Browsing by Subject "Hydrology"
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Item A Hydrological Model of Harrington Sound, Bermuda and its Surrounding Cave Systems(2013-04-23) Stoffer, Jonathan LHarrington Sound, located in east central Bermuda, is almost entirely enclosed by land except for a 26.4 m wide channel called Flatts Inlet. This limited connection to the open ocean restricts Harrington Sound?s tides, resulting in a near 3 hour delay and dampening the tidal range to 35% of those on the coast. By comparing the tidal amplitude and surface area of Harrington Sound, tidal exchange can be determined. Past research has shown Flatts Inlet only supplies the Sound with about half of its tidal water. The remaining tidal exchange enters and leaves the Sound either via groundwater influx through pores in the rock or through the traversable passageways of limestone cave systems in the land that encloses the Sound. The aim of this study was to model hydrodynamic tidal flux and current through marine caves into Harrington Sound. One of the goals of Bermuda?s cave habitat protection plan is to track tidal circulation of water through these cave systems. Information on such cave water transport would facilitate future pollution and nutrient exchange studies. This research was initiated during a six week trip to Bermuda by Jonathan Stoffer as he obtained tidal and water quality data from caves along the perimeter of Harrington Sound. Additional flow data was collected with instruments placed by local cave divers. A YSI 600XLM water quality sonde, Norteck Vector Current Meter, and an in-situ level Aqua TROLL were used to monitor tidal amplitude, periodicity, current velocity, and water quality in cave pools and submerged passages. Profiles of the top 1-2 meters of water at each pool were taken at 56 sites. Tidal gauges were placed in 27 major cave pools surrounding Harrington Sound, as well as Harrington Sound itself, for 48 hours, to monitor tidal propagation through the island. The vector current meter was placed for six weeks to measure water flow in and out of Harrington Sound in six cave passageways known to have high flow rates. The resulting data have been compared to atmospheric data obtained from the Bermuda Weather Service and analyzed using Microsoft Excel, MATLAB and ArcGIS. The final goal of this project was to create a hydrological model able to predict flow rate and water depth in Bermudian caves with water depth data from the ocean and Harrington Sound. In constructing a water budget for Harrington Sound, I was able to account for 72.3% of all tidal inflow and 43.3% of all tidal outflow from the Sound as passing through either Flatt?s Inlet or one of the six tested caves. In creating my tidal models, I was able to achieve an averaged sum of squared deviation (SSD) normalized against count ranging from 5.1x10^-4 to 8.4x10^-4 m^2. The flow model achieved a SSD of 3.8x10^-3 m^2. My data also suggest that exchange between Harrington Sound and other inland waters, through cave systems, does exist.Item Capillary pressure determination using the micropore membrane technique(2012-05) Williams, Akinlolu; Siddiqui, Shameem; Watson, Marshall C.; Menouar, Habib K.Generation of capillary pressure curves is essential to the evaluation of fluid flow phenomenon in the multi-phase region of a reservoir. It is used chiefly for the determination of oil and gas water contacts, the location of transition zones and modeling oil displacements through either water or gas flooding. Unfortunately its measurement is made unattractive by the time-consuming nature of its generation which could be up to six months in some cases. The micropore membrane technique of capillary pressure determination is a novel approach introduced by the Institut Français du Pétrole- IFP, which has the capacity to reduce the time required to generate a full suite of capillary pressure curves, namely – spontaneous imbibition, drainage and imbibition cycles to about a tenth of the time required for conventional methods such as the porous diaphragm restored state method. This research work was conducted to build a setup for capillary pressure measurement that replaces the conventional mercury injection and restored state techniques currently in use in the department’s core analysis laboratory. The setup was used to perform four distinct drainage runs on sandstones and dolomite with different petrophysical properties. Soltrol130-Brine pair was used for the fluid system while all the rock samples were characterized as water-wet. The drainage capillary pressure curves generated were analyzed on the basis of petrophysical analytical tools like pore entry pressure, irreducible water saturation and pore size distribution index. A homogeneity and heterogeneity correlation was established amongst the samples based on the shape of the drainage curves and the analytical tools and this trend was validated using CT scan images which were carried out on the dry core samples. Mercury injection capillary pressure (MICP) test was conducted on one of the samples and a very good match was obtained between the micropore membrane technique and MICP. Further validation of this method was carried