Suspended Sediment
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Niels F. Lake ◽  
Núria Martínez-Carreras ◽  
Peter J. Shaw ◽  
Adrian L. Collins

Abstract Purpose This study tests the feasibility of using a submersible spectrophotometer as a novel method to trace and apportion suspended sediment sources in situ and at high temporal frequency. Methods Laboratory experiments were designed to identify how absorbance at different wavelengths can be used to un-mix artificial mixtures of soil samples (i.e. sediment sources). The experiment consists of a tank containing 40 L of water, to which the soil samples and soil mixtures of known proportions were added in suspension. Absorbance measurements made using the submersible spectrophotometer were used to elucidate: (i) the effects of concentrations on absorbance, (ii) the relationship between absorbance and particle size and (iii) the linear additivity of absorbance as a prerequisite for un-mixing. Results The observed relationships between soil sample concentrations and absorbance in the ultraviolet visible (UV–VIS) wavelength range (200–730 nm) indicated that differences in absorbance patterns are caused by soil-specific properties and particle size. Absorbance was found to be linearly additive and could be used to predict the known soil sample proportions in mixtures using the MixSIAR Bayesian tracer mixing model. Model results indicate that dominant contributions to mixtures containing two and three soil samples could be predicted well, whilst accuracy for four-soil sample mixtures was lower (with respective mean absolute errors of 15.4%, 12.9% and 17.0%). Conclusion The results demonstrate the potential for using in situ submersible spectrophotometer sensors to trace suspended sediment sources at high temporal frequency.

2021 ◽  
Vol 9 (11) ◽  
pp. 1300
Troels Aagaard ◽  
Joost Brinkkemper ◽  
Drude F. Christensen ◽  
Michael G. Hughes ◽  
Gerben Ruessink

The existence of sandy beaches relies on the onshore transport of sand by waves during post-storm conditions. Most operational sediment transport models employ wave-averaged terms, and/or the instantaneous cross-shore velocity signal, but the models often fail in predictions of the onshore-directed transport rates. An important reason is that they rarely consider the phase relationships between wave orbital velocity and the suspended sediment concentration. This relationship depends on the intra-wave structure of the bed shear stress and hence on the timing and magnitude of turbulence production in the water column. This paper provides an up-to-date review of recent experimental advances on intra-wave turbulence characteristics, sediment mobilization, and suspended sediment transport in laboratory and natural surf zones. Experimental results generally show that peaks in the suspended sediment concentration are shifted forward on the wave phase with increasing turbulence levels and instantaneous near-bed sediment concentration scales with instantaneous turbulent kinetic energy. The magnitude and intra-wave phase of turbulence production and sediment concentration are shown to depend on wave (breaker) type, seabed configuration, and relative wave height, which opens up the possibility of more robust predictions of transport rates for different wave and beach conditions.

2021 ◽  
Vol 20 (1) ◽  
pp. 30-36
Lintang Nur Fadlillah ◽  
Atikah Nian Indrastuti ◽  
Afanin Fatkha Azahra ◽  
Margaretha Widyastuti

Aktivitas manusia di sekitar Sungai Winongo dapat berdampak pada kontaminasi logam berat dari limpasan permukaan dan buangan langsung. Sifat toksik pada logam perlu diperhatikan karena dapat terakumulasi dalam waktu yang lama dan merusak lingkungan. Evaluasi logam berat dapat dilakukan dengan cara pemantauan kualitas air dan kualitas sedimen untuk mengetahui tingkat pencemaran suatu perairan karena logam berat dan distribusi logam berat itu sendiri. Penelitian ini bertujuan untuk mengetahui level toksik perairan dilakukan analisis hasil dengan berbagai indeks, yaitu Faktor Risiko Ekologis (Er) dan Indeks Beban Polusi (PLI). Sampel air, sampel sedimen tersuspensi (TSS), dan sedimen pada dasar permukaan diambil pada masing-masing titik untuk diuji laboratorium menggunakan alat AAS (Atomic Absorption Spectrophotometry). Hasil analisis menunjukkan bahwa logam Cu dan Cr paling banyak ditemukan pada sedimen dasar, sedangkan logam Pb paling banyak ditemukan terlarut dalam air. Logam pada sedimen tersuspensi ditemukan sangat kecil yaitu <0,031. Konsentrasi logam pada sedimen tersuspensi tertinggi adalah 0,043 mg/L pada titik T4.  Berdasarkan perhitungan Er dan PLI, potensi risiko ekologis terhadap logam di Sungai Winongo rendah (Er<40) dan tidak terdapat polusi karena logam berat (PLI<1). Namun, analisis kualitas air menunjukkan untuk nilai Cu dan Pb melebihi baku mutu kelas 2. Penelitian ini dapat dijadikan penelitian awal dalam kajian logam berat di Sungai Winongo secara historis.ABSTRACTThe Increase of human activities around the Winongo River can have an impact on decreasing water quality due to pollution from household and small industrial waste. Metal contamination in the aquatic environment is an environmental issue that needs attention due to its toxicity. Moreover, it can be accumulated in aquatic environments for a long time. Monitoring water quality and sediment quality is important to determine the distribution of heavy metals sources and the level of pollution in the waters. This research aims to determine the water toxicity level. An analysis of the results was carried out with various indices, which are the Ecological Risk (Er) and Pollution Load Index (PLI) in the water samples, suspended sediment samples (TSS), and sediment at the bottom of the surface will be taken at each point for laboratory testing using AAS (Atomic Absorption Spectrophotometry). The concentration of heavy metals for Cu and Cr in the surface sediment respectively was found higher than its concentration in the river water. Meanwhile, Pb contents are found higher in river water. The contents of heavy metals are found less in the suspended sediment samples. The Er and PLI shows low pollution risk and low pollution status, respectively. It indicates that the Code River was still in low pollution status for Cu, Cr, and Pb contamination. On the other hand, the water quality analysis results Cu and Pb over the Water Quality Standard for Class 2. This study may serve as a useful reference and baseline for heavy metals research in Winongo River historically.

