Hydraulic Resistance due to Emergent Wetland Vegetation

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dc.contributor.authorPiercy, Candice Dawnen
dc.contributor.committeechairThompson, Theresa M.en
dc.contributor.committeememberHession, W. Cullyen
dc.contributor.committeememberBenham, Brian L.en
dc.contributor.committeememberDaniels, W. Leeen
dc.contributor.committeememberDiplas, Panayiotisen
dc.contributor.departmentBiological Systems Engineeringen
dc.date.accessioned2014-03-14T21:10:24Zen
dc.date.adate2010-04-22en
dc.date.available2014-03-14T21:10:24Zen
dc.date.issued2010-03-26en
dc.date.rdate2010-04-22en
dc.date.sdate2010-04-07en
dc.description.abstractModels to estimate hydraulic resistance due to vegetation in emergent wetlands are crucial to wetland design and management. Hydraulic models that consider vegetation rely on an accurate determination of a resistance parameter such as a friction factor or a bulk drag coefficient. At low Reynolds numbers typical of flows in wetlands, hydraulic resistance is orders of magnitude higher than fully turbulent flows and resistance parameters are functions of the flow regime as well as the vegetation density and structure. The exact relationship between hydraulic resistance, flow regime and vegetation properties at low-Reynolds number flows is unclear. The project goal was to improve modeling of emergent wetlands by linking vegetation and flow properties to hydraulic resistance. A 12.2-m x 1.2 m vegetated flume was constructed to evaluate seven models of vegetated hydraulic resistance through woolgrass (Scirpus cyperinus (L.) Kunth), a common native emergent wetland plant. Measurements of vegetation geometry and structure were collected after each set of flume runs. Study results showed at low stem-Reynolds numbers (<100), the drag coefficient is inversely proportional to the Reynolds number and can vary greatly with flow conditions. Empirical models that were developed from data collected in natural wetlands predicted flow velocity most accurately. Using data from this flume study, regression models were developed to predict hydraulic resistance. Results indicated stem Reynolds number, stem diameter, and vegetation area per unit volume were the best predictors of friction factor. Vegetation flexibility and water depth were also important parameters but to a lesser extent. The spatial distribution of hydraulic resistance was estimated in a small floodplain wetland near Stephens City, VA using the regression models developed from the flume data. MODFLOW was used to simulate a 4-hour flood event through the wetland. The vegetated open water surface was modeled as a highly conductive aquifer layer. On average, MODFLOW slightly underpredicted the water surface elevation. However, the model error was within the range of survey error. MODFLOW was not highly sensitive to small changes in the estimated surface hydraulic conductivity caused by small changes in vegetation properties, but large decreases in surface hydraulic conductivity dramatically raised the elevation of the water surface.en
dc.description.degreePh. D.en
dc.identifier.otheretd-04072010-173437en
dc.identifier.sourceurlhttp://scholar.lib.vt.edu/theses/available/etd-04072010-173437/en
dc.identifier.urihttp://hdl.handle.net/10919/37590en
dc.publisherVirginia Techen
dc.relation.haspartPiercy_CD_D_2010.pdfen
dc.rightsIn Copyrighten
dc.rights.urihttp://rightsstatements.org/vocab/InC/1.0/en
dc.subjectwetlandsen
dc.subjectvegetated flowen
dc.subjecthydraulic resistanceen
dc.subjectvegetationen
dc.subjectModelingen
dc.titleHydraulic Resistance due to Emergent Wetland Vegetationen
dc.typeDissertationen
thesis.degree.disciplineBiological Systems Engineeringen
thesis.degree.grantorVirginia Polytechnic Institute and State Universityen
thesis.degree.leveldoctoralen
thesis.degree.namePh. D.en

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