Sediment Management Research Articles

Metrics for short-term coastal characterization, protection and planning decisions of Sentina Natural Reserve, Italy

Geomorphological and sedimentological surveys of the emerged and submerged beach-dune system are fundamental for a successful management and protection strategies for coastal planning and development. In particular, these surveys can reveal if coastal areas are affected by erosion, pollution and loss of habitats under the seasonal anthropic pressure related to tourism, leisure and professional fishing, urbanisation and/or other activities impacting the coastal marine resources.In the present study we discuss the results of the multidisciplinary monitoring activities carried out within the Sentina Natural Reserve (Municipality of San Benedetto del Tronto, Adriatic side of Central Italy, at the south-eastern end of the Marche Region) proposing an exportable methodological approach. Due to the absence of buildings, the study area has not been considered in the coastal protection plan by regional and local authorities and, as a consequence, it is currently exposed to severe coastal erosion, the rate of which has been more precisely determined during the present study. This monitoring testifies that most of the seaward surface of the beach disappeared resulting in a general set back of the whole beach environment. In the last decades, several restoration strategies have been adopted to protect and restore the dunes and the back dunes habitats and the municipality also carried out an emergency action to nourish the beach, including the use of sand dredged from the nearby city harbor.With this sediment management approach, a tradeoff between safety of navigation of harbor inlet and habitat conservation of Natural Reserve have been reached, since beach nourishment can reduce coastal vulnerability and risk, even though its sustainability in the long term is still debated.

Reactivity of particulate element concentrations: apportionment assessment of suspended particulate matter sources in the Upper Rhône River, France

Suspended particulate matter (SPM) transport through rivers is a major vector of nutrients and pollutants to continental shelf areas. To develop efficient sediment management strategies, there is a need to obtain quantitative information on SPM sources. For many years, the geochemical properties of SPM have been commonly used as tracers to identify sediment sources. In large watersheds, with numerous sources, the expected alteration of tracers during their transport requires that their reactivity be taken into account. To overcome this issue, we tested the use of major and trace element signatures in the residual fraction of SPM, using two different extraction methods. This original fingerprinting approach was applied to the Upper Rhône River basin (~20,000 km2) in order to assess the respective SPM contributions of its main five tributaries (Arve, Ain, Fier, Guiers, and Bourbre Rivers) for contrasted hydrological conditions (base flow periods, flood events and dam flushing). By incorporating element concentrations previously corrected from particle size distribution in a mixing model coupled to Monte Carlo simulations, we estimated the associated uncertainties of the SPM contributions from each tributary. The relative SPM contributions obtained using this fingerprinting approach were compared with those calculated with a 1-D hydro-sedimentary model. The use of element concentrations, such as Zn, P, Cu, Pb, Mn, or Sr, in the total fraction of SPM as conservative fingerprinting properties was not suitable, since they are mainly bound (> 50%) to reactive carrier phases. By using Ba, Ni, Fe, Mg, Cu, Sr, and V concentrations in the SPM residual fraction, the apportionment modeling of SPM sources was successfully assessed. The fingerprinting approach showed that, in base flow conditions, SPM originated mainly from the Arve River. During dam flushing event, the fingerprinting approach consistently estimated that re-suspended sediments came from the Arve River, while the 1-D hydro-sedimentary model estimated a proportion of re-suspended sediment originating within the Rhône River. This original fingerprinting approach highlighted the relevance of using geochemical properties in the non-reactive fraction of SPM in order to obtain reliable information on spatial sources of SPM in a large river basin. This methodology opens up promising perspectives to better track SPM sources in highly reactive environments such as estuaries/delta or in historical sediment archives.

