It was in my freshman year at Princeton that I first experienced the dynamism of the Earth, traveling to eastern California for an introductory geology seminar. Roaming around the open expanses of the Owens Valley, I felt that the Earth had removed her mask, revealing crystallized lava flows, alluvial fans, and glacially carved valleys. Exploring the Mosaic Canyon in Death Valley, I could imagine the raging floods depositing conglomerate beds and cutting canyon walls into the gradually rising mountains. At the end of the freshman seminar, I wrote a paper on land subsidence in Mexico City caused by extraction of groundwater. Fascinated by the connection between human activities and underlying geological processes, my experience in the course led me to concentrate in Geological Engineering, and the research projects I pursued as an undergraduate reflected this interest in the human-geology connection. In the summer after my sophomore year, I researched strong ground motion and seismic site response through the Research Experience for Undergraduates (REU) program at University of Alaska-Fairbanks. During my senior year, I wrote my undergraduate thesis on the connection between air pollution and observed reductions in rainfall over Beijing, China. Among the things that I studied during college, I developed a particularly strong interest in rivers and streams. While spending a year studying at Nanjing University in China in 2005-6, I made friends with a hydrogeology student, Dong, who grew up in a small town not far from the Yellow River. As he grew older, Dong saw firsthand how industrialization caused the rapid degradation of the water supply in local streams and groundwater. While droughts became more common, floods also became more severe. Through meeting Dong, I became fascinated with the Yellow River and its historical record of capricious and destructive change. I learned that during the past three thousand years, the Yellow River has changed course at least fifty times, repeatedly building its channel to unstable levels due to the heavy load of sediment delivered from the intensively cultivated loess plateau in western China. Fascinated by fluvial geomorphology, in my junior year I pursued a research project on the effects of urbanization on Armory Run, a small storm drain fed stream on the Princeton University campus. I found that rapid conveyance of water through a buried network of tributary pipes effectively magnifies the effect of heavy rainfall, elevating peak discharges and causing rapid bank erosion and channel migration. Through a combination of field observations and modeling, I described this elevated hydrologic response and the deeply incised morphology of the stream channel. As an engineering student, the next obvious step in the Armory Run project was to design a solution to the erosion problem, which threatened an adjacent road and produced excessive sediment discharge into a downstream lake. In the fall of my senior year, I joined with three other engineering students to tackle this problem. While we considered drainage network changes that would slow the transport of rainwater into the stream, we decided to focus our efforts on the stream itself. We considered several physical changes to the stream, such as constructing meanders or adding roughening elements, which would dissipate flow energy and reduce the erosive force of the water. While instructive, we found that our attempts to design an effective restoration for the stream were hampered by our inability to reliably predict how the channel would respond to any possible changes (or how it would continue to evolve if we did nothing at all). A review of the literature on stream restoration revealed that current models of
channel evolution are largely descriptive, based on empirical relationships among hydraulic parameters. Attempts to explain channel evolution mechanistically usually rely on abstract concepts such as dissipation of river energy, which fail to explain the detailed physical dynamics of the river channel. As a result, we were ultimately faced with choosing a restoration scheme for Armory Run that depended on lumping our stream with other streams of the same general class of morphological characteristics, an unsatisfying design choice that ignored the particularities of our stream. Finding a detailed understanding of stream process to be sorely lacking, I was driven by the Armory Run project to seek a more foundational scientific approach to understanding the physics behind channel forming processes. Thus, I decided to pursue doctoral research on fluvial geomorphology under the direction of Professor Doug Jerolmack at the University of Pennsylvania. I was attracted to Dr. Jerolmack’s method of building simplified fluvial models to predict how specific physical mechanisms (such as the threshold avulsion of delta distributaries) contribute to the formation of complex, self-organizing behavior of fluvial networks (such as the branching pattern of deltas). His three-pronged approach to describing channel process, which links description of physical mechanism in the lab (e.g., flume experiments), construction of a numerical model, and confirmation through field observation, has inspired my own approach to pursuing a hypothesis on the granular mechanics of step-pool bedform topography in mountain streams, which I describe further in my proposed plan of research. My ultimate career aspiration is to become a professor at a major research university, where I would continue to pursue research to quantify how specific physical mechanisms produce the variety of river channel morphologies that we observe in nature. Our understanding of river process has implications for research on a variety of subjects, from physical description of aquatic habitats to reconstruction of past climate and tectonics through the sedimentary record. Furthermore, based on the challenges I faced in designing a stream restoration scheme for Armory Run, I believe that fundamental scientific research can inform solutions to practical problems such as river management. In my senior year at Princeton, I again returned to California for the freshman geology seminar, this time as a field teaching assistant. Guiding the freshmen in making observations about the rocks exposed all around them, I was reminded of how I myself had been shaped four years before as a freshman in this class. More importantly, I realized how exciting it can be to share with others my own wonder at earth’s elegant workings. Recently I began volunteering at a nearby community center in West Philadelphia, teaching a weekly class to predominantly African-American third-graders about the basics of earth science. I find that my students, when they get the chance to actually touch and see rocks, readily grasp earth science concepts and enthusiastically offer their own scientific ideas. In the future, while pursuing research, I also plan to make teaching a centerpiece of my work, utilizing the highly visual nature of my lab and field work as a means to demonstrate physical and geological concepts to others. By supporting my growth as a scientist through graduate school, the NSF fellowship will push me toward my goal of becoming a professor who produces original and significant research in geomorphology. The NSF fellowship will stimulate my development in all aspects of the research process, from formulating a research problem to designing an experiment, from analyzing data to presenting and teaching my work.
