The Benefits of Using an Acoustic Doppler Current Profiler for Hydraulic Modeling

To effectively model flows in rivers at bridge crossings, hydraulic engineers are faced with many challenges which often require one to use insufficient data or force one to use individual judgment and subjective estimations. For instance, having adequate bathymetric data under a bridge can be difficult due to challenges with access and limited survey points based by poor GPS coverage. In addition, calibration of hydraulic models is also problematic due to lack of flow parameters such as the flow distribution, direction and flow rate. By using an Acoustic Doppler Current Profiler (ADCP) data one can supplement the sparse bathymetric data under the bridge by tracking ones location via a bottom tracking algorithm in the instrument. This additional survey data can provide critical channel elevations near the foundations of bridges to provide more realistic flow modeling under a bridge. The California Department of Transportation (Caltrans) has developed software to easily combine GPS and ADCP location information to provide a substantial improvement in both the quality and quantity of collected survey points below a bridge. The use of this software and a comparison of bathymetric survey data with and without the use of the ADCP data is shown. While complex flow patterns approaching a bridge during floods are ideal cases for multi-dimensional hydraulic models, determining the appropriate boundary conditions for the model can still be challenging. In addition, often the hydraulic engineer lacks real calibration data to adjust roughness and other loss values. As a result, it is sometimes necessary to make simplifying assumptions about the flow distribution and flow rates and then accept the associated uncertainties. However, by collecting velocity information throughout a reach of river using an ADCP, it is possible for an engineer to more accurately adjust the model to fit the known flow conditions leading to an overall greater confidence in the scour predictions. An example of ADCP calibration data for use in 2-dimensional and 3-dimensional CFD models is provided