Perceptions of Sri Lankan Seafarers about the Necessity of Ratifying the Ballast Water Management Convention in Sri Lanka

The International Maritime Organization (IMO) developed and adopted the “International Convention for the Control and Management of Ships' Ballast Water and Sediments” (Ballast Water Management Convention or BWM Convention) in February 2004 to prevent the uptake or discharge of invasive alien species and harmful aquatic organisms and pathogens within ballast water and sediments [5]. The BWM Convention entered into force on the 08th of September 2017. In 2020, 85 countries have ratified the Convention, representing 91. 11 per cent of world merchant shipping tonnage [4]. Yet, Sri Lanka as a Flag State (FS) has still not ratified the BWM Convention [8]. This research explored the perception of the Sri Lankan seafarers about the necessity of ratifying the BWM Convention by Sri Lanka. The data for this qualitative/ quantitative study were gathered via interviews and questionnaires given to 80 merchant navy officers from both deck and engineering departments. Results of this study show that the Sri Lankan merchant navy officers bear the idea that Sri Lanka should ratify the BWM Convention as Sri Lankan waters receive ballast water from international vessels threatening the Sri Lankan marine ecosystems, economy and human health. Findings of the study revealed most of the Sri Lankan merchant navy officers have identified the need of ratifying the BWM Convention to preserve the coastal and marine environment and protect the endangered and indigenous aquatic species living in Sri Lankan waters. The respondents also viewed that Sri Lanka as a Port State (PS) should establish port reception facilities and provide training for port state control officers. Most of the merchant navy officers highlighted the need of a national policy framework strengthened by scientific research to address the issue. The financial incapacity to develop a task force and a national strategy, as well as the financial inability to develop scientific research skills and continuous monitoring & training were identified by the respondents as the main challenges to ratify the BWM Convention by Sri Lanka.

An Engineered and Sustainable Solution for Flood and Sediment Management in Kosi River, India

Flooding is one of the most devastating and frequent natural hazards in the Indian subcontinent. In India, Bihar is one of the most flood prone states. Floods hit the state almost every year and causes enormous loss of lives, property, agriculture and infrastructure. Bihar has about 6.88 million hectares of flood prone area which is about 73.06% of its geographical area. The Kosi river is the most unstable river in Bihar and known as the “Sorrow of Bihar” because floods in this river cause huge destruction almost every year by its course changing tendency in the plains of North Bihar. It is one of the largest tributary of the river Ganga originating from Himalayas in Tibet and joins the Ganga in Bihar after flowing through Nepal. Majority of the drainage area of this river (almost 85 %) lies in Tibet and Nepal while only 15% lies in Indian Territory. The river carries huge amount of sediment with flow every year (about 120 million m3/Year) which primarily causes change in the morphological behaviour of the river. Even after the adoption of several measures, mostly grey infrastructure for the flood management in the Kosi river, the flood devastation in the region is still continued. The grey infrastructure approach gives a false sense of security and it also results in many unintended negative consequences. The present paper analyses the problem of flooding in the Kosi river basin; explores the feasibility of innovative and green infrastructure based sustainable solutions. Considering the prime issue of sediments in the Kosi, a novel concept of detention cum siltation ponds have been proposed. These ponds require hardly 7.84-13.54% of the drainage basin of Kosi in India. The proposed detention cum siltation ponds with other green infrastructure measures for the flood and sediment management in the river basin have overarching benefits. The environmental and economic sustainability aspect adds a great value to feasibility of the proposed measures.

The vulnerability of tidal flats and multi-channel estuaries to dredging and disposal

Shipping fairways in estuaries are continuously dredged to maintain access for large vessels to major ports. However, several estuaries worldwide show adverse side effects to dredging activities, in particular affecting morphology and ecologically valuable habitats. We used physical scale experiments, field assessments of the Western Scheldt estuary (the Netherlands), and morphodynamic model runs to analyse the effects of dredging and future stresses (climate and sediment management) on a multi-channel system and its ecologically valuable intertidal flats. All methods indicate that dredging and disposal strategies are unfavourable to long-term morphology because dredging creates and propagates the imbalance between shallow and deeper parts of the estuary, causing a loss of valuable connecting channels and fixation of the tidal flats and main channel positions, while countering adverse effects by disposal strategy has limited effectiveness. Changing the disposal strategy towards main channel scour disposal can be economically and ecologically beneficial for the preservation of the multi-channel system. Further channel deepening will accelerate the adverse side effects, whereas future sea-level rise may revive the multi-channel system.

