River Suspended Sediment Concentration Research Articles

Using sediment tracing to assess processes and spatial patterns of erosion in grazed rangelands, Burdekin River basin, Australia

Identifying how agricultural practices can be changed to reduce sediment loss requires knowledge of the erosion processes and spatial areas contributing to end of catchment sediment loads. The Burdekin River basin in northeast Australia is a priority for such knowledge because of its large size (130,000km2), ongoing public investment in changing agricultural practices, and because sediment exports are known to affect the health of a significant aquatic ecosystem, the Great Barrier Reef (GBR). This study applied sediment tracing techniques within the Burdekin River basin to identify the contributions of surface versus subsurface soil, and spatial areas to fine sediment export. Tracer properties included fallout radionuclides and geochemistry. The contributions of each sediment source to river sediment were identified with 95% confidence intervals using a Monte-Carlo numerical mixing model. Between 77% and 89% of fine sediment loss in the study area was derived from subsurface soil sources. High-resolution monitoring of river suspended sediment concentrations indicated that sediment sources were in close proximity to the drainage network, since concentrations were higher on the rising limb than the falling limb of large hydrographs. Gully erosion is likely to be the dominant subsurface soil erosion process, although channel bank erosion and hillslope rilling cannot be discounted. The results contrast with previous sediment budget spatial modelling, which predicted that hillslope erosion was the dominant sediment source in the area, thus demonstrating the need to independently verify modelling predictions where input datasets are poor. The contribution of surface soil to river sediment was generally similar between catchments which were currently grazed and two catchments where livestock grazing ceased 7 years ago. Concurrent increases in vegetation cover in the non-grazed catchments indicate that surface erosion rates had declined, suggesting that subsurface soil erosion rates had also declined by a similar amount. The estimated contributions of spatial source areas within the large study catchments had narrower confidence intervals when source areas were defined using sediment from geologically distinct river tributaries, rather than using soil sampled from geological units in the catchment, since tributary sediment had less-variable geochemistry than catchment soil. Programs to reduce fine sediment losses from the Burdekin River basin should primarily focus on reducing sub-surface soil erosion proximal to the basin's drainage network. Understanding the biophysical processes of pollutant generation is important to help guide on-ground activities to improve water quality.

Prediction of Sediment Concentration in Rivers by Recursive Least-Squares and Linear Minimum Variance Estimators

AbstractPeaks of suspended sediment concentration in rivers appear before peak discharge appears. The observation of discharge is usually done in many rivers for river management, but the suspended sediment concentration is not always observed. The suspended sediment concentration is expressed by a sediment-rating curve over a long period of time. Coefficients in the sediment-rating curve are time varying. The time variation of the suspended sediment concentration is predicted by the sediment-rating curve with the recursive least-squares and the linear minimum variance estimators. Because the sediment-rating curve is linearized by the logarithmic transformation, we can apply the simple linear models such as recursive least-squares and linear minimum variance estimators for the prediction of the suspended sediment concentration. These methods indicate that the coefficients in the sediment-rating curve are time varying. These methods can estimate sediment discharge by identifying the coefficients in the sed...

Estimation of suspended sediment concentration from turbidity measurements using artificial neural networks

Suspended sediment concentration (SSC) is generally determined from the direct measurement of sediment concentration of river or from sediment transport equations. Direct measurement is very costly and cannot be conducted for all river gauge stations. Therefore, correct estimation of suspended sediment amount carried by a river is very important in terms of water pollution, channel navigability, reservoir filling, fish habitat, river aesthetics and scientific interests. This study investigates the feasibility of using turbidity as a surrogate for SSC as in situ turbidity meters are being increasingly used to generate continuous records of SSC in rivers. For this reason, regression analysis (RA) and artificial neural networks (ANNs) were employed to estimate SSC based on in situ turbidity measurements. The SSC was firstly experimentally determined for the surface water samples collected from the six monitoring stations along the main branch of the stream Harsit, Eastern Black Sea Basin, Turkey. There were 144 data for each variable obtained on a fortnightly basis during March 2009 and February 2010. In the ANN method, the used data for training, testing and validation sets are 108, 24 and 12 of total 144 data, respectively. As the results of analyses, the smallest mean absolute error (MAE) and root mean square error (RMSE) values for validation set were obtained from the ANN method with 11.40 and 17.87, respectively. However these were 19.12 and 25.09 for RA. It was concluded that turbidity could be a surrogate for SSC in the streams, and the ANNs method used for the estimation of SSC provided acceptable results.

