Natural Flood Research Articles

Quantifying the natural flood management potential of leaky dams in upland catchments, Part I: A data-based modelling approach

A novel application of data-based time series methods is proposed in this study to help overcome barriers to quantifying the impacts of Natural Flood Management measures from hydrological timeseries data which hitherto have prevented accurate assessment of the effectiveness of interventions. To demonstrate the value of this method, a transfer function noise model was fitted to stage data from a three year before-after-control-impact style monitoring study of leaky dams in an upland catchment in North Yorkshire, England. Using the data-based time series method, uncertainties associated with stage data were overcome. The models were able to simulate the peaks of flood events on one stream to within ±2 cm accuracy for 95% of events recorded during the baseline monitoring period. These simulations are used in this study’s companion paper to quantify leaky dam impacts on flood peak magnitude. The level of accuracy achieved in this study provides proof of concept for application of the approach to data from other environments and natural flood management interventions, which is crucial if natural flood management is to be used as a mainstream flood risk management measure.

Quantifying the natural flood management potential of leaky dams in upland catchments, Part II: Leaky dam impacts on flood peak magnitude

Leaky dams are an increasingly popular natural flood management measure, yet their impacts on flood peak magnitude have not yet been empirically quantified for a range of event types and magnitudes, even at the stream scale. In this study, the novel application of a transfer function noise modelling approach to empirical Before-After-Control-Impact stage data from an upland catchment allowed leaky dam effectiveness in reducing flood peak magnitude to be quantified. Flood peak stage and discharge magnitude changes were assessed from empirical data for 50 single and multi-peaked high flow events with return periods ranging from less than one year to six years. Overall, event peak magnitude was significantly reduced following the installation of eight leaky dams on the impact stream. Effectiveness was highly variable, but on average, flood peak magnitude was reduced by 10% for events with a return period up to one year. Some of the variability was explained by the size of the event and whether it was a single or multi-peaked event. This finding emphasises the need to manage expectations by considering both a range of event magnitudes and types when designing or assessing leaky dam natural flood management schemes.

Nature-based solutions in flood risk management: Unlocking spatial, functional and policy perceptions amongst practitioners in South-West England

Nature-based solutions (NBS) to flood risk management include natural flood management (NFM) and sustainable drainage systems (SuDS). Still relatively untested in practice, their applications have been separated functionally and spatially. In this article, it is suggested that the emerging approach of managing flood risk holistically over whole catchments is hampered by the persistence of such binaries. Structural, organisational and policy contexts that entrench these divisions are explored through the experiences of flood risk practitioners working in south-west England. Interviews with 11 practitioners working in different aspects of flood risk management within the English Severn and Wye region are analysed. The key findings are grouped into two broad categories: (1) impediments faced by practitioners in implementing NBS, including different spatial NBS understandings, implementation and planning challenges and, monitoring and maintaining NBS; (2) the need for effective NBS governance focused around policy links and community involvement and incentivisation. The analysis draws out three formats of network governance in support of the expansion of cross-sectoral arrangements to plan, implement and monitor NBS flood interventions across extended river catchments in the longer term: regional administration, local lead flood organisation and participant-governed. The focus on the UK, rooted in national contexts, applies conceptually to flood risk governance scenarios in other countries.

GREEN INFRASTRUCTURE FOR PROTECTING SHIRAZ'S HISTORIC URBAN FABRIC FROM FLOODING

Shiraz, a city known for its rich historical urban fabric, faces increasing challenges posed by climate change and extreme weather events, particularly floods. The rapid urbanization and limited stormwater management infrastructure have exacerbated the vulnerability of the city's historic areas to flooding. Due to the registration of 360 km of Shiraz historical fabric in the national register in 2023, the importance of planning to safeguard this precious heritage has become twice as crucial. This study explores the potential of urban green spaces as a sustainable approach to mitigate flood impacts on Shiraz's historic urban fabric. Through a comprehensive analysis of flood patterns, urban green spaces, and historic buildings, this research aims to identify the most flood-prone areas and assess the effectiveness of existing green spaces in minimizing flood risks. The study also evaluates the role of vegetation and permeable surfaces in stormwater management to reduce floodwater runoff and its impact on historical structures. The findings reveal that strategically designed and maintained urban green spaces can act as natural flood buffers, helping to regulate water flow, reduce surface runoff, and minimize flood-induced damage to historic buildings. By integrating green spaces into urban planning, policymakers can enhance the city's resilience to floods and preserve the unique character and heritage of Shiraz's historic urban fabric. This study advocates for incorporating green infrastructure and sustainable stormwater management practices as integral to urban planning strategies. By embracing nature-based solutions, Shiraz can safeguard its historical treasures and foster a more sustainable and resilient urban environment for current and future generations. This research aimed to assess the implications of reducing urban green spaces, particularly in the green belt surrounding Shiraz's historic urban fabric and Snag-e-Siah neighborhood, on the vulnerability of historical sites to flood damage and potential demolition. With the utilization of urban green spaces, flood damage to Shiraz's built heritage was investigated in this study using both quantitative and qualitative methods simultaneously. The study results showed that the reduction of urban green infrastructure significantly increased the damage caused by floods in the historical area of Shiraz.

