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1.
Agricultural zones are significant sediment sources, but it is crucial to identify critical source areas (CSAs) of sediment yield within these zones where best management practices (BMPs) can be applied to the best effect in reducing sediment delivery to receiving water bodies rather than the economically nonviable alternative of randomly or sweepingly implementing BMPs. A storm event of a specific magnitude and hyetograph profile may, at different times, generate a greater or lesser sediment yield. The widely used agricultural nonpoint source (AGNPS) model was used to identify CSAs for sediment losses in Southwestern Ontario's agriculture‐dominated 374‐ha Holtby watershed. A storm threshold approach was adopted to identify critical periods for higher sediment losses. An AGNPS model for the Holtby watershed was set up, calibrated, and validated for run‐off volume, peak flow rate, and sediment yield for several storms. The calibrated and validated model was run for storms of increasing return periods to identify threshold storm events that would generate sediment yield greater than an acceptable value for early and late spring, summer, and fall seasons. Finally, to evaluate the potential impacts of climate change, we shifted shorter duration summer storms into spring conditions and quantified the changes in sediment yield dynamics. A 6‐hr, 7.5‐year early spring storm would generate sediment losses exceeding the acceptable limit of 0.34 t ha?1 for the season. However, summer storms (2 hr, up to 100 years) tended to generate sediment yields below those of an identifiable threshold storm. If such shorter duration summer storms occurred in spring, the sediment yield would increase by more than fivefold. A 5‐year future storm would generate an equivalent effect of a 100‐year current spring event. The high sediment delivery to be expected will have significant implications regarding the future management of water quality of receiving waters. Appropriate placement of BMPs at CSAs will thus be needed to reduce such high sediment delivery to receiving waters.  相似文献   

2.
Plants influence river channel topography, but our understanding of the interaction among plants, flow, and sediment is limited, especially when sediment supply is variable. Using laboratory experiments in a recirculating flume with live seedlings in a mobile sand bed, we demonstrate how varying the balance between sediment supply and transport capacity shifts the relationship between plants and bar‐surface topography. Each experimental trial contrasted two sediment conditions, in which initially supply was maintained in equilibrium with transport via sediment recirculation, followed by sediment deficit, in which transport capacity exceeded supply, which was set to zero. For both sediment balances, the topographic response was sensitive to plant size, with larger plants inducing greater aggradation relative to a baseline condition. During sediment equilibrium, the positive relationship between plant size and topographic change also depended on species morphology (multi‐stemmed shrubs versus single‐stemmed plants). Plant morphology effects disappeared when the sediment balance shifted to a deficit, but the presence of plants had a greater impact on the magnitude of change compared to the topographic response under sediment equilibrium. Our results suggest that the interactions among sediment supply, plants, and topography may be strongest on rivers with a balance in sediment supply and transport capacity. Because of the large variability in fluvial sediment supply resulting from natural and anthropogenic influences, these interactions will differ spatially (e.g. longitudinally through a watershed) and at different temporal scales, from single flood events to longer time periods. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

3.
Hydrological process in arid zones differs substantially from that in better documented humid environments. The ponding point for infiltration is reached within 10 mins of first rain and overland flow forms the major component of basin runoff. Drainage densities are high, approaching 100 km.km?2, maximising the opportunity for both water and eroded soil to reach the channel network. The typical flood bore is not as abrupt as the mythology of desert streams would suggest. Nevertheless, the time of rise of the flood hydrograph is usually between 4 and 16 mins, giving credance to the notion of ‘flash flood’. Measured flows remain subcritical in the main, though Froude number exceeds unity for short periods around peak discharge. Flow is exceedingly turbulent, with Reynolds number > 105 even for much of the recession limb. As a result, suspended sediment concentrations by size grade are shown to be hydraulically controlled. However, the high degree of turbulence and wide availability of sediment from hillslope and channel sources also means that the mean size of the suspended load varies systematically with flow parameters. In this respect, ephemeral streams differ from perennial counterparts in humid environments where no clear-cut relationships exist. There is greater prospect of deriving a physically deterministic model of suspended sediment transport in desert streams. Implications for soil erosion and reservoir siltation are discussed, and sediment is traced from its source to its various sinks within the drainage basin.  相似文献   

