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1.
Research over the last decade has shown that the suspended sediment loads of many rivers are dominated by composite particles. These particles are also known as aggregates or flocs, and are commonly made up of constituent mineral particles, which evidence a wide range of grain sizes, and organic matter. The resulting in situ or effective particle size characteristics of fluvial suspended sediment exert a major control on all processes of entrainment, transport and deposition. The significance of composite suspended sediment particles in glacial meltwater streams has, however, not been established. Existing data on the particle size characteristics of suspended sediment in glacial meltwaters relate to the dispersed mineral fraction (absolute particle size), which, for certain size fractions, may bear little relationship to the effective or in situ distribution. Existing understanding of composite particle formation within freshwater environments would suggest that in‐stream flocculation processes do not take place in glacial meltwater systems because of the absence of organic binding agents. However, we report preliminary scanning electron microscopy data for one Alpine and two Himalayan glaciers that show composite particles are present in the suspended sediment load of the meltwater system. The genesis and structure of these composite particles and their constituent grain size characteristics are discussed. We present evidence for the existence of both aggregates, or composite particles whose features are largely inherited from source materials, and flocs, which represent composite particles produced by in‐stream flocculation processes. In the absence of organic materials, the latter may result solely from electrochemical flocculation in the meltwater sediment system. This type of floc formation has not been reported previously in the freshwater fluvial environment. Further work is needed to test the wider significance of these data and to investigate the effective particle size characteristics of suspended sediment associated with high concentration outburst events. Such events make a major contribution to suspended sediment fluxes in meltwater streams and may provide conditions that are conducive to composite particle formation by flocculation. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

2.
Properties of suspended particulate matter play a vital role in transport processes, but information from boreal lowland river systems with high organic loads is limited. This study analysed data from 2 years of sampling at 30 locations in Finland (204 samples in total) using suspended particulate matter samplers to determine effective and absolute particle size and organic fractions. Mean d50 value was 22 and 49 µm for absolute and effective particle size, respectively. The organic fraction content ranged from 2.1% to 36% (mean 9.6%), highlighting the importance of particle organic matter for suspended particulate matter flux in the region. The results indicated that the suspended particulate matter particle size distribution and load in the study region is dominated by composite particles. There were considerable spatial and temporal variations in transport of organic fractions, effective particle size and degree of aggregation (range 1.5–93%). Headwaters and, in particular, late summer and spring flood conditions with flow peaks produced the largest composite particles, whereas agriculture‐dominated sites produced smaller but more tightly compacted particles. Organic plant fibres appeared to play a vital role in floc formation in peat‐covered catchments, whereas in agriculture‐dominated catchments, land use‐derived aggregates dominated the composition. This study provides empirical evidence of the importance of effective particle size measurement in understanding the dynamics of suspended particulate matters in boreal lowland river systems. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

3.
Delivery of fine sediment to fluvial systems is of considerable concern given the physical and ecological impacts of elevated levels in drainage networks. Although it is possible to measure the transfer of fine sediment at high frequency by using a range of surrogate and automated technologies, the demands for assessing sediment flux and sediment properties at multiple spatially distributed locations across catchments can often not be met using established sampling techniques. The time‐integrated mass‐flux sampler (TIMS) has the potential to bridge this gap and further our understanding of fine sediment delivery in fluvial systems. However, these devices have undergone limited testing in the field. The aim of this paper was to provide a critical validation of TIMS as a technique for assessing fluvial fine sediment transfer. Fine sediment flux and sediment properties were assessed over 2 years with individual sampling periods of approximately 30 days. Underestimation of sediment flux ranged between 66% and 99% demonstrating that TIMS is unsuitable for assessing absolute sediment loads. However, assessment of relative efficiency showed that six of seven samplers produced statistically strong relationships with the reference sediment load (P < 0.05). Aggregated data from all sites produced a highly significant relationship between reference and TIMS loads (R2 = 0.80; P < 0.001) demonstrating TIMS may be suitable for characterizing patterns of suspended sediment transfer. Testing also illustrated a consistency in sediment properties between multiple samplers in the same channel cross section. TIMS offers a useful means of assessing spatial and temporal patterns of fine sediment transfer across catchments where expensive monitoring frameworks cannot be commissioned. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

