太湖流域经济发展及其对洪涝的影响

太湖流域是我国最发达的地区之一,流域社会经济发展迅速,经济总量在全国占重要地位。太湖流域经济发展的特点是：经济发展迅速、城市化规模大、流域内区域差异明显。本文就经济发展所带来的洪涝问题做了分析,具体表现为：经济发展,地区承灾能力下降,洪涝灾害损失加大;土地利用变化,流域产水量增加,改变了洪涝形势;地面下沉影响了防洪工程的效益;圩区建设在发挥巨大的防洪除涝效益的同时,也带来负面效益。     

Comparison of hydrodynamic models of different complexities to model floods with emergency storage areas

A flood emergency storage area (polder) is used to reduce the flood peak in the main river and hence, protect downstream areas from being inundated. In this study, the effectiveness of a proposed flood emergency storage area at the middle Elbe River, Germany in reducing the flood peaks is investigated using hydrodynamic modelling. The flow to the polders is controlled by adjustable gates. The extreme flood event of August 2002 is used for the study. A fully hydrodynamic 1D model and a coupled 1D–2D model are applied to simulate the flooding and emptying processes in the polders and flow in the Elbe River. The results obtained from the 1D and 1D–2D models are compared with respect to the peak water level reductions in the Elbe River and flow processes in the polders during their filling and emptying. The computational time, storage space requirements and modelling effort for the two models are also compared. It is concluded that a 1D model may be used to study the water level and discharge reductions in the main river while a 1D-2D model may be used when the study of flow dynamics in the polder is of particular interest. Further, a detailed sensitivity analysis of the 1D and 1D–2D models is carried out with respect to Manning's n values, DEMs of different resolutions, number of cross-sections used and the gate opening time as well as gate opening/closing duration. Copyright © 2008 John Wiley & Sons, Ltd.     

Modified sediments and subsurface hydrology in natural and recreated salt marshes and implications for delivery of ecosystem services

Recreation or restoration of salt marsh through the deliberate removal of flood defences (managed realignment or de‐embankment) is a common practice across Europe and the USA, with potential to enhance delivery of ecosystem services. However, recent research suggests that physical, chemical and ecological processes may be impaired in recreated sites as a result of the modified morphology, sediment structure and hydrology associated with both the restoration process and historic land use. This paper compares physical sediment properties and subsurface water levels recorded in paired natural and de‐embanked (recreated) salt marshes in SE England. Using a combination of statistical and time‐series modelling, significant differences between the natural and recreated marshes are identified. Sediment properties (bulk density, moisture content and organic content) within each marsh were statistically different and imply that de‐embanked sediments are compacted, which may affect subsurface water movement. Analysis of hydrological time series reveals that the de‐embanked salt marsh is characterized by a damped response to tidal flooding with elevated and less variable water levels. This, combined with analysis of hydrographs and hysteresis patterns over individual tidal cycles, suggests that fast, horizontal near‐surface flows enhanced by the relict land surface may play a greater role in drainage of the de‐embanked salt marsh. The importance of hydrological functioning in governing many important physical and biogeochemical processes in salt marshes suggests any modifications would have significant implications for the delivery of ecosystem services. Copyright © 2014 John Wiley & Sons, Ltd.     

Development of a polder module in the SWAT model: SWATpld for simulating polder areas in south‐eastern China

Polders are one of the most common artificial hydrological entities in the plain river network regions of China. Due to enclosed dikes, manual drainage, and irrigation intake operations, polders have had a significant impact on the hydrological processes of these areas. Distributed hydrological models are effective tools to understand and reproduce the hydrological processes of a watershed. To date, however, few models are able to simulate the drainage and irrigation intake interactions of polders at a watershed scale. This study develops a modified version of the Soil and Water Assessment Tool (SWAT) model, which is designed to better represent polders (SWATpld). The SWATpld model simulates drainage and irrigation intake processes by calculating the excess‐water storage in the inner rivers and irrigation schedule for paddy rice in the polder. Both SWAT and SWATpld models were tested for the Liyang watershed. SWATpld outperformed SWAT in simulating the daily discharge and intake of the experimental polder and predicting the monthly peak flow at the outlet of the Liyang watershed, which suggests that the modified model simulates the hydrological responses of the study watershed with polder operations more realistically than the original SWAT model does. Further evaluation at various locations and in various climate conditions would increase the confidence of this model.     

