Values Of Sediment Concentration Research Articles

A numerical study of mixing and sediment transport caused by tidal in the Bontang waters

Freshwater and sediment that carried by the river then flow into the bay will cause sediment transport and mixing in the bay, in this case the Bontang Waters. The three-dimensional finite difference baroclinic model system (ECOMSED) is used to do numerical studies of the mixing and sediment transport process, this model was simulated for 40 days and verified using tidal data that taken using CTD. The values of sediment concentration ranged from 1×10−6 to 1×10−5 gr/cm3 on the surface, with sediment transport ranging between 0 – 12 (gr/m2)/s. Salinity on the surface is 0 - 35 ppm, and the temperature is 25 - 40 ° C. Mixing occurred at one river mouth with a salinity profile of 25 ppm on the surface and 32 ppm at the bottom, the sediment concentration value was in the range of 1.2×10−5 gr/cm3 on the surface and decreased to 4×10−6 gr/cm3 at the bottom.

Vegetative-hydraulic parameters generated by agricultural crops for laminar flows under a semi-arid environment of Pernambuco, Brazil

The structural parameters of vegetation have an important influence on the resistance imposed to shallow flow under the soil, being important in the control of floods, water erosion and sediment transport in the watersheds. Therefore, in order to obtain the hydraulic characteristics of overland flow, the variables of hydraulic resistance generated by the vegetation to surface flow, and the interrill erosion rates under semi-arid region led to the introduction of agricultural crops, through which shallow flows were generated on elephant grass (Pennisetum purpureum), corn (Zea mays sp.) and in a bare Entisol, placed in a toeslope landscape position. Results showed that the flow regime was slow, laminar and interrill erosion occurred (Re < 500 and Fr < 1). Nevertheless, the hydraulic characteristics of overland flow (Vm, h, q and log f) were probably affected by the proximity to the water table, a hypothesis supported by the obtained values for the infiltration. However, corn and principally elephant grass showed high hydraulic resistance to superficial flow and interrill erosion conferred by the highest ground coverage (lowest Ci = 0.198), by the effect of the sub-factors CiI, CiII and CiIII, and the lowest values of sediment concentration (CS), runoff coefficient (C), interrill detachment rate (Di), and soil loss (SL). Our results support the purpose of introducing agricultural crops in the Brazilian semi-arid region since increasing resistance to interrill erosion can be provided. Elephant grass is a more appropriate crop to be inserted under land management protocols in the semi-arid environment.

Effect of concentration and size of sediments on hydro-abrasive erosion of Pelton turbine

Hydro-abrasive erosion caused by suspended sediments is a severe issue leading to frequent generation losses and failure of hydropower components especially in geologically young mountains like the Himalayas. To study the erosion behaviour of different materials under the same erosive and hydraulic conditions, experiments were performed simultaneously with different range of velocity, duration of exposure, sediment size, and concentration on a 1:8 down scaled Pelton buckets from an Indian hydropower plant (HPP) located in Himalayas. This work extends the research of Padhy and Saini (2009) for application in Pelton turbines fabricated from 6 materials such as 3 kinds of steel, 2 kinds of coatings and bronze for head up to 200 m. The values of sediment concentration for the tests were 500, 1500 and 3000 ppm, values mostly found in the HPPs. The developed erosion models were used to predict the erosion of the Pelton buckets from the study plant and are useful for proper planning of preventive measures and operation of the HPPs.

