Flood Storage Research Articles

Variable target water level control method in front of sluice in flood storage area based on storage balance model

Abstract To prevent the increase in flood disaster frequency, scale, and impact degree, a flood control engineering system with flood storage and detention areas, embankments, and reservoirs as the main body has been formed. Flood storage area is the key to the flood control engineering system, and its water level control performance is directly related to the success of flood control. According to the actual situation, the flood evolution simulation model in the flood storage area is constructed to obtain the evolution information of any unit of flood in the flood storage area. The dynamic control judgment coefficient of the water level is calculated, and the dynamic control program of the variable target water level in front of the sluice is formulated. Water level control can be realized by executing the established procedures. The above experimental data show that the proposed method can effectively control the water level in the flood storage area within the range of 26.03m ∼ 29.12m, and the minimum value of the corresponding risk rate is 3%, which fully proves that the proposed method has better dynamic control effect on the variable target water level in front of the sluice.

Flooding and flood water storage in karst systems of the Mediterranean region

Flooding is a recurring natural phenomenon that can have both life-giving and destructive aspects. In natural environments, floods are often an important element of the seasonal hydrologic cycle that provides water and nutrients to soil, supporting unique, rich and diverse ecosystems. However, flood events can also represent a destructive force that can endanger lives and cause significant damage in urban areas. Karst areas, in particular, are unique because of their special hydraulic characteristics in terms of flood occurrence, the dependence of ecosystems on such events, and attempts to actively store and manage floods. In this article, the hydraulic response of karst aquifers to heavy precipitation events, flood generation, and engineering interventions for flood control are discussed using several examples from karst areas in the Mediterranean region. Flooding mechanisms and regulatory structures in karst poljes are considered using several typical examples from the Dinaric mountain range. In addition, different variants of groundwater abstraction for increasing storage capacity and flood control are presented using examples from France and Montenegro. Managed aquifer recharge in karst areas and adjacent aquifers is demonstrated with examples from Jordan and Algeria. Finally, failed attempts at flood storage in karst reservoirs are presented with examples from Spain and Montenegro. These examples of flood retention in karst areas show the wide range of planning and technical measures and remind us of possible risks and failures in implementation as well as some positive and negative impacts on the environment and especially on ecosystems.

Progress in Ecosystem Services Research Under the Evolution of Land Use Landscape Patterns

Land use change (LUUC) is the most intuitive reflection of human activities and a key driver causing changes in ecosystem types and landscape pattern evolution [162]. Changes in land use patterns, structure, composition, intensity, and spatial patterns due to natural and anthropogenic factors affect ecosystem processes such as species movement, soil erosion, and patterns of biodiversity distribution, which in turn affect a wide range of ecosystem services, such as food provisioning, flood storage, soil retention, and soil and water conservation, and ultimately affect human well-being. Most studies have shown that changes in land use landscape patterns affect ecosystem services through multiple pathways, including changes in biodiversity, ecosystem processes and habitats. Land use change and ecosystem services have a reciprocal relationship, and the evolution of land use landscape pattern will directly affect or change the structure and function of ecosystems, which ultimately affects ecosystem services, while the results of the ecosystem services assessment can also provide a scientific basis for the formulation of relevant policies. Therefore, understanding the relationship between the evolution of land-use landscape patterns and the response of ecosystem services can not only clearly reveal the process of land-use landscape evolution, but also more accurately assess the function of ecosystem services, which can promote the scientific formulation and effective implementation of relevant planning and protection policies.

Prediction of Adaptability of Typical Vegetation Species in Flood Storage Areas under Future Climate Change: A Case in Hongze Lake FDZ, China

