Flood Regulation Research Articles

Anthropogenic activities mitigate the impacts of climate extremes on high flow regimes on the Loess Plateau

The hydrological cycle is anticipated to become increasing variable due to intensified global climate extremes and frequent floods. Understanding the evolution and driving mechanisms of floods in the context of climatic extremes is essential, particularly on the Loess Plateau (LP) where anthropogenic activities are significant. Here, we examined the spatiotemporal variability of climate extremes and their impacts on flood processes on the LP during 1956–2015. We employed a paired year approach to quantitatively assess the driving role of anthropogenic activities on flood changes in 11 major basins. Our findings indicated a general decline in extreme precipitation indices, while temperature has increased across most of the LP. Both annual runoff (Q) and high flow (Q5) magnitude significantly decreased in all basins. We identified that the major climatic indices driving Q5 included erosive precipitation amount, flood season precipitation, heavy precipitation amount, and maximum 7-day precipitation amount. Importantly, anthropogenic activities have mitigated the impact of climate extremes on Q5 regimes. Compared the post-2000 with reference period (1956–1979), under similar climatic conditions, we observed a reduction in the average Q5 magnitude by 30.19–78.14%, and a decrease in the average Q5 duration by 46.48–100.00% across the basins. The contributions of climate variability and anthropogenic activities to Q5 magnitude changes among 11 basins ranged from –37.58% to 22.02% and –56.84% to –15.08%, respectively, highlighting the crucial role of ecological restoration in reducing Q5 magnitude. These results underscore the importance of ecological restoration in flood regulation and offer valuable insights for basin management in the Yellow River Basin.

The performance of two urban flood regulation models using different input data

Increasing climate change has led to an increase in urban flood events. Events with a return period of twenty years become events with a period of two to three years. The primary objectives of this study are to evaluate the performance of flood regulation models using different input data and compare their performance for flood regulation supply (FRS) assessment. The assessment of the ecosystem services of urban FRS was performed using two models: Urban Flood Risk Mitigation (UFRM) by Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST) and IMECOGIP Waterflow Regulation (Retention Model) (WRRM). They rely on relatively accessible open-source data, require a short time to model each scenario and provide opportunities to interpret results in different spatial and measurement units. We performed several improvements to the input data, including updating the national ecosystem-type assessment for the case study area by connecting it with the Urban Atlas typology and proposing an approach for soil data refinement. The outputs of the two models show significant differences in FRS values for each land-use/land-cover (LULC) class. The UFRM assesses different impervious urban classes with different values, varying from very low to medium. In contrast, the WRRM assesses the FRS in densely sealed areas with one fixed value for low supply (where nearly all rainfall is transformed into runoff).

Blue Carbon Assessment in the Salt Marshes of the Venice Lagoon: Dimensions, Variability and Influence of Storm‐Surge Regulation

AbstractSalt marshes are intertidal coastal ecosystems shaped by complex feedbacks between hydrodynamic, morphological, and biological processes. These crucial yet endangered environments provide a diverse range of ecosystem services but are globally subjected to high anthropogenic pressures, while being severely exposed to climate change impacts. The importance of salt marshes as “blue carbon” sinks, deriving from their primary production coupled with rapid surface accretion, has been increasingly recognized within the framework of climate mitigation strategies. However, large uncertainties remain in salt marsh carbon stock and sequestration estimation. In order to provide further knowledge in salt marsh carbon assessment and investigate marsh carbon pool response to management actions, we analyzed organic matter content in salt marsh soils of the Venice Lagoon (Italy) from 60 sediment cores to the depth of 1 m and estimated organic carbon stock and accumulation rates in different areas. Organic carbon stocks and accumulation rates were highly variable in different marshes, being affected by organic and inorganic inputs and preservation conditions. Our estimates suggest that the studied marshes store 17,108 ± 5,757 tons of carbon per square kilometer in top 1‐m of soil and can accumulate 85 ± 25 tons of carbon per square kilometer per year. However, flood regulation may reduce the annual marsh CO2 sequestration potential by more than 30%. Our results contribute valuable information for regional carbon assessments, reinforcing the need for integrated coastal management policies to preserve the ecosystem services of coastal environments, and underscore the importance of considering local variability and methodological variations.

