Return Period Flood Research Articles

Risco hidrológico de falha da barragem sob mudanças climáticas

ABSTRACT Most water infrastructure was designed for climate conditions and demands that have been rapidly changing. In this study, we investigate flood magnitude and dam safety under climate change, using an ensemble of CMIP6 climate models, coupled to a hydrological model. We compare historical and future climate conditions of a watershed in Ceará, Northeast Brazil. Climate models revealed a wide range of risk levels of flood and hydrological failure. Half of the climate scenarios indicated a reduction in the flood return period. A flood associated with a 1000-year storm had an occurrence probability about 12 times higher when comparing the SSP5 8.5 scenario with historical conditions. In one more critical scenario, the water depth exceeded the height of the dam's crest. When considering a flood associated with a decamillennial storm, dam collapse risk was increased. Climate change might increase the risk of water infrastructure failure, which needs to be adapted to ensure the safety of the water system stakeholders.

Urban flash flood and extreme rainfall events trend analysis in Bamako, Mali

One of the consequences of climate change is the increasing rainfall intensity and frequency leading to flooding. Lately, some major cities in West Africa have been experiencing high frequency of flooding due to extreme rainfall. This study investigated the temporal trends in flash flood and extreme rainfall events in Bamako, Mali for the period 1982–2019. Rainfall observation data from both Mali Meteorological Agency and Climate Hazards Group Infrared Precipitation, and flood ground information’ collected from the Mali Civil protection service were used for this study. Five rainfall extreme indices established by Expert Team for Climate Change Detection Monitoring and Indices (ETCCDI) were analyzed to characterize extreme rainfall intensity and frequency indices. The Gumbel extreme value distribution was used to estimate the return period of flood and extreme rainfall for the period of 5 to 100 years based on the annual maximum daily rainfall. All the five extreme rainfall indices displayed an upward trends except the consecutive wet days (CWD) that showed a decreasing trend. Both the intensity and frequency of extreme rainfall were found to have increased over the study period. The analysis of the flood reports showed an increasing trend in Bamako from 1982 to 2019. The returned period revealed that about 58% of flood events in Bamako are caused by normal rainfall, with 33.3% being caused by extreme rainfall. It was also determined that most flood events were recorded in the years that had higher number of extremely wet days. The findings from this study have demonstrated that floods in Mali are prevalent and adaptation and mitigation strategies are needed.

Avaliação da capacidade de modelos hidrológicos-hidrodinâmicos de larga escala para mapear o risco de inundação no sul do Brasil

ABSTRACT Mapping flood risk areas is important for disaster management at the local, regional, and national scales. The aim of this study was to evaluate the ability of large-scale models to obtain flood hazard maps. The models were compared to the estimates developed by the Brazilian Geological Survey (CPRM) for different return periods (RP). The floods were evaluated for the municipalities of Uruguaiana, Montenegro and São Sebastião do Caí in the Rio Grande do Sul state. It was shown that the flood mapping generated by MGB covers larger areas (greater than 1000 km2; Siqueira et al. 2018), with a lower cost of obtaining for large scales. The - Hit Rate of the regional and continental MGB model versions with the CPRM maps ranged from about 40% to 90% in different cities, and the Hit Rate between the regional model and the CPRM map increased with the increased return period floods. The continental model compatibility was similar for all analyzed RPs. Our results suggest the agreement in terms of Hit Rate of current large-scale hydrological-hydrodynamic models to assess flood hazard.

Flood Modeling on Koya Catchment Area Using Hyfran, Web Map Service, and HEC-RAS Software

In this research, The boundaries of the Koya catchment area have been delineated, and valley paths in the region were drawn by using the Water Modeling System (WMS) software, Analysis of the morphometric information indicated that the morphometric characteristics of watersheds contribute to the floods. The average surface runoff depth depends on the curve number values that are determined based on the types of soil cover and soil class according to Harmonized World Soil Database HWSD software that indicates the soil class in the study area are Group B silt loam, The results obtained also show that the potential for surface runoff varies with land use and soil characteristics. Also, the value of the curve number (CN) was determined to be 71. The hydrological modeling was performed by the HEC-HMS program that simulates the process of rainfall to runoff using the SCS curve number model. A flood hydrograph was constructed at the catchment area outlet and the floodplain delineation was verified by the HEC-RAS software. The results indicated that the 100-year return period flood could Reach critical areas such as the urban area, agricultural area, residential areas. the results of this study indicate that there are suitable sites in the catchment areas for constructing small dams and ponds for water harvesting.

