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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

A comparative evaluation of surface runoff models and methods on small developing watersheds in Northern Virginia

Small, Aaron Brent 30 March 2010 (has links)
Increasing populations in urban regions have prompted the development of areas previously undisturbed. This development has spurred the formation of numerous models and methods to simulate the effects of urbanization on runoff processes. The engineer who must use these models and methods needs to be aware of their capabilities and performance. Many of the models assume that calibration will take place to improve the final results. Unfortunately, this is not the case for the majority of drainage studies. A qualitative and quantitative evaluation is made to help the engineer decide which model or method is applicable in certain situations. Simulations are performed on eight watersheds in northern Virginia. Nineteen models are evaluated and compared to gaged events as well as calibrated design storms. The models include EPA SWMM, PSRM-QUAL, TR-20, HEC-1, TR-55, variations of the rational method, three-unit hydrograph procedures, the USGS regression equations, and the Anderson method. Coverage is given for all of the models to outline their capabilities. Hydrographs are evaluated with respect to peak flow, time to peak flow, time base, volume, and overall shape. Statistical measures are introduced to quantitatively test the modeled hydrograph to a baseline reference hydrograph. The statistics yield many errors with the models being evaluated. A selection criteria is given where the models may be chosen based on their performance. The table is limited to the range of watersheds evaluated. Trends in each model toward basin area, land use condition, and general model type are discussed. A cross-calibration technique for improving the accuracy of some models is verified. / Master of Science
2

Floral richness inventory of an eastern U.S. forest

Mason, Nancy A. 16 June 2009 (has links)
Two watersheds on the southern end of Havens State Wildlife Management Area, Roanoke County, Virginia, were sampled for vascular plant species richness. Two-hundred and forty-eight species were identified. Three methods of sampling for species richness in eastern forests were compared: timed-search meanders, belt transects, and plots. Meanders and transects located more species in the same amount of time as plots. Plot sampling encompassed only two-thirds of the richness known from the site. Species-area and species-effort relationships were described by exponential models (number of species = In (area + 1), and number of species = In (time + 1)). Models were used to predict numbers of species which might have been found had more area been sampled or had more time been spent searching. Species-area models yielded more conservative, and probably more accurate, predictions than species-time models. Predictions of species numbers were reasonable for areas as large as 60 ha, but were rather large for areas the size of Havens (2800 ha). Sufficiency of search effort was judged using species-area and species-effort curves. However, it was difficult to tell whether the curves approached horizontal or not. Therefore, this was not a good technique to judge sampling adequacy. Species composition observed by each of the three methods was different. Composition of species lists was 65% similar between meanders and transects, and only 51-58% similar between plots and other methods. These figures were within an expected range. A combination of two methods or repeated meanders was recommended in order to identify a higher proportion of the species present. Seasonal and observer differences, and the effect of learning and taxonomy on richness estimates were discussed. / Master of Science

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