Using a multiphysics coupling-oriented flood modelling approach to assess urban flooding under various regulation scenarios combined with rainstorms and tidal effects

Climate change and rapid urbanisation have intensified urban flooding. Flood models constructed using hydrological and hydrodynamic approaches are crucial tools for simulating and regulating urban flooding processes. Urban flooding arises from the interplay of various physical processes in urban water systems, influenced by heterogeneous urban surfaces, underground structures, and intricate river networks influencing surface flow, which must be considered in flood models. For coastal cities with intricate drainage systems, the disasters of combined rainstorms and tidal flooding can be mitigated through river scheduling and real-time control of hydraulic structures. However, a lack of research on the effectiveness of flood regulations limits the application of flood models. This study proposes a flood modelling approach oriented towards the coupling of multiphysics processes, achieving a comprehensive simulation and regulation of the flood process. A surface flood control model was created by coupling hydrological and hydrodynamic processes using the Storm Water Management Model and the orthogonal storage cell model, enabled by data exchange synchronisation technology. Subsequently, the model’s accuracy was validated using observed rainstorm events, identifying drainage system overflows and land surface inundation. Finally, the developed model was applied to analyse the enhancing effect of tides on rainstorm-induced flooding and the impact of various control scenarios. This study offers theoretical direction for large-scale urban flood modelling and model development, offering significant references for revisiting urban planning and formulating flood prevention strategies under the joint impact of rainstorms and tides.

Including dynamic capacity impact in an improved model for optimal flood control operation in river-type reservoirs

Flood control operations in river-type reservoirs are significantly affected by both the dynamic reservoir capacity and flood propagation within the reservoir area. However, the traditional reservoir flood control optimal operation (RFCOO) model is usually based on the static capacity method, which may bring large errors in scheduling calculations for river-type reservoirs. To address this issue, an improved model, the reservoir dynamic capacity flood control optimal operation (RDCFCOO) model, that includes the influence of the dynamic reservoir capacity and flood propagation, was developed to improve the accuracy of flood regulation calculations in river-type reservoirs. This improved model includes a 1D unsteady flow simulation and a rederived objective function based on the maximum peak clipping criterion, and expresses the state transformation equations using the de Saint-Venant equations. Furthermore, a multi-core parallel DP (PDP) algorithm that incorporates reduction of state dimensionality (RSD) was developed to effectively derive optimal operation schemes. The improved model and algorithm developed herein were validated through an application to the Xiangjiaba Reservoir, China. The results show that: (1) By adding the item (qiw) to the objective function and substituting the de Saint-Venant equations for the water balance equation, the RDCFCOO model developed in this paper can account for the impact of dynamic capacity and flood propagation. As a result, it exhibits a more accurate and detailed flood control process that was closer to the actual conditions of river-type reservoirs compared to the RFCOO model; (2) By removing the invalid discrete state points from the search space and fully utilizing multi-core processors, the proposed PDP with RSD can significantly improve the computational efficiency of the DP in solving RDCFCOO problems. The improved model and algorithm can effectively improve the calculation accuracy of flood control optimal scheduling in river-type reservoirs and provide more information for decision-makers.

Supply and demand analysis and security pattern optimization of flood regulation ecosystem services adapted to the complex terrain of coastal estuaries: A case study in Xiamen

