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1.
We compare two approaches to modelling floodplain inundation: a raster‐based approach, which uses a relatively simple process representation, with channel flows being resolved separately from the floodplain using either a kinematic or diffusive wave approximation, and a finite‐element hydraulic model aiming to solve the full two‐dimensional shallow‐water equations. A flood event on a short (c. 4 km) reach of the upper River Thames in the UK is simulated, the models being validated against inundation extent as determined from satellite synthetic aperture radar (SAR) imagery. The unconstrained friction parameters are found through a calibration procedure, where a measure of fit between predicted and observed shorelines is maximized. The raster and finite‐element models offer similar levels of performance, both classifying approximately 84% of the model domain correctly, compared with 65% for a simple planar prediction of water surface elevation. Further discrimination between models is not possible given the errors in the validation data. The simple raster‐based model is shown to have considerable advantages in terms of producing a straightforward calibration process, and being robust with respect to channel specification. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

2.
The performances of a finite volume model (SFV) and finite element model (TELEMAC‐2D) in reproducing inundation on a 16 km reach of the river Severn, United Kingdom, are compared. Predicted inundation extents are compared with 4 airborne synthetic aperture radar images of a major flood event in November 2000, and these are used to calibrate 2 values of Manning's n for the channel and floodplain. The four images are shown to have different capacities to constrain roughness parameters, with the image acquired at low flow rate doing better in determining these parameters than the image acquired at approximately peak flow. This is assigned to the valley filling nature of the flood and the associated insensitivity of flood extent to changes in water level. The level of skill demonstrated by the models, when compared with inundation derived using a horizontal water free surface, also increases as flow rate drops. The two models show markedly different behaviours to the calibration process, with TELEMAC showing less sensitivity and lower optimum values for Manning's n than SFV. When the models are used in predictive mode, calibrated against one image and predicting another, SFV performs better than TELEMAC. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

3.
This paper outlines a numerical model for the prediction of floodplain inundation sequences, overbank deposition rates and deposit grain size distributions. The model has two main components: first, a simplified hydraulic scheme which predicts floodwater flow depths and velocities, and second, a sediment transport element which employs a mass balance relation describing suspended sediment dispersion by convective and diffusive processes and sediment deposition as a function of particle settling rates. These relationships are solved numerically on a finite difference grid that accurately replicates the complex topographic features typical of natural river floodplains. The model is applied to a 600 m reach of the River Culm, Devon, U.K. using data derived from a range of field and laboratory techniques. Continuous records of river stage and suspended sediment concentration provide the model's upstream boundary input requirements. These are supplemented by measurements of the in situ settling characteristics of the suspended sediment load. The model's sediment transport component is calibrated with the aid of a dataset of measured overbank deposition amounts derived from flood events over a 16 month period. The model is shown to predict complicated floodwater inundation sequences and patterns of suspended sediment dispersion and deposition, which are largely a product of the complex topography of the floodplain. These results compare favourably with observations of overbank processes and are an improvement over those of previous models which have employed relatively simple representations of floodplain geometry. © 1997 by John Wiley & Sons, Ltd.  相似文献   

4.
Two‐dimensional (2‐D) hydraulic models are currently at the forefront of research into river flood inundation prediction. Airborne scanning laser altimetry is an important new data source that can provide such models with spatially distributed floodplain topography together with vegetation heights for parameterization of model friction. The paper investigates how vegetation height data can be used to realize the currently unexploited potential of 2‐D flood models to specify a friction factor at each node of the finite element model mesh. The only vegetation attribute required in the estimation of floodplain node friction factors is vegetation height. Different sets of flow resistance equations are used to model channel sediment, short vegetation, and tall and intermediate vegetation. The scheme was tested in a modelling study of a flood event that occurred on the River Severn, UK, in October 1998. A synthetic aperture radar image acquired during the flood provided an observed flood extent against which to validate the predicted extent. The modelled flood extent using variable friction was found to agree with the observed extent almost everywhere within the model domain. The variable‐friction model has the considerable advantage that it makes unnecessary the unphysical fitting of floodplain and channel friction factors required in the traditional approach to model calibration. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

5.
The factors affecting the relationship between channel discharge and volume of inundation are discussed. For many floodplains this relationship is not simple, but involves hysteretic effects which vary according to the hydrological characteristics of individual floods and the way in which these interact with the surface form of the floodplain reach. Some methods of deriving or estimating the extent of the hysteresis on floodplain reaches are suggested, although an acute lack of available data prevents detailed examination at present. Further investigations are required before floodplain conductivity relations can be used as an aid to flood routing procedures or in floodplain management problems. A major priority must be the acquisition of sequential inundation data.  相似文献   

