Floodplain Development Research Articles

Late Pleistocene to Holocene alluvial deposits of the Inaouène Valley and their paleoenvironmental significance (north Morocco)

This study investigates the paleoenvironmental changes and fluvial dynamics in the Inaouène River Valley of central northern Morocco over the last 22,000 years. Through comprehensive field study and radiocarbon dating of Upper Pleistocene and Holocene alluvial deposits, the research identifies six main alluvial units reflecting distinct phases of fluvial activity and environmental conditions. These phases include coarse gravel aggradation between ∼22 and 15 cal kaBP, indicating a braided channel system, followed by multiple fine-dominated alluviation phases occurring at ∼13, ∼10, ∼6–5, ∼3, ∼0.7–0.3, and ∼0.1-0 cal kaBP. The trunk channel evolved from a low-sinuosity wandering style in the Early-Middle Holocene to a high-sinuosity pattern in the Late Holocene. Periods of landscape stability, evidenced by soil formation, were dated around 0.3 and 0.8 cal kaBP, with additional episodes estimated just after ∼12 cal kaBP and around 3.8 cal kaBP. Notably, the study also uncovered evidence of significant human intervention during the Middle Holocene.A comparison with other archives enabled us to reconstruct late Pleistocene and Holocene palaeoenvironmental conditions on both regional and supraregional scales, linking specific stages of floodplain development to prevalent influencing factors. Emphasizing the fluvial system response, we present a cause-effect model that focuses on long-lasting climatic phases (e.g., Last Glacial Maximum, MIS2-MIS1 transition, African Humid Period) as well as sub-millennial to centennial Rapid Climate Changes, North Atlantic cooling events, and solar activity minima. Human intervention played a key role in the Inaouène's evolution during the Middle Holocene, as evidenced by clear anthropogenic markers found in the associated deposits. These findings not only contribute to our understanding of the area's geomorphological history but also highlight its significant archaeological potential, opening new avenues for interdisciplinary research in this understudied region.The study offers new insights into central northern Morocco's late Quaternary alluvial geochronology and paleoenvironmental evolution, aligning with regional findings and contributing to a broader understanding of climate-driven landscape changes and human-environment interactions across North Africa and the Mediterranean.

A Nationwide Analysis of Community‐Level Floodplain Development Outcomes and Key Influences

A Nationwide Analysis of Community‐Level Floodplain Development Outcomes and Key Influences

Housing amenity and affordability shape floodplain development

Flood damage has severe and long-term repercussions for households and communities, and continued housing development in floodplains escalates damages over time. Policies and interventions to reduce damage depend on assumptions about housing stock and residents, but assessments of flood exposure to date largely focus on community-scale characteristics at a single point in time, masking potential within-community differences and their evolution through time. We measure residential development in the floodplain nationwide over time to characterize the type and value of U.S. floodplain housing stock and to assess how new development contributes to flood exposure. Over 4M U.S. residences built from 1700 to 2019 (4.8% of all residences built during that time) are located within current regulatory floodplains. These residences are concentrated at the affordable and expensive extremes of the housing value spectrum, reflecting deep differences in the social vulnerability of floodplain residents. Floodplain housing stock often differs substantially from the local market, with coastal floodplains containing relatively expensive housing and inland floodplains containing relatively affordable housing. New housing development has not occurred equally across these contexts. In the past two decades, more floodplain development has occurred in communities with relatively expensive floodplain housing, and mobile home construction in floodplains has slowed. The bifurcated patterns in floodplain housing, across values and geographies, demonstrate the importance of considering the specific population at risk and how it may differ from the broader community when tailoring flood risk management approaches.

