• 2-D bed sediment transport modeling of a reach on the Sagavanirktok River, Alaska

      Ladines, Isaac A.; Toniolo, Horacio; Barnes, David; Schnabel, Bill (2019-05)
      Conducting a 2-D sediment transport modeling study on the Sagavanirktok River has offered great insight to bed sediment movement. During the summer of 2017, sediment excavation of two parallel trenches began in the Sagavanirktok River, in an effort to raise the road elevation of the Dalton Highway to remediate against future floods. To predict the time in which the trenches refill with upstream sediment a 2-D numerical model was used. Three scenarios: (1) a normal cumulative volumetric flow, (2) a max discharge event, and (3) a max cumulative volumetric flow, were coupled with three sediment transport equations: Parker, Wilcock-Crowe and Meyer Peter and Müller for a total of 9 simulations. Results indicated that scenario (1) predicted the longest time to fill, ranging from 1-6 years followed by scenario (2), an even shorter time, and scenario (3) showing sustained high flows have the capability to nearly refill the trenches in one year. Because the nature of this research is predictive, limitations exist as a function of assumptions made and the numerical model. Therefore, caution should be taken in analyzing the results. However, it is important to note that this is the first time estimates have been calculated for an extraction site to be refilled on the Sagavanirktok River. Such a model could be transformed into a tool to project filling of future material sites. Ultimately, this could expedite the permitting process, eliminating the need to move to a new site by returning to a site that has been refilled from upstream sediment.
    • Alaska Arctic coastal plain gravel pad hydrology: impacts to dismantlement removal and restoration operations ; a study on the human - hydrology relationship in Arctic environments

      Miller, Ori; Barnes, David L.; Stuefer, Svetlana L.; Shur, Yuri (2019-08)
      To guard against thawing permafrost and associated thaw subsidence, the oil facilities in the Arctic are constructed on gravel pads placed on top of the existing arctic tundra, however the impacts of this infrastructure to the sensitive hydrology are not fully understood. Production in some of the older fields is on the decline; however oil exploration in the Arctic Coastal Plain is resulting in the discovery and development of new reserves. In the coming years, old sites will need to be decommissioned as production transitions to new sites. New facilities will also need to be designed and constructed. Oil companies in Alaska have historically conducted operations under leases issued through the Alaska Department of Natural Resources. The leases stipulate that once resource extraction operations are completed, the facilities must be decommissioned and the sites restored, however they are often vague in their requirements and are variable in their specifics from lease to lease. As the oil companies transition to the new sites, decisions must be made regarding what should be done with vacated gravel pads. The construction of gravel pads essentially destroys underlying arctic tundra. In undisturbed areas in the Arctic, the tundra itself creates an insulating layer that limits the seasonal thaw depth to around 0.5 m. Removal of this layer causes thaw depths to greatly increase impacting the stability of the ground and the hydrology of the surrounding area. Because of this impact, other possible restoration techniques are being considered, such as vegetating and leaving the pads in place. Water movement is one of the major driving factors in the arctic contributing to permafrost degradation. Groundwater carries with it heat, which is transferred to the soil as the groundwater moves. Therefore, hydrology plays a major role in the stability of the arctic environment. This is especially relevant in areas where gravel pads exist. Gravel pads are anthropogenic structures that have significant water storage potential. Because of the unique conditions in the Arctic, pore-water flow through these gravel pads is not yet well understood. The purpose of this study is to develop a more complete scientific understanding of the driving forces behind pad pore-water movement. This study expands on fieldwork from a prior hydrological field study conducted by others. The prior study is expanded through this work by developing an associated groundwater model to the gravel pad from the field study to examine the flow through it and the controlling factors for this flow. The study site used for this project is located in Prudhoe Bay and is the pad constructed for the very first production well in Prudhoe Bay in 1968. This study demonstrates that it is the topography of the silt layer beneath the gravel pads that is the most significant factor controlling pad pore-water movement. The results from the modeling study will assist engineers and environmental scientists in better understanding the groundwater flow. This understanding will aid in the decommissioning and restoration process and help inform decision making in regards to the future of the existing pads. The results may also be used to inform the development of new infrastructure such that any new pads which are built may be constructed with their relationship to the local hydrology more in mind.
    • An assessment of suspended sediment transport in Arctic Alaskan rivers