River suspended sediment concentration modeling using a neural differential evolution approach

Summary In this study, neural differential evolution (NDE) models are proposed to estimate suspended sediment concentration. NDE models are improved by combining two methods, neural networks and differential evolution. The accuracy of NDE models were compared with those of the adaptive neuro-fuzzy (NF), neural networks (NN) and rating curve (RC) models. The daily streamflow and suspended sediment data from two stations, Rio Valenciano Station and Quebrada Blanca Station, operated by the US Geological Survey (USGS) were used as case studies. The models’ accuracies were evaluated using mean square error (MSE) and determination coefficient ( R 2 ) statistics. A comparison of results indicated that the NDE models give better estimates than NF, NN and RC techniques. For the Rio Valenciano Station and Quebrada Blanca Station, it was found that the NDE models with MSE = 2549 mg 2 l −2 , R 2 = 0.884 and MSE = 240 mg 2 l −2 , R 2 = 0.942 in the test stage were superior in estimating suspended sediment concentration to the optimal neuro-fuzzy models with MSE = 0.2704 mg 2 l −2 , R 2 = 0.876 and MSE = 320 mg 2 l −2 , R 2 = 0.929, respectively.

Capacitive sensing technique for silt suspended sediment concentration monitoring

Automated, real-time, and continuous techniques for monitoring suspended sediment concentration in rivers and reservoirs can play an important role in the improvement of the quantity and quality of sediment data, and are valuable to the management of water environment, water conservancy, hazard prevention, and water resources. Research in the monitoring techniques has examined the possibility of using the characteristics of dielectric constants for detecting soil moisture and concentration of air-water two-phase flow, based on the fact that dielectric constants of sediment, air and water are different. A capacitance sensor was developed to monitor the silt suspended sediment concentration (SSSC) in a recent study, following the principle that as SSSC increases in the sediment-water mixture, the apparent dielectric constant of the water sample also increases and therefore the capacitance detected by the sensing system also increases. It is demonstrated that the variations in the concentration of silt sediment correlates positively with the variations in observed capacitance in a linear fashion, and correlates negatively with voltage outputs but also in a linear fashion. The correlation coefficients reached above 0.98. The overall errors in estimated concentrations range between 0.26% and 2.91%. Elements in the capacitance sensor system such as the frequencies of the signal generating system, areas of the electrode plates, and effects of sample temperature have also been evaluated. The results illustrated that the capacitance sensor techniques can be applied to monitoring SSSC automatically and continuously. Also, the range of SSSC in the experiment reached 200 kg/m 3; therefore, the application of this technique in practical SSSC monitoring is worthy of further research.

Evolutionary fuzzy models for river suspended sediment concentration estimation

This paper proposes the application of evolutionary fuzzy models (EFMs) for suspended sediment concentration estimation. The EFMs are improved by the combination of two methods, fuzzy logic and differential evolution. The accuracy of EFMs is compared with those of the adaptive neuro-fuzzy, neural networks and rating curve models. The daily streamflow and suspended sediment data belonging to two stations, Quebrada Blanca Station and Rio Valenciano Station, operated by the US Geological Survey (USGS) are used as case studies. The mean square errors and determination coefficient statistics are used for evaluating the accuracy of the models. Based on the comparison of the results, it is found that the EFMs give better estimates than the other techniques.

