Not all breaks are equal: Variable hydrologic and geomorphic responses to intentional levee breaches along the lower Cosumnes River,California

The transport of water and sediment from rivers to adjacent floodplains helps generate complex floodplain, wetland, and riparian ecosystems. However, riverside levees restrict lateral connectivity of water and sediment during flood pulses, making the re‐introduction of floodplain hydrogeomorphic processes through intentional levee breaching and removal an emerging floodplain restoration practice. Repeated topographic observations from levee breach sites along the lower Cosumnes River (USA) indicated that breach architecture influences floodplain and channel hydrogeomorphic processes. Where narrow breaches (<75 m) open onto graded floodplains, archetypal crevasse splays developed along a single dominant flowpath, with floodplain erosion in near‐bank areas and lobate splay deposition in distal floodplain regions. Narrow breaches opening into excavated floodplain channels promoted both transverse advection and turbulent diffusion of sediment into the floodplain channel, facilitating near‐bank deposition and potential breach closure. Wide breaches (>250 m) enabled multiple modes of water and sediment transport onto graded floodplains. Advective sediment transport along multiple flow paths generated overlapping crevasse splays, while turbulent diffusion promoted the formation of lateral levees through large wood and sediment accumulation in near‐bank areas. Channel incision (>2 m) upstream from a wide levee breach suggests that large flow diversions through such breaches can generate water surface drawdown during flooding, resulting in localized flow acceleration and upstream channel incision. Understanding variable hydrogeomorphic responses to levee breach architecture will help restoration managers design breaches that maximize desired floodplain topographic change while also minimizing potential undesirable consequences such as levee breach closure or channel incision.     

Integrating remotely acquired and field data to assess effects of setback levees on riparian and aquatic habitats in glacial‐melt water rivers

Setback levees, in which levees are reconstructed at a greater distance from a river channel, are a promising restoration technique particularly for alluvial rivers with broad floodplains where river‐floodplain connectivity is essential to ecological processes. Documenting the ecological outcomes of restoration activities is essential for assessing the comparative benefits of different restoration approaches and for justifying new restoration projects. Remote sensing of aquatic habitats offers one approach for comprehensive, objective documentation of river and floodplain habitats, but is difficult in glacial rivers because of high suspended‐sediment concentrations, braiding and a lack of large, well‐differentiated channel forms such as riffles and pools. Remote imagery and field surveys were used to assess the effects of recent and planned setback levees along the Puyallup River and, more generally, the application of multispectral imagery for classifying aquatic and riparian habitats in glacial‐melt water rivers. Airborne images were acquired with a horizontal ground resolution of 0.5 m in three spectral bands (0.545–0.555, 0.665–0.675 and 0.790–0.810 µm) spanning from green to near infrared (NIR) wavelengths. Field surveys identified river and floodplain habitat features and provided the basis for a comparative hydraulic analysis. Broad categories of aquatic habitat (smooth and rough water surface), exposed sediment (sand and boulder) and vegetated surfaces (herbaceous and deciduous shrub/forest) were classified accurately using the airborne images. Other categories [e.g. conifers, boulder, large woody debris (LWD)] and subdivisions of broad categories (e.g. riffles and runs) were not successfully classified either because these features did not form large patches that could be identified on the imagery or their spectral reflectances were not distinct from those of other habitat types. Airborne imagery was critical for assessing fine‐scale aquatic habitat heterogeneity including shallow, low‐velocity regions that were not feasible or practical to map in the field in many cases due to their widespread distribution, small size and poorly defined boundaries with other habitat types. At the reach‐scale, the setback levee affected the amount and distribution of riparian and aquatic habitats: (1) the area of all habitats was greater where levees had been set back and with relatively more vegetated floodplain habitat and relatively less exposed sediment and aquatic habitat, (2) where levees confine the river, less low‐velocity aquatic habitat is present over a range of flows with a higher degree of bed instability during high flows. As river restoration proceeds in the Pacific Northwest and elsewhere, remotely acquired imagery will be important for documenting its effects on the amount and distribution of aquatic and floodplain habitats, complimenting field data as a quantitative basis for evaluating project efficacy. Copyright © 2008 John Wiley & Sons, Ltd.     