      Lamb, Erica K.; Toniolo, Horacio; Schnabel, William; Kane, Douglas (2013-05)
      Provided here is an initial assessment of suspended sediment transport in several rivers on the North Slope of Alaska. This study was divided into two parts: the Umiat project, which involved the Chandler, Anaktuvuk and Itkillik Rivers, and the NPR-A study, which considered Prince, Seabee and Fish Creeks, as well as a brief look at the lkpikpuk River, Otuk Creek, Judy Creek and the Ublutuoch River. Methods used included depth-integrated suspended sediment samples, grab samples, automatic pump-style samplers, discharge measurements, bed sediment grain size analysis and the inclusion of a variety of meteorological measurements from other projects. With slightly less than two years of data collection from May 2011 to September 2012, an initial analysis was completed. Suspended sediment rating curves developed for the Anaktuvuk and Chandler Rivers over the two-year study period revealed a strong correlation between suspended sediment concentration (SSC) and discharge. The most data was collected for the Anaktuvuk and Chandler Rivers; on these rivers, suspended sediment discharge was also analyzed, showing that over 90% of suspended sediment transport occurred during the spring melt period in 2011. Spring melt was not measured in 2012, so analysis was only completed for 2011.
    • Climatic and physiographic drivers of peak flows in watersheds in the North Slope of Alaska

      Hinzman, Alexa Marion Hassebroek; Stuefer, Svetlana; Arp, Christopher; Barnes, David (2017-08)
      The failure to accurately predict peak discharge can cause large errors in risk analysis that may lead to damage to structures and in some cases, death. Creating linear regression (LR) equations that accurately predict peak discharges without historic data provides a method to estimate flood peaks in ungauged watersheds on the North Slope of Alaska. This thesis looks at the independent variables that drive, or are significant in predicting snowmelt peak discharge in the North Slope watersheds. The LR equations created use independent variables from meteorological data and physiographic data collected from four watersheds, Putuligayuk River, Upper Kuparuk River, Imnavait Creek and Roche Moutonnée Creek. Meteorological data include snow water equivalent (SWE), total precipitation, rainfall, storage, length of melt. Physiographic data summarize watershed area (2.2 km2 to 471 km2) and slope (0.15:100 to 2.7:100). This thesis compared various Flood Frequency Analysis techniques, starting with Bulletin 17B, multiple USGS regional methods and finally created LR equations for each watershed as well as all four watersheds combined. Five LR equations were created, three of the LR equations found SWE to be a significant predictor of peak flows. The first equation to estimate peak flows for all watersheds used only area and had a high R2 value of 0.72. The second equation for all watersheds included area and a meteorological independent variable, SWE. While the evidence presented here is quite promising that meteorological and physiographic data can be useful in estimating peak flows in ungauged Arctic watersheds, the limitations of using only four watersheds to determine the equations call for further testing and verification. More validation studies will be needed to demonstrate that viable equations may be applied to all watersheds on the North Slope of Alaska.
    • Connecting Alaskans: mixed-use safety and accessibility challenges in rural environments