out by conduction a re-run on one sample to ensure repeatability of the procedure and accuracy of data collected. The results of the re-run showed an excellent match with the initial run to validate the procedure and accuracy of the data acquisition process of this technique. The success of the validation process and the functionality, flexibility and dynamism of the experimental setup and also the reliability of the procedure all borne out of the reliability of results obtained, with each experiment concluded in about 24hours using reservoir fluids confirms the micropore membrane technique to be a robust, simple, convenient and time efficient method for the generation of representative capillary pressure data for reservoir rock samples.Item Characterizing the subglacial hydrology of Thwaites Glacier, West Antarctica using airborne radar sounding(2014-05) Schroeder, Dustin Matthew; Blankenship, Donald D.; Raney, R. Keith; Anderson, John B; Ghattas, Omar; Hesse, Marc A; Mohrig, DavidHydrologic, lithologic, and geothermal basal boundary conditions can exert strong, even dominating, control on the evolution, stability, and sea level contribution of ice sheets and glaciers. However, the scales at which the physical processes and observable signatures of this control occur are typically smaller than the spatial resolutions currently achievable using ice penetrating radar. Further, the strength of radar bed echo returns is affected by the material and geometric properties of the bed as well as englacial attenuation from unknown ice temperature and chemistry, making assessment of basal conditions from echo strengths difficult. To address these challenges in interpreting basal properties at glaciologically relevant scales, a new algorithmic approach is applied to measuring the radar scattering function of the bed in terms of the relative contribution of angularly narrow specular energy and isotropically scattered diffuse energy. This relative specularity content is insensitive to englacial attenuation and can be used to constrain the geometry of the bed down to the centimeter scale. This approach is applied to an airborne radar sounding survey of Thwaites Glacier, West Antarctica using the information in the along-track scattering function to assess the extent and geometry of water across the catchment and detect the transition of that water from distributed canals to concentrated channels. This information is also used to constrain the morphology of subglacial bedforms and infer that the distribution of deformable sediments and exposed bedrock is similar to deglaciated paleo ice streams that experienced meltwater intensive retreats. Finally, models of radar echo strength and subglacial water routing are compared to estimate a catchment-wide distribution of geothermal flux consistent with rift-associated magma migration and volcanism. These observations of basal conditions provide new context for the past, current, and future evolution of Thwaites Glacier, the West Antarctic Ice Sheet, and their contribution to global sea level.Item Comparison of Horton's, Smith's, and Green-Ampt's infiltration equations using flooding infiltrometer data in engineering applications(Texas Tech University, 1998-12) Anderson, Michael ColeThe hydrologic cycle represents the interaction of water between the earth's surface and the earth's atmosphere. Precipitation, evaporation, interception, infiltration, surface runoff, and subsurface flow make up the integral components of the hydrologic cycle (Veissman et al., 1989). The hydrologic cycle is of major interest to engineers. Many times, small, ungaged watersheds are the focus of engineering projects. The desired project outcome consists of the basin's direct runoff hydrograph because the runoff hydrograph provides a peak flow rate, time of peak flow, and a volume of direct runoff. Engineers use these values to design flood protection. Engineers are always searching for more accurate ways to model small, ungaged watersheds. The current standard practice is to use a design storm in conjunction with the Natural Resources Conservation Service (NRCS) Curve Number (CN) Procedure to predict abstractions for a storm event to produce a direct runoff hydrograph for the basin (Veissman et al., 1989). The NRCS-CN procedure is simple to use to estimate abstractions, but simplicity does not always produce the most accurate solution. The major research objective is to show that infiltration equations improve confidence in the results of a surface-runoff analysis for intense short-duration stormevents. The infiltration equations used for this research are the Horton (1933), Smith (1972), and Green-Ampt(1911) infiltration equations.Item Deep Water Mixing Prevents Harmful Algal Bloom Formation: Implications for Managed Fisheries Refugia(2012-10-19) Hayden, Natanya JeanneInflows affect water quality, food web dynamics, and even the incidence of harmful algal blooms. It may be that inflows can be manipulated to create refuge habitat for biota trying to escape poor environmental conditions, such as fish populations in lakes during times of toxic Prymnesium parvum blooms. Water availability sometimes can be an issue, especially in arid