Sediment Matters

The paper summarizes results of both empirical and modelling research of bedload transport in headwater streams of the Czech part of the Western Carpathians. Flysch lithology (i.e. alternation of less resistant claystones and sandstones) affects bedload transport parameters in view of relatively fine-sized sediment supply resulting in low flow resistance of channels. Flood competence method (Q20 flood) and marked particle displacement method (up to Q1–2 flow) was applied to determine critical conditions for the incipient motion of grains in channel bed. The beginning of bedload transport in flysch headwaters under lower values of critical conditions when compared to other regions was confirmed by application of the criteria of unit stream power and unit discharge. The simulated values of bedload transport intensity (1D transport model TOMSED) during a high-magnitude flood in both supply-limited and transport-limited headwaters are significantly lower than it was observed in torrents of the Alpine environment. In relation to unsuitable contemporary watershed management affecting the sediment transport (large check-dams, removing of large wood from local channels), trends of accelerated incision are observed in most headwater streams as well as in lower-gradient piedmountain gravel-bed rivers of the Flysch Belt of the Western Carpathians. Approaches of contemporary local watershed management are presented and some recommendations for the maintenance of channel stability predisposed by soft lithology (e.g. application of artificial step-pool sequences, management of woody debris in channels) are proposed.

Present-day state of channels shows a tendency towards the acceleration of processes linked with river bed lowering. Focusing on the Ostravice River and Bečva River basins in the Czech part of flysch Carpathians, the paper summarizes the results of energy potential aspects of contemporary Carpathian river channels. The study has been conducted with the use of the Bedload Assessment for Gravel-bed Streams (BAGS) spreadsheet-based program and unit stream power formula. Presented results show potential values of sediment transport with the identification of erosion and accumulation processes in channels. Selected channel cross-profiles include preserved gravel-bed reaches with an anabranching pattern as well as transformed reaches with accelerated deep erosion and occurrence of a single bedrock channel. The modelling shows potential transport trends in relation with the morphology of the channel. The results can be used to distinguish the reaches with erosion or accumulation trends. The modelling on cross-profiles with a low rate of fluvial erosion (anabranching channel pattern) shows a decrease in potential sediment transport. It is caused by increased or decreased (dis)connectivity in the longitudinal profile of the fluvial (dis)continuum system. It is influenced both by flow diversion through sub-channels and a decrease in sediment transport capacity. We define this area of active channel as a zone of reduced growth in transport capacity. In contrast, reaches with a single channel pattern show higher values of potential sediment transport caused by the absence of this zone of reduced growth in transport capacity. The results may be applied in form of a conceptual scheme to improve the management of local watersheds.

Rapid hydraulic structures—RHS—(called also boulder ramps) are modern, environment-friendly grade-control structures which mimic natural riffles and do not disturb longitudinal continuity of the stream for fish and benthic invertebrates. Due to the reduction of hydraulic gradient and backwater effect, such hydraulic structures change the pattern of sediment transport and deposition in the channel, facilitating persistence of alluvial streambed and the formation of gravel bars upstream and downstream of the structures. This is of key importance for preserving habitats for benthic invertebrates and the spawning ground of lithophilic fish if a stream has to be channelized. At the same time, properly designed rapid hydraulic structures must allow efficient transfer of sediment flux through their apron, helping to clean the structures of gravel and preventing their clogging. This study deals with observations and modeling of sediment transport in the vicinity of a rapid hydraulic structure in a mountainous gravel-bed channel. The study aims to: (i) show the effects of RHS on sediment transported along a stream channel, and (ii) to evaluate the performance of CCHE2D model in predicting sediment phenomena along the stream with rapid hydraulic structures. The studied structure is located in Porębianka Stream draining a flysch catchment in the Polish Carpathians. We measured and calculated hydraulic parameters characterizing the flow on and in the vicinity of the structure, such as velocity, dynamic velocity, shear stress, Froude number, Reynolds number and friction coefficient. The knowledge of those parameters allowed us, at the same time, to calculate sediment transport in the region of the structure using BAGS model for the Parker transport formula and parallel modeled the sediment transport with the CCHE2D model. The results show how the hydraulic structure (enabling the migration of fish and benthic invertebrates), operates in terms of sediment transport processes (basically, giving the answer to the question: what is the influence of RHS on sediment transport) which form the channel morphology in its vicinity. In that context the CCHE2D model is discussed with its advantages and impediments.

Rainfall and runoff induced erosion and sediment transport in hydrological watersheds are complex processes. This process has great importance in scientific research studies and engineering practice. The amount of sediment transported within the watershed is needed for hydrological and environmental problems. Sediment transport over a watershed can be estimated by time series analysis, empirical or mechanistic equations, monitoring, sampling, surveying, remote sensing or geographical information systems. As monitoring and sampling sediment transport process are costly and not easy to implement yet, modelling has become an alternating tool used for estimating sediment transport. Data-based empirical models as well as process-based hydrological models are available for this purpose, yet modelling is difficult and challenging. Challenges encountered in the modelling are the variability in the estimate of sediment calculated by each model, data requirement for the calibration of model parameters, complexity in the calibration and validation stages of the process-based models, uncertainty in the transport capacity approach used in model construction, etc. In this chapter, these challenges related to the modelling sediment matters are discussed with an emphasis on the process-based sediment transport models. A case study on Buyukcekmece dam reservoir in the greater municipality region of Istanbul, Turkey shows that order of magnitude different outputs are obtained when data-based models are used for estimating sediment transport in hydrological watersheds. Process-based models were paid particular attention on their microtopographical structure, parameterization and data requirement.