China experiences frequent heavy rainfall and flooding events, which have particularly increased in recent years. As flood storage zones (FDZs) play an important role in reducing disaster losses, their ecological restoration has been receiving widespread attention. Hongze Lake is an important flood discharge area in the Huaihe River Basin of China. Previous studies have preliminarily analyzed the protection of vegetation zones in the FDZ of this lake, but the future growth trend of typical vegetation in the area has not been considered as a basis for the precise protection of vegetation diversity and introductory cultivation of suitable species in the area. Taking the FDZ of Hongze Lake as an example, this study investigated the change trend of the suitability of typical vegetation species in the Hongze Lake FDZ based on future climate change and the distribution pattern of the suitable areas. To this end, the distribution of potentially suitable habitats of 20 typical vegetation species in the 2040s was predicted under the SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5 climate scenarios using the latest Coupled Model Intercomparison Project CMIP6. The predicted distribution was compared with the current distribution of potentially suitable habitats. The results showed that the model integrating high-performance random forest, generalized linear model, boosted tree model, flexible discriminant analysis model, and generalized additive model had significantly higher TSS and AUC values than the individual models, and could effectively improve model accuracy. The high sensitivity of these 20 typical vegetation species to temperature and rainfall related factors reflects the climatic characteristics of the study area at the junction of subtropical monsoon climate and temperate monsoon climate. Under future climate scenarios, with reference to the current scenario of the 20 typical species, the suitability for Nelumbo nucifera Gaertn decreased, that for Iris pseudacorus L. increased in the western part of the study area but decreased in the eastern wetland and floodplain, and the suitability of the remaining 18 species increased. This study identified the trend of potential suitable habitat distribution and the shift in the suitability of various typical vegetation species in the floodplain of Hongze Lake. The findings are important for the future enhancement of vegetation habitat conservation and suitable planting in the study area, and have implications for the restoration and conservation of vegetation diversity in most typical floodplain areas.

Evaluation of ecosystem services vis-à-vis perceptions and attitudes of local communities towards Wetland conservation in Kashmir Himalaya

Valuation of ecosystem services along with the perceptions and attitudes of local communities is crucial for sustainable management of wetlands. This study assesses changes in wetland area and bathymetry, and provides insights into local community's perceptions of ecosystem services, and attitudes towards wetland conservation in Kashmir Himalaya, India. High-resolution satellite data was used to assess land use land cover (LULC) changes within the wetland. The bathymetry changes were assessed by performing depth measurements before and after dredging in 2019 and 2022, respectively. Perceptions of ecosystem services and attitudes of residents towards wetland management were examined through surveys in 182 households from the target population of 334 families. The findings reveal that Khushalsar wetland provides important provisioning (food, fodder, thatching mats, fish, vegetables), regulating (flood control, carbon sequestration, water quality improvement), supporting (habitat, biomass and oxygen production, water and nutrient cycling), and cultural services (aesthetic, education, spiritual). The economic benefits from provisioning services range from 240 USD/yr for minor vegetables to 1201–1802 USD/0.05 ha/yr for Nelumbo nucifera. The analysis of LULC changes indicates a ∼16.5% reduction in wetland area from 1980 to 2017, with a further ∼10% decrease from 2017 to 2021, resulting in an overall loss of ∼25% (27.1 ha) in wetland area from 1980 to 2021. Bathymetric assessments reveal an increase in maximum depth from 427 cm in 2019 to 547 cm in 2022 following dredging activities. Socioeconomic analysis showed the significance of Khushalsar wetland as an important source of livelihood for local communities. Survey results indicate that all the respondents have positive attitudes towards the protection and management of the Khushalsar wetland. The study demonstrates that human conservation activities have significantly contributed to positive changes in the wetland such as increase in depth and flood storage capacity. The study concludes that government protection along with active participation of local communities is indispensable for sustainable management of wetlands.

SAR-based dynamic information retrieving of the Beijing-Tianjin-Hebei flood-inundation happened in July 2023, North China