Hydraulic Model for Flood Forecasting of Tajabad Khwar in Hayatabad Phase III Peshawar, Pakistan: A Case Study

Among all other natural disasters occurring throughout the world, floods are considered to be the worst and most devastating catastrophe as it causes loss of billions of lives. Flooding is caused due to inundation of water over the areas which are in close proximity of river or natural waterways resulting in severe damages to commercial and residential areas in the surrounding. Thus, an efficient flood forecasting system through the development of a combined hydrological and hydraulic model for the prediction of future flood events through marking the potential high-risk zone is required to minimize the damages. Due to large number of encroachments made in the waterway of Tajabad khwar located near Deans Residential Apartment of Hayatabad Phase III, a hydraulic model is developed for its flood forecasting as the floods in this khwar may cause severe damages to the inhabitants of the adjacent areas. In this research work, Flood zone maps are developed for 10 years, 20 years, 50 years, and 100 years flood return periods in order for deterring extent of the inundation as a result of these encroachments and to identify the areas at potential risk. Flood discharge for each return period was estimated using HEC-HMS software and was found to be 772, 1036, 1392 and 1666 m^3/sec for 10 years, 20 years, 50 years, and 100 years flood return periods respectively. The corresponding water surface elevation determine using HEC-RAS and was found to be 196 m, 197m, 201m, 202m. This model provides a basic idea for developing flood zone maps of a given period of return for the assessment of areas that can get adversely pretentious by floods.

Evaluation of Flood Mitigation Effectiveness of Nature-Based Solutions Potential Cases with an Assessment Model for Flood Mitigation

In recent years, climate change has been widely discussed around the world. The Intergovernmental Panel on Climate Change (IPCC) published the Sixth Assessment Report (AR6) in 2021, which stated that with the intensification of global warming, heavy rainfalls are becoming more severe and frequent. Economic development in recent years has also caused the proportion of impervious areas in urban regions to increase with the advancement of urbanization. When the two aforementioned factors are coupled together, the result is faster surface runoff speeds and reduced infiltration rates, which in turn result in worse flooding. Thus, water disaster mitigation is becoming a topic of great importance to developed and developing countries. This study examined five Nature-based Solutions (NbS) cases (A, B C, D, E) for the Nangang river in Taiwan. Case A is to design levees with a 100-year return period flood design standard. Under steady flow conditions, floods can be smoothly discharged downstream without any significant inundation in most situations. Case B and C used gabions with a 10-year return period flood design standard and discontinuous levees with a 25-year return period flood design standard, respectively. Though neither case is as effective in flood mitigation, both cases B and C can still reduce inundation from the flooding disaster relatively well. Case D is to dredge local areas of the main channel, but the steady flow simulation showed little flood mitigation effect. Case E is the implementation of “Room for the River”, and employs main channel dredging and floodplain land grading to increase flood conveyance capacity. Case E provides good flood mitigation.

Delineation of flood‐prone areas in cliffed coastal regions through a procedure based on the geomorphic flood index

AbstractThe geomorphic flood index (GFI) method provides a good representation of flood‐prone areas. However, the method does not account for floodwater transfers in undefined interbasins (UIBs), which represent intercluded small basins along the coastline likely to be flooded by adjacent major rivers. The present work addresses this shortcoming by complementing the GFI approach with an iterative procedure that considers UIBs and water transfers between basins. The methodology was tested on a coastal basin in southern Italy and the outcome was compared with a flood map obtained by a two‐dimensional hydraulic simulation. GFI performance as a morphological descriptor improved from 74% (standard method) to 94% with the addition of the iterative procedure. The proposed methodology, with the same parameterization, was applied on a second adjacent coastal basin obtaining improvements both in terms of true positive (from 56 to 79%) and false negative rates (from 44 to 21%). Finally, a sensitivity analysis to the flood return periods highlighted a strong influence on model parameterization for return periods below 20 years. This achievement represents a new development in the application of the GFI method, which can help stakeholders in a more time‐ and cost‐effective flood risk management in hazard‐prone areas.