Feasibility Study on Shore-based Treatment Technology of Ship’s Ballast

The International Convention on the Control and Management of Ballast Water and Sediment on Ships officially entered into force for our country on January 22, 2019. The Convention stipulates a series of requirements for the compliant discharge of ballast water. Compared with the ship’s own ballast water treatment facility, the ballast water bank-based treatment facility has the advantages of economy, environmental protection, and stability. In order to improve my country’s ability to implement the Ballast Water Convention and promote the construction of my country’s green ports, discussion and research on ballast water bank-based treatment technologies are necessary. This article describes the main methods of receiving and processing ship’s ballast on water and shore, analyzes the prospects and existing problems of receiving and processing ballast on water and on shore, and puts forward relevant suggestions for research on ballast water and shore treatment technology.

A STUDY OF SHIP BALLAST WATER TREATMENT TECHNOLOGIES AND TECHNIQUES

Ballast is a commonly used solution to ensure the stability and balance of ships during voyages. The volume of ballast water that is circulated by ships between different seas is extremely large, with which a lot of creatures move along. Organisms that follow the ballast water to a new environment mostly have a negative impact on the ecosystem there. Good ballast water management is an important measure to ensure that organisms do not migrate with the ballast water to other areas. Ballast water management requires specific regulations and regulatory policies that are relevant and applicable globally. The International Convention on the Control and Management of Ballast Water and Ship Sediments, adopted in 2004, has specified issues for ballast water management. Ballast water treatment technologies and techniques need to be studied so that the ballast water after treatment meets the requirements of the convention. This paper presents an overview of the technological and technical solutions currently being applied to treat ballast water to meet the requirements of the convention and points out the advantages and limitations of each solution. In the discussion, the authors also present a solution that combines many different ballast water treatment methods. This is a very effective solution, both technically and cost-effectively. The combined solution can be applied in the future to effectively treat ship ballast water.

Healthy Port Futures: Rethinking Sediments for Rivermouth Landscapes

Throughout the Great Lakes, port cities are often located on the rivermouth and where rivermouths once sorted, shaped, and moved the riverine sediment into the lake. Their current use as industrial navigation channels requires cyclical mechanical maintenance dredging. Past sediment management practices have either placed the riverine sediment nearshore in confined disposal facilities (CDFs) or out in deeper open water. Both practices remove the sediment from the nearshore system, preventing its potential use in coastal protection, habitat creation, wave attenuation, and sediment nourishment. However, novel rivermouth wetlands can draw from both strategies of containment (as in a CDF) and cost-efficiency of non-containment (open lake disposal) to allow for the processing and use of sediment. This article will describe one such attempt, conducted by the Great Lakes Protection Fund-supported Healthy Port Futures project. Through a collaborative design-research process, Healthy Port Futures used a range of tools to generate, speculate, model, visualize, and test wetland forms under a range of social, ecological, and hydrological conditions. This project, understood colloquially as “the Crescent,” proposed a semi-circular, partially open-cell wetland design as a response to the complexity of rivermouth conditions. Throughout this design-research process, the project sought to acknowledge uncertainty, assess risk, and explore a range of outcomes in order to redefine the public expectations around wetland creation and restoration, and reimagine innovation along the Great Lakes coast.

Streamflow and Sediment Yield Estimation, and Area Prioritization for Better Conservation Planning in the Dawe River Watershed of the Wabi Shebelle River Basin, Ethiopia