Measurement errors on sediment concentration from traditional runoff collection tanks and its correction possibility

Runoff plots are widely used worldwide to monitor water and soil losses. Sediment concentration in runoff collection tank is measured by stirring-sampling procedure, but this method may produce high measurement error due to the uneven mixing of collected sediments with water and soil particle deposition. This study aimed to identify the relationship between actual and measured sediment concentrations, so as to estimate the systematic error of sediment concentration measurement from runoff collection tank by traditional stirring-sampling procedure and the possibility to eliminate it. Four major soils including black soil, silt loess, clay loess, and purple soil in China were used to determine the correlation between the measured and designed sediment concentrations in laboratory. Tested sediment concentration was 1, 2, 5, 8, 10, 20, 50, 80, 100, 200, 500, 800, and 1000 kg/m3, and total sediment-laden water volume was 50 L and 100 L. Five samples were collected successively from collection tank for each treatment and their sediment concentrations were measured by conventional oven-drying method. The results showed that all the measured sediment concentration values were smaller than the designed ones, but both the measured and designed values were linearly correlated significantly with determination coefficients greater than 0.8, generally. In the whole tested concentration range, the systematical error was –0.19 to –319.95 kg/m3 and relative error was 0.30%-84.5% for the 4 tested soils and 2 total sediment-laden water volumes. These results indicated a necessity and possibility to correct conventional sediment concentration measurement value. The result is usable to assess and correct the measurement error of sediment concentrations from traditional runoff plot. Keywords: collection tank, measurement error, runoff plot, sediment concentration, stirring-sampling method DOI: 10.25165/j.ijabe.20191203.4208 Citation: Huang Y H, Zhao H, Li F H, Yuan P J, Wang W, Zhang G H. Measurement errors on sediment concentration from traditional runoff collection tanks and its correction possibility. Int J Agric & Biol Eng, 2019; 12(3): 77–83.

Suspended sediment yield characteristics variability in rivers of Kamchatka krai

The regularities of spatiotemporal variability of suspended sediment yield characteristics were studied. Based on the analysis of difference-integral yield curves, it was found that most of the rivers in Kamchatka krai are characterized by the presence of two relatively long trends in the suspended sediment yield variability: an increase until the end of the 1970s–early 1980s, and its subsequent decrease. This regularity disturbs in rivers under the influence of volcanic eruptions, where the most significant increasing of sediment yield is observed after major eruptions. Existent maps of mean annual suspended sediment concentration and mean annual specific suspended sediment yield were significantly specified (18 instead 4 and 13 instead two zones were marked respectively). The map of grain-size distribution of suspended sediment was compiled (three zones was marked in region under study). Maximum values of mean annual specific suspended sediment yield (more than 500 t km-2 yr-1), suspended sediment concentration (more than 1000 g m-3) and grain-size of sediments are observed in water runoff of volcanic areas. Minimum values of suspended sediment concentration, specific suspended sediment yield, as well as grain-size of sediments characterized the mainland part of the krai.

Effects of rainfall intensities on sediment loss and phosphorus enrichment ratio from typical land use type in Taihu Basin, China.

Soil erosion induced by rainfall has become one of the major environmental disasters. It can lead to degradation of land productivity and water pollution, which limit human survival and development. Therefore, understanding the effects of rainfall intensities on soil nutrient and sediment transportation from farmland via surface runoff is important. This study simulated three types of rainfall intensities (low intensity 0.83mmmin-1; medium intensity 1.17mmmin-1 and 1.67mmmin-1; and high intensity 2.50mmmin-1). Field plots were established to evaluate the effects of rainfall intensities on sediment yield and phosphorus enrichment ratio (ERP) in runoff sediment. Each plot was 2m long and 1m wide. The rainfall lasted for 30min after effective runoff generation. Runoff and sediment, as well as the phosphorus (P) concentration of sediment, were measured. Results showed that the low rainfall intensity had a longer time to begin runoff than high rainfall intensity. The runoff volume increased with the rainfall intensity; however, no obvious differences were observed in the runoff rate under three rainfall intensities, except for 2.50mmmin-1. The curve value of sediment concentration increased after 5-10min of effective runoff decreased slightly, and then relatively became stable after 20min of effective runoff. Although no obvious differences were observed in the dynamic changes of sediment concentration and rainfall intensity, a power function existed between rainfall intensity and sediment loss. The similar curves of ERP value showed that it was higher in the initial stage, decreased gradually, and reached a stable level after 25min of effective runoff, which varied around 1. During the rainfall-runoff event, no significant correlation was noted between ERP and sediment yield. Whether any relationship existed between them needs to be further studied by setting up different field plots under large-scale conditions. The findings of this study provide valuable aid to farmers on how to manage farmland effectively to prevent soil nutrient loss and reduce water eutrophication.