4.
Collecting a representative time‐integrated sample of fluvial fine‐grained suspended sediment (<63 μm) is an important requirement for the understanding of environmental, geomorphological, and hydrological processes operating within watersheds. This study (a) characterized the hydrodynamic behaviour of a commonly used time‐integrated fine sediment sampler (TIFSS) using an acoustic Doppler velocimeter (ADV) in controlled laboratory conditions and (b) measured the mass collection efficiency (MCE) of the sampler by an acoustic Doppler current profiler under field conditions. The laboratory results indicated that the hydrodynamic evaluations associated with the original development of the TIFSS involved an underestimation of the inlet flow velocity of the sampler that results in a significant overestimation of the theoretical MCE. The ADV data illustrated that the ratio of the inlet flow velocity of the sampler to the ambient velocity was 87% and consequently, it can be assumed that a representative sample of the ambient fine suspended particles entered into the sampler. The field results showed that the particle size distribution of the sediment collected by the TIFSS was statistically similar to that for the ambient sediment in the Red River, Manitoba, Canada. The MCE of the TIFSS in the field trials appeared to be as low as 10%. Collecting a representative sample in the field was consistent with the previous findings that the TIFSS is a suitable sampler for the collection of a representative sample of sufficient mass (e.g., >1 g) for the investigation of the properties of fluvial fine‐grained suspended sediment. Hydrodynamic evaluation of the TIFSS under a wider range of hydraulic conditions is suggested to assess the performance of the sampler during high run‐off events.  相似文献   

5.
The accurate measurement of suspended sediment (<200 μm) in aquatic environments is essential to understand and effectively manage changes to sediment, nutrient, and contaminant concentrations on both temporal and spatial scales. Commonly used sampling techniques for suspended sediment either lack the ability to accurately measure sediment concentration (e.g., passive sediment samplers) or are too expensive to deploy in sufficient number to provide landscape‐scale information (e.g., automated discrete samplers). Here, we evaluate a time‐integrated suspended sediment sampling technique, the pumped active suspended sediment (PASS) sampler, which collects a sample that can be used for the accurate measurement of time‐weighted average (TWA) suspended sediment concentration and sediment particle size distribution. The sampler was evaluated against an established passive time‐integrated suspended sediment sampling technique (i.e., Phillips sampler) and the standard discrete sampling method (i.e., manual discrete sampling). The PASS sampler collected a sample representative of TWA suspended sediment concentration and particle size distribution of a control sediment under laboratory conditions. Field application of the PASS sampler showed that it collected a representative TWA suspended sediment concentration and particle size distribution during high flow events in an urban stream. The particle size distribution of sediment collected by the PASS and Phillips samplers were comparable and the TWA suspended sediment concentration of the samples collected using the PASS and discrete sampling techniques agreed well, differing by only 4% and 6% for two different high flow events. We should note that the current configuration of the PASS sampler does not provide a flow‐weighted measurement and, therefore, is not suitable for the determination of sediment loads. The PASS sampler is a simple, inexpensive, and robust in situ sampling technique for the accurate measurement of TWA suspended sediment concentration and particle size distribution.  相似文献   

6.
Suspended sediment has been identified as a vector for nutrient and contaminant transport in the fluvial environment. A time‐integrated sampler (the Phillips sampler), which emerged over a decade ago as a cost‐effective tool for in situ suspended sediment collection, is increasingly being used to collect samples for the analysis of sediment properties such as particle size composition, and nutrient and contaminant concentrations. This study evaluates the sampler under both flume and field conditions for efficiency in the mass and grain size of the suspended sediment collected. The sampler was tested in a flume using both kaolinite and sediment samples (sieved to < 180 µm) collected from the Quesnel River, British Columbia, Canada. In the kaolinite trails, the sampler preferentially collected coarser grain sizes compared to the original sediment, probably due to finer sediment remaining in suspension and therefore passing through the sampler, and also possibly due to flocculation of the kaolinite upon introduction to the flume. Conversely, the sampler collected river sediment that was finer than the original sediment, probably due to some settling of coarser sediment observed at the bottom of the flume. Once allowance was made for these operational issues associated with the flume, maximum sediment mass efficiency for kaolinite and river sediment was 43% and 87%, respectively. Sediment collected by the time‐integrated sampler during field deployment and adjacent channel bed sediment were also compared. The sampler collected sediment with a representative grain size distribution. However, there were differences in the geochemical (arsenic and selenium) concentrations of channel bed sediment and sediment collected by the Phillips sampler which may be a function of differences in the behavior of geochemical elements associated with the two types of sediment. This work suggests that further research is needed to evaluate the role of the Phillips sampler in collecting sediment for contaminant and nutrient analysis. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

