Reservoir Sedimentation Research Articles

Improving acidic sandy soil properties for plant growth with dam reservoir sediments in the face of soaring fertiliser prices

Recent actions aimed at creating an environmentally sustainable economy, as well as very high inorganic fertiliser prices, have begun a ‘renaissance’ of alternative fertilisation. It includes utilisation of dam reservoir (DR) sediments. The aim of our study was to evaluate the agricultural value of non-toxic material to be dredged from a dam reservoir in the face of changing mineral fertiliser prices. The quality of sediments was established based on pot experiment: four different sediment dosages (5 %, 10 %, 20 %, 40 %) and three plants in rotation (maize, mustard and grass mix) were tested. Application of DR sediments into sandy soil improved its texture (depending on dose 4–31 % less sand, 50–412 % more silt and 40–70 % more clay) and sorption properties, increased pH (the soil was acidic). The content of total organic carbon increased 1.4–4.3 times, total nitrogen (N) 1.4–4.7 times, ammonium nitrogen 1.3–5.2 times, nitrate nitrogen 1.7–11.8 times, total phosphorus (P) ∼1.4 times and available phosphorus ∼2.0; most changes were statistically significant. Yield of all three plants increased significantly correspondingly to the sediment application. It shows that DR sediments might be a good alternative to chemical fertilisers. Since the catchment of the analysed reservoir is mostly agricultural, N and P compounds accumulated in sediments originated from farming. Therefore, using DR sediments as fertilisers closes the cycle of these elements; N and P compounds can be used by plants. Additionally, this alternative fertiliser is cheap – since the analysed reservoir has to be dredged, large amounts of sediments will be obtained as a ‘side-effect’ of this process. Agricultural application of this nutrient-rich material would transform sediments from waste into a resource. Recent steep increase of mineral fertilisers prices – in Poland, the prices in 2022 were 2–3 times higher than in 2018 – showed that we have to diversify fertiliser sources. Low cost, ecological sustainability and good physical and chemical properties make DR sediments, if not a substitute, a good addition to the traditional methods of agricultural fertilization.

High-temperature modification of steel slag using composite modifier containing silicon calcium slag, fly ash, and reservoir sediment

Steel slag (SS) is a kind of industrial solid waste, and its accumulation brings certain harm to the ecological environment. In order to promote the building material utilization of SS, high-temperature modification (HTM) of SS is performed using a composite modifier (CMSFR) containing silicon calcium slag (SCS), fly ash (FA), and reservoir sediment (RS). Then, the authors investigated the effect of CMSFR on the cementitious properties and volume soundness of SS mixture after HTM (SMHTM). After that, the mineral composition and microstructure of SMHTM were investigated through X-ray fluorescence analysis (XRF), X-ray diffraction (XRD), scanning electronic microscopy (SEM), energy dispersive spectrometry (EDS), and particle size analysis. It was found that the free CaO (f-CaO) content obviously decreased, and the cementitious properties improved in SMHTM. When the CMSFR content was 20% (SCS: FA: RS = 9:7:4), and the modification temperature (MT) was 1,250°C, the mass fraction of f-CaO in SMHTM dropped from 4.81% to 1.90%, down by 60.5%; the 28-day activity index of SMHTM increased to 85.4%, 14.3% higher than that of raw SS, which meets the technical requirement of Steel slag powder used for cement and concrete (GB/T 20491-2017): the activity index of grade I SS powder must be greater than or equal to 80%. As the mass fraction of CMSFR grew from 10% to 30%, new mineral phases formed in SMHTM, including diopside (CMS2), ceylonite (MgFe2O4), gehlenite (C2AS), tricalcium aluminate (C3A), and magnetite (Fe3O4). The HTM with CMSFR promotes the decomposition of RO phase (a continuous solid solution composed of divalent metal oxides like FeO, MgO, MnO, and CaO) in raw SS, turning the FeO in that phase into Fe3O4. The above results indicate that the SMHTM mixed with CMSFR can be applied harmless in cement and concrete, making low-energy fine grinding of SS a possibility.