climates, which limits this approach to management. Utilizing source water from deeper depths to displace surface waters, however, might effectively mimic inflow events. I test this notion by conducting in-lake mesocosm experiments with natural plankton communities where I manipulate hydraulic flushing. Results show that P. parvum cell density is reduced by 69%, and ambient toxicity completely ameliorates during pre-bloom conditions in the lake. During conditions of bloom development, population density is reduced by 53%, toxicity by 57%, and bloom proportions are never reached. There is minimal effect of these inflows on total phytoplankton and zooplankton biomass, and little effect on water quality. Shifts toward more rapidly growing phytoplankton taxa are observed, as are enhanced copepod nauplii. In other words, while inflows using deep waters suppress P. parvum bloom initiation and development, they are benign to other aspects of the lower food web and environment. The results from using deep lake water to suppress harmful algal blooms indicate this may be a promising management approach and further studies are recommended to test whether this mitigating effect can translate to a large-scale in-lake treatment.Item Effects of drought on climates in Texas(2016-05) Born, Katie Lynn; Maidment, David R.; McKinney, Daenne C.Drought is a growing global concern with severe ramifications for humanity. Texas is one of many places that faces recurring severe droughts, threatening the livelihood of its people. Within the bounds of Texas there are many different climates, and drought can effect these climates differently. The south east edge of the state tend to have a more humid temperate climate, whereas to the north west it becomes hot and arid. Within one state, the climate goes from subtropical to desert. This opens up the state to a lot of variability as to water supply. This Master's Report investigates the effects that drought has on the varied climates within Texas. Five areas in Texas were chosen to represent the most distinctive climatic shifts. Several hydrologic variables area accessed between regions and drought severity. The hydrologic variables examined are the 2-m above ground temperature, evapotranspiration, latent heat flux, sensible heat flux, net longwave radiation flux, net shortwave radiation flux, total hourly precipitation, and surface runoff. The scope of the analysis is limited to period of January 2000 to January 2013. Two one month periods were selected to highlight changes under dry conditions compared to normal to wet conditions; July 2007 and July 2011, respectively. In all of the areas examined, the earth was shown to be parched and dry after periods of less than average precipitation and more willing to take in water than leave it to be surface runoff. An initial investigation into the climates of the five areas showed that the temperatures in the more southeastern regions were more dramatically affected by the occurrence of drought. When drought came along to these southeastern regions, it transformed the climate into something more similar to that typically found in the northwestern regions. The more humid areas to the south east were consistently more dramatically affected by the drought than the arid regions to the north west. The more arid climates started out more similar to that of a drought ridden zone, leaving less room to change. However, all of the areas are significantly impacted by drought through a declining water supply.Item Environmentally related water trading, transfers and environmental flows: welfare, water demand and flows(Texas A&M University, 2008-10-10) Han, Man SeungThis dissertation reports on economic studies of Texas Interbasin Water Transfers (IBT) as a way to lessen expected water shortages, Texas minimum freshwater inflows requirements (FWIB) to protect environmental flows and the general policy setup when generators of environmental commodities might be able to sell credits in multiple markets. The Texas-based studies address economic, hydrological and environmental impacts, focusing on welfare gain, water demand, environmental flows and complementary relationship of environmental commodities. Conduct of the two Texas studies required development of a Texas surface water model. The developed model incorporates: (a) uncertain weather patterns and supply of water; (b) river flows in most of the Texas river basins - twenty-one basins excluding only the Rio Grande; (c) demand for water by agricultural, municipal and industrial/ mining water; (d) IBT possibilities; (e) evaporation losses; and (e) return flows across the modeled basins. In studying the interbasin water transfers, three IBT projects where chosen as economically justified relocating water largely for municipal and industrial/mining uses. These IBT projects had the effect of increasing water use and instream flows in the IBT destination basins, but decreasing those in the source basins. In studying the freshwater inflows the study revealed that the suggested inflow constraints were met on average and that the inflow levels for two basins had to be lowered for the constraints to be feasible. This suggests that the contemplated