Organic matter transport and retention in a blackwater stream recovering from flow augmentation and thermal discharge

Organic and inorganic seston, benthic organic matter and woody debris were studied in a blackwater stream/floodplain system recovering from flow augmentation and thermal discharges. The stream had received cooling waters from two nuclear reactors from the mid-1950s to 1968, resulting in flows over 10x greater than normal and temperatures that exceeded 70°C. Channel morphology was markedly altered, woody debris was removed or buried, and floodplain vegetation was destroyed. Fifteen years after termination of cooling water discharges, the stream continued to exhibit many characteristics of a disturbed system. Compared to an undistributed reference stream, the recovering stream had substantially less benthic organic matter, fewer snags and debris dams, and transported more organic and inorganic seston of all size fractions examined. Because of the importance of these biophysical factors in the structural morphology of blackwater streams, it is hypothesized that complete recovery will not be realized until the floodplain forest has matured and large woody debris is contributed to the stream channel.     

Carbon sequestration potential of process-based river restoration

Floodplain restoration can enhance the capacity for carbon sequestration by facilitating higher water tables, deposition of fine sediment, and increased input and residence time of organic matter. We measured floodplain soil organic carbon stocks in nine stream restoration projects across the western United States and compared them to nearby degraded and reference condition floodplains. Degraded floodplains had the lowest soil mean carbon stocks in the majority of floodplains measured (range 161–894 Mg C/ha), and reference stocks had the highest stocks (range 391–904 Mg C/ha) of those with statistically significant differences between the three categories. Across all sites measured, stream restoration sites, referred to as treatment sites, had stocks (range 203–1028 Mg C/ha) similar to degraded condition floodplains but the largest range. When modeled under degraded conditions, four out of nine of the treatment sites had significantly higher OC stocks than predicted. Climate and geologic variables are most influential in predicting carbon stocks, and floodplains in the interior western USA have the highest carbon stocks. As the demand for carbon sequestration increases due to climate change, ecologically responsible floodplain restoration provides a significant opportunity for carbon storage. However, despite the statistically significant relationships we observed in this dataset, the variations within the data in relation to degraded/treatment/reference categories illustrate the uncertainties in quantifying the effects of restoration on floodplain carbon stocks.     

复式断面河槽流速横向分布及其对滩唇形成的影响

通过对水流微小控制体进行受力分析,建立了复式断面流速横向分布模型,该模型考虑了侧向副流惯性力的影响。采用实验资料对该模型进行检验,模型计算值与实测值符合较好。运用该模型计算了不同条件下复式断面流速和挟沙力的横向分布,并定量分析了横向分布特性对滩唇形成的影响。分析表明,水流漫滩时,复式断面的横向挟沙力变幅较大,尤其是在主槽和河漫滩交界处,挟沙力减小迅速,而含沙量减小相对较小,泥沙发生淤积,容易形成滩唇。单从水流挟沙力角度考虑,水流漫滩后水深越小、滩槽的糙率差越大,越容易形成滩唇。     

Organic matter distribution in floodplains can be predicted using spatial and vegetation structure data

Riparian forest ecosystems play a significant role in the storage of organic carbon. However, the knowledge on the spatial patterns of organic matter distribution which is crucial to the assessment of the C sequestration potential of riparian ecosystems is still lacking. The aim of our study was to identify predictors of organic matter distribution in floodplain soils and vegetation. We analysed the depth distribution of soil horizons to 1 m below the surface, calculated the organic C content and quantified living biomass and woody debris at 67 sampling plots in the Donau–Auen National Park (Austria) along principle spatial gradients (longitudinal, lateral and vertical to river direction). Multiple regression models were fitted using hierarchical partitioning of spatial information, which was supplemented by forest stand parameters as possible predictors of soil C. The concentration of organic C in the subsoil horizons increased significantly with distance to the main channel. In addition, the thickness of soil horizons enriched with organic matter increased downstream which probably indicates the effect of riverbed changes over the last two centuries. Model prediction of soil parameters was improved with the inclusion of vegetation structure variables which are a consequence of local river dynamics. Highly dynamic locations indicated by higher stem numbers, greater understory vegetation cover, lower mean stem diameter and lower canopy cover showed significantly lower concentrations of soil organic C and lower total organic C stocks. We conclude that spatial information and vegetation structure can indicate gradients of geomorphic floodplain dynamic, which is the main driver of organic matter storage. Copyright © 2010 John Wiley & Sons, Ltd.     

