Planning ADCP Cross Section Measurement-Locations for Meandering Rivers

Acoustic instruments such as multibeam echosounders (MBES) and acoustic Doppler current profilers (ADCPs) can collect flow and bathymetric data at high spatial and temporal resolutions. Researchers are widely using MBES and ADCP instruments to advance our understanding of meandering river morphodynamics. Whereas MBES instrumentation produces a continuous bathymetric surface, ADCP usage acquires the three-dimensional flow field at a series of cross sections. The spacing of ADCP cross sections has generally been based on a rule of thumb, for example, a multiple of the channel width. ADCP cross section spacing is further constrained by the available survey time. Theoretical advances regarding the morphologic adjustment of meandering rivers over the past 50 years have provided a variety of mathematical models that quantitatively describe the flow in meandering rivers. This work has identified two important parameters: channel width-to-depth ratio and channel radius of curvature-to-width ratio. Though, width is a controlling factor, it is its ratios with respect to channel depth and radius of curvature, that are important. In addition, channel curvature may vary considerably along the river. Hence, determining ADCP cross section locations based on a multiplication factor of channel width is challenging. We developed a tool based on a linear model of meandering-river flow that determines the locations of ADCP cross sections given a user-specified allowable change in the depth-averaged flow field. The main input parameters are river centerline, width, depth, boundary roughness, and discharge. Model performance is evaluated using ADCP data sets obtained at the Tallahatchie River, MS, and Pearl River, LA/MS.