Impact of Lateral Gap on Flow Distribution, Backwater Rise, and Turbulence Generated by a Logjam

AbstractLogjams may form at natural obstructions and are also used as nature‐based solutions for river restoration and natural flood management. Previous research has described backwater rise due to logjams that span the full channel cross‐section and logjams with a gap between the lower edge of the logjam and the bed. Logjams that fill the channel depth, but not its width, leaving a lateral gap between the logjam and the channel bank, are also common natural formations and the focus of this study. The flow distribution between the logjam and the lateral gap, backwater rise, and wake turbulence are key factors in determining the ecologic and flood risk impact of a logjam. Specifically, relative to a channel‐spanning logjam, the introduction of a lateral gap can reduce backwater rise and increase the potential for trapping particles, such as nutrients or microplastics, within the wake region, but may also promote erosion in the gap. The choice of logjam and gap widths can be used to maximize flow and habitat diversity in rivers, while reducing erosion risk. We present experimental results demonstrating that the flow distribution between the logjam and the lateral gap can be predicted by assuming equal resistance through the logjam and gap sections. Further, we show that backwater rise can be determined from the predicted discharge through the logjam using a momentum balance developed for channel‐spanning logjams. Finally, turbulence generated within the jam was observed directly downstream of the logjam, and, for the densities considered, increased with jam density.

Stochastic Flood Simulation Method Combining Flood Intensity and Morphological Indicators

The existing flood stochastic simulation methods are mostly applied to the stochastic simulation of flood intensity characteristics, with less consideration for the randomness of the flood hydrograph shape and its correlation with intensity characteristics. In view of this, this paper proposes a flood stochastic simulation method that combines intensity and morphological indicators. Using the Foziling and Xianghongdian reservoirs in the Pi River basin in China as examples, this method utilizes a three-dimensional asymmetric Archimedean M6 Copula to construct stochastic simulation models for peak flow, flood volume, and flood duration. Based on K-means clustering, a multivariate Gaussian Copula is employed to construct a dimensionless flood hydrograph stochastic simulation model. Furthermore, separate two-dimensional symmetric Copula stochastic simulation models are established to capture the correlations between flood intensity characteristics and shape variables such as peak shape coefficient, peak occurrence time, rising inflection point angle, and coefficient of variation. By evaluating the fit between the simulated flood characteristics and the dimensionless flood hydrograph, a complete flood hydrograph is synthesized, which can be applied in flood control dispatch simulations and other related fields. The feasibility and practicality of the proposed model are analyzed and demonstrated. The results indicate that the simulated floods closely resemble natural floods, making the simulation outcomes crucial for reservoir scheduling, risk assessment, and decision-making processes.

ANALYSIS OF FLOOD HYDROGRAPH IN THE LANDAK SUB WATERSHED

This research is motivated by the natural flooding disaster in the Landak sub-watershed area, which can be caused by river overflow due to high rain intensity. Flood discharge can be calculated using the Synthetic Unit Hydrograph method if the available data is limited, such as only obtaining rainfall data and watershed characteristics.Several Synthetic Unit Hydrograph (SUH) methodologies, including SUH Snyder, Nakayasu, Soil Conservation Services (SCS), Gama I, ITB, and Limantara, were utilized in this study. The analyzed data included precipitation data and measured discharge data. Rainfall data are analyzed using the homogeneity test, statistical descriptors, and chi-squared to determine the planned flood discharge. Then, continue with the study of rainfall frequency and analysis of rainfall intensity so that the maximal discharge can be analyzed using three SUH methods: HSS Snyder, Nakayasu, and SCS. The analysis of measured release is conducted by statistically analyzing estimated discharge data.The analysis results are then compared to obtain the percentage error between the discharge plan and the minimum measured discharge. The results showed that the HSS Snyder method was selected for analyzing flood discharge in the Landak sub-watershed basin because it has the minimum percentage error from comparing planned release and measured discharge values. Therefore, for the calculation of flood discharge analysis of the Landak sub-watershed basin, the HSS Snyder method is used with the acquisition of flood discharge plans for the return period of 2, 5, 10, 20, 50, and 100 years of 648,880 m3/sec, 896,335 m3/sec, 1025,954 m3/sec, 1132,006 m3/sec, 1252,788 m3/sec, 1335,273 m3/sec.