The flood risk in coastal areas has been exacerbated by global climate change. Research on flood risk assessment is emerging from the perspective of supply and demand for flood regulation ecosystem services (FRES). However, there are still limitations in the evaluation of lowland regulation, implementation of intelligent algorithms, comparison of multi-grain FRES supply and demand, and overall optimization of security pattern. Therefore, we propose a comprehensive FRES supply assessment method that incorporates soil and vegetation, lowland, and water regulations. Additionally, we introduce the random forest model to enhance the FRES demand assessment approach. Two grain sizes of the sub-catchment area and grid unit are used to compare FRES supply and demand. Using Xiamen as a case study, this research unveils the following findings: (1) Significant disparities exist between the assessment outcomes of FRES based on multiple types of regulatory services and those solely considering soil and vegetation regulation. The areas with high FRES supply extend beyond upper mountain forests to include local lower plains exhibiting strong capabilities for lowland or water system regulation. (2) Consistent yet distinct results are observed when comparing two grain sizes. Imbalances in supply and demand occur in estuaries, bays, and densely built-up regions. Sub-catchment units exhibit wider distribution and concentration, while grid units display more dispersed patterns. (3) In terms of in-situ regulation, 26.77 km2 ecological protection area, 9.85 km2 ecological restoration area, and 119.59 km2 construction land flood control intervention area are demarcated. From a directional regulation perspective, 22 FRES corridors connecting source and sink areas along with 24 pinch points are identified. Optimizing security patterns through coordinated management of FRES supply and demand can enhance the resilience of coastal estuaries.

Biophysical and economic importance of the ecosystem service of flood regulation on the agricultural sector: Ameca-Mascota Basin, Jalisco and Jamapa Basin, Veracruz

El servicio ecosistémico (SE) de regulación de inundaciones es un beneficio que se obtiene de la capacidad de los ecosistemas para retener agua y disminuir la velocidad de las corrientes que se forman durante y después de un evento de precipitación. Este servicio se puede evaluar desde los puntos de vista biofísico y económico. En ambos casos, la valoración busca dimensionar el impacto de las inundaciones en términos físicos y monetarios sobre el bienestar de la sociedad. En ese sentido, el presente trabajo evaluó este SE bajo dos escenarios de precipitación (máxima registrada en un día con y sin evento hidrometeorológico extremo) sobre el sector agrícola para dos cuencas en México. En Ameca-Mascota, se inundarían entre 231 y 557 km2, lo cual afectaría entre 120 y 332 km2 de cultivos. En Jamapa, se inundarían entre 926 y 1,370 km2, esto afectaría entre 481 y 548 km² de cultivos y pastizales. En términos económicos, las inundaciones originarían pérdidas anuales en la producción entre USD$ 8.3 millones y USD$ 67 millones, y entre USD$ 11 millones y USD$ 88 para dichas cuencas, respectivamente. Los resultados de este tipo de estudios, tanto biofísicos como económicos, son un insumo valioso para fortalecer el manejo de las cuencas mediante la implementación de acciones de conservación y usos sostenibles de los servicios ecosistémicos.

Effect of land cover types evolution in megacities on flood regulation capacity: the case of Zhengzhou since 1990

Effect of land cover types evolution in megacities on flood regulation capacity: the case of Zhengzhou since 1990

Inconsistent Regulatory Mapping Quietly Threatens Rivers and Streams.

Even the most stringent environmental law cannot protect a river if its tributaries remain exposed to pollution and other threats upstream. Excluding a subset of watercourses from legal protection therefore threatens to alter freshwater ecosystems across entire river networks and the services they provide, such as drinking water and flood regulation. Considerable attention has been devoted to defining the scope of environmental laws protecting watercourses. Yet how these definitions are implemented through regulatory mapping, the cartography of waterbodies that legally qualify as watercourses and are thus protected, has not been examined outside of the United States. Here, we demonstrate the consequences of regulatory mapping on the extent of river networks that are protected, using France as a case study. By assembling the first map of France's watercourses protected under the Water Law, we estimate that a quarter of previously mapped hydrographic segments were excluded from protection and found stark geographical variations in the extent of protected ecosystems. Headwater and nonperennial segments are disproportionately excluded by 28% compared to their prevalence (67%) in the overall hydrographic network, with potentially far-reaching implications for biodiversity and people. We expect regulatory frameworks in most countries to be equally susceptible to local interpretation of legal definitions.