Migration Policy in Astrakhan Region in 1944-1945

This article examines the migration policy of the state in the Astrakhan region following its formation from 1944 to May 9, 1945. The study is based on materials from the archives of state and party authorities in the State Archive of the Astrakhan Region. The reasons, goals, content, and outcomes of the authorities’ migration policy are identified. The number of migrants is established, showcasing the geography of departure points and migration directions of the population. It is demonstrated that during the final stage of the war (1944 — May 9, 1945), the migration policy aimed to provide labor resources for the fishing industry, new livestock farms, and government initiatives for the development of the Volga-Akhtubinsk floodplain. In the years under consideration, migrations occurred on a voluntary basis and were incentivized by state benefits. In 1945, during the organization of relocations from the Volga-Akhtubinsk floodplain, migrants were recruited from areas with climates and soil conditions similar to those of the Astrakhan region (Kazakhstan). However, the challenging material and living conditions in the settlement areas led to mass return migrations. The Astrakhan region was unprepared to receive and integrate migrants due to insufficient funding for relocations and local authorities’ lack of attention to the needs of newcomers.

Environmental justice implications of flood risk in the contiguous United States – a spatiotemporal assessment of flood exposure change from 2001 to 2019

ABSTRACT Flood hazard is one of America’s most frequent and expensive natural hazards and causes enormous economic losses in the United States every year. Flood hazards disproportionately affect marginalized and socioeconomically disadvantaged populations. This disproportionate flood exposure constitutes a form of environmental injustice. Few studies have undertaken a large-scale assessment of the long-term change of flood exposure. To fill this gap, this study utilized land use and flood zone data from 2001 to 2019 at a 5-year interval to analyze spatiotemporal changes in flood exposure in the Contiguous United States (CONUS). Two indices, the Deviational Exposure Index and Socioeconomic Disparity Index, were introduced to measure flood exposure and the socioeconomic disparities associated with flood exposure. At the national level, the overall flood exposure in the CONUS decreased in the past two decades, indicating increasing awareness of flood risk in the country. But the local variations of flood exposure and its changing trends vary among communities. In general, coastal and riverine counties show a general avoidance of developing urban areas in flood zones, while inland counties show an opposite tendency of urban development in floodplains. The results of this study reveal socioeconomic and demographic disparities between communities in and out of flood zones and evaluate environmental injustice among disadvantaged populations. The knowledge learned from this study can not only help address environmental justice issues but also benefit the decision-making of the federal government and local authorities in urban development and smart growth when faced with flood risk.

Exploring The Synergies between Flood Risk and Urban Needs - Floodplain Development In Aceh River.

A Floodplain is an area next to a riverbed that is more or less frequently covered with water in times of high-water discharges from adjacent rivers. It usually has a high environmental value because of its heterogeneous habitats for wildlife species. However, the condition of rivers in each country could be unique and different, because of their history and location thus creating a different nuance. The object study of this research is a constructed floodway and flood plain in Krueng Aceh (Aceh River) owned and managed by the local government. Since the last big flood in 2000, this wide flat land remained dry in several areas and was used by some villagers to make a living. In 2020 it had cleared from several illegal land uses, resulted a grassland floodplain with low-intensity use which in theory is in a good direction. Meanwhile, in the perspective of urban needs, river development could also bring economic, social, and environmental benefits to community. The objective of this study is to investigate the concept of ecosystem services and human-landscape connectivity. The method used in this research is semi-qualitative research that combines theories and observation. In the context of ecosystem services identification through activities monitoring, it shows that cultural and provision services is the highest while regulating and supporting services still need further research. As for human-landscape connectivity, there are more ‘rooms’/spaces to develop align with the availability of cultural services.

How local governments avoid floodplain development through consistent implementation of routine municipal ordinances, plans, and programs

Abstract Avoiding floodplain development is critical for limiting flood damage, yet there is little empirical evidence of how local governments effectively avoid floodplain development. We conduct a mixed-methods study to explain how local floodplain management influences floodplain development in New Jersey, a state with high development pressure and flood risk. We find that 85% of towns developed relatively little in the floodplain from 2001 to 2019, and they achieved this with commonplace land use management tools and modest levels of local government capacity. One hundred twenty-six New Jersey towns put none of their new housing in the floodplain 2001–2019. Our findings run counter to common reports of rampant floodplain development requiring legal innovation and capacity-building campaigns and suggest alternative approaches for promoting floodplain avoidance. We find multiple paths to floodplain avoidance, weak support for previously identified drivers, and strong evidence that the keys to avoidance include having a few high-quality tools that are well-implemented, requiring consistency, coordination, and commitment of local officials. The multiple paths and importance of maximum, rather than average, quality might explain the mixed evidence in prior research connecting floodplain management actions and development outcomes. A lack of attention to towns that limit floodplain development impedes our ability to learn from and disseminate their successes. Contrary to our expectations, we show that floodplain avoidance can be and is achieved through routine municipal practices. Our findings underscore the importance of sustained commitment to development management as a core tool for limiting flood risk.

