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<p> Modeling groundwater is challenging: it is not readily visible and is difficult to measure, with limited sets of observations available. Even though groundwater models can reproduce water table and head variations, considerable drift in modeled land surface states can nonetheless result from partially known geologic structure, errors in the input forcing fields, and imperfect Land Surface Model (LSM) parameterizations. These models frequently have biased results that are very different from observations. While many hydrologic groups are grappling with developing better models to resolve these issues, it is also possible to make models more robust through data assimilation of observation groundwater data. The goal of this project is to develop a methodology for high-resolution land surface model runs over large spatial region and improve hydrologic modeling through observation data assimilation, and then to apply this methodology to improve groundwater monitoring and banking. </p><p> The high-resolution LSM modeling in this dissertation shows that model physics performs well at these resolutions and actually leads to better modeling of water/energy budget terms. The overarching goal of assimilation methodology is to resolve the critical issue of how to improve groundwater modeling in LSMs that lack sub-surface parameterizations and also run them on global scales. To achieve this, the research in this dissertation has been divided into three parts. The first goal was to run a commonly used land surface model at hyper resolution (1 km or finer) and show that this improves the modeling results without breaking the model. The second goal was to develop an observation data assimilation methodology to improve the high-resolution model. The third was to show real-world applications of this methodology. </p><p> The need for improved accuracy is currently driving the development of hyper-resolution land surface models that can be implemented at a continental scale with resolutions of 1 km or finer. In Chapter 2, I describe our research incorporating fine-scale grid resolutions and surface data into the National Center for Atmospheric Research (NCAR) Community Land Model (CLM v4.0) for simulations at 1 km, 25 km, and 100 km resolution using 1 km soil and topographic information. Multi-year model runs were performed over the southwestern United States, including the entire state of California and the Colorado River basin. Results show changes in the total amount of CLM-modeled water storage and in the spatial and temporal distributions of water in snow and soil reservoirs, as well as in surface fluxes and energy balance. We also demonstrate the critical scales at which important hydrological processes&mdash;such as snow water equivalent, soil moisture content, and runoff&mdash;begin to more accurately capture the magnitude of the land water balance for the entire domain. This proves that grid resolution itself is also a critical component of accurate model simulations, and of hydrologic budget closure. (Abstract shortened by UMI.)</p>

<p> This study was conducted to provide an improved understanding of the dynamics of river islands and to investigate the role of islands in regulating sediment flux within the fluvial system. </p><p> The study showed that the islands in entrenched geomorphic subreaches of the MSR form, erode, and reform in locations controlled by lateral constrictions. The geometry of the islands adjust on a decadal or even longer time scale in response to a disturbance or changes in water and sediment supply, and thus, the islands form part of a temporal and spatial continuum of bedforms. The formation of the islands regulates sediment flux through the reach. </p><p> The study reach of the Middle Snake River (MSR) in Idaho contains over 300 islands within approximately 200 km between Swan Falls Dam and Brownlie Reservoir. The hydrology of the study reach has been significantly altered by upstream dams on the mainstem and dams on tributaries within the study reach. </p><p> Data used in the study include: (1) historical aerial photos (1938/1939) and topographic maps (c1894-1906), (2) topographic and bathymetric survey data collected in 1997 through 1999, (3) flow measurements from 1911 to present, (4) bed material samples, (5) morphostratigraphic mapping of 194 islands and (6) stratigraphic soil profile data collected on 95 islands. The soil profile data included soil stratigraphy, soil samples (used for sediment gradations and pollen analyses), pedological descriptions, historical artifacts and charcoal fragments (used for carbon dating). A previously developed 1-dimensional hydraulic model of the study reach was used to evaluate the hydraulic conditions along MSR and to calculate the overtopping discharges of the islands. </p><p> Comparison of historical aerial and topographic data with 2012 aerial photography showed evidence of the growth and erosion of islands and reworking of island chains to form new configurations, illustrating the dynamic nature of the islands over the last approximately 100 years. The historical document review also showed that the location of almost all larger islands and island groups are controlled by lateral constrictions such as tributary fans. </p><p> Soil profile data, pollen analyses, historical artifacts and radiocarbon dating of soil charcoal were used to determine the approximate age of islands and to evaluate the erosional and depositional activity of the islands. The soil profile data showed an extreme range in age at some islands where the gravel platform of the islands is old (circa 7,000 years), but the overlying sediments are young (on the order of hundreds of years). </p><p> Two-dimensional sediment-transport models were developed to evaluate the baseline conditions and simulate island development. Baseline conditions modeling showed the gravel- to cobble-sized material forming the core of the islands is not mobilized under the current hydrology. The islands formed in response to more recent floods from silt-sand sized sediment supply, which explains the relatively young soils overlying older gravel cores. </p><p> Modeling results showed that: (1) the island geometry adjusts to a disturbance or a change in sediment supply, (2) the formation of islands regulates sediment flux, and (3) the islands form, erode, and reform in the same general locations, which supports the study hypotheses that islands form part of a temporal and spatial continuum of bedforms.</p>