Impact of Flood on Children Nutrition

Purpose: Particularly with regard to floods, landslides, drought, forest fires, and hot and cold waves of viral infections every year, Nepal is a very disaster-prone nation due to the high summer precipitation rates. More landslides occur in Nepal's river hills and Terai region throughout the summer (June to September) due to the heavy monsoonal rain that falls during this time. In the up-stem region of rivers, flooding is more likely to occur, and the down-stem region of rivers has a dipping issue. Sedimentation harms homes, agriculture, and human life all at once. The research aims to distinguish nutritional difference among under-five children with and without flood through Weight, Height and Mid-Upper Arm Circumference (MUAC) reading. Design/Methodology/Approach: The study was carried out in a Nepali region that had just experienced severe flooding. The nutritional status of children in flood-affected and non-flood-affected communities was assessed and compared as ex-post facto research. Used mixed methodologies (qualitative and quantitative) to analyse how floods affect in ECD children. Review of relevant literature on the consequences of a natural disaster (flood) on children who were affected by it. Establish the target population, take ethical issues into account, and ask the mother of the children to provide her informed consent. Face-to-face interviews were used to collect information from respondents. The children's height, weight, and mid-upper arm circumference were measured. The information was then analysed using SPSS and Ena (WHO software). Findings/Result: The floods affected children, who measured anthropometry and body mass and prepared results. Review of literature related to flood-affected children and the effects of natural floods (disasters). Define the target population, consider ethical considerations, and obtain informed consent from the children’s mother. The data shows flood-affected children are more malnourished than children in non-flood-affected in the sane social areas. In the Karnali River, unthinkable floods stop human life. During the flooding duration, almost all houses leave their homes for 1 to 4 weeks and stay as refuse in community buildings (community homes, schools, and Godam buildings). According to the Karnali River floods, this condition occurs 1–3 times per year. After every flooding, it takes huge cost for the maintenance of their home, toilet, and handpump to get back to their normal life. Originality/Value: This is the first empirical research in Nepal to compare and analyse the impact of flood on Children's nutrition status to draw the attention of policy maker and different societies working in the area. Paper Type: Review paper

Flood pulses and fish species coexistence in tropical rivers - a theoretical food web model

AbstractFreshwater fish diversity reaches its zenith in large tropical rivers. Although the origins of this diversity have been relatively well studied, the mechanisms that maintain high fish diversity in tropical rivers remain largely unknown. It has been hypothesized that the annual flood pulse, a perennial feature of many lowland rivers in the tropics, reduces competitive exclusion and consequently promotes species coexistence. During the high-water season, superabundant allochthonous resources and relatively low fish density may reduce intra- and interspecific competition. During the low-water season on the other hand, resource availability is low and predation pressure high, offsetting competitive differences between species and controlling fish population sizes. Here, we tested the potential role of these mechanisms for species coexistence using a food web model where fish species exhibit strong differences in competition strength and compete for finite resources. We simulated fish interactions when a regular flood pulse was either present or absent. We found that extinction rates in the simulations without an annual flood pulse were consistently higher when compared to those with a flood pulse, indicating more species could coexist when a regular annual flood pulse is present. If the flood pulse is a relevant mechanism for fish species coexistence, as our model results suggest, then flood pulse changes could result in species extinctions and lower fish diversity. Deforestation, climate change, and the construction of large hydropower dams are current drivers of hydrological change across the tropics, increasing the urgency to understand the role of natural flooding regimes for the maintenance of tropical freshwater fish diversity.