limits are too high and that either multiple basin or flow dependent limits need to be developed. The results also showed that under the average FWIB constraints and IBT implementation, welfare loss from the FWIB constraints was greatly reduced due to the IBT projects which were simultaneously implemented. In the study of multiple environmental commodity markets, the results indicate that generated credits should be sold in multiple markets only when market caps are set up close to socially efficient (so called first-best) caps: this implies that marginal benefit curves are very steep. However, restricting selling into just single market achieved the same net benefits as multiple markets did when market caps were set up at levels less than the first-best caps.Item Evaluation of Scale Issues in SWAT(2010-07-14) Mylevaganam, SivarajahIn Soil and Water Assessment Tool (SWAT), oftentimes, Critical Source Area (CSA), the minimum upstream drainage area that is required to initiate a stream, is used to subdivide a watershed. In the current literature, CSA has been used as a trial and error process to define the subwatershed levels. On the other hand, the ongoing collaboration of the United States Environmental Protection Agency Office of Water and the United States Geological Survey has promoted a national level predefined catchments and flowlines called National Hydrography Dataset (NHD) Plus to ease watershed modeling in the United States. The introduction of NHDPlus can eliminate the uncertain nature in defining the number of subwatersheds required to model the hydrologic system. This study demonstrates an integrated modeling environment with SWAT and NHDPlus spatial datasets. A spatial tool that was developed in a Geographical Information System (GIS) environment to by-pass the default watershed delineation in ArcSWAT, the GIS interface to SWAT, with the introduction of NHDPlus catchments and flowlines, was used in this study. This study investigates the effect of the spatial size (catchment area) of the NHDPlus and the input data resolution (cell/pixel size) within NHDPlus catchments on SWAT streamflow and sediment prediction. In addition, an entropy based watershed subdivision scheme is presented by using the landuse and soil spatial datasets with the conventional CSA approach to investigate if one of the CSAs can be considered to produce the best SWAT prediction on streamflow. Two watersheds (Kings Creek, Texas and Sugar Creek, Indiana) were used in this study. The study shows that there exists a subwatershed map that does not belong to one of the subwatershed maps produced through conventional CSA approach, to produce a better result on uncalibrated monthly SWAT streamflow prediction. Beyond the critical threshold, the CSA threshold which gives the best uncalibrated monthly streamflow prediction among a given set of CSAs, the SWAT performance can be improved further by subdividing some of the subwatersheds at this critical threshold. The study also shows that the input data resolution (within each NHDPlus catchments) does not have an influence on SWAT streamflow prediction for the selected watersheds. However, there is a change on streamflow prediction as the area of the NHDPlus catchment changes. Beyond a certain catchment size (8-9% of the watershed area), as the input data resolution becomes finer, the total sediment increases whereas the sediment prediction in high flow regime decreases. As the NHDPlus catchment size changes, the stream power has an influence on total sediment prediction. However, as the input data resolution changes, but keeping the NHDPlus catchment size constant, the Modified Universal Soil Loss Equation topographic factor has an influence on total sediment prediction.Item Evaluation of the conduit sizing portion of the design procedure for storm drain networks in Texas(Texas Tech University, 2004-08) Keister, Heather RaeNot availableItem The fluviageny, a method for analyzing temporal river fragmentation using phylogenetics(2015-05) Gordon, Andrew Lloyd; Howison, James; Arctur, David KPhylogenetic trees have historically been used to determine evolutionary relatedness between organisms. In the past few decades, as we've developed increasingly powerful computational algorithms and toolsets for performing analyses using phylogenetic methods, the use of these trees has expanded into other areas, including biodiversity informatics and geoinformatics. This report proposes using phylogenetic methods to create "fluviagenies" - trees that represent the effects of river fragmentation over time caused by damming. Faculty at the Center for Research in Water Resources at the University of Texas worked to develop tools and documentation for automating the creation of river segment codes (a.k.a., "fluvcodes") based on spatiotemporal data. Python was used to generate fluviageny trees from lists of these codes. The resulting trees can be exported into the appropriate data format for use with various phylogenetics programs. The Fishes of Texas Database (fshesoftexas.org), a comprehensive geospatial database of Texas fish occurrences aggregated and normalized from 42 museum collections around the world, was employed to create