English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

An equation for estimating stream reaeration coefficients from easily measured physical characteristics was developed for moderately sloped streams in Massachusetts. To define the equation, multiple-regression techniques were applied to 30 data sets containing 9 physical, hydrologic, and water-quality characteristics. Data on mean depth, water-surface slope, and mean streamflow velocity ranged from 0.4 to 6.3 feet, from 0.00017 to 0.015 feet per foot, and from 0.13 to 2.15 feet per second, respectively. Reaeration coefficients were measured using a steady-state, propane-gas tracer technique during mediumand low-flow periods in 1983 and 1984. Measured reaeration coefficients ranged from 0.4 to 67.7 base e units per day at 20 degrees Celsius. The regression analysis defines the relation between the reaeration coefficient, K2 , and the independent variables mean depth, D, water-surface slope, SL, and mean streamflow velocity, V, given by: K2 = 252.2 D~°' 176 70-355 5Lo-43 8j in which 252.2 is the regression constant for the equation. The equation was limited to three variables that were the most significant at the 95-percent confidence level because of the small size of the data base. The standard error of estimate for the reaeration equation is 37 percent. An error-analysis technique was used to compare the proposed equation with 19 published reaeration coefficient equations. The error analysis indicates that the proposed equation has the second lowest error (37 percent) for 20 stream reaches with slopes greater than 0.002 feet per foot. INTRODUCTION Stream reaeration coefficients are used in stream-water quality models to forecast the effects of organic loadings on DO (dissolved-oxygen) concentrations in streams. State water-pollution-control agencies, such as the MDWPC (Massachusetts Department of Environmental Quality Engineering, Division of Water Pollution Control) rely on stream DO models for decisions relative to the maintenance of stream water-quality standards set by each state in conjunction with the U.S. Environmental Protection Agency. The self-cleaning capacity of a river depends on DO concentrations and the capacity to replace oxygen removed by the reduction of organic wastes. When attempting to model the concentration levels of a nonconservative substance such as DO in open-channel flow, allowances must be made for dispersion, decay, and reaeration at the surface, and for deoxygenation resulting from biochemical demands, algal respiration, and interaction with benthic deposits. The use of a steady-state river model is based on the assumption that the dispersion coefficient is constant for a given stream reach over the time period being simulated. All of the other processes can be measured directly, except for reaeration, which can be determined indirectly or estimated from equations. Measured values for the reaeration coefficient can be determined from the dissolved-oxygen balance, distributed equilibrium, and by tracer methods. The dissolved-oxygen balance method consists of measuring the various sources and sinks of DO and determining the amount of reaeration needed to balance the equation. The disturbed-equilibrium method consists of artificially producing DO deficits by adding sodium sulfite to the stream and subsequently measuring upstream and downstream concentrations of DO at two different concentration levels. The tracer method consists of correlating the rate of desorption of a tracer gas with the rate of absorption of oxygen. However, in addition to being costly and time consuming, the balance and equilibrium methods are indirect determinations of oxygen transfer and are subject to measurement errors. These indirect methods of calculating the DO contribution from reaeration may be no more accurate than reaeration coefficients calculated from theoretical or empirical equations (Bennett and Rathbun, 1972). Recent advances in the tracer method, such as the U.S. Geological Survey's steady-state propane-gas tracer method (Yotsukura and others, 1983; 1984), offer a less costly, more accurate, reliable, and reproducible method of measuring reaeration coefficients in place. The gas-tracer method is useful for determining reaeration coefficients, because it also eliminates interferences of photosynthetic oxygen production and respiration of the suspended and attached aquatic plants (Bennett and Rathbun, 1972; Rathbun and others 1978; Yotsukura and others, 1983; 1984). The reaeration coefficients used in predictive models generally are estimated from theoretical, semiempirical, or empirical equations. Bennett and Rathbun (1972) state that the theoretical models of the dissolved-oxygen absorption process generally are not suitable to predict the reaeration coefficient in streams because the model parameters have been inadequately related to bulk-flow hydraulic variables. Semiempirical