Drawdown Phase Research Articles

Occurrence, Bioavailability, and Environmental Risk of Heavy Metals and Metalloids in the Sediment and Drawdown Area of Fengshuba Drinking Water Reservoir

ABSTRACT Heavy metal and metalloid pollution in reservoir systems has attracted widespread attention due to their toxic, persistent, and nonbiodegradable characteristics. This study investigated the distribution and risks of heavy metals and metalloids in the sediment and drawdown area of the Fengshuba reservoir system. Sediment phase exhibited substantial heavy metal and metalloid pollution and higher ecological risk that the drawdown phase. There were significant differences in the structure and composition of the total metal content and the bioavailable fraction between the sediment and the drawdown area, which indicates that the total metal content and the bioavailable fraction might dominantly regulate by a complex combination of sediment characteristics. Positive Matrix Factorization model was used to identify sources of heavy metals and metalloids pollution and revealed that heavy metals and metalloids contamination in Fengshuba reservoir might originate from anthropogenic activities. Evaluations from risk assessment show that As and Cd in the reservoir system may pose health risks. Knowledge of distribution, potential risk assessment, and source apportionment of heavy metals and metalloids in the Fengshuba drinking water is critical in promoting the sustainable development of the reservoir, developing water management and conservation strategies in the Fengshuba reservoir.

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.

Nutrient and algal responses to a managed drawdown in an agricultural riverine lake

ABSTRACT Water level of a shallow impounded riverine lake was lowered to help improve downstream flows and water quality within the Big Sunflower River in the agriculturally dominated Mississippi Delta, Mississippi, USA. A study was conducted to better understand how nutrient and algal processes within shallow lakes respond to relatively rapid water level changes to guide water resource management decisions. The drawdown was initiated in late summer and completed within six days, ending when outflow was <5% of peak flows. Water depths were reduced from 28-82%. Nutrients (phosphorus, nitrogen and carbon) and water column algal measurements (chlorophyll a, in-vivo chlorophyll, in-vivo phycocyanin, chlorophyll:phycocyanin ratio, and photosynthetic activity) were measured at three sites on days −7, −1, 0, 1, 2, 3, 6, 13, 20, 28, and 34, relative to the start of the drawdown. Nitrogen and phosphorus responses were bimodal, showing a decrease during the initial drawdown phase followed by increasing levels in the ensuing weeks. Algal responses showed complex interactions between nutrients and changes in light availability that were often indirectly related to hydrologic changes. Late summer to early fall drawdowns in small impoundments used to improve downstream flows can have minimal water quality impacts on the upstream impounded systems.

The drawdown phase of dam decommissioning is a hot moment of gaseous carbon emissions from a temperate reservoir

ABSTRACT Dam decommissioning (DD) is a viable management option for thousands of ageing dams. Reservoirs are large carbon sinks, and reservoir drawdown results in important carbon dioxide (CO2) and methane (CH4) emissions. We studied the effects of DD on CO2 and CH4 fluxes from impounded water, exposed sediment, and lotic water before, during, and 3–10 months after drawdown of the Enobieta Reservoir, north Iberian Peninsula. During the study period, impounded water covered 0–100%, exposed sediment 0–96%, and lotic water 0–4% of the total reservoir area (0.14 km2). Areal CO2 fluxes in exposed sediment (mean [SE]: 295.65 [74.90] mmol m−2 d−1) and lotic water (188.11 [86.09] mmol m−2 d−1) decreased over time but remained higher than in impounded water (−36.65 [83.40] mmol m−2 d−1). Areal CH4 fluxes did not change over time and were noteworthy only in impounded water (1.82 [1.11] mmol m−2 d−1). Total ecosystem carbon (CO2 + CH4) fluxes (kg CO2-eq d−1) were higher during and after than before reservoir drawdown because of higher CO2 fluxes from exposed sediment. The reservoir was a net sink of carbon before reservoir drawdown and became an important emitter of carbon during the first 10 months after reservoir drawdown. Future studies should examine mid- and long-term effects of DD on carbon fluxes, identify the drivers of areal CO2 fluxes from exposed sediment, and incorporate DD in the carbon footprint of reservoirs.

Effects of an impermeable layer on pore pressure response to tsunami-like inundation.