an example of how this tool might be used to analyze and hypothesize changes in fish populations as a consequence of river fragmentation. Additionally, this paper serves to theorize and analyze past and future potential uses for phylogenetic trees in various other fields of informatics.Item A geotemporal framework for hydrologic analysis(2005) Goodall, Jonathan Lee; Maidment, David R.Item Groundwater flow controls on coastal water quality and global groundwater ages(2015-05) Befus, Kevin Martin; Cardenas, Meinhard Bayani, 1977-; Gleeson, Thomas P; Hesse, Marc A; Paine, Jeffrey G; Sharp, John MHumanity relies on groundwater. But, current consumption may be outpacing groundwater renewal rates, and anthropogenic activities are altering its quality. This dissertation advances the state of knowledge of how local and regional groundwater dynamics affect its quality and quantity. First, I investigate groundwater discharge patterns and fluxes in three lakes in the Nebraska Sand Hills region and on the island of Rarotonga, Cook Islands, to understand the hydrologic connection between groundwater and surface water in these lacustrine and coastal settings. In Nebraska, I use electrical geophysical methods to characterize the spatial signature of groundwater recharge and discharge to and from the lakes using groundwater salinity patterns. On Rarotonga, a detailed field study of groundwater flow at the intertidal zone shows how groundwater flow influences the thermal regimes of nearshore environments, affecting the biota that live and chemical processes that occur near and below this dynamic interface. Next, a dense network of geophysical surveys across the coastal plain and into the lagoon on Rarotonga constrains multiple features of the larger-scale hydrologic system that are primarily controlled by the local carbonate and volcanic geology on the island. Finally, I give the first estimate of the global storage and spatial distribution of groundwater with a mean age since recharge of less than fifty years. I use several thousand two-dimensional groundwater flow and age-as-mass transport simulations parameterized by the best available hydrologic and geologic datasets. This global analysis suggested that ~6% of the groundwater stored in the upper 2 km of the Earth’s crust is younger than 50 years. Comparing this young groundwater storage to current groundwater depletion rates indicates that more than half of the irrigated areas depending significantly on groundwater could have already used up all of the young groundwater and are using groundwater more quickly than the storage is replenished. Together, these studies advance how to quantify groundwater as a renewable resource through the global estimation of groundwater storage associated with certain timespans and by analyzing the implications of groundwater flow on water quantity and quality in field settings.Item Hydrologic investigation of the NRCS curve number for Texas watersheds using historical records of rainfall and runoff(Texas Tech University, 2002-12) McLendon, DavidNot availableItem Hydrology of urban playa lakes in Lubbock, Texas(Texas Tech University, 1998-08) West, Eric LaneThe Southern High Plains region of Texas and New Mexico contains more than 20,000 small, circular depressions called playa lakes or playas. These playas create a unique physiographic phenomenon where many watersheds in the region are small closed basins in which no outlet from the watershed is present (Gustavson et al., 1994). The presence of playa lakes implies that runoff from the contributing watershed is focused into the playa lake, including chemical constituents associated with the runoff. Also, the fate of the runoff has only two possibilities, evaporation or infiltration. The chemical constituents are therefore treated naturally in playa waters, bound to playa sediments, or transported to the groundwater flow system. At one time, researchers believed that evaporation, rather than infiltration, controlled the fate of water entering playas in the High Plains. This includes work done by C V. Theis (1937) and the Texas Water Development Board (1965). However, more recent investigations are revealing that not only is infiltration significant in playa lakes, it is the primary source of recharge to the groundwater (Wood and Osterkamp, 1984b; Wood and Sanford, 1994; Wood, Rainwater, and Thompson, 1997). In an urban environment, such as the city of Lubbock, the existence of playa lakes is essential to storm drainage as well as recreation (Hertel and Smith, 1994). Little information has been collected concerning the hydrology of these urban playas, some of which have altered bed sediments due to development. In addition, rising groundwater levels and runoff quality concerns are major considerations for city engineers and administrators as well as researchers. Detailed investigations of urban playas will be a valuable tool for determining the interaction of stormwater runoff and groundwater flow systems.Item Implementation of a state hydrologic information system(2007-05) Jantzen, Tyler Landis, 1981-; Maidment, David R.As part of its goal to "unite the nation's water information, to make it universally accessible and