The spatial and temporal patterns of aggradation in a temperate,upland, gravel‐bed river     

Emma K. Raven  Stuart N. Lane  Rob I. Ferguson  Louise J. Bracken 《地球表面变化过程与地形》2009,34(9):1181-1197

Intensive field monitoring of a reach of upland gravel‐bed river illustrates the temporal and spatial variability of in‐channel sedimentation. Over the six‐year monitoring period, the mean bed level in the channel has risen by 0·17 m with a maximum bed level rise of 0·5 m noted at one location over a five month winter period. These rapid levels of aggradation have a profound impact on the number and duration of overbank flows with flood frequency increasing on average 2·6 times and overbank flow time increasing by 12·8 hours. This work raises the profile of coarse sediment transfer in the design and operation of river management, specifically engineering schemes. It emphasizes the need for the implementation of strategic monitoring programmes before engineering work occurs to identify zones where aggradation is likely to be problematic. Exploration of the sediment supply and transfer system can explain patterns of channel sedimentation. The complex spatial, seasonal and annual variability in sediment supply and transfer raise uncertainties into the system's response to potential changes in climate and land‐use. Thus, there is a demand for schemes that monitor coarse sediment transfer and channel response. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Evaluation of floodplain variability considering impacts of climate change     

Mohammad Karamouz  Navideh Noori  Ali Moridi  Azadeh Ahmadi 《水文研究》2011,25(1):90-103

In this study, an approach is presented for handling hydraulic uncertainties in the prediction of floodplain. Different factors affect river flood characteristics. Furthermore, the high changeability of flooding conditions leads to high variability of the inundation. River morphology is one of the most effective factors in river flood characteristics. This factor is influenced by sedimentation and erosion in the river cross sections, which affects the discharge variation. The depth and the width of the river cross section lead to an increase or decrease in the river flow path. This results in changes in the extent of the floodplain based on the generated rainfall. The inundated region boundaries are determined by utilizing the mean first‐order second‐moment analysis. The proposed method is applied to the Kajoo River in the south‐eastern part of Iran. Determination of floodplain uncertainty is a damage‐reduction policy in this region. Also, it is useful to prepare the necessary activities for overcoming the flood hazards. Climate change is the second effective factor on the floodplain uncertainties. Climate change affects the magnitude, extent and depth of inundation and it may intensify the flood problem. Therefore, the future rainfall pattern of the study area under climate change is simulated to evaluate its impacts on the river flow characteristic. Subsequently, a hydraulic routing model is used to determine floodplain. Finally, the copula function is used to estimate the joint probability of the changes in the inundation area due to changes in river morphology and the rainfall changes due to impacts of climate change. Results show that the uncertainties of the extent of floodplain are affected by climate change and river morphology, leading to noticeable changes in the magnitude and frequency of floods. Evaluating these impacts and estimating corresponding river discharges will help in the study of river dynamics, and will also contribute towards devising effective mitigation and management strategies. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

A comparison of one‐ and two‐dimensional approaches to modelling flood inundation over complex upland floodplains     

V. Tayefi  S. N. Lane  R. J. Hardy  D. Yu 《水文研究》2007,21(23):3190-3202

A much understudied aspect of flood inundation is examined, i.e. upland environments with topographically complex floodplains. Although the presence of high‐resolution topographic data (e.g. lidar) has improved the quality of river flood inundation predictions, the optimum dimensionality of hydraulic models for this purpose has yet to be fully evaluated for situations of both topographic and topological (i.e. the connectivity of floodplain features) complexity. In this paper, we present the comparison of three treatments of upland flood inundation using: (a) a one‐dimensional (1D) model (HEC‐RAS v. 3·1·2) with the domain defined as series of extended cross‐sections; (b) the same 1D model, but with the floodplain defined by a series of storage cells, hydraulically connected to the main river channel and other storage cells on the floodplain according to floodplain topological characteristics; (c) a two‐dimensional (2D) diffusion wave treatment, again with explicit representation of floodplain structural features. The necessary topographic and topological data were derived using lidar and Ordnance Survey Landline data. The three models were tested on a 6 km upland reach of the River Wharfe, UK. The models were assessed by comparison with measured inundation extent. The results showed that both the extended cross‐section and the storage cell 1D modes were conceptually problematic. They also resulted in poorer model predictions, requiring incorrect parameterization of the main river to floodplain flux in order to approach anything like the level of agreement observed when the 2D diffusion wave treatment was assessed. We conclude that a coupled 1D–2D treatment is likely to provide the best modelling approach, with currently available technology, for complex floodplain configurations. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

