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Rodney R. Knight

Publications and source records attributed to Rodney R. Knight.

13 recordsLinked to original sources
USGS2015

Evaluation of statistical and rainfall-runoff models for predicting historical daily streamflow time series in the Des Moines and Iowa River watersheds

Daily records of streamflow are essential to understanding hydrologic systems and managing the interactions between human and natural systems. Many watersheds and locations lack streamgages to provide accurate and reliable records of daily streamflow. In such ungaged watersheds, statistical tools and rainfall-runoff models are used to estimate daily streamflow. Previous work compared 19 different techniques for predicting daily streamflow records in the southeastern United States. Here, five of the better-performing methods are compared in a different hydroclimatic region of the United States, in Iowa. The methods fall into three classes: (1) drainage-area ratio methods, (2) nonlinear spatial interpolations using flow duration curves, and (3) mechanistic rainfall-runoff models. The first two classes are each applied with nearest-neighbor and map-correlated index streamgages. Using a threefold validation and robust rank-based evaluation, the methods are assessed for overall goodness of fit of the hydrograph of daily streamflow, the ability to reproduce a daily, no-fail storage-yield curve, and the ability to reproduce key streamflow statistics. As in the Southeast study, a nonlinear spatial interpolation of daily streamflow using flow duration curves is found to be a method with the best predictive accuracy. Comparisons with previous work in Iowa show that the accuracy of mechanistic models with at-site calibration is substantially degraded in the ungaged framework.

Iowa, Minnesota↗
USGS2014

Hydrologic data for the Obed River watershed, Tennessee

The Obed River watershed drains a 520-square-mile area of the Cumberland Plateau physiographic region in the Tennessee River basin. The watershed is underlain by conglomerate, sandstone, and shale of Pennsylvanian age, which overlie Mississippian-age limestone. The larger creeks and rivers of the Obed River system have eroded gorges through the conglomerate and sandstone into the deeper shale. The largest gorges are up to 400 feet deep and are protected by the Wild and Scenic Rivers Act as part of the Obed Wild and Scenic River, which is managed by the National Park Service. The growing communities of Crossville and Crab Orchard, Tennessee, are located upstream of the gorge areas of the Obed River watershed. The cities used about 5.8 million gallons of water per day for drinking water in 2010 from Lake Holiday and Stone Lake in the Obed River watershed and Meadow Park Lake in the Caney Fork River watershed. The city of Crossville operates a wastewater treatment plant that releases an annual average of about 2.2 million gallons per day of treated effluent to the Obed River, representing as much as 10 to 40 percent of the monthly average streamflow of the Obed River near Lancing about 35 miles downstream, during summer and fall. During the past 50 years (1960–2010), several dozen tributary impoundments and more than 2,000 small farm ponds have been constructed in the Obed River watershed. Synoptic streamflow measurements indicate a tendency towards dampened high flows and slightly increased low flows as the percentage of basin area controlled by impoundments increases.

Tennessee↗
USGS2013

Ecological limit functions relating fish community response to hydrologic departures of the ecological flow regime in the Tennessee River basin, United States

Ecological limit functions relating streamflow and aquatic ecosystems remain elusive despite decades of research. We investigated functional relationships between species richness and changes in streamflow characteristics at 662 fish sampling sites in the Tennessee River basin. Our approach included the following: (1) a brief summary of relevant literature on functional relations between fish and streamflow, (2) the development of ecological limit functions that describe the strongest discernible relationships between fish species richness and streamflow characteristics, (3) the evaluation of proposed definitions of hydrologic reference conditions, and (4) an investigation of the internal structures of wedge-shaped distributions underlying ecological limit functions. Twenty-one ecological limit functions were developed across three ecoregions that relate the species richness of 11 fish groups and departures from hydrologic reference conditions using multivariate and quantile regression methods. Each negatively sloped function is described using up to four streamflow characteristics expressed in terms of cumulative departure from hydrologic reference conditions. Negative slopes indicate increased departure results in decreased species richness. Sites with the highest measured fish species richness generally had near-reference hydrologic conditions for a given ecoregion. Hydrology did not generally differ between sites with the highest and lowest fish species richness, indicating that other environmental factors likely limit species richness at sites with reference hydrology. Use of ecological limit functions to make decisions regarding proposed hydrologic regime changes, although commonly presented as a management tool, is not as straightforward or informative as often assumed. We contend that statistical evaluation of the internal wedge structure below limit functions may provide a probabilistic understanding of how aquatic ecology is influenced by altered hydrology and may serve as the basis for evaluating the potential effect of proposed hydrologic changes.

