Thesis (MS)--Montana State University--Bozeman, 2009. / Typescript. Chairperson, Graduate Committee: Cathy Whitlock. Includes bibliographical references (leaves 72-77).

In large-scale civil structures, a limited number of sensors are placed to monitor the health of civil structures to reduce maintenance, communication and energy costs. In this thesis, the problem of optimal sensor location placement to infer the health of civil structures is explored. First, a comparative study of approaches from the fields of control engineering and civil engineering is conducted . The widely used civil engineering approaches such as effective independence (EI) and modal assurance criterion (MAC) have limitations because of the negligence of modes and damping parameters. On the other hand, control engineering approaches consider the entire system dynamics using impulse response-type sensor measurement data. Such inference can be formulated as an estimation problem, with the dynamics formulated as a second-order differential equation. The comparative study suggests that damping dynamics play significant impact to the selection of best sensor location---the civil engineering approaches that neglect the damping dynamics lead to very different sensor locations from those of the control engineering approaches. In the second part of the thesis, an initial attempt to directly connect the topological graph of the structure (that defines the damping and stiffness matrices) and the second-order dynamics is conducted.

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Fens are abundant in the San Juan Mountains. By exploring the geomorphology and geochemistry of fen wetlands, the functions that fens serve can be better understood. In this research, two main studies were conducted involving the geomorphology and geochemistry of fens. The first study involved a complex investigation of the geomorphology of five fen sites in the San Juan Mountains near Silverton, Colorado. Geomorphic maps were constructed for each fen site at a scale of ~1:3,000. A geomorphic classification scheme was then made based on fen location, and fens were placed in one of three categories: 1) valley-bottom, 2) valley-side, and 3) terrace. Fen circularity and elongation values were calculated for thirty fens to determine morphometry. A pattern for elongation of fens emerged between the three types of alpine fens with valley-bottom fens having an average elongation value of 1.7, valley-side 2.4, and terrace 1.9. Valley-side fens are more elongated than valley-bottom and terrace fens, which exhibit similar elongation values. In addition, sediment samples at each site were sectioned along visual breaks in the sediment column and were sieved. Mean phi values were calculated for each section and at each site. The mean phi values at California Gulch, Glacial Lake Ironton, Howardsville, Red Mountain Pass North, and Red Mountain Pass South, are 0.2112, 0.9045, 1.6028, 0.0178, and 1.0516, respectively. Overall, coarse-grained particles are associated with valley-side fens, and medium-grained particles are associated with valley-bottom and terrace fens. The second part of the study involved investigating the geochemistry of fen sediment. The geochemistry portion of this research focused on concentration and isotopic ratios of Pb and the amount of 137Cs in fen sediment to better understand variations of Pb with depth and calculate approximate sedimentation rates. Based on isotopic ratios of Pb, binary mixing was determined with the presence of ore mineralized Pb and non-ore mineralized. Binary mixing of two types of ore-mineralized Pb is present at the Howardsville fen and both ore-mineralized and non-ore mineralized Pb is present at the Red Mountain Pass North fen. Based on 137Cs in fen sediment at Howardsville, an average rate of deposition of sediment is approximately 0.16 cm/yr, with a visible change in sedimentation rates pre- and post-1960s.

In the past few decades, wildfires have increased in size and severity in the Southwest and across the western US. These recent trends in fire behavior are a drastic change in arid, ponderosa pine and mixed conifer forests of the Southwest compared with tree-ring records of fire history for the past ~ 400 years. This study presents a late Holocene record (~ 3,000 years) of fire history and related changes in fire regimes with climate variability over annual to multi-decadal time scales. Tree-ring and alluvial-sediment sampling sites were paired in four small, tributary basins located in the western San Juan Mountains of Colorado. In our study sites, tree-ring records show that fire return intervals were longer and fire behavior was more severe on the north-facing slopes with relatively dense mixed conifer stands. Increased fire barriers and steep topography decreased the fire frequency and extent relative to gentle terrain elsewhere in the range and leading to a lack of synchrony among fire years in different parts of the study area. The alluvial-sediment record showed four peaks in high-severity fire activity over the past 3,000 years ranging between 200 - 400 years in length. The timing of peaks coincided with decadal-length drought episodes and were often preceded by multiple decades of above average winter precipitation. The sampling of alluvial-sediment and tree-ring data allowed for site-level comparisons between recent alluvial deposits and specific fire years interpreted from the tree-ring records. We found good correspondence between the type of fire-related sediment deposit (i.e. geomorphic response) in the alluvial record and the extent of mixed and high-severity fire estimated from the tree-ring record, and the correspondence was well-supported by the debris flow probability model results. The two paleofire data tend to represent particular components of the historical fire regime, with alluvial-sediments biased towards infrequent, high-severity events during recent millennia, and the tree-ring record biased toward lower severity fires during recent centuries. The combined analyses of different paleofire proxy types in the same study sites, therefore, can enhance and expand our understanding of fire and climate history beyond what is possible with either proxy alone.

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