A Functional Form for Fine Sediment Interception in Vegetated Environments

The body of literature seeking to evaluate particle interception in vegetated, aquatic environments is growing; however, comparing the results of these studies is difficult due to large variation in flow regime, particle size, vegetation canopy density, and stem configuration. In this work, we synthesize data from these studies and develop a functional form of particle interception efficiency (η) as a function of stem Reynolds number (Rec), stem diameter, vegetation frontal area, particle–collector diameter ratio, flow velocity, and kinematic viscosity. We develop this functional relationship based on a dimensional analysis and hypothesize that the coefficients would exhibit regimes within different Rec ranges. We test this hypothesis by synthesizing data from 80 flume experiments reported in the literature and in-house flume experiments. Contrary to our hypothesis, data from different Rec ranges follow a single functional form for particle interception. In this form, η varies strongly with collector density and particle–collector diameter ratio, and weakly with Rec and particle–fluid density ratio. This work enables more accurate modeling of the flux terms in sedimentation budgets, which can inform ongoing modeling and management efforts in marsh environments. For example, we show that by integrating the new functional form of particle interception into established models of marsh elevation change, interception may account for up to 60% of total sedimentation in a typical silt-dominated marsh ecosystem with emergent vegetation.

Application of Multi-Source Data Fusion Method in Updating Topography and Estimating Sedimentation of the Reservoir

The underwater terrain of a reservoir can experience significant changes due to the effects of erosion and siltation during decades of operation. Therefore, existing topographic data no longer reflect current reservoir terrains and need to be updated. In this paper, we propose a fast and economical method for updating the topography of a reservoir. According to multi-source data fusion, we effectively integrated sonar sounding data, cartographic data, and manual measurement data to update and reconstruct the bottom topography of a reservoir in Northeast China. By comparing the updated topography with the measured elevation, the average error of the simulation results is only 0.56%, which shows that the updated topography can accurately reflect the actual topography of the reservoir. Furthermore, by using the surface volume tool in ArcGIS, we developed the original and updated the elevation and volume curves of the reservoir. Finally, the amount of silting and its distribution in the reservoir were obtained by calculating the difference between the original and updated elevation and volume curves. The results show that the total sedimentation volume in the researching reservoir is about 4.3 million m3, which is mainly concentrated in the areas with an elevation below 50 m and above 60 m.

Multidecadal Sediment Balance Modelling of a Cascade of Alpine Reservoirs and Perspectives Based on Climate Warming

This paper presents a comprehensive methodology to model and determine the annual sediment balance of a complex system of interconnected reservoirs, based on the detailed interpretation of a multi-decadal data series of reservoir management and modelling of sediment fluxes. This methodology is applied to the reservoirs of Oberaar, Grimsel, Räterichsboden, and Trift, which are located in the Swiss Alps. Additionally, the effects of climate warming on the annual sediment yield are investigated. Modelling results show that at present, the hydropower cascade formed by Oberaar, Grimsel, and Räterichsboden retains about 92% of the annual sediment yield, of which only the finest fraction leaves the system and enters the river network. Very fine sediments (d < 10 μm) account for 28% of the total sedimentation rate and in the case of Oberaar, it can reach up to 46% of the total sedimentation rate. Under a climate warming scenario, both sediment yield and runoff are expected to increase in terms of the annual average throughout the XXIst century, which will likely lead to greater annual inputs of sediments to the reservoirs. This, in turn, will lead to a higher sedimentation rate and suspended sediment concentration in the reservoirs, unless active management of the sediment fluxes is implemented.

