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1.
Worldwide convectively accelerated streams flowing in downstream-narrowing river sections show that riverbed vegetation growing on alluvial sediment bars gradually disappears, forming a front beyond which vegetation is absent. We revise a recently proposed analytical model able to predict the expected longitudinal position of the vegetation front. The model was developed considering the steady state approximation of 1-D ecomorphodynamics equations. While the model was tested against flume experiments, its extension and application to the field is not trivial as it requires the definition of proper scaling laws governing the observed phenomenon. In this work, we present a procedure to calculate vegetation parameters and flow magnitude governing the equilibrium at the reach scale between hydromorphological and biological components in rivers with converging boundaries. We collected from worldwide rivers data of section topography, hydrogeomorphological and riparian vegetation characteristics to perform a statistical analysis aimed to validate the proposed procedure. Results are presented in the form of scaling laws correlating biological parameters of growth and decay from different vegetation species to flood return period and duration, respectively. Such relationships demonstrate the existence of underlying selective processes determining the riparian vegetation both in terms of species and cover. We interpret the selection of vegetation species from ecomorphodynamic processes occurring in convectively accelerated streams as the orchestrated dynamic action of flow, sediment and vegetation characteristics. © 2019 John Wiley & Sons, Ltd.  相似文献   

2.
Solute transport in rivers is controlled by surface hydrodynamics and by mass exchanges with distinct retention zones. Surface and hyporheic retention processes can be accounted for separately in solute transport models with multiple storage compartments. In the simplest two component model, short term storage can be associated to in-channel transient retention, e.g. produced by riparian vegetation or surface dead zones, and the long-term storage can be associated to hyporheic exchange. The STIR (Solute Transport In Rivers) multiple domain transport model is applied here to tracer test data from three very different Mediterranean streams with distinctive characteristics in terms of flow discharge, vegetation and substrate material. The model is used with an exponential residence time distribution (RTD) to represent surface storage processes and two distinct modeling closures are tested to simulate hyporheic retention: a second exponential RTD and a power-law distribution approximating a known solution for bedform-induced hyporheic exchange. Each stream shows distinct retention patterns characterized by different timescales of the storage time distribution. Both modeling closures lead to very good approximations of the observed breakthrough curves in the two rivers with permeable bed exposed to the flow, where hyporheic flows are expected to occur. In the one case where the occurrence of hyporheic flows is inhibited by bottom vegetation, only the two exponential RTD model is acceptable and the time scales of the two components are of the same magnitude. The significant finding of this work is the recognition of a strong signature of the river properties on tracer data and the evidence of the ability of multiple-component models to describe individual stream responses. This evidence may open a new perspective in river contamination studies, where rivers could possibly be classified based on their ability to trap and release pollutants.  相似文献   

3.
The prediction of the morphological evolution of renaturalized streams is important for the success of restoration projects. Riparian vegetation is a key component of the riverine landscape and is therefore essential for the natural rehabilitation of rivers. This complicates the design of morphological interventions, since riparian vegetation is influenced by and influences the river dynamics. Morphodynamic models, useful tools for project planning, should therefore include the interaction between vegetation, water flow and sediment processes. Most restoration projects are carried out in USA and Europe, where rivers are highly intervened and where the climate is temperate and vegetation shows a clear seasonal cycle. Taking into account seasonal variations might therefore be relevant for the prediction of the river morphological adaptation. This study investigates the morphodynamic effects of riparian vegetation on a re‐meandered lowland stream in the Netherlands, the Lunterse Beek. The work includes the analysis of field data covering 5 years and numerical modelling. The results allow assessment of the performance of a modelling tool in predicting the morphological evolution of the stream and the relevance of including the seasonal variations of vegetation in the computations. After the establishment of herbaceous plants on its banks, the Lunterse Beek did not show any further changes in channel alignment. This is here attributed to the stabilizing effects of plant roots together with the small size of the stream. It is expected that the morphological restoration of similarly small streams may result in important initial morphological adaptation followed by negligible changes after full vegetation establishment. Copyright © 2018 John Wiley & Sons, Ltd.  相似文献   

4.
Pristine river corridors were characterized by island and floodplain development driven by the inter‐play of flows, sediments and woody vegetation. Here we explore these relationships within topographically controlled settings within the upper, middle and lower reaches of a large, semi‐natural alpine to mediterranean river. These reaches have expanding or contracting valley floors within which we show that there are more or less predictable patterns of stream power and rates of vegetation growth, reflecting water availability during dry periods and also the availability of sand and finer sediment. We relate these to the pattern of island distribution that is repeated within the three reaches and is indicative of the engineering role of riparian trees. Islands are shown to develop within thresholds defined by stream power, rates of woody vegetation growth and rates of sedimentation, and to develop most quickly where riparian species include those capable of sprouting from driftwood. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

