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1.
High‐frequency water discharge and suspended sediment concentration (SSC) databases were collected for 3 years on four contrasted watersheds: the Asse and the Bléone (two Mediterranean rainfall regime watersheds) and the Romanche and the Ferrand (two rainfall–snowmelt regime watersheds). SSCs were calculated from turbidity recordings (1‐h time step), converted into SSC values. The rating curve was calculated by means of simultaneous SSC measurement taken by water sampling and turbidity recording. Violent storms during springtime and autumn were responsible for suspended sediment transport on the Asse and the Bléone rivers. On the Ferrand and the Romanche, a large share of suspended sediment transport was also caused by local storms, but 30% of annual fluxes results from snowmelt or icemelt which occurred from April to October. On each watershed, SSC up to 50 g l?1 were observed. Annual specific fluxes ranged from 450 to 800 t km?2 year?1 and 40–80% of annual suspended sediment fluxes occurred within 2% of the time. These general indicators clearly demonstrate the intensity of suspended sediment transport on these types of watersheds. Suspended sediment fluxes proved to be highly variable at the annual scale (inter‐annual variability of specific fluxes) as well as at the event scale (through a hysteresis loop in the SSC/Q relationship) on these watersheds. In both cases, water discharge and precipitations were the main processes involved in suspended sediment production and transport. The temporal and spatial variability of hydro‐meteorological processes on the watershed provides a better understanding of suspended sediment dynamics. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

2.
Soil erosion by water is a pressing environmental problem caused and suffered by agriculture in Mediterranean environments. Soil conservation practices can contribute to alleviating this problem. The aim of this study is to gain more profound knowledge of the effects of conservation practices on soil losses by linking crop management and soil status to runoff and sediment losses measured at the outlet of a catchment during seven years. The catchment has 27.42 ha and is located in a commercial farm in southern Spain, where a package of soil conservation practices is an essential component of the farming system. The catchment is devoted to irrigated annual crops with maize–cotton–wheat as the primary rotation. Mean annual rainfall‐induced runoff coefficient was 0.14 and mean annual soil loss was 2.4 Mg ha?1 y?1. Irrigation contributed to 40% of the crop water supply, but the amount of runoff and sediment yield that it generated was negligible. A Principal Components Analysis showed that total soil loss is determined by the magnitude of the event (rainfall and runoff depths, duration) and by factors related to the aggressiveness of the events (rainfall intensity and preceding soil moisture). A third component showed the importance of crop coverage to reduce sediment losses. Cover crops grown during autumn and early winter and crop residues protecting the soil surface enhanced soil conservation notably. The role of irrigation to facilitate growing cover crops in Mediterranean environments is discussed. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

3.
Upland erosion and the resulting reservoir siltation is a serious issue in the Isábena catchment (445 km2 Central Spanish Pyrenees). During a three‐month period, water and sediment fluxes have been monitored at the catchment outlet (Capella), two adjacent subcatchments (Villacarli, 41 km2; Cabecera, 145 km2) and the elementary badland catchment Torrelaribera (8 ha). This paper presents the results of the monitoring, a method for the calculation of a sedigraph from intermittent measurements and the derived sediment yields at the monitored locations. The observed suspended sediment concentrations (SSCs) demonstrate the role of badlands as sediment sources: SSCs of up to 280 g l?1 were encountered for Villacarli, which includes large badland areas. SSCs at the Cabecera catchment, with great areas of woodland, barely exceeded 30 g l?1. SSCs directly at the sediment source (Torrelaribera) were comparable to those at Villacarli, suggesting a close connection within this subcatchment. At Capella, SSCs of up to 99 g l?1 were observed. For all sites, SSC displayed only a loose correlation with discharge, inhibiting the application of a simple sediment rating curve. Instead, ancillary variables acting as driving forces or proxies for the processes (rainfall energy, cumulative discharge, rising/falling limb data) were included in a quantile regression forest model to explain the variability in SSC. The variables with most predictive power vary between the sites, suggesting the predominance of different processes. The subsequent flood‐based calculation of sediment yields attests high specific sediment yields for Torrelaribera and Villacarli (6277 and 1971 t km?2) and medium to high yields for Cabecera and Capella (139 and 410 t km?2) during the observation period. In all catchments, most of the sediment was exported during intense storms of late summer. Later flood events yield successively less sediment. Relating upland sediment production to yield at the outlet suggests considerable effects of sediment storage within the river channel. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