      Sorensen, Carrie L.; Belz, Nathan; Goddard, Scott; Barnes, David (2017-12)
      Connectivity in transportation networks, or lack thereof, is a challenge that many people have to deal with. Alaska has many rural communities that are inaccessible by conventional modes of transportation. In order for people to reach these communities and move between them unconventional modes of transportation are needed. However, very few studies have been done on unconventional transportation modes such as ATVs and snowmachines and the level to which they contribute to connecting people and how to help limit traumatic injuries of users. This study focuses on Alaska and three primary datasets. First, the Pacific North West Transportation Survey developed by the University of Alaska Fairbanks and the University of Idaho. Second, Alaska Trauma Registry data obtained from Division of Public Health and Safety. Thirdly, publicly available GIS transportation network and populated place data. These three data sets accomplish the following objectives: (1) document preferences and perceptions of mixed-use safety, (2) to better understand the reasons for injuries and fatalities involving ATVs and snowmachines, and (3) to identify potential mixed-use conflict areas by geographic mapping of traumas. From this analysis a better understanding of ATV mode use was discovered. ATVs are used for a variety of trip purposes including: commuting, running errands, chores, and recreation. ATVs are used on and near roadways 24% of the time. There are twice as many ATV-related traumas in connected places than in isolated places, and 3 times more ATV related traumas in highway connected places than secondary road connected places. Snowmachines are used on and near roadways 23% of the time and have 3 times as many traumas in highway connected places than secondary road connected places. Highway connected places have a significantly higher risk of having ATV and snowmachine traumas than road connected places. This indicates that part of the issue could be the amount of traffic in connected areas, or perhaps the frequency of use of ATVs rather than automobiles in non-connected areas leading to fewer mixed-use scenarios.
    • Establishing and testing detection methods for anti-icing and deicing chemicals using spectral data

      Fulton, Gabriel; Belz, Nathan; Meyer, Franz; Stuefer, Svetlana (2019-08)
      Snow and ice accumulation on pavement reduce roadway surface friction and consequently result in diminished vehicle maneuverability, slower travel speeds, reduced roadway capacity, and increased crash risk. Though the use of chlorides and other freeze-inhibiting substances have been shown to reduce these negative factors, methods to quantify and analyze snow and ice remediation methods as well as the imposed loss of material are needed to allow state and municipal agencies to better allocate winter maintenance resources and funding. The use and application of chlorides, sand, and their related mixtures have proven to be highly effective for controlling or removing the development of ice on the roadway surface. However, if the amount of salt in solution becomes too dilute, then it no longer retains the capacity to control the development of, or to melt, ice on the roadway and may prove to be more detrimental by allowing the previously melted material to refreeze with a smoother (i.e., more slippery) surface state. The goal of this project was to determine to what extent winter roadway surfaces can be analyzed using spectrometry to determine the longevity and coverage of various types of applications. Using a systematically paired analysis of changes in spectrometric curves as solution concentrations change, relationships were generated which detected change in deicing and anti-icing compounds reliably in a lab setting. Field results were less reliable, suggesting that further comparisons and a more in-depth spectral library are needed.
    • Evaluating short rotation poplar biomass on an experimental land-fill cap near Anchorage, Alaska

      Byrd, Amanda G. (2013-05)
      Biomass energy has enjoyed a resurgence of scientific interest recently. Indeed, biomass may have the potential to replace diesel fuel as the primary source of heating in some parts of Alaska. In addition to forest biomass, short rotation crops have been considered as a sustainable source of woody biomass, and a potential sink for carbon sequestration. In this study, Populus balsamifera was evaluated as a short rotation crop for use as an energy source in Southcentral Alaska. Growth and yield rates were measured on an established P. balsamifera stand under a two-year rotation, yielding an annual biomass production of 5,530 kg/ha/yr. A fertilizer application study was conducted and demonstrated no effect on growth. Energy content of P. balsamifera measured 19,684 kJ/Kg, with a total energy yield of 217,715 MJ/ha after two years. Carbon sequestered below ground was estimated at least 5,338 kg/ha. Biomass may not be carbon neutral, but the carbon emitted from burning biomass is at least partially renewable. With use in high-efficiency boilers, there is potential for biomass to offset costs, and even save money by displacing diesel heating fuel.
    • An evaluation of the use of moderate resolution imaging spectroradiometer (MODIS)-derived aerosol optical depth to estimate ground level PM2.5 in Alaska