2021 ◽  
Vol 13 (22) ◽  
pp. 4549
Sergey Chalov ◽  
Kristina Prokopeva ◽  
Michał Habel

This study presents detailed suspended sediment budget for the four Siberian river deltas, representing contrasting conditions between Northern and Southern environments. Two of the studied rivers empty their water and sediments into the marine located in the permafrost zone in the Arctic region (Lena and Kolyma), and the other two (Selenga and Upper Angara) flow into Lake Baikal located in the steppe and forest-steppe zone of Southern Siberia. For the first time, these poorly monitored areas are analyzed in terms of the long-term and seasonal changes of spatial patterns of suspended sediment concentrations (SSC) over distributaries systems. Remote sensing reflectance is derived from continuous time series of Landsat images and calibrated with the onsite field measurements of SSC. Seasonal variability of suspended sediment changes over deltas was captured for the period from 1989 to 2020. We identify significant variability in the sedimentation processes between different deltas, which is explained by particularities of deltas networks and geomorphology and the existence of specific drivers—continuous permafrost impact in the North and abundant aquatic vegetation and wetland-dominated areas in the South. The study emphasizes that differences exist between Northern and Southern deltas regarding suspended sediments transport conditions. Mostly retention of suspended sediment is observed for Southern deltas due to sediment storage at submerged banks and marshlands located in the backwater zone of the delta during high discharges. In the Northern (arctic) deltas due to permafrost impacts (melting of the permafrost), the absence of sub-aquatic banks and river to ocean interactions of suspended sediment transport is mostly increased downwards, predominantly under higher discharges and along main distributary channels. These results shine light on the geochemical functions of the deltas and patterns of sequestering various metals bound to river sediments.

2021 ◽  
Sagy Cohen ◽  
Jaia Syvitski ◽  
Thomas Christopher Ashley ◽  
Roderick William Lammers ◽  
Balazs M. Fekete ◽  

Water ◽  
2021 ◽  
Vol 13 (22) ◽  
pp. 3172
Devika Nair ◽  
K. G. Evans ◽  
Sean Bellairs ◽  
M. R. Narayan

Mining can cause environmental disturbances and thus mined lands must be managed properly to avoid detrimental impacts in the future. They should be rehabilitated in such a way that post mining landforms behave similarly as the surrounding stable undisturbed areas. A challenge for government regulators and mine operators is setting closure criteria for assessment of the stability of the elevated post-mining landforms. Stability of a landform is often measured by the number and incision depth of gullies. This can assess mass stability and bulk movement of coarse material. However, there is a need for a more sensitive approach to assess catchment disturbances using the concept of waves of fine suspended sediment and thus determine the dynamics of recovery of a post mining landform. A more environmentally meaningful approach would be to assess the fine suspended sediment (FSS, silt + clay (0.45 µm < diameter < 63 µm)) leaving the system and entering downstream waterways. We propose assessing stability through relationships between rainfall event loads of FSS and event discharge (Q) in receiving streams. This study used an innovative approach where, instead of using instantaneous FSS concentration, it used total FSS load in waves of sediment driven through the system by rainfall runoff events. High resolution stream monitoring data from 2004 to 2015 in Gulungul and Magela Creeks, Northern Territory, Australia, were used to develop a relationship between sediment wave and event discharge, ∑FSS α f(Q). These creeks are adjacent to and receive runoff from Ranger Mine. In 2008, a 10 ha elevated waste rock landform was constructed and instrumented in the Gulungul Creek catchment. The earthworks required to build the landform created a considerable disturbance in the catchment, making a large volume of disturbed soil and substrate material available for erosion. Between 2008 and 2010, in the first two wet seasons immediately after construction, the downstream monitoring site on Gulungul Creek showed elevated FSS wave loads relative to discharge, compared with the upstream site. From 2010 onwards, the FSS loads relative to Q were no longer elevated. This was due to the establishment of vegetation on the site and loose fine sediment being trapped by vegetation. Large scale disturbance associated with mining and rehabilitation of elevated landforms causes elevated FSS loads in receiving streams. The predicted FSS loads for the stream as per the relationships between FSS and event discharge may not show a 1:1 relation with the observed loads for respective gauging stations. When downstream monitoring shows that FSS wave loads relative to rainfall runoff event discharge reduce back to pre-construction catchment levels, it will indicate that the landform is approaching equilibrium. This approach to assess landform stability will increase the sensitivity of assessing post-mining landform recovery and assist rehabilitation engineers to heal the land and benefit owners of the land to whom it is bestowed after rehabilitation.

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