Hydraulic and geomorphic processes in an overbank flood along a meandering,gravel‐bed river: implications for chute formation          下载免费PDF全文

Lee R. Harrison  Thomas Dunne  G. Burch Fisher 《地球表面变化过程与地形》2015,40(9):1239-1253

Hydraulic interactions between rivers and floodplains produce off‐channel chutes, the presence of which influences the routing of water and sediment and thus the planform evolution of meandering rivers. Detailed studies of the hydrologic exchanges between channels and floodplains are usually conducted in laboratory facilities, and studies documenting chute development are generally limited to qualitative observations. In this study, we use a reconstructed, gravel‐bedded, meandering river as a field laboratory for studying these mechanisms at a realistic scale. Using an integrated field and modeling approach, we quantified the flow exchanges between the river channel and its floodplain during an overbank flood, and identified locations where flow had the capacity to erode floodplain chutes. Hydraulic measurements and modeling indicated high rates of flow exchange between the channel and floodplain, with flow rapidly decelerating as water was decanted from the channel onto the floodplain due to the frictional drag provided by substrate and vegetation. Peak shear stresses were greatest downstream of the maxima in bend curvature, along the concave bank, where terrestrial LiDAR scans indicate initial floodplain chute formation. A second chute has developed across the convex bank of a meander bend, in a location where sediment accretion, point bar development and plant colonization have created divergent flow paths between the main channel and floodplain. In both cases, the off‐channel chutes are evolving slowly during infrequent floods due to the coarse nature of the floodplain, though rapid chute formation would be more likely in finer‐grained floodplains. The controls on chute formation at these locations include the flood magnitude, river curvature, floodplain gradient, erodibility of the floodplain sediment, and the flow resistance provided by riparian vegetation. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Sensitivity of a hydraulic model to channel erosion uncertainty during extreme flooding          下载免费PDF全文

Jefferson S. Wong  Jim E. Freer  Paul D. Bates  David A. Sear  Elisabeth M. Stephens 《水文研究》2015,29(2):261-279

Recent research into flood modelling has primarily concentrated on the simulation of inundation flow without considering the influences of channel morphology. River channels are often represented by a simplified geometry that is implicitly assumed to remain unchanged during flood simulations. However, field evidence demonstrates that significant morphological changes can occur during floods to mobilize the boundary sediments. Despite this, the effect of channel morphology on model results has been largely unexplored. To address this issue, the impact of channel cross‐section geometry and channel long‐profile variability on flood dynamics is examined using an ensemble of a 1D–2D hydraulic model (LISFLOOD‐FP) of the ~1 : 2000 year recurrence interval floods in Cockermouth, UK, within an uncertainty framework. A series of simulated scenarios of channel erosional changes were constructed on the basis of a simple velocity‐based model of critical entrainment. A Monte‐Carlo simulation framework was used to quantify the effects of this channel morphology together with variations in the channel and floodplain roughness coefficients, grain size characteristics and critical shear stress on measures of flood inundation. The results showed that the bed elevation modifications generated by the simplistic equations reflected an approximation of the observed patterns of spatial erosion that enveloped observed erosion depths. The effect of uncertainty on channel long‐profile variability only affected the local flood dynamics and did not significantly affect the friction sensitivity and flood inundation mapping. The results imply that hydraulic models generally do not need to account for within event morphodynamic changes of the type and magnitude of event modelled, as these have a negligible impact that is smaller than other uncertainties, e.g. boundary conditions. Instead, morphodynamic change needs to happen over a series of events to become large enough to change the hydrodynamics of floods in supply limited gravel‐bed rivers such as the one used in this research. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Dynamic flood topographies in the Terai region of Nepal     

E.H. Dingle  M.J. Creed  H.D. Sinclair  D. Gautam  N. Gourmelen  A.G.L. Borthwick  M. Attal 《地球表面变化过程与地形》2020,45(13):3092-3102