5.
While it is well recognized that vegetation can affect erosion, sediment yield and, over longer timescales, landform evolution, the nature of this interaction and how it should be modeled is not obvious and may depend on the study site. In order to develop quantitative insight into the magnitude and nature of the influence of vegetation on catchment erosion, we build a landscape evolution model to simulate erosion in badlands, then calibrate and evaluate it against sediment yield data for two catchments with contrasting vegetation cover. The model couples hillslope gravitational transport and stream alluvium transport. Results indicate that hillslope transport processes depend strongly on the vegetation cover, whereas stream transport processes do not seem to be affected by the presence of vegetation. The model performance in prediction is found to be higher for the denuded catchment than for the reforested one. Moreover, we find that vegetation acts on erosion mostly by reducing soil erodibility rather than by reducing surface runoff. Finally, the methodology we propose can be a useful tool to evaluate the efficiency of previous revegetation operations and to provide guidance for future restoration work. © 2019 John Wiley & Sons, Ltd.  相似文献   

6.
River ecological functioning can be conceptualized according to a four‐dimensional framework, based on the responses of aquatic and riparian communities to hydrogeomorphic constraints along the longitudinal, transverse, vertical and temporal dimensions of rivers. Contemporary riparian vegetation responds to river dynamics at ecological timescales, but riparian vegetation, in one form or another, has existed on Earth since at least the Middle Ordovician (c. 450 Ma) and has been a significant controlling factor on river geomorphology since the Late Silurian (c. 420 Ma). On such evolutionary timescales, plant adaptations to the fluvial environment and the subsequent effects of these adaptations on fluvial sediment and landform dynamics resulted in the emergence, from the Silurian to the Carboniferous, of a variety of contrasted fluvial biogeomorphic types where water flow, morphodynamics and vegetation interacted to different degrees. Here we identify several of these types and describe the consequences for biogeomorphic structure and stability (i.e. resistance and resilience), along the four river dimensions, of feedbacks between riparian plants and hydrogeomorphic processes on contrasting ecological and evolutionary timescales. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

7.
This paper reviews the role of alluvial soils in vegetated gravelly river braid plains. When considering decadal timescales of river evolution, we argue that it becomes vital to consider soil development as an emergent property of the developing ecosystem. Soil processes have been relatively overlooked in accounts of the interactions between braided river processes and vegetation, although soils have been observed on vegetated fluvial landforms. We hypothesize that soil development plays a major role in the transition (speed and pathway) from a fresh sediment deposit to a vegetated soil‐covered landform. Disturbance (erosion and/or deposition), vertical sediment structure (process history), vegetation succession, biological activity and water table fluctuation are seen as the main controls on early alluvial soil evolution. Erosion and deposition processes may not only act as soil disturbing agents, but also as suppliers of ecosystem resources, because of their role in delivering and changing access (e.g. through avulsion) to fluxes of water, fine sediments and organic matter. In turn, the associated initial ecosystem may influence further fluvial landform development, such as through the trapping of fine‐grained sediments (e.g. sand) by the engineering action of vegetation and the deposit stabilization by the developing aboveground and belowground biomass. This may create a strong feedback between geomorphological processes, vegetation succession and soil evolution which we summarize in a conceptual model. We illustrate this model by an example from the Allondon River (Switzerland) and identify the research questions that follow. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

8.
Dynamic interaction between river morphodynamics and vegetation affects river channel patterns and populations of riparian species. A range of numerical models exists to investigate the interaction between vegetation and morphodynamics. However, many of these models oversimplify either the morphodynamics or the vegetation dynamics, which hampers the development of predictive models for river management. We have developed a model coupling advanced morphodynamics and dynamic vegetation, which is innovative because it includes dynamic ecological processes and progressing vegetation characteristics as opposed to commonly used static vegetation without growth and mortality. Our objective is to understand and quantify the effects of vegetation‐type dependent settling, growth and mortality on the river pattern and morphodynamics of a meandering river. We compared several dynamic vegetation scenarios with different functional trait sets to reference scenarios without vegetation and with static vegetation without growth and mortality. We find distinct differences in morphodynamics and river morphology. The default dynamic vegetation scenario, based on two Salicaceae species, shows an active meandering behaviour, while the static vegetation scenario develops into a static, vegetation‐dominated state. The diverse vegetation patterns in the dynamic scenario reduce lateral migration, increase meander migration rate and create a smoother floodplain compared to the static scenario. Dynamic vegetation results in typical vegetation patterns, vegetation age distribution and river patterns as observed in the field. We show a quantitative interaction between vegetation and morphodynamics, where increasing vegetation cover decreases sediment transport rates. Furthermore, differences in vegetation colonization, density and survival create distinct patterns in river morphology, showing that vegetation properties and dynamics drive the formation of different river morphologies. Our model demonstrates the high sensitivity of channel morphodynamics to various species traits, an understanding which is required for floodplain and stream restoration and more realistic modelling of long‐term river development. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

