Quantifying Tradeoffs Associated with Hydrologic Environmental Flow Methods

Freshwater management requires balancing and tradingoff multiple objectives, many of which may be competing. Ecological needs for freshwater are often described in terms of environmental flow recommendations (e.g., minimum flows), and there are many techniques for developing these recommendations, which range from hydrologic rules to multidisciplinary analyses supported by large teams of subject matter experts. Although hydrologic rules are well acknowledged as overly simplified, these techniques remain the state‐of‐the‐practice in many locations. This article seeks to add complexity to the application of these techniques by studying the emergent properties of hydrologic environmental flow methodologies. Two hydrologic rules are applied: minimum flow criteria and sustainability boundaries. Objectives and metrics associated with withdrawal rate and similarity to natural flow regimes are used to tradeoff economic and environmental needs, respectively, over a range of flow thresholds and value judgments. A case study of hypothetical water withdrawals on the Middle Oconee River near Athens, Georgia is applied to demonstrate these techniques. For this case study, sustainability boundaries emerge as preferable relative to both environmental and economic outcomes. Methods applied here provide a mechanism for examining the role of stakeholder values and tradeoffs in application of hydrologic rules for environmental flows.     

序批式反应器内多尺度三相流动的数值模拟

提出1个混合模型来数值模拟序批式反应器内气-液-固三相的多尺度流动.该混合模型采用Level Set方法模拟曝气气泡的运动,应用离散颗粒方法处理活性污泥固体的运动,运用体积平均的Navier-Stokes方程描述液相的流动.模型考虑了颗粒-气泡、颗粒-流体以及气泡-流体之间的相互作用.通过模拟反应器内曝气气泡生成、上升以及污泥沉淀的动态过程,检验了模型的可行性.流动结构的模拟结果显示,在反应器中污泥与污水均有明显的环流特征.气泡与颗粒相互作用引起的气泡破碎行为会导致反应器内大量小气泡的生成以及污泥颗粒的弥散.反应器内这些流体动力学特征使得污泥与污水达到充分混合,有利于生物降解处理.     

Experimental investigation of bubbly flow and turbulence in hydraulic jumps

Many environmental problems are linked to multiphase flows encompassing ecological issues, chemical processes and mixing or diffusion, with applications in different engineering fields. The transition from a supercritical flow to a subcritical motion constitutes a hydraulic jump. This flow regime is characterised by strong interactions between turbulence, free surface and air–water mixing. Although a hydraulic jump contributes to some dissipation of the flow kinetic energy, it is also associated with increases of turbulent shear stresses and the development of turbulent eddies with implications in terms of scour, erosion and sediment transport. Despite a number of experimental, theoretical and numerical studies, there is a lack of knowledge concerning the physical mechanisms involved in the diffusion and air–water mixing processes within hydraulic jumps, as well as on the interaction between the free-surface and turbulence. New experimental investigations were undertaken in hydraulic jumps with Froude numbers up to Fr = 8.3. Two-phase flow measurements were performed with phase-detection conductivity probes. Basic results related to the distributions of void fraction, bubble frequency and mean bubble chord length are presented. New developments are discussed for the interfacial bubble velocities and their fluctuations, characterizing the turbulence level and integral time scales of turbulence representing a “lifetime” of the longitudinal bubbly flow structures. The analyses show good agreement with previous studies in terms of the vertical profiles of void fraction, bubble frequency and mean bubble chord length. The dimensionless distributions of interfacial velocities compared favourably with wall-jet equations. Measurements showed high turbulence levels. Turbulence time scales were found to be dependent on the distance downstream of the toe as well as on the distance to the bottom showing the importance of the lower (channel bed) and upper (free surface) boundary conditions on the turbulence structure.     