6.
The respiratory potential [i.e. electron transport system activity (ETSA)] of soils and sediments from five floodplain habitats (channel, gravel, islands, riparian forest and grassland) of the Urbach River, Switzerland, and actual respiration rate (R) of the same samples exposed to experimental inundation were measured. Measurements were carried out at three incubation temperatures (4°C, 12°C and 20°C), and ETSA/R ratios (i.e. exploitation of the overall metabolic capacity) were investigated to better understand the effects of temperature and inundation on floodplain functional heterogeneity. Furthermore, ETSA/R ratios obtained during experimental inundation were compared with ETSA/R ratios from field measurements to investigate the exploitation in total metabolic potential at different conditions. Lowest ETSA and R were measured in samples from channel and gravel habitats, followed by those from islands. Substantially higher values were measured in soils from riparian forest and grassland. Both ETSA and R increased with increasing temperature in samples from all habitats, while the ETSA/R ratio decreased because of a rapid response in microbial community respiration to higher temperatures. The metabolic capacity exploitation (i.e. ETSA/R) during experimental inundation was lowest in predominantly terrestrial samples (riparian forest and grassland), indicating the weakest response to wetted conditions. Comparison of experimentally inundated and field conditions revealed that in rarely flooded soils, the metabolic capacity was less exploited during inundation than during non‐flooded conditions. The results suggest high sensitivity in floodplain respiration to changes in temperature and hydrological regime. ETSA/R ratios are considered good indicators of changes in metabolic activity of floodplain soils and sediments, and thus useful to estimate the impact of changes in hydrological regime or to evaluate success of floodplain restoration actions. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

7.
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   

8.
The performance of two modelling approaches for predicting floodplain inundation is tested using observed flood extent and 26 distributed floodplain level observations for the 1997 flood event in the town of Usti nad Orlici in the Czech Republic. Although the one‐dimensional hydrodynamic model and the integrated one‐ and two‐dimensional model are shown to perform comparably against the flood extent data, the latter shows better performance against the distributed level observations. Comparable performance in predicting the extent of inundation is found to be primarily as a result of the urban reach considered, with flood extent constrained by road and railway embankments. Uncertainty in the elevation model used in both approaches is shown to have little effect on the reliability in predicting flood extent, with a greater impact on the ability in predicting the distributed level observations. These results show that reliability of flood inundation modelling in urban reaches, where flood risk assessment is of more interest than in more rural reaches, can be improved greatly if distributed observations of levels in the floodplain are used in constraining model uncertainties. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

9.
The main objective of this study was to quantify the error associated with input data, including various resolutions of elevation datasets and Manning’s roughness for travel time computation and floodplain mapping. This was accomplished on the test bed, the Grand River (Ohio, USA) using the HEC-RAS model. LiDAR data integrated with survey data provided conservative predictions, whereas coarser elevation datasets provided a positive difference in the travel time (11.03–15.01%) and inundation area (32.56–44.52%). The minimum differences in travel time and inundation area were 0.50–4.33% and 3.55–7.16%, respectively, when the result from LiDAR integrated with survey data was compared with a 10-m DEM integrated with survey data. The results suggest that a 10-m DEM in the channel and LiDAR data in the floodplain combined with survey data would be appropriate for a flood warning system. Additionally, Manning’s roughness of the channel section was found to be more sensitive than that of the floodplain. The decrease in inundation area was highest (8.97%) for the lower value of Manning’s roughness.  相似文献   

10.
When studying hydrological processes with a numerical model, global sensitivity analysis (GSA) is essential if one is to understand the impact of model parameters and model formulation on results. However, different definitions of sensitivity can lead to a difference in the ranking of importance of the different model factors. Here we combine a fuzzy performance function with different methods of calculating global sensitivity to perform a multi‐method global sensitivity analysis (MMGSA). We use an application of a finite element subsurface flow model (ESTEL‐2D) on a flood inundation event on a floodplain of the River Severn to illustrate this new methodology. We demonstrate the utility of the method for model understanding and show how the prediction of state variables, such as Darcian velocity vectors, can be affected by such a MMGSA. This paper is a first attempt to use GSA with a numerically intensive hydrological model. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