EFFECTS OF GEOMORPHIC PROCESS DOMAINS ON RIVER ECOSYSTEMS: A COMPARISON OF FLOODPLAIN AND CONFINED VALLEY SEGMENTS

The geomorphic template of streams and rivers exerts strong controls on the structure and function of aquatic ecosystems. However, relationships between stream geomorphology and ecosystem structure and function are not always clear and have not been investigated equally across spatial scales. In montane regions, rivers often alternate between canyon‐confined segments and unconfined floodplain segments. Yet, few studies have evaluated how this pattern influences aquatic ecosystems. Here, we compared five confined river segments to five paired floodplain segments in terms of allochthonous inputs, aquatic primary producer and invertebrate production, stream retentive capacity, and aquatic invertebrate community composition. We found that floodplains had a higher (up to 4×) retentive capacity, a greater richness (58%) of aquatic invertebrates, and a distinctly different invertebrate community, relative to confined segments. Contrary to our expectations, allochthonous inputs were approximately 2× greater for confined segments, and aquatic primary and invertebrate production exhibited no consistent differences between segment types. However, results did indicate that floodplains had greater overall community respiration than confined segments. Together, these findings suggest that floodplain and confined segments do indeed differ in terms of aquatic ecosystem structure and function but not entirely as expected. Confined segments had greater allochthonous inputs but a lower capacity to retain those inputs, whereas floodplains had a high capacity to retain transported organic matter and also a more diverse community of invertebrates and higher overall community respiration to ‘digest’ retained organic matter. If these findings are generalizable, then they would indicate that confined segments are sources for organic matter within river networks, whereas floodplains act as filters, removing and processing organic matter transported from upstream confined segments. Copyright © 2013 John Wiley & Sons, Ltd.     

Regional differences in nutrient limitation in floodplains of selected European rivers: implications for rehabilitation of characteristic floodplain vegetation

Extremely high river discharges in 1993 and 1995 along the Dutch rivers Rhine and Meuse have increased the public awareness of possible safety threats. As a result the ‘Space for Rivers’ program was implemented, aiming at restoring physical space for the rivers in combination with ecological rehabilitation. However, the development of species‐rich vegetation types in these floodplain areas is lagging behind restoration targets and biogeochemical constraints may play a vital role in this. Biogeochemical, hydrological and vegetation data were collected in 111 plots in both rehabilitated and original floodplains in regulated and more pristine river systems in The Netherlands and Poland. Soil nutrient and soil pore water data were summarized by factor analysis and the subsequent principal components were compared to vegetation and hydrological data by correlation analysis. The correlation analyses between vegetation parameters including nutrient stoichiometry and the biogeochemical soil variables resulted in a remarkable difference between pristine and impacted river systems. The results suggest a clear N‐limitation of plant growth in pristine floodplains, and apparent absence of limitation in regulated, impacted floodplains. In addition, results indicate that flooding events do not lead to one‐way transport of sediment and nutrients from the river into the floodplains; rather they indicate that highly dynamic hydrological conditions prevent soils from accumulating organic matter and nutrients. This study shows that nutrient limitation in regulated floodplains shifted from distinctly N‐limited plant growth to no nutrient limitation at all, probably due to decades of high fertilizer and manure application and nutrient input by the rivers during flooding. The consequence of our findings for rehabilitation activities is that it might be necessary to restore nitrogen limitation in floodplain systems in order to create opportunities for a species‐rich floodplain vegetation, through nutrient removal by hay‐making. Copyright © 2006 John Wiley & Sons, Ltd.     

Impact of a 100‐year flood on vegetation,benthic invertebrates,riparian fauna and large woody debris standing stock in an alpine floodplain

This paper investigates the impact of a 100‐year flood in May 1999 on community composition and large woody debris standing stock in an alpine floodplain (Isar, Germany). Detailed pre‐flood data sampled from 1993 to 1998 are compared with the situation directly after the flood. In those parts of the Isar floodplain mainly covered with pioneer vegetation prior to flooding, the coverage of unvegetated gravel bars increased by 22% following the flood. However, the flood did not remove larger amounts of older successional vegetation stages (willow thickets, floodplain forest). No significant changes in the benthic invertebrate fauna were recorded. The lowest densities of riparian ground beetles (Carabidae) within the study were recorded one month after the flood. Two months later, the ground beetle densities increased to the highest values ever recorded, indicating the ground beetle's high potential for recolonization. These results highlight the degree of resilience of both the aquatic and the riparian invertebrate fauna. The flood also caused a significant increase in large woody debris standing stock; in one section the number of logs increased tenfold and the volume increased by a factor of 20, leading to the assumption that most woody debris in alluvial flood‐plains is provided by catastrophic events. Copyright © 2004 John Wiley & Sons, Ltd.     

