomorphology, Coimbra, Portugal, 12–16 Sep 2022, ICG2022-294, https://doi.org/10.5194/icg2022-294, 2022.