Mean Annual Sediment Yield Research Articles

Mediterranean river systems of Andalusia, southern Spain, and associated deltas: A source to sink approach

The northern shores of the semi-isolated Mediterranean Sea with its low tidal range and a relatively voluminous fluvial supply of sediments constitute an ideal delta forming environment. In this paper, we examine the present-day and multi-decadal behaviour of 26 river systems from Andalusia, southern Spain, forming deltas in the Alboran Sea, the westernmost basin in the Mediterranean Sea. Eastern, Central and Western Andalusian watersheds have been defined based on geomorphological, climatological and hydrological characteristics. A comprehensive data set has been compiled, including satellite images, aerial photographs, a digital elevation model, thematic maps, time series of precipitation, temperature and water discharge, and the damming history of individual river basins. This data set has been used to analyse basin morphology and hydrology, and anthropogenic impact. Several modelling approaches have been applied to obtain the water budget and mean annual sediment yield of 12 of the 26 studied river systems. In addition, the periodicities of water discharge events and their possible link with North Atlantic Oscillation (NAO) fluctuations have been also studied. A decreasing trend has been observed in most water discharge time series during the last decades, which has been attributed to natural factors. Although it could have been expected that the diminution of water discharge may have caused a reduction in sediment load, calculated sediment discharge time series do not show any significant tendency. In general, sediment yield shows an opposite relationship with basin area. A comparative analysis of Spanish Mediterranean deltas indicates that in terms of sediment transport Andalusian river systems are quite efficient despite the small size of their catchments. Repetitive flood events and the consequent suspension plumes off river mouths play a major role in the development of deltaic and prodeltaic bodies. Nowadays, 42% of the study area is regulated, although to date the effect of dam building is hardly noticeable on river mouths.

High rates of sediment transport by flashfloods in the Southern Judean Desert, Israel

A system has been installed to automatically monitor rainfall, streamflow, bedload discharge and suspended sediment concentration in the arid to hyper-arid setting of Nahal Rahaf, Southern Judean Desert in Israel. The Rahaf gauging station is located in a relatively steep, wide channel with an unsteady bed driven by flash floods. It is an attempt to deploy modern automatic equipment for continuous sediment transport monitoring in harsh, arid fluvial environments. Unit bedload discharges are the highest recorded hitherto, suggesting they may represent an upper end member in the worldwide climate–bedload discharge relationship. Suspended sediment concentration is much higher than is typical of perennial fluvial humid environments. There is high correlation between suspended sediment concentration and water discharge on an event scale, with diverse intra-event relations. The sediment yield of individual events is large, but the small number of floods limits the mean annual sediment yield to low values in this arid environment. This also has environmental implications, as large-scale quarrying requires a long period of self-restoration in such an arid fluvial setting. Copyright © 2005 John Wiley & Sons, Ltd.

The application of semi-quantitative methods and reservoir sedimentation rates for the prediction of basin sediment yield in Spain