北江大堤典型堤段管涌试验研究与分析

用北江大堤典型堤段的堤基粉细砂砾在玻璃水槽中模拟不同砂层厚度、埋深、层次结构及接触面粗糙度等条件下的管涌试验。论证了接触面加糙后能使临界坡降由光滑面的0．10提高到0．13～0．20。较细的上层砂和较粗的下层砂砾将有可能使临界坡降减小30％左右。最后，根据多层地基渗流理论推导出堤基渗流管涌发展的计算公式，并用三维有限元计算进行了验证。该公式可以用来估算管涌突发时的涌砂范围和继续向上游冲蚀发展的距离，以便判别危害大堤安全的程度。     

The influence of soil desiccation on plant production,nutrient uptake and plant nutrient availability in two French floodplain grasslands

The effects of summer soil desiccation on plant production and plant nutrient availability (determined by wet chemical extraction) in floodplain grasslands along the rivers Allier and Loire in France were investigated. Soil desiccation in these river floodplains is the result of human interference with the natural flooding regime of rivers, such as dam construction and gravel mining. Flooding periods along the Allier have a longer duration (maximum of 202 days as opposed to 38 days for the Loire). The main comparison was between floodplain grasslands along the two rivers. Additional comparisons were made between relatively high lying, wetter areas (‘ridges’) and low lying, drier areas (‘swales’) within both floodplains. Thus, areas with different soil moisture content were examined, independent of river influences. The availability of P was higher in the Allier floodplain than in the Loire floodplain, but it was similar between ridges and swales. It was concluded that P-availability was not related to soil wetness, but to river sedimentation. Plant production, plant nutrient uptake, and biologically mediated soil processes, such as N-mineralization and nitrification, were all higher on the wetter Allier floodplain and in the wetter swales. These higher process rates were noted where higher amounts of soil bound carbon and nutrients were found as well. Plant production, N-mineralization and nitrification were moisture limited at the dry ridge on the Loire floodplain, as moisture levels were below the wilting point here (pF>4.2). On the wetter parts of the floodplain, plant production was N-limited. This was concluded from low tissue N/P ratios (about 10) and a positive relation between plant production and N-mineralization. On the wetter parts, the rate of N-mineralization depended on the size of soil organic-N pools. The size of these pools was positively related to soil wetness, which can be interpreted as a positive effect of river flooding. Reduced flooding lowers the nutrient input to floodplains and contributes to the occurrence of soil desiccation in summer, which results in lower nutrient cycling and reduced accumulation of soil organic matter. These effects have negative consequences for important floodplain functions, such as nutrient retention and biomass production. © 1998 John Wiley & Sons, Ltd.     

堤防险情及其处置

长江中下游堤防多位于由表层弱透水层及下卧透水层组成的双层地基上，堤防及其地基、边滩在汛期出现的险情有散浸，管涌，流土、接触冲刷引起的渗水流砂、漏洞，穿堤建筑物渗漏，滑坡，崩岸，溢溢等。     

Coarse woody debris in stream channels in relation to river channel management in woodland areas

Although river channel management now generally uses soft rather than hard engineering techniques the considerable research achieved for woodland river channels has not been completely collated with reference to management implications. Research results from 22 research papers show how debris dams have a significant influence upon the morphological, the process and the ecological aspects of channels; vary in their permanence, and differ in stability according to the overall organic matter budget. A summary diagram contrasts the impact of dams on river channel morphology, process and ecology before and after dam removal. Four major types of specific recommendation about the management of channels in woodland areas are identified from 29 research papers are that (1) management should be undertaken against a background knowledge of the behaviour of coarse, woody debris under natural conditions and that the organic matter budget should be disturbed as little as possible; (2) logging operations should minimize the amount of disturbance to, and disruption of, channel processes; (3) management should optimize the maintenance of habitat diversity and minimize the ecological disturbance to the channel; (4) in some areas specific management practices may require the introduction of new material into the channel. These recommendations are applied to the New Forest, southern U.K., which has a long history of clearance and management of coarse woody debris and where the requirements for clearance in relation to fish, drainage, and aesthetic impact can be achieved by minimizing the amount of removal of material from the river channel. In managing channels with debris dams in woodland areas, it is desirable to work with the river in a holistic basin context.     