      Mathers, Alyson Marie McPhetres; Aggarwal, Srijan; Belz, Nathan; Perkins, Robert (2018-12)
      The air quality monitoring (AQM) network in Alaska is limited to major urban areas and national parks thus leaving a large proportion of the state unmonitored. To evaluate the use of Moderate Resolution Imaging Spectroradiometer (MODIS)-derived aerosol optical depth (AOD) to predict ground-level PM2.5 concentrations and thereby increase the spatial coverage of the AQM network in Alaska, MODIS AOD was first validated against ground-based measurements of AOD in Utqiagvik and Bonanza Creek Alaska. MODIS AOD from 2000 to 2014 was obtained from MODIS collection 6 using the dark target land and ocean algorithms between the months of April and October. Based on validation results, individual Aqua and Terra products are valid for both locations at 10-kilometer and 3-kilometer resolution. In addition, combined Aqua and Terra MODIS AOD products are valid for both locations at 3-kilometer resolution and 10-kilometer resolution for Utqiagvik. The available PM2.5 data was then compared for satellite retrieval and all retrieval days to determine if there was sufficient data and the amount of bias introduced by possible low retrieval rates. Overall, Juneau had the lowest retrieval rates while Fairbanks and North Pole had the highest retrieval rates. In addition, Juneau appeared to have relatively high bias while stations located in Anchorage, Palmer, Fairbanks and North Pole had relatively low bias. Based on these findings, no models were developed for Juneau (southeast Alaska). Multilinear regression models were then developed for southcentral (Anchorage and Palmer) and interior (Fairbanks and North Pole) Alaska where the log-transform of PM2.5 was the response and meteorological data and the log-transform of MODIS AOD were the predictors. MODIS AOD appeared to be most highly correlated with PM2.5 in interior Alaska, while there was little to no correlation between MODIS AOD and PM2.5 in southcentral Alaska. All models underestimate surface PM2.5 concentrations which may be due to the high percentage of low PM2.5 values used to develop the models and the limited retrieval rates. Alternative modeling methods such as mixed-effects modeling may be necessary to develop adequate models for predicting surface PM2.5 concentrations. The MLR models did not perform well and should not be used to predict ground-based PM2.5 concentrations. Further research using alternative modeling methods should be performed. Model performance may also be improved by only using higher concentrations of PM2.5 to develop models. Overall, the limited spatial coverage of Alaska's air quality monitoring network and the low temporal resolution of MODIS-derived AOD make modeling the relationship between MODIS AOD and PM2.5 difficult in Alaska.
    • Groundwater flow in a vertical plane at the interface of permafrost

      Paturi, Sairavichand; Barnes, David L.; Leigh, Mary Beth; Shur, Yuri (2017-08)
      Groundwater dynamics in discontinuous permafrost aquifers are complex. The topography of permafrost redirects flow in difficult-to-predict directions that can be tens of degrees off from the regional flow direction. Large zones of permafrost vertically separate aquifers into supra and sub-permafrost portions. The flow dynamics in each portion of the aquifer may be dissimilar due to different controlling boundary conditions. In areas of discontinuities in permafrost, known as open taliks, groundwater in the two portions of the aquifer may mix. These areas of mixing are the focus of this study, in particular, the groundwater dynamics in taliks located in the floodplain of lower reaches of rivers. The study hypothesizes that groundwater flow in floodplain taliks of lower reaches of rivers will bifurcate between the supra and sub-permafrost portions of a discontinuous permafrost aquifer. To test this hypothesis gradient, magnitudes and flow directions were determined at several depths ranging from the water table to 150 ft. (45.7 m) below ground surface, using a linear interpolation scheme in various locations in a floodplain talik. Errors in water level measurements due to instrument errors as well as vertically moving wells were propagated into the gradient calculations by Monte Carlo analysis. Results from this research show that a vertical divide in groundwater flow forms a short distance below the top of permafrost. Groundwater flow above the divide routes into the unconfined supra-permafrost portion of the aquifer. Water below the divide flows into the confined portion of the aquifer below permafrost. The position of the vertical groundwater divide may adjust in relation to the water table position. Additionally, a methodology is presented for stochastically propagating measurement errors into gradient analyses by Monte Carlo analysis. Understanding the flow dynamics in discontinuous permafrost aquifers is key to the understanding of contaminant transport, aquifer recharge, and resource development in subarctic environments.
    • Investigation of thermal regimes of lakes used for water supply and examination of drinking water system in Kotzebue, Alaska