Navigating or adding to complexity? Exploring the role of catchment partnerships in collaborative governance

An enduring challenge for environmental governance is how to coordinate multiple actors to achieve more collaborative and holistic management of complex socio-ecological systems. Catchment partnerships are often thought able to achieve this, so here we ask: do such partnerships actually help navigate complexity, or merely add to it? We answer this question by analysing the experiences of four voluntary UK catchment partnerships. Our data combined a structured desk-based analysis of partnership documents, with semi-structured interviews with partnership coordinators, chairs and partner representatives. These data were analysed using a qualitative thematic approach informed by the literatures on catchment management and collaborative governance of complexity. We found that partnerships both add to and help navigate the complexity of holistic and inclusive environmental management. Maintaining partnerships entails costs for partners, and partnerships connect messily and multitudinously to other initiatives. However, the partnerships were all judged as worthwhile, and made progress towards goals for water quality, biodiversity and river restoration. They were especially valued for envisioning and initiating complex activities such as Natural Flood Management. Communication and networking by partnership coordinators and partners underpinned these achievements. Aspects of pre-existing governance systems both enabled and constrained the partnerships: in particular, statutory agencies responsible for policy delivery were always important partners, and delivering partnership plans often depended on public-sector grants. This draws attention to the pervasive effect of governmentality in collaborative governance. More attention to analysing—and supporting—such partnerships is worthwhile, complemented by reflection on the limits to environmental governance in the face of complexity.

Natural flood management: Lessons and opportunities from the catastrophic 2021–2022 floods in eastern Australia

AbstractNatural flood management (NFM), a nature‐based solution to flood mitigation where hydrological and biophysical processes are harnessed to reduce flow velocity, erosive energy and flood risk, is an emerging global theme of water and river management. The catastrophic 2021 and 2022 floods in eastern Australia are used to assess the hydrological properties of discrete events and to start an investigation of whether widespread changes in flood hydrology are occurring. We find that most coastal rivers in New South Wales (NSW) had a noticeable decrease in flood wave celerity (increase in flood travel time) when the 2021 and 2022 floods are contrasted with equivalent floods since the 1970s and that several also exhibit increases in flood peak attenuation. For some rivers, there is a coincident trend between these changing flood properties, riparian vegetation regrowth (regreening) and geomorphic recovery over the last +30 years. These may be the first signals that passive riparian management is counteracting some of the more severe hydrological effects of floods on these rivers and that some degree of NFM is possible. Lessons from this work are that there is an immediate opportunity to implement large‐scale NFM in coastal catchments of NSW, but this will only occur if we re‐examine current flood mitigation and adaption strategies and recognise and prioritise nature‐based solutions that include space‐to‐flood and corridors of river recovery, as essential parts of the modern flood mitigation toolkit.

Spatial Evaluation of a Natural Flood Management Project Using SAR Change Detection

This study proposes an evaluation method using C-band Sentinel-1 synthetic aperture radar (SAR) data to provide evidence of flood characteristic changes after the restoration of a floodplain. A portable, flexible evaluation framework has replicated previous change detection research approaches to analyse a Natural Flood Management (NFM) project on the Sussex Ouse river in southern England, conducted by the Sussex Flow Initiative (SFI), to ascertain how control measures have helped mitigate flood risk. GIS operations were conducted on the mapped results of the change detection procedure to identify how flood area, form and compactness have been affected after the NFM installation restored a floodplain to slow river flow and how these changes relate to the overall aims of the project. Innovative means were employed to verify the change detection methodology by sampling flood records from internet-published drone footage. The overall accuracy achieved using the Change Detection and Thresholding (CDAT) technique was 75%. The use of SAR data provides evidence of how NFM features function during significant flood events, providing a mapped delineation of the actual flood extent. A comprehensive scorecard has been developed to evaluate the positive and negative outcomes of the spatial changes that have manifested in post-restoration floods, in comparison to inundation before the installation. Results from this study have been included in the annual report of the SFI project to demonstrate how key features have attenuated flood waters in accordance with design intentions.