Tennessee River basin↗
USGS2012

Predicting ecological flow regime at ungaged sites: A comparison of methods

Nineteen ecologically relevant streamflow characteristics were estimated using published rainfall–runoff and regional regression models for six sites with observed daily streamflow records in Kentucky. The regional regression model produced median estimates closer to the observed median for all but two characteristics. The variability of predictions from both models was generally less than the observed variability. The variability of the predictions from the rainfall–runoff model was greater than that from the regional regression model for all but three characteristics. Eight characteristics predicted by the rainfall–runoff model display positive or negative bias across all six sites; biases are not as pronounced for the regional regression model. Results suggest that a rainfall–runoff model calibrated on a single characteristic is less likely to perform well as a predictor of a range of other characteristics (flow regime) when compared with a regional regression model calibrated individually on multiple characteristics used to represent the flow regime. Poor model performance may misrepresent hydrologic conditions, potentially distorting the perceived risk of ecological degradation. Without prior selection of streamflow characteristics, targeted calibration, and error quantification, the widespread application of general hydrologic models to ecological flow studies is problematic. Published 2012. This article is a U.S. Government work and is in the public domain in the USA.

Kentucky, Tennessee↗
USGS2012

Invertebrate response to changes in streamflow hydraulics in two urban areas in the United States

Stream hydrology is foundational to aquatic ecosystems and has been shown to be a structuring element for fish and invertebrates. The relations among urbanization, hydraulics, and invertebrate communities were investigated by the U.S. Geological Survey, National Water-Quality Assessment Program by using measures of stream hydraulics in two areas of the United States. Specifically, the hypothesis that the effects of urbanization on streamflow and aquatic biota are transferable across geographic regions was tested. Data from sites in Raleigh, North Carolina, and Milwaukee–Green Bay, Wisconsin, were compared and indicate that increasing urbanization has an effect on hydraulic characteristics (Reynolds number, shear stress, and stream power for example) in each metropolitan area, though limited commonality of significant correlations was noted between areas. Correspondence of significant correlations between invertebrate and hydraulic metrics between study areas also was limited. The links between urbanization, hydraulics, and invertebrates could be seen only in the Raleigh data. Connections among these three elements in the Milwaukee–Green Bay data were not clear and likely were obscured by antecedent land cover. Observed biotic differences due to hydrology and urbanization characteristics are not similar between geographic regions.

Scientific Investigations Report↗
USGS2011

Modelling ecological flow regime: an example from the Tennessee and Cumberland River basins

Predictive equations were developed for 19 ecologically relevant streamflow characteristics within five major groups of flow variables (magnitude, ratio, frequency, variability, and date) for use in the Tennessee and Cumberland River basins using stepbackward regression. Basin characteristics explain 50% or more of the variation for 12 of the 19 equations. Independent variables identified through stepbackward regression were statistically significant in 78 of 304 cases (α > 0.0001) and represent four major groups: climate, physical landscape features, regional indicators, and land use. Of these groups, the regional and climate variables were the most influential for determining hydrologic response. Daily temperature range, geologic factor, and rock depth were major factors explaining the variability in 17, 15, and 13 equations, respectively. The equations and independent datasets were used to explore the broad relation between basin properties and streamflow and the implication of streamflow to the study of ecological flow requirements. Key results include a high degree of hydrologic variability among least disturbed Blue Ridge streams, similar hydrologic behaviour for watersheds with widely varying degrees of forest cover, and distinct hydrologic profiles for streams in different geographic regions. Published in 2011. This article is a US Government work and is in the public domain in the USA.

Alabama;Georgia;Kentucky;Mississippi;North Carolin↗
USGS2011

If the creeks don't rise: the May 2010 Flood in Nashville

The aftermath, recovery, and lessons of the future following a major flood that inundated the greater Nashville area one year ago are the subjects of this article. The authors discuss what led up to the event, its impacts, and what, if anything, can be done to prevent or diminish the reoccurrence of such flooding in the future.

