Flood risk attenuation in critical zones of continental Portugal using sustainable detention basins

Backward induction-based multi-layer approach for watershed flood management in arid regions

Managing floods in interconnected nonurban and urban areas of arid regions prone to flash floods requires a more dynamic and integrated approach than traditional linear methods. In this regard, this study proposes a novel multi-stage decision-making framework which reshapes the traditional cascade approach to flood management by addressing the interdependencies between upstream and downstream regions. The proposed cyclic decision-making process involves five main steps: First, the Hydraulic and Hydrological (H/H) conditions in urban and nonurban areas were modeled using the SWMM. Then, a multi-stage optimization framework was constructed, in the first step of which the detention dams' location and dimensions were optimized in the nonurban area. Next, to link the first and second stages of the optimization, COPRAS method was employed for selecting the critical upstream management strategies. These strategies were determined as the input for the flood network optimization in the second stage. Finally, the Backward Induction Game Theory (BIGT) method was employed to find the best management strategy, under which not only the upstream conditions were considered in downstream flood protection but also stakeholders' conflicts were totally resolved by choosing the Nash Equilibrium. Our findings revealed that the implementation of the selected scenario could reduce flood peaks at the entrance of urban areas by 60.7 % and enhance shock absorption by 81.8 %. In fact, we guarantee that it is possible to propose a scenario encompassing drainage and detention dams' characteristics that, in addition to resolving stakeholders' conflicts of interest, can reduce the risk of flooding in complex watersheds. Moreover, the framework transforms the sequential, one-way cascade decision-making process into a continuous cycle, where upstream and downstream's H/H conditions and stakeholders' preferences are evaluated in coordination to achieve an agreement. Also, this framework helps decision-makers access the most sustainable solutions considering hydrological and socio-economic points of view.

Novel approach to the derivation of dam breach parameters in 2D hydrodynamic modeling of earthquake induced dam failures

Current methods of dam breach analyses adopt a deterministic approach. Applying these methods to Concrete Faced Rockfill Dams (CFRD) is fraught with huge levels of uncertainty, especially in the context of natural hazards. The frequency and magnitude of rainfall and earthquakes are higher in today's world. In the literature, the complete collapse of dams is modelled on dam breach parameters that define the dam break outflow but are not related to the return periods of natural hazards. As more new dams are constructed to control the floods in intra-plate seismic regions, this study presents a novel approach to the derivation of generalized dam break parameters for CFRD based on the structural analysis of Finite Element Model (FEM) simulations for peak ground accelerations corresponding to 475 and 2475 year return periods. Furthermore, the occurrence of rainfall and earthquake for different return periods are modelled using 2D hydrodynamic simulations. Results show the significance of generalized dam breach parameters for planning and managing CFRDs during earthquakes. The study emphasizes the utilization of structural analysis outputs for the hydraulic modeling of dam breaks, which will result in more specific and accurate dam break parameters. Additionally, the study has shown that the flood risk and the severity will increase with the intensity of earthquake and rainfall magnitudes. Disaster mitigation strategies can be optimized by considering the integrated occurrence of rainfall and earthquakes based on the probability of occurrence, demonstrated using a case-study dam. Another significant outcome of the study is the effect of soil saturation condition during a dam break, which reveals that areas within 40 km of the dam breach location might be worst affected.

Characterizing the 2020 summer floods in South China and effects on croplands

Floods occur more frequently in the context of climate change; however, flood monitoring capacity has not been well established. Here, we used a synergic mapping framework to characterize summer floods in the middle and lower reaches of the Yangtze River Plain and the effects on croplands in 2020, from both flood extent and intensity perspectives. We found that the total flood extent was 4936 km² from July to August, and for flood intensity, 1658, 1382, and 1896 km² of areas experienced triple, double, and single floods. A total of 2282 km² croplands (46% of the flooded area) were inundated mainly from Poyang and Dongting Lake Basins, containing a high ratio of moderate damage croplands (47%). The newly increased flooding extent in 2020 was 29% larger than the maximum ever-flooded extent in 2015-2019. This study is expected to provide a reference for rapid regional flood disaster assessment and serving mitigation.

The COP27 screened through the lens of global water security

Water security is an expression of resilience. In the recent past, scientists and public organizations have built considerable work around this concept launched in 2013 by the United Nations as "the capacity of a population to safeguard sustainable access to adequate quantities of acceptable quality water for sustaining livelihoods, human well-being, and socio-economic development, for ensuring protection against water-borne pollution and water-related disasters, and for preserving ecosystems in a climate of peace and political stability". In the 27th Conference of the Parties (COP27), held in Sharm El-Sheikh (Egypt) in last November, water security was considered a priority in the climate agenda, especially in the adaption and loss and damage axes. This discussion paper represents the authors' opinion about how the conference coped with water security and what challenges remain to attend. As discussion paper, it had the purpose to stimulate further discussion in a broader scientific forum.