PERENCANAAN INSTALASI PENGOLAHAN AIR LIMBAH PADA INDUSTRI TAHU (Studi Kasus Pabrik Tahu WD Lamper Lor Semarang Selatan)

In the production process, the tofu industry produces solid and liquid waste. The waste contains organic matter with high levels of BOD, COD, and TSS and does not meet quality standards. If the waste is directly discharged into the environment, it will reduce the carrying capacity of the environment. This research was conducted at the WD Lamper Lor Tofu Factory, with the aim of planning the design and RAB for the construction of the wastewater treatment plant at the Tofu Factory. This research uses quantitative analysis methods which are presented in the form of numbers which are then explained and interpreted in the form of descriptions. The quality of BOD, COD, TSS, and pH were 144 mg/L, respectively; 380 mg/L; 98 mg/L; and 4.34. Based on the quality standards, the wastewater does not meet the requirements, so it is necessary to plan a wastewater treatment plant. Researchers plan the processing stages, namely Reservoir, Equalization, Anaerobic Digester, Gas Storage, Presettlement Tub, Anaerobic Biofilter, and Final Sedimentation Tub. The estimated effluent from the processing of BOD, COD, and TSS is 2,916 mg/L, respectively; 7.695 mg/L; 2.116 mg/L. In addition to processing it into water that is fit for reuse, the design of this wastewater treatment plant produces methane gas that can be used for the tofu-making process or can be used on a household scale. The total budget plan for the planning of the Wastewater Treatment Plant at the WD Tofu Factory is 31,106,117.05.

Spatial-temporal evolution of sediment transport in the upper Yangtze River Basin considering the cumulative impacts of mega reservoirs

The intensive construction of large dams in the upper Yangtze River Basin (UYRB) has formed large-scale cascade reservoirs and obviously altered the flow regime and sediment transport of the basin. However, few studies have quantitatively described the cumulative impact of these reservoirs on sediment interception. In this study, a flow and sediment transport model that fully considers the operation processes of 24 mega reservoirs in the UYRB was established, and the spatial and temporal variations in sedimentation from 2011 to 2080 were elucidated, assuming repeated series of daily input flow discharge and sediment concentration during 2011–2020 and monthly water operation levels of 24 reservoirs during 2018–2021 as boundary conditions. The results showed an annual average sedimentation of more than 300 Mt in the UYRB during 2011–2060, which falls to 270 Mt in the period 2061–2080, and more than 80% of the sedimentation occurs in the flood season. Nearly 80% of the total sedimentation during 2010–2080 was observed in the mainstream reservoirs, especially the four mega reservoirs in the lower Jinsha River and the Three Gorges Reservoir (TGR), which accounted for 31.9% and 22.7% of the total sedimentation, respectively. The proportion of sedimentation in mainstream reservoirs will further increase with increasing operation periods. Most reservoirs in the UYRB will not reach sedimentation equilibrium by 2080, except for reservoirs in the Min River Basin. The ratio of siltation capacity to average annual sediment yield determines the percentage of residual siltation capacity of each reservoir. The operation of the cascade reservoirs in 2013–2020 had no more immediate impact on the middle and lower Yangtze River than that in 2003–2012, when the TGR started impoundment. However, the joint operation of these cascade reservoirs has changed the spatial distribution of sedimentation in the UYRB, and will lead to prolonged impacts on downstream channel erosion.

Assessment of reservoir trapping efficiency and hydropower production under future projections of sedimentation in Lancang–Mekong River Basin

Sedimentation poses a significant threat to the long-term sustainability of hydropower generation. However, there is a lack of studies examining the relationship between sediment trapping efficiency and electricity generation on a basin-wide scale over time. This study aims to assess the efficiency of hydropower production in terms of reservoir sediment trapping. Modified Brune's method examined the relationship between trapped sediments in reservoirs and hydropower production, considering sediment projections for the near future. We divided the cases of existing and planned reservoirs in the mainstream river and subbasins to assess cumulative sediment trapping. Using the Lancang-Mekong River Basin as a case study, the following main findings were observed. Firstly, the existing reservoirs, under baseline conditions (2018), had the potential to trap approximately 60.9% or 82 Mt/yr of the total sediment load. Secondly, around 69% or 110 Mt/yr of the total sediments could be significantly trapped when considering the existing reservoirs and those planned according to the development plan of riparian countries. Thirdly, the hydropower production efficiency of most reservoirs in 2030 and 2040 experienced a significant decline of approximately 10%–20% and more than 30%, respectively. Therefore, sediment management is crucial for maintaining efficient hydropower production and achieving sustainable hydropower development through effective planning strategies.