4.
The suspended sediment response of a small catchment subjected to farmland abandonment and subsequent plant recolonization was studied in relation to its hydrological functioning. The analysis of data over a seven‐year period demonstrated that suspended sediment yield was greatly influenced by the occurrence of intense, low‐frequency events. Greater amounts of suspended sediment were exported during spring, when the catchment was hydrologically more active. Rainfall intensity and baseflow at the start of a flood event had a strong influence on the sediment response, suggesting that several hydrological processes were active within the catchment. SSC (suspended sediment concentration)‐Q hysteretic loop analysis at the event scale aided understanding of the sedimentological and hydrological behaviour of the catchment. During the study period the SSC‐Q loops showed a high degree of seasonality and two main patterns strongly related to catchment wetness were distinguished. When the catchment was dry (mainly during summer and the beginning of autumn) the predominant process was infiltration excess runoff over sparsely vegetated areas close to the main channel. Under these conditions, floods exhibited a counter‐clockwise hysteretic loop and were characterized by a small streamflow response, short duration and high SSC. Under wet conditions (mainly during winter and spring), saturation excess runoff was increasingly dominant over vegetated areas. Under these conditions, floods exhibited a clockwise hysteretic loop, and were characterized by a larger streamflow response, longer duration and higher suspended sediment yield. The lower SSC during the falling stage of the hydrograph is likely to be due to dilution effects related to the contribution of clean water resulting from enlargement of the saturated areas, together with an increase in the baseflow discharge. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

5.
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   

6.
Ditch cleaning in drained peatland forests increases sediment loads and degrades water quality in headwater streams and lakes. A better understanding of the processes controlling ditch erosion and sediment transport in such systems is a prerequisite for proper peatland management. In order to relate hydrological observations to key erosion processes in headwater peatlands drained for forestry, a two‐year study was conducted in a nested sub‐catchment system (treated with ditch cleaning) and at two reference sites. The treated catchment was instrumented for continuous discharge and turbidity monitoring, erosion pin measurements of changes in ditch bed and banks and time‐integrated sampling of suspended sediment (SS) composition. The results showed that ditch cleaning clearly increased transient suspended sediment concentrations (SSCs) and suspended sediment yields (SSYs), and resulted in temporary storage of loosely deposited organic sediment in the ditch network. After exhaustion of this sediment storage, subaerial processes and erosion from ditch banks became dominant in producing sediment for transport. Recorded SSCs were higher on the rising limbs of event hydrographs throughout the study period, indicating that SS transport was limited by availability of erosion‐prone sediment. A strong positive correlation (R2 = 0.84, p < 0.001) between rainfall intensity (above a threshold of 1 mm h?1) and average SSC obtained on the rising limb of hydrographs for the sub‐catchment showed that soil detachment from ditch banks by raindrop impact can directly increase SSC in runoff. At the main catchment outlet, variation in SSC was best explained (R2 = 0.67, p < 0.05) by the linear combination of initial discharge (?), peak discharge (+) and the lag time from initial to peak discharge (?). Based on these factors, ditch cleaning slightly increased peak discharges and decreased transit times in the study catchment. The implications of the results for water pollution management in peatland forests are discussed. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