11.
For large‐scale sites, difficulties for applying coupled one‐dimensional (1D)/2D models for simulating floodplain inundation may be encountered related to data scarcity, complexity for establishing channel–floodplain connections, computational cost, long duration of floods and the need to represent precipitation and evapotranspiration processes. This paper presents a hydrologic simulation system, named SIRIPLAN, developed to accomplish this aim. This system is composed by a 1D hydrodynamic model coupled to a 2D raster‐based model, and by two modules to compute the vertical water balance over floodplain and the water exchanges between channel and floodplain. Results are presented for the Upper Paraguay River Basin (UPRB), including the Pantanal, one of the world's largest wetlands. A total of 3965 km of river channels and 140 000 km2 of floodplains are simulated for a period of 11 years. Comparison of observed and calculated hydrographs at 15 gauging stations showed that the model was capable to simulate distinct, complex flow regimes along main channels, including channel‐floodplain interactions. The proposed system was also able to reproduce the Pantanal seasonal flood pulse, with estimated inundated areas ranging from 35 000 km2 (dry period) to more than 120 000 km2 (wet period). Floodplain inundation maps obtained with SIRIPLAN were consistent with previous knowledge of Pantanal dynamics, but comparison with inundation extent provided by a previous satellite‐based study indicates that permanently flooded areas may have been underestimated. The results obtained are promising, and further work will focus on improving vertical processes representation over floodplains and analysing model sensitivity to floodplain parameters, time step and precipitation estimates uncertainty. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

12.
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   

13.
The Mekong Delta is one of the largest and most intensively used estuaries in the world. Each year it witnesses widespread flooding which is both the basis of the livelihood for more than 17 million people but also the major hazard. Therefore, a thorough understanding of the hydrologic and hydraulic features is urgently required for various planning purposes. While the general causes and characteristics of the annual floods are understood, the inundation dynamics in the floodplains in Vietnam which are highly controlled by dikes and other control structures have not been investigated in depth. Especially, quantitative analyses are lacking, mainly due to scarce data about the inundation processes in the floodplains. Therefore, a comprehensive monitoring scheme for channel and floodplain inundation was established in a study area in the Plain of Reeds in the northeastern part of the Vietnamese Delta. This in situ data collection was complemented by a series of high‐resolution inundation maps derived from the TerraSAR‐X satellite for the flood seasons 2008 and 2009. Hence, the inundation dynamics in the channels and floodplains, and the interaction between channels and floodplains, could be quantified for the first time. The study identifies the strong human interference which is governed by flood protection levels, cropping patterns and communal water management. In addition, we examine the tidal influence on the inundation in various parts of the Delta, since it is expected that climate change‐induced sea level rise will increase the tidal contribution to floodplain inundation. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

14.
A prototype two-dimensional finite element flow model for depth-averaged free surface flows was developed for floodplain environments. Limited refinement of the model's physical representation was undertaken and the enhanced scheme applied to an 11 km river channel/floodplain reach in the U.K. Preliminary model results indicate that this modelling approach can be used to identify dynamic variations in the flow field parameters over length scales of the order of 10-100 m. Potentially, such data have the ability to permit detailed analysis of short-term floodplain sedimentary dynamics.  相似文献   

15.
D. Yu  S. N. Lane 《水文研究》2006,20(7):1541-1565
High‐resolution data obtained from airborne remote sensing is increasing opportunities for representation of small‐scale structural elements (e.g. walls, buildings) in complex floodplain systems using two‐dimensional (2D) models of flood inundation. At the same time, 2D inundation models have been developed and shown to provide good predictions of flood inundation extent, with respect to both full solution of the depth‐averaged Navier–Stokes equations and simplified diffusion‐wave models. However, these models have yet to be applied extensively to urban areas. This paper applies a 2D raster‐based diffusion‐wave model to determine patterns of fluvial flood inundation in urban areas using high‐resolution topographic data and explores the effects of spatial resolution upon estimated inundation extent and flow routing process. Model response shows that even relatively small changes in model resolution have considerable effects on the predicted inundation extent and the timing of flood inundation. Timing sensitivity would be expected, given the relatively poor representation of inertial processes in a diffusion‐wave model. Sensitivity to inundation extent is more surprising, but is associated with: (1) the smoothing effect of mesh coarsening upon input topographical data; (2) poorer representation of both cell blockage and surface routing processes as the mesh is coarsened, where the flow routing is especially complex; and (3) the effects of (1) and (2) upon water levels and velocities, which in turn determine which parts of the floodplain the flow can actually travel to. It is shown that the combined effects of wetting and roughness parameters can compensate in part for a coarser mesh resolution. However, the coarser the resolution, the poorer the ability to control the inundation process, as these parameters not only affect the speed, but also the direction of wetting. Thus, high‐resolution data will need to be coupled to a more sophisticated representation of the inundation process in order to obtain effective predictions of flood inundation extent. This is explored in a companion paper. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

16.
《水文科学杂志》2013,58(6):1007-1012
Abstract

The effects of human activities on flood propagation, during the period 1878–2005, in a 190-km reach of the middle—lower portion of the River Po (Northern Italy) are investigated. A series of topographical, hydrological and inundation data were collected for the 1878 River Po geometry and the June 1879 flood event, characterised by an inundated area of 432 km2. The aim of the study is two-fold: (1) to show the applicability of flood inundation models in reconstructing historical inundation events, and (2) to assess the effects of human activities during the last century on flood propagation in the middle—lower portion of the River Po. Numerical simulations were performed by coupling a two-dimensional finite element code, TELEMAC-2D, with a one-dimensional finite difference code, HEC-RAS.  相似文献   