Investigation of the film-forming flooding mechanism of molecular deposition in tight oil reservoirs

Most of the oil fields in China have entered the stage of high-water-content development, which has become the primary means to improve the recovery rate of high-water-content oil fields by changing the injection agent. MDFFA membrane oil drive technology is a new type of tertiary oil recovery technology that uses an aqueous solution as the transfer medium; however, it is rarely applied in the field of tight oil reservoirs in China. In this study, molecular film-wall microgravity and water-wall microgravity were compared for tight reservoirs in the Shengli oilfield. It was concluded that the MDFFA dominates in competitive adsorption, breaks through and removes the hydrated layer, and finally adsorbs firmly on the pore wall to form a nanoscale ultrathin film. The application conditions of the MDFFA were also explored, and its wetting angle was tested. Further, the variation law of MDFFA adsorption was studied, and the mechanism of MDFFA drag reduction was explained in terms of reducing the boundary layer effect and water injection friction resistance. The natural cores procured from the Shengli tight oil field were analyzed for MDFFA membrane drive cores, and a reasonable injection concentration was selected. Through a series of mechanistic and experimental studies, we provided theoretical and technical references for the development of increased tight oil production.

The impacts of dam construction on elemental deposition in a reservoir receiving mountaintop coal mining materials

Waters MN, Bernhardt ES, Gerson JR. 2023. The impacts of dam construction on elemental deposition in a reservoir receiving mountaintop coal mining materials. Lake Reserv Manage. 39:246–258. Dam construction and associated reservoirs can become depositional basins capable of concentrating material inputs from human-altered landscapes. Landscape disturbances such as agriculture and urban expansion have been shown to impact erosional processes into reservoirs, whereas less is known of material originating from intense mining operations. Mountaintop mining (MTM), a prevalent form of surface coal mining in the Central Appalachian ecoregion of the United States, can impact stream ecosystems by altering flows, conductivity, and associated elements. We applied paleolimnological techniques to determine depositional impacts in the Mud River Reservoir downstream of the Hobet Mine, West Virginia, the largest surface mine complex in the United States. Paleolimnological measurements included carbon (C), selenium (Se), sulfur (S), magnesium (Mg), phosphorus (P), nitrogen (N), calcium (Ca), and photosynthetic pigments. Our study focused on 3 primary objectives: (1) determine the materials associated with MTM that are stored in the sediment, (2) calculate the storage rate of Se, a known contaminant from this area, following dam construction (1995 CE), and (3) identify physical, environmental, and biological mechanisms associated with dam construction and how they influence elemental deposition in reservoirs. Results from sediment cores show increases in the storage of inorganic carbon (IC), Se, and Ca for both core sites throughout the period of reservoir existence, with Se deposition related to physical and environmental conditions that are associated with reservoir genesis. These data show that dam construction altered environmental processes on MTM elements, which could have lasting impacts on reservoir biota and downstream environments long after reclamation efforts are applied.

Mercury isotopes trace historical mercury pollution from Pb[sbnd]Zn smelter in China

Lead–zinc (PbZn) smelting is one of the largest anthropogenic emission sources of mercury (Hg) in China and the world. In the last few decades, Hg emission control devices have been employed in PbZn smelters to reduce Hg emissions. To evaluate the effectiveness of Hg emission control, this study uses Hg isotopes to trace the sources of Hg in soils and reservoir sediments near the Zhuzhou smelter, the largest Zn production facility in China. The results showed that Hg concentrations in reservoir sediments were higher than those in soils at the three study sites, suggesting that reservoir sediments accumulate more Hg than soils do under the same conditions. Hg concentrations and deposition fluxes in reservoir sediments have dramatically decreased since the year 2000, suggesting the effectiveness of Hg emission control in the Zhuzhou smelter. Mercury isotope compositions in soil suggest binary mixing of Hg from the Zhuzhou smelter and the local background, and the contribution of Hg from the Zhuzhou smelter to soils and sediment is mainly a function of location and distance from the source. The model output suggested that approximately 61–75% of Hg in reservoir sediments was sourced from the Zhuzhou smelter. This study demonstrates that legacy Hg will continue to be a source to local ecosystems, even after Hg emission control has been implemented for decades.