Traditionally, the problems in predicting sediment yield at the basin scale are related to model's high data requirements, the focus on a limited amount of erosion and sediment transport processes and a general lack of systems knowledge. Here, we explore the performance of semi-quantitative approaches to predict mean annual area-specific sediment yield (SSY) at the scale of small to medium-sized basins. The Factorial Scoring Model (FSM) [Verstraeten, G., Poesen, J., de Vente, J., Koninckx, X., 2003. Sediment yield variability in Spain: a quantitative and semiqualitative analysis using reservoir sedimentation rates. Geomorphology 50 (4), 327–348], the PSIAC model [PSIAC, 1968. Pacific Southwest Inter-Agency Committee. Report of the water management subcommittee on factors affecting sediment yield in the Pacific southwest area and selection and evaluation of measures for reduction of erosion and sediment yield] and some variations of these models were applied to predict SSY for the 60 reservoirs, using the reservoir sedimentation rates as published by Avendaño Salas et al. [Avendaño Salas, C., Sanz Montero, E., Gómez Montaña, J.L., 1997. Sediment yield at Spanish reservoirs and its relationship with the drainage basin area. Dix-neuvième Congrès des Grands Barrages. Commission Internationale De Grands Barrages, Florence, pp. 863–874]. The FSM explained 72% of the variability found in reservoir sedimentation rates, which is significantly better than estimates based on basin area alone, explaining only 22%. The FSM uses five factors (i.e. topography, lithology, vegetation cover, gullies, basin shape) to characterise a drainage basin in the vicinity (<5 km) of the reservoir and the main tributaries feeding the reservoir, by providing a score. An index is calculated by multiplying the scores per factor. Together with basin area, this index is used to predict SSY. The PSIAC model works in a comparable way, though some other factors are used (i.e. topography, climate, runoff, lithology, soil, vegetation, land use, upland erosion, channel erosion), basin area is not part of the relation and the index is calculated by summation of all scores. PSIAC explained 58% of the variation in SSY. Advantages of both models over physically based and other empirical models are that less data are required, gully erosion is included and the importance of connectivity in the landscape is recognised. This study thus demonstrates that semi-quantitative approaches can provide fairly accurate and reliable estimates of SSY at the scale of small to medium sized basins, with relatively low data requirements.

Drainage, sediment transport, and denudation rates on the Nanga Parbat Himalaya, Pakistan

The Nanga Parbat Himalaya presents some of the greatest relief on Earth, yet sediment production and denudation rates have only been sporadically addressed. We utilized field measurements and computer models to estimate bank full discharge, sediment transport, and denudation rates for the Raikot and Buldar drainage basins (north slope of Nanga Parbat) and the upper reach of the Rupal drainage basin (south slope). The overall tasks of determining stream flow conditions in such a dynamic geomorphic setting is challenging. No gage data exist for these drainage basins, and the overall character of the drainage basins (high relief, steep flow gradients, and turbulent flow conditions) does not lend itself to either ready access or complete profiling. Cross-sectional profiles were surveyed through selected reaches of these drainage basins. These data were then incorporated into software (WinXSPRO) that aids in the characterization (stage, discharge, velocity, and shear stress) of high altitude, steep mountain stream conditions. Complete field measurements of channel depths were rarely possible (except at several bridges where the middle of the channel could actually be straddled and probed) and, when coupled with velocity measurements, provided discrete points of field-measured discharge calculations. These points were then used to calibrate WinXSPRO results for the same reach and provided a confidence level for computer-generated results. Flow calculations suggest that under near bank full conditions, the upper Raikot drainage basin produces discharges of ∼61 cm and moves about 11,000 tons day −1 (9980 tons day −1) of sediment through its channel. Bank full conditions on the upper portion of the Rupal drainage basin generate discharges of ∼84 cm and moves only about 3800 tons day −1 (3450 tons day −1) of sediment. Although the upper Rupal drainage basin moves more water, the lower slope of the drainage basin (0.03) generates a much smaller shear stress (461 Pa) than does the higher slope (0.12) of the upper Raikot drainage basin (1925 Pa). Dissolved and suspended sediment loads were measured from water/sediment samples collected throughout the day and night over a period of 10 days at the height of the summer melt season but proved to be a minor variable in transport flux. Channel bed loads were measured using a pebble count method of bank material and then used to generate ratings curves of bed loads relative to discharge volumes. When coupled with discharge data and basin area, mean annual sediment yield and denudation rates for Nanga Parbat are produced. Denudation rates calculated in this fashion range from 0.2 mm year −1 in the slower, more sluggish Rupal drainage basin to almost 6 mm year −1 in the steeper, faster flowing Raikot and Buldar drainage basins.