      Bendlova, Tereza; Arp, Christopher D.; Duffy, Lawrence K.; Schnabel, William E.; Barnes, David L. (2012-08)
      Many villages in Arctic Alaska rely on lakes for water supply, such as the Alaskan City of Kotzebue, and these lakes may be sensitive to climate variability and change, particularly thermal regimes and corresponding effects on water quality. Thus, I initiated a study of water supply lakes in Kotzebue to collect data for developing a model to hindcast summer thermal regimes. Surface (Tws) and bed (Twb) temperature data collected from two water supply lakes and two control lakes from June 22nd-August 28th 2011 showed a similar pattern in relation to air temperature (Ta) and solar radiation with more frequent stratification in the deeper lakes. The average Tws for all lakes during this period was 14.5°C, which was 3.4°C higher than Ta for the same period. I modeled Tws from 1985 to 2010 using Ta, and theoretical clear-sky solar radiation (TCSR) to analyze interannual variability, trends, and provide a baseline dataset. Similar to patterns in Ta for this period, I found no trend in mean Tws for the main lake used for water supply (Devil's Lake), but considerable variation ranging from 12.2°C in 2000 to 19.2°C in 2004. My analysis suggests that 44% of years during this 25 year period maximum daily Tws surpassed 20°C for at least one day. This hindcasted dataset can provide water supply managers in Kotzebue and other Arctic villages with a record of past conditions and a model for how lakes may respond to future climate change and variability that could impact water quality.
    • Long term evaporation pan data to estimate potential evaporation during the warm season on the Alaskan North Slope: Imnavait Creek basin

      Mumm, John Paul; Kane, Douglas L.; Toniolo, Horacio; Schnabel, William (2017-12)
      Evapotranspiration plays a significant role in the hydrologic cycle of all basins, yet is only ccasionally measured in the Arctic. One simple index method to evaluate evapotranspiration is the evaporation pan. The energy environment surrounding the simple evaporation pan varies considerably from that of the natural environment. Yet, an evaporation pan is a sound way to determine and estimate the potential evapotranspiration, and actual evapotranspiration can be estimated from evaporation pan data by determining and employing a pan coefficient. An evaporation pan was initially installed in 1986 in the northern foothills of the Brooks Range on the North Slope of Alaska in Imnavait Creek Basin, collecting data for 22 years. The total summer maximum, average, minimum and standard deviation of pan evaporation were 34.9 cm, 29.9 cm, 19.7 cm and 9.3 cm, respectively from 1986 to 2008 (1989 missing). Both, the seasonal water balance and the Priestley-Taylor method for the 2.2 km² Imnavait Creek catchment were used to produce seasonal estimates of actual evapotranspiration. When used in conjunction with the evaporation pan measurements, an average pan coefficient of 0.58 was found in both cases, which was very similar to what was found in an earlier study on Imnavait Creek Basin. The evaporation pan results can also be correlated effectively with other measured variables (such as thawing degree days, air temperature, net radiation, vapor pressure deficit, precipitation, wind speed, and wind direction); this is a method that allows one to predict potential evapotranspiration in areas where it is not measured at broader spatial scales.
    • Pre-stress loss due to creep in precast concrete decked bulb-tee girders under cold climate conditions