7.
The dynamics of suspended sediment transport were monitored continuously in a large agricultural catchment in southwest France from January 2007 to March 2009. The objective of this paper is to analyse the temporal variability in suspended sediment transport and yield in that catchment. Analyses were also undertaken to assess the relationships between precipitation, discharge and suspended sediment transport, and to interpret sediment delivery processes using suspended sediment‐discharge hysteresis patterns. During the study period, we analysed 17 flood events, with high resolution suspended sediment data derived from continuous turbidity and automatic sampling. The results revealed strong seasonal, annual and inter‐annual variability in suspended sediment transport. Sediment was strongly transported during spring, when frequent flood events of high magnitude and intensity occurred. Annual sediment transport in 2007 yielded 16 614 tonnes, representing 15 t km?2 (85% of annual load transport during floods for 16% of annual duration), while the 2008 sediment yield was 77 960 tonnes, representing 70 t km?2 (95% of annual load transport during floods for 20% of annual duration). Analysis of the relationships between precipitation, discharge and suspended sediment transport showed that there were significant correlations between total precipitation, peak discharge, total water yield, flood intensity and sediment variables during the flood events, but no relationship with antecedent conditions. Flood events were classified in relation to suspended sediment concentration (SSC)–discharge hysteretic loops, complemented with temporal dynamics of SSC–discharge ranges during rising and falling flow. The hysteretic shapes obtained for all flood events reflected the distribution of probable sediment sources throughout the catchment. Regarding the sediment transport during all flood events, clockwise hysteretic loops represented 68% from river deposited sediments and nearby source areas, anticlockwise 29% from distant source areas, and simultaneity of SSC and discharge 3%. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

8.
Influence of the rainfall regime on erosion and transfer of suspended sediment in a 905‐km² mountainous catchment of the southern French Alps was investigated by combining sediment monitoring, rainfall data, and sediment fingerprinting (based on geochemistry and radionuclide concentrations). Suspended sediment yields were monitored between October 2007 and December 2009 in four subcatchments (22–713 km²). Automatic sediment sampling was triggered during floods to trace the sediment origin in the catchment. Sediment exports at the river catchment outlet (330 ± 100 t km‐2 yr‐1) were mainly driven (80%) by widespread rainfall events (long duration, low intensities). In contrast, heavy, local and short duration storms, generated high peak discharges and suspended sediment concentrations in small upstream torrents. However, these upstream floods had generally not the capacity to transfer the sediment down to the catchment outlet and the bulk of this fine sediment deposited along downstream sections of the river. This study also confirmed the important contribution of black marls (up to 70%) to sediment transported in rivers, although this substrate only occupies c. 10% of the total catchment surface. Sediment exports generated by local convective storms varied significantly at both intra‐ and inter‐flood scales, because of spatial heterogeneity of rainfall. However, black marls/marly limestones contribution remained systematically high. In contrast, widespread flood events that generate the bulk of annual sediment supply at the outlet were characterized by a more stable lithologic composition and by a larger contribution of limestones/marls, Quaternary deposits and conglomerates, which corroborates the results of a previous sediment fingerprinting study conducted on riverbed sediment. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

9.
In this study, we investigated rainfall, run‐off, and sediment transport dynamics (414 run‐off events and 231 events with sediment information) of a humid mountain badland area—the Araguás catchment (Central Pyrenees, Spain)—from October 2005 to September 2016. Use of this long‐term database allows characterization of the hydrological response, which consist of low‐magnitude/high‐frequency events and high‐magnitude/low‐frequency events, and identification of seasonal dynamics and rainfall‐run‐off thresholds. Our results indicate that the Araguás catchment, similarly to other humid badlands, had high hydrological responsiveness (mean annual run‐off coefficient: 0.52), a non‐linear relationship of rainfall with run‐off (common in Mediterranean environments), and seasonal hydrological and sedimentological dynamics. We created and validated a multivariate regression model to characterize the hydrological variables (stormflow and peak discharge) and sedimentological variables (mean and maximum suspended sediment concentrations and total suspended sediment load). In summer and at the beginning of autumn, the response was mainly related to rainfall intensity, suggesting a predomination of Hortonian flows. In contrast, in spring and winter, the responses were mainly related to the antecedent conditions (previous rainfall and baseflow), suggesting the occurrence of saturated excess flow processes, and the contribution of neighbouring vegetated areas. The multivariate analysis also showed that total sediment load is better predicted by a multivariate regression model that integrates pre‐event, rainfall, and run‐off variables. In general, our models provided more accurate predictions of small‐magnitude/high‐frequency events than high‐magnitude/low‐frequency events. This study highlights the high inter‐ and intra‐annual variability response in humid badland areas and that long‐term records are needed to reduce the uncertainty of hydrological and sedimentological responses in Mediterranean badland areas.  相似文献   