Impact of reservoir operation policies on nitrogen cycling processes and water quality dynamics in a large water supply reservoir

Reservoir operation policies affect reservoir nitrogen (N) cycling and budgets through complex influences on physical and biogeochemical processes in water and sediment. However, the underlying influencing mechanisms, especially the impact of operations on sediment processes, remain unclear. This study combines a coupled hydrodynamic-eutrophication-sediment model and a reservoir operation model to clarify reservoir operation impact on N cycling processes in water and sediment as well as impact on stored and discharged water quality. Three typical reservoir operation policies (i.e., standard, hedging, and eco-friendly) were selected to create operation scenarios. The hydrodynamic-eutrophication-sediment model was used to simulate N cycling processes and N concentrations in stored and discharged water under each scenario. Using China's Danjiangkou Reservoir as a case study, results revealed that reservoir operation policies significantly affected spatiotemporal dynamics of N cycling processes and water quality. Specifically, reservoir sediment acted as a N source, contributing to annual net release of 9.5–16.1 Gg N. Higher water levels promoted sediment ammonium release through effects on reservoir submerged area and sediment temperature. Moreover, denitrification processes in water and sediment collectively contributed to annual N removal of 14.0–16.9 Gg N. Annual N removal was greater in the higher water level scenario despite its lower denitrification rate per unit area. Additionally, these processes and hydrodynamic conditions combine to affect N forms and concentrations. The N concentration in the lower water level scenario was generally higher, risking algal bloom outbreaks in the shallow-water zone. This study is intended to help guide reservoir operation policymaking to account for N management while also coordinating water quantity and quality targets.

Source apportionment of heavy metal(loid)s in sediments of a typical karst mountain drinking-water reservoir and the associated risk assessment based on chemical speciations.

As important place for water storage and supply, drinking-water reservoirs in karst mountain areas play a key role in ensuring human well-being, and its water quality safety has attracted much attention. Source apportionment and ecological risks of heavy metal(loid)s in sediments of drinking-water reservoir are important for water security, public health, and regional water resources management, especially in karst mountain areas where water resources are scarce. To expound the accumulation, potential ecological risks, and sources of heavy metal(loid)s in a drinking-water reservoir in Northwest Guizhou, China, the surface sediments were collected and analyzed based on the combined use of the geo-accumulation index (Igeo), sequential extraction (BCR), ratios of secondary phase and primary phase (RSP), risk assessment code (RAC), modified potential ecological risk index (MRI), as well as the positive matrix factorization methods. The results indicated that the accumulation of Cd in sediments was obvious, with approximately 61.9% of the samples showing moderate to high accumulation levels, followed by Pb, Cu, Ni, and Zn, whereas the As and Cr were at low levels. A large proportion of BCR-extracted acid extractable and reducible fraction were found in Cd (72.5%) and Pb (40.3%), suggesting high bioavailability. The combined results of RSP, RAC, and MRI showed that Cd was the major pollutant in sediments with high potential ecological risk, while the risk of other elements was low. Source apportionment results of heavy metal(loid)s indicated that Cd (75.76%) and Zn (23.1%) mainly originated from agricultural activities; As (69.82%), Cr (50.05%), Cu (33.47%), and Ni (31.87%) were associated with domestic sources related to residents' lives; Cu (52.36%), Ni (44.57%), Cr (34.33%), As (26.51%), Pb (24.77%), and Zn (23.80%) primarily came from natural geological sources; and Pb (47.56%), Zn (22.46%) and Cr (13.92%) might be introduced by mixed sources of traffic and domestic. The contribution ratios of the four sources were 18.41%, 36.67%, 29.48%, and 15.44%, respectively. Overall, priority control factors for pollution in relation to agricultural sources included Cd, while domestic sources are primarily associated with As. It is crucial to place special emphasis on the impacts of human activities when formulating pollution prevention and control measures. The results of this study can provide valuable reference and insights for water resources management and pollution prevention and control strategies in karst mountainous areas.