Long-term data show alarming decline of majority of fish species in a Lower Mekong basin fishery

Overexploitation, habitat fragmentation, and flow alteration are major threats to freshwater biodiversity that can lead to fisheries collapse and species extinction. These threats are particularly alarming in poorly monitored ecosystems where resource use supports the livelihoods of numerous people. The Tonle Sap Lake in Cambodia is such an ecosystem, supporting one of the world's largest freshwater fisheries. Tonle Sap Lake fishes are the focus of indiscriminate harvest affecting species stocks, community composition and food-web structure. Changes in the magnitude and timing of the seasonal flood pulse have also been linked to declines in fish stocks. Yet, changes in fish abundance and species-specific temporal trends remain poorly documented. Analyzing 17 years' time series of fish catch data for 110 species, we show that fish populations have declined by 87.7 %, owing to a statistically significant decline for >74 % species, particularly the largest ones. Despite large variations in species-specific trends - going from locally extinct to >1000 % increase - declines were found across most migratory behaviors, trophic positions or IUCN threat categories, though uncertainty regarding the magnitude of effect precluded us drawing conclusions in some cases. These results, reminiscent of alarming declines in fish stocks in many marine fisheries, provide unequivocal evidence that Tonle Sap fish stocks are increasingly depleted. The consequences of this depletion on ecosystem function are unknown but will undoubtedly affect the livelihoods of millions of people, stressing the need to set-up management strategies aimed to protect both the fishery and its associated diversity. Flow alteration, habitat degradation / fragmentation - especially deforestation of seasonally inundated areas and overharvest - have been reported as major drivers in population dynamics and community structure, highlighting the need for management efforts aimed at preserving the natural flood pulse, protecting flooded forest habitats, and reducing overfishing.

Leaky dams augment afforestation to mitigate catchment scale flooding

AbstractDespite calls for large‐scale afforestation to alleviate flooding, the effectiveness of such action remains unclear. Simulations with the SHETRAN hydrological model are therefore carried out for the 335‐km2 Irthing catchment and its 1‐10‐km2 headwater catchments in northwest England to determine: (a) whether forests can reduce flood peak discharges in a large catchment; (b) the proportion of the catchment that requires afforestation to be effective; and (c) the extent to which a combination of afforestation and natural flood management features (leaky dams) improves upon afforestation on its own. Four‐year simulations were run with a range of forest covers and extents of leaky dam installation, the latter modelled as a channel hydraulic resistance. Hydrograph, flood frequency and peak discharge magnitude responses to forest cover simulated (and observed) in the headwater catchments are replicated in simulations at the full scale. Afforestation on its own can reduce the frequency of given flood magnitudes but has a variable impact on individual peak discharge magnitudes. For the Irthing, a 76% forest cover reduces the mean discharge of 20 peaks in a partial duration flood series by 10% relative to the current 21% forest cover but reduces the largest peak by only 2.5%. Accompanying adverse effects include 17.5% reduction in long‐term runoff and loss of agricultural land. By contrast, leaky dams mitigate flood frequencies and peak discharges effectively, over a range of discharge magnitudes, with no reduction of annual runoff. The dam installation required for a 10% mean peak discharge reduction reduces the largest peak by 22%. The flow resistance increases by which the dams are simulated have still to be translated into specific dam designs. Nevertheless, and considering the figures indicatively, dam installation in 20% of the Irthing streams with Strahler orders of 1–3 achieves a 10% peak discharge reduction with only 35% forest cover and 7.5% runoff reduction. The study illustrates the potential for a dense network of leaky dams to augment the impact of afforestation on flood mitigation, especially at the largest discharges, while minimizing adverse impacts on water resources and food security.

Field-based monitoring of instream leaky barrier backwater and storage during storm events

Engineered leaky barriers are increasingly used as natural flood management methods providing ecosystem and water quality benefits in addition to flood attenuation, complementing hard engineering flood defences. Field-based monitoring of a natural flood management site, Wilde Brook in the Corvedale catchment, England (UK) studied the rainfall-runoff relationship for a 5.36 km reach with 105 leaky barriers over two years. Paired pressure transducers were placed upstream and downstream of three channel spanning leaky barriers, allowing evaluation of upstream backwater rise relative to rainfall intensity, storm magnitude, and frequency. By increasing backwater rise, the leaky barriers caused overbank flows, resulting in a reduction in the cross-sectional area velocity after the event. The incidence of overbank flow depended on the local stream cross-sectional profile, barrier properties, location in the reach, and storm magnitude. Barrier operational flow conditions were classified into five modes according to relative bank inundation and barrier submergence extent. The backwater rise magnitude depended on barrier physical properties and evolution over time through cycles of accretion and build-up of brash and leafy material in the barrier, in addition to local bedload sediment transport dynamics, where instances of scour around the barriers were observed. Backwater rise and net volume hydrographs showed rapid filling up behind the barriers on the rising limb and slower water release on the falling limb. For a ∼ 4 yr return period storm event, results indicated that one leaky barrier increased storage volume by up to 102 m3, which translates to an overall net volume increase of ∼ 10,700 m3 for the full reach. These new findings provide quantitative evidence of leaky barrier backwater and storage performance, and leaky barrier design recommendations for storms up to a 4 yr return period. This evidence can be used to develop and validate flood modelling generalised approaches for smaller, more frequent storms, and work towards the development of an approach for modelling leaky barriers for larger storm magnitudes.