Toward integrated dam assessment: evaluating multi-dimensional impacts of the Grand Ethiopian Renaissance Dam on Sudan

Abstract The Grand Ethiopian Renaissance Dam (GERD) on the Nile is expected to influence many ecosystem services, such as flood regulation, hydro-electricity production, food supply, and habitat provision, among others. Understanding these impacts (positive and negative) requires a comprehensive evaluation framework. This study develops and applies an integrated simulation framework for assessing the impacts of the GERD on Sudan, focusing on the simultaneous economywide effects of riverine flood hazards, irrigation water supply, hydropower generation, and floodplain-dependent industries, namely traditional fired clay brick production. The simulation framework incorporates three models: a river infrastructure system model, a flood model, and a Computable General Equilibrium Model. Results indicate positive impacts for hydropower generation and flood control, marginal benefits for water supply to existing irrigation, and negative consequences for brick production and the construction sector. Assuming that the GERD starts its long-term operation in 2025, we find an overall positive economic impact on Sudan’s Gross Domestic Product in 2025, with an increase of up to just over 0.1%, subject to river flow conditions. Recognizing the differences in impacts across sectors and income groups, the study emphasizes the need for interventions that ameliorate negative effects. While the study captures several impacts, other effects on the environment, recession agriculture, and soil fertility require further investigation. Still, our findings underscore the importance of adopting an integrated simulation approach to dam evaluation, acknowledging the interconnected nature of water and related sectors in national economies.

Impact and Mechanism of Medium and Small Flood Regulation in the Three Gorges Reservoir on the Phytoplankton in Tributary Bays

The regulation of small- and medium-sized floods （RSMF） has become the main mode of regulation in the flood season of the Three Gorges Reservoir （TGR）. To study the response of phytoplankton in the tributary bays of the TGR to the RSMF, a typical eutrophic tributary of the TGR, Xiangxi River, was investigated for the spatiotemporal distribution characteristics of phytoplankton and nutrients in the main and tributary streams from 2020 to 2021. The response characteristics of phytoplankton in the tributary bays to the RSMF were analyzed. The results indicated that during the RSMF, the chlorophyll a （Chl-a） in the water body of the Xiangxi River decreased with the increase in the water level in front of the dam, whereas during the reservoir impounding at the end of flood season, the concentration of Chl-a increased again. During the RSMF, the Chlorophyta and Diatoma were the main communities of planktonic algae in the Xiangxi River. The phytoplankton community changed with the RSMF. When the water level fluctuation increased, diatoms were the main species, whereas when the water level fluctuation was small, blue and green algae were the main species. The concentration of Chl-a was more sensitive to changes in TN concentration. When the flow velocity was >0.25 m·s-1 or the suspended sediment content was >10 mg·L-1, the concentration of Chl-a in the water was inhibited. After 2010, the typical outbreak time of algal blooms in the Xiangxi River Reservoir Bay shifted to the flood season, with only two non-flood season algal blooms. Further attention needs to be paid to the response of algal blooms in the reservoir to small- and medium-sized flood control during the flood season.

Old-growth Ficus trees provide soil water and carbon storage to urban greenspaces in a Brazilian metropolis

Urban flooding has been considered one of the most severe natural disasters around the world, and urban greenspaces can provide important flood regulation ecosystem services. In Belo Horizonte (Brazil), the woody vegetation, especially the old-growth Ficus trees, appears to protect an urban park against the flooding of the Arrudas river. Thus, we compared the soil water content, soil water-holding capacity, soil aggregation and porosity among a highly permeable urban park planted with herbaceous and woody species, including Ficus, a semi-permeable parking lot with only Ficus and an impermeable site without trees (Disturbed Site-DS). The soil water content and water holding capacity of the urban park did not differ from that of the Ficus site, but it was lower than DS. These results were correlated with soil organic matter (SOM) content, soil aggregation and porosity, suggesting that Ficus trees play an important role in the hydrological cycle. To understand how the Fiscus species provide such soil permeability, we compared the aboveground plant biomass, soil fertility and soil carbon sequestration (total soil carbon, soil organic matter, humic and fulvic acids and soil isotopic δ13 C) in plots with Ficus and without this species within the park as well as in a preserved urban forest and a disturbed square. The outstanding plant biomass produced by Ficus species explained the high soil carbon sequestration, particularly in humic organic matter, favouring soil aggregation, porosity and water retention. Therefore, Ficus species may be considered an exceptional C-sequestering species, contributing for soil stabilization and the hydrological cycle in urban greenspaces.