Tsunami hazards have been observed to cause soil instability resulting in substantial damage to coastal infrastructure. Studying this problem is difficult owing to tsunamis’ transient, non-uniform and large loading characteristics. To create realistic tsunami conditions in a laboratory environment, we control the body force using a centrifuge facility. With an apparatus specifically designed to mimic tsunami inundation in a scaled-down model, we examine the effects of an embedded impermeable layer on soil instability: the impermeable layer represents a man-made pavement, a building foundation, a clay layer and alike. The results reveal that the effective vertical soil stress is substantially reduced at the underside of the impermeable layer. During the sudden runup flow, this instability is caused by a combination of temporal dislocation of soil grains and an increase in pore pressure under the impermeable layer. The instability during the drawdown phase is caused by the development of excess pore-pressure gradients, and the presence of the impermeable layer substantially enhances the pressure gradients leading to greater soil instability. The laboratory results demonstrate that the presence of an impermeable layer plays an important role in weakening the soil resistance under tsunami-like rapid runup and drawdown processes.

Flexural‐isostatic reconstruction of the Western Mediterranean during the Messinian Salinity Crisis: Implications for water level and basin connectivity

AbstractDuring the Messinian Salinity Crisis (MSC, 5.97–5.33 Ma), thick evaporites were deposited in the Mediterranean Sea associated with major margin erosion. This has been interpreted by most authors as resulting from water level drop by evaporation but its timing, amplitude and variations between subbasins are poorly constrained due to uncertainty in post‐Messinian vertical motions and lack of a clear time‐correlation between the marginal basin and offshore records. The Balearic Promontory and surrounding basins exemplify a range of responses to this event, from margin erosion to up to a kilometre thick Messinian units in the abyssal areas containing the majority of the MSC halite. The Balearic Promontory contains unique patches of halite with thickness up to 325 m at intermediate depths that provide valuable information on water level during the stage of halite deposition. We compile seismic markers potentially indicating ancient shorelines during the drawdown phase: the first is marked by the transition from the MES to UU based on seismic data. The second is the limit between the bottom erosion surface (BES) and abyssal halite deposits. We restore these shorelines to their original depth accounting for flexural isostasy and sediment compaction. The best‐fitting scenario involves a water level drop of ca. 1,100 ± 100 m for the Upper unit level and 1,500 ± 100 m for the BES level. According to our results, halite deposition began in the Central Mallorca Depression at 1,300–1,500 m depth, perched hundreds of metres above the deep basins, which were at 1,500–1,800 m (Valencia Basin) and &gt;2,900 m (Algerian Basin). The hypothesis that erosion surfaces were formed subaerially during the drawdown phase is consistent with a model of halite deposition before/during the water level drop of at least 1,000 m, followed by the deposition of the Upper unit until the MSC is terminated by the reinstatement of normal marine conditions.

Financial Literacy and Suboptimal Financial Decisions at Older Ages

Over the life-cycle, wealth holdings tend to be highest in the early part of retirement. The quality of financial decisions among older adults is therefore an important determinant of their financial security during the asset drawdown phase. This paper assesses how financial literacy shapes financial decision-making at older ages. We devised a special module in the Singapore Life Panel survey to measure financial literacy to study its relationship with three aspects of household financial and investment behaviors: credit card debt repayment, stock market participation, and adherence to age-based investment glide paths. We found that the majority of respondents age 50+ has some grasp of concepts such as interest compounding and inflation, but fewer know about risk diversification. We provide evidence of a statistically significant positive association between financial literacy and each of the three aspects of suboptimal financial decision-making, controlling for many other factors, including education. A one-unit increase in the financial literacy score was associated with an 8.3 percentage point greater propensity to hold stocks, and a 1.7 percentage point higher likelihood of following an age-appropriate investment glide path. The financial literacy score is only weakly positively linked with timely credit card balance repayment, both in terms of statistical significance and estimate size.

Financial Literacy and Suboptimal Financial Decisions at Older Ages

Over the life-cycle, wealth holdings tend to be highest in the early part of retirement. The quality of financial decisions among older adults is therefore an important determinant of their financial security during the asset drawdown phase. This paper assesses how financial literacy shapes financial decision-making at older ages. We devised a special module in the Singapore Life Panel survey to measure financial literacy to study its relationship with three aspects of household financial and investment behaviors: credit card debt repayment, stock market participation, and adherence to age-based investment glide paths. We found that the majority of respondents age 50+ has some grasp of concepts such as interest compounding and inflation, but fewer know about risk diversification. We provide evidence of a statistically significant positive association between financial literacy and each of the three aspects of suboptimal financial decision-making, controlling for many other factors, including education. A one-unit increase in the financial literacy score was associated with an 8.3 percentage point greater propensity to hold stocks, and a 1.7 percentage point higher likelihood of following an age-appropriate investment glide path. The financial literacy score is only weakly positively linked with timely credit card balance repayment, both in terms of statistical significance and estimate size.