Estimating sediment yield and streamflow, as well as identifying soil erosion processes, are necessary for properly designing superior management techniques, monitoring and evaluating various management scenarios, and prioritizing better conservation planning. Therefore, this study estimates Streamflow and sediment yield and prioritizes the catchment sub-watersheds for conservation planning in the Dawe River watershed. In the incessant-time step, sediment load data is generated by developing a sediment rating curve. Statistical measures were used to weigh the SWAT's performance in estimating streamflow and sediment output over the calibration (2000-2008) and validation (2009-2013) periods. The model's performance in estimating the monthly streamflow was 0.73, 0.55, and 0.79 for NSE, R-factor, and R2, respectively, according to the calibration results. For sediment yield, the Nash Sutcliffe efficiency (NSE), R-factor, and R2 were 0.77, 0.47, and 0.82, respectively. Estimated sediment output rates were higher in agricultural lands with eutric and rendzic leptosols soil types and gradients in the study watershed. For the indicated sub-watersheds in the catchment, the three best sediment management scenarios (BMPs) were considered: S1 (filter strip), S2 (terrace/bund), and S3 (reforestation). With the implementation of S1, S2, and S3, the sediment yield was reduced by 15.7 percent, 21.3 percent, and 24.9 percent, respectively, based on the chosen BMPs. As a result, adopting S3 for the Dawe River watershed for productive sediment reductions should be encouraged. As a result, our findings point to the best strategy for negotiating a stronger conservation plan.

Evaluating Rare Earth Elements as Tracers of Fluvial Processes: Fine Sediment Transport and Deposition in a Small Stream

HighlightsNatural sediments labeled with rare earth elements can effectively be used as tracers for quantifying fine sediment transport and deposition.Two artificial floods in a small stream (100 ha watershed, 1.5 year return flow of 515 L s-1) transported fine sediment 0 m to >850 m at a maximum flow rate of 55 L s-1.Sediment deposition per unit area was greater in the channel than in the near-channel floodplain.Use of two distinct tracers demonstrated resuspension extent during sequential high-flow events.Presence of large wood in the channel was associated with reduced streamflow rate, decreased suspended sediment transport velocity, increased channel sediment deposition, and reduced near-floodplain sediment deposition.Abstract. Effective sediment management requires an understanding of the lag time between best management practice implementation and observable changes in the target water body. To improve our understanding of sediment lag times, we tested a method to label locally sourced sediments with rare earth elements to quantify fine sediment flow-through and storage in fluvial systems. We injected sediments labeled with lanthanum and ytterbium into a small stream during two artificial flood events. During the floods, we collected and quantified suspended sediments and sediment deposition in the stream channel and floodplain at four cross-sections within our study reach. Two down-gradient (90 m and 850 m) time-integrated suspended sediment samplers evaluated total travel distance. Sediment tracer observations of particle transport distances ranged from 0 m to at least 850 m at a maximum flow rate of 55 L s-1 (stream 1.5 year flow was 515 L s-1). Sediment deposition per unit area was greater in the channel than in the floodplain. The majority of sediment tracer mass injected into the stream entered storage within the first 69 m of the reach. Some particles that deposited following the first flood were resuspended and either transported downstream or redeposited within the study reach. Our results support the further use of rare earth elements as sediment tracers to inform water quality and sediment transport models, and to provide estimates of lag times between management actions and downstream improvements. Keywords: Fine sediment, Flood, Fluvial geomorphology, Lag time, Large wood, Rare earth elements, Sediment deposition, Sediment transport, Tracer.

USING SPECIFICATION OF OVERBURDEN TO IMPROVE NUMERICAL LONGSHORE SEDIMENT TRANSPORT MODELING

The Sebastian Inlet Florida Coastal Processes Model computes sediment transport pathways in the nearshore to support sediment management activities. Longshore sediment transport rates are computed by the model and compared with field data. The model is run with two alternative specifications of hard bottom to investigate the impact on computed transport rates. One alternative specifies known hard bottom outcrop locations and the second, a uniform one-meter overburden throughout the model domain. The uniform overburden specification improved longshore sediment transport rate computations throughout the model domain. The goal of this work is to improve upon nearshore sediment transport and morphology by addressing uncertainty in hard bottom locations and ephemeral coverage. This paper documents the modeling effort and the changes necessary to improve model performance in the nearshore.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/u1bNOca5qUo