useful, and to provide access to the data sources," (CUAHSI, 2007) the Consortium of Universities for the Advancement of Hydrologic Science, Inc. (CUAHSI) has developed a Hydrologic Information System (HIS). An HIS is a tool that provides such uniform access to multiple sources of hydrologic data within a geospatial context, as described in CUAHSI's goal. While the CUAHSI HIS provides access to hydrologic data on a national scale, the need for access to statewide, regional and local hydrologic data has also been recognized. This thesis provides a background for hydrologic information technology, outlines the framework from which a statewide HIS should be created, and describes the Texas HIS prototype created in cooperation with the Texas Natural Resources Information System (TNRIS).Item Interactions between precipitation, evapotranspiration, streamflow, and groundwater in the Southern High Plains(Texas Tech University, 1999-12) Van Hooser, Kara J.The Texas South High Plains region (SHP) is one of the most productive agricultural areas of the nation. Because the climate is semi-arid, water is a principal concern. The general long-term decline in ground-water levels is of concern to planners and agricultural users alike (High Plains Underground Water District No.1 (HPUWD) 1998). Some planners are concerned about a general decline in the watershed runoff yield for streams originating or draining portions of the SHP (Wyatt 1998). The purpose of this research project is to examine the relations between groundwater withdrawals, potential evapotranspiration, and variations in precipitation. In addition, general trends in precipitation, streamflow, groundwater levels, and potential evapotranspiration were examined. This information is important for regional water management issues such as describing low flow conditions for drought definition, identifying locations of declining streamflow, which may decrease property value and evaluating potential contributions from precipitation enhancement. In addition, this information will serve as a baseline for quantification of the effects of alternative management practices on the watersheds.Item Interpreting the Earth's time varying geopotential as observed from space and comparisons to global models of hydrologic transport(2004) Thompson, Paul Frank; Tapley, Byron D.Measurements of temporal changes in Earthís gravitational field were measured using six years of satellite laser ranging (SLR) to Lageos-1 and Lagoes-2 and the results were compared to geophysical models of mass variability for the atmosphere, ocean, and continental hydrology. Annual estimates of spherical harmonic gravity coefficients (degree and order four expansion) derived from the SLR observations when compared to combinations of the mass models had degree correlations that generally exceeded the 90% confidence limit and agreed to about the 1 mm level in terms of geoid height anomaly. The Gravity Recovery and Climate Experiment (GRACE) is measuring Earthís gravitational field approximately every month at spatial scales of a few hundred kilometers. In order to achieve smaller temporal and spatial scales, it is necessary to account for the effects of short period, non-tidal, mass variability which was not previously included in other gravity determinations. Orbital simulations of GRACE showed that the highest degrees were impacted the most by unmodeled variability in the atmosphere, oceans, and continental hydrology (a factor of ~20 increase in degree error in the case of the atmosphere). The use of approximate models gave the greatest reduction in aliasing error for the mid-degrees and higher; however, the lowest degrees (~2-5) were dominated by the sensitivity of the GRACE processing system to systematic error. GRACE data processing that used a combined atmosphere-ocean de-aliasing (AOD) model showed improvement in the gravity estimates consistent with the simulations: the shorter spatial wavelengths (higher degrees) were improved while the longest spatial wavelengths (particularly important for time-variable gravity studies) were relatively unaffected. Monthly gravity solutions from GRACE resolved features on the order of 2-3 mm geoid height anomaly when smoothed to 400-km spatial scales. Comparisons with the Global Land Data Assimilation System (GLDAS) terrestrial water storage model indicated a high degree of correlation up to spatial wavelengths of 600 km or larger; a significant improvement over the spatial and temporal scales obtained with SLR observations. However, temporal variability in the degree 2 coefficients, particularly the zonal, seemed to be better resolved by SLR observations than by GRACE observations.Item A Mexican case study for world water online(2012-05) Espinoza Dávalos, Gonzalo Enrique; Maidment, David R.; McKinney, Daene C.World Water Online is a global system of hydrologic data. It is an integration of geospatial and temporal information across spatial scales: global, national, regional and local. This global water information system has no parallel, and its scope would be extended with the active participation of the global water community. Its consolidation depends on the accessibility of countries’ databases