Late Paleozoic seismic sequence stratigraphy and paleogeography of the paleo-Loppa High in the Norwegian Barents Sea

Abstract The paleo-Loppa High in the SW Barents Sea is a ridge structure, which developed during the late Paleozoic when the earliest phase of the Atlantic rifting between Greenland and Norway occurred. The southwest of the Barents Sea, located at the northern margin of Pangaea during the Carboniferous and Permian, was characterized by a structural style of half-graben geometries. The northward drift of the northern Pangaea triggered changes in regional climatic conditions that are reflected in the preserved sedimentary deposits. 2D/3D seismic combined with well and core data were used to define depositional seismic sequences and to understand the stratigraphic evolution of the paleo-Loppa High during the late Paleozoic. Based on the geometry of the defined seismic sequences and the character of observed sedimentary facies, a paleogeographic reconstruction of the key stages in the paleo-Loppa High evolution is also proposed and discussed in relation to local tectonic, global sea-level oscillations, and climatic changes. A total of seven seismic sequences, ranging from clastic-dominated to transitional clastic-carbonate sedimentation followed by an evaporitic drawdown phase, then shifting to carbonate-dominated sequences and finally capped by silica- and chert-dominated deposits, have been defined and represent the infill evolution of the paleo-Loppa High. Tectonics processes associated with the rifting are the principal controls in the 3-D morphology of the defined sequences. Sea-level fluctuations and climate changes have modified the biotic evolution and were responsible of the small-scale features inside each sequence. A renewed interest, in the study of the late Paleozoic sedimentary deposits of the paleo-Loppa High, has been manifested due to the recent discoveries of hydrocarbons in the Gohta and Alta prospects.

Investment Horizons, Time Diversification and Sustainable Withdrawal Rates for a Retirement Investment in UK Markets

We examine the sustainability of wealth and associated risks faced by a retiree in the drawdown phase of retirement. Risks are assessed using a range of commonly recommended withdrawal rates, and applied to common investment strategies in the UK markets. We consider the issue of time diversification of risk, in the context of expected retirement horizons. Our results demonstrate that after allowing for compounding effects and for regular investment withdrawals, the risk of financial ruin increases with the length of the retirement horizon, contrary to the premise of time diversification of risk.

Australian Superannuation: The Current State of Play

AbstractThis article focuses on the challenges facing superannuation, the income replacement pillar of Australia's retirement income system, as it matures. We discuss four questions: In an era when households are making critical and complex choices that most have never previously confronted, how should policy‐makers and private providers guide choices? How should superannuation be taxed? How should the drawdown phase be structured? And to what extent will the Superannuation Guarantee be able to meet the objective of providing retirement income to substitute or supplement the age pension? This article attempts to provide perspective on each of the issues and concludes with a statement of research need.

Superannuation Tax Concessions and the Age Pension: A Principled Approach to Savings Taxation

This paper discusses the tax and transfer treatment of private superannuation retirement saving and the public means tested age pension in Australia. Superannuation savings benefit from concessional treatment in Australia’s tax system by comparison with other forms of saving, measured against an income or consumption tax benchmark. In the drawdown phase, the age pension means test offsets this generous treatment for those in the middle but not at the top end of the distribution. However, it does so in a way that generates disincentives for work in retirement and, perversely, for saving, before and during retirement. We canvass a range of principled approaches that would provide support for saving across the life course while being more neutral and fair in both savings and drawdown phases. We conclude that a more coherent retirement tax and transfer system can be achieved by reducing tax concessions and making the age pension means test less harsh. In the long term, the tax and transfer treatment of retirement savings should be aligned with the treatment of savings in general.