Modelling hydrological processes and nutrient retention in plain polders

Application of the Soil and Water Assessment Tool (SWAT) model is limited in plain polders, where hydrological and nutrient processes are confined by water conservancy facilities such as dikes and pumping stations. Watershed delineation techniques are proposed to enable SWAT to simulate these processes in a plain polder in Jiangxiang Town (Nanchang County, Jiangxi Province, China). Drainage unit division and multiple-outlet modelling approaches are introduced, and the main river network and land features are incorporated into a digital elevation model (DEM), so that drainage unit delineation can agree well with real flow direction and concentration. The impoundments of pumping stations are regarded as functioning like reservoirs, which are set up in the SWAT model to simulate confined hydrological processes. The results show that confined hydrological and nutrient processes in plain polders are simulated well; the retention rates of total nitrogen and total phosphorus are estimated as, respectively, 39% and 29% in both streams and impoundments.     

Effect of the spatial organization of land use on muddy flooding from cultivated catchments and recommendations for the adoption of control measures

Sediment‐laden runoff from arable fields has increasingly been recognized as a threat to housing, infrastructure and watercourses in Western Europe. Research suggests that land‐use change is far more important than any changes in rainfall in explaining recent increases in muddy flooding. However, the importance of changes in the organization of fields in the catchment has been overlooked. The loss of field boundaries has led to the loss of traditional sites of sediment deposition and an increase in the risk of sediment export via valley‐bottom ephemeral gullies. Successful schemes to combat muddy flooding have been pioneered in Flanders. The installation of grassed waterways in topographically controlled concentrated runoff pathways and the creation of sediment deposition structures are effective and efficient muddy flooding control measures. A supportive legislative and financial framework is also essential. The situation in Flanders is contrasted to that in the South Downs National Park, UK, where few measures to combat muddy flooding have been introduced and a supportive framework is lacking. Copyright © 2015 John Wiley & Sons, Ltd.     

Challenging assumptions of future coastal habitat development around the UK

One habitat management requirement forced by 21st century relative sea‐level rise (RSLR), will be the need to re‐comprehend the dimensions of long‐term transgressive behaviour of coastal systems being forced by such RSLR. Fresh approaches to the conceptual modelling and subsequent implementation of new coastal and peri‐marine habitats will be required. There is concern that existing approaches to forecasting coastal systems development (and by implication their associated scarce coastal habitats) over the next century depend on a certain premise of orderly spatial succession of habitats. This assumption is shown to be questionable given the possible future rates of RSLR, magnitude of shoreline retreat and the lack of coastal sediment to maintain the protective morphologies to low‐energy coastal habitats. Of these issues, sediment deficiency is regarded as one of the major problem for future habitat development. Examples of contemporary behaviour of UK coasts show evidence of coastal sediment starvation resulting from relatively stable RSLR, anthropogenic sealing of coastal sources, and intercepted coastal sediment pathways, which together force segmentation of coastal systems. From these examples key principles are deduced which may prejudice the existence of future habitats: accelerated future sediment demand due to RSLR may not be met by supply and, if short‐ to medium‐term hold‐the‐line policies predominate, long‐term strategies for managed realignment and habitat enhancement may prove impossible goals. Methods of contemporary sediment husbandry may help sustain some habitats in place but otherwise, instead of integrated coastal organization, managers may need to consider coastal breakdown, segmentation and habitat reduction as the basis of 21st century coastal evolution and planning. Copyright © 2006 John Wiley & Sons, Ltd.     

Development of flood hazard maps of Bangladesh using NOAA-AVHRR images with GIS

Abstract

Flood hazard maps were developed using remote sensing (RS) data for the historical event of the 1988 flood with data of elevation height, and geological and physiographic divisions. Flood damage depends on the hydraulic factors which include characteristics of the flood such as the depth of flooding, rate of the rise in water level, propagation of a flood wave, duration and frequency of flooding, sediment load, and timing. In this study flood depth and “flood-affected frequency” within one flood event were considered for the evaluation of flood hazard assessment, where the depth and frequency of the flooding were assumed to be the major determinant in estimating the total damage function. Different combinations of thematic maps among physiography, geology, land cover and elevation were evaluated for flood hazard maps and a best combination for the event of the 1988 flood was proposed. Finally, the flood hazard map for Bangladesh and a flood risk map for the administrative districts of Bangladesh were proposed.     

FLOW PATTERNS AND DAMAGE OF DIKE OVERTOPPING

Damage of a dike may result in severe damage and suffering. To reduce downstream damage and loss of life, it is important to study the process of breaching of the damaged dike. It is not possible to understand the damage process without a clear understanding of the flow patterns encountered. In the present study, data obtained from nine experimental runs are analyzed. The flow patterns and progressive damage of dike overtopping are investigated. Two types of phenomena at the dike surface: erosion; and erosion and sliding, are observed during the overtopping event. Four stages of dike damage can be distinguished. The degradation rate of the dike crest is found to be dependent on the downstream slope of the dike. The degradation rate is higher when the downstream slope is steeper.     