7.
Some of the problems associated with the estimation of contaminant loads transported by rivers using infrequent samples are described. The reliability of many load estimates, particularly those for substances where particulate-associated transport predominates, is questioned. A case study of the accuracy and precision of estimates of the suspended sediment load of the River Exe at Thorverton for the period 1978–1980 is used to demonstrate the potential reliability of loads calculated using a variety of estimation procedures. Underestimation and lack of precision are shown to be important problems.  相似文献   

8.
Hysteresis in the relationship between suspended sediment concentration and flow during run-off events is commonly used to inform on sediment sources and hydrological pathways. Less attention, however, has been paid to comparing the water and sediment hydrographs, which provide a more direct appreciation of in-event sediment dynamics and their relationship with the upstream catchment characteristics. The aim of this study is to better understand the catchment and hydrological controls on the phasing of water and sediment discharges during events and, in particular, to explore what controls sediment concentrations late on event recessions. Continuous records of flow and turbidity data (calibrated to suspended sediment concentration) were collected from 17 catchments across New Zealand for this purpose. Relationships between event sediment yield and peak flow showed, as anticipated, higher event sediment loads were generated in pasture compared with forested catchments and were also higher from catchments in more erodible terrain. One novel result was that these differences were greater during smaller, more frequent events, whereas the loads from larger flood events tended to converge between pasture and forest catchments. Another novel result was that event sediment load tends to be evenly split between rising and falling stages of the hydrograph in pasture catchments, but forested catchments yield more of their event loads on flood recessions, probably because of delayed erosion or more sediment sources remote from the channel network. Land cover, distance of the sediment sources from the monitoring site, and size of the catchments control sediment concentrations late on event recession. Pasture-dominated and more erodible catchments show longer sediment recessions and therefore stay dirtier for longer time periods. In addition, the size of previous flood events appeared to control the extent of sediment exhaustion after the flood peaks in some catchments.  相似文献   

9.
1 INTRODUCTION The particle size of sediment eroded from basins can provide basic information about erosion processes (Meyer et al., 1980), which can be divided into sheet wash sediment processes on hill slopes and fluvial sediment processes in rivers. In…  相似文献   

10.
In spite of the important relationship between sediment particle size and the transport/deposition of adsorbed pollutants in fluvial systems, little information regarding the size characteristics of suspended sediment transported by southern Ontario Great Lakes tributaries is currently available. This paper examines long-term sediment and hydrometric data collected by the Water Resources Branch of Environment Canada in order to provide information on (1) typical particle size distributions of suspended sediment, (2) relationships between source material and particle size characteristics of suspended sediment, and (3) temporal variation in the particle size characteristics of suspended sediment from six southern Ontario rivers. Results illustrate the complex behaviour and variability of sediment particle size transport in these rivers and demonstrate the need for a better understanding of seasonal effects on sediment availability and conveyance processes in fluvial systems.  相似文献   

11.
Fine sediment delivery to and storage in stream channel reaches can disrupt aquatic habitats, impact river hydromorphology, and transfer adsorbed nutrients and pollutants from catchment slopes to the fluvial system. This paper presents a modelling tool for simulating the time‐dependent response of the fine sediment system in catchments, using an integrated approach that incorporates both land phase and in‐stream processes of sediment generation, storage and transfer. The performance of the model is demonstrated by applying it to simulate in‐stream suspended sediment concentrations in two lowland catchments in southern England, the Enborne and the Lambourn, which exhibit contrasting hydrological and sediment responses due to differences in substrate permeability. The sediment model performs well in the Enborne catchment, where direct runoff events are frequent and peak suspended sediment concentrations can exceed 600 mg l?1. The general trends in the in‐stream concentrations in the Lambourn catchment are also reproduced by the model, although the observed concentrations are low (rarely exceeding 50 mg l?1) and the background variability in the concentrations is not fully characterized by the model. Direct runoff events are rare in this highly permeable catchment, resulting in a weak coupling between the sediment delivery system and the catchment hydrology. The generic performance of the model is also assessed using a generalized sensitivity analysis based on the parameter bounds identified in the catchment applications. Results indicate that the hydrological parameters contributing to the sediment response include those controlling (1) the partitioning of runoff between surface and soil zone flows and (2) the fractional loss of direct runoff volume prior to channel delivery. The principal sediment processes controlling model behaviour in the simulations are the transport capacity of direct runoff and the in‐stream generation, storage and release of the fine sediment fraction. The in‐stream processes appear to be important in maintaining the suspended sediment concentrations during low flows in the River Enborne and throughout much of the year in the River Lambourn. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