River space: A hydro-bio-geomorphic framework for sustainable river-floodplain management

The lateral dimension of an alluvial river – floodplains – provides a plethora of goods and services for human needs. Also, it supports the richest and diverse riverine ecosystems on Earth. But over-utilization of floodplain resources had impacted functions of river system adversely. So, the present study attempts to formulate a hydro-bio-geomorphological framework to assess the lateral dimension of a river system for sustainable management of river-floodplains and termed as river space in this paper. The study illustrates river space at seven hydro-meteorological sites situated on the main stem of the Ganga river in the ~750 km stretch that lies between Haridwar and Prayagraj cities. For hydrological aspect, the flood frequency analysis is used to identify flood inundation widths for floods of different return periods with the help of the rating curve and derived cross-section from satellite imagery. Bio-geomorphological aspects are taken into consideration for corroborating the hydrologically assessed river widths (lateral dimension). The present study suggests that the minimum river space should be equal to the lateral width corresponding to the 1-year return period flood. In the present hydro-meteorological sites in the middle Ganga plains, it ranges from 2 to 21 km. Overall, the present study gives an insight of a simple and logical approach that could be beneficial for the biomic restoration of rivers and their floodplains.

The analysis of urban flood risk propagation based on the modified susceptible infected recovered model

Increasing urban flood posed serious threat to urban safety and sustainable development, and resulted in great loss and damage. It was significant and indispensable to master the potential change of urban flood for flood risk mitigation and adaption. Floods not merely caused the physical losses, but also led to potential damage and harm during flood risk propagation. Studies have mainly focused on the physical features of flood risk and post-disaster reconstruction, while few have discussed the potential risk consequence considering flood risk propagation. Therefore, this study analyzed flood risk propagation based on modified Susceptible Infected Recovered (SIR) model. We performed flood simulation and modelling, mapped urban flood risk in consideration of flood risk propagation, and estimated flood losses in Nanjing with flood return periods of 5, 10, 20, 50, and 100 years. Results indicated that inundated area occupied 517.19, 654.11, 657.92, 834.49 and 1045.80 km2 with return periods from 5 to 100 years respectively. Jianye District showed high flood risk and it was suggested to protect people’s lives and assets to reduce susceptibility and vulnerability, and enhance urban drainage capacity for recovery improvement. Moreover, total economic losses reached $27.85, $30.89, $32.91, $35.50 and $38.55 billion and led to the 14.38%, 15.94%, 15.94%, 18.32% and 19.90% GDP loss rate respectively. This study could support the effective flood risk mitigation practice for adaptive urban development.

Process‐Based Flood Risk Assessment for Germany

AbstractLarge‐scale flood risk assessments are crucial for decision making, especially with respect to new flood defense schemes, adaptation planning and estimating insurance premiums. We apply the process‐based Regional Flood Model (RFM) to simulate a 5000‐year flood event catalog for all major catchments in Germany and derive risk curves based on the losses per economic sector. The RFM uses a continuous process simulation including a multisite, multivariate weather generator, a hydrological model considering heterogeneous catchment processes, a coupled 1D–2D hydrodynamic model considering dike overtopping and hinterland storage, spatially explicit sector‐wise exposure data and empirical multi‐variable loss models calibrated for Germany. For all components, uncertainties in the data and models are estimated. We estimate the median Expected Annual Damage (EAD) and Value at Risk at 99.5% confidence for Germany to be €0.529 bn and €8.865 bn, respectively. The commercial sector dominates by making about 60% of the total risk, followed by the residential sector. The agriculture sector gets affected by small return period floods and only contributes to less than 3% to the total risk. The overall EAD is comparable to other large‐scale estimates. However, the estimation of losses for specific return periods is substantially improved. The spatial consistency of the risk estimates avoids the large overestimation of losses for rare events that is common in other large‐scale assessments with homogeneous return periods. Thus, the process‐based, spatially consistent flood risk assessment by RFM is an important step forward and will serve as a benchmark for future German‐wide flood risk assessments.