Modeling linkages between erosion and connectivity in an urbanizing landscape

Erosion and connectivity are spatially varied processes key to determining sediment transport and delivery to downstream waterbodies. However, we find few studies that explicitly model the linkages of where erosion and connectivity coincide and where they contradict, particularly in urbanizing settings. In this study, we couple in-stream aquatic sensing, the Revised Universal Soil Loss Equation (RUSLE), the Index of Connectivity (IC), and the Sediment Delivery Ratio (SDR), together with Monte Carlo uncertainty analysis, to generate a new Erosion-Connectivity Mapping (ECM) framework. We evaluate ECM accuracy with field assessment of thirty-five sites spread across five lowland watersheds (mean slope <5°) in Johnson County, Kansas, USA, which differ primarily in their land use, ranging from 21% to 89% urban. RUSLE modeling results indicate erosion is controlled by topography with high risk areas near streambanks roadway systems. SDR and IC were positively related at the five sites (R2 = 0.78, p < 0.05) with the highest values in the most urbanized watershed, indicating that anthropogenic change augments connectivity. The ECM results indicate that while only 5±1% of the study area is both highly erodible and highly connected, these areas represent 37±4% of total watershed-scale erosion. Our modeling results indicate that erosion is more likely to be the limiting factor in sediment transport, as opposed to connectivity, as there are generally more locations that are well-connected to hydrologic transport but resistant to erosion. Our field assessment provided broad support for the ECMs; however, field assessment indicated that geospatial modeling underpredicts how closely related erosion and connectivity are in the field and we suggest that future models consider this coupling more explicitly. This study provides a method for combining RUSLE and IC in a new tool (ECM) to identify spatial patterns in sediment erosion-connectivity to aid in the understanding and management of watershed sedimentation.

Sedimentation and its response to management strategies of the Three Gorges Reservoir, Yangtze River, China

The Three Gorges Dam (TGD), on the upper valley of the Yangtze River, China, is the largest water conservancy and power generation project in the world. Problematic sedimentation in the Three Gorges Reservoir (TGR) is related to the reservoir lifetime, hydropower generation, riverbed erosion, and sustainable development of ecosystems. In this study, measures to holistically and systematically address sedimentation in the TGR are -discussed and demonstrated, including upstream sediment trapping, regulatory optimisation with respect to sediment peaks and reservoir tail sedimentation reduction, and sediment dredging. Owing to upstream reservoir sediment trapping, the incoming sediment load of the TGR has decreased markedly. Results showed that the annual incoming sediment was only 164 million tons, nearly 70% lesser than the preliminary design value. By intercepting the sediment in the upstream reservoirs and conducting sediment peak regulation, the volume and rates of sedimentation in the TGR decreased significantly. Meanwhile, through sediment peak regulation during the flood season, increased volumes of sediment could be discharged downstream, thereby relieving sediment starvation downstream of the TGD. Overall, through adoption of the related sedimentation management strategies, sediment deposition decreased considerably, to approximately 33% of the preliminary design value, thereby successfully addressing the sediment problems in the TGR. Useful sedimentation management strategies learned from the TGR experience can be applied elsewhere to ensure the sustainable use and management of reservoirs.

Sediment Management: Hydropower Improvement and Habitat Evaluation

It is predicted that 60% of all new energy investments over the next 20 years will be in renewables [...]

Model Development for Estimation of Sediment Removal Efficiency of Settling Basins Using Group Methods of Data Handling

Settling basins are generally used as sediment removal structures in which flow velocity is reduced, resulting in surplus settlement of sediment particles. The accuracy of the available empirical equations for sediment removal efficiency is checked using data available in the literature. The existing relationships of removal efficiency were not found to yield satisfactory results. Therefore, the data were reanalyzed and new models were developed using nonlinear regression and the group method of data handling (GMDH). On the basis of various performance parameters, it was observed that the proposed nonlinear regression model had the highest accuracy compared with other available relationships. It was also observed that the efficiency estimated using the GMDH model (R=0.960, AAD=14.698, and RMSE=0.094) was more accurate than that estimated by the regression model (R=0.863, AAD=30.675, and RMSE=0.171). Sensitivity analysis indicated that the ratio of particle fall velocity to average flow velocity in the basin was the most effective parameter for sediment removal efficiency. This work will help in quantifying and subsequently improving the management of surplus sediment in canals.