Estimation of suspended sediment concentration in rivers using acoustic methods

Acoustic Doppler current meters (ADV, ADCP, and ADP) are widely used in water systems to measure flow velocities and velocity profiles. Although these meters are designed for flow velocity measurements, they can also provide information defining the quantity of particulate matter in the water, after appropriate calibration. When an acoustic instrument is calibrated for a water system, no additional sensor is needed to measure suspended sediment concentration (SSC). This provides the simultaneous measurements of velocity and concentration required for most sediment transport studies. The performance of acoustic Doppler current meters for measuring SSC was investigated in different studies where signal-to-noise ratio (SNR) and suspended sediment concentration were related using different formulations. However, these studies were each limited to a single study site where neither the effect of particle size nor the effect of temperature was investigated. In this study, different parameters that affect the performance of an ADV for the prediction of SSC are investigated. In order to investigate the reliability of an ADV for SSC measurements in different environments, flow and SSC measurements were made in different streams located in the Aegean region of Turkey having different soil types. Soil samples were collected from all measuring stations and particle size analysis was conducted by mechanical means. Multivariate analysis was utilized to investigate the effect of soil type and water temperature on the measurements. Statistical analysis indicates that SNR readings ob tained from the ADV are affected by water temperature and particle size distribution of the soil, as expected, and a prediction model is presented relating SNR readings to SSC mea surements where both water temperature and sediment characteristics type are incorporated into the model. The coefficients of the suggested model were obtained using the multivariate anal ysis. Effect of high turbidity conditions on ADV performance was also investigated during and after rain events.

Climate and land-use changes affecting river sediment and brown trout in alpine countries—a review

Catch decline of freshwater fish has been recorded in several countries. Among the possible causes, habitat change is discussed. This article focuses on potentially increased levels of fine sediments going to rivers and their effects on gravel-spawning brown trout. Indications of increased erosion rates are evident from land-use change in agriculture, changes in forest management practices, and from climate change. The latter induces an increase in air and river water temperatures, reduction in permafrost, changes in snow dynamics and an increase in heavy rain events. As a result, an increase in river sediment is likely. Suspended sediment may affect fish health and behaviour directly. Furthermore, sediment loads may clog gravel beds impeding fish such as brown trout from spawning and reducing recruitment rates. To assess the potential impact on fine sediments, knowledge of brown trout reproductive needs and the effects of sediment on brown trout health were evaluated. We critically reviewed the literature and included results from ongoing studies to answer the following questions, focusing on recent decades and rivers in alpine countries. Have climate change and land-use change increased erosion and sediment loads in rivers? Do we have indications of an increase in riverbed clogging? Are there indications of direct or indirect effects on brown trout from increased suspended sediment concentrations in rivers or from an increase in riverbed clogging? Rising air temperatures have led to more intensive precipitation in winter months, earlier snow melt in spring, and rising snow lines and hence to increased erosion. Intensification of land use has supported erosion in lowland and pre-alpine areas in the second half of the twentieth century. In the Alps, however, reforestation of abandoned land at high altitudes might reduce the erosion risk while intensification on the lower, more easily accessible slopes increases erosion risk. Data from laboratory experiments show that suspended sediments affect the health and behaviour of fish when available in high amounts. Point measurements in large rivers indicate no common lethal threat and suspended sediment is rarely measured continuously in small rivers. However, effects on fish can be expected under environmentally relevant conditions. River bed clogging impairs the reproductive performance of gravel-spawning fish. Overall, higher erosion and increased levels of fine sediment going into rivers are expected in future. Additionally, sediment loads in rivers are suspected to have considerably impaired gravel bed structure and brown trout spawning is impeded. Timing of discharge is put forward and is now more likely to affect brown trout spawning than in previous decades. Reports on riverbed clogging from changes in erosion and fine sediment deposition patterns, caused by climate change and land-use change are rare. This review identifies both a risk of increases in climate erosive forces and fine sediment loads in rivers of alpine countries. Increased river discharge and sediment loads in winter and early spring could be especially harmful for brown trout reproduction and development of young life stages. Recently published studies indicate a decline in trout reproduction from riverbed clogging in many rivers in lowlands and alpine regions. However, the multitude of factors in natural complex ecosystems makes it difficult to address a single causative factor. Further investigations into the consequences of climate change and land-use change on river systems are needed. Small rivers, of high importance for the recruitment of gravel-spawning fish, are often neglected. Studies on river bed clogging are rare and the few existing studies are not comparable. Thus, there is a strong need for the development of methods to assess sediment input and river bed clogging. As well, studies on the effects to fish from suspended sediments and consequences of gravel beds clogging under natural conditions are urgently needed.