Estimation of sedimentation rates under Mediterranean conditions deduced from the Mishmar Ayyalon Reservoir, Israel

Fischhendler, I., Enzel, Y., Gvirtzman, H. 2003. Estimation of sedimentation rates under Mediterranean conditions deduced from the Mishmar Ayyalon Reservoir, Israel. Isr. J. Earth Sci. 52: 21–29. The Mishmar Ayyalon Reservoir was constructed in 1955 and its watershed drains the upper basins of Nahal Ayyalon and Nahal Nachshon (160 km). It has a water storage capacity of 7.3 × 10 m and is the only reservoir located within the western-flowing drainage basins that drains the mountain backbone of central Israel. Because the reservoir has never overflowed, the sediments that accumulated on its floor during the last 44 years provide a unique record of sedimentation rates and total sedimentation. A pit 3.3 m deep was dug into the sediment and variable-thickness layers, associated with specific years or flood events, were identified. Based on the sediment that was exposed in the pit and considering the original volume–elevation data of the reservoir, we have estimated the total sediment volume. Specific sediment layers were correlated with specific storms (and their resulting floods), based on three distinctive historical marker beds. The total sediment volume, which has been deposited by at least 22 significant floods, was calculated to be about 456,000 m. Approximately 30% of the sediment reached the reservoir during the two largest consecutive floods of the winter of 1963/4. Approximately 70% of the sediment was produced by a small number of very large floods. The mean annual specific suspended sediment yield for the catchment of the reservoir is 114 t km year, which is a typical sediment yield for land under minimal cultivation.

Sediment yields and soil loss rates from different land uses on Triassic shales in western Sydney, NSW

Sedimentation surveys of small dams demonstrate that land use is the dominant factor generating high sediment yields in the ungullied shale catchments of western Sydney where rainfall erosivity and soil erodibility are relatively constant. A single urban catchment produced 6.5 t/ha.year and cropped catchments an average of 6.7 ± 1.99 t/ha.year, whereas grazed woodland/forest and grazed pasture exported averages of only 2.5 ± 0.57 and 2.9 ± 1.02 t/ha.year, respectively. These yields are high by Australian standards and the farm dam sediments are enriched in both clay and phosphorus, in comparison to catchment topsoils. Empirical soil loss equations based on the Universal Soil Loss Equation (USLE) [Modified Universal Soil Loss Equation (MUSLE), Soiloss and Revised Universal Soil Loss Equation (RUSLE)] accurately predicted the measured sediment yields, with Soiloss being the most accurate. Although Soiloss is the only empirical equation to use Australian data, it is only marginally better than MUSLE, a simplified version of the USLE used for teaching. RUSLE predictions of soil loss rates were closely correlated with measured sediment yields but required inputs for poorly defined parameters. European land uses in the South Creek catchment, the largest shale catchment in western Sydney, have probably increased mean annual sediment yield by 4.4 times over that in 1788. Further increases are likely with increasing urbanisation.

Modelling mean annual sediment yield using a distributed approach

AbstractIn this paper a spatially distributed model for the calculation of sediment delivery to river channels is presented (SEDEM: SEdiment DElivery Model). The model consists of two components: (1) the calculation of a spatial pattern of mean annual soil erosion rates in the catchment using a RUSLE (Revised Soil Erosion Equation) approach; and (2) the routing of the eroded sediment to the river channel network taking into account the transport capacity of each spatial unit. If the amount of routed sediment exceeds the local transport capacity, sediment deposition occurs. An existing dataset on sediment yield for 24 catchments in central Belgium was used to calibrate the transport capacity parameters of the model. A validation of the model results shows that the sediment yield for small and medium sized catchments (10–5000 ha) can be predicted with an average accuracy of 41 per cent. The predicted sediment yield values with SEDEM are significantly more accurate than the predictions using a lumped regression model. Moreover a spatially distributed approach allows simulation of the effect of different land use scenarios and soil conservation techniques. Copyright © 2001 John Wiley &amp; Sons, Ltd.