Forecasting of sediment concentration in rivers is a very important process for water resources assignment development and management. In this paper, a neural network approach is proposed to predict suspended sediment concentration from streamflow. A comparison was performed between artificial neural network, sediment rating-curve and multilinear regression models. It was based on a 5 years period of continuous streamflow, suspended sediment concentration and mean water temperature data of West Virginia, Little Coal River, Danville station operated by the United States Geological Survey. Based on comparison of the results, it is found that the artificial neural network model gives better estimates than the sediment rating-curve and multilinear regression techniques.

The scope of this paper is to analyse the impact and the uncertainty of climate change on soil erosion and consequent sediment yield in the River Elbe catchment by ensemble modelling techniques. The model ensemble comprises five bias-corrected and gridded climate data-sets that origin from coupled runs of global circulation models (GCM) and regional circulation models (RCM) that were driven by both the C20 and the A1B emission scenarios. The data-sets were aggregated for climate normals that are referred to as C20 (1961–1990), ‘near future’ (2021–2050) and ‘far future’ (2071–2100). Furthermore, the HYRAS data-set that covers the period 1961–1990 of gridded station data was used as the actual climate data. First, the PESERA-model was chosen as a climate impact model to simulate soil erosion on a 500 × 500 m grid within the entire River Elbe catchment based on relief-data, land cover, soil, crop and the aforementioned climate data. Second, the simulated annual average soil erosion for the actual climate and each projected climate was used to calculate sediment delivery with the approach of spatially distributed sediment delivery ratios (SDR-approach). The actual simulated soil erosion using the actual climate data is in good agreement with other published soil erosion maps for this scale. Furthermore, averaged soil erosion per land use class meets reported data in literature well. Highest soil erosion rates are simulated in the South-East of the catchment and in the range of hills in the central part of the River Elbe catchment. Simulated sediment yield was over predict by a factor of two, that can be attributed because of the methods sensitivity of the underlying river network map and the temporal shift between both periods of actual climate data and reference data on suspended solids load. Sediment delivery slightly drops in the ‘near future’ and ‘far future’, which coincidences with decreasing summer rainfalls. However, results of sediment delivery are largely dominated by the chosen GCM-RCM models. It is concluded that the impact of climate change on soil erosion is lower than the impact of potential land cover change.

In Brahmaputra basin of India, the social sanctions and belief system maintained a balance between resource potential and their utilization for a long time but due to the increase in the demographic pressure and indiscriminate use of natural resources, imbalance has been created. Socio-economic constraints like shifting cultivation, land tenure system, small size of land holdings, unabated deforestation, free range grazing and undulating terrain have affected the sediment yield and, quantity and quality of available water. The mean annual sediment yield per ha from the Brahmaputra basin constitutes, 23.2 tonnes of soil and, 26.1, 4.2, 19.4, 0.93, 0.58, 2.3 and 1.79 kg of N, P₂O₅, K₂O, Mn, Zn, Ca and Mg, respectively. The Brahmaputra river in India has more than 100 tributaries of which 15 in the north and 10 in the south are fairly large. It was estimated that about 660 m³ km⁻² of sediment load is brought by the northern and 100 m³ km⁻² by the southern tributaries to the main river channel, annually. To evolve eco-friendly and sustainable farming systems to replace sediment encouraging practice of shifting cultivation, a multidisciplinary, long-term study was undertaken with seven land use systems on micro watersheds viz.; livestock based (grasses and fodders), forestry, agro-forestry, agriculture, agri-horti-silvi-pastoral, horticulture and shifting cultivation, to monitor their comparative efficacy with regard to in-situ retention of rain water, water quality and sediment yield. The sediments emanating from the farming systems affected the surface and groundwater quality, the magnitude of which was highly related to the use of amount of fertilizers and other agricultural chemicals in the basin.

Projections of climate-induced changes in temperature and precipitation let expect also altered frequencies and intensities of extreme hydrological events such as floods or prolonged periods of low river discharges. Particularly such extremes may, moreover, lead to modified inputs of particulate matter into rivers and estuaries, and may thus affect the quality of estuarine sediments. This study focuses on the assessment of potential climate-induced changes of particle-bound contaminant concentrations in the estuaries of the rivers Elbe, Ems and Weser and the resulting challenges for sediment management in the navigable waterways there. The estimation of climate-induced changes of contaminant concentrations in estuarine particulate matter (PM) was based on results of projections on the fluvial PM input into the Elbe estuary in the near (2021–2050) and far future (2071–2100) and on assumed extreme changes of such inputs. A mixing model using the concentrations of selected contaminants as indicators for marine and fluvial PM was applied. Distinct changes of contaminant concentrations were found only for the far future and with the assumed extreme PM inputs in the inner Elbe estuary. And only for the inner Elbe estuary the worst-case scenario indicated that concentrations of some organochlorine contaminants in the far future exceed the national assessment criteria for the handling of dredged material within coastal waterways more distinct than today. Therefore, adaptations of practices for the management of dredged material to higher particulate matter contaminations should be considered there in the medium or long-term perspective.