Monitoring event-based suspended sediment concentration by artificial neural network models

This paper is concerned with monitoring the hourly event-based river suspended sediment concentration (SSC) due to storms in Jiasian diversion weir in southern Taiwan. The weir is built for supplyi...

Development of a river delta: a case study of Cimanuk river mouth, Indonesia

AbstractThis paper describes delta development processes with particular reference to Cimanuk Delta in Indonesia. Cimanuk river delta, the most rapidly growing river delta in Indonesia, is located on the northern coast of Java Island. The delta is subject to ocean waves of less than 1 m height due to its position in the semi‐enclosed Java Sea in the Indonesian archipelago. The study has been carried out using a hydrodynamic model that accounts for sediment movement through the rivers and estuaries. As an advanced approach to management of river deltas, a numerical model, namely MIKE‐21, is used as a tool in the management of Cimanuk river delta. From calibration and verification of hydrodynamic model, it was found that the best value of bed roughness was 0·1 m. For the sediment‐transport model, the calibration parameters were adjusted to obtain the most satisfactory results of suspended sediment concentration and volume of deposition. By comparing the computed and observed data in the calibration, the best values of critical bed shear stress for deposition, critical bed shear stress for erosion and erosion coefficient were 0·05 N m−2, 0·15 N m−2, and 0·00001 kg m−2 s−1, respectively.The calibrated model was then used to analyse sensitivity of model parameters and to simulate delta development during the periods 1945–1963 and 1981–1997. It was found that the sensitive model parameters were bed shear stresses for deposition and erosion, while the important model inputs were river suspended sediment concentration, sediment characteristics and hydrodynamic. The model result showed reasonable agreement with the observed data. As evidenced by field data, the mathematical model proves that the Cimanuk river delta is a river‐dominated delta because of its protrusion pattern and very high sediment loads from the Cimanuk river. It was concluded that 86% of sediment load from the Cimanuk river was deposited in the Cimanuk delta. Copyright © 2008 John Wiley & Sons, Ltd.

Yangtze River Sediment: In Response to Three Gorges Reservoir (TGR) Water Impoundment in June 2003

The well-known and enormously controversial Three Gorges Reservoir (TGR) on the Yangtze River, China, impounded about 9.936 × 109 m3 of water (between Qingxichang and Huanglingmiaodou) for the first time from May 25 to June 10, 2003, finally elevating the water level to about 135 m above mean sea level at the dam. Mainly on the basis of daily, monthly, and annual water and sediment data sets of the Yangtze River at mainstream hydrological stations above and below the TGR Dam in 2003, we preliminarily examined the effects made by the TGR water impoundment in June 2003 on the Yangtze River sediment. According to sediment transport balance method, the estimated amount of suspended sediment impounded in the TGR is (1) about 3.1816 × 106 t between Qingxichang and Huanglingmiaodou during June 1 to June 10; (2) about 1.247 × 108 t between Cuntan and Yichang in 2003, which in June accounted for 25.9% and from June to December accounted for 99.2%; and (3) about 1.359 × 108 t between Cuntan and Yichang in 2003, if considering eroded sediment from the channel between the TGR Dam and Yichang. The TGR sedimentation resulting from the TGR water impoundment leads to unnaturally clear water discharged from the TGR Dam, which results in the Yangtze River suspended sediment concentration and sediment load downstream of the TGR Dam in 2003 being reduced more than those above the TGR Dam, and the channel just below the TGR Dam significantly eroded (about 4.759 × 105 t between Yichang and Shashi from June 1 to June 10).