9.
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10.
Transporting capacity of overland flow on plane and on irregular beds   总被引：2，自引：0，他引：2  
In this paper the transporting capacity of thin flows, in the laminar and transitional flow regime, is studied. Experiments were carried out on irregular as well as on plane beds, using two totally different set-ups. The results of these two types of experiment were convergent. In both cases, sediment concentration was clearly related to grain shear velocity and unit stream power, expressed as the product of mean velocity and slope (Yang, 1973). The data agreed with those of Kramer and Meyer (1969). For a sandy bed, the unit stream power relationship was able to predict reasonably well the sediment concentrations measured on a mulched surface. For laminar and transitional flows, both the unit stream power and the shear velocity are related in the same way to slope and unit discharge. The unit stream power is a parameter which in particular can be very easily measured and might therefore become useful in obtaining a quick estimate of the transporting capacity of a thin flow. However, before a sediment transport equation for thin flows can be developed, more information is needed about the influence of the flow regime and grain size and density.  相似文献   

11.
Stream-water temperature is a key variable controlling chemical, biological, and ecological processes in freshwater environments. Most models focus on a single river cross-section; however, temperature gradients along stretches and tributaries of a river network are crucial to assess ecohydrological features such as aquatic species suitability, growth and feeding rates, or disease transmission. We propose SESTET, a deterministic, spatially explicit stream temperature model for a whole river network, based on water and energy budgets at a reach scale and requiring only commonly available spatially distributed datasets, such as morphology and air temperature, as input. Heat exchange processes at the air–water interface are modelled via the widely used equilibrium temperature concept, whereas the effects of network structure are accounted for through advective heat fluxes. A case study was conducted on the prealpine Wigger river (Switzerland), where water temperatures have been measured in the period 2014–2018 at 11 spatially distributed locations. The results show the advantages of accounting for water and energy budgets at the reach scale for the entire river network, compared with simpler, lumped formulations. Because our approach fundamentally relies on spatially distributed air temperature fields, adequate spatial interpolation techniques that account for the effects of both elevation and thermal inversion in air temperature are key to a successful application of the model. SESTET allows the assessment of the magnitude of the various components of the heat budget at the reach scale and the derivation of reliable estimates of spatial gradients of mean daily stream temperatures for the whole catchment based on a limited number of conveniently located (viz., spanning the largest possible elevation range) measuring stations. Moreover, accounting for mixing processes and advective fluxes through the river network allows one to trust regionalized values of the parameters controlling the relationship between equilibrium and air temperature, a key feature to generalize the model to data-scarce catchments.  相似文献   

12.
Geomorphology has increasingly considered the role of biotic factors as controls upon geomorphic processes across a wide range of spatial and temporal scales. Where timescales are long (centennial and longer), it has been possible to quantify relationships between geomorphic processes and vegetation using, for example, the pollen record. However, where the biotic agents are fauna, longer term reconstruction of the impacts of biological activity upon geomorphic processes is more challenging. Here, we review the prospect of using environmental DNA as a molecular proxy to decipher the presence and nature of faunal influences on geomorphic processes in both present and ancient deposits. When used appropriately, this method has the potential to improve our understanding of biotic drivers of geomorphic processes, notably fauna, over long timescales and so to reconstruct how such drivers might explain the landscape as we see it today. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