Sediment balance of a cascade of alpine reservoirs based on multi-decadal data records

Reservoir sedimentation is a major concern in the operational management of dams and appurtenant structures. The increasing volume of sediments deposited in reservoirs leads to a loss of water storage, undermining the purpose itself of the dam for human use or protection. The deposition of sediments (mostly fine) in the vicinity of the dam’s operational structures, such as bottom outlets and power intakes, may result in partial or total blockage of these structures. To cope with these problems, it is essential to determine the sediment balance of the reservoirs, by assessing the origin and quantity of the in- and out-fluxes of sediments. This paper presents a methodology to determine the annual sediment balance of a system of interlinked reservoirs across several decades, as well as its application to the alpine hydropower cascade formed by the Oberaar, Grimsel and Räterichsboden reservoirs located in Switzerland. At that aim, the annual sediment fluxes and the sedimentation rates of each reservoir were characterized. Also, the percentage of fine sediments (dm < 10 μm) included in the total sedimentation rate was estimated. The results reveal that the annual sedimentation rate of the lowermost reservoir of the system (Räterichsboden) is highly altered by the flushing operations of the reservoir upstream (Grimsel). Also, for the uppermost reservoir of the system (Oberaar), the volume of fine sediments deposited annually can reach up to 46% of the total sedimentation rate.

Transformation of different reaches of the Niida River (Japan) after extreme flood

Extreme floods can have different effects on the river bottom relief depending on several factors. The geomorphological impact of the extreme flood occurring in the Niida River basin (Fukushima prefecture, Honshu inland, Japan) on the channels and river bottom of different reaches of the river is analyzed. High-resolution satellite images and field assessments were used for quantitative evaluation of river bottom transformation which mainly occurred in the lower reach of the Niida river. The lower reach of the Niida River was divided on three subzones according the channel gradient changes. Each sub-zones is correspond with the dominance of a certain type of channel (straight, meandering and wandering). It was found that bank erosion exceeded in- channel deposition in 1,7-2,7 times for all types of river channel in the low reach located within the coastal floodplain. However, floodplain sedimentation is the most active processes for the river sections with meandering and wandering types of the river channel. Floodplain sedimentation exceed bank-erosion in 2.2 times for river sections with the meandering type of channel and in 2.9 time for the river sections with wandering type of channel. It was found that bank erosion exceeded in- channel deposition in 1,7-2,7 times for all types of river channel in the low reach located within the coastal floodplain. However, floodplain sedimentation is the most active processes for the river sections with meandering and wandering types of the river channel. Floodplain sedimentation exceed bankerosion in 2.2 times for river sections with the meandering type of channel and in 2.9 time for the river sections with wandering type of channel. The bank erosion exceeds floodplain deposition in 1,2 times only within the river sections with straight type of channel. Total sedimentation (in-channel + floodplain) in 2.6 times higher than bank erosion in the lower reach of the Niida River after extreme flood event with probability 4-5%.

Stochastic Analysis Method in Application of Longshore Sedimentation

Huanghua is one of the important ports in China. During its constructing stage, Huanghua port encountered the heavy sedimentation after each typhoon or other storm weather processes. In the feasibility study, the predicted yearly amount of sedimentation is far less than that observed. In order to obtain the reasonable design amount of sedimentation, the stochastic analysis methods are involved in this paper to predict the total sedimentation of different design return periods with corresponding confidence intervals. For the prediction of typhoon or storm (wind speed and duration) induced sedimentation, the trivariate joint probability of wind speed, duration and corresponding sedimentation can be obtained by stochastic simulation technique based on the importance sampling procedure.

Late Quaternary history of the Lake O'Hara region, British Columbia – an evaluation of sedimentation rates and bulk amino acid ratios in lacustrine records