Estimating suspended sediment concentrations from turbidity measurements and the calibration problem

AbstractIn situ turbidity meters are being increasingly used to generate continuous records of suspended sediment concentration in rivers. However, the usefulness of the information obtained depends heavily on the existence of a close relationship between fluctuations in suspended sediment concentration and turbidity and the calibration procedure that relates suspended sediment concentration to the turbidity meter's signal. This study assesses the relationship between suspended sediment concentration and turbidity for a small (1·19 km2) rural catchment in southern Brazil and evaluates two calibration methods by comparing the estimates of suspended sediment concentration obtained from the calibrated turbidity readings with direct measurements obtained using a USDH 48 suspended sediment sampler. With the first calibration method, the calibration relationship is derived by relating the turbidity readings to simultaneous measurements of concentration obtained from suspended sediment samples collected from the vicinity of the turbidity probe during flood events. With the second method, the calibration is based on the readings obtained from the turbidity meter when the probe immersed in samples of known concentration prepared using soils collected from the catchment. Overall, there was a close link between fluctuations in suspended sediment concentration and turbidity in the stream at the outlet of the catchment, and the estimates of sediment concentration obtained using the first calibration method corresponded closely with the conventionally measured sediment concentrations. However, use of the second calibration method introduced appreciable errors. When the estimated sediment concentrations were compared with the measured values, the mean errors were ± 122 mg l−1 and + 601 mg l−1 for the first and second calibration procedures respectively. Copyright © 2007 John Wiley & Sons, Ltd.

Global variability of daily total suspended solids and their fluxes in rivers

The daily variability of river suspended sediment concentration (Cs) and related yield ( Y) is studied at 60 global stations. The data set covers natural conditions (e.g. pre-reservoir data), ranging from the humid tropics to subarctic and arid regions, located in all types of relief (yearly runoff q* from 0.1 to 55 l s −1 km −2). Basin area ranges from 64 km 2 to 3.2 million km 2. Survey lengths range from 1 to 20 years with a median of 3 years. Median values (Cs 50, q 50, Y 50) and discharge-weighted averages for Cs* and Y* range from 5 to 29 000 mg l −1 and 10 to 5000 kg km −2 day −1, respectively. A set of indicators of variability are proposed for sediment concentration, water and sediment discharges including mean to median ratios (Cs*/Cs 50, Y*/ Y 50), the percentage of sediment flux discharged in 2% of time (Ms 2), the percentage of time necessary to carry half of the sediment flux (Ts 50), and quantiles of Cs, q and Y distributions corresponding to the discharge-weighted averages. Since most of the sediment flux is discharged in less than 25% of the time, “truncated rating curves” metrics are proposed between the Cs vs. q relationship for periods of high flux. Temporal variability decreases with increasing basin size, lake abundance, and is higher for basins influenced by glaciermelt and snowmelt. The least variable sediment flux regimes are noted for the Mississippi at its mouth, the Rhone Lacustre, the St. Lawrence and the Somme, a medium-sized French phreatic river. The most variable flux regimes were for small- to medium-sized basins (i.e. <1000 to 10 000 km 2) such as steep Andean Bolivian basins, Thai basins, the Eel (CA) and Walla Walla (OR) rivers. A proposed global scale typology is based on six classes key variability indicators.