Pilot Field Implementation of Suction Dredging for Sustainable Sediment Management of Dam Reservoirs

AbstractThe buildup of sediment deposits in reservoirs is a long-standing problem with serious consequences on the reservoirs’ functionality and the ecology of their river systems. In the last two ...

Current advisory interventions for grazing ruminant farming cannot close exceedance of modern background sediment loss – Assessment using an instrumented farm platform and modelled scaling out

Water quality impairment by elevated sediment loss is a pervasive problem for global water resources. Sediment management targets identify exceedance or the sediment loss ‘gap’ requiring mitigation. In the UK, palaeo-limnological reconstruction of sediment loss during the 100–150 years pre-dating the post-World War II intensification of agriculture, has identified management targets (0.20−0.35 t ha−1 yr−1) representing ‘modern background sediment delivery to rivers’. To assess exceedance on land for grazing ruminant farming, an integrated approach combined new mechanistic evidence from a heavily-instrumented experimental farm platform and a scaling out framework of modelled commercial grazing ruminant farms in similar environmental settings. Monitoring (2012–2016) on the instrumented farm platform returned sediment loss ranges of 0.11−0.14 t ha−1 yr−1 and 0.21−0.25 t ha−1 yr-1 on permanent pasture, compared with between 0.19−0.23 t ha−1 yr-1 and 0.43−0.50 t ha−1 yr−1and 0.10−0.13 t ha−1 yr−1and 0.25−0.30 t ha−1 yr-1 on pasture with scheduled plough and reseeds. Excess sediment loss existed on all three farm platform treatments but was more extensive on the two treatments with scheduled plough and reseeds. Excessive sediment loss from land used by grazing ruminant farming more strategically across England, was estimated to be up to >0.2 t ha−1 yr−1. Modelled scenarios of alternative farming futures, based on either increased uptake of interventions typically recommended by visual farm audits, or interventions selected using new mechanistic understanding for sediment loss from the instrumented farm platform, returned minimum sediment loss reductions. On the farm platform these were 2.1 % (up to 0.007 t ha−1 yr−1) and 5.1 % (up to 0.018 t ha−1 yr-1). More strategically, these were up to 2.8 % (0.014 t ha−1 yr−1) and 4.1 % (0.023 t ha−1 yr−1). Conventional on-farm measures will therefore not fully mitigate the sediment loss gap, meaning that more severe land cover change is required.

Factors controlling discharge-suspended sediment hysteresis in karst basins, southwest China: Implications for sediment management

Assessment of river sediment sources, transport, and controlling factors in karst regions is critical to the development of effective soil erosion and sediment management strategies. This 2-year study used a hysteresis index of discharge and suspended sediment data, combined with the basin's inherent geological characteristics, to assess sediment sources and hydrological connectivity at six sites in an agricultural karst watershed of southwest China. Principal component analysis was further used to describe sediment control by rainfall (antecedent precipitation, precipitation duration, amount, and intensity) and stream hydrology (maximum and total discharge, flood intensity, and runoff coefficient). Results indicate that the annual sediment yield (0.8–6.6 Mg km2 a−1) is low and sediment transport in karst areas is dependent on continuous rainfall. Ground substance component (GSC) and geomorphology characteristics determine the hydrology connectivity and sediment availability. In a sub-basin (CQ) marked by a peak cluster depression with good vegetation, sediment mainly comes from the paddy land, and the surface stream shows clockwise hysteresis. During storms, surface water enters the underground system from sinkholes, resulting in Figure-8 hysteresis with multiple sediment peaks. In another predominantly agricultural sub-basin (HTP), the thick layers of paddy and loess soil surrounding the river channel provide an accessible sediment source, resulting in clockwise hysteresis. The surface outlet of the watershed (HZ) is affected by an upstream reservoir, but bank erosion and sediment activation are evident during storms. The subsurface outlet (MSK) of the watershed shows more anti-clockwise hysteresis due to the activation of the conduit network in the wet season, surface water draining into the underground river and the distant sediment sources. This study shows that discharge-suspended sediment concentration hysteresis analysis can provide a reference for soil and water conservation decision-making in karst areas.