Past anthropogenic land use change caused a regime shift of the fluvial response to Holocene climate change in the Chinese Loess Plateau

Abstract. The Wei River catchment in the southern part of the Chinese Loess Plateau (CLP) is one of the centers of the agricultural revolution in China. The area has experienced intense land use changes since ∼6000 BCE, which makes it an ideal place to study the response of fluvial systems to past anthropogenic land cover change (ALCC). We apply a numerical landscape evolution model that combines the Landlab landscape evolution model with an evapotranspiration model to investigate the direct and indirect effects of ALCC on hydrological and morphological processes in the Wei River catchment since the mid-Holocene. The results show that ALCC has not only led to changes in discharge and sediment load in the catchment but also affected their sensitivity to climate change. When the proportion of agricultural land area exceeded 50 % (around 1000 BCE), the sensitivity of discharge and sediment yield to climate change increased abruptly indicating a regime change in the fluvial catchment. This was associated with a large sediment pulse in the lower reaches. The model simulation results also show a link between human settlement, ALCC and floodplain development: changes in agricultural land use led to downstream sediment accumulation and floodplain development, which in turn resulted in further spatial expansion of agriculture and human settlement.

The Natural Consequences of Land Use Change on Transformation and Vegetation Development in the Upper Odra Floodplain

River channels are regulated in various ways and the fertile soils of valleys are occupied for agricultural purposes, accompanied by human settlements. In many places on the floodplains, gravel or sand is mined and former pits fill with water. The consequences are changes in water relations, changes in land use and land cover. Natural riparian ecosystems gradually disappear. In addition, river valleys are susceptible places for the spread of invasive plant species. In the section of the Upper Odra Valley discussed in this article, all of the aforementioned factors have played roles in shaping modern habitats. The present study shows the impact of human-induced changes on the transformation of the plant cover of the Upper Odra Floodplain. In designated transects, we studied land use changes from 1910 to the present day and examined plant species diversity. The results show that the more heavily transformed floodplain adjacent to the channelized channel has a higher level of species diversity than agricultural areas located along a section of the river with a natural channel course. Most of the river valleys are colonized by geographically invasive alien species, such as Reynoutria japonica, Reynoutria sachalenesis and Impatiens glandulifera, which have contributed to the fact that all of the species typical of the ash, poplar and willow riparian forests characteristic of this habitat type have retreated, which is the main reason for the very low biodiversity.

Resilience in Urban and Architectural Design—The Issue of Sustainable Development for Areas Associated with an Embankment

The dynamically changing world poses new challenges to urbanized areas, e.g., related to water management in the architectural and urban context. Improving retention and strengthening blue-green infrastructure can be based on technical, semi-natural and natural methods, which are less invasive. Various forms are used in the city space: flow control, detention, retention, filtration, infiltration, and treatment. The implementation of the green order strategy and shaping sustainable development in the context of designing the city’s resilience is associated with shaping spatial policy and urban planning assumptions for the transformation of public spaces and new investments in urbanized areas in crisis. The shaping of waterfronts in the city and green and blue infrastructure significantly shape the parameters of the environment and the regenerative capacity of the urban ecosystem. The aim of this work was to show the relationship between the problem of embankments and the possibilities of developing space in their proximity, including areas exposed to the risk of flooding. The relationships determined by the goal were verified in comparative studies, a repeatable method of collecting, processing, analyzing, and interpreting the obtained data was used. The issue was presented in a broader context of flood risk and water management in the area of Lake Zegrze, collisions and spatial conflicts were analyzed. The results are presented in the context of detailed water management data for the complex of Riva Zegrze facilities, which is a model example regarding the sustainable development of areas on embankments, considering their specific floodplain development possibilities. The effects of the research allowed for the formulation of conclusions, including in terms of implementation, in the field of urban and architectural design for areas associated with an embankment.