4.
Sediment export from glaciated basins involves complex interactions between ice flow, basal erosion and sediment transfer in subglacial and proglacial streams. In particular, we know very little about the processes associated with sediment transfer by subglacial streams. The Haut Glacier d'Arolla (VS, Switzerland) was investigated during the summer melt season of 2015. LiDAR survey revealed positive surface changes in the ablation zone, indicating glacier uplift, at the end of the morning during the period of peak ablation. Instream measures of sediment transport showed that suspended load and bedload responded differently to diurnal flow variability. Suspended load depended on the availability of fine material whereas bedload depended mainly on the competence of the flow. Interpretation of these results allowed development of a conceptual model of subglacial sediment transport dynamics. It is based upon the mechanisms of clogging (deposition) and flushing (transport/erosion) in sub-glacial channels as forced by diurnal flow variability. Through the melt season, the glacier hydrological response evolves from being buffered by glacier snow cover with a poorly developed subglacial drainage system to being dominated by more rapid ice melt with a more hydraulically efficient subglacial channel system. The resultant changes in the shape of diurnal discharge hydrographs, and notably higher peak flows and lower base flows, causes sediment transport to become discontinuous, with overnight clogging and late morning flushing of subglacial channels. Overnight clogging may be sufficient to reduce subglacial channel size, creating temporarily pressurized flow and lateral transfer of water away from the subglacial channels, leading to the late morning glacier surface uplift. However, without further data, we cannot exclude other hypotheses for the uplift. © 2018 John Wiley & Sons, Ltd.  相似文献   

5.
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6.
The rates and styles of channel adjustments following an abrupt and voluminous sediment pulse are investigated in the context of site and valley characteristics and time‐varying sediment transport regimes. Approximately 10.5 x 106 m3 of stored gravel and sand was exposed when Barlin Dam failed during Typhoon WeiPa in 2007. The dam was located on the Dahan River, Taiwan, a system characterized by steep river gradients, typhoon‐ and monsoon‐driven hydrology, high, episodic sediment supply, and highly variable hydraulic conditions. Topography, bulk sediment samples, aerial photos, and simulated hydraulic conditions are analyzed to investigate temporal and spatial patterns in morphology and likely sediment transport regimes. Results document the rapid response of the reservoir and downstream channel, which occurred primarily through incision and adjustment of channel gradient. Hydraulic simulations illustrate how the dominant sediment transport regime likely varies between study periods with sediment yield and caliber and with the frequency and duration of high flows. Collectively, results indicate that information on variability in sediment transport regime, valley configuration, and distance from the dam is needed to explain the rate and pattern of morphological changes across study periods. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

7.
A record spanning almost 20 years of suspended sediment and discharge measurements on two reaches of an agricultural watershed is used to assess the influence of in‐channel sediment supplies and bed composition on suspended sediment concentrations (SSC). We analyse discharge‐SSC relationships from two small streams of similar hydrology, climate and land use but widely different bed compositions (one dominated by sand, the other by gravel). Given that sand‐dominated systems have more fine sediment available for transport, we use bed composition and the relative proportion of surface sand and gravel to be representative of in‐channel sediment supply. Both high flow events and lower flows associated with onset and late recessional storm flow (‘low flows’) are analysed in order to distinguish external from in‐channel sources of sediment and to assess the relationship between low flows and sediment supply. We find that SSC during low flows is affected by changes to sediment supply, not just discharge capacity, indicated by the variation in the discharge‐SSC relationship both within and between low flows. Results also demonstrate that suspended sediment and discharge dynamics differ between reaches; high bed sand fractions provide a steady supply of sediment that is quickly replenished, resulting in more frequent sediment‐mobilizing low flow and relatively constant SSC between floods. In contrast, SSC of a gravel‐dominated reach vary widely between events, with high SSC generally associated with only one or two high‐flow events. Results lend support to the idea that fine sediment is both more available and more easily transported from sand‐dominated streambeds, especially during low flows, providing evidence that bed composition and in‐channel sediment supplies may play important roles in the mobilization and transport of fine sediment. In addition, the analysis of low‐flow conditions, an approach unique to this study, provides insight into alternative and potentially significant factors that control fine sediment dynamics. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