Implementation of airborne trace element monitoring with devitalised transplants of Hypnum cupressiforme Hedw.: assessment of temporal trends and element contribution by vehicular traffic in Naples city

A biomonitoring of airborne trace elements was performed in 2006 in Naples urban area through the exposure of devitalised Hypnum cupressiforme for 10 weeks at 4 m height. In one street, the moss was exposed at different heights to assess vertical gradients of element concentrations. Results were compared with those of a 1999 biosurvey. Correlations among Al, Fe and Ti suggested a soil particles contribution to element uptake. Cu, Mo and Fe were related with traffic flows. Long-range transport contributed to Cd, Cu and Mo accumulation in moss at higher heights. As in 1999, the airborne element load was higher in coastal sites, more affected by marine aerosols and traffic. In all sites, contents of Cd, Fe, Pb, Ni and V in moss were remarkably lower than in 1999, indicating a positive effect of actions set up in recent years to reduce the traffic and to improve the city air quality.     

End-of-life flows of multiple cycle consumer products

Explicit expressions for the end-of-life flows (EOL) of single and multiple cycle products (MCPs) are presented, including deterministic and stochastic EOL exit. The expressions are given in terms of the physical parameters (maximum lifetime, T, annual cycling frequency, f, number of cycles, N, and early discard or usage loss). EOL flows are also obtained for hi-tech products, which are rapidly renewed and thus may not attain steady state (e.g. electronic products, passenger cars). A ten-step recursive procedure for obtaining the dynamic EOL flow evolution is proposed. Applications of the EOL expressions and the ten-step procedure are given for electric household appliances, industrial machinery, tyres, vehicles and buildings, both for deterministic and stochastic EOL exit, (normal, Weibull and uniform exit distributions). The effect of the physical parameters and the stochastic characteristics on the EOL flow is investigated in the examples: it is shown that the EOL flow profile is determined primarily by the early discard dynamics; it also depends strongly on longevity and cycling frequency: higher lifetime or early discard/loss imply lower dynamic and steady state EOL flows. The stochastic exit shapes the overall EOL dynamic profile: Under symmetric EOL exit distribution, as the variance of the distribution increases (uniform to normal to deterministic) the initial EOL flow rise becomes steeper but the steady state or maximum EOL flow level is lower. The steepest EOL flow profile, featuring the highest steady state or maximum level, as well, corresponds to skew, earlier shifted EOL exit (e.g. Weibull). Since the EOL flow of returned products consists the sink of the reuse/remanufacturing cycle (sink to recycle) the results may be used in closed loop product lifecycle management operations for scheduling and sizing reverse manufacturing and for planning recycle logistics. Decoupling and quantification of both the full age EOL and of the early discard flows is useful, the latter being the target of enacted legislation aiming at increasing reuse.     

Environmental flows for rivers and economic compensation for irrigators

Securing flows for environmental purposes from an already fully utilized river is an impossible task--unless users are either coerced into freeing up water, or offered incentives to do so. One sensible strategy for motivating users to liberate volumes is to offer them economic compensation. The right amount for that compensation then becomes a key environmental management issue. This paper analyses a proposal to restore and maintain ecosystems on a stretch of the Río Conchos in northern Mexico, downstream from a large irrigation district that consumes nearly all local flows. We present here estimates of environmental flow requirements for these ecosystems and compute compensation figures for irrigators. These figures are derived from crop-specific irrigation water productivities we statistically estimate from a large set of historical production and irrigation data obtained from the district. This work has general implications for river ecosystem management in water-stressed basins, particularly in terms of the design of fair and effective water sharing mechanisms.     

A Tale of Two Rivers: Implications of Water Management Practices for Mussel Biodiversity Outcomes During Droughts

Droughts often pose situations where stream water levels are lowest while human demand for water is highest. Here we present results of an observational study documenting changes in freshwater mussel communities in two southern US rivers during a multi-year drought. During a 13-year period water releases into the Kiamichi River from an impoundment were halted during droughts, while minimum releases from an impoundment were maintained in the Little River. The Kiamichi observed nearly twice as many low-flow events known to cause mussel mortality than the Little, and regression tree analyses suggest that this difference was influenced by reduced releases. During this period mussel communities in the Kiamichi declined in species richness and abundance, changes that were not observed in the Little. These results suggest that reduced releases during droughts likely led to mussel declines in one river, while maintaining reservoir releases may have sustained mussel populations in another.     