Molluscan Faunal Changes from Brackish to Freshwater Deposits in the Lower Cretaceous Itsuki Formation of the Tetori Group, Japan

This paper focuses on the molluscan faunal changes in the nonmarine deposits of the Lower Cretaceous (Barremian) Itsuki Formation of the Tetori Group, central Japan. In the lower part of the Itsuki Formation, the transition from brackish to freshwater environments is recognized by lithofacies, sedimentary structures, and fossil indices of molluscs and plant remains. The molluscan assemblages include eleven gastropod species and six bivalve species, and one new gastropod species, Probaicalia okurai sp. nov., is described. The brackish habitats in the delta-front were dominated by Myrene tetoriensis, which usually formed shell beds. The newly founded freshwater habitats on the fluvial environments were populated by Campeloma onogoense and Sphaerium coreanicum as pioneer immigrants. With the development of the fluvial floodplain, a variety of aquatic and semiaquatic microenvironments formed, thereby providing various habitats suitable for small gastropods.

Impacts of climate change on global total and urban runoff

Climate models consistently project that frequency, severity, and duration of hydroclimatic extremes will increase over this century under climate change. Urban flooding and runoff in general have become prominent issues for many cities and regions, arising from a combination of altered precipitation patterns, urban growth, development in floodplains, and increases in impervious surfaces. In this study, we first validate total (grid cell-level) runoff from the fully coupled Community Earth System Model (CESM) historical simulations against one observed-runoff/streamflow-based dataset and one reanalysis dataset, and further analyze both grid cell-level runoff and urban subgrid runoff under future climate change scenarios. We calculated global annual average of monthly runoff from the period 1986–1995 for the validation and calculated bias and correlation coefficients between CESM and each of the datasets. Additionally, we analyzed future grid cell and urban runoff across three CMIP6 coupled Shared Socioeconomic Pathways and Representative Concentration Pathways – 2–4.5, 3–7.0, and 5–8.5 – and evaluated changes between the future period of 2041–2050 and the same past period of 1986–1995 for each scenario. Results show spatial consistency and robustness between the CESM simulations and both datasets. However, there is some spatial inconsistency in the areas highlighted as major runoff producers, such as the Amazon basin and Southeast Asia, as well as mountainous regions outside the United States. Grid cell-level runoff and urban runoff projections suggest that future hydroclimatic conditions will vary depending on the climate scenario. However, certain locations, such as Madagascar, Indonesia, and the Himalayan mountain range, consistently see decreases in both grid cell-level runoff and urban runoff across all scenarios, and locations such as Nigeria and Ecuador consistently see increases in both grid cell runoff and urban runoff across all scenarios. Our findings provide quantitative insights on hydrology representation in the global Earth system model and advance the understanding of the impacts of large-scale climate change on future local-scale urban runoff.

Growing Safely or Building Risk?

Problem, research strategy, and findings Limiting housing and infrastructure in flood-prone places has long been recognized as critical to managing long-term risk. However, due to the difficulty of tracking development at small spatial scales, little empirical research has been conducted to explain differences between communities’ floodplain development patterns. We analyzed new construction across 5 million parcels in the state of North Carolina to develop standardized measures of floodplain development and evaluated the relationships between flood risk management effort and development outcomes. Statewide, for every property removed through buyouts from 1996 to 2017, more than 10 new residences were built in floodplains. At the community level, indicators of flood risk management effort (participation in the Community Rating System and use of buyouts) did not consistently align with floodplain development outcomes. Based on a sample of urban and suburban counties, we found more than 75,000 acres of vacant floodplain land currently zoned for development. Although we did not capture the full range of flood risk mitigation practices, results indicate that local development policies often run counter to efforts to limit long-term risk. Takeaway for practice Land use planning and floodplain management have the potential to play a larger role in flood risk mitigation. Modifying federal programs to more strongly disincentivize floodplain development could enhance local regulation and minimize future flood exposure. Given extensive undeveloped floodplain land and projected climate change, additional effort to manage development is needed to limit increases in flood risk.