平原圩区磷素流失过程模拟

圩区是太湖流域平原区的主要地理单元,其磷素流失是造成平原区水污染的重要原因之一,定量模拟圩区磷素流失过程是非点源磷污染控制的重要环节.以太湖流域的典型圩区——尖圩为研究对象,根据物质守恒原理构建圩区磷素流失过程模型,模型考虑了圩区自然降雨、人工灌溉、洪涝排水、地面渗漏、作物需水、水面蒸发、沟渠磷素拦截等过程,充分体现了圩区系统磷素流失特征;通过已有研究案例、实地监测与野外调研相结合的方法确定模型参数;模拟结果表明:(1)与太湖流域平原非圩区相比,圩区的年度磷素流失量较低(-0.17~0.54 kg/(hm2·a)),并且年度差异显著;(2)人工灌溉与自然降雨是圩区磷素输入的主要渠道,其磷素输入量分别为0.27~0.69、1.05~1.19 kg/(hm2·a);水体下渗和洪涝排水是圩区磷素的输出途径,其磷素输出量分别为1.04~1.06、0.65~0.93 kg/(hm2·a).     

Modelling the effects of climatic and hydrological regime changes on the sediment dynamics of the Fraser River Basin,British Columbia,Canada

Future sediment dynamics may be affected by changing climates or hydrological regimes because of the close link between hydrology and sediment erosion, deposition, and transport. Previously, investigations of these potential changes have been constrained by a combination of limited observational data, hydrological drivers, and appropriate mechanistic models. Additionally, there is often ambiguity regarding how to disentangle the impacts of climate and hydrology from direct human factors such as reservoirs and land‐use change, which often exert more control over sediment dynamics. In this study, we utilize a recently developed, large‐scale, distributed, mechanistic sediment transport model to project future sediment erosion, deposition, and transportation within the Fraser River Basin in British Columbia, Canada—a basin with historical water flux and sediment load observations and limited anthropogenic influences upstream of its delta. The sediment model is driven by synthetic land‐surface hydrology derived from Scenarios A1B, A2, and B1 of the Special Report on Emissions Scenarios, which were provided by the Pacific Climate Impacts Consortium. Resulting simulations of water flux and sediment load from 1965 to 1994 are first validated against observational data then compared with future projections. Future projections show an overall increase in annual hillslope erosion and in‐channel transportation, a shift towards earlier spring peak erosion and transportation, and longer persistence of the sediment signal through the year. These shifts in timing and annual yield may have deleterious effects on spawning sockeye salmon and are insufficient to counteract future coastal retreat caused by sea‐level rise.     

Root properties of vegetation communities and their impact on the erosion resistance of river dikes

Predicted climate change and the associated sea level rise poses an increased threat of flooding due to wave overtopping events at sea and river dikes. To safeguard the land from flooding it is important to keep the soil erosion resistance at the dikes high. As plant roots can be very effective in reducing soil erosion rates by concentrated flow, the main goal of this study is to explore the variability in root system characteristics of five dike vegetation communities along the Scheldt River (Belgium) and to assess their effectiveness in controlling soil erosion rates during concentrated flow. This study is the first one to investigate systematically the erosion‐reducing potential of the root properties of representative dike vegetation communities in a temperate humid climate. Results show that the presence of Urtica dioica resulted in large differences in root length density (RLD) among dike vegetation communities. Observed RLD values in the topsoil ranged from 129 to 235 km m^‐3 for dike vegetation communities without U. dioica, while smaller values ranging from 22 to 58 km m^?3 were found for vegetation communities with U. dioica. The erosion‐reducing effect of the dike vegetation communities was estimated based on a global Hill curve model, linking the RLD to the soil detachment ratio (SDR; i.e. the ratio of the soil detachment rate for root‐permeated topsoils to the soil detachment rate for root‐free topsoils). Concentrated flow erosion rates are likely to be reduced to 13–16% of the erosion rates for root‐free topsoils if U. dioica is absent compared to 22–30% for vegetation communities with U. dioica. Hence, to maintain a high resistance of the soil against concentrated flow erosion it is important to avoid the overgrowth of grassland by U. dioica through an effective vegetation management. Copyright © 2016 John Wiley & Sons, Ltd.     

