Browsing by Author "Helena Mitasova, Committee Member"

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A Comparative Study between FLEXPART-WRF and HYSPLIT in an Operational Setting: Analysis of Fire Emissions across complex geography using WRF
(2010-04-07) Pagano, Lara Elizabeth; Ryan Boyles, Committee Chair; Sethu Raman, Committee Member; Hugh Devine, Committee Member; Helena Mitasova, Committee Member
Transport and dispersion models are frequently used by the meteorological community to understand and predict the trajectories of anthropogenic, natural and accidental chemical releases of hazardous materials. There are several reputable dispersion models that can handle a wide range of applications under the direction of global, synoptic or mesoscale forecasts. One such application is the forecast of smoke emissions from wildfires which is important to operational air quality and meteorology communities. Fire emissions have direct impacts to property and respiratory health. Operational meteorologists are responsible for providing meteorological support to emergency management agencies within their county warning area in the event of incidents involving harmful chemical releases, radiation and smoke emissions. A comparative study between two dispersion models during recent wildfire events across complex geography is presented to identify the sensitivities of each dispersion model and the operational benefits of utilizing each model for smoke emission forecasts. FLEXPART-WRF is a Lagrangian dispersion model that predicts the transport and dispersion of trace gases forward or backward from a point, line or area source. Similar to FLEXPART-WRF, the HYbrid Single Particle Integrated Trajectory (HYSPLIT) model simulates the dispersive nature of the environment. Model configuration differences include the prerequisite meteorological data, density correction, dispersion algorithms and removal calculations. Mesoscale meteorological models are needed to provide the ambient environment as well as simulate the small scale flux exchanges and boundary layer processes that can affect dispersion simulations on a local and regional scale. Therefore, both dispersion models are using meteorological input from the WRF ARW mesoscale atmospheric model using both a 12 km and 4 km grid-resolution domain. Two fire events, one along the coast of the Mid-Atlantic (Evans Road Case) and the other within the Appalachians (South Mountain Case), are investigated for this analysis. Simulations are analyzed to identify the relative performance of each dispersion model given identical meteorological input. The dispersion models are evaluated for accurate dispersive simulations and also on their ability to support operational forecast needs. Satellite observations provided by the National Environmental Satellite, Data and Information Service along with other remote sensing tools are used for evaluation of dispersion model performance. The spatial analysis, based on both case studies and resolutions, indicates that HYSPLIT disperses particles 10-20 degrees to the right of FLEXPART-WRF for at least a portion of the simulations. FLEXPART-WRF better replicates the observed plume and also yields a higher air concentration throughout most of the simulations, especially downwind. These differences in plume compositions and concentrations are likely linked to the differing diffusion equations. While the air concentration differences are small compared to the amount being released, the spatial differences are statistically significant. To account for the air concentration differences, dry deposition is analyzed. HYSPLIT sporadically deposited significantly more mass to the ground compared to FLEXPART-WRF. These deposition differences impact the diffusion process and account for only part of the concentration variations. This study suggests that FLEXPART-WRF performs better compared to HYSPLIT and may serve as an improved operational tool.
Estimation of Coastal Evolution through Coupled Wave Modeling and GIS Techniques.
(2010-10-25) Jin, Qiang; Margery Overton, Committee Chair; Montserrat Fuentes, Committee Member; Billy Edge, Committee Member; Helena Mitasova, Committee Member
Modeling Erosion on Construction Sites
(2004-11-23) Moore, Amber Dawn; Helena Mitasova, Committee Member; Greg Jennings, Committee Member; Keith Cassel, Committee Co-Chair; Rich McLaughlin, Committee Chair
Our first objective was to develop suitable construction site parameters for the validated WEPP erosion prediction model. Predicted values were correlated with field observations for runoff and sediment yield. Runoff volumes and sediment yields similar to those measured on an active construction site were achieved by removing the A horizon from the soil input parameter and applying a landcover parameter with no ground cover and minimal roughness. Increasing critical shear stress to 384 Pa (as recommended by an erosion mat manufacturer) efficiently predicted runoff volume (E = 0.66) and sediment yield (E = 0.57) when compared to a construction site stabilized with straw, tar and erosion blankets. Our second and third objectives were to use to evaluate state-approved sediment traps and riparian buffers with WEPP and GeoWEPP, and to create erosion and sediment control scenarios that would achieve the NC water quality standard of 50 Nephlometric Turbidity Units. Two sediment traps on an actual school construction site were modeled with WEPP, and a 15.2 m width forest buffer on a planned golf course site was modeled with GeoWEPP. WEPP predicted average trapping efficiencies of sediment traps A and B to meet the NC standard of 70 % trapping efficiency. WEPP predicted runoff from sediment trap B met the turbidity standard for 11 % of the modeled storm events. GeoWEPP predicted that the riparian buffers would not meet the turbidity standard for any of the modeled storm events. The existing sediment controls were adjusted to meet water quality standards by increasing sediment trap size, replacing free-draining traps rock outlets with standing pools behind culvert outlets, extending the riparian buffer, and adding vegetation to highly erosive areas determined by GeoWEPP. Turbidity standards were met on watershed A by removing the outlet from the second sediment trap and increasing the trap area 6-fold. WEPP and GeoWEPP are useful for modeling construction sites and for designing erosion control scenarios, although the new parameters and the GeoWEPP model will need to be validated on other construction sites to improve confidence in the model output.