13.
Bar colonization by vegetation and subsequent island formation is a key bio-geomorphological process in fluvial landscape evolution. Here we investigate morphological and ecological evolution of river islands over timescales from single floods to decades, focusing on islands initiated by deposited trees that sprout to form vegetated patches. On a braided reach of the high-energy Tagliamento River, Italy, we monitored 30 pioneer islands of 1 to 17 years age in comparison with unvegetated bar surfaces, open areas between islands, and established island surfaces. We integrated morphological, surface sediment and vegetation properties of islands initiated by different flood events, combining evidence from remotely-sensed and ground observations, flow and climate time series. At a decadal timescale, pioneer islands aggrade rapidly to the elevation of the mean annual flood, showing a steady increase in vegetation canopy height, fining of surface sediments from predominantly gravel to silty-sand with a notable clay and organic fraction. The standing vegetation included over 130 species, with the largest number on island surfaces of intermediate elevation and flood disturbance. As islands age, standing vegetation becomes comprised mainly of competitor species with transient seed banks and typical of woodland, scrub, pasture and wetland habitats, whereas the winter seedbank is dominated on all surfaces by ruderal species with persistent seedbanks, mainly associated with aquatic, wetland, pasture, arable and wasteland habitats. At shorter timescales, the biogeomorphological trajectory of pioneer islands is initiated by large flood events that control the elevation of deposited trees, and subsequent flows that control tree survival and establishment. Island morphological evolution depends on the frequency-magnitude of sediment and seed delivery and redistribution by flood and possibly wind events, whereas island ability to retain sediments reflects the degree of vegetation establishment, which in the short-term may vary with seasonal to annual moisture supply, substrate characteristics and climatic growth conditions. © 2018 John Wiley & Sons, Ltd.  相似文献   

14.
Wetlands on the Vecht river plain in the Netherlands are threatened by pollution of ground water on the adjacent ridge ‘Het Gooi’. To assess the impact of this pollution, information is needed on the present groundwater flow pattern and hydrochemical processes occurring during flow. In the determination of hydrochemical processes past changes in flow patterns must be taken into consideration.

Over the past 600 years impoldering and groundwater extraction have induced important hydrological changes in the study area. Exercises with a two-dimensional finite difference groundwater model were used to study the effects of these changes on regional groundwater flow patterns. Steady-state simulations along a vertical section were carried out for four different points in time, namely, the 14th century, 1885, 1941 and 1985. Changes in flow patterns are inferred from a comparison of the steady-state simulations. The results indicate that groundwater flow changed from a simple pattern under natural conditions to a complex flow pattern dominated by artificially man-controlled hydraulic heads at present.

The computer simulations are used to estimate the effect of changes in flow patterns on regional groundwater composition. Data on the distribution of chloride and oxygen-18 in ground water provide a verification of the estimated effects and information on the present position of the fresh-brackish groundwater interface in the study area. Isochrones calculated by the model are used to estimate the position of this front where data on water composition are absent. The future displacement of the fresh-brackish groundwater front is inferred from the position of successive isochrones, assuming that the present flow pattern will remain in steady state.

The computer simulations provide a general framework for the determination of hydrochemical processes in future studies addressing the impact of groundwater pollution on wetlands in the river plain.  相似文献   


15.
The dynamics of dissolved and particulate N, P and organic C were examined for field drains, through a headwater (4 km2), into a mesoscale stream (51 km2) and river (1844 km2) catchment. Distributions of N and P forms were similar in the agricultural headwater and field drains; annual P fluxes of particulate and dissolved forms were of equal magnitude, whilst N was dominated by NO3–N. Across all scales organic P was an important, often dominant, component of the dissolved P. Temporal variation in nutrient concentrations and proportions was greatest in the headwater, where storms resulted in the generation of large concentrations of suspended particulate matter, particulate and dissolved P, particularly following dry periods. The data suggest that groundwater and minor point source inputs to the mesoscale catchment buffered the temporal variability in hydrochemistry relative to the headwater. Summer low flows were associated with large PO4–P concentrations in the mesoscale catchment at a critical time of biological sensitivity. At the largest river catchment scale, organic forms of C, N and P dominated. Inorganic nutrient concentrations were kept small through dilution by runoff from upland areas and biological processes converted dissolved N and P to particulate forms. The different processes operating between the drain/headwater to the large river scale have implications for river basin management. Given the prevalence of organic and particulate P forms in our catchment transect, the bioavailability of these fractions needs to be better understood.  相似文献   

16.
Stream power can be an extremely useful index of fluvial sediment transport, channel pattern, river channel erosion and riparian habitat development. However, most previous studies of downstream changes in stream power have relied on field measurements at selected cross‐sections, which are time consuming, and typically based on limited data, which cannot fully represent important spatial variations in stream power. We present here, therefore, a novel methodology we call CAFES (combined automated flood, elevation and stream power), to quantify downstream change in river flood power, based on integrating in a GIS framework Flood Estimation Handbook systems with the 5 m grid NEXTMap Britain digital elevation model derived from IFSAR (interferometric synthetic aperture radar). This provides a useful modelling platform to quantify at unprecedented resolution longitudinal distributions of flood discharge, elevation, floodplain slope and flood power at reach and basin scales. Values can be resolved to a 50 m grid. CAFES approaches have distinct advantages over current methodologies for reach‐ and basin‐scale stream power assessments and therefore for the interpretation and prediction of fluvial processes. The methodology has significant international applicability for understanding basin‐scale hydraulics, sediment transport, erosion and sedimentation processes and river basin management. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