Tennessee↗
USGS2011

Regression models of ecological streamflow characteristics in the Cumberland and Tennessee River Valleys

Predictive equations were developed using stepbackward regression for 19 ecologically relevant streamflow characteristics grouped in five major classes (magnitude, ratio, frequency, variability, and date) for use in the Tennessee and Cumberland River watersheds. Basin characteristics explain 50 percent or more of the variation for 10 of the 19 equations. Independent variables identified through stepbackward regression were statistically significant in 81 of 304 coefficients tested across 19 models (⬚ < 0.0001) and represent four major groups: climate, physical landscape features, regional indicators, and land use. The most influential variables for determining hydrologic response were in the land-use and climate groups: daily temperature range, percent agricultural land use, and monthly mean precipitation. These three variables were major explanatory factors in 17, 15, and 13 models, respectively. The equations and independent datasets were used to explore the broad relation between basin properties and streamflow and its implications for the study of ecological flow requirements. Key results include a high degree of hydrologic variability among least disturbed Blue Ridge streams, similar hydrologic behavior for watersheds with widely varying degrees of forest cover, and distinct hydrologic profiles for streams in different geographic regions.

Tennessee and Cumberland Rivers↗
USGS2010

Harmful algal blooms: A case study in two mesotrophic drinking water supply reservoirs in South Carolina

Algal blooms can be harmful and a nuisance in a variety of aquatic ecosystems, including reservoirs and lakes. Cyanobacterial(blue-green algae) harmful algal blooms are notorious for producing both taste-and-odor compounds and potent toxins that may affect human health. Taste–and-odor episodes are aesthetic problems often caused by cyanobacterial-produced organic compounds (geosmin and methylisoborneol) and are common in reservoirs and lakes used as source water supplies. The occurrences of these taste-and-odor compounds and toxins (like microcystin) can be sporadic and vary in intensity both spatially and temporally. Recent publications by the U.S. Geological Survey address this complexity and provide protocols for cyanotoxin and taste-and-odor sampling programs. A case study conducted by the U.S. Geological Survey, in cooperation with Spartanburg Water, monitored two mesotrophic reservoirs that serve as public drinking water supplies in South Carolina. Study objectives were (1) to identify spatial and temporal occurrence of the taste-and-odor compound geosmin and the cyanotoxin microcystin and (2) to assess the associated limnological conditions before, during, and after these occurrences. Temporal and spatial occurrence of geosmin and microcystin were highly variable from 2007 to 2009. The highest geosmin concentrations tended to occur in the spring. Microcystin tended to occur in the late summer and early fall, but occurrence was rare and well below World Health Organization guidelines for finished drinking water and recreational activities. No current U.S. Environmental Protection Agency standards are applicable to cyanotoxins in drinking or ambient water. In general, elevated geosmin and microcystin concentrations were the result of complex interactions between cyanobacterial community composition, nutrient availability, water clarity, hydraulic residence time, and stratification.

South Carolina↗
USGS2008

Relating streamflow characteristics to specialized insectivores in the Tennessee River Valley: a regional approach

Analysis of hydrologic time series and fish community data across the Tennessee River Valley identified three hydrologic metrics essential to habitat suitability and food availability for insectivorous fish communities in streams of the Tennessee River Valley: constancy (flow stability or temporal invariance), frequency of moderate flooding (frequency of habitat disturbance), and rate of streamflow recession. Initial datasets included 1100 fish community sites and 300 streamgages. Reduction of these datasets to sites with coexisting data yielded 33 sites with streamflow and fish community data for analysis. Identification of critical hydrologic metrics was completed using a multivariate correlation procedure that maximizes the rank correlation between the hydrologic metrics and fish community resemblance matrices. Quantile regression was used to define thresholds of potential ranges of insectivore scores for given values of the hydrologic metrics. Increased values of constancy and insectivore scores were positively correlated. Constancy of streamflow maintains wetted perimeter, which is important for providing habitat for fish spawning and increased surface area for invertebrate colonization and reproduction. Site scores for insectivorous fish increased as the frequency of moderate flooding (3 times the median annual streamflow) decreased, suggesting that insectivorous fish communities respond positively to less frequent disturbance and a more stable habitat. Increased streamflow recession rates were associated with decreased insectivore scores. Increased streamflow recession can strand fish in pools and other areas that are disconnected from flowing water and remove invertebrates as food sources that were suspended during high-streamflow events.

