Browsing by Author "Kuo, Chin Y."
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- Adhesive areal sampling of gravel bed streamsFripp, Jon Brooks (Virginia Tech, 1991-05-05)The characteristics of a given stream or river are linked to the material that makes up its channel bed. Usually, a vertical stratification by particle size can be recognized. The presence a coarser surface layer is considered to be one of the most important features of a gravel bed stream. Since this surface layer consists of a distinct population of material, it is necessary to be able to separate it from the underlying material and quantify it distinctly. This is done through surface sampling. Two of the most common adhesive areal sampling techniques, and the subject of the present work, are known as clay and wax sampling. If the material obtained in an areal sample is analyzed as a frequency distribution by weight, it has been shown that the size distribution is biased in favor of the larger particles when compared to the results of a bulk sample. The present research shows that this bias is dependent not only upon the sampling method used to remove the material but also upon the size distribution of the sample itself. Not only are the raw results of areal samples not comparable with volumetric samples, but they are not comparable with other areal samples. Before any comparisons are made among areal samples, it is recommended that the size distribution of each areal sample be first converted into the size distribution that would have resulted from an equivalent volumetric sample. The features and limitations of the gravel simulation model that is used to obtain the necessary conversion formula is also the subject of the present work. In addition, the conversion of both matrix and framework supported gravel mixtures that has been areally sampled with either clay or wax, is addressed. Finally, criteria for approximating the minimum depth required for a volumetric sample is presented.
- Control of salinity intrusion caused by sea level riseGudmundsson, Kristinn (Virginia Tech, 1991-05-24)The objectives of this research are to take advance steps to assess the potential impacts of sea level rise on our nation's estuarine environments and water resources management. Specific engineering solutions to control salinity intrusion are studied. Structure measures such as construction of tidal barriers, tidal locks, and through long term stream flow augmentation are investigated for their suitability. Quantification of the extent of the impacts is accomplished by means of computer model simulations. A laterally integrated two-dimensional. time dependent. finite difference numerical model is used to study time-varying tidal height. current and salinity. Through a selected estuary. parametric studies on scenarios of projected sea level rise, stream flow, channel roughness, change in cross-section profile, etc. are performed in order to have an in-depth understanding of estuarine processes for cases such as present condition versus future sea level rise, with or without control measures. The results of the parametric studies are summarized and engineering applications of individual control methods are discussed.
- The development of an evaluation method for best management practices on agricultural landsStavros, Robert William (Virginia Polytechnic Institute and State University, 1987)To help local, rural planners make decisions on which Best Management Practices (BMPs) are most appropriate for the control of Non-Point Sources of Pollution (NPSP) within their jurisdiction, a method is developed for unbiased site-specific evaluation of BMPs appropriateness. An appropriate BMP is functional, practical and cost effective. The method developed is a rational method suitable for the general evaluation of agricultural BMPs to control NPSP in rural watersheds. The method is functional, practical, and cost effective because it uses existing data and personnel wherever and whenever possible. Unlike other NPSP modeling methods, this method lends itself to the selective application of BMPs throughout the watershed based on its actual land use and physical composition. This means, BMP's can be applied to the entire watershed uniformly or applied to a subset of the watershed based on selection criteria such as field slope, soil type, or existing cover crop. In addition, a combination of selection criteria can be used, and a combination of BMPs. This flexibility in selecting various BMPs and BMP combinations, allows planners to pose many different schemes for controlling NPSP within the watershed. The results of the schemes can be compared to determine which scheme is the most appropriate for use within the specific watershed. The method developed relies heavily on the United States Department of Agriculture's Soil Conservation Service's (SCS) Universal Soil Loss Equation (USLE) and uses data already being collected by the SCS and the Agricultural Stabilization and Conservation Service (ASCS). The method does require the creation of Hydrologic Response Units (HRUs) comprised of unique combinations or soil type and land use areas. To demonstrate the method's ability to select an effective BMPs for a watershed, a series of BMP scenarios were evaluated. The BMP scenarios were divided into three categories: a uniform application of a BMP throughout the watershed; a selective application of a BMP throughout the watershed and; the selective application of a set of BMP's throughout the watershed. Using a series of trial runs, the benefits of using the method were demonstrated. For example, similar results were obtained using a cropping BMP of "Corn, grain, soybean and cover" throughout the sample, and a ''no-till" BMP on 3 percent of the sample. This type of information was used by economic modelers to help target precious BMP implementation dollars. As an indirect result of the method's HRU development, it was possible to test the independence of each of the USLE factors within the Nansemond/Chuckatuck watershed. The results of the Duncan's Multiple Range Test shows an interdependence between the "soil type and the cover", "overland flow versus cover", and "overland flow versus soil type".