Runoff‐induced sediment yield over dune slopes in the Negev Desert. 1: Quantity and variability

AbstractAlthough extensive data exist on runoff erosion and rates for non‐sandy hillslopes, data for arid dune slopes are scarce, owing to the widespread perception that the high infiltrability of sand will reduce runoff. However, runoff is generated on sandy dunes in the Hallamish dune field, western Negev Desert, Israel (P ≈ 95 mm) due to the presence of a thin (usually 1–3 mm) microbiotic crust. The runoff in turn produces erosion.Sediment yield was measured on ten plots (140–1640 m2) on the north‐ and south‐facing slopes of longitudinal dunes. Two plots facing north and two facing south were subdivided into three subplots. The subplots represented the crest of the active dune devoid of crust, the extensively crusted footslope of the dune, and the midslope section characterized by a patchy crust. The remaining plots extended the full length of the dune slope.No runoff and consequently no water‐eroded sediments were obtained from the crest subplots devoid of crust. However, runoff and sediment were obtained from the mid‐ and footslope crusted subplots. Sediment yield from the footslope subplots was much higher than from the midslopes, despite the higher sediment concentration that characterized the midslope subplots.The mean annual sediment yield at the Hallamish dune field was 432 g per metre width and was associated with high average annual concentrations of 32 g l−1. The data indicate that owing to the presence of a thin microbiotic crust, runoff and water erosion may occur even within arid sandy dune fields. Copyright © 2001 John Wiley &amp; Sons, Ltd.

A suspended sediment yield predictive equation for river basins in the South Western river basin system of Ghana

An empirical equation that can be used for estimating the suspended sediment yields of river drainage basins without sediment data has been established for basins in the sub-tropical forest Southwestern river basin system of Ghana. The power law equation relates mean annual specific suspended sediment yield (t km-2 yr-1) of the drain-age basin to the basin area (km2) and the mean daily stream discharge (m3/s) of the river at the outlet of the draiinage basin. Values of the parameters of the equation were computed from the least squares linear regression fit to the logarithmic transforms of observed mean annual specific suspended sediment yield, mean daily stream discharge and basin area data at selected river gauging stations in the basin system. The equation was found to fit the observed data very well with a high coefficient of multiple determination, R2 of 0.95. The fit was found to be better than those relating mean annual specific suspended sediment yield to basin area or runoff only. Since many stream gauging stations in the country have no records on fluvial sediment, the empirical equation can be used to obtain preliminary estimates of expected sediment load of streams for engineering design of hydraulic structures such as reservoirs. Journal of Applied Science and Technology (JAST) , Vol. 5, Nos. 1 & 2, 2000, pp. 108 - 113

The implications of general circulation model estimates of rainfall for future erosion: a case study from Brazil

One consequence of global change will be shifts in the probability of occurrence of soil erosion by water. This could have serious consequences for those areas of the world which are present-day `hotspots' for erosion. By means of a case study, this paper suggests an approach to quantifying the change in risk of serious erosion for sites in such areas. The case study focuses on future erosion under intensive soya bean cultivation in the Mato Grosso area of Brazil. On the area's highly erodible latosols, current erosion problems are severe. Scenarios of change future climate change are taken from general circulation models (GCMs) and used to perturb current-climate weather data. These are input to an erosion model (water erosion prediction project (WEPP)-CO2), together with local knowledge regarding current and probable future land use, in order to estimate future changes in erosion rates. WEPP-simulated average annual sediment yield increases in one of the scenarios and decreases in the other two, reflecting the range of uncertainty in predictions of future rainfall. Using the `best-guess' climate scenario from the UK Meteorological Office's HADCM2 GCM, the increase in mean annual sediment yield is 27%. Increases are disproportionately greater in wetter years. Average rates for individual months increase by over 100%. Erosion increases most on those parts of the hillslope profile which are currently hardest-hit by erosion. At present, an annual sediment yield of 5 t ha −1 is currently exceeded in about 1 year in 2. The HADCM2 simulations suggest that an equal or greater rate will occur in about 70% of years by around 2050. A rate of at least 10 t ha −1 yr −1 is currently exceeded in about 1 year in 5. The HADCM2 simulations suggest that this will rise, to about 1 year in 4.