Tennessee↗
USGS2004

Water quality in the lower Tennessee River Basin, Tennessee, Alabama, Kentucky, Mississippi, and Georgia, 1999-2001

This report contains the major findings of a 1999?2001 assessment of water quality in the Lower Tennessee River Basin. It is one of a series of reports by the National Water-Quality Assessment (NAWQA) Program that present major findings in 51 major river basins and aquifer systems across the Nation. In these reports, water quality is discussed in terms of local, State, and regional issues. Conditions in a particular basin or aquifer system are compared to conditions found elsewhere and to selected national benchmarks, such as those for drinking-water quality and the protection of aquatic organisms. This report is intended for individuals working with water-resource issues in Federal, State, or local agencies, universities, public interest groups, or in the private sector. The information will be useful in addressing a number of current issues, such as the effects of agricultural and urban land use on water quality, human health, drinking water, source-water protection, hypoxia and excessive growth of algae and plants, pesticide registration, and monitoring and sampling strategies. This report is also for individuals who wish to know more about the quality of streams and ground water in areas where they live, and how that water quality compares to the quality of water in other areas across the Nation. The water-quality conditions in the Lower Tennessee River Basin summarized in this report are discussed in detail in other reports that can be accessed from the Lower Tennessee River Basin Web site (http://tn.water.usgs.gov/lten/lten.html). Detailed technical information, data and analyses, collection and analytical methodology, models, graphs, and maps that support the findings presented in this report in addition to reports in this series from other basins can be accessed from the national NAWQA Web site (http://water.usgs.gov/nawqa).

Alabama, Georgia, Kentucky, Mississippi, Tennessee↗
USGS2002

Water quality of the Flint River basin, Alabama and Tennessee, 1999-2000

The U.S. Geological Survey monitored eight stream sites in the Flint River Basin during the period January 1999 through May 2000, to characterize patterns in the occurrence of pesticides, fecal-indicator bacteria, and nutrients in relation to season and streamflow conditions and to land-use patterns. This study is part of the National Water-Quality Assessment Program, which was designed to assess water quality as it relates to various land uses. Every water sample collected from the Flint River Basin had detectable levels of at least two pesticides; 64 percent of the samples contained mixtures of at least five pesticides. In general, pesticides detected most frequently and at highest concentrations in streams corresponded to the pesticides with the highest rates of use in the watersheds. Detections of fluometuron, norflurazon, and atrazine were more frequent (by a margin of 15 percent or more) in samples from the Flint River when compared with the frequencies of pesticide detections at 62 agricultural stream sites across the Nation. Detections of fluometuron in the Flint River were more frequent even when compared with a cotton-cultivation subset of the 62 sites. For most pesticides, maximum concentrations did not exceed criteria to protect aquatic life; however, maximum concentrations of atrazine, cyanazine, and malathion exceeded aquaticlife criteria in at least one sample. Concentrations near or exceeding the aquatic-life criteria occurred only during the spring and summer (April-July), and generally occurred during storm flows. Less than 5 percent of the estimated mass of pesticides applied annually to agricultural areas in the Flint River Basin was transported to the stream at the monitoring points on the Flint River near Brownsboro, Alabama, and on Hester Creek near Plevna, Alabama. The pesticides with the highest ratios (greater than 3 percent) of the amount transported instream to the amount applied?atrazine, metolachlor, fluometuron, and norflurazon?are preemergent herbicides applied to the soil before the crops have emerged, which increases the probability of transport in surface runoff. Concentrations of the fecal-bacteria indicator Escherichia coli (E. coli) in the Flint River and Hester Creek exceeded the U.S. Environmental Protection Agency criterion for recreation in almost all storm samples, and in many samples collected up to 6 days following a storm. Concentrations in the Flint River were strongly correlated with sample turbidity, suggesting that turbidity might be useful as a surrogate for estimating E. coli concentrations. Concentrations of the nutrients nitrogen and phosphorus in samples from the Flint River generally exceeded thresholds indicating eutrophic potential, whereas concentrations in samples from Hester Creek were generally below the thresholds. When compared with nutrient data from a set of 24 agricultural basins across the southeastern region of the United States, concentrations in the Flint River and Hester Creek were slightly above the regional median. Base-flow concentrations of certain pesticides, nutrients, and E. coli were compared to land-use information for eight sites in the Flint River Basin. The highest base-flow concentrations of aldicarb sulfoxide, fluometuron, and phosphorus were found in the tributaries with the greatest density of cotton acreage in the watershed. Similarly, high base-flow concentrations of total nitrogen were correlated with a high percentage of cultivated land in the watershed. Lack of information about distribution of stream access by livestock weakened the analysis of correlation between livestock and base-flow concentrations of E. coli and nutrients. Input of dissolved and suspended chemicals from the Flint River during storms influences water quality in the reach of the Tennessee River from which the City of Huntsville, Alabama, withdraws about 40 percent of its drinking water. During the storm of April 2-5, 2000, concentrations of several pesticides were

Water-Resources Investigations Report↗