Climate change-induced rainfalls have elevated the likelihood of flood occurrences, disrupting severely the normal functioning of people. Especially in the geographically unique Beijing-Tianjin-Hebei (BTH) plain in north China, an unanticipated sudden and long-duration flood-inundation happened in the summer of 2023 (referred to as the ‘23.7’ BTH flood). To address the dynamic information and recreate the flood evolution, we constructed a flood retrieving and analysis procedure to elucidate the development process and its impacts. First, accurately extract the temporal inundation extent of floods. Subsequently, we implemented the selected knowledge-driven algorithm to retrieve the dynamic information of flood evolution, including inundation extent, water depth, and shortest inundation duration. Furthermore, hazard-bearing bodies like cultivated land, population, and buildings were analyzed to improve our understanding of the flood impact. We uncovered that the ‘23.7’ BTH flood had caused extensive inundation and notably affected the Daqing River System, where the flood breached the river bank and submerged both buildings (0.96 km2) and cultivated land (241.46 km2), and led to prolonged inundation in the Baiyangdian area, which persisted for up to 30 days. This disastrous event highlights the great requirements to boost upstream flood storage capacity and enhance preparedness and rapid response capabilities for abnormal floods.

Composite water value: A way forward to balance the development and protection of transboundary lakes

Transboundary lakes are shared by multiple administrative regions. The key to balance the development and protection of transboundary lakes is to properly measure the value of water resources. Most of previous studies on the measurement of lake water resources value have not fully considered the ecosystem service function. This paper proposes a new concept “composite water value” to measure the value of transboundary lakes by integrating the external runoff value and the internal runoff value of water resources. The study constructs a composite water value measurement system for transboundary lakes, further analyzes its influencing factors,and applies the system to the case of Nansi Lake, a representative transboundary lake in eastern China. The results show that: (1) The composite water value of lakes is influenced by various factors, including industrial structure, water withdrawal, and water use methods, which impact the external runoff water value; meanwhile, the composite water quality and fluctuations in lake level are closely associated with the internal runoff water value. From 2008 to 2021, the average annual composite water value of Nansi Lake was 39.628 billion yuan, exhibiting a "rising-falling-fluctuating rising" trend due to pollution control policies, reduced precipitation, and enhanced water-saving technologies successively. (2) From a long-term perspective, it is necessary to focus on the internal runoff water use value of lakes. The internal runoff water value of Nansi Lake has been over 75% of the composite water value, and flood storage and water conservation are important manifestations of its ecosystem service value. (3) The external runoff water value of lake is closely related to the internal runoff water value, and relevant departments need to consider the balance between the water withdrawal of multiple cities along the lake and the retained water volume of the lake to achieve the maximum benefit of composite water value.

Shaping the future of conservation: a model for restoring oxbows in Iowa and beyond

Oxbows, once an abundant and natural feature of the landscape, have been nearly eliminated due to the effects of the Anthropocene, consequently impacting water quality, flood storage capacity, and the wildlife that depend on this habitat. These depressional basins within floodplains naturally accumulate sediment over time, but the sedimentation rate of oxbows over the last 100 years has greatly increased. The primary sources of sediment are from human activity, including erosion from agricultural fields and urban developments, drainage alterations, precipitation changes associated with climate change, and disconnection from their rivers and natural river hydraulics. Outlined in this manuscript is a step-by-step guide for restoring oxbows, based on 20 years of experience and lessons learned implementing oxbow restorations in Iowa on first-, second-, and third-order streams. Our goal is to provide conservation services providers and others interested in restoring degraded oxbows with the tools and expertise to confidently restore oxbows to achieve conservation goals.

Leeds FAS2 FSR: environmental challenges for the design of an in-river control structure

As flood-risk authorities look to counter increasing peak river flows due to a changing climate, traditional linear flood defences are in many cases proving to be an unsustainable method of managing flood risk. Full containment of flows in the river channel will require ever-increasing defence heights, cutting off communities from their rivers and natural heritage. Upstream flood storage provides a potential alternative means of flood management, allowing the peak of the flood to attenuate and downstream river levels to be kept within a tolerable range. The Leeds Flood Alleviation Scheme Phase 2 uses a combined approach: linear defences are constructed in urban reaches and complemented by an online flood storage reservoir (FSR) upstream of the city. The FSR halves the annual probability of defences overtopping within the city centre from 1 to 0.5%, achieved through active variable flow control at the FSR. This paper explores some of the challenges faced in the design and construction of the in-river flow control structure which is integral to the operation of the FSR. In particular this paper will consider some of the key environmental objectives for the scheme and offer considerations for working in a dynamic and environmentally sensitive fluvial environment.