17.
Inundation patterns in two of the largest savanna floodplains of South America were studied by analysis of the 37‐GHz polarization difference observed by the Scanning Multichannel Microwave Radiometer (Nimbus‐7 satellite). Flooded area was estimated at monthly intervals for January 1979 through to August 1987 using mixing models that account for the major landscape units with distinctive microwave emission characteristics. Results are presented separately for five subregions in each of the two floodplain regions to show the spatial as well as temporal variability in inundation patterns. The total area inundated during the 9 years varied between 2069 and 78 460 km2 in the Llanos de Moxos (also spelled as Mojos; median area, 23 383 km2) and 1278 and 105 454 km2 in the Llanos del Orinoco (median, 25 374 km2), not including the open‐water area of permanent lakes and river channels. The correlation between flooded area and river stage was used to extend the inundation records over a 30‐year period in the Moxos (1967–97) and a 58‐year period (1927–85) in the Orinoco. Interannual variability in inundation is greater in the Moxos than the Orinoco. Comparison of these data, however, with a previously published analysis of the Pantanal wetland shows that inundation patterns in these two floodplain regions are not as variable across years as they are in the Pantanal. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

18.
This paper investigates the possibility of linking finite element modelled two-dimensional hydraulics with floodplain sedimentation rates derived from radionuclide dating techniques. The TELEMAC-2D system is used to simulate the full dynamic velocity vector and water depth distributions for a 1 in 12 year flood event for the River Culm, Devon. These are compared to patterns of medium-term (30– 100 years) sedimentation rates and a degree of correlation is found to exist. This information is used to comment on the complexity of flow and sediment deposition interactions in floodplain environments and to provide a research design for the development of a more fully integrated floodplain morphodynamic model. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

19.
The effect of land reclamation on the migration and accumulation of heavy metals and some pollutants in small rivers is determined. The study was conducted in the Middle Amur lowland in different phases of hydrological regime and at different extent of floodplain inundation. The formation of the hydrological regime in small rivers in this area is governed by the irregular annual runoff distribution. The seasonal character of flood periods requires water samples to be taken before spring flood (April) and after floods have passed (September–October), and at various extent of floodplain inundation. The field studies of water-courses were carried out in 2009–2014. The water samples were analyzed to determine the concentrations of heavy metals (iron, manganese, copper, nickel, cobalt, lead and zinc), suspended substances, organic carbon (total, dissolved, and suspended), humic and fulvic acids, and volatile organic compounds. The mobility of heavy metals in surface watercourses was shown to reflect the effect of drainage and surface runoff from soil horizons, an increase in the concentrations of suspended and organic compounds, especially, fulvic acids, which enhance their geochemical mobility. During floods, an increase in heavy metals washout from floodplain soils and the dilution of their concentrations causes the formation of a single-type concentration series of heavy metals. In addition, the processes of pollutants migration show an effect of changes in the geomorphological characteristics of floodplain–channel complexes and a decrease in flow velocity in watercourses in the areas where land reclamation was applied. Thus, all factors mentioned above lead to a decrease in water pollution index in the river.  相似文献   

20.
Restoring hydrologic connectivity between channels and floodplains is common practice in stream and river restoration. Floodplain hydrology and hydrogeology impact stream hydraulics, ecology, biogeochemical processing, and pollutant removal, yet rigorous field evaluations of surface water–groundwater exchange within floodplains during overbank floods are rare. We conducted five sets of experimental floods to mimic floodplain reconnection by pumping stream water onto an existing floodplain swale. Floods were conducted throughout the year to capture seasonal variation and each involved two replicate floods on successive days to test the effect of varying antecedent moisture. Water levels and specific conductance were measured in surface water, soil, and groundwater within the floodplain, along with surface flow into and out of the floodplain. Vegetation density varied seasonally and controlled the volume of surface water storage on the floodplain. By contrast, antecedent moisture conditions controlled storage of water in floodplain soils, with drier antecedent moisture conditions leading to increased subsurface storage and slower flood wave propagation across the floodplain surface. The site experienced spatial heterogeneity in vertical connectivity between surface water and groundwater across the floodplain surface, where propagation of hydrostatic pressure, preferential flow, and bulk Darcy flow were all mechanisms that may have occurred during the five floods. Vertical connectivity also increased with time, suggesting higher frequency of floodplain inundation may increase surface water–groundwater exchange across the floodplain surface. Understanding the variability of floodplain impacts on water quality noted in the literature likely requires better accounting for seasonal variations in floodplain vegetation and antecedent moisture as well as heterogeneous exchange flow mechanisms. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

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