Flood inundation modelling on agricultural land in Legonkulon Sub-district, Subang Regency, Indonesia

Flood has been an issue in many sectors, including agricultural land. The disaster has been severe to many places in Indonesia, including Subang Regency, and in particular Legonkulon Subdistrict, where the area was traversed by Cipunagara River. The study showed the flood inundation projections for various return periods and portrayed the significance of flood occurrences from Cipunagara River on agricultural lands within the area. The model was established using DEMNAS topographic data, where Lognormal Distribution was selected for the design rainfall based on goodness of fit tests. Afterwards, Snyder SUH Method was performed to estimate the peak discharge for Q2, Q10, Q50, and Q100, resulting 1,568.24 m3/sec, 2,228.89 m3/sec, 2,754.87 m3/sec, and 2,968.74 m3/sec, respectively. As for the inundation model, HEC-RAS 5.0.7 (one-dimensional Saint-Venant equation) was utilized to construct the model. Finally, the study showed that from a total agricultural land area of 2,385.45 Ha within the Legonkulon Sub-district, areas that were inundated by the overflow of Cipunagara River for Q2, Q10, Q50, and Q100 were 738.53 Ha, 792.33 Ha, 816.74 Ha, and 825.15 Ha, respectively. It was concluded that the agricultural land in Legonkulon Subdistrict was prone to the overflow of Cipunagara River even from low return period floods.

Determination of River Water Level Triggering Flood in Manghinao River in Bauan, Batangas, Philippines

Flooding is one of the problems experienced by many countries no matter what their economic status is. Even rich and developed countries experience it too. Flooding is mainly caused by natural events such as typhoons and monsoon rains even anthropogenic causes that sometimes could not be stopped even if there are flood control structures in place. The Philippines is located in the Pacific Ring of Fire and is visited by an average of 20 typhoons each year. People are used to experiencing flooding and it is about time that we somehow do something about it. There have been many technologies available right now that could aid us to improve our capability to adapt to such phenomena. Heavy precipitation is usually experienced during the monsoon season that leads to severe flooding in a specific area. The application of HEC-RAS (Hydrologic Engineering Centre’s River Analysis System) Modelling Software was used in the study in Manghinao River for comprehensive hazard mapping and risk assessment in the downstream area of the Bauan River for 100-year return period flood. 2D flood hazard simulation was done and the river water level that would trigger flooding downstream was identified. At 0.5 m of flood height, people are considered immobilized to move from one place to another so the best time to evacuate people is before the flood reaches that level. Results showed that LGU has 4 hours to evacuate people starting when the river water at the gaging station reads 0.5 m, this gives them enough time to give warning and ask people to move to evacuations sites to prevent them being stranded in their houses. This study can support future planning and for the development of flood control plans and flood mitigation measures to minimize the losses due to flood disasters in Batangas Province, Philippines particularly in the Bauan area.

Global compound floods from precipitation and storm surge: Hazards and the roles of cyclones

AbstractDuring simultaneous or successive occurrences of precipitation and storm surges, the interplay of the two types of extremes can exacerbate the impact to a greater extent than either of them in isolation. The compound flood hazards from precipitation and storm surges vary across regions of the world because of the various weather conditions. By analyzing in-situ observations of precipitation and storm surges across the globe, we found that the return periods of compound floods with marginal values exceeding the 98.5th percentile (i.e., equivalent to a joint return period of 12 years if the marginal variables are independent) are < 2 years in most areas, while those in northern Europe are > 8 years due to weaker dependence. Our quantitative assessment shows that cyclones (i.e., tropical cyclones (TCs) and extratropical cyclones (ETCs)) are the major triggers of compound floods. More than 80% of compound floods in East Asia and > 50% of those in the Gulf of Mexico and northern Australia are associated with TCs, while in northern Europe and the higher latitude coast of North America, ETCs contribute to the majority of compound floods (i.e., 80%). Weather patterns characterized by deep low pressure, cyclonic wind, and abundant precipitable water content are conducive to the occurrence of compound floods. Extreme precipitation and extreme storm surges over Europe tend to occur in different months, which explains the relatively lower probability of compound floods in Europe. The comprehensive hazard assessment of global compound floods in this study serves as an important reference for flood risk management in coastal regions across the globe.

Simultaneous flood risk analysis and its future change among all the 109 class-A river basins in Japan using a large ensemble climate simulation database d4PDF

This study investigated simultaneous flood risk among all the 109 class-A river basins over Japan using the big data of (over 1000 years) annual maximum hourly flow simulated from a large ensemble climate simulation database for policy decision making for future climate change, and proposed a novel approach in its geospatial analysis by applying two informatics techniques: the association rule analysis and graph theory. Frequency analysis of the number of rivers with the annual maximum flow over the flow capacity in the same year (defined as simultaneous flooding here) indicated that simultaneous flood risk will increase in the future climate under 4-degree rise scenarios in Japan, whose increment is larger than the variation of sea surface temperature projections. As the result, the return period of simultaneous flooding in eight river basins (the same number as in a severe storm in western Japan, 2018, causing the second worst economic damage since 1962) is estimated at 400 years in the historical experiment, 25 years in the 4-degree rise experiment. The association rule and graph theory analyses for the big data of annual maximum flows in the future climate scenarios indicated that simultaneous flood occurrence is dominated by spatial distance at a national scale as well as by the spatial relation between mountainous ridges and typhoon courses at a regional scale. Large ensemble climate simulation data combined with the informatics technology is a powerful approach to simultaneous flood risk analysis.

