By training, my area of research is focused on the mechanics of sediment transport and it is mostly process oriented. Throughout my career, I have worked with gravel-bed rivers in mountain streams of the Pacific Northwest; with cohesive bed and bank rivers found in different parts of the country including the Eastern US; and with sand-bed rivers found in the US Midwest. By doing that, I had the great opportunity to encounter complex and multidisciplinary problems. One of those is the problem of bed load intermittency. In particular, I have looked how intermittency in bed load transport affects the prediction of bed load fluxes in rivers which are dominated by big rocks (boulders) leading to the creation of clusters. Along that line, I have also looked how boulders modify near-bed turbulence and the flow characteristics around them. In addition, the effects of boulders in retaining incoming sediment have been examined in the laboratory and in the field using state-of-the-art sensors such as RFIDs and impact plates. I have also used Eulerian and Lagrangian approaches to determine the mobility of particles and assess the variability in bed load fluxes.
Moving to another central area of my research, I have worked with fine sediments originated from the landscapes in trying to understand their origin, their pathways and travel times. To do so, I have used landscape-oriented models and field sensors to model runoff-triggered transport as well as transport due to anthropogenic activities such as agriculture and deforestation. I have coupled these numerical approaches with the use of stable isotopes and radionuclides to provide a way of verifying the modeling results. Recently, I have coupled the landscape-oriented models with biogeochemical models to determine the effects of erosion on carbon sequestration potential and examine alternative conservation practices for sustaining landscapes with organic-rich soils. Another issue that I have examined is the connectivity of landscapes and rivers. In that sense, I have looked the migration of banks due to fluvial and mass erosion as well as mass wasting. My group has developed unique devices to measure the rate of bank erosion and identify in the laboratory and in-situ, the onset of bank erosion. To address all the above problems, I have worked with people from a number of different disciplines and published in 35 different journals. I view science and engineering to be co-existent and that has been the basis of my research philosophy.
Last but not least, I have worked in a number of practical projects from Alaska to the Tacoma Narrows, Hudson River, Po river, Missouri river and Columbia and estuarine environments to address issues of the implications that bed degradation has on infrastructure as it relates to bridges, dams, and contaminated sediments. In all of those projects, I have tried to bring the fundamentals into solving real life problems. I am always striving to work with different people and learn new things.
Research Themes
Flow and Sediment Interaction
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Understanding the mechanisms involved in the transport and fate of non-cohesive soils in natural channel systems remains an open case in water-related engineering disciplines. The main challenge in studying non-cohesive sediments is the complex character of the bed geometry that governs that velocity, as well as the turbulence structure of flow, which in turn, controls the sediment carrying capacity of the flow. Bed geometry is controlled by stochastic processes and is subject to drastic changes due to changes in the flow condition. Bedforms, clusters, step-pools are few examples of such complicated bed geometry.
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Landscape Processes
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Landscape processes are non-linear in nature due to complex interactions in pedology, geology, biology, and hydrology. These processes remain altogether a challenging problem with several societal implications. Some of the perplex questions associated with landscape processes are the effects of scale in monitoring and modeling, the integration of all phases (i.e., surface and subsurface) in monitoring and modeling, and the development of economic and environmental indicators for alternative scenarios and modeling assessment purposes. Recognizing the critical need for developing an integrated and scientifically sound framework in landscape research, interdisciplinary groups began to emerge, beyond traditional disciplines, with some innovative concepts for watershed modeling.
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Hydraulic Structures
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Hydraulic structures are typically used for flood control, flood conveyance, irrigation purposes, fish passage, banks protection, navigation, recreation, and ecological restoration. A hydraulic structure must meet the safety, functional, and aesthetic goals for its purpose. Thus, valuation studies must be carried out before and after the construction of the structure to assess its impacts. The structure must be of sufficient size that natural flooding is not worsened and to ensure that the structure can withstand the design flood and remain traversable. This ensures the protection of residents and property upstream and downstream of a structure.
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Instrumentation
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Often access, logistic or economic constraints do not allow time consuming and expensive flow or bedload rate measurements. Our research focuses on examining the potential of Infra-Red (IR) Image Velocimetry for estimating the flow discharge in ungaged streams and determining flow patterns on the water surface using hot water, which is also an environmentally friendly flow tracer. Furthermore, this research is examining the potential of passive acoustic sensors (geophones) for continuous and low cost surrogate bedload measurement, as well as Radio Frequency Identification (RFID) tracer particles for capturing the dynamics of bedload particle motion.
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