Application of a regional procedure to assess the risk to fish from high sediment concentrations

Periods of high suspended sediment concentration in rivers can affect the behaviour, health and habitat of freshwater fish. A simple regional model relating daily mean suspended sediment concentration in rivers to flow and percentage of cropped and urban land has been applied to the Lower Swale, UK. The model uses a GIS catchment coverage of hydrological response units (HRUs) of area 5–8 km 2, each of which is assumed hydrologically independent and drains to an identified river reach. The sediment delivery properties of each HRU are a function of its land use characteristics determined from existing databases, and hydrological conditions determined from effective rainfall measurements. Daily mean suspended sediment concentrations for each river reach were derived by cumulating simulated HRU flows and sediment loads down successive reaches. A map of the modelled 10% quantile sediment concentrations is presented for both HRUs and river reaches. The map is substantially different from existing erosion risk maps because the delivery model is driven by flow in addition to land use, rather than by soil type. Frequency curves showing the exceedance probability of mean simulated sediment concentrations over 1–6-day durations have been derived using peaks-over-threshold techniques. Maps of the risk of harm to fish, based on the probability of 1- and 4-day sediment concentrations exceeding 80 mg l −1, are presented. Such maps can be used to assess the impact of sediment on fish and for setting appropriate river water quality objectives.

A phase-space reconstruction approach to prediction of suspended sediment concentration in rivers

The use of phase-space reconstruction approach for understanding and predicting suspended sediment concentration dynamics in rivers is investigated. According to this approach, the dynamic changes of the suspended sediment concentration phenomenon are represented by reconstructing (or embedding) the single-dimensional (or variable) suspended sediment concentration series in a multi-dimensional phase-space. After representing the dynamics in the phase-space, a local approximation method is employed for making predictions. The approach is employed for representing and predicting the dynamics of the daily suspended sediment concentration observed in the Mississippi River basin (at St. Louis, MO) in the United States of America. The predicted suspended sediment concentrations are found to be in very good agreement with the observed ones; not only are the major trends well captured but the minor (noisy) fluctuations reasonably preserved as well. The near-accurate predictions indicate the appropriateness of the phase-space reconstruction approach for understanding the suspended sediment concentration phenomenon. The results (i.e. optimal embedding dimension) also reveal that the suspended sediment concentration dynamics are dominantly influenced by three variables, suggesting that the suspended sediment concentration (and other sediment transport related) phenomena could be viewed from a low-dimensional chaotic dynamic perspective.

Development of a sediment delivery model for application in large river basins

This paper presents an analysis of available data on suspended sediment concentrations in rivers within the Yorkshire region. It identifies the main control on the mean suspended sediment concentration across 62 medium-sized catchments (5–380 km2) to be that of land cover/use, with the percentage of cropped and suburban/urban land accounting for 71·5% of the variation between catchments. Twenty-two of the sites have associated flow gauging, and analysis of this reveals a strong flow dependence for catchments with a high percentage of arable land. In the case of urbanized catchments, there is considerable scatter owing to the influence of point source inputs: notably sewage effluent, combined sewer overflows, drainage from colliery waste and mine waters. This scatter is due not only to the inherent variability within these point sources, which is not flow related, but also to the variable degree of dilution by flow in the main stream. As a first-order approximation, a simple regression model, in which sediment concentration is a function of the daily mean flow and the percentage of cropped and suburban/urban land cover can be used to generate daily time-series of sediment concentration. This model has been applied within the LOIS catchment delivery model and performs well across a wide range of catchment types. Results are presented for four catchments representative of the Yorkshire region. Copyright © 1999 John Wiley & Sons, Ltd.

Development of a sediment delivery model for application in large river basins

This paper presents an analysis of available data on suspended sediment concentrations in rivers within the Yorkshire region. It identifies the main control on the mean suspended sediment concentration across 62 medium-sized catchments (5–380 km2) to be that of land cover/use, with the percentage of cropped and suburban/urban land accounting for 71·5% of the variation between catchments. Twenty-two of the sites have associated flow gauging, and analysis of this reveals a strong flow dependence for catchments with a high percentage of arable land. In the case of urbanized catchments, there is considerable scatter owing to the influence of point source inputs: notably sewage effluent, combined sewer overflows, drainage from colliery waste and mine waters. This scatter is due not only to the inherent variability within these point sources, which is not flow related, but also to the variable degree of dilution by flow in the main stream. As a first-order approximation, a simple regression model, in which sediment concentration is a function of the daily mean flow and the percentage of cropped and suburban/urban land cover can be used to generate daily time-series of sediment concentration. This model has been applied within the LOIS catchment delivery model and performs well across a wide range of catchment types. Results are presented for four catchments representative of the Yorkshire region. Copyright © 1999 John Wiley & Sons, Ltd.