<p> Determining the hydraulic properties of aquifer and aquitards (K,T,and S) is very important in hydrogeologic studies. These parameters can be identified by methods such as laboratory permeability and borehole hydraulic response test. Because these approaches are sometimes costly, involving drilling test holes, and often may not be feasible, numerical modeling approaches can be considered as alternatives. In the following study, numerical modeling is applied to simulate groundwater flow system to determine the hydraulic properties of a weathered/fractured zone in a valley located within the Appalachian Plateau Geomorphic Province. The Appalachian Plateau is characterized by relatively flat-laying but intensely eroded bedrock, comprising cyclical sequences of Pennsylvanian age sedimentary bedrock dominated by sandstone, siltstone, shale, coal, claystone, and occasionally limestone. Fractured/weathered sandstone is potentially the main bedrock groundwater transmitting formation. The extent of fractures is from the ground surface to about 120-150 ft (or roughly 30-40m) under the ground surface. The main groundwater flow occurs from within the intergranular pore space through fractures and along bedding planes of the bedrock. </p><p> The water level at a perennial stream in the valley can be considered as the phreatic ground-water level. Therefore, the elevation points along this stream may serve as model calibration points. Because the outflow from the valley is almost entirely via the creek, and creek water represents the groundwater level all along the valley, the model is calibrated and verified by the creek water elevations and the amount of water discharging through the valley. The site- specific hydrogeologic interpretation and evaluation technique presented in this study may be very well applicable to the significant portions of the Allegheny Plateau with similar geomorphologic, tectonic and lithologic characteristics.</p><p> </p>

<p> Quantification of groundwater-surface water exchange and the role of hyporheic flow in this exchange is increasingly of interest to a wide range of disciplines (e.g., hydrogeology, geochemistry, biology, ecology). The most direct method to quantify groundwater-surface water exchange is a seepage meter, first developed in the 1940s. Widespread use of the traditional 1970s-era 55-gallon half-barrel seepage meter has shown that the method is subject to potential errors, particularly in flowing waters (e.g., streams, rivers, tidal zones). This study presents two new direct seepage measurement devices, the Shelby tube and the seepage blanket, designed to minimize potential measurement errors associated with flowing surface waters. The objective of the study is to develop and test the new methods by comparing results (specific discharge, hydraulic conductivity, and dissolved constituent concentration) to established methods. Results from both laboratory and field testing suggest that the new devices have utility in quantifying the water and dissolved constituent exchange between surface water and groundwater.</p>