12.
Since the 1970s, there has been both continuing and growing interest in developing accurate estimates of the annual fluvial transport (fluxes and loads) of suspended sediment and sediment‐associated chemical constituents. This study provides an evaluation of the effects of manual sample numbers (from 4 to 12 year?1) and sample scheduling (random‐based, calendar‐based and hydrology‐based) on the precision, bias and accuracy of annual suspended sediment flux estimates. The evaluation is based on data from selected US Geological Survey daily suspended sediment stations in the USA and covers basins ranging in area from just over 900 km2 to nearly 2 million km2 and annual suspended sediment fluxes ranging from about 4 Kt year?1 to about 200 Mt year?1. The results appear to indicate that there is a scale effect for random‐based and calendar‐based sampling schemes, with larger sample numbers required as basin size decreases. All the sampling schemes evaluated display some level of positive (overestimates) or negative (underestimates) bias. The study further indicates that hydrology‐based sampling schemes are likely to generate the most accurate annual suspended sediment flux estimates with the fewest number of samples, regardless of basin size. This type of scheme seems most appropriate when the determination of suspended sediment concentrations, sediment‐associated chemical concentrations, annual suspended sediment and annual suspended sediment‐associated chemical fluxes only represent a few of the parameters of interest in multidisciplinary, multiparameter monitoring programmes. The results are just as applicable to the calibration of autosamplers/suspended sediment surrogates currently used to measure/estimate suspended sediment concentrations and ultimately, annual suspended sediment fluxes, because manual samples are required to adjust the sample data/measurements generated by these techniques so that they provide depth‐integrated and cross‐sectionally representative data. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.  相似文献   

13.
Large rivers have been previously shown to be vertically heterogeneous in terms of suspended particulate matter (SPM) concentration, as a result of sorting of suspended solids. Therefore, the spatial distribution of suspended sediments within the river section has to be known to assess the riverine sedimentary flux. Numerous studies have focused on the vertical distribution of SPM in a river channel from a theoretical or experimental perspective, but only a few were conducted so far on very large rivers. Moreover, a technique for the prediction of depth‐integrated suspended sediment fluxes in very large rivers based on sediment transport dynamics has not yet been proposed. We sampled river water along depth following several vertical profiles, at four locations on the Amazon River and its main tributaries and at two distinct water stages. Depending on the vertical profile, a one‐ to fivefold increase in SPM concentration is observed from river channel surface to bottom, which has a significant impact on the ‘depth‐averaged’ SPM concentration. For each cross section, a so‐called Rouse profile quantitatively accounts for the trend of SPM concentration increase with depth, and a representative Rouse number can be measured for each cross section. However, the prediction of this Rouse number would require the knowledge of the settling velocity of particles, which is dependent on the state of aggregation affecting particles within the river. We demonstrate that in the Amazon River, particle aggregation significantly influences the Rouse number and renders its determination impossible from grain‐size distribution data obtained in the lab. However, in each cross section, the Rouse profile obtained from the fit of the data can serve as a basis to model, at first order, the SPM concentration at any position in the river cross section. This approach, combined with acoustic Doppler current profiler (ADCP) water velocity transects, allows us to accurately estimate the depth‐integrated instantaneous sediment flux. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

14.
Abstract The suspended sediment load in the middle Yellow River basin (YRB) cannot be well predicted by capacity‐based transport formulas because a large fraction of suspended sediment load is composed of wash load. This study evaluated the spatial variations of sediment rating curves (SRCs) in the middle YRB. Both power and linear SRCs were used to fit daily flow and suspended sediment concentration (SSC) historical data at 49 gauging stations throughout the middle YRB. The spatial variation in regression coefficients was investigated, and the relationship between regression coefficients and the physical characteristics of watersheds was discussed. The results indicate that SRC regression coefficients vary with drainage area and basin slope, but their responses to these parameters are remarkably different in watersheds with different underlying surfaces, which indicates the significance of sediment availability, erodibility, and grain size distribution. For power SRCs representing sediment transport in unsaturated flows, the regression coefficients are more closely correlated with the drainage area in loess regions and with the basin slope in rock mountain regions. For linear SRCs representing sediment transport in saturated flows, saturated SSCs vary with coarse (particle size > 0.05 mm) and fine (particle size < 0.01 mm) fractions in suspended sediment. The maximum saturated SSC among the different gauging stations is associated with the optimal grain size composition of suspended sediment, which has been proposed for loess regions in previous studies. This study provides theoretical support for estimating the regression parameters for sediment transport modelling, especially in ungauged basins.  相似文献   