Late Holocene river dynamics and sedimentation in the Lower Ganga plains, India

Packages of fluvial systems in the Lower Ganga plains (LGP) archive the changes in stratigraphic architecture induced by perturbations in the climatic system. In some parts of this landscape, where the fluvial sequences predominate, the role of climate in landsculpting is strongly indicated by the presence of sediment architecture. The present study is focused on the formation of alluvial plains of the Ajay River in the Rarh region that represent a region's environmental templates for understanding the landscape of LGP. The sedimentological, geomorphological, and optically stimulated luminescence (OSL) chronological investigations were attempted to document sedimentation patterns and the timing of deposition. The stratigraphic data from two exposed cliff sections and three boreholes are compared with proxy records to understand the Indian Summer Monsoon (ISM) controls on alluvial sedimentation for the last ~2.4 ka. The fluvial packages in the study area correspond to two significant channel phases: Period‐I (2.4–1.3 ka) and Period‐II (800–200 years ago). Period‐I is characterized by the episodes of floodplain development and lateral migration of the trunk river during Marine Isotope Stage (MIS) I, especially around 2 ka corresponding to the Roman Warm (RW) period in the Indian subcontinent. The sediment filling was high during ~2.4 ka due to ISM intensification, but in the later stage, the sedimentation was at a fairly steady rate. Conversely, Period‐II is characterized by flooding phenomena and aggradation of channel bodies across much of the present valley area during the last 800 years. The distinct flood events occurred during the times of significant shifts in ISM, from fluvial dormancy to sudden outbursts of monsoons (end of Little Ice Age [LIA] ~ 19th century), indicating that climatic patterns can be associated with the occurrences of abrupt flood events. The alluvial records fit well with the historical, instrumental, and published proxy data on the ISM validating the chronology and the potential of sedimentary archives for further studies related to the palaeoenvironment and palaeogeography.

Channel Deformations and Hazardous Processes of the Left-Bank Tributaries of The Angara River (Eastern Siberia)

The influence of anthropogenic and natural factors in the trends and mechanisms of development at various topological levels is determined based on relevant information on the structure and dynamics of fluvial systems in the south of Eastern Siberia in various geodynamic settings. This article considers the current spatial and temporal dynamics of the hydrological conditions of the vast territory of the Angara River and its influence on channel deformations and the manifestation of dangerous processes. An analysis of fluctuations in the maximum runoff using differential integral curves resulted in the identification of six periods of water content according to the maximum annual discharges for the period spanning from the beginning of observations to 2020 for the rivers under consideration. The dynamics and intensity of manifestation of hydrological and geological hazardous processes are demonstrated using a series of studies conducted under various geodynamic conditions. Catastrophic floods brought on by enhanced cyclonic activity are accompanied by the destruction of the bank. The highest rate of bank erosion in the plains is 1.5 to 2 m per year, and for rivers in mountains and piedmonts it is 2 to 6 m per year. An analysis of the dynamics of the development of floodplain–channel complexes in the Upper Angara region makes it possible to distinguish two zones of actively developing floodplain–channel complexes: piedmont and estuarine, separated by a relatively stable plain zone.

Reimagining flood plain development with geography at heart

ABSTRACT Claims that the catastrophic flooding events of 2022 which devastated the Northern Rivers region of New South Wales were unprecedented are demonstrated here to be ill-informed. Additionally, flood mitigation efforts will not be able to protect Lismore and surrounding communities from the ravages of future floods. It is essential that geographical realities be at the heart of planning decisions to protect flood prone communities in future. The inescapable fact is that catastrophic floods will recur in the region. The lesson for this region, and for others throughout Australia which are subject to severe flooding, is that planned withdrawal of critical services, commercial premises and vulnerable housing from the flood plain is the only sure way to protect people, their homes and livelihoods from repeated devastation. Geography matters indeed.