8.
Depth profiles of particle streamwise velocity, concentration and bedload sediment transport rate were measured in a turbulent and supercritical water flow. One‐size 6 mm diameter spherical glass beads were transported at equilibrium in a two‐dimensional 10% steep channel with a mobile bed. Flows were filmed from the side by a high‐speed camera. Particle tracking algorithms made it possible to determine the position, velocity and trajectory of a very large number of particles. Approximately half of the sediment transport rate was composed by rolling grains, and the other half by saltation. This revealed a complex structure, with several concentration and flux peaks due to rolling, and one peak due to saltation. With an increase of the sediment transport rate, the depth structure remained the same at the water/granular interface, with peak value increases but with no shift in elevations. The saltation region expanded towards higher elevations with an increase of the particle velocity commensurate to the water velocity. The proportion of the sediment transport rate in saltation did not vary significantly. The particle streamwise velocity profiles exhibited three segments: an exponential decay in the bed, a linear increase where rolling and saltation co‐existed, and above this, a logarithmic‐like shape due to saltating particles. These results are comparable to profiles measured and modelled in dry granular free surface flows and in more intense bedload such as sheet flows. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

9.
Proglacial suspended sediment transport was monitored at Haut Glacier d'Arolla, Switzerland, during the 1998 melt season to investigate the mechanisms of basal sediment evacuation by subglacial meltwater. Sub‐seasonal changes in relationships between suspended sediment transport and discharge demonstrate that the structure and hydraulics of the subglacial drainage system critically influenced how basal sediment was accessed and entrained. Under hydraulically inefficient subglacial drainage at the start of the melt season, sediment availability was generally high but sediment transport increased relatively slowly with discharge. Later in the melt season, sediment transport increased more rapidly with discharge as subglacial meltwater became confined to a spatially limited network of channels following removal of the seasonal snowpack from the ablation area. Flow capacity is inferred to have increased more rapidly with discharge within subglacial channels because rapid changes in discharge during highly peaked diurnal runoff cycles are likely to have been accommodated largely by changes in flow velocity. Basal sediment availability declined during channelization but increased throughout the remainder of the monitored period, resulting in very efficient basal sediment evacuation over the peak of the melt season. Increased basal sediment availability during the summer appears to have been linked to high diurnal water pressure variation within subglacial channels inferred from the strong increase in flow velocity with discharge. Basal sediment availability therefore appears likely to have been increased by (1) enhanced local ice‐bed separation leading to extra‐channel flow excursions and[sol ]or (2) the deformation of basal sediment towards low‐pressure channels due to a strong diurnally reversing hydraulic gradient between channels and areas of hydraulically less‐efficient drainage. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

10.
Novel modelling was utilised in the present study to reveal significant relationships between the abundance of the Australian freshwater stream-specialist fish Galaxias olidus and metrics defining flow regimes across a region dominated by temporary streams. It was revealed that increases in total abundance were linked to metrics (both 1- and 3-year periods) that indicate greater water availability and the persistence of water in pools across the year, namely the average duration of zero-flow days over the low-flow season (negatively) and total duration of bankfull flows across the year (positively). The analysis identified 3-year metrics as being more important to the abundance of 0+ fish rather than annual ones. Taken together, these findings describing the flow requirements of a stream specialist will help to guide implementation of environmental flows, but will also highlight the need for continued exploration of flow–ecology relationships.  相似文献   