10.
The summer discharge pattern of the Skeldal River, which drains a 560 km2 partly glacierized catchment in north‐east Greenland, is dominated by diurnal oscillations reflecting variations in the melt rate of snow and ice in the basin. Superimposed on this diurnal pattern are numerous short‐lived discharge fluctuations of irregular periodicity and magnitude. The larger fluctuations are described and attributed to both rainfall events and periodic collapse of the glacier margin damming flow from beneath the Skelbrae glacier. Other minor fluctuations are less readily explained but are associated with changes in the channelized and distributed reservoirs and possibly temporary blockage of subglacial conduits caused by ice melt with subsequent damming. Fluctuations in suspended sediment concentration (SSC) are normally associated with discharge fluctuations, although examples of ‘transient flushes’ were observed where marked increases in SSC occurred in the absence of corresponding discharge variations. A strong relationship between the event discharge increase and event SSC increase for rainfall‐induced events was established, but no such relationship existed for non‐rainfall‐induced events. There is some evidence for an exhaustion effect in the SSC patterns both at the event time‐scale and as the month proceeds. A mean suspended sediment load of 1765 ± 0·26 t day?1 was estimated for the study period, which would be equivalent to a suspended sediment yield of 732 ± 4 t km?2 year?1. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

11.
Sediments produced from eroding cultivated land can cause on‐site and off‐site effects that cause considerable economic and social impacts. Despite the importance of soil conservation practices (SCP) for the control of soil erosion and improvements in soil hydrological functions, limited information is available regarding the effects of SCP on sediment yield (SY) at the catchment scale. This study aimed to investigate the long‐term relationships between SY and land use, soil management, and rainfall in a small catchment. To determine the effects of anthropogenic and climatic factors on SY, rainfall, streamflow, and suspended sediment concentration were monitored at 10‐min intervals for 14 years (2002–2016), and the land use and soil management changes were surveyed annually. Using a statistical procedure to separate the SY effects of climate, land use, and soil management, we observed pronounced temporal effects of land use and soil management changes on SY. During the first 2 years (2002–2004), the land was predominantly cultivated with tobacco under a traditional tillage system (no cover crops and ploughed soil) using animal traction. In that period, the SY reached approximately 400 t·km?2·year?1. From 2005 to 2009, a soil conservation programme introduced conservation tillage and winter cover crops in the catchment area, which lowered the SY to 50 t·km?2·year?1. In the final period (2010–2016), the SCP were partially abandoned by farmers, and reforested areas increased, resulting in an SY of 150 t·km?2·year?1. This study also discusses the factors associated with the failure to continue using SCP, including structural support and farmer attitudes.  相似文献   

12.
The solute and suspended‐sediment load following five rainstorms (2005–2007) with varied intensities were studied at the Vernegà experimental watershed, north‐western Spain. Two land‐use areas are located within this watershed, the upstream one (forest) with 160 ha a 100% forested area, and the downstream one (agricultural) with 97 ha being 9 ha conventional agricultural field and 88 ha forest. This study investigates the capacity of each land‐use to yield water, suspended sediment concentration (SSC) and dissolved solid concentration (DSC). The hypothesis is that DSC and SSC from the agricultural area are greater than DSC and SSC of the forest area. Results showed that the agriculture area produced significantly greater mean DSC than in the forest area, the main contribution was the Ca2+ (24·68 ± 46·52 mg l?1) ion at the agricultural area. A long‐term sediment production rate at the agricultural outlet was calculated (69·1 tonnes per 100 years) based on the total sediment discharge (TSD) and the recurrence interval of the largest event of the five rainstorms (October 2005). Geographic information system (GIS) spatial data layers of the watershed were produced to determine the relation of tracks, landforms, slopes and forest management to SSC yield in the forest outlet (133·89 ± 308·14 mg l?1) during the five rainstorms. Agriculture practices are the main cause of soil erosion at the study area. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