Equitable buyouts? Learning from state, county, and local floodplain management programs

Climate change-exacerbated flooding has renewed interest in property buyouts as a pillar of managed retreat from coastal zones and floodplains in the United States. However, federal buyout programs are widely critiqued for being inaccessible and inequitable. To learn whether and how subnational buyout programs overcome these limitations, we examined five leading US state, county, and local buyout programs to see what they teach us about redesigning future federal policies. Our mixed-methods research used interviews and document analysis to develop case studies, juxtaposed subnational strategies against a review of critiques of federal buyouts, and focus group discussions with subnational buyout managers and experts to identify limitations of their programs. We find that subnational programs can be more inclusive and better respond to resident needs as compared to existing federal programs due to their access to dedicated, non-federal funding and their standing institutional status, which allows them to learn and evolve over time. Nevertheless, these programs lack coordination with and control over agencies that permit development and produce affordable housing. This gives buyout programs limited power in shaping the overall equity of who lives in floodplains and who has access to affordable, resilient housing after a buyout. Their experiences suggest federal programs can support managed retreat nationwide by increasing support for institutional and staff capacity at state and county levels, encouraging efforts to bridge institutional silos at subnational levels, and holistically mainstream climate considerations into regional floodplain development, affordable housing production, and flood risk mitigation.

“Can seawalls help American cities adapt to coastal flooding?”

PurposeThis study aims to combine information about sea level rise (SLR), the probability distribution of storm surge, a flood damage function and the value of property by elevation along the coast of selected cities to measure expected flood damage. The selected six cities all have nearby long-term tidal stations that can be used to estimate the probability distribution of floods. The model is calibrated to each city. The study then compares the cost of building higher seawalls today along the coast versus the benefit of each wall (the reduction in expected flood damage).Design/methodology/approachThe combination of coastal storms and SLR has led to extensive flood damage across American cities. This study creates a simple generic model that evaluates whether seawalls would be effective at addressing this flooding problem. The paper develops an approach that readily measures the expected flood benefits and costs of alternative coastal seawalls. The approach takes account of near term SLR and the probability distribution of storm surge. The model finds seawalls are effective only in cities where many buildings are in the 25-year flood plain.FindingsCities with many buildings built on land below 2 m in elevation (the 25-year flood plain) have high expected flood damage from storms and SLR. Cities which already have many buildings in this flood plain would benefit from seawalls. Assuming seawalls are built above the high tide line, the optimal wall height that maximizes net benefits is between 0.9 to 1.2 m. These relatively low seawalls block 70%–83% of expected flood damage in these cities. Fair flood insurance is the least cost strategy for handling the remaining damages that overtop the optimal seawalls.Research limitations/implicationsThe analysis evaluates whether or not to build a seawall the length of each city at high tide lines. However, the analysis also finds several long stretches of coast in two cities where a wall is not warranted because there are few vulnerable buildings. Future analyses should consider seawalls in more spatially detailed sections of each city. Each section could then be analyzed independently. Whether or not more complex hydrodynamic models are needed to evaluate coastal resilience planning should also be explored. Alternative solutions such as planned retreat and nature-based solutions should be compared with seawalls in future studies as well.Practical implicationsCities should be careful to avoid development in the 25-year flood plain because of high expected flood damage. Cities that have low elevation areas subject to frequent flooding should consider seawalls to reduce frequent flooding. Because they are very costly and have low expected benefits, high walls that can stop a one-hundred-year storm are generally not worth building.Social implicationsThe analysis reveals that the most important factor determining the vulnerability of cities along the eastern coastline of the USA is the number of buildings built below 2 m in elevation (the 25-year flood plain). Cities should use zoning to discourage further development in the 25-year flood plain. Cities which already have many buildings in this flood plain would benefit from city-wide seawalls. Assuming these walls are built at mean high-high tide, the optimal height of current seawalls should be relatively modest – averaging about 0.9–1.2 m above ground. Using fair insurance for the remaining risk is less expensive than building taller walls. In particular, the cost of seawalls that protect against a major hurricane surge are over three times the expected benefit and should not be built. As decades pass and observed sea level progresses, seawalls and the boundary of the 25-year flood plain should be reevaluated.Originality/valueThis paper develops a coastal flood model that combines SLR and the probability distribution of storm surges with the value of property by elevation to estimate the expected damage from storm surge. The model is relatively easy to calibrate making it a practical tool to guide city flood planning. The authors illustrate what insights such a model gives about coastal resilience to flooding across six cities along the Eastern US coastline.