- Effective properties for flow in heterogeneous porous mediaZhu, Junlin (Virginia Tech, 1990)Modeling of groundwater flow and chemical transport calls for a good characterization of heterogeneity of soil properties. The effects of variabilities of soil properties at local scale on the mean behavior of heterogeneous flows were investigated via Monte Carlo method. Assuming log-normal distribution of conductivity and capillary pressure head being a stochastic process, the mean behavior model defined by effective properties was derived to predict the mean behavior of heterogeneous flows. Effective parameters were evaluated numerically and were parameterized in terms of statistics of randomly distributed soil properties and flow characteristics. Monte Carlo simulations were performed to reveal the mean behaviors of steady unsaturated gravity flows, transient areal source infiltration and transient point source infiltration in heterogeneous porous media. The most important findings include (a) the effective conductivity is between the geometric mean and the arithmetic mean, (b) the effective conductivity is time dependent. The derivation of a mean behavior model and the capability of parametrizing the effective properties make it possible to use current deterministic models to predict the mean behavior with minimum changes in the constitutive relations, specifically adding the dependence on the flow characteristic to the K-S-P relations. The mean model derived in this study was applied to a field site, good agreement was found between the model prediction and field data.
- Effectiveness of BMPs for stormwater management in urbanized watershedsKuo, Chin Y.; Loganathan, G. V.; Cox, William E.; Shrestha, Surendra Prakash, 1957-; Ying, Ker-Jen (Virginia Water Resources Research Center, Virginia Polytechnic Institute and State University, 1988-12)
- Evaluation of sediment yields due to urban developmentKuo, Chin Y. (Water Resources Research Center, Virginia Polytechnic Institute and State University, 1976)
- An examination of stream reaeration coefficients and hydraulic conditions in a pool-and-riffle streamSmoot, James Lloyd (Virginia Polytechnic Institute and State University, 1988)Oxygen transfer between flowing surface waters and the atmosphere can be mathematically described as a first-order reaction and is known as stream reaeration. The first-order rate coefficient or stream reaeration coefficient is a necessary input parameter to stream water-quality models and is partially controlled by the hydraulic conditions of the stream. These coefficients may vary for a given stream reach because of varying hydraulic characteristics brought about by streamflow changes. Hydraulic measurements and reaeration coefficient determinations were made on four pool-and-riffle reaches of Middle Fork Beargrass Creek near Louisville, Kentucky using the hydrocarbon gas tracer technique. Measurements were made on each reach for up to seven streamflow conditions ranging from extremely low to medium. Contrary to published findings applicable to reaches not characterized by a series of pools and riffles, the reaeration coefficient was shown to increase with increasing streamflow for all four reaches studied. Therefore, stream water-quality models developed for these, or similar, stream reaches using reaeration coefficients determined at normal streamflow conditions may over estimate the influence of atmospheric reaeration under a much lower flow condition, such as extreme low flow--the selected critical condition for which water-quality models are commonly developed. Twenty-five published equations used for estimating stream reaeration coefficients were evaluated using the measured hydraulic and reaeration data and were shown to generate highly variable and generally inaccurate predictions. Over half of the equations generated mean prediction errors of more than 50 percent. The best equation overall generated a mean prediction error of 15 percent. The equations were also shown to be highly sensitive to the methods used for determining the input parameter values. Four equations were statistically developed from the data collected in this research. Two of the equations provided more accurate estimates for the four studied reaches than any of the 25 published equations. Mean prediction errors for the two were 1.2 and 9.2 percent. For verification, the developed equations were also evaluated against the 25 published equations using published reaeration and hydraulic data from 39 hydrocarbon gas tracer measurements on other streams. The two developed equations which were most accurate for the four study reaches were also determined to be superior to all of the 25 published equations using the verification data. Mean prediction errors for the two equations using the verification data were 2.3 and 5.5 percent.