13.
This paper investigates suspended sediment transport and dynamics of two nested agricultural lowland Mediterranean catchments with a difference of two orders of magnitude in the surface area (i.e., 1 and 264 km2). The effects of the drainage catchment area over the specific suspended sediment yield are assessed by using the nested approach over various timeframes. A detailed analysis of the rainfall–runoff–sediment transport relationships during the 2‐year study period shows that the hydrological and sedimentological responses were extremely variable for both catchments. Very low or no correlations were observed between the rainfall intensity and the selected hydrological variables and sediment loads. However, remarkable or high correlations were obtained between the rainfall intensity and the maximum and average suspended sediment concentrations, indicating that rainfall per unit time has little control on the hydrological response, but that, simultaneously, its high‐erosive power triggers sediment production, increasing the sedimentary response of the catchments. This study also illustrates how sediment is mainly transported during floods, producing predominantly clockwise hysteretic loops. Moreover, the small headwater catchment exerts a reduced (or even negligible) effect over the hydro‐sedimentary response of the larger downstream catchment, caused by the reduced sediment availability in a landscape with an inherent disconnection of the sediment pathways.  相似文献   

14.
This study concerns the problem of water erosion in the Sahel. Surface water and sediment yields (suspended matter and bedload) were monitored for 3 years (1998–2000) at the outlet of a small grazed catchment (1·4 ha) in the northern part of Burkina Faso. The catchment consists of about 64% sandy deposits (DRY soil surface type), which support most of the vegetation, and about 34% of crusted bare soils (ERO soil surface type). The annual solid‐matter export is more than 90% suspended sediment, varying between 4·0 and 8·4 t ha?1. The bedload represents less than 10% of soil losses. In a single flood event (10 year return period), the sediment yield can reach 4·2 t ha?1. During the period studied, a small proportion (20 to 32%) of the floods was thus responsible for a large proportion (80%) of the solid transport. Seasonal variation of the suspended‐matter content was also observed: high mean values (9 g l?1) in June, decreasing in July and stabilizing in August (between 2 and 4 g l?1). This behaviour may be a consequence of a reorganization of the soil surfaces that have been destroyed by trampling animals during the previous long dry season, vegetation growth (increase in the protecting effect of the herbaceous cover) and, to a lesser extent, particle‐supply limitation (exhaustion of dust deposits during July). The particle‐size distribution in the suspended matter collected at the catchment outlet is 60% made up of clay: fraction ≤2 µ m. The contribution of this clay is maximum when the water rises and its kaolinite/quartz ratio is then close to that of the ERO‐type surfaces. This indicates that these surfaces are the main source of clay within the catchment. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

15.
Mingbin Huang  Lu Zhang 《水文研究》2004,18(10):1885-1898
Since the late 1950s a series of soil conservation practices have been implemented in the Loess Plateau. It is important to assess the impact of these practices on hydrology at the catchment scale. The Jialuhe River catchment, a tributary of the Yellow River, with a drainage area of 1117 km2 in the Loess Plateau, was chosen to investigate the hydrological responses to conservation practices. Parametric and non‐parametric Mann–Kendall tests were utilized to detect trends in hydrological variables or their residuals. Relationships between precipitation and hydrological variables were developed to remove the impact of precipitation variability. Significant linear decreasing trends in annual surface runoff and baseflow were identified during the treated period from 1967 to 1989, and the rate of reduction was 1·30 and 0·48 mm/year, respectively. As result, mean annual surface runoff and baseflow decreased by 32% over the period of 1967 to 1989. Seasonal runoff also decreased during the treated period with the greatest reduction occurring in summer and the smallest reduction in winter. The response of high and low daily flow to conservation practices was greater than average flows. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

