Froude scaling limitations in modeling of turbidity currents

The scaling problem associated with the modeling of turbidity currents has been recognized but is yet to be explored systematically. This paper presents an analysis of the dimensionless governing equations of turbidity currents to investigate the scale effect. Three types of flow conditions are considered: (i) conservative density current; (ii) purely depositional turbidity current; and (iii) mixed erosional/depositional turbidity current. Two controlling dimensionless numbers, the Froude number and the Reynolds number, appear in the non-dimensional governing equations. When densimetric Froude similarity is satisfied, the analysis shows that the results would be scale-invariant for conservative density current under the rough turbulent condition. In the case of purely depositional flows, truly scale-invariant results cannot be obtained, as the Reynolds-mediated scale effects appear in the bottom boundary conditions of the flow velocity and sediment fall velocity. However, the scale effect would be relatively modest. The Reynolds effect becomes more significant for erosional or mixed erosional/depositional turbidity currents as Reynolds-mediated scale effects also appear in the sediment entrainment relation. Numerical simulations have been conducted at three different scales by considering densimetric Froude scaling alone as well as combined densimetric Froude and Reynolds similarity. Simulation results confirm that although the scaling of densimetric Froude number alone can produce scale-invariable results for conservative density currents, variations occur in the case of turbidity currents. The results become scale invariant when densimetric Froude and Reynolds similarities are satisfied simultaneously.     

Continuous improvement at EG&G: The waste reduction pays (WARP) initiative

EG&G is a Fortune 200 company with annual sales of $2.7 billion. It designs and manufactures laboratory and field-test instruments and electronic and mechanical components for commercial customers. EG&G provides systems engineering, precision component manufacturing, and test-site operating and management services to many government agencies and laboratories. It employs 34,000 people worldwide. Recognizing the need to improve its business practices as they related to environmental excellence, EG&G initiated policies, procedures, and programs to establish itself as an environmentally responsible company. Waste reduction was designated priority number one in EGG's environmental program. Our major customers are also making waste reduction a high visibility program. For example, on August 3, 1993, the president signed Executive Order 12856 making pollution prevention at federal facilities a goal of this administration. This article describes the EG&G Waste Reduction Pays (WARP) program, developed for use by all its operating entities, and why it is a model program to implement Executive Order 12856. It also depicts how the implementation of the program at federal facilities differs, in some respects, from that at other EG&G operating units.     

OXIDIZED NITROGEN IN PRECIPITATION,THROUGHFALL, AND STREAMFALL FROM A FORESTED WATERSHED IN OKLAHOMA1

ABSTRACT: Oxidized nitrogen (nitrite + nitrate N) concentrations were measured from bulk precipitation, bulk through-fall, and streamflow in a 7.86 hectare forested watershed in southeastern Oklahoma during the wet season from March through June 1983. Oxidized nitrogen inputs comparable to results of other studies were recorded during the 19 rainstorms sampled. Oxidized nitrogen concentrations appeared to increase after rainfall interacted with the pine and hardwood canopies and were inversely related to both rainfall and through-fall depth. Oxidized N concentrations in streamflow were greatest during the rising limb of storm flow with subsequent decreases during the falling limb of storm hydrographs and lowest during base flow. The oxidized N inputs from bulk precipitation were considerably greater than outputs from streamflow resulting in a net retention of oxidized nitrogen within the watershed during the study period.     

Biological Pollutants: Alien Fishes in Mountain Lakes

Many lakes in the national parks of the Canadian Rockies were stocked with alien fish species in the early to mid 20th century. Changes to Parks Canada's mandate require the original communities of these lakes to be restored. We document the changes to invertebrate communities caused by the stocking of alien fishes into three fishless alpine lakes, and describe the results of two restoration experiments, one the reintroduction of Hesperodiaptomus arcticus, a planktonic predator that had been eliminated from Snowflake Lake by stocked fish, and the other the removal of brook trout (Salvelinus fontinalis) from Bighorn Lake. In both cases, there were great changes to the zooplankton communities, which required several years to complete, probably because of the cold water and unproductive nature of the lakes. Many of the invertebrate species extirpated by stocked alien fishes co-exist with native fish species in nearby lakes. Possible reasons are discussed.     

