Amanda L. Cox

Verification of a depth-integrated sample arm as a means to reduce solids stratification bias in urban stormwater sampling

A new water sample collection system was developed to improve representation of solids entrained in urban stormwater by integrating water-quality samples from the entire water column, rather than a single, fixed point. The depth-integrated sample arm (DISA) was better able to characterize suspended-sediment concentration and particle size distribution compared to fixed-point methods when tested in a controlled laboratory environment. Median suspended-sediment concentrations overestimated the actual concentration by 49 and 7% when sampling the water column at 3- and 4-points spaced vertically throughout the water column, respectively. Comparatively, sampling only at the bottom of the pipe, the fixed-point overestimated the actual concentration by 96%. The fixed-point sampler also showed a coarser particle size distribution compared to the DISA which was better able to reproduce the average distribution of particles in the water column over a range of hydraulic conditions. These results emphasize the need for a water sample collection system that integrates the entire water column, rather than a single, fixed point to properly characterize the concentration and distribution of particles entrained in stormwater pipe flow.

Maximum Velocity Effects from Vane-Dike Installations in Channel Bends

Channel bends are associated with secondary, helical currents, shifts of conveyance to the outer channel, and variable lateral sedimentation patterns. Outer-bank erosion is of primary concern, resulting in stream-course migration that may place valuable infrastructure and land holdings in jeopardy. In such cases, in-stream river structures such as vane dikes are commonly implemented to restrict the channel course to desired boundaries. Vane dikes are normally installed in series, extending laterally from the outer channel bank into the stream, thereby reducing flow velocity at the outer bank and increasing flow velocity along the channel center and inner bank. Flows around vane dikes and similar transverse in-stream structures have been modeled both numerically and physically in the past, yet the effects on flow velocity within a channel bend due to vane-dike installations have not yet been fully realized. With a focus on the stabilization of two channel bends in the upper regions of the Rio Grande River, a scaled physical model was constructed for the evaluation of various vane-dike field configurations. Structure plan-form angle, spacing, and length were altered between configurations and comprehensive hydraulic data were collected at flow depths below, at, and above structure height. To address flow velocity effects from the structures, a dimensional analysis of influencing parameters was performed, and maximum conditions were used for regression analyses. A series of equations were generated which represent maximum changes in flow velocities at the outerbank, inner-bank, and centerline locations within a channel bend from the installation of vane-dike fields.

Articulated Concrete Block Stability Assessment for Embankment-Overtopping Conditions

AbstractArticulated concrete block (ACB) revetment systems are widely used for channel lining and embankment protection. Current approaches for prediction of ACB system stability use a moment stability analysis with a ratio of the boundary shear stress to critical shear stress to account for all hydrodynamic forces, which results in the exclusion of the flow velocity. Two embankment-overtopping laboratory data sets for a given ACB system were initially evaluated using the current industry-accepted design method. A new stability analysis method, termed the shear and velocity stability assessment method, was developed for ACB systems with embankment-overtopping flow, which uses a moment stability analysis in which hydrodynamic forces are computed using both boundary shear stress and flow velocity. A database was developed that included overtopping tests for three ACB systems with varying embankment slopes and lengths. The current design methodology accurately predicted stability for 67% of the tests and the...

Rectilinear Inverse Distance Weighting Methodology for Bathymetric Cross-Section Interpolation along the Mississippi River

AbstractIn frequently monitored fluvial systems, such as the middle Mississippi River, large databases of hundreds of cross-section surveys are often needed for assessment of long-term morphologic ...

Bendway Weir Riprap Sizing Criteria

AbstractBendway weirs are submerged, in-stream rock structures that redirect impinging flow away from outer-banks toward the center of a channel. Riprap weirs are composed of stone and sized using the average channel velocity in conjunction with existing design guidance. A physical model study and field study were conducted to determine the magnitude of the convective velocity that accelerates around the tip or toe of the weir. The ratio of the maximum tip velocity to the average channel velocity (prior to weir installation) was determined to be approximately 1.70. Stone sizing criteria that significantly increase the riprap median size over traditional approaches were presented for consideration.

Effect of Urban Debris on Hydraulic Efficiency of an Elliptical Sharp-Crested Weir

AbstractAn elliptical sharp-crested weir design was developed for detention pond outlets to address discharge, pollution, and maintenance concerns. The weir was designed in an effort to efficiently pass debris through an outlet as well as having the ability to easily remove any debris attached to the weir plate. Interactions between various types of debris materials were investigated using a 1:2 Froude-scale physical model. Stage discharge data were collected to quantify reduced hydraulic efficiencies with the presence of debris in the weir plate. Nine debris tests were conducted using plastic bags, newspapers, and turf reinforcement mat material. Reductions in hydraulic efficiencies were quantified from the resulting data. Plastic bags and newspapers produced the greatest reduction in hydraulic capacity, whereas turf reinforcement mat material generated the smallest reduction. Observations regarding the ability of debris material to pass through the weir at increased flows were also made using the physic...

Effectiveness of Artificial Substrate in Capturing and Retaining Sturgeon Eggs

Over the past 50 years, there has been a well-documented collapse in white sturgeon recruitment in the Kootenai River, and white sturgeon has been listed as an endangered species since 1994. Libby Dam, constructed along the Kootenai River in northwest Montana, started operation in 1974, which is believed to be the last successful year for white sturgeon recruitment. Lack of appropriate spawning substrate is thought to be a primary factor responsible for white sturgeon population recruitment failure. White sturgeon are broadcast spawners that release adhesive, negatively buoyant eggs that sink to the riverbed. Three- to six-foot sand waves (or dunes) now exist in the reach where spawning occurs. Available information suggests that suffocation and high egg mortality occur where the bed is composed of shifting sand substrate. A Substrate Enhancement Pilot Project Implementation Plan was developed by the Seattle District, U.S. Army Corps of Engineers, to test the effectiveness of various types of artificial substrate for improving spawning success in the reach downstream of Libby Dam. 1:20 Froude-scale physical modeling of different artificial substrate designs was conducted at the Colorado State University Hydraulics Laboratory. This investigation involved three separate tests of rock riprap placed as a mass on the riverbed that projected above the effects of the sand waves. This paper presents an analysis of the flow velocities and turbulent Reynolds stresses that developed over the surface of each artificial substrate. In addition, an evaluation of the effectiveness of each substrate to trap and retain sturgeon eggs is presented.