through the system. In this study, a test case using Mexican data within World Water Online is created, applying the CUAHSI framework, web services and standards. The resulting Mexican-HIS unifies the water information for the nation regardless of data provider, improving storage practices and allowing additional querying and retrieving functionalities: World Water Online is a source of information and also a supplier of web-based processing services. In the second part of this study, a precipitation-runoff analysis using the data in the system is performed.Item Modeling of soil moisture dynamics of grasslands in response to CO₂ and biodiversity manipulations at BioCON(2014-12) Flinker, Raquel Henriques; Cardenas, Meinhard Bayani, 1977-; Caldwell, Todd G.Increasing atmospheric carbon dioxide (CO₂) leads to global warming. This can have several impacts on climate and on plant biodiversity, and has been the topic of many studies. The objective of this thesis was to understand the effects of higher atmospheric CO₂ on soil moisture dynamics in the grasslands of central Minnesota using detailed hydrologic modeling to explain previous experimental observations at the BioCON site, a free-air CO₂ enrichment experiment. The hydraulic properties and texture of soils collected from BioCON were determined in the laboratory through grainsize analysis and continuous evaporative drying to determine soil moisture retention curves and hydraulic conductivities. These results were used as input for numerical soil water flow and energy balance models. The models showed that vegetation presence and atmospheric CO₂ concentrations significantly affected the soil moisture dynamics. Summer evapotranspiration (ET) had a higher variation for bare plots than for vegetated plots. This likely occurred because the vegetation provided a buffer against the variations in weather conditions. Vegetation not only retains part of the precipitation on its leaves, it also retains water in its structure and transpires while carrying out photosynthesis. Higher water content was also seen for the bare plots than for the vegetated soils. For some vegetated plots, there were differences between simulated and observed soil moisture. This could have been caused by a difference in plant composition and could suggest that different plant species can respond differently to varying CO₂ atmospheric concentrations leading to different soil moisture dynamics. In addition to this, smaller ET values and higher soil water content values at vegetated elevated CO₂ conditions than at ambient CO₂ conditions were simulated. This was expected, as higher atmospheric CO₂ is linked to higher plant water efficiency and larger biomass. For the simulations, higher values for stomatal resistance and higher plant and plant residue biomass were used. If increasing CO₂ conditions in fact decreases ET, regional weather patterns could be affected as less ET could delay the speed that water flows through the water cycle.Item Modeling the Hydrologic Impact of Arundo Donax on the Headwaters of the Nueces River Using the Swat Model(2014-08-06) Jain, ShaileeThe invasive species Arundo donax (hereafter Arundo), has invaded the riparian zones of the Rio Grande River and the rivers of the Texas Hill Country over the last two decades. Arundo, also known as the giant cane, is a robust herbaceous plant that can grow in many different climatic conditions. Arundo was first observed along the Nueces River in 1994 by the Nueces River Authority (NRA). It then spread rapidly downstream due to its high growth rate and/or stream flow and completely displaced the native vegetation, primarily P. virgatum (hereafter switchgrass), in the riparian zone wherever it got established. An eradication program was started in 2010 by the NRA to remove Arundo from the Nueces River. The objective of this research project was to (1) develop an algorithm to simulate the propagation of Arundo, (2) study changes in streamflow patterns during pre- and post- Arundo invasion periods, (3) calibrate and validate the Soil Water Assessment Tool (SWAT) for the Nueces River Headwater (HUC 12110101) watershed in central Texas, and (4) assess the effects of the invasion of Arundo on the watershed hydrology by comparing it to the native grass species switchgrass (Panicum virgatum) that used to be the dominant species in the watershed. Arundo parameters appropriate for the Nueces River were added to create a new crop category in the SWAT database. Calibration and validation of SWAT were based on measured streamflow data available at the USGS gage (USGS 08910000) on the Nueces River for the period 1960 to 1994. Switchgrass, the native vegetation, was chosen as the plant to compare Arundo with so that the difference in hydrology could be understood. The results revealed that accumulated evapotranspiration was not statistically different between Arundo and switchgrass for the period of 16 years (1995-2010). There was also no difference in the water yields of Arundo and switchgrass. In conclusion it appears that Arundo in the Nueces River has not caused any changes in water uptake compared to the native grass, switchgrass, that previously dominated the headwaters.