Lake O'Hara (subalpine) and Opabin Lake (alpine) are situated directly adjacent to a high section of the Continental Divide in the central Canadian Rocky Mountains. Core samples recovered from the lakes show a consistent stratigraphy comprising gyttja and underlying inorganic clastic sediments. The gyttja contains Bridge River (2350 years BP) and Mazama (6800 years BP) tephras and is separated from the lower clastic sediments by a sharp, conformable contact. Radiocarbon dates obtained from conifer needles, extracted from directly above the contact, indicate that deglaciation had proceeded upvalley from the O'Hara basin priorto ca. 10 100 years BP. Preliminary palaeobotanical and macrofossil data suggest that a Pinus–Abies forest with lesser Picea was established in the vicinity of Lake O'Hara by this time. Consequently, the minimum age of moraine systems situated downvalley from Lake O'Hara is Late Wisconsinan.Mean annual sedimentation rates were derived from sediment thickness data from 14 Lake O'Hara and 2 Opabin Lake cores. Averaged total sedimentation rate values from the Lake O'Hara cores are 0.13 mm/year (post-Bridge River), 0.13 mm/year (Mazama – Bridge River) and 0.05 mm/year (11 000 years BP – Mazama). Averaged total sedimentation rate values from the Opabin Lake cores are 0.19 mm/year (post-Bridge River), 0.07 mm/year (Mazama – Bridge River), and 0.06 mm/year (8530 years BP – Mazama). Higher total sedimentation rates in post-Bridge River sediments of Opabin Lake are presumably related to climatic conditions associated with more extensive upvalley ice during the last ca. 2300 years. Highly variable sedimentation rate data obtained from the Lake O'Hara cores suggest that the use of sedimentation rate data as a proxy record of upvalley glacial activity is inappropriate in the Lake O'Hara setting where inflowing glacial stream systems are interrupted by upvalley lake basins.Aspartic acid D/L ratios were derived from bulk gyttja samples of known age from seven Lake O'Hara and one Opabin Lake core. In all but two cases, aspartic acid D/L ratios increase consistently with respect to sediment age. The increasing downcore trends in the aspartic acid D/L ratios suggest the possibility of using amino acid data from bulk gyttja samples as a check for reworking in cases where chronostratigraphic markers are absent.

Geochemistry of zinc, copper and lead in the sediments of the estuary and Gulf of St. Lawrence

Total elemental concentrations (Zn, 8–215 ppm; Cu, 3–76 ppm; Pb, 9–66 ppm) vary texturally and regionally in the sediments of the St. Lawrence estuary and open Gulf of St. Lawrence.Chemical and mineralogical analyses indicate that 8–39% of the total Zn, 7–20% of the total Cu and 15–26% of the total Pb are weakly held by fine-grained organic material, oxide grain coatings, ion exchange positions and carbonates in the sediments. These concentrations are potentially available to the biota. The remaining concentrations (61–93% of the total) are not readily available but are locked up in fine-grained sulphide, oxide and silicate minerals.The highest concentrations of the detrital and non-detrital contributions occur in the pelites or muds of the upper estuary. Seaward these concentrations decrease as the natural and anthropogenic supply of dissolved and suspended particulate matter from the St. Lawrence River diminishes. The upper estuary acts as a sink for these elements because most of the non-detrital Zn, Pb and Cu supplied are removed here by adsorption onto fine-grained suspended terrestrial organic material from solution or before entry (Cu) and transferred to the bottom along with other fine-grained material in response to the present depositional conditions. Decreasing concentrations of these elements are deposited seaward and the sedimentation intensities of the non-detrital elements remain constant with fluctuations in total sedimentation intensity in the lower estuary and open Gulf of St. Lawrence.Biogeochemically, Zn is a contaminant and Pb and Cu are potential contaminants of the upper estuary sediments. Zn and Pb are potential contaminants in the lower estuary but all the elements are at or near natural levels in the open gulf sediments.

Rates of Accumulation of Phosphorus Forms in Lake Erie Sediments

Six Lake Erie sediment cores from locations of widely different sedimentation rates show that rate of input and sedimentation of apatite phosphorus at a given locality has been approximately constant during the last few hundred years relative to total sedimentation rate at the same locality. Apatite is not a significant source of soluble phosphorus for Lake Erie. By contrast, rate of sedimentation of nonapatite inorganic phosphorus (NAIP) and organic phosphorus has steadily increased in accordance with increased loadings in recent years of the source material, namely phosphorus of anthropogenic origin. The rate of sedimentation of these two forms of phosphorus at a given locality varied greatly within the lake, and was greatest where the most fine-grained sediments were accumulating. It was concluded that the sediments of Lake Erie contain sufficient orthophosphate-retaining sites to prevent major regeneration of phosphate under any conceivable condition provided the overlying water remains oxic.