TEST OF EMPIRICAL SEDIMENT TRANSPORT RELATIONS AGAINST EXPERIMENTAL SWASH DATA UNDER THE NON-CAPACITY MODELING FRAMEWORK

Swash sediment transport and beach deformation has received great attention in the past two decades. Quantification of swash-induced sediment transport rate is of vital importance for accurate prediction of beach deformation in the swash zone. Two empirical parameters are involved in this quantification, empirical relations for sediment transport capacity and the bed shear stress that may be used in the former. Since the swash zone is highly unsteady, of short cross-shore distance, sediment transport in this zone may be of high possibility to be lag of the flow variation. Thus we have firstly developed a non-capacity sediment transport model for the swash zone. This model appreciates the fact that the actual sediment transport rate may not be necessarily equal to the sediment transport capacity of the flow. In contrast to traditional capacity models that calculate sediment transport rate using directly empirical relations (Hu et al. 2015), the non-capacity model uses the advection-diffusion equation to calculate depth-averaged sediment concentration firstly, and afterwards compute sediment transport rate as flow depth*velocity*concentration. We have also noted that some empirical relations for sediment transport capacity may predict physically unrealistic high values of sediment concentration in the swash zone. This is attributed to the vanishing water depth in the swash zone, whereas existing empirical relations are developed for relatively large water depths (Hu et al. 2015; Li et al. 2017).

Assessing environmental changes in abandoned German vineyards. Understanding key issues for restoration management plans

Land degradation in vineyards is a big concern which should be considered by farmers, enterprises and policymakers. Due to intense tillage, the use of herbicides and heavy machinery, vine plantations are registering a decrease in soil fertility and, subsequently, in productivity. Recently, farmers have decided to abandon the vineyards, but any restoration planning is being carried out to recover biodiversity or to reduce soil and water losses. Nowadays, there is no information about environmental changes after the abandonment in terms of possible soil property changes and erosion in Central European vineyards such as in Germany. Therefore, the main aims of this preliminary study were to compare: i) soil properties and soil profiles of one cultivated vineyard and an abandoned one; and, ii) to assess the activation of soil erosion processes using a small portable rainfall simulator. Our results showed that the vineyard registered several differences in soil properties among slope positions and soil profile characteristics due to tillage and trampling effects, showing clear marks of compaction and soil detachment in the lower parts. Also, in this cultivated field, higher means and maxima of soil losses (g m-2) and sediment concentration (g l-1) values than in the abandoned plot were quantified, being the main driving factors the vegetation cover and the inclination. On the other hand, in the abandoned vine plantation, a rapid homogenization of soil profiles and soil properties were found along the hillslope, where a deeper organic horizon was consistently developed above a compacted and rocky horizon, which was generated during the cultivation phase. Due to the high compaction due to the machinery cultivation and the difficulties for the roots to make deep into the soil, the infiltration defaulted and the amount of runoff and runoff coefficient were higher in the abandoned plots than in the cultivated ones.

Evaluation of Meltwater Quality Using Dissolved Ions Chemistry and Multivariate Statistical Methods: A Case Study of the Manimahesh Glacier, Ravi Basin, Himachal Pradesh, India