16.
Sediment yield can be a sensitive indicator of catchment dynamics and environmental change. For a glacierized catchment in the High Arctic, we compiled and analyzed diverse sediment transfer data, spanning a wide range of temporal scales, to quantify catchment yields and explore landscape response to past and ongoing hydroclimatic variability. The dataset integrates rates of lake sedimentation from correlated varve records and repeated annual and seasonal sediment traps, augmented by multi‐year lake and fluvial monitoring. Consistent spatial patterns of deposition enabled reconstruction of catchment yields from varve‐ and trap‐based fluxes. We used hydroclimatic data and multivariate modeling to examine annual controls of sediment delivery over almost a century, and to examine shorter‐term controls of sediment transfer during peak glacier melt. Particle‐size analyses, especially for annual sediment traps, were used to further infer sediment transfer mechanisms and timing. Through the Medieval Warm Period and Little Ice Age, there were no apparent multi‐century trends in lake sedimentation rates, which were over three times greater than those during the mid‐Holocene when glaciers were diminished. Twentieth‐century sedimentation rates were greater than those of previous millennia, with a mid‐century step increase in mean yield from 240 to 425 Mg km?2 yr?1. Annual yields through the twentieth century showed significant positive relations with spring/summer temperature, rainfall, and peak discharge conditions. This finding is significant for the future of sediment transfer at Linnévatnet, and perhaps more broadly in the Arctic, where continued increases in temperature and rainfall are projected. For 2004–2010, annual yields ranged from 294 to 1330 Mg km?2 yr?1. Sediment trap volumes and particle‐size variations indicate that recent annual yields were largely dominated by spring to early summer transfer of relatively coarse‐grained sediment. Fluvial monitoring showed daily to hourly sediment transfer to be related to current and prior discharge, diurnal hysteresis, air temperature, and precipitation. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

17.
Sediment transport from mountainous to lowland areas is considered one of the most important geomorphological processes. In the present study, variations in transported sediment loads and dissolved loads have been studied over 3 years (2008–2011) for two forested catchments located in the Lesser Himalayan region of India. Seasonal and annual suspended sediment flux was strongly influenced by amounts of rainfall and streamflow. On average, 93% of annual load was produced during the monsoon, of which 62–78% occurred in only five peak events. Sediment production by the degraded forest catchment (Bansigad) was 1.9-fold (suspended sediment load) to 5.9-fold (bedload) higher than the densely forested catchment (Arnigad). The dissolved organic matter potentially influences total dissolved solids in the stream. Heavy rainfall triggers both stream discharge and landslides, which lead to higher bedload transport. Total denudation rates for Arnigad and Bansigad were estimated at 0.68 and 1.02 mm?year?1, respectively.  相似文献   

18.
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   

19.
A 235.5 km2 headwater catchment of the Krishna River in the Deccan plateau lavas is dry for eight months of the year but receives intense monsoonal rains during four months. High initial suspended sediment concentrations fall as rapid vegetation growth provides increasing protection. During a six-year period annual suspended sediment yields from the deeply weathered kaolinitic soils ranged between 36.9 and 275.3 t km?2 in dry and wet years respectively.  相似文献   

20.
Effects of gully and channel erosion on the export of sediments are in general well understood, but the effects on carbon (C) and nitrogen (N) export remain an open question. We examined these effects and the role of flow magnitude, total wet season rainfall, catchment size and the C and N content and solubility of most probable sediment sources in a subtropical catchment. We sampled the baseflow and the rising stage of high‐flow events for one wet season and analysed 5 years of water quality data from event sampling stations. Total suspended sediment was the main variable explaining N export followed by rainfall, flow and catchment size. N was exported mainly in particulate organic form and C in dissolved form. The quality of most probable sediment source fractions explains these results and points to fractionation during transport into C and N richer and C and N poorer fractions, with travel distance ultimately determining the average quality of transported sediment for different flow magnitudes. Erosion would have caused a lower C and N concentration in sediments, a lower proportion of mineralized N, a larger proportion of dissolved organic C and a larger C : N ratios of the soluble fraction as compared with unincised grassed valleys. This would alter the rates of nutrient cycling and energy flow within and across ecosystem compartments in streams receiving this export. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

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