Walter E. Frick

Non-empirical closure of the plume equations

Abstract A plume model capable of predicting trajectories, dilution, width, and other important plume properties may be developed with very little empirical input, namely, common plume assumptions and the Taylor entrainment hypothesis. The Taylor hypotheses is necessary in cases of little or no current, but, as current increases, it decreases in importance until the point is reached where it may be omitted. In such instances the model may be practically non-empirical. An objective model of this nature is necessary because there is always some doubt that empirical models may be generalized—especially when known data, to which they are fitted, are subject to relatively large uncertainty as plume data are. The resulting model predicts a wide range of plume behavior and, far from being complex, is even easily adapted for use with personal computers.

Visual Plumes mixing zone modeling software

Abstract The US Environmental Protection Agency has a history of developing plume models and providing technical assistance. The Visual Plumes model (VP) is a recent addition to the public-domain models available on the EPA Center for Exposure Assessment Modeling (CEAM) web page. The Windows-based VP adapts, modifies, and enhances the earlier DOS-based PLUMES with a new interface, models, and capabilities. VP is a public platform for mixing zone models designed to encourage the continued improvement of plume theory and models by facilitating verification and inter-model comparison. Some examples are presented to illustrate VP’s new capabilities. One demonstrates its ability, for reasonably one-dimensional estuaries, to estimate background concentrations due to tidal re-circulation of previously contaminated receiving water. This capability depends on the optional linkage to time-series input files that enables VP to simulate mixing zone and far-field parameters for long periods. Also described are the new bacterial decay models used to estimate depth changes in first-order decay rates based on environmental stressors, including solar insolation, salinity, and temperature. The nascent density phenomenon is briefly described as it is potentially important to Outer Continental Shelf (OCS) oil exploration discharges.

Improved prediction of bending plumes

Integral plume models harbor a fundamental, often significant error because the standard implementation of control volumes, or elements, is inconsistent with the overall geometry of the problem. The error, called the negative volume anomaly, occurs irregularly, being contingent on there being strong bending and large plume diameter. When present it causes entrainment, i.e., dilution, to be overestimated. It is of practical significance because dilution estimates are used to design and assess diffusers. The anomaly arises when constructed round element faces intersect, as they do when plume diameters are large and plume bending is pronounced, inadvertently generating negative volume and a faulty integration of the governing equations. A modified control volume is proposed to correct the error, and its performance is demonstrated. Its development yields clues to other plume behavior, for example, how plume trajectories may respond to the asymmetrical addition of mass and its distribution in the element.

Red Alder (Alnus rubra) Distribution Influences Nitrate Discharge to Coastal Estuaries: Comparison of Two Oregon Watersheds

Abstract We determined nutrient export from the Yaquina and Alsea Rivers as part of a larger program for evaluating nutrient sources to coastal waters. The Yaquina and Alsea data indicated that one river typically contained twice the amount of dissolved nitrate-N, although temperature, conductivity and the concentrations of other nutrients were similar. We developed a nitrate export model using multiple linear regression (MLR) to analyze the discriminating variables that included nutrient concentrations and hardwood cover containing approximately 90% red alder (Alnus rubra), a nitrogen-fixing tree species. Using data from the Coastal Landscape Analysis and Modeling Study (CLAMS), hardwood cover was found to be most prevalent in the upper (gaged) Yaquina watershed. Estimated nitrate export was 2.02 Mg km-2 y-1 in the Yaquina and 1.24 Mg km-2 y-1 in the Alsea for 2006. However, the annual nitrate-N exported from the entire Alsea basin (1560 Mg) was slightly greater than that of the Yaquina basin (1320 Mg) since the Alsea is about twice as large with proportionally greater discharge. Various factors, including the relatively low nitrate concentrations in local rainfall and the lack of local primary anthropogenic sources, indicated that red alder density may be the primary source of higher concentrations in the Yaquina, relative to the Alsea River. The regression model developed in this study can provide a rapid estimate of nitrate-N export based on water discharge data and hardwood distribution in the Oregon Coast Range.