Estimation of Catchment Parameters of Snyder's Synthetic Method for Water Resources Planning and Flood Management in Sri Lanka

Snyder's synthetic unit hydrograph method is widely recognized for synthesizing unit hydrographs. This paper illustrates a study demonstrating how to estimate catchment parameters using Snyder's synthetic method for hydro-meteorological stations maintained by the Irrigation Department and its application to Sri Lanka. Updated Snyder's Unit Hydrograph parameters, including coefficient accounting for flood wave and storage condition (Cp) and coefficient representing variations of catchment slop and storage (Ct) for 15 river gauge stations spread across the island, have been presented in this paper. The Cp values vary from 0.22 to 0.7, and the Ct values vary from 0.48 to 5.76. Updating the Snyder parameters is a long-term requirement, and these values can be used to update the previous values estimated in 1980.

Flood Modeling in a Composite System Consisting of River Channels, Flood Storage Areas, Floodplain Areas, Polder Areas, and Flood-Control-Protected Areas

The Linhuaigang flood control project (LFCP), situated on the Huaihe River, China, uses the river channels upstream of the LFCP, together with the hinterland areas outside the channels, to retain and store fluvial floodwaters that exceed the downstream channel’s discharge capacity. The hinterland areas are split into seven flood storage areas, three floodplain areas, eight polder areas, and three flood-control-protected areas, and they are connected to the river in various ways. A coupled hydrodynamic model was established to simulate the hydrodynamic and water volume exchange between the river channels and the hinterland areas. The flood storage area, under the control of a flood diversion sluice, was simulated with a 2D hydrodynamic model, and the inflow process initiated by the flood diversion sluice was simulated as a control structure. The polder area was generalized as a reservoir that would be filled in several hours once put into use because of its small size. The uncontrolled inflow process between the flood-control-protected areas and the channel was simulated by means of a dam break model, which could simulate levee breaching. The flooding within the flood-control-protected area, which represents a vast space, was simulated with a 2D hydrodynamic model. The floodplain area was laterally connected to the river channel along the river levee. The difference between the simulated and the measured flood peak water stage did not exceed 0.2 m in 2003 and 2007, indicating that the accuracy of the model was relatively high. In the scenario of a design flood with a return period of 100 years, the flood storage areas and the LFCP were used in the following order: Mengwa, Qiujiahu, Nanrunduan, Shouxihu, Jiangtanghu, Chengxihu, Chengdonghu, and the LFCP. When the Huaihe River encounters a flood with a return period of 1000 years that exceeds the design standard, the highest water stage upstream of the LFCP and Zhengyangguan shall not exceed 29.30 m and 27.96 m after the use of all the flood storage areas, floodplain areas, and flood-control-protected areas. The results of this research can provide technical support for the flood risk management of the LFCP.

Impacts of climate change on flood volumes over North American catchments

Climate change is expected to increase the frequency and intensity of extreme events, such as droughts and floods. Assessing the impacts of climate change on flood volumes is crucial to provide better management of flooding disasters given the devastating consequences they can cause. Using flood volume instead of flood peak is critical because the latter focuses on the highest possible discharge observed during a flood event, while flood volume also considers flow duration, which is an important factor in terms of the hazard caused to the surrounding environment. This study aims to evaluate the overall impact of climate change on floods caused by long-duration flows exceeding synthetic flooding thresholds. These flows are used to compute flood storage with various flow thresholds increasing from the 50th to 95th percentile of annual maximum observed discharge over a large sample of 1403 North American catchments. This study also aims to evaluate the contribution of each uncertainty source of the ensemble approach (climate models, bias-correction methods, and hydrological models) on future flood volumes. The results show that flood volumes are expected to decrease in western mountainous areas, the Great Lakes region, and the Maritimes, while increases are expected over most of eastern North America. The study finds that climate models contribute the most to the variance of flood volume uncertainty, followed by hydrological models. Overall, this study provides projected flood volume changes for North American catchments from a comprehensive ensemble that includes eleven climate models driven by two RCP scenarios and four hydrological models of varying complexity. This leads to a large-sample assessment of future flood volumes that could be useful to policymakers for making better-informed decisions in flood risk management.