Analyses of 13 sediment cores and 2800 km of 3.5 kHz seismic profiles reveal that the majority of the sediments on the Labrador continental slope was deposited by hemipelagic settling and ice-rafting (53%), debris flows (7%) and turbidity currents (34%) during the Wisconsinan Glaciation. Only minor amounts (6%) are attributed to contour current activity and related processes. Eight sedimentary facies were differentiated which include (1) hemipelagic (H); (2) hemipelagic (HI) with ice-rafted detritus (IRD); (3) debris-flow deposits (subfacies D1, D2, D3), spill-over turbidite (T), headspill turbidite (TH), turbidite (TI) alternating with IRD; and (4) contourite (C) and nepheloid-flow deposits (N). / Six major glacial advances were identified in Mid- to Late-Wisconsinan (64-10 ka) slope sediments by 6 very dark hemipelagic units containing abundant sinistral-coiling, cold-water foraminifera. The associated ice-retreat phases are characterized by the occurrence of turbidites, debris-flow deposits, nepheloid-flow deposits, and ice-rafted debris (IRD).

Recent measurements of dissolved oxygen (DO) along the Laurentian Trough revealed the presence of hypoxic waters in the bottom 50 meters of the water column of the Lower St. Lawrence Estuary (LSLE). In addition to the change in the oceanic regime on the continental shelf at the mouth of the Gulf of St. Lawrence proposed by others, a large sediment oxygen demand along the LSLE though to contribute to this DO depletion. To verify the latter hypothesis, I developed a laterally integrated, two-dimensional model of the DO distribution for the bottom waters of the Laurentian Trough. The fluid transport is parameterized in a simple advection-diffusion finite-element grid where the sedimentation of organic matter feeds the mineralization processes that lead to O2 depletion in the deep waters. Using realistic parameters obtained from field data, the diagenetic model reproduces the measured sediment oxygen demands (SODs) along the Gulf of St. Lawrence portion of the trough but overestimates them in the lower estuary. Since our modeled estuary DO levels are comparable to the measured DO values when a large SOD is applied, we suggest that the oxygen fluxes, calculated from the DO gradients measured with micro-electrodes across the sediment-water interface of cores recovered in the LSLE, are underestimated.

Understanding the controls on water movement on forested uplands is critical in predicting the potential effects of disturbance on the sustainability of water resources. I examined the controls on vertical and lateral water movement on forested uplands on a range of landforms (coarse textured outwash, fine textured moraine) and time periods (individual events, during snowmelt, through the growing season, annually, and long-term) at the Utikuma Region Study Area (URSA) on the sub-humid Boreal Plains of Alberta, Canada. To quantify vertical and lateral water movement, hydrometric and tracer measurements were made under natural and experimental conditions at plot and hillslope scales. Vertical flow and unsaturated zone storage dominated hydrologic response to snowmelt and rainfall at the plot and hillslope scales. Plot-scale snowmelt infiltration was greater than near-surface runoff, and when runoff occurred it was limited to south-facing outwash hillslopes underlain by concrete frost. Rainfall simulation studies showed that even under the extreme conditions tested, vertical flow and storage dominated the hydrologic response. Soils at field capacity and precipitation inputs of 15-20 mm or greater at high intensities were required to generate lateral flow via the transmissivity feedback mechanism. The threshold soil moisture and precipitation conditions are such that lateral flow will occur infrequently under natural conditions. Seasonal vertical water movement under natural conditions was greater on outwash than moraine uplands. The maximum downward vertical movement occurred in response to snowmelt, with little subsequent movement over the growing season. Recharge following snowmelt was similar for outwash and moraine sites and was followed by declining water tables through the growing season. Tracer estimates of long-term root zone drainage were low, while estimates of recharge for the moraine were high, raising questions about the appropriateness of this method for these sites. These results emphasize the dominance of vertical relative to lateral water flow on Boreal Plain uplands. Detailed understanding of the controls on water movement can be used to predict the potential effects of disturbance on hydrology and water resources. / Ecology

Thesis (M.S. - Renewable Natural Resources)--University of Arizona, 1986. / Includes bibliographical references (leaves 122-124).