Potential impact of diversion canals and retention areas as climate change adaptation measures on flood risk reduction: A hydrological modelling case study from the Chao Phraya River Basin, Thailand

The countries of Southeast Asia are projected to experience severe flood damage and economic impacts from climate change, compared with the global average. Hence adaptation by incorporating infrastructures is essential, but it has been seldom explicitly included in the simulations projecting climate change impacts on flood risk in these countries. Quantifying the effects of infrastructure is the key to climate change impact and adaptation assessment. Therefore, this study was conducted in the Chao Phraya River Basin (CPRB) in Thailand to examine the adaptation potential of (i) existing structural and non-structural measures that include reservoir and diversion dams, diversion canals, and water retention areas, and (ii) the combined adaptation measures, a combination of alterations made to the existing diversion canals and retention areas, on reducing future floods using the H08 global hydrological model (GHM). The results revealed that the impact of existing measures on the future flood reduction was smaller than the increase caused by warming in the CPRB. Conversely, the combined adaptation measures successfully mitigated the effect of warming by redirecting nearly 50 % of the diverted river flow to the ocean and storing 30 % of the diverted flow in the retention areas. Although a remarkable reduction was noted in the basin-wide flood risk, the effect of adaptation measures greatly varied across the basin. The combined adaptation measures largely reduced the number of flooding days by close to 100 at many of the considered stations within the basin, except for extreme flood events (historical 1-percentile flood events). This further reveals that the feasibility of adaptation measures in alleviating the extreme future floods will be limited in flood-vulnerable basins and thus require area-based prioritization for flood management. The modelling framework implemented in this study can be easily adapted to different GHMs and regions and should be examined for their applicability.

Proposal for Flood Risk Mitigation in the Upper Tanaro Valley (Western Alps—North-Western Italy)

Flood risk in Italy is a key aspect for the administrative authorities, from the national to the local level. This is especially true in Northern Italy, where the Po River, the most important river of the peninsula, and its river basin are located. In North-Western Italy, the Po Basin is described by numerous sub-basins, among which is the Tanaro River basin: here, in the last decades, floods have produced significant damage, causing an increased concern to local and regional administrations. The main goal of this study was to identify suitable sites for the construction of dams, having the function of retention basins, aiming to mitigate the flood risk in the Upper Tanaro Valley. First, using a qualitative approach, suitable sites were identified using available public data provided by regional administrations and field data obtained from geomorphological surveys, later elaborated in a Geographic Information System (GIS) environment. Several models were then produced using conventional methods to evaluate the hydrological characteristics of the study area and to assess the efficiency of each site in terms of flood water flow rate reduction: the performance was evaluated at control sections chosen in urban areas along the Upper Tanaro Valley. The results show that it is possible to find suitable locations for risk mitigation structures. These models also allowed for a rapid cost-effectiveness evaluation, which led to the definition of the best-performing site. The Upper Tanaro Valley case study here analyzed contributes to proving the importance of an integrated approach based on geomorphological, geo-hydrological, and hydraulic evaluations when dealing with the choice of a flood risk mitigation strategy.

A combined GIS-MCDA approach to prioritize stream water quality interventions, based on the contamination risk and intervention complexity

Water management decisions are complex ever since they are dependent on adopted politics, social objectives, environmental impacts, and economic determinants. To adequately address hydric resources issues, it is crucial to rely on scientific data and models guiding decision-makers. The present study brings a new methodology, consisting of a combined GIS-MCDA, to prioritize catchments that require environmental interventions to improve surface water quality. A Portuguese catchment, Ave River Basin, was selected to test this methodology due to the low water quality. First, it was calculated the contamination risk of each catchment, based on a GIS-MCDA using point source pressures, landscape metrics, and diffuse emissions as criteria. This analysis was compared to local data of ecological and chemical status through ANOVA and the Tukey test. The results showed the efficiency of the method since the contamination risk was lower for catchments under a good status and higher in catchments with a lower classification. In a second task, it was calculated the intervention complexity using a different GIS-MCDA. For this approach, it was chosen five criteria that condition environmental interventions, population density, slope, percentage of burned areas, Strahler order, and the number of effluent discharge sites. Both multicriteria methods were combined in a graphical analysis to rank the catchments intervention priority, subdividing the prioritization into four categories from 1st to 4th^, giving a higher preference for catchments with high contamination risk and low intervention complexity. As a result, catchments with a good status were dominantly placed under low intervention priority, and catchments with a lower ecological status were classified as a high priority, 1st and 2nd. In total, 248 catchments were spatially ranked, which is an essential finding for decision-makers, that are willing to safeguard the catchment water quality.

Impacts of riparian width and stream channel width on ecological networks in main waterways and tributaries

Riparian buffer width and stream channel width have different impacts on ecological networks (e.g., plant cover, regeneration, exotics, erosion, habitat, and stressors) and provide various ecosystem services. The protection of riparian zones of increasing widths for higher-order streams and connected tributaries alongside mega-reservoirs and around dams is of great global significance. However, it remains unclear which protection strategies are most effective for such zones. By applying a rapid field-based approach with 326 transects on an inundated area of 58,000 km² within the Three Gorges Dam Reservoir (TGDR) in China, we found that riparian buffer areas were influenced differently by broad-ranging widths. The riparian buffer width of 101.84 ± 72.64 m (mean ± standard deviation) had the greatest impact on the main waterway, whereas the stream channel width of 99.87 ± 97.10 m was most influential in tributaries. The correlation coefficient strengths among ecological and stress parameters (independently) were relatively greater in the main waterway riparian zones; the highest value was r = 0.930 using Pearson correlation (p < 0.05). In contrast, stress parameters revealed substantial and strong relationships with ecological parameters in tributaries, with the highest value being r = 0.551. Riparian width had the strongest influence on buffer vegetation scales, high-impact exotics, and bank stability. In comparison, channel width had the greatest effect on tree roots, dominant tree regeneration, and agricultural farming. These parameters showed distinctive responses in the shapes of indexing in higher-order streams and connected tributaries. These observations confirm the urgent need for research on regional-based extended riparian areas managed by the same administration strategies. Revised guidelines are needed to protect massive dam and reservoir ecosystems from further deterioration.

Watersheds, Anthropogenic Activities and the Role of Adaptation to Environmental Impacts

Runoff has shaped the Earth into watersheds, and humans have appropriated many of them [...]