A simple method to assess flood regulation supply in urban lawns

Floods have an important impact on life and loss of goods. Urban green spaces are crucial to mitigating flood impact. However, their capacity to prevent floods depends on their condition, especially in areas highly affected by human activities such as lawns. Here, we developed a simple method to assess flood regulation using soil penetration resistance as a proxy and tested it on an urban lawn in Vilnius (Lithuania) in winter. We developed an experimental design using an app for collecting data and working with it in a GIS environment. To understand their spatial relations, geostatistical (e.g., semi-variogram model and ordinary kriging mapping) and spatial statistics ((Moran's global autocorrelation index and Cluster and Outlier Analysis (Anselin Local Moran's I)) tools were applied. The preliminary results from the tested method showed that the lawn studied has different capacities to retain floods due to the management practices. Nevertheless, it is essential to be applied in different soil moisture conditions since flood regulation (soil penetration resistance) can be variable throughout the year.•A novel method was developed to estimate flood regulation using soil penetration resistance as a proxy;•An urban lawn was used to test the method and identify areas with low and high capacity for flood regulation;•The method quickly assesses lawn flood retention capacity in different environments.

Changes in gross ecosystem product and its response to land use changes in forest resource dominant regions: A case study of Zixi County, Jiangxi Province, China.

Forests are one of the most important terrestrial ecosystems and play a crucial role in the construction of ecological civilization. Understanding the changes in gross ecosystem product (GEP) and its response to land use change in areas with unique advantages in forest resources is of great significance for promoting sustainable development. We examined the GEP of Zixi County of Jiangxi Province. Based on the theory and method of ecosystem value accounting, and on the basis of the general indicator system for regulating services (water source conservation, soil conservation, oxygen supply, carbon fixation, climate control, flood regulation, water purification, air cleaning, species conservation) and the general indicator system for cultural services (landscape recreation, education), we added negative oxygen ions and health care indicators and introduced forest ecosystem service correction coefficients to construct a GEP indicator system and method with unique advantages in forest resources. We evaluated the spatio-temporal variations of GEP in 2010, 2017 and 2020, and quantified the impact of land use/land cover change on GEP by means of elasticity index and value profit and loss analysis. The results showed that the GEP of Zixi County in 2010, 2017 and 2020 was 16.788 billion, 26.817 billion, and 38.407 billion yuan, respectively. Forests contri-buted the largest amount of GEP, followed by wetland, farmland, grassland, and town. During the study period, the added value of GEP mainly came from forest ecosystems. Land use change had an important impact on GEP. From 2010 to 2020, the total land use change area in the study area was 8501.88 hm2. The amplitude of land use change was grassland (-2811.17 hm2)>town (1428.06 hm2)>forest (1357.67 hm2)>wetland (1031.05 hm2)> farmland (-1005.01 hm2). The absolute changes of various land use types were mainly occurred from 2017 to 2020. The elasticity index of each indicator on forest ecosystems was significantly higher than that of other ecosystems, indicating that GEP had the highest sensitivity to changes in forest area. The results of value profit and loss analysis showed that urban development had reduced GEP to some extent, while the protection of forest and wetland had increased GEP. From 2010 to 2020, the conversion of land use types in Zixi County led to an increase of 1.865 billion yuan in GEP, indicating that land use change in Zixi County had a positive ecological impact on the whole. Our results reflect the green development effect of Zixi County after becoming a national ecological civilization construction demonstration county, which could provide decision-making support for high-quality development, high-level protection and sustainable development and utilization of land resources in the future, and provide reference for other similar areas of GEP accounting.