A global geochemical mass budget applied to the Congo basin rivers: Erosion rates and continental crust composition

Rivers carry the products of continental denudation either in a dissolved form (chemical erosion) or in a solid form (physical erosion). We focus in this paper on the relationship between physical erosion and chemical erosion. We establish the mass budget of the Congo Basin Rivers using chemical complementarities between river suspended sediments, sandy bedload, and dissolved load of the Congo Basin rivers reported in a previous paper (Dupré et al., 1995). A series of equations are presented, assuming that the physical and chemical erosion processes are in a steady state during one year. The total mass of river-borne material (dissolved and particulate) transported in the river over a given period of time should balance the mass of upper continental crust eroded during this time.We show that the local continental crust on each drainage basin can be estimated and solve our steady-state weathering model using an inversion procedure. The very good agreement between modelled and measured values of the river-suspended sediment concentrations validates the steady-state hypothesis in this wet tropical area. Consequently, in this area, the sediment yield provide a good estimate of the rates of mechanical denudation. This result also validates the calculation of the chemical and isotopic composition of the local continental upper crust using the bulk river load. Erosion rates for the silicate upper crust and thus independent of the lithological variability (silicates, evaporites, and carbonates) of the drainage basins are calculated. Mechanical erosion rates and chemical erosion rates for the Congo Basin at Brazzaville are 8 t/km2/y and 5 t/km2/y. The corresponding consumption of atmospheric CO2 by weathering process is estimated to 51 × 103 mol/km2/an. These weathering and consumption rates are low in spite of the severity of the weathering conditions, of the high soil temperature, and of the intensity of precipitations. These conclusions indicate the limiting influence the dynamic equilibrium of soils for silicate weathering. Finally, by estimating the local continental crust chemical composition before the onset of erosion processes, especially for the most soluble elements, we can test the model of Taylor and McLennan.

Application of a digital filter for modelling river suspended sediment concentrations

The relationship between suspended sediment concentration and discharge in a river system is the result of a complex interaction of factors within the basin and of specific storm events. Nevertheless, estimation of suspended sediment concentrations during storm events is essential for prediction of loadings from storm-controlled river basins to the receiving waters. The Venoge River, a tributary of Lake Geneva, Switzerland, with a basin area of 237 km 2, has been monitored during eight storm events between October 1986 and November 1987. A digital filter is used to simulate the suspended sediment response during individual events with the principal factors being antecedent flow, maximum discharge and time during which maximum flow was attained. The measured and calculated sediment concentration curves were assessed using a x 2-test. It was concluded that the two curves were similar in shape at 95% confidence interval. However, the model is not always capable of simulating the phase lead effect of the sediment distribution curve relative to the hydrograph. This problem is most evident during high-intensity storms at periods of low base flow; and consequently, loadings calculated for individual storms of this type could be overestimated. Fortunately, the model provides good predictions during less-intense, longer-duration events and therefore loadings calculated by summing events for an annual period will tend not to be overestimated. Further work is necessary to evaluate the model for additional events, in particular spring snow melt, and to determine its applicability to other river systems.

A NOTE ON INEXPENSIVE TELEMETRY OF RIVER SEDIMENT CONCENTRATIONS

Synopsis An inexpensive method for continuous monitoring of suspended sediment concentrations in rivers has recently been developed at the University of Natal. The instrument uses newly available solid state electronic circuitry and has been thoroughly laboratory-tested. The circuitry and the operation of the instrument are described in general terms.