Thesis (Ph. D.)--Oregon State University, 1999. / Typescript (photocopy). Includes bibliographical references (leaves 106-114). Also available on the World Wide Web.

No description available.

<p>Peatlands cover 170 million hectares of Canada's land and are long thought to be resistant to consumption by wildfire. However, boreal peatlands are likely to become increasingly vulnerable to wildfire as climate change lowers water tables and exposes deeper peat to burning. Currently, the Canadian Forest Fire Weather Index (FWI) System is used to assess vulnerability of peat to ignition and consumption, despite being developed for upland soils. Given the need to assess wildfire risk in peatlands, this study investigated the range and variability of key variables relevant to wildfire hydrology of the subsurface and canopy across five peatlands. Road impacted and drained peatlands were included to examine the influence of drying on afforestation (a surrogate for a future drier climate) and extend the range of parameterizations for peatlands.</p> <p>Increased drying led to significant increases in canopy fuel loads coupled with increased interception (upwards of 97%) and canopy storage, highlighting failures of the current FWI rainfall routine. Increased drying led to enhanced transpiration across impacted (≈ 2.8 mm d^-1) compared to pristine sites (≈ 0.68 mm d^-1). However, increases in above ground vulnerability were somewhat offset by ecohydrological feedbacks serving to increase peat moisture retention in the drier sites. But the most severely impacted peatland displayed the poorest moisture retention qualities of all peatlands perhaps indicating the existence of a threshold response to drying induced afforestation on peat moisture retention properties.</p> <p>Our findings suggest that modified FWI components are suitable for predicting the general moisture status and fire danger in boreal peatlands, highlighting key areas in the parameter to be improved.</p> / Master of Science (MSc)

No description available.

Groundwater provides a fundamental resource for modern life. Throughout the world, groundwater is managed by storing (recharging) it underground in natural aquifers for future withdrawal and consumptive use. In Arizona, over 4 million people benefit from managed aquifer storage, but little effort is made to track the movement of recharged water through the subsurface. Motivated by current limitations in our ability to monitor percolation and groundwater movement at the scale of a recharge facility, an effort to collect time-lapse gravity data was carried out at the Southern Avra Valley Storage and Recovery Project (SAVSARP) operated by the City of Tucson, Arizona. In addition to collecting water-level data 12 wells, there were three primary gravity experiments: (1) five continuously-recording gravity meters (2 iGrav superconducting gravity meters and 3 gPhone gravity meters) were installed semi-permanently in control buildings adjacent to the recharge basins, (2) absolute gravity measurements were made at nine locations over a 17 month period, and (3) three relative-gravity campaigns were carried out on a network of 70 stations. This large-scale controlled experiment, with known infiltration and pumping rates, resulted in one of the most comprehensive datasets of its kind. Gravity data led to several hydrologic insights, both through direct measurement and modeling. First, the infiltration rate could be estimated accurately based on the initial rate of gravity change during infiltration, regardless of the specific yield. Using two gravity meters, the depth, and therefore speed, of the wetting front beneath a recharge basin was observed, including the time at which the water table was reached. Spatial maps of gravity change from relative gravity surveys show areas where infiltration efficiency is highest, and where groundwater accumulates; storage accumulated preferentially to the west of the recharge basins, away from pumping wells. Such information would be valuable for planning the location of pumping wells at a new facility. Gravity data were useful for calibration of a Modflow-NWT groundwater-flow model using the Unsaturated Zone Flow package to simulate recharge; the reduction in the posterior parameter distribution compared to the a priori estimate was substantial and similar to head data. In contrast to model-simulated head data, model-simulated gravity data were less sensitive to more distant model elements and more effective for calibration of a superposition-type model. Observed head data had a strong regional signal reflecting basin-scale conditions with only minor variation associated with individual recharge basins, and were therefore of limited usefulness for model calibration. Together, the methods developed by the study and interpretations they made possible suggest that gravity data are an effective way to better understand large-scale infiltration and groundwater movement.