Flood hazard maps used to inform and build resilience in remote communities in the Terai region of southern Nepal are based on outdated and static digital elevation models (DEMs), which do not reflect dynamic river configuration or hydrology. Episodic changes in river course, sediment dynamics, and the distribution of flow down large bifurcation nodes can modify the extent of flooding in this region, but these processes are rarely considered in flood hazard assessment. Here, we develop a 2D hydrodynamic flood model of the Karnali River in the Terai region of west Nepal. A number of scenarios are tested examining different DEMs, variable bed elevations to simulate bed aggradation and incision, and updating bed elevations at a large bifurcation node to reflect field observations. By changing the age of the DEM used in the model, a 9.5% increase in inundation extent was observed for a 20-year flood discharge. Reducing horizontal DEM resolution alone resulted in a <1% change. Uniformly varying the bed elevation led to a 36% change in inundation extent. Finally, changes in bed elevation at the main bifurcation to reflect observed conditions resulted in the diversion of the majority of flow into the west branch, consistent with measured discharge ratios between the two branches, and a 32% change in inundation extent. Although the total flood inundation area was reduced (−4%), there was increased inundation along the west bank. Our results suggest that regular field measurements of bed elevation and updated DEMs following large sediment-generating events, and at topographically sensitive areas such as large river bifurcations, could help improve model inputs in future flood prediction models. This is particularly important following flood events carrying large sediment loads out of mountainous regions that could promote bed aggradation and channel switching across densely populated alluvial river systems and floodplains further downstream. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd  相似文献   

Impact of climate change on floodplain inundation and hydrological connectivity between wetlands and rivers in a tropical river catchment   总被引：1，自引：0，他引：1       下载免费PDF全文

Fazlul Karim  Cuan Petheram  Steve Marvanek  Catherine Ticehurst  Jim Wallace  Masud Hasan 《水文研究》2016,30(10):1574-1593

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A coupled sediment routing and lateral migration model for gravel‐bed rivers     

Emma K. Raven  Rob Ferguson  Stuart N. Lane 《水文研究》2011,25(12):1887-1898

We describe additions made to a multi‐size sediment routing model enabling it to simulate width adjustment simultaneously alongside bed aggradation/incision and fining/coarsening. The model is intended for use in single thread gravel‐bed rivers over annual to decadal timescales and for reach lengths of 1–10 km. It uses a split‐channel approach with separate calculations of flow and sediment transport in the left and right sides of the channel. Bank erosion is treated as a function of excess shear stress with bank accretion occurring when shear stress falls below a second, low, threshold. A curvature function redistributes shear stress to either side of the channel. We illustrate the model through applications to a 5·6‐km reach of the upper River Wharfe in northern England. The sediment routing component with default parameter values gives excellent agreement with field data on downstream fining and down‐reach reduction in bedload flux, and the width‐adjustment components with approximate calibration to match maximum observed rates of bank shifting give plausible patterns of local change. The approach may be useful for exploring interactions between sediment delivery, river management and channel change in upland settings. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Channel response to an extreme flood and sediment pulse in a mixed bedrock and gravel‐bed river          下载免费PDF全文

Andrew Nelson  Kathy Dubé 《地球表面变化过程与地形》2016,41(2):178-195

We exploit a natural experiment caused by an extreme flood (~500 year recurrence interval) and sediment pulse derived from more than 2500 concurrent landslides to explore the influence of valley‐scale geomorphic controls on sediment slug evolution and the impact of sediment pulse passage and slug deposition and dispersion on channel stability and channel form. Sediment slug movement is a crucial process that shapes gravel‐bed rivers and alluvial valleys and is an important mechanism of downstream bed material transport. Further, increased bed material transport rates during slug deposition can trigger channel responses including increases in lateral mobility, channel width, and alluvial bar dominance. Pre‐ and post‐flood LiDAR and aerial photographs bracketing the 2007 flood on the Chehalis River in south‐western Washington State, USA, document the channel response with high spatial and temporal definition. The sediment slug behaved as a Gilbert Wave, with both channel aggradation and sequestration of large volumes of material in floodplains of headwaters' reaches and reaches where confined valleys enter into broad alluvial valleys. Differences between the valley form of two separate sub‐basins impacted by the pulse highlight the important role channel and channel‐floodplain connectivity play in governing downstream movement of sediment slug material. Finally, channel response to the extreme flood and sediment pulse illustrate the connection between bed material transport and channel form. Specifically, the channel widened, lateral channel mobility increased, and the proportion of the active channel covered by bars increased in all reaches in the study area. The response scaled tightly with the relative amount of bed material sediment transport through individual reaches, indicating that the amount of morphological change caused by the flood was conditioned by the simultaneous introduction of a sediment pulse to the channel network. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Implications of climate change in the twenty‐first century for simulated magnitude and frequency of bed‐material transport in tributaries of the Saint‐Lawrence River     