A Comparison of Main and Side Channel Physical and Water Quality Metrics and Habitat Complexity in the Middle Mississippi River

Worldwide large rivers have been severely modified by human intervention. Many modifications result in disconnection of the river from floodplain and off‐channel habitats generally characterized by lower velocities and Copyright © 2016 John Wiley & Sons, Ltd. shallower depths relative to the main channel, conditions vital to many organisms. Extensive levees on the Middle Mississippi River (MMR) have cut off backwater systems and disconnected the river from 80% of its floodplain. However, the system is characterized by large side channels associated with islands. We examined a long term data set for differences in physical (e.g. depth and velocity) and water quality metrics (e.g. temperature, suspended solids, dissolved oxygen, chlorophyll, % organic matter) between the main and side channels of a 128‐km reach of the MMR. We compared variability between main and side channels using the coefficient of variation (COV). All metrics differed between habitats. Side channels were shallower with lower velocities and had greater mean and COV of % organic matter and more variable dissolved oxygen concentrations. Velocity, temperature, and suspended solids were similar in the spring. COVs were lowest in both habitats during the spring for all metrics except temperature and DO. Resource management in the MMR tends to focus on maintaining existing side channels because of the difficulty of working in the heavily used navigation channel. This study shows that these actions protect areas that function differently than the main channel for most of the year. However, our results also highlight the need for restoration activities aimed at restoring floodplain connectivity, especially during the spring. Copyright © 2016 John Wiley & Sons, Ltd.     

Improved ecological development model for lower Yellow River floodplain,China

In this study, a model for the development of the wide floodplain in the lower Yellow River Basin, in China was developed. This model includes flood control schemes using grading criteria, enables sediment deposition in partitioned zones, and allows free exchange between channel runoff and sediment. The wide floodplain located between the main channel and levees is divided into three typical regions: the tender, low, and high floodplains. Different ecological models should be applied when these floodplains are constructed. This paper describes the associated research ideas and methodology, and clarifies several key issues, including sediment prediction and regulation, land planning, land use, and a multi-dimensional framework of safeguard measures for industries on the lower Yellow River floodplain. A refined ecological development model is proposed for the lower Yellow River floodplain, and future work on ecological and sustainable development of the lower floodplain is suggested. To establish a comprehensive system integrating runoff and sediment resource regulation in the Yellow River Basin, future work should focus on runoff and sediment exchange mechanisms in the wandering lower reaches. Furthermore, it is necessary to improve theories on floodplain planning and ecological construction, and these theories should be integrated with the research findings on land development across the lower Yellow River floodplain.     

Riprap Effect on Hydraulic Fracturing Process of Cohesive and Non-cohesive Protective Levees

A comprehensive experimental study was conducted to evaluate the effects of soil properties and the rip-rap as well as cohesive and non-cohesive soil material and the riprap particle size on the breaching process and the failure mechanism of the levee. The results showed the crucial role of the riprap coverage and the soil properties in the breaching of the protective levees. In this regard, breaching was developed in both vertical and transverse directions. In the levee without riprap coverage, breach development was observed in the transverse direction while the levee was eroded in the streamwise direction. In contrast, in the levee with riprap coverage, breach development mainly occurred in the vertical direction. Furthermore, the flow rate across the breach was higher in the tests with no riprap compared to those with the riprap coverage. Comparisons suggested that the shorter the failure time, the longer the equilibrium time. The present research has some major implications for coastal and hydraulic engineering designs since the construction of levees is of great importance. Furthermore, the findings can be used to predict flooding and erosion induced by the embankment failure.