The hydrogeochemical study on glacial meltwater gives important information about the quality of meltwater and weathering processes controlling dissolved ions chemistry in the glacierized area. Anionic abundance in the Manimahesh Glacier meltwater shows a trend of HCO3− > SO42− > Cl− = NO3−, whereas cationic abundance in the meltwater shows a trend of Ca2+ > Mg2+ > K+ > Na+. On the basis of high equivalent ratios of (Ca + Mg) versus (Na + K) and (Ca + Mg) versus TZ+ (total cations) and low equivalent ratio of (Na + K) versus TZ+, carbonate-type weathering has been identified as a major hydrogeochemical process regulating solute chemistry of the Manimahesh Glacier meltwater followed by silicate weathering. About 80% of bicarbonate in the meltwater of investigation area was mainly generated from carbonate weathering, whereas 20% of bicarbonate was produced from silicate weathering. The result of statistical methods (correlation, principal component and cluster analysis) shows that meltwater quality of the Manimahesh Glacier is mainly governed by carbonate and silicate-type weathering, oxidation of pyrite, dissolution of sulphate minerals and atmospheric input. The average value of suspended sediment concentration (SSC) in the glacier meltwater was calculated to be 46 mg/l and 63 mg/l during the month of June and July 2014, respectively, showing higher concentration of SSC during the month of July (peak-flow period) followed by June (low-flow period).

Effectiveness of N-waves for predicting morphological changes due to tsunamis

The research on morphological changes caused by tsunamis has increased considerably in the last few years, yet the processes behind this phenomenon are still not fully understood. This paper analyzes and compares numerical simulations of morphological changes caused by the leading elevation and leading depression N-waves and tsunami waves propagating over a channel with a simple bed slope. The simulations were carried out by means of a coupled flow, sediment transport and morphodynamic two-dimensional-vertical numerical model. The modeled channel bed was composed of cohesionless sediments, and range of values for the bed slope and the wave height were employed. Four tsunami waveforms were studied to test the appropriateness of N-waves in modeling the morphological changes caused by tsunamis. On the modeling performed here, runup values were quite well represented by N-waves. N-waves also represented qualitatively well the morphological changes caused by tsunamis. Yet, values of flow velocities and suspended sediment concentration showed more severe deviations from the modeled results corresponding with tsunami waves, very likely due to differences on the steepness of the waves. Therefore, even when N-waves can and have been used to represent tsunami runup and inundation distance, our results suggest that they should be considered with caution when intended to predict magnitudes of tsunami flow velocities and consequently morphological changes. The use of N-waves to simulate morphological changes caused by tsunamis is not yet converging and must be further investigated.

Sedimentary architecture and depositional environment of Kudat Formation, Sabah, Malaysia

Kudat Formation originated from deep marine environment. Three lithofacies association of deep marine turbidity channel was discovered in three Members of the Kudat Formation in Kudat Peninsula, Sabah, Malaysia. Turbidite and deep marine architecture elements was described based on detailed sedimentological studies. Four architecture elements were identified based on each facies association and their lithology properties and character: inner external levee that was formed by turbidity flows spill out from their confinement of channel belt; Lobes sheet that was formed during downslope debris flows associated with levee; Channel fill which sediments deposited from high to low density currents with different value of sediment concentration; and overbank terrace which was formed by rapid suspension sedimentation. The depositional environment of Kudat Formation is shelf to deep marine fan.

Numerical simulations of flow and sediment transport within the Ning-Meng reach of the Yellow River, northern China

Effective management of a river reach requires a sound understanding of flow and sediment transport generated by varying natural and artificial runoff conditions. Flow and sediment transport within the Ning-Meng reach of the Yellow River (NMRYR), northern China are controlled by a complex set of factors/processes, mainly including four sets of factors: (1) aeolian sediments from deserts bordering the main stream; (2) inflow of water and sediment from numerous tributaries; (3) impoundment of water by reservoir/hydro-junction; and (4) complex diversion and return of irrigation water. In this study, the 1-D flow & sediment transport model developed by the Yellow River Institute of Hydraulic Research was used to simulate the flow and sediment transport within the NMRYR from 2001 to 2012. All four sets of factors that primarily control the flow and sediment transport mentioned above were considered in this model. Compared to the measured data collected from the hydrological stations along the NMRYR, the simulated flow and sediment transport values were generally acceptable, with relative mean deviation between measured and simulated values of <15%. However, simulated sediment concentration and siltation values within two sub-reaches (i.e., Qingtongxia Reservoir to Bayan Gol Hydrological Station and Bayan Gol Hydrological Station to Toudaoguai Hydrological Station) for some periods exhibited relatively large errors (the relative mean deviations between measured and simulated values of 18% and 25%, respectively). These errors are presumably related to the inability to accurately determine the quantity of aeolian sediment influx to the river reach and the inflow of water from the ten ephemeral tributaries. This study may provide some valuable insights into the numerical simulations of flow and sediment transport in large watersheds and also provide a useful model for the effective management of the NMRYR.