2-D integrated numerical modeling for the potential of solitary wave-induced residual liquefaction over a sloping porous seabed

A 2-D integrated numerical model is developed for liquefaction due to the build-up of pore pressure in porous sloping seabed subject to solitary wave loading. In the integrated 2-D model, the propagation of a solitary wave over a porous sloping seabed is governed using the volume-averaged Reynolds averaged Navier–Stokes equations, in which discontinuity of the flow (i.e., wave breaking due to shoaling, hydraulic jump during the wave drawdown phase) can be captured with $$k-\epsilon $$ model, while Biot’s consolidation equations are used for linking the solid–pore fluid interaction. Regarding the wave-induced residual soil response, a new 2-D pore pressure build-up model is developed with the new definition of the source term where the phase-resolved oscillatory shear stress is involved. The initial consolidation state of the sloping seabed foundation is considered under hydrostatic load using theory of poro-elasticity. The numerical results indicate that compared to a 1:6 slope, the wave-breaking process is more likely to occur in the case of a mild 1:15 slope due to wave shoaling and that a mild 1:15 slope experiences a longer duration of the wave run-up and drawdown compared to that in a steep 1:6 slope. Furthermore, the results suggest that the potential for liquefaction first occurs near the intersection between the initial shore line and the bed boundary. Then it will be extended both laterally and vertically to the neighboring points. The depth of the liquefaction zone increases and the width of the liquefaction zone decreases as the bed slope increases. Parametric studies indicate that the build-up of residual pore pressure can accumulate to a large value in the case of soil with lower permeability and lower relative density under larger wave loading.

Dinámica estacional de la vegetación litoral en el complejo lagunar inundable Zapatosa, Colombia

Floodplain lakes and associated wetlands in tropical dry climates are controlled by pronounced and severe seasonal hydrologic fluctuations. We examined the plant community response to a bimodal flooding pattern in the Zapatosa Floodplain Lake Complex (ZFLC), Northern Colombia. We measured floristic and quantitative change in four sampling periods emphasizing seasonal differences in plant abundance and life-form structure. Of 79 species identified in the lake complex, 52 were used to characterize eight community types via classification and ordination procedures. Results showed that community structure does not change significantly during the flooding/receding stages. But maximum drawdown phase significantly disrupts the aquatic community structure and the exposed shorelines become colonized by ruderal terrestrial plants. Early rainfalls at the beginning of the wet season are emphasized as an important feature of plant regeneration and community development. The general strategy of the ZFLC vegetation can be framed into the flood pulse concept of river-floodplain systems. Thus, plant communities are mainly responding to disturbances and destruction events imposed by extreme water level fluctuations.

Sediment response to tsunami loading: mechanisms and estimates

Tsunami effects on soil stability are evaluated by imposing hypothetical, but typical, tsunami loads on an idealised beach condition of a plane beach with homogeneous sediments. Under this model tsunami condition, the extent of sediment motion in the form of bed load and suspended load on the beach is demonstrated. Sediment motions are particularly significant in the nearshore area between the initial shoreline and the maximum tsunami drawdown. During the drawdown phase, pore-pressure gradients develop by rapid reduction in water pressure on the bed, creating soil instability, and triggering momentary liquefaction in some locations. Such effects of pore-pressure gradients are quantitatively evaluated with a proposed modified Shields parameter. The analysis used for the model tsunami case is further applied to laboratory data and real field data collected in Kesen-numa, Japan, during the 2011 East Japan tsunami.

Unintended Impacts and the Gendered Consequences of Peacekeeping Economies in Liberia

Despite increased international attention to managing the potential impacts of peacekeeping on host countries, unintended consequences continue to emerge. This article focuses particularly on the alternative economies that peacekeeping operations generate and the differential economic impacts on individuals who come into contact with peacekeepers. Based on empirical evidence derived from fieldwork in Liberia, the article highlights the everyday lives of women whose livelihoods have been affected by the presence of peacekeeping missions. It also discusses how such economies adjust during the peacekeeping drawdown phase, and explores the dynamics that such economies have on specific segments of the Liberian population. The argument is that, while peacekeeping economies are critical in stimulating the local economy and providing livelihoods during and in the immediate aftermath of war, they have negative unintended impacts that need mitigation.

Is hydrological manipulation an effective management tool for rehabilitating chronically flooded, brackish-water wetlands?

In this study, the effectiveness of experimentally reinstating a drawdown phase at Dowd Morass, a large, chronically inundated brackish-water wetland in the Gippsland Lakes Ramsar site of south-eastern Australia was examined. Rehabilitation was most successful in sites that had been shallowly flooded prior to drawdown and that remained dry for longest.

Analysis of the Cross-Correlation between Seismicity and Water Level in the Koyna Area of India

The main objective of this study is the joint analysis of water level and seismicity recorded at Koyna (India), which is a unique site where reservoir-triggered earthquakes have been continually occurring over the last 50 years. Statistically significant cross-correlation coefficients between the daily water level and the daily number of earthquakes (with magnitudes greater than or equal to 2.2) suggest a time lag of 223 days, indicating reservoir-induced enhanced seismic activity mainly during the drawdown phase of the reservoir. The time lag and the mean earthquake depth provide a vertical hydraulic diffusivity of D ∼0.2 m2/s for the area.