Investigating Flood Characteristics and Mitigation Measures in Plain-Type River-Connected Lakes: A Case Study of Poyang Lake

The flow of plain-type river-connected lakes is affected by both upstream and downstream rivers, and the hydrological conditions are very complex. Poyang Lake, situated in Jiangxi Province, is the largest river-connected lake in the Yangtze River Basin. Its unique geographical features and complex hydrological conditions have made it a heavy disaster area and a frequent area of floods since ancient times. As typical mitigation measures of Poyang Lake, semi-restoration polder areas and flood storage and detention areas play a crucial role in the flood control of Poyang Lake. Taking Poyang Lake as an example, this article studies the flood characteristics of Poyang Lake based on the measured hydrological data. Furthermore, by using the weir (gate) outflow formula to construct the hydraulic model of semi-restoration polder areas and DHI MIKE to construct the hydrodynamic model of Kangshan flood storage and detention area, the flood diversion capacity of the two, and the flood diversion effect under the super-historical flood in 2020 are analyzed. The results show that compared with the non-use of mitigation measures, the maximum cumulative reduction in Xingzi water level can be reduced by 0.68 m and 0.48 m when semi-restoration polder areas and Kangshan flood storage and detention areas are used alone. Finally, the article puts forward some thoughts and suggestions on the flood control of Poyang Lake. The research results can offer some reference to the flood risk management of plain-type river-connected lakes.

Diversity of Aquatic Macrophyte Species of Pardi Wetland, Valsad District, Gujarat, India: Social-economic and Ethnobotanical importance

Wetlands, which serve as a transition between land and water, are a source of concern across the world in terms of resource evaluation and use, environmental protection, pollution control, eco-restoration, biodiversity conservation, and so on. Wetlands are an important aspect of human civilization because they provide drinking water, food, improved water quality, sediment retention, flood storage, transportation, recreation, and climate stabilization, among other things. Despite their numerous advantages, wetlands are increasingly subjected to anthropogenic pressures and are rapidly disappearing. Valsad district is the developing district of Gujarat state, located between 20°37'48.00" N and 72°55'48.00" E, making it one of Gujarat's rainiest districts and having many wetland ecosystems with great aquatic biodiversity. The present investigation aimed to list, find, and investigate wetlands, with a focus on macrophyte species, because of their high socioeconomic and ethnobotanical relevance. The current study identified a total of 43 macrophyte species, which are organized into 35 genera and 24 different families. Out of the 43 macrophyte species, 40 were recorded as angiosperms, 02 as pteridophytes, and 01 as macroalgae. In the present investigation, existing macrophyte species were evaluated based on their ecological classification, life form classification, and their wetland indicator status. This research not only showed the diversity of indigenous macrophytes but also discusses the utilization of aquatic plants for socioeconomic and ethnobotanical purposes, which enhance the traditional medicinal knowledge about the macrophytes.

The State of Texas Wetlands: A Review of Current and Future Challenges

With roughly 3.9 million acres of wetlands, 2.3% of its total land area, Texas has the fifth largest wetland acreage in the United States. As of 1990, there was an estimated 52% reduction in the state's original wetland acreage, but there has been no recent assessment of statewide wetland loss or gain since then. Wetlands provide critical ecosystem services, including wildlife habitat, flood storage and control, aquifer recharge, water quality improvement, and pollutant breakdown and storage of greenhouse gasses as well as human recreational opportunities including boating, paddling, fishing, hunting, birdwatching, hiking, and nature photography. Texas wetlands face intensifying challenges in the coming decades. Regulatory and legislative action should be forward-facing, anticipating effects of climate change, sea level rise, and urban expansion. Incorporating new technologies will allow for more timely and cost-efficient large-scale monitoring of wetland loss and gain. The residents of Texas are largely in support of active management of the state’s water resources; academic institutions, state and federal agencies, and conservation-minded private entities should work together to ensure the wetlands of Texas persist for wildlife and the generations to come.

Development and Applications of CO2-Responsive Gels in CO2 Flooding and Geological Storage.