11.
Climate change has a significant influence on streamflow variation. The aim of this study is to quantify different sources of uncertainties in future streamflow projections due to climate change. For this purpose, 4 global climate models, 3 greenhouse gas emission scenarios (representative concentration pathways), 6 downscaling models, and a hydrologic model (UBCWM) are used. The assessment work is conducted for 2 different future time periods (2036 to 2065 and 2066 to 2095). Generalized extreme value distribution is used for the analysis of the flow frequency. Strathcona dam in the Campbell River basin, British Columbia, Canada, is used as a case study. The results show that the downscaling models contribute the highest amount of uncertainty to future streamflow predictions when compared to the contributions by global climate models or representative concentration pathways. It is also observed that the summer flows into Strathcona dam will decrease, and winter flows will increase in both future time periods. In addition to these, the flow magnitude becomes more uncertain for higher return periods in the Campbell River system under climate change.  相似文献   

12.
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13.
ABSTRACT

To assess seasonal patterns of suspended sediment load and its erosion–transport interactions, 17 years of river monitoring data from the Isser River Basin (northwest Algeria) were studied, considering continuous and event-scale approaches. The results show significant differences in sediment yield and transport processes between dry and wet periods. A rate of 8 t ha?1 year?1 was estimated from continuous analysis, with values of 4.3 and 13 t ha?1 year?1 for wet and dry periods, respectively. Estimates of soil delivery ratio pointed to higher values during dry periods and the dominance of hillslope erosion processes. At the event scale, the hysteresis loops confirmed these seasonal patterns in transport dynamics. The calibration of the MUSLE model highlighted the severity of rainfall during the dry period. These results emphasize the importance of seasonality in erosion and transport processes with special relevance in terms of climate change predictions.  相似文献   

14.
It is common to use idealised materials to study the dynamics of granular transport in fluid flows, but the impact of this choice upon sediment behaviour has not been extensively explored. To tackle this research gap, two experiments were undertaken to explore the influence of a finer grain input to a channelized coarser granular flow driven by a shallow fluid flow. The first set of runs was undertaken using spherical glass beads, and the second set with natural fluvial sediment. The transport system approximates a narrow slice through the bedload at the bottom of a river. In the runs with natural grains, the infiltration of fine sediment into the bed was similar to the spherical glass beads, but with reduced infiltration capacity. We ascribe this behaviour to irregular and variable pore shapes and sizes in the natural material. The behaviour of the bedload in the natural material runs matched that of the bead runs only when the feed contained a high content of fines. When the feed contained a low content of fines the transport of natural grains was more complex, including the emergence of migrating collections of grains. However, the overall changes in bed and water slope due to the finer grain input were comparable in both sets of experiments. We conclude that artificial, idealised materials qualitatively represent sedimentary phenomena, but that quantitative differences in the outcomes must be expected. © 2020 John Wiley & Sons, Ltd.  相似文献   

15.
Temporal variability in suspended sediment delivery processes was studied during three seasons in a 7·9 km2 catchment at Cape Bounty, Melville Island, Nunavut in the Canadian High Arctic. Discharge was controlled primarily by the magnitude of snowmelt, with limited inputs from ground ice melt and precipitation. Years with greater snowpack non‐linearly increased sediment yield and resulted in seasonal counter‐clockwise hysteresis, while a year with low snowpack resulted in reduced sediment yield and clockwise hysteresis, and indicates that sediment was increasingly available after the onset of streamflow. In addition to the event‐scale hysteresis observed during the nival discharge peak, diurnal clockwise hysteresis was observed during all three seasons and suggests daily exhaustion of sediment supplies. These results indicate that the channel snowpack plays a primary role over sediment accessibility during the nival discharge peak. Similarly, grain size analysis of suspended material in the river showed that the coarsest mean grain size was transported during the early phase of peak nival discharge and indicates that isolated sources of coarse material were being accessed by high velocity flow. Snowpack is present through the peak nival period and conditions sediment availability by isolating channel sediments from high‐energy flow. These results indicate sediment delivery characteristics in small High Arctic catchments reflect complex interactions with channel snowpack and disproportionate responses to flow conditions that differ from glacial and temperate settings. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

