EFFECTS OF NO-FLOW RIVER CONDITIONS ON THE PLATTE RIVER WELL FIELD1

ABSTRACT: Effects of no-flow river conditions on the quantity and quality of water in the Platte River well field of the City of Grand Island, Nebraska, were examined utilizing a finite-difference computer simulation model specifically developed for this well field. Results suggest that the effects of these no-flow periods on water quality may be most important. In particular, the no-flow periods eliminate the hydraulic barrier between the well field and an area north of the River that is contaminated with nitrate (concentrations in the 20 to 40 mg/1 NO₃-N range). They also change the direction and velocity of movement of the contaminated ground water. Simulation results indicate that contaminated ground water moves toward the well field with a velocity of 0.42 ft/d after 30 days of no-flow and 1.43 ft/d after 180 days of no-flow. Limiting no-flow conditions to 10 consecutive days would protect the well field.     

STATISTICAL METHODS AND SAMPLING DESIGN FOR ESTIMATING STEP TRENDS IN SURFACE-WATER QUALITY1

ABSTRACT: This paper addresses two components of the problem of estimating the magnitude of step trends in surface water quality. The first is finding a robust estimator appropriate to the data characteristics expected in water-quality time series. The Hodges-Lehmann class of estimators is found to be robust in comparison to other nonparametric and moment-based estimators. A seasonal Hodges-Lehmann estimator is developed and shown to have desirable properties. Second, the effectiveness of various sampling strategies are examined using Monte Carlo simulation coupled with application of this estimator. The simulation is based on a large set of total phosphorus data from the Potomac River. To assure that the simulated records have realistic properties, the data are modeled in a multiplicative fashion incorporating flow, hysteresis, seasonal, and noise components. The results demonstrate the importance of balancing the length of the two sampling periods and balancing the number of data values between the two periods. The inefficiency of sampling at frequencies much in excess of 12 samples per year is demonstrated. Rotational sampling designs are discussed, and efficient designs, at least for this river and constituent, are shown to involve more than one year of active sampling at frequencies of about 12 per year.     

A TAU-LIKE TEST FOR TREND IN THE PRESENCE OF MULTIPLE CENSORING POINTS1

ABSTRACT: A common problem arises in testing for trends in water quality when observations are reported as “less than detection limit.” If a single detection limit is used for the entire study, existing non-parametric statistical methods, modified for ties, are applicable. If, however, the detection limit varies during the course of the study, resulting in multiple detection limits, then the commonly used trend detection methods are not appropriate. A statistic similar to Kendall's tau, but based on expected ranks, is proposed. Monte Carlo simulations show that the normal approximation to the distribution of this statistic is quite good, even for small samples and a large proportion of censored observations. The statistic is also shown to have greater power than the ad-hoc method of treating all observations less than the target censored observation as tied.     

NONPARAMETRIC TESTS FOR TREND DETECTION IN WATER QUALITY TIME SERIES1

ABSTRACT: A review of nonparametric tests for trend leads to the conclusion that Mann-Whitney, Spearman, and Kendall tests are the best choice for trend detection in water quality time series. Recently these tests have been adapted to account for dependence and seasonality in such series (Lettenmaier, 1976; Hirsch, et al., 1972; Hirsch and Slack, 1984). For monotonic trends, a procedure allowing to select the pertinent tests considering the characteristics of time series is proposed and the practical limitations of the tests are also brought out. This procedure has been applied to identify the appropriate trend detection test for the time series of nine water quality parameters at Lake Laflamme (Québec). When a time series can be tested with the Mann-Whitney, Kendall, Spearman, or Lettenmaier (1976) test, the number of observations required to detect trends of a given magnitude, for selected significance and power levels can be calculated with the power function of the t test. When the test proposed by Hirsch, et al. (1984), Hirsch and Slack (1984), or Farrell (1980) need to be used, the number of observations can only be estimated approximately from the results of empirical power studies.     

MUNICIPAL RESPONSES TO VOLATILE ORGANIC COMPOUNDS IN WISCONSIN GROUND WATER1

ABSTRACT: Contamination of ground water supplies with volatile organic compounds is a new and significant problem. Municipalities and their community water systems are often the first to discover ground water contamination because of the monitoring programs they are required to carry out. When contamination exceeds standards, some action is required. The responses of Wisconsin municipalities to volatile organic compounds that exceed standards in their ground water sources is described. Actions to protect human health are prompt, but the survey results indicate plumes of contaminated ground water are usually not treated. They may continue to migrate and contaminate other private and public wells.     

Evaluating the effects of spatial monitoring policy on groundwater quality portrayal

What size sample is sufficient for spatially sampling ambient groundwater quality? Water quality data are only as spatially accurate as the geographic sampling strategies used to collect them. This research used sequential sampling and regression analysis to evaluate groundwater quality spatial sampling policy changes proposed by California's Department of Water Resources. Iterative or sequential sampling of a hypothetical groundwater basin's water quality produced data sets from sample sizes ranging from 2.8% to 95% coverage of available point sample sites. Contour maps based on these sample data sets were compared to an original (control), mapped hypothetical data set, to determine at which point map information content and pattern portrayal are not improved by increasing sample sizes. Comparing series of contour maps of ground water quality concentration is a common means of evaluating the geographic extent of groundwater quality change. Comparisons included visual inspection of contout maps and statistical tests on digital versions of these map files, including correlation and regression products. This research demonstrated that, down to about 15% sample site coverage, there is no difference between contour maps produced from the different sampling strategies and the contout map of the original data set.     