     

Effect of flood regime on tree growth in the floodplain and surrounding uplands of the Wisconsin River

Flood regime and vegetation flood tolerance interact to influence tree growth in riverine landscapes. We studied tree growth in floodplain and upland forests of the Wisconsin River. About a century ago, levees set back from the river were constructed on this floodplain. The levee restricts some floodplain area from overbank flood events, but leaves a portion of active floodplain still inundated by floods. We addressed two questions: (1) how do growth rates of flood‐tolerant and flood‐intolerant tree species in the floodplain differ with flood regime? (2) At the stand level, how does growth rate differ with flood regime and between floodplain and upland areas? Annual tree growth rates from 1991 to 2000 were determined from tree increment cores for both individual species and stands. Tree growth rates of individual species varied between flood regimes. The most flood‐tolerant species (Betula nigra and Fraxinus pennsylvanica) grew faster in areas with active flooding, while the growth of less flood‐tolerant species (Quercus velutina and Q. ellipsoidalis) was depressed in swales and active floodplain. However, stand‐level tree growth did not differ between the floodplain and upland, or between flood regimes within the floodplain. Therefore, variation in the growth of individual species may not scale up to create differences in stand‐level tree growth because forest community composition varies spatially with flood regime. We suggest that growth rates are similar among sites because each community comprises of species adapted to their current flood regime. Copyright © 2008 John Wiley & Sons, Ltd.     

AHP法在河岸发展与河川管理评估方法之研究

台湾地区近年来经济发展促使国民对河川区域内土地利用及休闲游憩空间的需求也相应增加,为能适度开发该土地之经济价值,且在不影响河防安全之前提下,民众可依水利法及河川管理办法相关规定向河川管理机关申请许可使用,因此目前河川区域实际已是在多元利用中.本研究为探讨河川相关使用行为及亲水性活动之合适性,确立河川区域内使用行为评估体系,并运用多评准决策之分析阶层程序法(AHP),针对河防安全考虑、生态及自然环境维护及人文环境等条件提出一套评定量化的评估方法,建立评定各类许可使用行为对河防安全及河川环境维护之评估指数.研究结果显示,应用本文所提出之评估方法对于目前各种使用行为进行定性定量评估,显示评估后之指数分布情形,亦切实反应台湾河川目前实务管理现况情形.     

Effect of depth on food‐web interactions in a thermally stratified floodplain lake following inundation

We investigated the controlling mechanisms of microbial and metazooplankton food‐web components at the surface‐ and bottom‐water layers of a thermally stratified floodplain lake (Lake Sakada?, Kopa?ki Rit floodplain, Croatia) during its connection with the river. Throughout the study, the lake was stratified continuously. The permutational multivariate analysis of variance provided evidence that only the surface‐water layer was impacted on by the flow and flood pulses, whereas the bottom‐water layer represented a zone of stable environmental conditions. The water depth was by one order of magnitude more important in determining environmental variables and plankton abundance than the hydrological phases. Under such circumstances, path analysis provided evidence that the planktonic food‐web interactions were strongly influenced by the sample layer, regardless of the flooding conditions. The transfer of organic matter to higher trophic levels at the surface was dominated by herbivory and, to a lesser extent, by predation, whereas bottom‐water layer was represented by additional routes (bacterivory and omnivory). The transfer of organic matter was different through the investigated water layers, of which the surface‐water layer was additionally structured by the floodplain hydrology.     

Biogeomorphic characterization of floodplain forest change in response to reduced flows along the Apalachicola River,Florida

The Apalachicola–Chattahoochee–Flint (ACF) River basin is an important ecological and economic component of a three‐state region (Florida, Alabama and Georgia) in the southeastern U.S. Along the Apalachicola River in northwest Florida, the duration of floodplain inundation has decreased as a result of declining river levels. Spring and summer flows have diminished in volume because of water use, storage and evaporation in reservoirs, and other anthropogenic and climatic changes in the basin upstream. Channel erosion from dam construction and navigation improvements also caused river levels to decline in an earlier period. In this paper, we document trends in floodplain forest tree species composition for the interval spanning these influences. Historic tree inventories from the 1970s were compared to present‐day forests through non‐metric multidimensional scaling, indicator species analysis (ISA) and outlier detection. Forests are compositionally drier today than in the 1970s. Overstory to understory compositional differences within habitats (levees, high/low bottomland forest and backswamps) are as large as the species contrasts between habitats. Present‐day forests are also compositionally noisier with fewer indicator species. The largest individual declines in species density and dominance were in backswamps, particularly for Fraxinus caroliniana Nyssa ogeche and Nyssa aquatica. We discuss how contrasts in the compositional change signal for levee and backswamp landform habitats reflect a complex biogeomorphic response to fluctuating river flows for alluvial rivers in humid climates. Copyright © 2009 John Wiley & Sons, Ltd.