Scour and flow field around a spur dike in a 90° bend

Spur dike is an important element in fiver training that creates rapid variations in flow field, sediment transport and bed topography. The mechanism of flow and sediment transport in a channel bend is very complex, especially when a spur dike is constructed in a bend. Most of previous investigations on flow behavior and scour around spur dike were carried out in straight channels. In this paper results of experiments on flow field and scour around a spur dike in a 90 degree channel bend are presented, Sand with uniform grain size was used as the bed material, Experiments were conducted for different locations and different lengths of spur dikes at the bend with different values of discharge, The three dimensional flow fields around a spur dike were investigated, The maximum depth of scour was correlated to the Froude numbers, lengths and the locations of spur dike in the bend.     

Peculiarities of the hydrological regime of the Ganges and Brahmaputra river mouth area

The basic peculiarities of the hydrological regime of one of the largest mouth areas of the world, i.e., the common mouth of the rivers of Ganges and Brahmaputra, are discussed. The main features of natural conditions (including climatic) of the mouth of these rivers and the delta drainage system are characterized. The hydrological regime of the Ganges and Brahmaputra rivers, the largest rivers of South Asia, is studied in greater detail; the quantitative assessments of the water and sediment runoff of these rivers are specified. Provision is made for revealing the basic peculiarities of river flow distribution among numerous delta branches, annual floods during southwest monsoons, tidal phenomena in the maritime zone of the delta, and disastrous storm surges and inundations in the period of tropical cyclones. Flood control measures taken in Bangladesh to protect the population and lands are described.     

The formation and closure of the Big Breach of Sacalin spit associated with extreme shoreline retreat and shoreface erosion

We document a case of exceptionally large natural breaching of a sandy spit (Sacalin spit, Danube Delta) using multiannual to seasonal surveys of topography and bathymetry on successive cross-barrier and shoreface profiles, LiDAR data, satellite imagery, and wind and wave data. The large breach, which quickly reached 3.4 km in May 2014, is attributed to morphological preconditioning of the narrow (50–150 m) barrier, which was susceptible to breaching even during moderate storm conditions. The event switched the barrier's decadal evolution from low cross-shore transport to high cross-shore transport over the barrier, which is an order of magnitude larger than during the non-breach period. Upper shoreface erosion, as indicated by the extensive erosion down to −4 m, indicates that this zone is a significant source for the rebuilding of the barrier. Barrier recovery and widening trigger a negative feedback which limits the back-barrier sediment transfer. As a result, back-barrier deposition decreases whilst the barrier aggradation through overwash becomes more frequent. The Big Breach (TBB) closed naturally in three years. The very high deposition rate of sediment in the breach is a testimony of the high sediment volumes supplied by the longshore transport and the high sediment released through shoreface retreat, and resulted in widening the barrier to a maximum of 1 km. Since the newly-formed barrier shoreline retreated 500 m, this reveals that barrier breaching is an important mechanism which significantly accelerates the landward migration of the barrier system and is a proof of the highly non-linear morphodynamics involved in the barrier island translation. © 2019 John Wiley & Sons, Ltd.     

Temporal variability of contemporary floodplain sedimentation in the Rhine–Meuse delta,The Netherlands

It is often believed that extreme but infrequent events are most important in the development of landforms. When evaluating the overall effect of large floods on floodplain sedimentation, quantitative measurements of both high- and low-magnitude events should be considered. To analyse the role of flood magnitude on floodplain sedimentation, we measured overbank sedimentation during floods of different magnitude and duration. The measurements were carried out on two embanked floodplain sections along the rivers Rhine and Meuse in The Netherlands, using sediment traps made of artificial grass. The results showed an increase in total sediment accumulation with flood magnitude, mainly caused by enhanced accumulation of sand. At low floodplain sections the increase in sediment deposition was smaller than expected from the strong increase in suspended sediment transport in the river. Spatial variability in sediment accumulation was found to depend both on flood magnitude and duration. Deposition of sand on natural levees mainly takes place during high-magnitude floods, whilst low floods and slowly receding floods are important for the deposition of silt and clay in low-lying areas, at greater distance from the main channel. © 1998 John Wiley & Sons, Ltd.     