A hierarchical approach to fisheries planning and modeling in the Columbia River Basin

The Columbia River Basin is the scene of a massive effort to restore populations of Pacific salmon (Oncorhynchus spp.) and steelhead (O. mykiss). Efficient restoration is confounded by a high level of complexity, competing sociopolitical goals and values, and uncertainty about key system properties. Simulation models and other tools of systems analysis are important to development of a comprehensive, regionally acceptable strategy. Hierarchy theory provides a useful paradigm for organized complexity within the Columbia Basin and the basis for a trilevel hierarchical structure for organizing and integrating models. Life-stage models compose the most basic simulation units at the lowest level in the proposed hierarchical modeling structure. Each life-stage model simulates a distinct period in the life cycle of anadromous salmonids. Population models at the intermediate level simulate the complete life cycles of salmon and steelhead populations. At the highest level in the hierarchy, interpopulation models simulate extensive, long-term processes that affect multiple species and stocks. A hierarchical system of models is preferable to a single model or to a group of models lacking formal structure. A principal advantage is that models have the correct spatial and temporal resolution for analyzing questions at different scales. A hierarchical structure also facilitates the flow of information among models, and aids in understanding the impacts of uncertainty. Constructing a hierarchy of models should involve both bottom-up and top-down perspectives that maintain logical consistency among models, while allowing unique model structures appropriate for each level in the hierarchy.     

Evaluating the effectiveness of air quality management within the class I area of great smoky mountains national park

The Clean Air Act Amendments of 1977 designated national parks and wilderness areas larger than 1894 ha to be class I areas for air quality management, setting more restrictive criteria than the National Ambient Air Quality Standards. Class I areas are afforded the greatest degree of air quality protection under the Clear Air Act of 1970. In recent years, several studies have documented air pollution effects in the Great Smoky Mountains National Park (GSMNP), the second-largest class I area in the eastern United States. Air pollution problems of greatest concern in the GSMNP are effects of acid deposition, visibility impairment, and tropospheric ozone. Several recent events have increased concerns about air quality management in the class I area of the GSMNP. A forum, sponsored by the Southern Appalachian Man and the Biosphere Cooperative (SAMAB), was held in March 1992, which involved representative. parties-at-interest and began to address strategies for better management of air resources in the Southern Appalachians. This paper summarizes those discussions and recommendations and reports actions occurring as a result of the forum. Another objective of this paper is to present a conceptual framework for more effective management of the class I area of the GSMNP.     

MEASURED AND PREDICTED VELOCITY AND LONGITUDINAL DISPERSION AT STEAI)Y AND UNSTEADY FLOW,COLORADO RIVER,GLEN CANYON DAM TO LAKE MEAD1

ABSTRACT: The effect of unsteadiness of dam releases on velocity and longitudinal dispersion of flow was evaluated by injecting a fluorescent dye into the Colorado River below Glen Canyon Dam and sampling for dye concentration at selected sites downstream. Measurements of a 26-kilometer reach of Glen Canyon, just below Glen Canyon Dam, were made at nearly steady dam releases of 139, 425, and 651 cubic meters per second. Measurements of a 380-kilometer reach of Grand Canyon were made at steady releases of 425 cubic meters per second and at unsteady releases with a daily mean of about 425 cubic meters per second. In Glen Canyon, average flow velocity through the study reach increased directly with discharge, but dispersion was greatest at the lowest of the three flows measured. In Grand Canyon, average flow velocity varied slightly from subreach to subreach at both steady and unsteady flow but was not significantly different at steady and unsteady flow over the entire study reach. Also, longitudinal dispersion was not significantly different during steady and unsteady flow. Long tails on the time-concentration curves at a site, characteristic of most rivers but not predicted by the one-dimensional theory, were not found in this study. Absence of tails on the curves shows that, at the measured flows, the eddies that are characteristic of the Grand Canyon reach do not trap water for a significant length of time. Data from the measurements were used to calibrate a one-dimensional flow model and a solute-transport model. The combined set of calibrated flow and solute-transport models was then used to predict velocity and dispersion at potential dam-release patterns.     

RELATION BETWEEN STREAM-WATER QUALITY AND GEOHYDROLOGY DURING BASE-FLOW CONDITIONS,ROBERTS CREEK WATERSHED,CLAYTON COUNTY,IOWA1

ABSTRACT: An investigation to determine the relation between stream water quality and geohydrology in the Roberts Creek watershed, Clayton County, Iowa, was conducted during selected base-flow periods in 1988–90. Discharge measurements were made and water samples collected for analyses of nutrients and selected herbicides in 19 subbasins along the main stem and tributaries of Roberts Creek. The areal extent of unconsolidated and bedrock units subcropping in each subbasin was quantified. The hydrologic data were correlated statistically with the geologic data to determine relations. Roberts Creek generally gained water and had larger nitrogen concentrations in subbasins in which bess and alluvial material were underlain primarily by low-permeability till and shale units. Roberts Creek generally lost water and had lower nitrate concentrations in subbasins with subcroppmg karstic units. Nitrogen concentrations decreased in streams underlain by the karstic units because the nitrogen removed by biological processes was not replaced by ground-water inflow. Seepage from Roberts Creek to ground water in areas of subcropping karstic carbonate rocks reduced the flow, which reduced the velocity, causing increased residence time of water in the stream. The additional residence time may allow additional time for biological processes to remove nitrogen from solution. There was no significant relation between dissolved orthophosphate or atrazine and the underlying geology.