A tracer study of headspace ventilation in a collector sewer

A field-scale tracer test was conducted to evaluate in-situ ventilation rates in a major collector sewer. The sewer under study was approximately 11 km long and ranged from 0.61 to 2.1 m in diameter. For the purposes of the tracer testing, the collector was divided into four reaches, each of which was tested individually. The tracer test involved injecting a measured volume of CO gas into a manhole over a short time period. CO concentrations were then measured in the collector headspace at selected manholes along the length of the reach. The technique employed successfully measured average headspace velocities over extended lengths of the collector. In a section that had a relatively stagnant headspace, approximately 1.1 km of sewer could be evaluated, with substantial tracer loss attributed to losses to manholes. In a section of the sewer with elevated headspace velocities, a section approximately 7.0 km long was successfully tested with one injection of tracer gas. The velocities observed in the collector varied substantially with time and location in the collector. The lowest velocities measured were in the upstream sections, with a minimum observed value of 3.8 m/min. The highest velocities were observed in the downstream sections, with a maximum value of 31.5 m/min. The presence of a substantial drop structure appeared to reduce the headspace velocity in the upstream reach. In general, there was an increasing trend in gas-phase flows with distance along the length of the collector. Flows at the discharge end of the collector were almost 2 orders of magnitude greater than those at the beginning.     

一种改进的多学习教与学优化算法

针对传统教与学算法在解决复杂多峰函数优化问题时,具有局部最优且搜索开发能力较差的缺点,提出了一种改进的多学习教与学优化算法,新算法为学员的每一维加入不同的教学因子,设计了基于学员均值比较的教师选择策略和向教师及学员学习的多学习策略。基于多个单峰和多峰函数的仿真结果表明,新算法跟传统的、改进的教与学算法相比,在稳定性、寻优精度和收敛速度方面更具优势。     

Modeling Streamflow and Water Quality Sensitivity to Climate Change and Urban Development in 20 U.S. Watersheds

Watershed modeling in 20 large, United States (U.S.) watersheds addresses gaps in our knowledge of streamflow, nutrient (nitrogen and phosphorus), and sediment loading sensitivity to mid‐21st Century climate change and urban/residential development scenarios. Use of a consistent methodology facilitates regional scale comparisons across the study watersheds. Simulations use the Soil and Water Assessment Tool. Climate change scenarios are from the North American Regional Climate Change Assessment Program dynamically downscaled climate model output. Urban and residential development scenarios are from U.S. Environmental Protection Agency's Integrated Climate and Land Use Scenarios project. Simulations provide a plausible set of streamflow and water quality responses to mid‐21st Century climate change across the U.S. Simulated changes show a general pattern of decreasing streamflow volume in the central Rockies and Southwest, and increases on the East Coast and Northern Plains. Changes in pollutant loads follow a similar pattern but with increased variability. Ensemble mean results suggest that by the mid‐21st Century, statistically significant changes in streamflow and total suspended solids loads (relative to baseline conditions) are possible in roughly 30‐40% of study watersheds. These proportions increase to around 60% for total phosphorus and total nitrogen loads. Projected urban/residential development, and watershed responses to development, are small at the large spatial scale of modeling in this study.     

Predicting System-Scale Impacts of Oyster Clearance on Phytoplankton Productivity in a Small Subtropical Estuary

Oyster populations in south Florida estuaries have declined in part through altered salinity driven by anthropogenic changes in freshwater inputs. In particular, the St. Lucie Estuary (SLE) in southeastern Florida has suffered widespread loss of oyster habitat. With efforts underway to improve water quality and oyster habitat in the SLE, the goal of this study was to develop a model to assess ecosystem level impacts of oyster restoration. Phytoplankton and oyster biomass modeling targets were established from observational data collected from 2005 to 2009. Modeled oyster biomass production and filtration fluctuated with temperature, salinity, and total suspended solids from a combination of observational and predicted input functions in 10-year simulations (1998–2007). Model estimates of oyster biomass fluctuated with salinity from near zero after extreme freshwater discharge in 2002–2003 and 2004–2005 to maximum values near 150.0 and 200.0 g?C?m^?2 in spring 1999 and fall 2006. There was potential for algal blooms as turnover time for the phytoplankton standing stock (15.6 days) was faster than water mass turnover (21.0 days). While >1,000 days were required for 50 ha of oyster habitat to filter the entire volume of the estuarine segment, filter time reduced to <20 days with an estimated fivefold increase in net consumption of phytoplankton if the oyster habitat was increased to 300 ha. Re-establishment of biologically desirable salinity envelopes would stabilize oyster survival allowing the possibility for successful habitat restoration to benefit water quality and faunal attributes of the St. Lucie Estuary.