Geology topics

Chad R. Wagner

Publications and source records attributed to Chad R. Wagner.

22 records · Page 2Linked to original sources

USGS2007

Simulation of Water-Surface Elevations and Velocity Distributions at the U.S. Highway 13 Bridge over the Tar River at Greenville, North Carolina, Using One- and Two-Dimensional Steady-State Hydraulic Models

The use of one-dimensional hydraulic models currently is the standard method for estimating velocity fields through a bridge opening for scour computations and habitat assessment. Flood-flow contraction through bridge openings, however, is hydrodynamically two dimensional and often three dimensional. Although there is awareness of the utility of two-dimensional models to predict the complex hydraulic conditions at bridge structures, little guidance is available to indicate whether a one- or two-dimensional model will accurately estimate the hydraulic conditions at a bridge site. The U.S. Geological Survey, in cooperation with the North Carolina Department of Transportation, initiated a study in 2004 to compare one- and two-dimensional model results with field measurements at complex riverine and tidal bridges in North Carolina to evaluate the ability of each model to represent field conditions. The field data consisted of discharge and depth-averaged velocity profiles measured with an acoustic Doppler current profiler and surveyed water-surface profiles for two high-flow conditions. For the initial study site (U.S. Highway 13 over the Tar River at Greenville, North Carolina), the water-surface elevations and velocity distributions simulated by the one- and two-dimensional models showed appreciable disparity in the highly sinuous reach upstream from the U.S. Highway 13 bridge. Based on the available data from U.S. Geological Survey streamgaging stations and acoustic Doppler current profiler velocity data, the two-dimensional model more accurately simulated the water-surface elevations and the velocity distributions in the study reach, and contracted-flow magnitudes and direction through the bridge opening. To further compare the results of the one- and two-dimensional models, estimated hydraulic parameters (flow depths, velocities, attack angles, blocked flow width) for measured high-flow conditions were used to predict scour depths at the U.S. Highway 13 bridge by using established methods. Comparisons of pier-scour estimates from both models indicated that the scour estimates from the two-dimensional model were as much as twice the depth of the estimates from the one-dimensional model. These results can be attributed to higher approach velocities and the appreciable flow angles at the piers simulated by the two-dimensional model and verified in the field. Computed flood-frequency estimates of the 10-, 50-, 100-, and 500-year return-period floods on the Tar River at Greenville were also simulated with both the one- and two-dimensional models. The simulated water-surface profiles and velocity fields of the various return-period floods were used to compare the modeling approaches and provide information on what return-period discharges would result in road over-topping and(or) pressure flow. This information is essential in the design of new and replacement structures. The ability to accurately simulate water-surface elevations and velocity magnitudes and distributions at bridge crossings is essential in assuring that bridge plans balance public safety with the most cost-effective design. By compiling pertinent bridge-site characteristics and relating them to the results of several model-comparison studies, the framework for developing guidelines for selecting the most appropriate model for a given bridge site can be accomplished.

North Carolina↗

USGS2007

Cause and solution for false upstream boat velocities measured with a StreamPro acoustic doppler current profiler

In 2003, Teledyne RD Instruments introduced the StreamPro acoustic Doppler current profiler which does not include an internal compass. During stationary moving-bed tests the StreamPro often tends to swim or kite from the end of the tether (the instrument rotates then moves laterally in the direction of the rotation). Because the StreamPro does not have an internal compass, it cannot account for the rotation. This rotation and lateral movement of the StreamPro on the end of the tether generates a false upstream velocity, which cannot be easily distinguished from a moving-bed bias velocity. A field test was completed to demonstrate that this rotation and lateral movement causes a false upstream boat velocity. The vector dot product of the boat velocity and the unit vector of the depth-averaged water velocity is shown to be an effective method to account for the effect of the rotation and lateral movement.

Conference Paper↗

USGS2006

Application of the loop method for correcting acoustic doppler current profiler discharge measurements biased by sediment transport

A systematic bias in discharge measurements made with an acoustic Doppler current profiler (ADCP) is attributed to the movement of sediment near the streambed-an issue widely acknowledged by the scientific community. This systematic bias leads to an underestimation of measured velocity and discharge. The integration of a differentially corrected Global Positioning System (DGPS) to track the movement of the ADCP can be used to avoid the systematic bias associated with a moving bed. DGPS systems, however, cannot provide consistently accurate positions because of multipath errors and satellite signal reception problems on waterways with dense tree canopy along the banks, in deep valleys or canyons, and near bridges. An alternative method of correcting for the moving-bed bias was investigated by the U.S. Geological Survey.

Scientific Investigations Report↗

USGS2004

Results of a Two-Dimensional Hydrodynamic and Sediment-Transport Model to Predict the Effects of the Phased Construction and Operation of the Olmsted Locks and Dam on the Ohio River near Olmsted, Illinois

The Olmsted two-dimensional hydrodynamic and sediment-transport model was developed in cooperation with the U.S. Army Corps of Engineers, Louisville District. The model was used to estimate the effects that the phased-construction sequence and operation of the Olmsted Locks and Dam had on sediment-transport patterns in the 11.9-mile study reach (Ohio River miles 962.6 to 974.5), particularly over an area of endangered orange-footed pearly mussel (Plethobasus cooperianus) beds beginning approximately 2 miles downstream of the dam construction. A Resource Management Associates?2 (RMA-2) two-dimensional hydrodynamic model for the reach was calibrated to a middle-flow hydraulic survey (350,000 cubic feet per second) and verified with data collected during low- and high-flow hydraulic surveys (72,500 and 770,000 cubic feet per second, respectively). The calibration and validation process included matching water-surface elevations at the construction site and velocity profiles at 15 cross sections throughout the study reach. The sediment-transport aspect of the project was simulated with the Waterways Experiment Station's Sed2D model for a 6-year planned-construction period (construction-phase modeling) and a subsequent 3-year operational period (operational-phase modeling). The sediment-transport results from the construction and operational models both were compared to results of concurrent baseline simulations to determine the changes in erosional and depositional patterns induced by the dam construction and operation throughout the study reach and more importantly over the area of the endangered mussel beds. Simulation of the phased-in-the-wet Olmsted Locks and Dam construction and subsequent operation period resulted in a maximum additional deposition of approximately 2 feet over a localized region of the mussel beds when compared to the bed change simulated with baseline conditions (river conditions that included only the completed locks section). Most areas on the mussel beds experienced less than 0.5 feet of cumulative bed change between the baseline and construction phases during the nine annual hydrographs. The bed change over the 9 year Olmsted Locks and Dam simulation reveals a continuous downstream progression and deepening of the main channel and deposition along the right bank with limited lateral migration toward the more densely populated mussel-bed areas. The sensitivity of the mussels to sediment deposition is difficult to quantify; therefore, the effect of simulated deposition on the welfare of the mussels is uncertain. The model also will provide the U.S. Army Corps of Engineers a tool to predict the locations of high deposition in navigable sections, which can save engineers time and resources when monitoring the need for dredging operations.

Water-Resources Investigations Report↗