Gel systems are widely used as plugging materials in the oil and gas industry. Gas channeling can be mitigated by reducing the heterogeneity of the formation and the mobility ratio of CO2 to crude oil. Cracks and other CO2 leaking pathways can be plugged during the geological storage of CO2 to increase the storage stability. By adding CO2-responsive groups to the classic polymer gel's molecular chain, CO2 responsive gel is able to seal and recognize CO2 in the formation while maintaining the superior performance of traditional polymer gel. The application of CO2 responsive gels in oil and gas production is still in the stage of laboratory testing on the whole. To actually achieve the commercial application of CO2 responsive gels in the oil and gas industry, it is imperative to thoroughly understand the CO2 responsive mechanisms of the various types of CO2 responsive gels, as well as the advantages and drawbacks of the gels and the direction of future development prospects. This work provides an overview of the research progress and response mechanisms of various types of CO2 responsive groups and CO2 responsive gels. Studies of the CO2 responsive gel development, injectivity, and plugging performance are comprehensively reviewed and summarized. The shortcomings of the existing CO2 responsive gels system are discussed and the paths for future CO2 responsive gel development are suggested.

China's CO2 pipeline development strategy under carbon neutrality

Under China's goal of carbon neutrality, there is a huge demand for carbon dioxide (CO2) capture, utilization, and storage technology (CCUS). CO2 transport, as a crucial link in the CCUS industrial chain, will inevitably rely on the construction of long-distance CO2 pipelines and infrastructure. Due to the late start and small scale of China's CO2 pipeline construction, and the relative lag in related technologies and policies, it is urgent to make systematical planning and achieve relevant technological breakthroughs for the future construction of CO2 pipeline network as a public infrastructure. Therefore, a three-stage pipeline development path is proposed based on the analysis of the spatial distribution characteristics and the temporal pattern of large-scale commercial development of CO2 carbon sources and storage in China. Moreover, solutions and suggestions are proposed upon the developments analysis in China from the perspectives of pipeline transportation technology, safety evaluation, materials and equipment, and integrity. The results show that the construction of CO2 pipeline network as an important CCUS infrastructure will accelerate with the development of the global CCUS industry; the spatial distribution of CO2 emission sources and storage is unbalanced in China, with 65.8% from the eastern and central China, and CO2 flooding and geological storage contributing to most of large-scale CO2 pipeline transportation. The conclusions are as follows. First, the three-stage development path is a million-ton demonstration project of supercritical CO2 transmission pipeline before China peaks carbon emissions. After the achievement of carbon peak, a 10 million-ton regional network architecture of CO2 pipeline network centered on basins will be built, and trunk pipelines between regions will be formed before achieving carbon neutrality, establishing the national carbon transmission network with a transportation capacity of 10 × 108 ton, and a total mileage of approximately 6 × 104 km. Second, we should carry out research on the technology and equipment for the full phase CO2 pipeline transportation onshore and offshore, improve the domestic pipeline transportation technology, and promote the continuous improvement of the regulatory system in the pipeline transportation industry, so as to facilitate the implementation of demonstration projects.

A Political Historical Examination of the Tianhu Embankment Case at Dongting Lake (1937–1949)

Abstract Water disputes between Hunan and Hubei provinces persisted from the late Qing Dynasty to the Republic of China, and the Tianhu Embankment case stands as a representative conflict between the two provinces concerning lake and river management. The dispute originated from the construction of embankments by people from Hunan in the Datong Lake, a sub-lake of Dongting Lake. People from Hubei argued that the embankments significantly reduced the flood storage capacity of Dongting Lake and that river floods would directly inundate the riverside counties. On the contrary, people from Hunan argued that the construction of the Tianhu Embankment did not hinder water management and that the key to solving the problem of water disasters lay in dredging rivers and not in destroying the fertile farmland that tens of thousands of people relied on for survival. From 1936 until the collapse of the Guomindang government’s rule on mainland China, a dispute lasting over a decade unfolded over the issue of dismantling the Tianhu Embankment. Both provinces used various tactics, such as leveraging local interpersonal networks, creating public opinion through news media, and using “people-oriented” rhetoric. This issue was frequently mentioned in official correspondences between the Executive Yuan of the Guomindang government and the two provinces. Numerous high-ranking officials from both provinces were involved in the dispute, and it even escalated to the point where Chiang Kai-shek had to intervene. Though the case remained unresolved for a long time, it was temporarily concluded at the end of 1947 with the symbolic dismantling of nine outlets in the major dikes of the Dongheng East Islet and the Orphan Embankment. However, these outlets were soon refilled by people from Hunan, making the case an unresolved legacy of the Guomindang Government on the mainland. Reviewing the development and outcome of this case, the Guomindang Government always appeared as a conciliator in the dispute, but ended up yielding ground and making a muted exit. The helplessness and impotence that the Nationalist Government displayed in resolving this problem vividly illustrate its weak governance capability.