Assessment of transportation system disruption and accessibility to critical amenities during flooding: Iowa case study

Natural disasters, such as flooding, can cause severe social, environmental, and economic damage to a community. Transportation infrastructure plays an essential role in flood response and recovery efforts. However, flooding may disturb road functionality and generate direct and indirect adverse impacts, including the loss of access to essential services. This paper presents a comprehensive analysis of flood impacts on road network topology and accessibility to amenities for major communities in the State of Iowa using graph-theoretic methods, including single-source shortest path analyses. We assessed the disruption of transportation networks on the accessibility to critical amenities (e.g., hospitals) under 100 and 500-year flood scenarios. Our analysis methodology leads toward the development of an integrated real-time decision support system that will allow decision-makers to explore “what if” flood scenarios to identify vulnerable areas and population in their authority. These analyses could promote possible improvements (e.g., temporary relocation of critical services) to mitigate the consequences of road system failure during flooding. Due to varying environmental conditions at specific locations and effects on road topology under flood events, the results show differential impacts in edge and node losses as well as access to critical services. Results indicate that floods can lead to edge losses of up to 18%, and not only large cities but also some small cities can experience significant vulnerability to flooding. Some new or reconstructed bridges have failed to operate during analyzed flood events. During the 100 and 500-year flood return periods, the total number of inaccessible bridges within the selected cities is 184 and 294, respectively. Our work found that the shortest path length to the closest critical amenity under baseline condition can flip to the second or higher-orders during flooding. Many critical amenities have been found at risk of flooding in the studied cities.

Characterization of the 2014 Indus River Flood Using Hydraulic Simulations and Satellite Images

Rivers play an essential role to humans and ecosystems, but they also burst their banks during floods, often causing extensive damage to crop, property, and loss of lives. This paper characterizes the 2014 flood of the Indus River in Pakistan using the US Army Corps of Engineers Hydrologic Engineering Centre River Analysis System (HEC-RAS) model, integrated into a geographic information system (GIS) and satellite images from Landsat-8. The model is used to estimate the spatial extent of the flood and assess the damage that it caused by examining changes to the different land-use/land-cover (LULC) types of the river basin. Extreme flows for different return periods were estimated using a flood frequency analysis using a log-Pearson III distribution, which the Kolmogorov–Smirnov (KS) test identified as the best distribution to characterize the flow regime of the Indus River at Taunsa Barrage. The output of the flood frequency analysis was then incorporated into the HEC-RAS model to determine the spatial extent of the 2014 flood, with the accuracy of this modelling approach assessed using images from the Moderate Resolution Imaging Spectroradiometer (MODIS). The results show that a supervised classification of the Landsat images was able to identify the LULC types of the study region with a high degree of accuracy, and that the most affected LULC was crop/agricultural land, of which 50% was affected by the 2014 flood. Finally, the hydraulic simulation of extent of the 2014 flood was found to visually compare very well with the MODIS image, and the surface area of floods of different return periods was calculated. This paper provides further evidence of the benefit of using a hydrological model and satellite images for flood mapping and for flood damage assessment to inform the development of risk mitigation strategies.

The Use of a Uniform Technique for Harmonization and Generalization in Assessing the Flood Discharge Frequencies of Long Return Period Floods in the Danube River Basin

The flow regime conditions of the Danube River are continually changing. These changes are the result of natural processes and anthropogenic activities. The territory of the Danube River Basin is one of the most flood-endangered regions in Europe and assessing the design discharges along the Danube channel is complicated by the different estimation methods that are applied in particular countries. For this reason, it is necessary to harmonize flood design value assessment methods. The long-term maximum annual discharge series of the Danube River and other rivers in the Danube basin were analyzed and used to estimate the flood design values. We used the Log-Pearson type III distribution, which is one of the most widely used theoretical probability distributions to estimate extremes. This distribution can be flexibly applied to extreme values depending on the skew coefficient. We also analyzed the effect of the inclusion and exclusion of the historical extremes in the processed dataset. The results show that the inclusion of historical floods and the regionalization of the Log-Pearson type III distribution skew parameter can change the design discharges.