- Formulation of the particle size distribution effects on the rheology and hydraulics of highly-concentrated suspensionsDabak, Turgay (Virginia Polytechnic Institute and State University, 1986)A formulation was developed for the rheological characterization of highly concentrated suspensions, accounting for the physical effects of particle size distribution. A number of dimensionless parameters were developed signifying the physical characteristics of the solids and the vehicle fluid, and functionally related to the yield-stress and a flow parameter. Each of these expressions of the formulation contains an empirical dimensionless coefficient accounting for the interparticle and fluid/solid interactions that are not explained by the physical parameters involved. A formulation and a methodology were also developed for predicting the shear viscosity behavior of highly concentrated suspensions at low and high shear-rates through the use of three parameters signifying effects of particle size distribution. A number of applications were made using various non-coal and limited coal-liquid mixture data reported in the literature to demonstrate the general validity of the formulations. A methodology was proposed for the analysis of the particle size distribution effects on the overall optimum energy efficiency during hydraulic transportation and particle size reduction. The computer model developed for this purpose was employed to evaluate the transportation energy consumption and the energy consumed in the grinding process to prepare the slurry, in pipes of various sizes and lengths for a coal slurry of various specified particle size distributions and concentrations. Correlations obtained indicated the sensitivity of transportation energy efficiency to various parameters including the maximum packing concentration, relative concentration, specific surface area of particles, surface area mean size, pipe size and length, and annual mixture throughput. The results of combined energy calculations have shown that the particle size distribution and related physical parameters can significantly affect the energy efficiency due to both grinding and transportation, and the delivered cost of slurry fuels.
- Lift on a sphere in shear flow near flat channel bedYing, Ker-Jen (Virginia Tech, 1991)The lift and drag forces exerting on a sphere immersed in a shear flow above a flat channel bed are evaluated by solving the steady three-dimensional Navier-Stokes equations. The numerical technique which combines the Newton iteration method and the finite element method is used to solve the non-linear Navier-Stokes equations. The technique first linearizes the non-linear terms in the partial differential equations, then solves the linearized equations by the finite element method. The Newton iteration method is used to linearize the non-linear equations. Since the iteration method requires a good initial guess, the linear solution of the partial differential equations is used for the initial guess, where the linear solution is the obtained by solving the differential equations without non-linear terms. The computer model developed can evaluate the lift coefficients of a sphere stationed at various distance from the channel bed. The computational results agree very well with the experimental measurements cited in the literature. The lift coefficient of the sphere changes with the undisturbed approaching velocity profile as well as the gap ratio which is the ratio of the distance between the sphere and the channel bed and the diameter of sphere. For fixed gap ratios, higher Reynolds number gives smaller lift coefficient than that of the lower Reynolds number. On the other hand, the lift coefficient also changes with the diameter of sphere for each fixed gap ratio. For small gap ratios, the lift coefficient increases as the diameter of sphere increases. For large gap ratios, the lift coefficient increases in the negative (downward) direction as the diameter of sphere increases.
- Methods of analyzing instream flowsLoganathan, G. V.; Kuo, Chin Y.; McCormick, T. C. (Timothy C.), 1861- (Virginia Water Resources Research Center, Virginia Polytechnic Institute and State University, 1985-10)
- Simulation of phosphorus transport in vegetative filter stripsLee, Dowon (Virginia Polytechnic Institute and State University, 1987)This study investigated the effectiveness of vegetative filter strips (VFS) in removing phosphorus from surface runoff. Dissolved and particulate nutrients were treated separately due to differing transport and removal mechanisms. Nutrient transport in VFS appears to be a function of runoff rate, concentration and size distribution of suspended solids, and biological factors that influence hydrologic and chemical processes in filter strips. Three sets of experimental field plots were constructed to simulate VFS. Each set consisted of three plots containing sediment and nutrient source areas and 0.0, 4.6, or 9.1 m grass filter strips. Artificial rainfall was applied to the plots, and surface runoff, soil, and plant material samples were collected and physically and chemically analyzed. The VFS reduced surface runoff, suspended solids, and phosphorus losses. Most removal of sediment and phosphorus was accomplished in the first few meters of the VFS. The filter strips did not remove phosphorus as effectively as sediment, due to their ineffectiveness for filtering dissolved phosphorus and sediment-bound phosphorus associated with fine particles. The VFS often increased orthophosphorus losses in surface runoff. Laboratory batch experiments of phosph~rus desorption reaction suggested that plant residues, living plant canopy, and soil components of the strips could release dissolved phosphorus to surface runoff. A modified Elovich equation and a diffusion-control model were used to describe the phosphorus release from the plant and soil materials. A computer model, GRAPH, was developed to simulate phosphorus transport in VFS by incorporating phosphorus transport submodels into the VFS model in SEDIMOT II, a stormwater and sediment transport model. The model considers the effects of advection processes, infiltration, biological uptake, phosphorus desorption from the soil surface to runoff, the adsorption of dissolved phosphorus to suspended solids in runoff, and the effects of dynamic changes in the sediment size distribution on chemical transport. GRAPH was verified using the results of the physical plot simulations. The model's predictions and observed phosphorus transport compared favorably. Sensitivity analysis suggested that sediment and phosphorus removal was sensitive to the input parameters in the order: filter length and width, grass spacing, and filter slope and surface roughness. Increased filter width and length and aboveground biomass increased orthophosphorus loss from VFS.