Flow-driven soil erosion processes and the size selectivity of eroded sediment on steep slopes using colluvial deposits in a permanent gully

Colluvial deposits with loose, coarse material are easily erodible in permanent gullies, but the mechanisms of erosion and sedimentation during overland flow remain obscure. Hence, the processes and mechanisms of the transportation of soil particles by overland flow were investigated in this study. Experiments were carried out in a 5.0m long by 1.0m wide flume using colluvial deposits. The slope gradient varied from 36 to 84%, and the flow rate ranged from 0.72Lm−2min−1 to 2.88Lm−2min−1. The runoff rate and sediment yield rapidly increased with increasing overland duration. Runoff and sediment were highly variable when the flume was treated with a high flow rate compared with a low flow rate, with the fluctuation of sediment concentration under the high flow rate usually reaching 500gL−1. The slope gradient and overland flow rate have strong impacts on sediment transport capacity. The mean flow velocity and the unit stream power can be an optimal composite force predictor for estimating sediment transport capacity. Experimental results also revealed that the percentage of gravel-sized particles increased with increasing flow rate and slope gradient, but silt and clay fractions observed opposite trend. The average enrichment ratio (ER) of gravel was usually <1. However, the ER of silt and clay fractions decreased following the increase of the flow rate and slope gradient, and the values stabilized in the range of 1.1 to 1.4. The predicted values of runoff, sediment yield, and sediment concentrations were simulated by an empirical equation with measured values, and the regression coefficients were 0.983, 0.996 and 0.877, respectively. When the flow rate was >2.16Lm−2min−1, the bed load transport became an important mechanism; however, the simulation model overestimated these values.

Pengaruh Sudut dan Jari-Jari Saluran Menikung terhadap Konsentrasi Aliran Sedimen Suspensi arah Transversal

The change in channel dimension has a great effect on the flow hydraulic parameters. Likewise, the angle and radius of the bend are not the same will also affect the concentration of suspended sediment flow. To determine the effect of angle and radius of the bend, the measurement of susupended sediment concentration was done at 4 (four) location in Mataram irrigation channel curve. The four locations describe 2 channels having relatively the same angle but having different radius, and 2 (two) channels having the same relative radius but having different angles. Measurement of suspended sediment concentration in tranversal direction is done some depth point used by opcon probe. The results of the research for different angle of bend shows that from the interance to the end of the channel bend so the trend of suspended sediment concentration value are decreases. After the end of the channel bend started there is no more the angle influenced, the trend value of suspended sediment concentration are constant. As for the different radius, the value of suspended sediment concentration is still relatively the same and there is no change significantly. This shows that the relation or influence between the length of the radius of the bend with the value of the suspended sediment concentration is not visible

Sheet flow measurement in the north passage of Yangtze estuary with pedestal based synchronous field survey system

In order to measure sheet flow near the bottom in the north passage of Yangtze Estuary during the typhoon, a submerged synchronous field survey system composited of Nortek AquaPro, Nortem AquaPro HR, AWAC and OBS 3+ was equipped on a pedestal based structure. The system was used to survey sheet flow field during the flooding season in 2015. The pedestal base synchronous field survey system can give reasonable estimation about stability of itself, and also capture simultaneously the wave climate as well as the current feature and the sediment concentration near the bottom. Analyzing the data collected by the system, it is found that the tidal current dominates the sedimentation concentration near the bottom in the Yangtze Estuary without waves, and the only peak value of suspended sediment concentration occurs at the fall slack time. The suspended sediment concentration above 50cm to the bottom is usually not larger than 15kg/m3, and it is not significantly correlated with the wave. When typhoon happens, the suspended sediment concentration increases significantly below 30cm to the bottom. There are two peaks of the suspended sediment concentration at the spring slack and the fall slack time respectively.