Biostratigraphy of Upper Permian-Lower Triassic Reservoir Units in one of the South Pars Field wells

In this study, the biostratigraphy of the reservoir sediments of the upper part of the Dalan Formation (Late Permian, Lopingian) and the reservoir part of the Kangan Formation (Early Triassic) from one of the well in the northern part of South Pars field are studied. The results of studies are presented as three local biozones recognized and defined. Based on these studies, a Late Permian age (Dorashamian/Changhsingian) for the upper Dalan Member an Early?—Middle Triassic age (Scythian?—Anisian) for the lower part of the Kangan Formation, suggested. Also, based on microfossils stratigraphical distribution, and studying succession and continuity of locally defined biozones, it was distinguished a hiatus between Dalan and Kangan formations. Therefore it could be mentioned that the Dorashmian age is the youngest part of the Dalan Formation.

Bio-physical determinants of sediment accumulation on an offshore coral reef: A snapshot study

Sediments are found on all coral reefs around the globe. However, the amount of sediment in different reservoirs, and the rates at which sediments move between reservoirs, can shape the biological functioning of coral reefs. Unfortunately, relatively few studies have examined reef sediment dynamics, and associated bio-physical drivers, simultaneously over matching spatial and temporal scales. This has led to a partial understanding of how sediments and living reef systems are connected, especially on clear-water offshore reefs. To address this problem, four sediment reservoirs/sedimentary processes and three bio-physical drivers were quantified across seven different reef habitats/depths at Lizard Island, an exposed mid-shelf reef on the Great Barrier Reef. Even in this clear-water reef location a substantial load of suspended sediment passed over the reef; a load theoretically capable of replacing the entire standing stock of on-reef turf sediments in just 8 h. However, quantification of actual sediment deposition suggested that just 2 % of this passing sediment settled on the reef. The data also revealed marked spatial incongruence in sediment deposition (sediment trap data) and accumulation (TurfPod data) across the reef profile, with the flat and back reef emerging as key areas of both deposition and accumulation. By contrast, the shallow windward reef crest was an area of deposition but had a limited capacity for sediment accumulation. These cross-reef patterns related to wave energy and reef geomorphology, with low sediment accumulation on the ecologically important reef crest aligning with substantial wave energy. These findings reveal a disconnect between patterns of sediment deposition and accumulation on the benthos, with the ‘post-settlement’ fate of sediments dependent on local hydrodynamic conditions. From an ecological perspective, the data suggests key contextual constraints (wave energy and reef geomorphology) may predispose some reefs or reef areas to high-load turf sediment regimes.

Removal of lead and copper ions from geothermal brine at various temperatures and salinities using chemically crosslinked chitosan

The control of mineral precipitation is a major challenge in several industry segments such as geothermal energy. In this study, the focus was on the prevention of lead and copper containing precipitations from geothermal fluids as frequently found at geothermal sites exploiting sedimentary basins such as from Rotliegend formations. A filter-material was applied to remove scale-forming heavy metal ions from the fluid and thus lowering the concentration of respective minerals below saturation. The filter-material was based on the cheap and abundant biopolymer chitosan and as such is easily available and environmentally harmless. The adsorption performance of lead and copper was investigated under various temperature and salinity conditions. The used synthetic solutions of the heavy metals contained also NaCl or CaCl2 as matrix electrolyte to take into account the salinity of geothermal fluids from sedimentary reservoirs. The obtained results from adsorption experiments showed that the concentration of lead and copper in the fluid could be lowered considerably in static batch tests as well as in dynamic flow-through tests over an extended time period. The adsorption rate increased towards higher temperatures when varied between 25 °C and 70 °C. However, despite chemical crosslinking the chitosan adsorption material exhibits a limited thermal stability with the adsorption performance deteriorating at elevated temperatures.

Inherited anthropogenic disturbance and decadal sediment dynamics in a mountain fluvial system: The case of the Marecchia River canyon, Northern Apennines