Mitigation of ecological impacts on fish of large reservoir sediment management through controlled flushing – The case of the Verbois dam (Rhône River, Switzerland)

Sediment trapping within reservoirs is a worldwide phenomenon which impairs the ecological functioning of upstream and downstream ecosystems. It also reduces reservoir water storage volume, which lessens the services dams provide such as hydropower production or flood control and questions their sustainability. Hydraulic flushing is a widely used operation to recover the reservoir volume, but ecological impacts are massive. Recently, environmental awareness led dam operators to modify their management practices: ‘Controlled Sediment Flushing Operations’ (CSFOs) include environmental objectives in their implementation and are designed to be less harmful for aquatic ecosystems by controlling the flow and Suspended Sediment Concentration (SSC) downstream. However, CSFOs are not yet widespread, their ecological impacts are poorly documented, and comparisons with ‘classical’ flushing operations are unreported. Here, we analysed impacts on fish of the first CSFO of the Verbois reservoir in 2016, both upstream and downstream of the dam, and compared these with those from the empty flushing of 2012 using the same methodology (Grimardias et al., 2017). Time-series of hydroacoustics surveys enabled us to estimate the fish abundance in the reservoir, while radiotelemetry measured movements and apparent survival below the dam for four representative species. The 2016 CSFO lasted 10 days, and released a mean Suspended Sediment Concentration (SSC) of 3.47 g·L−1 (peak = 11.98 g·L−1). The fish density as assessed by the mean acoustic scattering strength SA in the reservoir did not change significantly pre- and post-CSFO, and SA seasonal estimates of year 2016 did not differ from those of 2015 and 2017. The apparent survival estimated from capture-recapture survey of marked fish (N = 118) decreased significantly during the CSFO for all species and differed across species, while the distances moved downstream increased. By comparison with the 2012 empty flushing, the 2016 CSFO allowed fish to remain in the reservoir, while impacts below the dam were mostly behavioural rather than lethal. Overall, despite significant impacts, the CSFO advantageously replaced ‘classical’ flushing from an ecological viewpoint. Provided that an acceptable balance between economical, ecological and technical aspects is found, CSFO can be considered for many reservoirs while accounting for their biological and physical site-specificity.

Assessment of the Anthropogenic Sediment Budget of a Littoral Cell System (Northern Tuscany, Italy)

In the present study we describe a straightforward and highly replicable methodology to assess the anthropogenic sediment budget within a coastal system (the Northern Tuscany littoral cell, Italy), specifically selected in a partially natural and partially highly urbanized coastal area, characterized by erosion and accretion processes. The anthropogenic sediment budget has been here calculated as an algebraic sum of sediment inputs, outputs and transfer (m3) within a 40 year time interval (1980–2020). Sediment management strongly influences the sediment budget and, even if its evaluation is crucial to assess the efficiency of a coastal management policy, it is often difficult to quantify the anthropogenic contribution to sedimentary processes. Different types of intervention are carried out by a variety of competent authorities over time (Municipalities, Marinas, Port Authorities), and the correct accountability of sediment budget is no longer known, or possible, for the scientific community. In the Northern Tuscany littoral cell, sedimentation is concentrated in a convergent zone and updrift of port structures, which have determined a series of actions, from offshore dumping and disposal into confined facilities (sediment output), to bypassing and redistribution interventions (sediment transfer); conversely, river mouths and coastal areas protected by groins and barriers are subjected to severe erosion and coastline retreat, resulting in many beach nourishments (sediment input). The majority of coastal protection interventions were carried out to redistribute sand from one site to another within the study area (2,949,800 m3), while the sediment input (1,011,000 m3) almost matched the sediment output (1,254,900 m3) in the considered time interval. A negative anthropogenic sediment budget (−243,900 m3) is here documented.