Field application of a multi-frequency acoustic instrument to monitor sediment for silt erosion study in Pelton turbine in Himalayan region, India

High sediment load passing through hydropower components erodes the hydraulic components resulting in loss of efficiency, interruptions in power production and downtime for repair/maintenance, especially in Himalayan regions. The size and concentration of sediment play a major role in silt erosion. The traditional process of collecting samples manually to analyse in laboratory cannot suffice the need of monitoring temporal variation in sediment properties. In this study, a multi-frequency acoustic instrument was applied at desilting chamber to monitor sediment size and concentration entering the turbine. The sediment size and concentration entering the turbine were also measured with manual samples collected twice daily. The samples collected manually were analysed in laboratory with a laser diffraction instrument for size and concentration apart from analysis by drying and filtering methods for concentration. A conductivity probe was used to calculate total dissolved solids, which was further used in results from drying method to calculate suspended solid content of the samples. The acoustic instrument was found to provide sediment concentration values similar to drying and filtering methods. However, no good match was found between mean grain size from the acoustic method with the current status of development and laser diffraction method in the first field application presented here. The future versions of the software and significant sensitivity improvements of the ultrasonic transducers are expected to increase the accuracy in the obtained results. As the instrument is able to capture the concentration and in the future most likely more accurate mean grain size of the suspended sediments, its application for monitoring silt erosion in hydropower plant shall be highly useful.

POSTFIRE: A model to map forest fire burn scar and estimate runoff and soil erosion risks

Forest fires in the Euro-Mediterranean region burn about 450,000 ha each year. Combustion of standing vegetation and the leaf litter leave the soil bare and vulnerable to runoff and erosion thereby increasing downstream risks of flooding. Typically, wildfires near or in the Wildland Urban Interface (WUI) occur on uplands and runoff generated from the burned area concentrates downstream in high density urban areas. Local authorities must decide on a range of post-fire measures to mitigate risks quickly since most large fires occur late in summer shortly before the fall-winter rainy season. A GIS-based model that maps the burn scar and quantifies fire impacts on runoff and soil erosion is a useful tool in defining a strategy. The POSTFIRE model executes 54 routines semi-automatically in IDRISI TerrSet and maps the burn scar using pre and post-fire satellite images, calculates the impact of a fire on total rainfall event runoff, and maps soil erosion rates. In addition to satellite images, the model requires a Digital Elevation Model (DEM), a mask of the general contour of the fire, land cover map, and tables of runoff coefficients and sediment concentration values for the land covers. All other input files are generated automatically by the model.Burn scar classification, runoff and soil erosion maps were compared for two fires in SE France based on SPOT and Landsat images. Differences in burn scar area estimated from unsupervised KMeans classifications of dNDVI and dNBR indices range from 3% to 15% depending on the fire. dNDVI burn scars had slightly greater areas than dNBR derived maps, and SPOT burn scar classifications were slightly greater in area than from Landsat images. Estimated post-fire stream discharge values were about 2–2.5 times greater than pre-fire values and differed by less than 10% between indices and sensors. Similarly, post-fire erosion rates (2.0–2.5Tha−1) were consistent among indices and sensors and coherent with field measurements of erosion. Preliminary results indicate the model is simple to use, adaptable to local conditions, and provides realistic outputs for the burn scar, discharge, and soil erosion maps after a forest fire. Model modules, instructions, and sample data can be downloaded here: https://goo.gl/PjDv68.