Dynamique sédimentaire actuelle d'un système fluvial méditerranéen: l'Agly (France): Present sediment yield from a Mediterranean fluvial system: the Agly river (France)

The purpose of this study is to investigate the mechanical and chemical erosion rates in the Agly catchment (1 045 km 2) in order to estimate the whole sediment budget of a Mediterranean fluvial system. The climate of the catchment is characterized by a marked contrast between dry and humid conditions, with the occurrence of heavy downpours during only a few days of the year. As a consequence, the bedload charge and nearly all the suspended sediment load are transported during these events. Bedload charge is in deficit according to the fluvial geomorphology showing inner channels in bedrock. Dissolved solids, on the other hand, are transported much more uniformly over the year and reveal a dominance of carbonate weathering in the overall chemical erosion rates. On the basis of daily discharge data for the last thirty years, and taking all three transport pathways together (bedload, total suspended solids, total dissolved solids), the estimated mean annual sediment yield is 192 t·km −2·yr −1 and total denudation rate in the basin of 0.77 mm·yr −1, which is rather low for the Mediterranean area.

Sediment yield and seasonal soil erodibility for semiarid cropland in western Canada

Despite its importance to the degradation of the land resource, few estimates of soil loss or soil erodibility for water erosion from cropland have been made for the semiarid Brown soil zone of western Canada. To estimate these, we calibrated the event-based Modified Universal Soil Loss Equation with measured sediment yield for three 5-ha fields near Swift Current, Saskatchewan. The calibration used predetermined C, LS, P, and warm-season K factors with all erositivities and the K factors for other seasons optimized. Using this calibrated equation with 31 yr of measured runoff data, mean annual sediment yield for a conventional-tillage spring wheat-fallow cropping system on an undulating landscape (0 to 5% slopes) was estimated to be 0.8 Mg ha−1 yr−1. Estimated erosion from fallow land from 16 March to 15 April constituted 86% of the mean annual sediment yield. Erosion occurring during rainfall-runoff were relatively unimportant, accounting for about 4% of the estimated total sediment yield. An exceptionally severe rainstorm was predicted to have caused erosion of many Mg ha−1but the frequency of such events on a given field is too low to greatly affect mean annual erosion. Apparent field-scale soil erodibility was least in the winter (November to 15 March) when the soil would typically be frozen to the surface and was greatest in April when the soil would typically be partially frozen. Apparent erodibility in the summer and in late March was intermediate between those values. Key words: Erosion, runoff, snow, Universal Soil Loss Equation

Rates of fluvial erosion in basins with a Mediterranean type climate

Rates of erosion in mediterranean type climate areas are variable and they depend on climatic, physiographic and human factors. Available data from four mediterranean climatic areas are analysed, in order to find a relationship between sediment yield trends and precipitation values within each area and to compare trends along different areas. It may be inferred that there is a decrease in sediment yield with increasing precipitation; two distinctive curves are noticed: one for Israel and Spain, with a sediment peak at 300 mm of annual precipitation and a decreasing rate of 50 t/km −2/yr −1 for 100 mm of increasing annual rainfall, and the other for the Pacific coast areas — California and Chile — with a sediment peak at 400 mm and a faster decreasing rate of 100 t/km −2/yr −1 every 100 mm increase of rainfall. Non climatic factors, such as relief and human impact, may explain the higher rate of sediment yield for the Pacific coastal areas. The general trend of the “Langbein-Schumm curve”, determining an established correlation between mean annual precipitation and sediment yield, is valid for the analysed areas.

Glacial Sediment Production and Development of Hydro-Electric Power in Glacierized Areas