Latest Pleistocene and Holocene Floodplain Evolution in Central Europe—Insights from the Upper Unstrut Catchment (NW-Thuringia/Germany)

The upper Unstrut River is located in Germany at the modern Central European climate boundary of Cfb and Dfb climate. The river drains a loess landscape, which has experienced important environmental changes throughout the last 12,000 years. To evaluate the impacts of these changes on floodplain evolution, a multi-proxy research program, consisting of 2D electrical resistivity tomography profiling (ERT), vibracoring, and sedimentological investigations, 14C and OSL dating were applied. From base to top the investigations the following fluvial deposits were revealed: (1) gravels embedded in a fine-grained sediment matrix (interpreted as fluvial bedload deposits); (2) silty sediment with pedogenic features (interpreted as overbank floodplain deposits); (3) peat and tufa deposits (interpreted as wetland deposits) intercalated by pedogenetically influenced silty sediments (interpreted as overbank deposits); (4) humic silty sediment with some pedogenic features (interpreted as overbank floodplain deposits); and (5) silty sediments (interpreted as overbank deposits). Radiocarbon and luminescence dates yielded the following periods for sediment formation: (1) Younger Dryas to Preboreal period (around 11.6 cal ka BP); (2) Preboreal to early Atlantic period (approx. 11.6 to 7.0 cal ka BP); (3) early Atlantic to late Subboreal period (approx. 7.3 to 3.4 cal ka BP); (4) late Subboreal to early Subatlantic period (2.9 to 2.3 cal ka BP); and (5) late Subatlantic period (approx. 1.0 to 0.6 cal ka BP). The results suggest that floodplain development during the latest Pleistocene and early Holocene (approx. 11.6 to 7.0 cal ka BP) was considerably controlled by climatic conditions and short-term climate variabilities, which caused gravel deposition and overbank sedimentation. Afterwards floodplain conditions varied between rather stable (peat and tufa development, initial soil formation) and active periods (deposition of overbank fines). In this context, active periods with increased sediment input prevailed from approx. 5.1 to 3.4 cal ka BP, 2.9 to 2.3 cal ka, and 1.0 to 0.6 cal ka BP, temporally corresponding well with increased land-use phases of the past. In conclusion this study demonstrates that the investigated Unstrut catchment has reacted very sensitively to natural and human-induced changes during the latest Pleistocene and Holocene. Consequently, this high vulnerability to external changes should be considered in future river predictions or river management.

Recruitment of migratory fish in free‐flowing rivers with limited floodplain development

Abstract Hydrological connectivity is a basic feature of river ecosystems, responsible for important ecological processes. Human activities, however, have progressively modified natural connectivity, threatening the maintenance of aquatic biodiversity. Neotropical potamodromous fish depend heavily on fluvial connectivity to complete their life cycles. However, important ecological aspects remain poorly understood, especially in river systems with limited floodplain development (i.e. channelized rivers and drylands), where the environment poses constraints to fish recruitment. The Uruguay River Basin is such a system, with several migratory fish, small floodplain areas, and limited information about recruitment dynamics and nursery grounds. The lack of information on critical habitats limits conservation and management actions, especially in scenarios of increasing environmental degradation and river regulation. This study investigated recruitment dynamics of migratory fishes in the Middle Uruguay River, a long fluvial segment targeted for hydropower development. The study investigated spatial variations in the abundance, composition and size structure of juvenile fish among different sites along an extensive fluvial gradient (ca. 650 km), comparing the main channel with tributaries. Juveniles of migratory fish were widely distributed in the region, totalling nine species, with a predominance of Characiformes. Spatial distribution was variable among species and size classes, with a differential use of tributaries, wetlands and the main channel. Juvenile composition differed between sampling sites and environments, and was correlated with different limnological and spatial variables. Greater abundances occurred in the mouth of a tributary where a small floodplain develops during the wet season. The results emphasize the importance of fluvial connectivity for fish migration, dispersal and recruitment, providing valuable information about migratory fishes in river systems with limited wetland development. These findings have significance for the management and conservation of migratory fish under scenarios of hydropower expansion, as comprehensive studies on recruitment are rare in free‐flowing rivers.