Evaluating the relative contributions of vegetation and flooding in controlling channel widening: the case of the Nepean River, southeastern Australia

Many lowland stream channels have dramatically widened over the last two centuries. There has been considerable debate about whether this widening was caused by an unusually large flood, by a series of large floods, or by decreased bank stability caused by clearing of riparian vegetation. The relative effects of floods and vegetation can be disentangled in southeastern Australia where streams have undergone both clearing of bank vegetation, and decadal sequences of relatively higher and lower flood magnitude and frequency. Archival aerial photographs of the Nepean River, in southeastern Australia, suggest that banks did not erode during periods of low flood magnitude (drought-dominated regime: from 1901–1949) whether they were cleared or not. However, during periods of flood-dominated regime (1950 to 1970s) only cleared stream banks eroded. Thus, on the upper Nepean River, clearing alone was insufficient to trigger erosion by small floods, and even large floods were unable to erode vegetated banks. The conclusion is that substantial channel widening in this river required both clearing of bank vegetation, and periods of unusually large and frequent floods. This conclusion is supported by geomechanical modelling that examine the reduction in bank shear strength arising from the loss of tree-root reinforcement. The modelling also suggests that bank instability arising from devegetation amplifies the potential for bank failure during the drawdown phase of a flood, leading to channel widening.

Counterproliferation and US Nuclear Strategy

The Bush administration took office with a strong agenda to and revitalize US nuclear posture. In a speech to National Defense University in May 2001, President G. W Bush said he would change size, composition, character of our nuclear in a way that reflects reality that Cold War over. He said his goal was to move quickly to reduce nuclear forces and that he was committed to achieving a credible deterrent with lowest possible number of nuclear weapons consistent with our national security needs.'This mainly been understood to relate to Russia, which administration says no longer an contingency for US nuclear planning.2 Officials often describe this shift as most significant in US nuclear policy since beginning of Cold War. As a result, nuclear posture review completed at end of 2001 continued drawdown of nuclear that was initiated in 199 1 by implementing force structure decisions made in 1992 strategic arms reduction treaty (START II) agreement, 1994 nuclear posture review, and 1997 Helsinki framework. This included a retirement of Peacekeeper intercontinental ballistic missile and four ballistic missile submarines and a trimming of remaining warheads to a START Ill-like force level of roughly 5400 warheads, of which no more than 2200 could be operationally deployed strategic warheads. Today, nearly two decades after Cold War ended, we're still in that drawdown phase of 1990s. Yet Russia still main focus of US nuclear planning due to sheer size of its nuclear arsenal and retreat from democracy.Other components of change, however, were not drivers for nuclear cuts or a reduction of role of nuclear weapons, but for an expanded role against other adversaries. One of these was China, which 2001 nuclear posture review determined is a country that could be involved in an immediate or potential contingency that setting requirements for [US] nuclear strike capabilities due to the combination of China's still developing strategic objectives and its ongoing modernization of its nuclear and nonnuclear forces. 3 And in February 2006, quadrennial defense review determined that China has greatest potential to compete militarily with United States among major emerging powers. 4 As a result of this strategic perspective, nuclear planning against China increased, with majority of US ballistic missile submarines patrolling in Pacific instead of Atlantic, and long-range bombers conducting periodic forward deployments to Guam much like they did during Cold War.The third component of concerned proliferators, regional states that are seeking to acquire weapons of mass destruction. Whereas strategic nuclear planning during Cold War was focused on Soviet Union, China, and their allies, discovery of Iraq's extensive WMD program in 19 91 and North Korea's nuclear weapons program resulted in a broadening of US nuclear weapons policy and doctrine against regional proliferated themselves. Essentially overnight, declaratory policy for what and where US nuclear might be employed ballooned to nuclear, chemical, and biological weapons and facilities. At times, radiological and high-explosive weapons and ballistic missiles have also been on list. Military planners worked long hours to translate new language into an expanded list of potential targets and new strike plans.Up until mid-1990s, this development was substantial but timid and often denied by officials because of emphasis at time on securing international support for an indefinite extension of nonproliferation treaty. Broadening nuclear planning and targeting non-nuclear members of nonproliferation treaty could derail effort, but once treaty was extended policy gradually became more overt. …