Previous Research Experience A very gross classification of earth systems divides what is above (the atmosphere) from what is below (the crust, mantle, and core). Then, there is the huge fuzzy area in between – the earth surface. Because above and below are linked in so many ways, delineating what exactly encompasses the earth surface interface (soils, glaciers, ocean, atmospheric boundary layer, etc.) can be a tricky business. As a graduate student at University of Pennsylvania, my research on bedform topography and sediment transport in rivers lies squarely at this fuzzy earth surface boundary, affected by such diverse factors as tectonic uplift, climatic variation, and biological alteration of erosion and deposition. I believe that my undergraduate research background at Princeton University, covering earth systems above, below, and in between, prepares me both with a set of specific research skills and with a broad appreciation and understanding of the complexity I will inevitably face in my graduate research. As residents of Anchorage, Alaska, experienced in the devastating 1964 Prince William Sound earthquake, the unconsolidated structure of certain surficial sediments can contribute just as devastatingly to earthquake damage as the actual seismic waves traveling from the earthquake hypocenter. This connection between surficial geology and earthquake strong ground motion formed the basis for my research project for the Research Experience for Undergraduates (REU) program in the summer of 2005. For this project, which I completed independently under Dr. Martirosyan of the University of Alaska-Fairbanks Geophysical Institute, I compiled eighteen months’ seismic data from ten accelerometers in the Fairbanks area and created a MATLAB program to filter noise and produce a spectral signature of shaking at each accelerometer location. This earthquake analysis allowed me to determine how specific surficial geological units amplify or attenuate certain frequencies of ground vibrations. The findings of this research were presented at an oral session of the annual American Geophysical Union conference (Dec. 2005). On the northwest coast of Andros Island in the Bahamas, surface biogeomorphic facies correspond strongly to elevation and position with respect to branching tidal channels. Knowing the conditions under which these facies arise allows for interpretation of channel migration and avulsion history based on facies progressions in core samples. In the spring of 2007, for a class on earth surface processes taught by Professor Adam Maloof at Princeton University, I participated in a group research project with two other students on survey analysis of tidal channel facies on Andros Island. We spent four days on Andros Island collecting topographic and surface facies data around a tidal channel meander, which we compared to a high-resolution satellite image showing spatial variation in vegetation. My role in the project was to use GIS and image processing software to identify correlations among elevation, channel position, and surface facies. Based on these data, I described a trend of decreasing elevation away from the channel, as well as changes in biogeomorphic facies corresponding to these elevation changes. Urbanization alters the hydrology of streams as impervious surfaces increase overland flow and storm drain networks accelerate conveyance of water into streams. Changes in hydrologic response caused by urbanization then produce visible changes in stream morphology, often to the detriment of natural ecosystems and human
infrastructure. These urbanization-induced changes in hydrologic response and channel form are apparent on Armory Run, a small storm drain fed stream on the Princeton University campus that I researched independently for a junior independent project in the spring of 2007 and as part of a four-person team for a stream restoration design project in the fall of 2007. Professor James A. Smith of Princeton University advised both of these projects. Working independently in the spring, I used a total station to survey channel topography, installed stream gauges to collect streamflow time series, and compiled storm drain and land-use data in GIS to construct a drainage basin model. Based on these results, I showed that peak streamflows respond to extremely short duration rain rates (<10 minutes), producing hydrograph peaks that deviate drastically from base flow. Working collaboratively in the fall, I assisted in mapping of geomorphic units, sampling of sediment size distributions, and further topographic surveying. As part of this project, I performed a statistical analysis of rainfall records in order to predict peak rain rates for various return intervals, which served as the input for drainage basin modeling and formed the baseline for proposed design alternatives. In the end, we identified a major debris dam as an important control on stream channel morphology to be considered in future stream restoration schemes. Evidence of declining summer rainfall in Beijing suggests that heavy particulate air pollution affects precipitation. For my undergraduate senior thesis, an independent project again advised by Professor James A. Smith, I explored the connection between urbanization and air pollution. I used the Weather Research and Forecasting (WRF) model to carry out a series of long-term simulations of summer precipitation, which demonstrated a progression of rainfall in Beijing from an orographic mechanism in the early summer to a lowland convective mechanism in the late summer. The project was continued through the summer of 2008 in Beijing, and included a review of the Chineselanguage literature on rainfall formation mechanisms in Beijing and sensitivity modeling of orographic and land-use effects on precipitation. Through each of the projects that I pursued as an undergraduate, I gained valuable skills directly applicable to the research on step-pool bedform topography that I am beginning to pursue as a graduate student. In processing noisy time series data and producing power spectra for the Alaska earthquake project, I practiced many of the same techniques that I am now applying to preliminary analysis of frequency-magnitude relationships for avalanches in a steadily building pile of rice. Through the Bahamas tidal channel project, I learned to process images to infer distributions of biogeomorphic facies, a skill that will certainly come in handy when I analyze photos of surface sediment size distributions for flume experiments and field observations of step-pool topography. Field techniques obtained through the Armory Run stream project, such as surveying of channel morphology, computation of sediment size distributions, and monitoring of stream flows, will also be applied in future field investigations. And experience gained in utilizing a complex atmospheric model for the Beijing precipitation project will apply as I construct a numerical model for the granular mechanics of a step-pool system. The research projects I pursued as an undergraduate reflected my desire to expose myself to a variety of research areas, both to explore my personal interests and to build a broad foundation for future work that I might pursue. Based on my undergraduate experience, I ultimately chose to focus my graduate studies at University of Pennsylvania on fluvial geomorphology, though I believe my broad exposure as an undergraduate to
multiple geophysical disciplines allows me to see the connections between my specific research and larger geological questions.