17.
Changes in streamflow and water table elevation influence oxidation–reduction (redox) conditions near river–aquifer interfaces, with potentially important consequences for solute fluxes and biogeochemical reaction rates. Although continuous measurements of groundwater chemistry can be arduous, in situ sensors reveal chemistry dynamics across a wide range of timescales. We monitored redox potential in an aquifer adjacent to a tidal river and used spectral and wavelet analyses to link redox responses to hydrologic perturbations within the bed and banks. Storms perturb redox potential within both the bed and banks over timescales of days to weeks. Tides drive semidiurnal oscillations in redox potential within the streambed that are absent in the banks. Wavelet analysis shows that tidal redox oscillations in the bed are greatest during late summer (wavelet magnitude of 5.62 mV) when river stage fluctuations are on the order of 70 cm and microbial activity is relatively high. Tidal redox oscillations diminish during the winter (wavelet magnitude of 2.73 mV) when river stage fluctuations are smaller (on the order of 50 cm) and microbial activity is presumably low. Although traditional geochemical observations are often limited to summer baseflow conditions, in situ redox sensing provides continuous, high‐resolution chemical characterization of the subsurface, revealing transport and reaction processes across spatial and temporal scales in aquifers.  相似文献   

18.
B. Yellen  D.F. Boutt 《水文研究》2015,29(15):3261-3275
In humid regions, where gaining river conditions generally prevail, daily hydroelectric dam releases alter downstream surface water–groundwater interactions by reversing the head gradient between river and adjacent groundwater. Previously, it has been noted that artificial stage changes due to dam releases enhance hyporheic exchange. Here we investigate the regulated Deerfield River in northwestern Massachusetts at multiple scales to evaluate how changing downstream geologic conditions along the river mediate this artificial hyporheic pumping. Water budget analysis indicates that roughly 10% of bank‐stored water is permanently lost from the 19.5‐km river reach, likely as a result of transpiration by bank vegetation. An adjacent reference stream with similar dimensions and geomorphology, but without hydropeaking, shows predictable gaining conditions. Field observations from streambed piezometers and thermistors show that water losses are not uniform throughout the study reach. Riparian aquifer transmissivity in river sub‐reaches largely determines the magnitude of surface water–groundwater exchange as well as net water loss from the river. These newly documented losses from hydropeaking river systems should inform decisions by river managers and hydroelectric operators of additional tradeoffs of oscillatory dam‐release river management. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

19.
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20.
After more than 300 years of widespread and intensive river management, few examples of complex, unmanaged river systems remain within Europe. An exception is the Fiume Tagliamento, Italy, which retains a riparian woodland margin and unconfined river channel system throughout almost the entire 170 km length of its river corridor. A research programme is underway focusing on a range of related aspects of the hydrology, fluvial geomorphology and ecology of the Tagliamento. This paper contributes to that programme by focusing on large wood retention. The paper adopts a simple force:resistance approach at the scale of the entire river corridor in order to identify reaches of the river with a high wood retention potential. Information on the character of the river corridor is derived from 1:10 000 scale topographic maps. A range of indices measured at 330 transects across the river corridor supports a classification of the geomorphological style of the river which reflects the presence and abundance of properties previously identified in the literature as large wood retention sites. This classification provides a qualitative representation of the ‘resistance’ of the corridor to wood movement and thus its overall wood‐retention potential. The map‐derived indices are also used to extrapolate estimates of the ten year return period flood to each of the 330 transects so that the downstream pattern of unit stream power can be quantified as an index representing ‘force’ in the analysis. Although input of wood is an important factor in many river systems, it is assumed not to be a limiting factor along the Tagliamento, where riparian woodland is abundant. Field observations of large wood storage illustrate that wood retention at eight sites along the river reflects the presence and abundance of the features incorporated in the classification of geomorphological style, including the complexity of the channel network, the availability of exposed gravel areas, and the presence of islands. In general at the time of survey in August 1998, open gravel areas were estimated to store approximately 1 t ha−1 of wood in single‐thread reaches and 6 t ha−1 in multiple‐thread reaches. Established islands were estimated to store an average of 80 t ha−1 of wood. Nevertheless, there was considerable variability between sites, and pioneer islands, which are not represented on maps or readily identified from air photographs because of their small size, were estimated to store an order of magnitude more wood than established islands. Furthermore, the wood storage from this sample of eight sites did not reflect variability in estimated unit stream power. A series of areas for further research are identified, which can be explored using field data, and which will throw more light on the processes of wood retention in this extremely dynamic fluvial environment. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

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