We evaluate decadal coarse sediment dynamics along the Marecchia River of the Northern Apennines, a fluvial system with a history of gravel mining that led to the incision of a 6-km-long canyon. To this purpose, we subdivided the river into 21 reaches, seen as sediment reservoirs, to examine (1) historical variations in active channel width (1955−2019) in conjunction with (2) change in alluvial sediment storage (2009−2019), by differencing two sequential LiDAR digital elevation models (DEMs) within the active channel footprint. Combined examination of lateral (widening or narrowing) and vertical (aggradation or degradation) channel changes allowed the identification of composite styles of reservoir adjustment, as well as the refinement of geomorphic inference solely based on changes in active channel width. In particular, we find that different styles of decadal adjustment (1) are compatible with supply- and transport-limited conditions, as constrained by degree of confinement, stream channel slope, and active channel width; and (2) indicate different stages of evolution at reservoirs located upstream and downstream of the canyon head (dynamic equilibrium vs. transient response). The persistence of this geomorphic divide is supported over historical time scales by distinctive trends in planform channel changes, suggesting that sedimentary signal propagation downstream becomes abruptly interrupted at the canyon head. Over this 10-year natural experiment, the spatial pattern of erosion along the canyon exemplifies a striking case of transient response to anthropogenic forcing, where decadal topographic change, modulated by varying styles of hillslope-channel coupling, declines nonlinearly downstream. Depth of incision along the canyon increases progressively upstream, suggesting that the canyon head has been evolving toward a more unstable configuration with no significant change in sediment supply. This tendency, which points to a possible runaway style of development as bedload wearing on weak pelitic side walls continues, may hold basic implications for our understanding of channel incision into bedrock and strath terrace formation.

Hydrostatic pressure drives microbe-mediated biodegradation of microplastics in surface sediments of deep reservoirs: Novel findings from hydrostatic pressure simulation experiments

Microplastics originate from the physical, chemical, or biological degradation of plastics in the environment. Once ingested by organisms at the bottom of the food chain, microplastics are passed on to organisms at higher trophic levels, posing a threat to human health. The distribution of microplastics and the metabolic pathways involved in their microbial degradation in surface sediments of drinking water reservoirs are still poorly understood. This study analyzed the occurrence patterns of microplastics and microbial community structure associated with microplastic biodegradation in surface sediments from a deep reservoir at various hydrostatic pressures. Based on the results of Fourier-transform and laser direct infrared spectroscopy, elevating the pressure resulted in altered sizes and shapes of microplastics in sediment samples with the presence of microorganisms. The influence of hydrostatic pressure on small-sized microplastics (20–500 μm) was pronounced. For instance, high pressure accelerated the breakdown of fibers, pellets, and fragments into smaller-sized microplastics. In particular, the mean size of polyethylene terephthalate microplastics decreased from 425.78 μm at atmospheric pressure to 366.62 μm at 0.7 Mpa. Metagenomic analysis revealed an increase in the relative abundances of plastic-degrading genera, such as Rhodococcus, Flavobacterium, and Aspergillus, in response to elevated pressures. Eight functional genes for biodegradation of polystyrene, polyethylene, and polyethylene terephthalate microplastics were annotated, including paaK, ladA, tphA3. Of these, tphA3 gene abundance was negatively influenced by hydrostatic pressure, providing direct evidence for the pathway by which microbial metabolism of polyethylene terephthalate led to decreased microplastic size under high pressure conditions. This study presents novel insights into hydrostatic pressure-driven microbial community structure, functional gene abundance, and key metabolic pathways associated with biodegradation of microplastics in reservoir sediments.

Genetic types of mud volcanism in the Cydonia and Acidalia regions of Mars

Small cone/mound-shaped structures are widespread on the northern plains of Mars. They are usually interpreted as mud volcanoes because of their close morphological resemblance to mud volcanoes on Earth (for example, in Azerbaijan and near the Sea of Azov). If this interpretation is correct, the small cones/mounds could be evidence of the existence of an extensive subsurface mud source, which, in turn, could be formed by the bottom sediments of a large water reservoir (ocean) that existed on the northern plains of Mars in the past eras of this planet’s geological history. Compared to mud volcanoes on Earth, the morphology of small cones/mounds on Mars varies over a wider range and, which may be due to a greater variety of mechanisms of formation of Martian cones/ mounds. In this study, we studied the morphology of small hills in the Cydonia and eastern Acidalia regions, which are located near the dichotomous boundary within the northern plains of Mars and found that there are 5types of cones/mounds, whose morphology probably characterizes the water-mud reservoir features.