15.
Suspended sediments in fluvial systems originate from a myriad of diffuse and point sources, with the relative contribution from each source varying over time and space. The process of sediment fingerprinting focuses on developing methods that enable discrete sediment sources to be identified from a composite sample of suspended material. This review identifies existing methodological steps for sediment fingerprinting including fluvial and source sampling, and critically compares biogeochemical and physical tracers used in fingerprinting studies. Implications of applying different mixing models to the same source data are explored using data from 41 catchments across Europe, Africa, Australia, Asia, and North and South America. The application of seven commonly used mixing models to two case studies from the US （North Fork Broad River watershed） and France （Bldone watershed） with local and global （genetic algorithm） optimization methods identified all outputs remained in the acceptable range of error defined by the original authors. We propose future sediment fingerprinting studies use models that combine the best explanatory parameters provided by the modified Collins （using correction factors） and Hughes （relying on iterations involving all data, and not only their mean values） models with optimization using genetic algorithms to best predict the relative contribution of sediment sources to fluvial systems.  相似文献   

16.
Hugh G. Smith 《水文研究》2008,22(16):3135-3148
Historically upland headwater catchments in south‐eastern Australia have undergone extensive gully erosion that has removed large amounts of sediment to lowlands. Recent research suggests these upland areas may continue to dominate fine sediment loads in lowland rivers. Improved understanding of sediment transfer through upland headwater catchments may have implications for interpreting downstream sediment supply. In this study a nested catchment design was utilized to examine suspended sediment yields and delivery from a small tributary sub‐catchment (1·64 km2) to the study catchment outlet (53·5 km2). Monitoring of suspended sediment concentration and discharge was undertaken for a period of nearly two years and used to estimate suspended sediment loads. Estimated total suspended sediment exports over the period of monitoring were 24·16 t from the sub‐catchment and 550·3 t from the catchment, which are generally less than previous reported small catchment yields in south‐eastern Australia. The extent of sediment delivery was examined using between‐site ratios of specific sediment yield per unit area and incised channel length. Sediment delivery was high under average rainfall conditions, but seasonally dependent. Both suspended sediment yields and the extent of delivery peaked over spring months, supplemented by remobilization of sediment stored during summer months in the main catchment channel. The findings of this study suggest much of the suspended sediment exported from small incised upland sub‐catchments (1–2 km2) may be delivered to downstream reaches under average rainfall conditions, which, in conjunction with the findings of previous research supports the potential importance of contributions from these areas to suspended sediment loads in lowland rivers during high flow periods. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

17.
A comprehensive understanding of the dynamics of erosion and sedimentation in reservoirs under different management conditions is required to anticipate sedimentation issues and implement effective sediment management strategies. This paper describes a unique approach combining fluvial geomorphology tools and morphodynamic modeling for analyzing the sediment dynamics of an elongated hydropower reservoir subjected to management operations: the Génissiat Reservoir on the Rhône River. Functional sub‐reaches representative of the reservoir morphodynamics were delineated by adapting natural river segmentation methods to elongated reservoirs. The segmentation revealed the link between the spatial and temporal reservoir changes and the variability of longitudinal flow conditions during reservoir management operations. An innovative modeling strategy, incorporating the reservoir segmentation into two sediment transport codes, was implemented to simulate the dynamics of erosion and sedimentation at the reach scale during historic events. One code used a bedload approach, based on the Exner equation with a transport capacity formula, and the other used a suspended load approach based on the advection–dispersion equation. This strategy provided a fair quantification of the dynamics of erosion and sedimentation at the reach scale during different management operations. This study showed that the reservoir morphodynamics is controlled by bedload transport in upper reaches, graded suspended load transport of sand in middle reaches and suspended load transport of fine sediments in lower reaches. Eventually, it allowed a better understanding of the impact of dam management on sediment dynamics. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