      Vandermeer, Drew E.; Ahn, Il-Sang; Liu, Juanyu (2019-05)
      This report presents guidelines for estimating pre-stress loss in high-strength precast pretensioned concrete Decked Bulb-Tee (DBT) bridge girders in cold climate regions. The guidelines incorporate procedures yielding more accurate predictions of shrinkage and concrete creep than current 2017 American Association of State Highway and Transportation Officials (AASHTO) specifications. The results of this report will be of particular interest to researchers and cold climate bridge design engineers in improved predictions of design life and durability. The use of high-strength concrete in pre-tensioned bridge girders has increased in popularity among many state highway agencies. This fact is due to its many beneficial economic and constructability aspects. The overall cost of longer girders with increased girder spacing in a bridge that is precast with high strength concrete can be significantly reduced through the proper estimating factors. Recent research indicates that the current provisions used for calculating prestress losses in cold regions for high-strength concrete bridge girders may not provide reliable estimates. Therefore, additional research is needed to evaluate the applicability of the current provisions for estimating pre-stress losses in high-strength concrete DBT girders. Accurate estimations of pre-stress losses in design of pre-tensioned concrete girders are affected by factors such as mix design, curing, concrete strength, and service exposure conditions. The development of improved guidelines for better estimating these losses assists bridge design engineers for such girders and provide a sense of security in terms of safety and longevity. The research includes field measurements of an environmentally exposed apparatus set up to measure shrinkage, creep and strain in cylinders loaded under constant pressure for a full calendar year.
    • Processes controlling thermokarst lake expansion rates on the Arctic coastal plain of Northern Alaska

      Bondurant, Allen C.; Arp, Christopher D.; Jones, Benjamin M.; Daanen, Ronald P.; Shur, Yuri L. (2017-08)
      Thermokarst lakes are a dominant factor of landscape scale processes and permafrost dynamics in the otherwise continuous permafrost region of the Arctic Coastal Plain (ACP) of northern Alaska. Lakes cover greater than 20% of the landscape on the ACP and drained lake basins cover an additional 50 to 60% of the landscape. The formation, expansion, drainage, and reformation of thermokarst lakes has been described by some researchers as part of a natural cycle, the thaw lake cycle, that has reworked the ACP landscape during the course of the Holocene. Yet the factors and processes controlling contemporary thermokarst lake expansion remain poorly described. This thesis focuses on the factors controlling variation in extant thermokarst lake expansion rates in three ACP regions that vary with respect to landscape history, ground-ice content, and lake characteristics (i.e. size and depth). Through the use of historical aerial imagery, satellite imagery, and field-based data collection, this study identifies the controlling factors at multiple spatial and temporal scales to better understand the processes relating to thermokarst lake expansion. Comparison of 35 lakes across the ACP shows regional differences in expansion rate related to permafrost ice content ranging from an average expansion rate of 0.62 m/yr on the Younger Outer Coastal Plain where ice content is highest to 0.16 m/yr on the Inner Coastal Plain where ice content is lowest. Within each region, lakes vary in their expansion rates due to factors such as lake size, lake depth, and winter ice regime. On an individual level, lakes vary due to shoreline characteristics such as local bathymetry and bluff height. Predicting how thermokarst lakes will behave locally and on a landscape scale is increasingly important for managing habitat and water resources and informing models of land-climate interactions in the Arctic.
    • Snowmelt hydrology in the upper Kuparuk watershed, Alaska: observations and modeling

      Dean, Kelsey M.; Stuefer, Svetlana; Verbyla, David; Schnabel, William (2019-08)
      The Fourth National Climate Assessment Report (2018) indicates that Alaska has been warming at a rate two times greater than the global average with the Arctic continuing to be experiencing higher rates of warming. Snowmelt driven runoff is the largest hydrologic event of the year in many Alaska Arctic river systems. Changes to air temperature, permafrost, and snow cover impact the timing and magnitude of snowmelt runoff. This thesis examines the variability in hydrometeorological variables associated with snowmelt to better understand the timing and magnitude of snowmelt runoff in headwater streams of Arctic Alaska. The objectives of this thesis are to: (1) use observational data to evaluate trends in air temperature, precipitation, snow accumulation, and snowmelt runoff data; (2) relate precipitation, snow cover, and air temperature to snowmelt runoff using the physically-based Snowmelt Runoff Model (SRM) to test the applicability of the model for headwater streams in the Arctic. The focus of this study is the Upper Kuparuk watershed area, located in Alaska on the north side of the Brooks Range, where several monitoring programs have operated long enough to generate a 20-year climate record, 1993-2017. Long-term air temperature, precipitation, and streamflow data collected by the University of Alaska Fairbanks at the Water and Environmental Research Center and other agencies were used for statistical analysis and modeling. While no statistically significant trends in snow accumulation and snowmelt runoff were identified during 1993-2017, observations highlight large year-to-year variability and include extreme years. Snow water equivalent ranges from 5.4 to 17.6 cm (average 11.0 cm), peak snowmelt runoff ranges from 3.84 to 50.0 cms (average 22.4 cms), and snowmelt peak occurrence date ranges from May 13 to June 5 for the Upper Kuparuk period of record. The spring of 2015 stands out as the warmest, snowiest year on record in the Upper Kuparuk. To further investigate the runoff response to snowmelt in 2015, remote sensing snow data was analyzed and recommended parameters were developed for SRM use in the Upper Kuparuk watershed. Recommended parameters were then applied to 2013 snowmelt runoff as a test year. Model results varied between the two years and provide good first-order approximation of snowmelt runoff for headwater rivers in the Alaska Arctic.
    • Structural health monitoring of Klehini River bridge