- A statistical approach to urban stormwater detention planningSegarra, Rafael Ivan (Virginia Polytechnic Institute and State University, 1988)A statistical model has been developed to study the long-term behaviour of a stormwater detention unit. This unit stores a portion of the incoming runoff, corresponding to the empty space available in the unit, from which runoff is pumped to a treatment plant. The objective is to avoid, as much as possible, the discharge of untreated runoff to receiving bodies of water. The model was developed by considering the arrival of independent runoff events at the urban catchment. The process variables of event depth, duration, and interevent time were treated as independent, identically distributed random variables. A storage equation was formulated from which the probability of detention unit overflow was obtained. With this distribution it was possible to define the trap efficiency of the unit in terms of the long-term fraction of the runoff volume trapped by the storage unit. The trap efficiency expressions define storage/ treatment isoquants, which represent the combinations of storage capacity, treatment rate, and the sewer system runoff trapping capacity, which provide a fixed level of runoff control. A pollutant load model was also formulated, based on a first-order washoff model. This model was used to define pollutant control isoquants. Optimal values of the required storage capacity and treatment rate were obtained by treating the isoquants as production functions. Applying the results of production function theory, a cost minimization problem was solved for the value of the storage capacity and treatment rate, for prescribed runoff and pollutant trap efficiency levels. The results obtained with the statistical model compared well with results obtained from major simulation models. The statistical approach offers an advantage in that no simulation is required to obtain the isoquants, as the expressions are analytical, thus greatly simplifying the optimization process. Also, the evaluation of the storage unit pollutant trap efficiency can be easily evaluated for any type of pollutant whose washoff rate is known.
- A study of infiltration trenchesKuo, Chin Y.; Zhu, J. L.; Dollard, L. A. (Virginia Water Resources Research Center, Virginia Polytechnic Institute and State University, 1989)
- A synthetic unit sedimentgraph for ungaged watershedsChen, Victor J. (Virginia Polytechnic Institute and State University, 1984)The concept of the unit sediment graph is important and useful in the study of non-point source pollutant transport, in the estimation of sediment yield and in the design of sediment basins. At the present time, a physically sound method of deriving unit sediment graphs for ungauged small watersheds is not available. Based on synthetic principles as well as linear and time-invariant principles, applied to the systems approach of hydrology, a synthetic model has been developed to derive the unit sediment graph and to generate the sediment graph for an ungauged watershed. The model is limited to the generation of single peak sediment graphs where the sediment particle sizes of interest range from 0.002 mm to 1.0 mm. Seven small watersheds located in the lower Potomac River Basin were selected for this study. For each watershed about 12 storm events were included in the study. Available hourly rainfall and streamflow data were collected and used for model calibration. Results of both"spatial" and"temporal" verification show that agreement between the synthetic and actual sediment graphs is fairly good. A new rigorous definition regarding the unit sediment graph has been established. The study is based on a one-hour unit sediment graph which is defined as the direct sediment graph resulting from 1 unit of effective sediment yield of a storm of 1-hour duration generated uniformly over the basin at a uniform rate. Thus, the one-hour sediment graph of a storm for a specified watershed can be generated by convolving the one-hour unit sediment graph with the effective sediment erosion of one hour duration provided that the rainfall record and characteristics of that watershed are known.
- Vessel induced physical effects related to navigation changes on the Kanawha River, West VirginiaJordan, David M. (Virginia Tech, 1988-09-05)The U.S. Army Corps of Engineers is investigating ways to improve lockage efficiency at the Marmet Locks on the Kanawha River, West Virginia. These improvements are needed to meet projected future river traffic demands. A physical effects prediction model has been developed to evaluate the changes on the river due to changes in future traffic patterns and tow configurations. The model has been verified based on the field measured data which cover a wide range of traffic conditions. The model consists of selected equations which simulate ambient velocities; wind waves; diverging waves; squat and backwater generated by the tows; and propeller jet velocities and its associated entrainment velocities. Based on the calculated velocities, concentrations of suspended sediment induced by the disturbance are estimated, at the time of disturbance and after suspended sediments have been allowed to settle. Field data on tow induced velocity changes in a back channel and a tributary are also analyzed. The effects of passing recreational boats has also been measured in the main channel.