16.
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17.
Two controlled flow events were generated by releasing water from a reservoir into the Olewiger Bach, located near Trier, Germany. This controlled release of near bank‐full flows allowed an investigation of the fine sediment (<63 µm) mobilized from channel storage. Both a winter (November) and a summer (June) release event were generated, each having very different antecedent flow conditions. The characteristics of the release hydrographs and the associated sediment transport indicated a reverse hysteresis with more mass, but smaller grain sizes, moving on the falling limb. Fine sediment stored to a depth of 10 cm in the gravels decreased following the release events, indicating the dynamic nature and importance of channel‐stored sediments as source materials during high flow events. Sediment traps, filled with clean natural gravel, were buried in riffles before the release of the reservoir water and the total mass of fine sediment collected by the traps was measured following the events. Twice the mass of fine sediment was retained by the gravel traps compared with the natural gravels, which may be due to their altered porosity. Although the amount of fine sediment collected by the traps was not significantly related to measures of gravel structure, it was found to be significantly correlated to measures of local flow velocity and Froude number. A portion of the traps were fitted with lids to restrict surface exchange of water and sediment. These collected the highest amounts of event‐mobilized sediments, indicating that inter‐gravel lateral flows, not just surface infiltration of sediments, are important in replenishing and redistributing the channel‐stored fines. These findings regarding the magnitude and direction of fine sediment movement in gravel beds are significant in both a geomorphic and a biological context. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

18.
Assessment of the impact of changes in climate and land use and land cover (LULC) on ecosystem services (ES) is important for planning regional-scale strategies for sustainability and restoration of ES. The Upper Narmada River Basin (UNRB) in peninsular India has undergone rapid LULC change due to recent agricultural expansion. The impact of future climate and LULC change on ES in the UNRB is quantified and mapped using the Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST 3.3.0) tool. Our results show that water yield is projected to increase under climate change (about 43% for representative concentration pathway 4.5 for 2031–2040), whereas it is projected to decrease under the LULC change scenario. Sediment export is projected to increase (by 54.53%) under LULC change for 2031–2040. Under the combined effect of climate and LULC change, both water yield and sediment export are expected to increase. Climate change has a greater impact on projected water yield than LULC change, whereas LULC has greater impact on sediment export. Spatial analysis suggests a similar trend of variation in relative difference (RD) of ES in adjacent sub-basins. The quantified changes in ES provisioning will benefit future land management, particularly for operation of the Rani Avanti Bai Sagar Reservoir downstream of the UNRB.  相似文献   

19.
In debris‐flow‐prone channels, normal fluvial sediment transport occurs (nearly exclusively in suspended mode) between episodic debris‐flow events. Observations of suspended sediment transport through a winter season in a steepland gully in logged terrain revealed two event types. When flows exceeded a threshold of 270 l s−1, events yielded significant quantities of sediment and suspended sediment concentration increased with flow. Smaller events were strongly ‘supply limited’; sediment concentration decreased as flow increased. Overall, there is no consistent correlation between runoff and sediment yield. Within the season, three subseasons were identified (demarcated by periods of freezing weather) within which a pattern of fine sediment replenishment and evacuation occurred. Finally, a signature of fine sediment mobilization and exhaustion was observed within individual events. Fine sediment transport occurred in discrete pulses within storm periods, most of the yield occurring within 5 to 15% of storm runoff duration, so that it is unlikely that scheduled sampling programs would identify significant transport. Significant events are, however, generally forecastable on the basis of regional heavy rainfall warnings, providing a basis for targeted observations. Radiative snowmelt events and rain‐on‐snow remain difficult to forecast, since the projection of temperatures from the nearest regular weather station yields variable results. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

20.
This review displays over 700 rates of sediment transport by oscillatory flow from 20 sources. Sediments include fine sands to pebbles, both of quartz and of lightweight materials, and the transport rates in water range over seven orders of magnitude. Most data are average gross (to and fro) bedload rates collinear with laboratory flow over a horizontal sediment bed, although other situations with net transport, suspended load, or oblique field waves are considered.As peak flow velocity nears twice the threshold velocity for sediment motion, bedload appears to be fully developed and the transport rate is near that given by a simple formula including flow frequency and peak velocity, and sediment size and density. At lesser peak velocities, bedload rates are markedly smaller and distinctly different regimes of sediment mobilization and transport may be identified.  相似文献   

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