Quantifying rates, controls, and spatiotemporal dynamics of water and nitrogen fluxes through the streambed of West Bear Creek, North Carolina, USA
(2008-12-08) Kennedy, Casey David; Reide Corbett, Committee Member; David DeMaster, Committee Member; Helena Mitasova, Committee Member; David Genereux, Committee Chair
This paper presents results on the rates and spatiotemporal dynamics of the coupled water flux (v) and nitrogen (N) fluxes (mainly fNO3 and fDON for nitrate and dissolved organic N) through a streambed in an agricultural watershed in North Carolina. Physical and chemical variables were measured at numerous points in the streambed of a 0.26 km reach: hydraulic conductivity (K) and head gradient (J), and concentrations of NO3- and other N species in the streambed groundwater, from which water (v=KJ) and N fluxes (e.g., fNO3=v[NO3-]) through the streambed were computed, mapped, and integrated in space. The result was a novel set of streambed maps of the linked variables (K, J, v, N concentrations and fluxes), showing their spatial variability and how it varied over a year (based on 7 bimonthly sets of maps). Mean fNO3 during the study year was 154 mmol m-2 day-1; this NO3- flux, together with that of DON (fDON = 17 mmol m-2 day-1) accounted for >99% of the total dissolved N flux through the streambed. Repeat measurements at the same locations on the streambed show significant temporal variability in fNO3, largely controlled by changes in v rather than changes in [NO3-]. One of the clearest and most temporally-persistent aspects of spatial variability was lateral variability across the channel from bank to bank. K and v had â€œcenter-highâ€ patterns (greater values in the center of the channel); this distribution of K (ultimately a reflection of sediment dynamics in the channel) apparently focuses groundwater discharge toward the center of the channel. The opposite â€œcenter-lowâ€ pattern was found for J, [NO3-], and (to a lesser extent) fNO3. Contrary to suggestions in some prior work, J was not a good index for v. fNO3 was characterized by localized zones of high and low values that changed in size and shape over time but remained in basically the same locations (the same was true of K, J, [NO3-], though less so for v), with 70% of NO3- flux occurring through about 38% of the streambed area. Lateral distributions of the physical hydrologic attributes (K, J, v) were highly symmetrical across the channel, while those of [NO3-] and fNO3 showed higher values on the right than left, likely a reflection of different N use on opposite sides of the stream. These and other results show the streambed-based approach taken here can offer a number of insights not possible with reach mass-balance approaches in which net exchange between a stream reach and surrounding groundwater is calculated using surface water data.
Stream Network Delineation from High-Resolution Digital Elevation Models.
(2006-12-08) Colson, Thomas Payton; Helena Mitasova, Committee Member; James D. Gregory, Committee Chair; Stacy A. C. Nelson, Committee Co-Chair; Montserrat Fuentes, Committee Member
Effective environmental management requires an accurate inventory of the resources to be managed. Decision makers often lack the technical expertise necessary to understand the limitations of environmental data. The State of North Carolina is re-surveying elevations using Light Detection and Ranging to re-delineate floodplains. These data allow analysts to predict flood inundation extents of design storms in order to better manage flood-prone terrain. Conversely, many environmental management functions in North Carolina, such as calculating stream length for hydrologic modeling and riparian buffer protection, rely upon outdated paper maps such as the USGS topographic map series for the determination of the location of stream "blue lines". These cartographic products are inadequate for use in headwater stream mapping when compared to field observations yet no better data source has been found to achieve the accuracy needed for local site planning. This research evaluated the horizontal accuracy and completeness of currently available stream maps compared to stream networks derived from DEMs obtained from the USGS, the North Carolina Floodplain Mapping Program, and interpolated from LiDAR bare-earth elevation points. A unique system combining software and hardware was developed to map headwater catchments with global positioning systems and was used to perform field data collection at nine catchments distributed across four physiographic regions. A method of determining the horizontal accuracy of stream lines shown on maps was developed and used to show that stream networks delineated using high-resolution, interpolated DEMs are more accurately positioned than those on previously published maps or stream networks delineated from currently available DEMs.
Sustainability in Amazonian Development: Human Welfare and Environmental Quality in Colonization Settlements in the Brazilian Amazon.
(2010-07-30) Macintyre, Charles; Erin Sills, Committee Chair; Mullan, Katrina, Committee Member; Frederick Cubbage, Committee Member; Helena Mitasova, Committee Member