Patrick M. Verhaar  Pascale M. Biron  Robert I. Ferguson  Trevor B. Hoey 《水文研究》2011,25(10):1558-1573

More frequent extreme flood events are likely to occur in many areas in the twenty‐first century due to climate change. The impacts of these changes on sediment transport are examined at the event scale using a 1D morphodynamic model (SEDROUT4‐M) for three tributaries of the Saint‐Lawrence River (Québec, Canada) using daily discharge series generated with a hydrological model (HSAMI) from three global climate models (GCMs). For all tributaries, larger flood events occur in all future scenarios, leading to increases in bed‐material transport rates, number of transport events and number of days in the year where sediment transport occurs. The effective and half‐load discharges increase under all GCM simulations. Differences in flood timing within the tributaries, with a shift of peak annual discharge from the spring towards the winter, compared to the hydrograph of the Saint‐Lawrence River, generate higher sediment transport rates because of increased water surface slope and stream power. Previous research had shown that channel erosion is expected under all GCMs' discharge scenarios. This study shows that, despite lower bed elevations, flood risk is likely to increase as a result of higher flood magnitude, even with falling base level in the Saint‐Lawrence River. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

A fast simplified model for predicting river flood inundation probabilities in poorly gauged areas          下载免费PDF全文

Christian Massari  Angelica Tarpanelli  Tommaso Moramarco 《水文研究》2015,29(10):2275-2289

The capability of a simple kinematic‐storage model (KSM) is analysed to be used as a tool for a Decision Support System for the evaluation of probability inundation maps in near real time in poorly gauged areas. KSM simulates the floodplain as a storage and assumes no exchange of momentum with the channel. For the in‐bank flow, the storage is modified through a coefficient for taking the variations of channel cross sections into account. The generalized likelihood uncertainty estimation approach is used for addressing the probability flood maps along with their associated uncertainties. The model is tested on two river reaches along the Tiber River in Central Italy where observed inundation maps are available for two recent flood events. Despite the inherent uncertainties present in the input data and in the model structure, the results show that the model reproduces reasonably well, in terms of both precision and accuracy, the observed inundated areas. Tests were performed at different digital elevation model resolutions, showing a small effect of the geometry on the maximum performance obtained. The very low computational times, the parsimony of the model and its low sensitivity to the quality of the geometry representation of the channel and the floodplain makes KSM very appealing for flood forecasting and early warning system applications in poorly gauged and inaccessible areas. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Hydrologic and geomorphic flow thresholds in the Lower Brazos River,Texas, USA     

Jonathan D. Phillips 《水文科学杂志》2013,58(9):1631-1648

Abstract

River science and management often require a design or reference discharge. The common (and sometimes unavoidable) use of such discharges may, however, obscure the fact that the magnitude and frequency of critical flows can differ due to various hydrological, geomorphological, and ecological criteria. Threshold stages and discharges were identified for six lower Brazos River, Texas gaging stations corresponding to thalweg connectivity, bed inundation, high sub-banktop flows, channel–floodplain connectivity (CFC), and overbank flooding. Critical flows were also identified for estimated thresholds for sandy bedform and medium gravel mobility, critical specific stream power for potential channel modifications, and cohesive-bank channel erosion. These thresholds have variable relationships to mean, median, and maximum flows. For four of the six stations, daily recurrence probabilities for all but flood flows are at least 1%, and as high as 11%. All stations achieve channel–floodplain connectivity at stages less than banktop. Estimated threshold flows for sediment mobility and channel erosion occur relatively frequently, with daily probabilities of 2–77%. Critical flows for bank erosion occur least often, and for sandy bedform and gravel mobility most often. Thalweg connectivity is always maintained at all sites, while bed inundation flows have a daily probability of about 80% or more. Overall, results suggest that no single flow level is dominant in hydrological or geomorphic dynamics, and that the frequency of a given threshold varies considerably even along a single river. The results support the idea that multiple flow levels and ranges are necessary to create and maintain the hydrological, geomorphological, and ecological characteristics of rivers, and that no single flow level is a reliable determinant of fluvial state.