The Effect of River Flow and Land use land Cover Dynamics on Reservoir Sedimentation in a Small ASAL Tropical Basin in Kenya

The Effect of River Flow and Land use land Cover Dynamics on Reservoir Sedimentation in a Small ASAL Tropical Basin in Kenya

Balancing Sediment Connectivity and Energy Production via Optimized Reservoir Sediment Management Strategies

AbstractSediment connectivity plays a fundamental role in sustaining ecosystem goods and services in fluvial systems, including hydropower production. Dams alter the natural processes of sediment transport by trapping sediment and reshaping downstream hydrology and geomorphology. Due to these processes' interconnected nature, dams' impacts extend in time and space beyond the dam site to the entire river system. System‐scale approaches to reduce dam impacts commonly only consider dam siting, overlooking the potential of sediment management strategies integrated into the dam operations to offer more flexible solutions for mitigation. Herein, we contribute a sediment routing model (D‐CASCADE) to assess the impacts of reservoirs and their management strategies on river sediment connectivity. D‐CASCADE is applied to the 3S river system, a tributary of the Mekong River, a hotspot of potential dams in the Lower Mekong. We analyze three dam development portfolios. The effect of reservoir management is examined by assessing daily sediment delivery with specific dam release strategies. Model results predict sediment yield to the Mekong to reduce by 31%–60%. Finally, we explore trade‐offs between hydropower generation and sediment connectivity across cascades of multiple reservoirs. Results show that repeated flushing operations during the early wet season could significantly increase sediment delivery with minimal (max 6%) hydropower losses. While poor trade‐offs between sediment and hydropower have been locked‐in in the Mekong, our results highlight the potential of including sediment connectivity models in multi‐objective decision‐making frameworks to devise integrated water and sediment management strategies that mitigate connectivity disruptions while minimizing losses in other sectors.

A Study of the Sedimentation and Storage Capacity Depletion of a Reservoir

Abstract Theoretical and empirical equations have previously been proposed to compute the sediment trap efficiency of a reservoir. The empirical equations were developed by analyzing a limited amount of field data for reservoirs in selected areas; thus, their suitability is restricted to reservoirs in regions with similar hydrological characteristics. In this study, a sediment trap-efficiency equation, which accounts for the dynamic behavior of sedimentation and the hydraulic conditions of a reservoir, was deduced from the principle of mass conservation. Using this equation, the approximate analytical expression for the storage capacity of the reservoir was obtained. Both equations were applied to investigate real-life problems involving the impacts of reservoir sedimentation, and their predicted solutions were compared with the field data and the results of the theoretical and empirical equations. The results of this investigation reveal that the proposed equations are capable of simulating the sediment trapping and storage capacity depletion characteristics of large reservoirs, which are a measure of the adverse effect of sedimentation on the performance of hydraulic structures. These equations can potentially be incorporated into a large-scale watershed model for estimating a sediment budget.

Exposed sediments in a temperate-climate reservoir under dam decommissioning contain large stocks of highly bioreactive organic matter

Dam decommissioning (DD) is used to solve economic and social problems posed by old dams. However, we ignore the effect of DD on the content and reactivity of large stocks of organic matter (OM) buried in reservoir sediments. We explored temporal changes in the content and reactivity of sediment OM during the first 580 days after the drawdown phase of DD of a large reservoir in the N Iberian Peninsula. We determined the content of sediment OM as organic carbon (OC) in bulk sediment OM and water-extractable OM (WEOM). We estimated the reactivity of bulk sediment OM as its respiration rate and carbon-to-nitrogen ratio, and that of sediment WEOM as its respiration rate, percent biodegradable dissolved OC (%BDOC), and SUVA254. The content of bulk sediment OM was 84 ± 5.1 (mean ± SE) mg OC/ g dry sediment, comparable to the values in the literature on sediment OM in dry sediments from lentic, but higher than in lotic ecosystems. The content of sediment WEOM was 0.81 ± 0.05 mg DOC/g dry sediment, higher than the values in the literature on sediment WEOM from lakes, soils, and rivers. On average, 41 % of WEOM was consumed by microorganisms in two days of incubation, showing the great reactivity of this OM fraction. The content of bulk sediment OM and the respiration rate of WEOM showed a nonlinear temporal trend, while %BDOC increased linearly with sediment exposure time. The labile OM produced by the vegetation that rapidly recolonized the reservoir and photoreactions may explain the temporal increase in %BDOC. Our results suggest that exposed sediments can be a source of labile OM and high C emissions in the river reach downstream of the reservoir after DD.