This paper discusses the results of a sediment-monitoring programme carried out in connection with hydro-electric power development plans in the river basins surrounding the Jostedalsbreen ice cap in Norway. Whereas the highest suspended-sediment transport rates occur during years with several flash-flood events, the bed load is more dependent upon the duration of large magnitude flood events. Bed-load transport has been obtained from annual measurements of deltaic growth in small lakes at the front of glaciers. During the years 1968–86, the mean ratio of bed load to total load amounted to 0.30–0.50% of the total load, but in years with large magnitude floods this ratio decreased. The mean annual suspended sediment yield of Norwegian glaciers ranges from 100 tonnes km2 a−1 to 1300 tonnes km2 a−1. Valley glaciers cause the highest erosion rates, with the exception of the small cirque glacier, Trollbergdalsbreen, which is thought to be a soft bed glacier. The investigation programme undertaken involved monitoring the volume of suspended sediments, together with the size distribution, mineralogy and shape of grains. In general, the valley glaciers supply more sand than the smaller cirque glaciers, whereas particles in the fine sand and silt-size ranges in almost all of the glaciers are angular in shape. Methods of comparing the abrasive capacity of the sediment load at various intakes in a power plant are discussed. Long-term sediment supply from the glaciers was investigated by studies of varves and rythmites in sediment cores from glacier-fed lakes.

Glacial Sediment Production and Development of Hydro-Electric Power in Glacierized Areas

This paper discusses the results of a sediment-monitoring programme carried out in connection with hydro-electric power development plans in the river basins surrounding the Jostedalsbreen ice cap in Norway. Whereas the highest suspended-sediment transport rates occur during years with several flash-flood events, the bed load is more dependent upon the duration of large magnitude flood events. Bed-load transport has been obtained from annual measurements of deltaic growth in small lakes at the front of glaciers. During the years 1968–86, the mean ratio of bed load to total load amounted to 0.30–0.50% of the total load, but in years with large magnitude floods this ratio decreased. The mean annual suspended sediment yield of Norwegian glaciers ranges from 100 tonnes km2 a−1 to 1300 tonnes km2 a−1. Valley glaciers cause the highest erosion rates, with the exception of the small cirque glacier, Trollbergdalsbreen, which is thought to be a soft bed glacier. The investigation programme undertaken involved monitoring the volume of suspended sediments, together with the size distribution, mineralogy and shape of grains. In general, the valley glaciers supply more sand than the smaller cirque glaciers, whereas particles in the fine sand and silt-size ranges in almost all of the glaciers are angular in shape. Methods of comparing the abrasive capacity of the sediment load at various intakes in a power plant are discussed. Long-term sediment supply from the glaciers was investigated by studies of varves and rythmites in sediment cores from glacier-fed lakes.

Spatial and temporal patterns of suspended-sediment yield in the Saskatchewan River basin

Long-term suspended-sediment concentration and load records are available for 23 Water Survey of Canada sediment-monitoring stations in the Saskatchewan River basin, where the drainage areas range from 10 to over 300 000 km2. Mean annual sediment yield is greatest in the western Alberta Plains along the Oldman and Red Deer rivers (over 100 t km−2 year−1) and tends to increase downstream along the North and South Saskatchewan rivers until major reservoirs in Saskatchewan intervene. Average sediment concentration shows a pattern of variation similar to that of yield. Temporal aspects of suspended-sediment transport vary along the drainage network. The range and skewness of the yield–duration and concentration–duration curves are greater in the intermediate-size basins close to the Rocky Mountains and in two small basins with Prairie sources than they are in the large Prairie streams with mountain sources and the glacier-fed upper North Saskatchewan River. Similarly, infrequent flows transport a larger proportion of the annual load in the smaller Foothills and western Plains basins than in the large Prairie streams because of differences in drainage area and discharge regime.

Rates of soil loss from mountain footpaths: an experimental study in the Drakensberg Mountains, South Africa

In a three-year study at Kamberg Nature Reserve, measured annual rates of soil loss from an experimental path showed that under some circumstances path erosion can exceed soil loss tolerance and mean annual sediment yield from the Tugela river cachment, in which the experimental site was located. Further, burning of vegetation adjacent to the path caused a disproportionate increase in rates of soil erosion, and quantities of soil eroded were significantly related to some rainfall parameters. The study concludes that design of path networks must take burning régimes and spatial variation of rainfall into account if path maintenance costs are to be minimized.

Variations in mean annual sediment yield as a function of mean annual precipitation

Statistical analysis of available data; no simple relationship between annual precipitation and sediment yield