Research on the Path and Practice of Ideological and Political Construction in the Course of Water Resources and Hydropower Planning

Through the construction path of courses’ ideological and political teaching objectives, education goals, teaching methods, assessment systems, etc., the corresponding knowledge points of course ideological and political education are constructed in this course, and ideological and political elements are integrated into the teaching module. Find the right entry point for ideological and political education based on the course content and infiltrate ideological and political education in a targeted manner. Integrating ideological and political practice cases of comprehensive utilization of water resources, regulation of benefits, flood regulation, and water energy calculation into the entire teaching process. Fully utilize the advantages of professional course resources and combine them with the needs and development resources of the country, transforming them into unique advantages in ideological and political education through courses. At the same time, we will deeply explore and extract the core values and concepts of patriotism, social responsibility, and cultural confidence contained in professional courses, ensuring that ideological and political education can be fully integrated into all aspects of this course teaching. By integrating the connotation of teaching and educating people into the main aspects of classroom teaching, we can enhance the attractiveness of ideological and political education in the Water Resources and Hydropower Planning professional course and effectively promote the construction and development of this professional course.

Ecological conservation redline delineation in flood detention areas: A case study in Anxiang County, Yangtze River Basin, China

Ecological conservation redline (ECRL) is a rigorously defined regulatory boundary established within critical zones, including ecological functional areas, ecologically sensitive regions, and vulnerable areas. It serves as the foundational threshold for preserving the ecological security of both national and regional contexts. Flood detention areas constitute a pivotal facet within the realm of ecological functionality. The delineation of ECRL boundaries for these flood detention areas aims to optimize the ecological structural composition, augmenting their capacity to provide ecosystem services. This endeavor holds profound implications of practical significance. However, there is currently a lack of methods for delineating ECRLs in flood detention areas. To address the above problem, taking Anxiang County in the Yangtze River Basin of China as an example, this study establishes a regional flood regulation service evaluation method through in-depth investigation and analysis of the ecosystem in the area. The method considers the importance of the evaluation of five ecosystem services, including flood regulation, water conservation, soil conservation, biodiversity conservation, and carbon sequestration. Based on these evaluations, the ECRL for Anxiang County is ultimately determined, with the area of 198.62 km2, accounting for 18.12% of the total area. Additionally, from the perspective of ecosystem service spatial transfer, a quantitative study is conducted on the ecosystem service radiation effect of the ECRL in Anxiang County, estimated to be approximately 1,462 million CNY. Overall, this study provides a theoretical basis for delineating ECRL in flood detention areas and developing corresponding ecological compensation systems for the watershed.

Impacts of climate change and land cover factor on runoff in the Coastal Chinese Mainland region

The increasingly frequent storms pose significant threats to the sustainable development of coastal regions, particularly in densely populated and economically vibrant areas. Comprehending the dynamics and intricate mechanisms underlying runoff generation is crucial in the context of climate change and anthropogenic interference. Based on hydro-meteorological and land-use data from 1980 to 2018, this study investigates the runoff variation and its driving factors in the Coastal Chinese Mainland (CCM). The aims of this study are to reveal the temporal and spatial trends of runoff yield, to clarify the sensitivity of runoff in coastal cities to the integrated and individual parameters of climate change and anthropogenic interference, including precipitation (P), potential evapotranspiration (E0), and land cover factor (n), and to support the establishment of spatially tailored adaptation strategies. The results show that: (1) runoff has generally increased over the study period, particularly in regions such as the Yangtze River Delta, Shandong, and Guangxi, while it has decreased in western Liaoning and eastern Guangdong; (2) in the northern CCM with larger aridity index, the land cover factor plays a dominant role in runoff production, while in the wetter southern CCM, precipitation is more influential, and potential evapotranspiration mainly hinders runoff generation all over CCM; (3) urban expansion tends to negatively impact n, while the loss of grasslands and shrinkage of croplands tend to undermine the value of n. To facilitate the achievement of sustainable development goals in the CCM, it is imperative to introduce a more comprehensive and theoretical framework that encompasses the natural, technical, and social dimensions of human-water systems into traditional flood regulation and water resource management. This framework should promote interdisciplinary collaboration from an integrated perspective, to bridge the administrative and watershed boundaries, to effectively address the complex challenges posed by climate change and anthropogenic activities on runoff and water resources in coastal regions, and to enhance the realization of local sustainable development goals (UN SDGs).