Arsenic release dynamics of paddy field soil during groundwater irrigation and natural flooding

Irrigation water in rice cultivation significantly affects the arsenic (As) mobilization in the paddy field soil. This research assessed the effect of rainwater (RW) and groundwater (GW) on the dissolution dynamics of arsenic (As) in paddy field soil. Up-flow column flooding experiments were conducted continuously for 80 d with simulated RW and GW to evaluate As dissolution phenomena in actual field conditions. Arsenic dissolution from the soil was lower in GW (309 μg/kg) irrigation than in RW flooding conditions (1086 μg/kg). The redox potential (Eh) of the soil pore water decreased, and pH increased over-irrigation time in both flooding conditions. The dissolution of arsenic (As) and iron (Fe) in the soil pore increased, while the dissolution of manganese (Mn) decreased over flooding time. The release of As in the soil pore water was attributed to the dissolution of Fe–As and Mn–As minerals and microbial reduction of As. Fe–As dissolution ratios in the soil pore water were relatively low and estimated as 0.68 mol/mol and 4.9 mol/mol for RW and GW, respectively. The dissolution of As and Mn dominated in the initial phase (0–40 d) of flooding, while the dissolution of As and Fe dominated in the second phase (40–80 d). The release of As was much lower in GW flooding than in RW flooding conditions. The Presence of Ca, Mg, and Mn in the GW facilitated the reduction of As dissolution by precipitating Ca–As and Mg–As and the oxidizing dissolved Mn in the soil pore water. The findings of this study provide valuable insights into the mechanisms of As release during monsoon flooding and groundwater flooding to assess the potential risks of As contamination in rice grown in paddy field soils.

What approaches exist to evaluate the effectiveness of UK-relevant natural flood management measures? A systematic map

BackgroundThis systematic map principally sought to understand the different forms of effectiveness that existing studies evaluate in relation to Natural Flood Management (NFM) in the UK with a supplementary question of whether studies engaged with climate change and future flood risk. NFM measures seek to protect, enhance, emulate, or restore the natural function of rivers as part of approaches to flood risk management (FRM). While there is agreement in both academic and practice/policy literature that NFM should be part of a holistic FRM strategy to address current and future flood risk, the specifics of how to expand the application of and consistently implement NFM successfully in practice are less well known. A core focus of this study is on how the effectiveness of NFM measures is evaluated in different studies based on approaches drawn from the Environmental Impact Assessment (EIA) literature: procedural, substantive, transactive and normative. The systematic map also examines how studies account for climate change, which is a crucial issue given the connections between NFM and climate change adaptation and resilience.MethodsWe searched 13 bibliographic databases, Google scholar as a web-based search engine, and 21 organisational sites. Articles were screened by title, abstract, and full text based on defined eligibility criteria. Checks were performed for consistency amongst reviewers. Forms of effectiveness were coded on the basis of the included studies in the systematic map. The quantity and characteristics of the available evidence are summarised with the frequencies of effectiveness forms for each NFM measure are presented in heat maps.Review findingsA total of 216 articles reported eligible studies that were coded as part of the systematic map. Overall, the systematic map shows that the majority of studies considered at least one approach to effectiveness; however, very few studies considered multiple forms of effectiveness. The systematic map also demonstrates that climate change is considered systematically by around one-quarter of studies although many studies make claims about NFM’s effectiveness in the face of future climatic change.ConclusionsNFM can be effective in several different ways owing to their multiple benefits; however, there are evidence gaps around understanding these different forms of effectiveness. This is particularly marked for studies considering transactive and normative effectiveness. Interdisciplinary studies are more likely to consider multiple forms of effectiveness. This systematic map also found that whilst 75% of studies mention future climate change in their studies, only 24.1% contain a systematic consideration of the issue through, for example, using climate change projections. NFM is also at risk of climate change (e.g. through drought) and therefore it is imperative that study designs seek to incorporate consideration of effectiveness under future climate change. Policymakers should be made aware of the lack of understanding of how NFM measures perform under future climate change.