Suspended sediment transport analysis in two Italian instrumented catchments

Suspended sediment transport in streams is an effective indicator of soil erosion at the watershed scale. This process was studied using the data obtained from two continuous monitoring stations installed in Italian watersheds, the Rio Cordon and Torrente Carapelle. The catchments have substantially different climatic, morphological and land use characteristics. The Rio Cordon, a small Alpine watershed, has been monitored since 1986, while in the Torrente Carapelle, a medium-size Mediterranean watershed, the monitoring station has provided data since 2007. Several flood events with suspended sediment transport were isolated in the two catchments, excluding those determined by snowmelt in the Rio Cordon as this process does not affect the Carapelle watershed. Analysis of the events showed different behavior in terms of hysteresis loop trends between water discharge (m3 s-1) and suspended sediment concentration (g l-1) values, as the Rio Cordon confirms clockwise relationships most frequently, while counter-clockwise trends represent the majority of cases for the Carapelle Torrent. The different behavior of the two watersheds was further analyzed by evaluating relationships between the main hydrological parameters related to suspended sediment transport. Runoff controls the total sediment budget in both catchments. In contrast, it was noted that the runoff process does not interfere in the magnitude of the suspended sediment transport in the Rio Cordon catchment, while variations due to the larger size of the catchment area characterize the events in the Carapelle watershed. Lastly, a flow peak threshold that determines the advance or delay of the hydrograph peak with respect to the sedigraph peak was established for the Carapelle Torrent, while it was not reported in the Rio Cordon.

ANN modelling of sediment concentration in the dynamic glacial environment of Gangotri in Himalaya.

The present study explores for the first time the possibility of modelling sediment concentration with artificial neural networks (ANNs) at Gangotri, the source of Bhagirathi River in the Himalaya. Discharge, rainfall and temperature have been considered as the main controlling factors of variations in sediment concentration in the dynamic glacial environment of Gangotri. Fourteen feed forward neural networks with error back propagation algorithm have been created, trained and tested for prediction of sediment concentration. Seven models (T1-T7) have been trained and tested in the non-updating mode whereas remaining seven models (T1a-T7a) have been trained in the updating mode. The non-updating mode refers to the scenario where antecedent time (previous time step) values are not used as input to the model. In case of the updating mode, antecedent time values are used as network inputs. The inputs applied in the models are either the variables mentioned above as individual factors (single input networks) or a combination of them (multi-input networks). The suitability of employing antecedent time-step values as network inputs has hence been checked by comparative analysis of model performance in the two modes. The simple feed forward network has been improvised with a series parallel non-linear autoregressive with exogenous input (NARX) architecture wherein true values of sediment concentration have been fed as input during training. In the glacial scenario of Gangotri, maximum sediment movement takes place during the melt period (May-October). Hence, daily data of discharge, rainfall, temperature and sediment concentration for five consecutive melt periods (May-October, 2000-2004) have been used for modelling. High Coefficient of determination values [0.77-0.88] have been obtained between observed and ANN-predicted values of sediment concentration. The study has brought out relationships between variables that are not reflected in normal statistical analysis. A strong rainfall: sediment concentration and temperature: sediment concentration relationship is shown by the models which are not reflected in statistical correlation. It has also been observed that usage of antecedent time-step values as network inputs does not necessarily lead to improvement in model performance.

Combining deterministic modelling with artificial neural networks for suspended sediment estimates

Estimates of suspended sediment concentrations and transport are an important part of any marine environment assessment study because these factors have a direct impact on the life cycle and survival of marine ecosystems. This paper proposes to implement a combined methodology to tackle these estimates. The first component of the methodology comprised two numerical current and wave models, while the second component was based on the artificial intelligence technique of neural networks (ANNs) used to reproduce values of sediment concentrations observed at two sites. The ANNs were fed with modelled currents and waves and trained to produce area-specific concentration estimates. The trained ANNs were then applied to predict sediment concentrations over an independent period of observations. The use of a data set that merged together observations from both the mentioned sites provided the best ANN testing results in terms of both the normalised root mean square error (0.13) and the mean relative error (0.02).