Relative contributions of main factors to water levels in Wuchengxiyu Region, China

The rapid urbanization and frequent occurrence of extreme weather have made flooding more frequent; tide-sensitive areas are more prone to flooding due to tide level. However, the extent of their respective impacts on flood variability in the context of the combined effects remains to be explored. Therefore, analysis of the driveability of the water level is important for regional flood control. Land use data from 1985 to 2015 was used in this study to analyze the characteristics of the changes. General trends, abrupt variability, and persistence of rainfall, tide, and water level data from 1957 to 2018 were analyzed. The influence of rainfall, tide level factors and underlying surface on water level variation was analyzed qualitatively and the contribution of the three factors to water level variation was quantified. The results indicate that the most important directions of land-type transformation were the construction land and arable land. Within the rainfall sequence, only the 3d rainfall sequence exhibited a significant increasing trend, while both tide level and water levels showed significant increasing trends. The 3d rainfall sequence and tide level sequence are significantly positively correlated with water level sequences, whereas among the underlying surface factors, only construction land and unused land are significantly positively correlated with water levels. Furthermore, the contribution rates of driving factors vary across different regions. In the Changzhou region, the underlying surface factors dominated with a relative influence of 62%., whereas for other regions, the combined relative influences of rainfall and tide level are 57.2%, 52.8%, 60.4%, and 66.9%, The methods and results of this study contribute to regional flood regulation.

Channel-forming discharge based on the extreme value identification of sediment-carrying capacity index

Channel-forming discharge (Dcf) is an important parameter in river management and reservoir flood regulation. Applying the methods for calculating Dcf to reaches downstream reservoirs characterized by drastic changes in water and sediment conditions and long-term scouring status is difficult. Based on the riverbed-shaping principle of sediment-laden water flow, while simultaneously considering the active action of water flow and response of the riverbed, this study proposes a new method for calculating Dcf by identifying the extreme value of the suspended sediment-carrying capacity index. The application of this method to the middle and lower reaches of the Yangtze River showed that after the impoundment of the Three Gorges Reservoir, Dcf in this section was reduced by an amplitude between 2500 and 4700 m3/s. The results can be used to guide the operation of the Three Gorges Reservoir and the management of the middle and lower reaches of the Yangtze River, thus providing reference for other river channels downstream of the reservoir.

Dammed context: Community perspectives on ecosystem service changes following Poland's first dam removal

AbstractDecisions to build or remove dams and other large engineered hydraulic infrastructures are always entangled in social and environmental impacts, which are often evaluated formally through bureaucratic processes. In Europe dam removals are relatively infrequent, even though extensive hydraulic infrastructure has degraded biodiversity and water quality. The Wilkówka dam in southern Poland was required to be removed rapidly, primarily due to engineering failures during its construction. Using survey methods, we examine the local community's perceptions of the net environmental and social impacts of the Wilkówka dam removal. In surveying the opinions of households, 62% of respondents expressed that decisions about the removal were taken without sufficient community consultation, and 92% felt that the dam had been removed despite their opposition. Although the dam had been built recently and had failed to operate at design capacity, respondents reported strong attachments to the services they perceived it to provide, including water supply, flood regulation and cultural significance. In spite of the possibility of an environmental disaster and long‐term environmental degradation, most surveyed households would have preferred it to have been renovated or reconstructed. In short, the removal of the Wilkówka dam was perceived by local households but also by local officials as bringing about a net loss in socially relevant ecosystem services, despite the urgent need for removal perceived by regional and national authorities. The local community's rapid attachment to the dam despite its potential negative impacts on biodiversity and the local environment were primarily attributable to the high expectations as to the hydrological services that the dam was to provide (water supply, flood regulation and its larger symbolic value as an infrastructural investment in the community). This work provides an empirical demonstration of the importance of understanding the social, ecological and technological context within decision‐making processes regarding dam removals, and its implications may improve the planning and implementation of future dam removal projects.