Observations from Cassini VIMS and ISS show localized but extensive surface brightenings in the wake of the 2010 September cloudburst. Four separate areas, all at similar latitude, show similar changes: Yalaing Terra, Hetpet Regio, Concordia Regio, and Adiri. Our analysis shows a general pattern to the time-sequence of surface changes: after the cloudburst the areas darken for months, then brighten for a year before reverting to their original spectrum. From the rapid reversion timescale we infer that the process driving the brightening owes to a fine-grained solidified surface layer. The specific chemical composition of such solid layer remains unknown. Evaporative cooling of wetted terrain may play a role in the generation of the layer, or it may result from a physical grain-sorting process.

The inverse problem of groundwater hydrology is difficult to solve and yet critical for the reliability of model predictions. In this dissertation, the problem is posed within the framework of maximum likelihood estimation by means of an estimation criterion which includes head measurements as well as prior information of the model parameters. Parameters that can be estimated include the principal values and directions of transmissivity (or hydraulic conductivity), storativity (or specific storage), recharge rates, boundary heads or fluxes, leakances, and parameters controlling the error structure of the data. In transient problems, the initial steady-state of the system can also be derived and/or taken advantage of. To minimize the estimation criterion, its gradient is evaluated by a finite element adjoint state method which leads to considerable savings in computer time and storage. The minimization -, performed -by a -combination- of gradient methads, is sbawn, bath theoretically and with examples, to result in stable solutions for a wide range of realistic situations. Synthetic and field examples are included to demonstrate various features of the approach. Applications of the methodology to problems of model selection, network design, and quantification of the worth of data are highlighted.

Pinal Creek, Arizona has been contaminated by discharge of acidic (pH = 5.8-6.3) and metal-rich ground water that was released from mining activities. In the stream, pH increases from approximately 6.0 to 7.8, while dissolved Mn(II) decreases from approximately 70.0 to 50.0 mg/L over 3 km downstream of the point of groundwater discharge. It was hypothesized that the spatial variation of in-stream pH is controlled by CO₂ gas-exchange and affects transport of dissolved Mn(II) through pH-dependent microbial oxidation in hyporheic zones. An existing transport model was extended to include carbonate equilibria, CO₂ degassing and pH-dependent Mn(II) removal processes and applied to predict the alkalinity-inorganic carbon (Cτ)-pH balance and transport of Mn(II) in natural stream based on field and laboratory experiments. The simulation results reproduced the overall trends of alkalinity, Cτ, and pH, and were in good agreement with dissolved Mn(II) in downstream concentrations. A multi-parametric sensitivity analysis (MPSA) was used to identify the relative sensitivity of predictions to physical and chemical parameters used in the extended transport model. MPSA results imply that CO₂ degassing and pH-dependent microbial oxidation are the most important factors controlling the spatial variation in pH and reactive uptake of dissolved Mn(II) in the stream system. Using stream tracer injections, streambed sediments and aquatic vegetation areas were identified as physical-storage zones within the stream where biogeochemical reactions were enhanced. The traditional one-storage transport model was extended to describe the hyporheic processes associated with two independent transient storage zones. The extended model was used to evaluate the applicability and accuracy of one-storage transport model to two-storage stream system. One-storage transport model has very strict limitation in its application for the two-storage stream system and is only valid if two retention times of transported solutes are very close (Tr₁/Tr2 1.0). The presented field and modeling approaches, which include model extension for the processes of CO₂ degassing and pH-dependent biogeochemical reactions, and generalized sensitivity analysis can improve our understanding of transport of metal contaminants in natural stream-aquifer system.

No description available.

Hydraulic conductivity (K), porosity and cation exchange capacity (CEC) were determined at the laboratory scale on samples of the Wildmoor Sandstone and Kidderminster Formations of the Birmingham Triassic sandstone. The impact of the rock colour was considered in a semi-quantitative manner using the Munsell Colour System. SEM, flushing experiments and image analysis of thin-section photomicrographs were used to assess the role of rock fabric in the development of hydraulic and chemical properties. The image analysis was carried out on colour images using a custom-written code. XRD, point counting and geophysical methods were utilised to assess the mineralogical variation between samples, the presence of iron and manganese oxides within the sandstone was quantified. The study found significant negative correlations between porosity and CEC in all samples, while a correlation between K and CEC was only observed in samples with a lower colour saturation. A significant role for manganese oxides in the development of CEC in the Triassic Sandstone of Birmingham has been identified. The study has concluded that a significant part of the CEC within these rocks is due to the presence of a reducible phase. This has significant implications for migration of contaminants, particularly those entrained in a reducing plume.