A saturated riparian buffer (SRB) is an edge-of-field conservation practice that reduces nitrate export from agricultural lands by redistributing tile drainage as shallow groundwater and allowing for denitrification and plant uptake. We propose an approach to improve the design of SRBs by analyzing a tradeoff in choosing the SRB width, and we apply the approach to six sites with SRBs in central Iowa. A larger width allows for more residence time, which increases the opportunity for removing nitrate that enters the buffer. However, because the SRBs considered here treat only a portion of the tile flow when it is large, for the same difference in hydraulic head, a smaller width allows more of the total tile flow to enter the buffer and therefore treats more of the drainage. By maximizing the effectiveness of nitrate removal, defined as the ratio of total nitrate removed by the SRB to total nitrate leaving the field in tile drainage, an equation for the optimal width was derived in terms of soil properties, denitrification rates, and head difference. All six sites with existing SRBs considered here have optimal widths smaller than the current width, and two are below the minimum width listed in current design standards. In terms of uncertainty, the main challenges in computing the optimal width for a site are estimating the removal coefficient for nitrate and determining the saturated hydraulic conductivity. Nevertheless, including a width that accounts for site conditions in the design standards would improve water quality locally and regionally.

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is an MA/Ph.D. student in Anthropology/Civil Engineering, who completed his Master of Science in Biochemistry at Iowa State University and his Bachelor of Science in Chemistry at Hartwick College. His first master's thesis focused on the structural analysis of the schizophrenic gene DISC1 using transmission electron microscopy and hydrogen-deuterium exchange mass spectrometry. For his second master's thesis, he focuses on identifying the individual and institutional factors that contribute to a "culture of disengagement" from the ethical dimension of engineering work among students in the engineering profession. His Ph.D. project is funded by the NSF and is concerned with promoting and improving engineering students' ethical behavior and sensitivity through on-campus student organizations. His academic interests include mental health, international development, human rights, and engineering ethics. Currently, his ambition is to work within an international organization such as UNESCO and to be an advocate for promoting science and technology as critical tools of sustainable development as well as to participate in the dialogue between scientists, policy-makers, and society. Luan enjoys traveling, reading, and watching documentaries.

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Accurate measurement of the shear strength profile in the upper 1 m of soft sediments is crucial for pipeline and riser design, particularly for deep water developments. In this paper, some existing approaches for the strength characterization of seabed surficial sediments are reviewed and the conclusion reached that performing in-situ strength tests within box core samples is the most reliable means of characterizing the shear strength of soft surficial sediments. A box corer for recovering high quality undisturbed sample of the very soft seabed surficial sediments (upper 0.5 m of the seabed) and a new manually operated penetrometer (DMS) for measuring profiles of undisturbed and remoulded undrained shear strength within the box core sample are described. Field data for DMS tests in box cores recovered from a site in the Gulf of Mexico are presented and compared with the strength data measured by motorized miniature vane tests to evaluate the potential of the DMS in characterizing the shear strength of seabed surficial sediments. These data showed that performing DMS tests in box core sample can provide a reliable and time effective means of obtaining strength profiles (undisturbed and remoulded) of soft seabed surficial sediments. Introduction Accurate characterization of seabed surficial sediments has became increasingly important due to escalating hydrocarbon field developments in water depths that are now approaching 3000 m, for which the cost of in-field flowlines and pipelines for exporting hydrocarbon products to shore forms a significant portion of the overall field development cost. However, the low strength of the surficial sediments, in the upper 0.5 to 1 m of the seabed, has rendered soil sampling and strength testing extremely difficult and has posed a major challenge in measuring the shear strength profile accurately, particularly in deep water. Typically, the shear strength of the seabed surficial sediments lies in the range 0 to 5 kPa, although in some deposits such as off the West African coast, a crust with strength of 10 to 15 kPa may be found (Borel et al. 2005; Ehler et al. 2005). In this paper, some existing approaches for measuring the strength profile of seabed surficial sediment will first be reviewed. Subsequently, a box corer that is able to recover high quality undisturbed samples of the surficial sediments and a new manually operated penetrometer (DMS) for measuring undisturbed and remoulded undrained shear strength within the box cores will be described. Data from a field trial in the Gulf of Mexico will be presented, and compared with the strength data measured by motorized miniature vane shear tests, to evaluate the potential of the box corer and the DMS in the characterization of soft surficial sediments from deepwater sites.