Reconstruction of eroded and deposited sediment volumes of the embanked River Waal,the Netherlands,for the period ad 1631–present

In the last few centuries humans have modified rivers, and rivers have responded with noticeable changes in sedimentary dynamics. The objective of this study is to assess these responses of the sedimentary dynamics. Therefore, we calculated a sediment budget for eroded and deposited sediment volumes in a ~12‐km long floodplain section of the largest semi‐natural embanked but still dynamic lower Rhine distributary, for ~50‐years time slices between ad 1631 and present. This is the period during which embanked floodplains were formed by downstream migration of meander bends between confining dykes. Our sediment budget involves a detailed reconstruction of vertical and lateral accretion rates and erosion rates of floodplain sediment. To do so, we developed a series of historical geomorphological maps, and lithogenetic cross‐sections. Based on the maps and cross‐sections, we divided the floodplain into building blocks representing channel bed and overbank sediment bodies. Chronostratigraphy within the blocks was estimated by interpretation of heavy metal profiles and from optically stimulated luminescence (OSL) dating results. Sediment budgets were hence calculated as a change of volume of each building block between time steps. The amount of lateral accretion initially increased, as a result of island and sand bar formation following embankment. From the eighteenth century onwards, there was a decrease of lateral processes in time, which is a result of straightening of the river by human activities, and a reduction of water and sediment supply due to the construction of a new upstream bifurcation. With straightening of the river, the floodplain area grew. Artificial fixation of the channel banks after ad 1872 prevented lateral activity. From then on, overbank deposition became the main process, leading to a continuous increase of floodplain elevation, and inherent decrease of flooding frequency and sediment accumulation rate. Copyright © 2014 John Wiley & Sons, Ltd.     

Relative sea-level rising and its control strategy in coastal regions of China in the 21st century

Nearly 55% of Chinese GNP is out of and 70% of large-middle cities are located in the coastal regions, where there are vast plains and river-mouth deltas, covering 14% of the total land area and 40% of the nation抯 population. Since the 1980s, the coastal…     

Input-output Balances of Nutrients and Plankton in a Flooded Area of the Lower Odra

The retention of particulate matter of the Odra River in flooded areas was estimated by determining suspended particulate matter (SPM) elimination and particle-bound nutrient retention in a polder area of the Lower Odra Valley national park. Water and suspended matter samples collected before, during, and after the 1997 summer flood at the inlet and the outlet of the investigated polder (Polder A/B close to Schwedt) offer the opportunity to balance the matter retention inside the floodplain. The maximum level of retained SPM (more than 80%) was calculated for the record flood of summer 1997, while in ordinary winter floods retention differs between 33% and 70%. Basic properties of the flowing particles like settling velocity, density, loss on ignition etc. change on their way through the polder area. In the investigated Polder A/B a retention of at least 50% of particle-bound phosphorus which was independent of the incoming suspended matter load from the Odra River was observed. The retention of particle-bound nitrogen and carbon varied seasonally to different extents. The presented balance demonstrates that particle-bound nutrient retention in polders is an important factor in the self-purification process of the river system. Some additional effort was done to study changes of plankton composition: during a joint field experiment in spring 1998, the authors determined biological parameters (abundance and biomass of phytoplankton and zooplankton) of water samples at polder inflow and outflow points.     

Determining flow patterns and emplacement dynamics from tsunami deposits with no visible sedimentary structure

In the absence of eyewitness reports or clear sedimentary structures, it can be difficult to interpret tsunami deposits or reconstruct tsunami inundation patterns. The emplacement dynamics of two historical tsunami deposits were investigated at seven transects in Okains Bay, New Zealand, using a combined geospatial, geomagnetic and sedimentological approach. The tsunami deposits are present as layers of sand and silt intercalated between soils and become finer and thinner with distance inland. The deposits are attributed to the 1960 and possibly the 1868 tsunamis, based on radiometric dating and correlation with historical records. Measurements of Magnetic Fabric (MF: Anisotropy of Magnetic Susceptibility) and particle size were used to reconstruct the evolution of flow dynamics laterally and vertically. A combination of statistical methods, including spatial autocorrelation testing, Spearman's rank order correlation, Principal Component Analysis (PCA) and K‐means cluster analysis, was applied to examine relationships between MF parameters and sediment texture, and infer depositional hydrodynamics. Flow patterns deduced from MF show the estuary channel acted as a conduit for inundation, with flow commonly aligned sub‐perpendicular to the estuary bed. MF and sediment data suggest deposition occurred from settling during laminar flow. Evidence of both uprush and backwash deposition, as well as wave reflection from infrastructure, was found. Statistical analysis of data showed significant relationships between grain size parameters and MF parameters associated with flow speed and magnetic fabric type. PCA and cluster analysis differentiated samples into two primary hydrodynamic groups: (1) samples deposited from laminar flow; and (2) samples deposited close to the limit of inundation, which includes samples deposited further inland, those affected by flow convergence, and those in the upper part of tsunami deposits. This approach has potential as a tool for reconstructing hydrodynamic conditions for palaeotsunamis and by combining spatial and statistical analyses, large‐scale investigations can be more easily performed. Copyright © 2016 John Wiley & Sons, Ltd.