18.
Simultaneous field monitoring of runoff and suspended sediment loads from a 30 ha, artificially‐drained, mixed‐agricultural catchment in Herefordshire, UK indicates field drains are the dominant pathway for the transfer of runoff and sediment to the stream. Surface runoff pathways draining 6·2% of the catchment area transported around 1% of the catchment sediment load, while subsurface runoff in field drains draining 26·5% of the catchment transported around 24% of the sediment load. The explanations offered here for the dominance of drainflow—the spatial limitation of surface runoff generation and low hillslope‐stream connectivity of surface runoff compared with subsurface runoff—are also likely to apply to other artificially‐drained lowland agricultural catchments in the UK. These catchments are usually on poorly‐drained soils, and land management can have a considerable effect on the operation of runoff pathways and the transfer of sediment from hillslope to stream. As a result, subsurface inputs may also dominate sediment transfers in other underdrained catchments. The focus on sediment and pollutant losses via surface runoff pathways means that pollution inputs from subsurface, preferential pathways have been unfairly neglected, and it may be more important to focus on subsurface sediment and sediment‐associated pollution inputs for mitigation rather than inputs from surface pathways. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

19.
Seasonal suspended sediment transfer in glaciated catchments is responsive to meteorological, geomorphological, and glacio-fluvial conditions, and thus is a useful indicator of environmental system dynamics. Knowledge of multifaceted fluvial sediment-transfer processes is limited in the Alaskan Arctic – a region sensitive to contemporary environmental change. For two glaciated sub-catchments at Lake Peters, northeast Brooks Range, Alaska, we conducted a two-year endeavour to monitor the hydrology and meteorology, and used the data to derive multiple-regression models of suspended sediment load. Statistical selection of the best models shows that incorporating meteorological or temporal explanatory variables improves performances of turbidity- and discharge-based sediment models. The resulting modelled specific suspended sediment yields to Lake Peters are: 33 (20–60) t km−2 yr−1 in 2015, and 79 (50–140) t km−2 yr−1 in 2016 (95% confidence band estimates). In contrast to previous studies in Arctic Alaska, fluvial suspended sediment transfer to Lake Peters was primarily influenced by rainfall, and secondarily influenced by temperature-driven melt processes associated with clockwise diurnal hysteresis. Despite different sub-catchment glacier coverage, specific yields were the same order of magnitude from the two primary inflows to Lake Peters, which are Carnivore Creek (128 km2; 10% glacier coverage) and Chamberlin Creek (8 km2; 23% glacier coverage). Seasonal to longer-term sediment exhaustion and/or contrasting glacier dynamics may explain the lower than expected relative specific sediment yield from the more heavily glacierized Chamberlin Creek catchment. Absolute suspended sediment yield (t yr−1) from Carnivore Creek to Lake Peters was 27 times greater than from Chamberlin Creek, which we attribute to catchment size and sediment supply differences. Our results provide a foundational understanding of the current sediment transfer regime and are useful for predicting changes in fluvial sediment transport in glaciated Alaskan Arctic catchments.  相似文献   

20.
The transport of sediment from six small (0.2 to 17.6 km2) headwater catchments is described. The catchments under investigation were located in relation to predominant lithological deposits within the Cretaceous rock succession; two of the areas were underlain by (Weald) clay, two by sandstone (Ashdown Sand and Tunbridge Wells Sand) and two by chalk. The climate of the region under investigation is temperate, with an average annual precipitation (850 mm) in excess of potential evapotranspiration (450 mm). The transport of suspended material from within the catchments was examined by collecting samples of the water-sediment mixture draining the areas, using hand held depth-integrating and permanently installed stage sampling systems. The results of the regularly maintained sampling programme, over a two-year period, are described. Attempts were made to both measure and compute bed load transport. Suspended sediment concentrations are compared between catchments and related to hydrological characteristics. The nature of the material in transit is examined. Sediment rating curves are derived for each of the headwater catchments, defining the relationship in the form y = Axb (where y = suspended sediment concentration (mg/1) and x = water discharge (m3/s)). Annual rating curves are used to derive annual suspended sediment loads by combination with water discharge data, using a log-incremental computerized approach. Multiple regression techniques have been used to examine annual loads in terms of hydrological and morphological characteristics of the headwater catchments. Based on the field information available, a generalized model for the relationship between suspended sediment concentration and water discharge is described. Finally, the derived annual loads from the headwater catchments are combined with both limited observations from the larger Sussex rivers and data available for other catchment investigations in the British Isles, to produce a series of prediction equations for catchment yield under temperate climatic conditions.  相似文献   

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