In recent years the hydrological service in Austria developed and implemented a new, continuous, long term suspended sediment monitoring system taking the spatial and temporal variability of the suspended sediment transport process into consideration. The new monitoring strategy and analysis concept during the data processing was applied at 28 measurement sites for the period from 2009 to 2011. Furthermore a lot of investigation was done to verify and validate the suspended sediment data in preparation for the annual publication. The results of analysis of the suspended sediment concentrations, transport rates, loads and yields in Austrian Rivers confirm the well done verification and validation and allow conclusions about the respective suspended sediment transport processes.

The Olifants primary catchment area, consists of nine sub-catchments marked from B1 to B9, extends over the border between South Africa and Mozambique, and has a total area of approximately 87,000 km². The B1 catchment, where most of the mining activities surround the major towns of Witbank (Emalahleni) and Middleburg, in turn straddles the provinces of Mpumalanga and Limpopo. Although industrial and agricultural activities are also important, the contribution of contamination from the mining activities within the catchment is significant as the result of intense mining activities of various mineral commodities such as coal and from ferrochrome processing plants located in Emalahleni and Middleburg towns with in the catchment area and yet not fully quantified. This paper investigates the severity of the mining impacts on the water resources and the ecosystem of the Olifants primary catchment area and in particular, the upper reaches of the catchment. The paper discusses the results of research which focused on deciphering the severity and the sources water contamination, and on how to minimise the dispersion of these metals into the streams, and on the relationship of the water quality and metal loadings on the sediments. Stream sediment and water samples have been collected and analysed. The sediments were analysed by Simultaneous X-ray Fluorescence and Inductively Coupled Plasma-Mass Spectrometry techniques for metal loadings. The areas were marked by anomalous level determined at 50th percentile threshold of Fe, Mn, Ni, Cr, Co, V, Pb in Emalahleni and Al, Fe, Mn, Cr, As, Zn, Pb and U in Middleburg. The ICP-MS and IC analytical techniques were used in the assessment of water quality data. From the stream sediments regional geochemistry at catchment level and for this investigation, the sediments that were found marked by high levels of Na, K, Mg, Al, Ca, Mn, and Fe signature can be attributed to the coal mines as a probable source. Whereas the sediment quality of the areas like Emalahleni and Middleburg towns, where mining of coal (with many abandoned mines) and ferrochrome processing is happening simultaneously, there are anomalous level of Cr, Ni, V and As, which is a signature of the Bushveld PGE mines material. The SO₄ ²⁻ concentration of above 500 mg/kg on the water quality, which has exceeded the Department of Water Affairs water quality guideline for domestic and industrial use, is an evidence for contamination. The approach adopted herein suggests that the stream sediment and water quality data can be used in characterizing or fingerprinting impacted areas.

All over the world, river basins are under pressure from human activities that affect their chemical and ecological statuses and exhaust available natural resources. Sediment is an essential, integral and dynamic part of the river basins and sediment issues may affect various environmental, social and legal objectives pursued there. Sediment management becomes necessary if the intensity of anthropogenic interventions in the sediment status overwhelms the resilience of ecologic endpoints of the river system or if sediment dynamics and/or sediment status strongly affect human uses. Despite the progress that has been made in the knowledge of sediment management during the last 20 years, practical examples of comprehensive river-basin-scale sediment management concepts are by no means state-of-the-art, and even concepts that focus on only one of the sediment issues are sparse. In Europe, approaches to the management of waters have been radically altered with the introduction of the European Water Framework Directive (WFD). The International Commission for the Protection of the Elbe (ICPER) had declared good sediment quality as one of its key targets. The first Elbe management plan prepared under the WFD (2010–2015) highlights contamination and insufficient hydromorphological conditions as two of the most important supra-regional issues in water resources management. The plan underlines that contaminated sediments and unbalanced sediment conditions are among the main reasons for the failure to meet the WFD management objectives. As a consequence, the member states in the ICPER decided to develop a sediment management concept in preparation for the management cycle from 2016 to 2021. For the first time, an integrated sediment management concept was developed in support of management planning in a large international river basin. The concept is related to the river basin, i.e. it considers cause-effect relations in the entire river basin district Elbe. It combines the issues of sediment quantity, hydromorphology, and sediment quality as well as ecological and use-oriented sediment aspects in one concept. The conclusions rely on analyses of risks resulting from an insufficient status of the sediment budget, ecological functions, ecosystem services, and sediment-dependent uses of the river.