      Xiao, Feng (2012-08)
      The objective of the research is to improve the safety of bridge structures in the state of Alaska through implementation of innovative structural health monitoring (SHM) technologies. The idea is to evaluate structural integrity and serviceability, and to provide reliable information for changing structural response, etc. of monitored bridges. Based on the finite element model's moving load analysis, modal analysis results and field inspection, this study was used to establish a bridge SHM system for a particular bridge including a preferred sensor layout, system integrator and instrumentation suitable for Alaska's remote locations with harsh weather. A variety of sensors were proposed to measure and monitor structural and environmental conditions to assist in the evaluation of the performance of the Klehini River Bridge. This system is able to provide more reliable information on the real structural health condition. It can be used to improve safe performance of this bridge. As a new safety and management tool, this SHM system will complement traditional bridge inspection methods. Implementation of an effective monitoring system will likely result in a reduction in inspection manpower, early detection of deterioration/damage, development of optimum inspection cycle and repair schedules before deterioration/damage grows to a condition where major repairs are required.
    • The effects of scale and spatial heterogeneities on diffusion in volcanic breccias and basalts: Amchitka, Alaska

      Benning, Jennifer Lyn; Barnes, David; Kelley, John; Perkins, Robert; Schnabel, William (2008-12)
      Aqueous phase diffusion of molecules in fractured crystalline rock can play a dominant role in the fate and transport of contaminants, particularly if advective flows are very slow. The importance of the role of diffusion, typically a very slow process, also becomes an important mechanism to consider if the contaminants are long-lived in the subsurface, and thus their fate and transport must be considered over very long time-scales. Owing to the inherently heterogeneous nature of the subsurface, quantification of diffusive transport in the subsurface is extremely complex. The main objective of this study was to investigate the effects of the inherent heterogeneities of the subsurface on the diffusive transport of radionuclides, with a focus on the former underground nuclear test site at Amchitka Island, Alaska. Commonly, the through-diffusion experiment is utilized to estimate transport parameters, the diffusivity and the effective porosity, for porous media samples. The available methods of mathematically deriving these parameters from these experiments are generally known to be subjective and unreliable. Thus, one phase of this study applied the results of through- diffusion experiments to investigate the applicability of the available solution methods to derive these parameters. The results indicated that a semi-analytical solution provided the most reliable parameter estimations. This knowledge was then applied to studies designed to understand the impacts of scale and spatial heterogeneities on diffusion at the study site. Multiple Amchitka Island core samples, both from the same and from various geologic layers, in varying sizes were analyzed in the laboratory via tracer-based and electrical methods, to quantify the diffusive properties and the effects of heterogeneities for Amchitka Island. The studies indicated that the transport properties for Amchitka Island are widely varying, by orders of magnitude, and are indicative of a geologically layered subsurface system; these results are extremely important for the long-term modeling of the fate and transport of radionuclides at Amchitka Island. Finally, in light of these studies, the question of long-term stewardship for the Amchitka Island test site was investigated and recommendations were provided, with the goal of providing an improved plan for the long-term monitoring and management of the site.