Management of treated pulp and paper mill effluent to achieve zero discharge

Pulp and paper mills are one of the major effluent generating industries in the world. In most cases, mill effluent (treated or raw) is discharged back into a river, creek, stream or other water body; resulting in negative environmental impacts, as well as social concerns, among the downstream users. Pulp and paper mill effluent management, which could result in zero discharge into downstream water bodies, would present the best management option to address socio-environmental concerns. This paper presents such an effort aimed at closing the water cycle by using treated effluent from the mill to irrigate forage and fodder crops for producing animals feed. The treated effluent is delivered from the mill through gravity into a winter storage dam of 490ML capacity. For irrigation applications on 110ha of farmland, which is 42% of the total farmland, the water is pumped from the winter storage dam to five individual paddocks with Centre Pivot (CP) irrigators and one rectangular paddock with a Soft Hose Travelling (SHT) irrigator. From October 2001 to June 2006, a total of 2651mm of wastewater was applied at the farm. The impact assessment results, obtained from field monitoring, investigations and analysis, indicated that the closed water cycle effluent management strategy described had resulted in a lessening of the impact on water resources usually associated with paper mills. However, social attitudes to the use of crops that have been irrigated with recycled waters and the resulting impact on market value of the produce may still be a major consideration.     

Numerical study of choked two-phase flow of hydrocarbons fluids through orifices

Valves and orifices are the most widely devices of flow control used in oil and gas industry. In particular, they are installed in relief piping system in order to control the discharge flow during potential plant overpressuring scenarios, thus ensuring plant safety. It is a common practice to flow liquid and gas mixtures through such restriction devices.Rigorous models are available to precisely size pressure relief devices operating in single phase flow; however for two-phase flow, no models are considered sufficiently reliable for predicting the relevant flow conditions.In the present paper, two-phase flow of hydrocarbons fluids through an orifice under critical conditions has been numerically investigated.The existing literature has been analyzed and data on two-phase flow of highly volatile mixtures of hydrocarbons through openings have been collected. A comparison has been carried out with numerical simulations carried out by the multiphase flow simulation tool OLGA by SPT.The Henry–Fauske model has been used as orifice choke model and the orifice discharge flow coefficient, required as input by OLGA, has been calculated by Chisholm's model.Comparison between OLGA's results and experimental data shows that Henry–Fauske model markedly underestimates the mass flow rate through the orifice, if Chisholm's model is used to calculate discharge coefficient. It was found that the error of the model could be minimized using different values of orifice discharge coefficient (C_d).A new discharge flow coefficient model, suitable for choked two-phase flow across orifices, is proposed in this study and it has been determined to match the above mentioned experimental measurements.     

Emergy analysis of the urban metabolism of Beijing

Cities can be modeled as if they were superorganisms with a range of metabolic processes. Research on this urban metabolism can contribute to solving urban environmental problems by revealing details of the metabolic throughput of the system. A key issue is how to find a common basis for measuring the environmental and economic values. By providing a single unified unit, emergy theory integrates the natural and socioeconomic systems and thoroughly evaluates a system's metabolism. We analyzed Beijing's urban metabolic system using emergy synthesis to evaluate its environmental resources, economy, and environmental and economic relations with the regions outside the city during 14 years of development. We compared Beijing's emergy indices with those of five other Chinese cities and of China as a whole to assess Beijing's relative development status. These indices are the emergy self-support ratio (metabolic dependence), the environmental load ratio (metabolic loading), empower density (metabolic pressure), emergy used per person (metabolic intensity per capita), and the monetary equivalent of emergy (emdollars; metabolic intensity). Based on our emergy analysis, Beijing's socioeconomic system is not self-sufficient, and depends greatly on external environmental resources. Its GDP is supported by a high percentage of emergy purchased from outside the city. During the study period, Beijing's urban system showed an increasing dependence on external resources for its economic development. Beijing's loading and pressure on the ecological environment is continuously increasing, accompanied by continuously increasing human emergy consumption. In the future, it will become increasingly necessary to improve Beijing's metabolic efficiency.