Estimation of the return periods of maxima rainfall and floods at the Pra River Catchment, Ghana, West Africa using the Gumbel extreme value theory

The Pra river catchment in Ghana is adversely affected by perennial flooding from high-intensity rainfall events. To aid in flood management at the catchment, the Gumbel extreme value distribution has been used to estimate the return periods of maxima rainfall, flood, and consecutive dry and wet days (CDD and CWD) for a period of 5 to 100 years. The results revealed an expected increase in maxima rainfall, CDD and CWD. Maxima rainfall favours the south of the catchment while the CDD decreases northward. Furthermore, an increase in the magnitude of CWD observed at the centre of the catchment had a maximum of approximately 30 days for the 100 year return period, while lower flood volumes had a higher recurrence of 50% to 100% for 1 to 2 year return periods. The inclusion of a projected increase in anthropogenic activities and climate factors at the catchment will slightly affect the magnitude of these variables for the various return periods. Nonetheless, the findings in this study will be of essential input to policy implementation of the Integrated Water Resource Management Plan for river catchments in Ghana, West Africa.

Climate Change and Changes in Compound Coastal‐Riverine Flooding Hazard Along the U.S. Coasts

AbstractThe cooccurrence of coastal and riverine flooding leads to compound events with substantial impacts on people and property in low‐lying coastal areas. Climate change could increase the level of compound flood hazard through higher extreme sea levels and river flows. Here, a bivariate flood hazard assessment method is proposed to estimate compound coastal‐riverine frequency under current and future climate conditions. A copula‐based approach is used to estimate the joint return period (JRP) of compound floods by incorporating sea‐level rise (SLR) and changes in peak river flows into the marginal distributions of flood drivers. Specifically, the changes in JRP of compound major coastal‐riverine flooding defined based on simultaneous exceedances above major coastal and riverine thresholds, are explored by midcentury. Subsequently, the increase in the probability of occurrence of at least one compound major coastal‐riverine flooding for a given period of time is quantified. The proposed compound flood hazard assessment is conducted at 26 paired tidal‐riverine stations along the Contiguous United States coast with long‐term data and defined flood thresholds. We show that the northeast Atlantic and the western part of the Gulf coasts are experiencing the highest compound major coastal‐riverine flood probability under current conditions. However, future SLR scenarios show the highest frequency amplification along the southeast Atlantic coast. The impact of changes in peak river flows is found to be considerably less than that of SLR. Climate change impacts, especially SLR, may lead to more frequent compound events, which cannot be ignored for future adaptation responses in estuary regions.

Predetermination of flood flows by different methods: Case of the catchment area of the Biskra Oued (North-East Algeria)

For several years now, the problem of extreme rainfall events has been acutely felt in Algeria, particularly the risk of flooding which threatens several towns, which have already faced this hazard with tragic consequences. To fight against floods, a long series of flood flow measurements is necessary, which unfortunately is not the case most of the time (Daifalah et al Technol Sci Rev Sum 34:74–84, 2017). This is the case of the Wadi Biskra catchment area. The stopping of the hydrometric stations of El kantara, and Djemoura; controlling this catchment area, over an area of 2787 km2, poses a serious data problem. To overcome this handicap, we have used the values of maximum flows, the recent series available covers a period of 28 years (1968–1995). Whereas the Djemoura station: the recent series available covers a period of 22 years (1972/1993), which fits well with the Gumbel law. From the adjustment line, the values of probable floods for different return periods of 2–1000 years were determined. To protect the population against floods caused by floods, operational and reliable forecasting tools are required. The rain-flow model uses knowledge of rainfall. It is applicable at any point in the hydrographic network. Among these hydrological models, a probabilistic model (Gradex) has been chosen to assess the risks of extreme floods, and which allows extrapolation to different return periods. To achieve our second objective, which is the possibility of reconstructing flood flows using empirical formulae based on precipitation. The two formulas used for the determination of the flood flows (Turazza formula and Sokolvosky formula) gave identical results to those measured at the gauging station.