An integrated modeling approach to evaluate the impacts of nature-based solutions of flood mitigation across a small watershed in the southeast United States

Abstract. Floods are among the most destructive natural hazards in the world, posing numerous risks to societies and economies globally. Accurately understanding and modeling floods driven by extreme rainfall events has long been a challenging task in the domains of hydrologic science and engineering. Unusual catchment responses to flooding cause great difficulty in predicting the variability and magnitude of floods, as well as proposing solutions to manage large volumes of overland flow. The usage of nature-based solutions (NBSs) has proved to be effective in the mitigation of flood peak rate and volume in urban or coastal areas, yet it is still not widely implemented due to limited knowledge and testing compared to traditional engineering solutions. This research examined an integrated hydrological and hydraulic modeling system to understand the response of an at-risk watershed system to flooding and evaluate the efficacy of NBS measures. Using the Hydrologic Engineering Center Hydrologic Modeling System and River Analysis System (HEC-HMS and HEC-RAS) software, an integrated hydrologic–hydraulic model was developed for Hurricane Matthew- (2016) and Florence-driven (2018) floods across the Little Pee Dee–Lumber River watershed, North and South Carolina (the Carolinas), US. The focus was on Nichols, a small town that has disproportionately been impacted by flooding during these two hurricane events. The present article proposes a methodology for selecting, modeling, and evaluating the performance of NBS measures within a catchment, which can be extended to other case studies. Different NBS measures, including flood storage ponds, riparian reforestation, and afforestation in croplands, were designed, modeled, and evaluated. Hurricane Matthew's flooding event was used for evaluating the NBS scenarios given its high simulation accuracy in flood inundation compared to the less accurate results obtained for Hurricane Florence. The scenario comparison evidenced that large-scale natural interventions, such as afforestation in croplands, can reduce the inundated area in Nichols by 8 % to 18 %. On the contrary, the smaller-scale interventions such as riparian reforestation and flood storage ponds showed a negligible effect of only 1 % on flood mitigation.

Spatio-temporal variation and hazard assessment of potentially toxic metal element contamination in sediments and water before and after a water-level fluctuation cycle in the Three Gorges Reservoir, Wanzhou, China.

Previous investigations on heavy metals in the water-sediment compartment focused on their spatial distribution, and the influence of sediment pH and organic matter (OM) on metal environmental occurrences. However, there are limited studies on the effects of physicochemical properties on the migration and transformation of heavy metals in the water-sediment compartments. This study investigated the relationship between the physicochemical properties of sediments and the distribution and chemical speciation of heavy metals, and the potential environmental risk of heavy metals in water and sediment using Risk Assessment Code (RAC) values and the Tessier five-step extraction method. Adsorption and desorption experiments showed that the sediment had weak adsorption and the strongest desorption capacity for Cd. Results of the pH, OM, surface element content, and X-ray diffraction (XRD) patterns suggested that cadmium (Cd) was more likely to partition into the water phase from the sediment during the flooding and water storage periods. When pH was 7-8 and OM content was 3.6-5.9%, the sediment-water distribution coefficient of Cd was low due to its large ionic radius, and the surface adsorption sites were saturated by other elements. These studies can provide a theoretical basis for the management and pollution control of the Three Gorges Reservoir.