Dam Break Analysis of Sermo Dam

Sermo Dam is located in the Special Region of Yogyakarta and serves multiple purposes including providing drinking water, supplementing irrigation systems in the Kalibawang area, and flood control. According to data published by the World Commission, 60% of mitigation measures taken to overcome the impact of dam structure failures are unsuccessful. The simulation of dam failure serves as a crucial aspect of flood mitigation plans and strategies because it is more destructive than natural flood waves. This research used HEC-RAS 5.0.7 to examine the flood inundation mapping and simulate dam failure in two dimensions. However, Dam Break Analysis was adopted to provide a Dam Emergency Action Plan Guide to guide managers and the community. The overtopping scenario was adapted to model the failure of the Sermo Dam based on the frequent occurrence of heavy and extreme precipitation in the affected area. Data were analyzed using unsteady flow and PMF discharge with peak inflow discharge of 1276.6 m³/s, which result in an inundation area of 9394 hectares and a maximum flood height of 17 m. Dam failure-induced floods tend to potentially affect eight sub-districts including Kokap, Pengasih, Sentolo, Wates, Panjatan, Galur, Lendah, and Temon. The piping scenario is also considered based on the potential damage that tends to occur. In the piping scenario, the biggest flooding area was 5112 hectares with a maximum flood height of 13 m. About six sub-districts are potentially affected by dam failure-induced floods with Kokap and Sentolo being excluded from the list. Therefore, it is crucial to establish early warning systems and infrastructure to mitigate disaster risks. The results of this research can also inform evacuation planning, damage estimation, and post-flood rehabilitation efforts in the affected areas.

Environmental and spatial determinants of fish community structure in an Afro‐tropical river ecosystem

AbstractWe investigated the relative influence of local environmental and spatial factors in structuring the community composition of fish at 15 sampling sites along the longitudinal gradient of the Lower Niger River Basin (LNRB) in dry and rainy seasons using distance‐based redundancy analysis and variation partitioning analysis. We collected a total of 3807 fish specimens representing 42 species. Our result indicated that the fish community composition differed between the upper and lower regions of the river. The communities in the upper region is influenced by high‐nutrient concentrations, while downstream sites were characterized by high concentrations of suspended solids. Variation partitioning revealed higher contributions of spatial than environmental predictors on fish community composition, with a higher total predicted variance in dry season. The variations in the community composition between upper and lower region may be attributable to the differences in the nature of anthropogenic activities within the regions, which influenced the local conditions differently. Differences in flow dynamics between upper and lower regions as attributable to black and white floods in the LNRB modify the connectivity between sites. Dispersal among sites may be more limited downstream than in the upper region, particularly in the dry season, because damming in the upper region also interrupts the natural flood regime such that there are low water levels in the lower region, which spatially isolate fish communities at certain sampling sites. The relatively higher total predicted variance during dry season may be attributable to the temporal differences in abiotic conditions between sites, which may have influenced site level community composition and abundance differently.

A century of channel change caused by flow augmentation on Sixth Water Creek and Diamond Fork River, Utah, USA

AbstractThe Diamond Fork River in central Utah, USA experienced extreme flow augmentation via transbasin flows. Beginning in 1916, irrigation water was delivered through a tributary, Sixth Water Creek, with daily summer flows regularly exceeding a 500‐year flood at the point of introduction. Flows were dramatically reduced by management action in 2004 but with mandated minimum flows. We examined the geomorphic response of Sixth Water and Diamond Fork using aerial imagery, lidar, topographic cross sections, and sediment transport measurements. River channel response varied with valley confinement and with position in the watershed, which determined the magnitude of augmented flow relative to natural floods and the amount of sediment supply. Confined, steep sections of Sixth Water incised many meters into bedrock, whereas partially confined and unconfined sections developed a braided form even under conditions of general incision. With the removal of flow augmentation, smaller natural floods on Sixth Water are unable to transport bed material and the channel remains static. On the alluvial lower Diamond Fork, a lower slope, upstream sediment supply, and larger natural floods produced a dynamic shifting channel that widened in response to natural floods. After flow augmentation, a coarsened bed is partially mobile and channel narrowing appears to be limited by artificial baseflow, which prevent vegetation establishment in the channel.