and empirical equations developed from experimental data predict reaeration coefficients adequate for streams of the type on which the equations are based, but large errors may occur when the equations are applied to other types of streams or to conditions outside the range of independent variables considered in the equations derived from empirical data. Because of stringent water-quality standards imposed on State streams and the high costs of determining stream-reaer4tion coefficients, there is a need to develop an equation that will estimate reaeration coefficients reliably from easily measured physical, hydraulic, and water-quality characteristics. In response to this need, the U.S. Geological Survey, in cooperation with the MDWPC, has developed regionalized predictive equations using the Survey's steady-state propane-gas tracer method. This gas-tracer method provides the data needed to derive a reaeration.-estimating equation. Purpose and Scope igression This report describes the multiple-re an equation for estimating reaeration The equation is based on easily measured tics of stream channels. The equation is com estimating equations by using measured data to the equations to predict reaeration coefficients coefficients physical pared techniques used to derive of Massachusetts streams, and hydraulic characteristo other commonly used determine the accuracy of all in Massachusetts streams. Tracer studies were performed on 16 stream reaches representative of most streams in Massachusetts. The Survey's newly developed steady-state, gas-tracer technique was was used to measure in-situ reaeration coefficients. Reaeration coefficients, mean streamflow velocities, and nine easily measured physical, hydraulic, and water-quality characteristics were measured in 30 studies during mediumand low-flow periods between August 1983 and December 1984. Approach As a result of searching reaeration literature, nine physical, hydraulic, and water quality characteristics were selected to be correlated with the reaeration coefficient: Water-surface slope, mean velocity, depth, width, roughness coefficient, color, methylene blue active substances concentration, specific conductance, and suspended-solids concentration. Sixteen reaches on 11 rivers (fig. 1) were selected for combined time-oftravel and reaeration-tracer studies on the basis of their regional location, consistency of reach characteristics, and accessibility. Reach and study-site descriptions can be found in Appendix A. Thirty combined tracer studies were conducted on the 16 reaches. When possible, two or more tracer studies were performed on the same reach at different discharge rates. All studies were conducted at a steady discharge with little or no wind. Reach physical, hydraulic, and water-quality characteristics were measured during each tracer study and samples were collected for water-quality analysis. Water-surface slope was determined using differential leveling between reference points established at the ends of each study reach. All studies were initially evaluated for completeness and accuracy of time-of-travel data. Initial propane-gas desorption coefficients were determined using steady-state, gas-tracer injection techniques outlined in Yotsukura and others (1983). For each tracer study, the transfer of measurement error was estimated. The reaeration-coefficient estimating equation was developed from reaeration coefficients and the corresponding reach characteristics determined for the 30 combined tracer studies. Step-forward, multiple-regression analyses were conducted to relate reaeration coefficients to channel characteristics. Only those characteristics significant at a 95-percent confidence level were retained. Reaeration coefficients were estimated from widely used equations using the channel characteristics determined for all 30 tracer studies. All estimating equations, including the equation developed for this report, were ranked according to the accuracy of their predicted reaeration values compared to measured values from the 30 tracer studies. Acknowledgments The authors wish to acknowledge and thank the many persons and organizations who have kindly given their time, information, and guidance to this study in particular, personnel from the Massachusetts Division of Water Pollution Control's Westborough, Massachusetts, office who assisted with the W e st B ra n ch N o rt h R iv e r ne ar G ri sw o ld vi lle A ss a b e t R iv er n ea r W es t C o n co rd S ud bu ry R iv er at C o n co rd W e st B ra n ch N o rt h R iv er ne ar A da m sv ill e N o rt h R iv er a t G ri sw o ld vi lle M id dl e B ra nc h W e st fie ld R iv er / ne ar M id d le fie ld ^ ^ 4 2 3 0 / \ -, -> M id dl e B ra nc h W e st fie ld R iv er at N o rt h C h e st e r W es t B ra nc h W e st fie ld R iv e r at C h e st e r A b e rj o n a R iv er

A procedure for estimating reaeration coefficients for Massachusetts streams