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The James River Estuary hosts a salt wedge during its tidal cycle that is typical in estuarine environments but is atypical in its V-shape. Linear frequency-modulated acoustic signals in the 500–5000 Hz range were transmitted during the advance and retreat of the salt wedge during the James River Estuary acoustics field experiment from April 18–25, 2019. Using simple instrumentation, correlations were made between the acoustical characteristics and observational parameters such as current profiles and geological descriptors and features. Data analyzed included acoustic data from underwater hydrophones positioned at three depths through the water column, echosounder data collected across the front, low-angle radar images of the surface, and modeled salinity. Received signal data shows lower energy level when the front occupies the acoustic transect and higher, mixed signal levels as the front moves away from the acoustic transect. A decrease in signal level of about 8 dB within 1.25 hours was recorded due to attenuation from scattering and absorption by bubble clouds and fish, sound refraction, ducting, bottom scatter and flow noise. Understanding of these transmission and propagation loss patterns can aid in the acoustic interpretation of data collected in constrained or denied environments and facilitate a future predictive capability in autonomous underwater vehicle (AUV) sonar systems. Lieutenant Commander, United States Navy Approved for public release. distribution is unlimited

The James River Estuary acoustic field experiment of 2019 (JRE2019) was designed to focus on acoustic characteristics of the James River estuarine environment using simple instrumentation, and correlate the acoustical characteristics to observational parameters such as current profiles and geological descriptors. A central objective is the investigation of the impact of bubbles on sound propagation within the estuarine front. Experimentation was conducted over an 8-day period in April, 2019, and was sponsored by the Office of Naval Research (ONR). This report provides technical details of the logistics, instrumentation, execution and initial results of the acoustical observations made during this field effort. Further analysis and results will be published separately in scientific journal articles. Prepared for: The Office of Naval Research, Code 32, and the Office of Naval Research, Global. Approved for public release; distribution is unlimited.

The effect of the joint action of M2 and M4 tidal flow, residual flow and spatial settling lag on the lateral entrapment of sediment is examined in tidally dominated estuaries with an idealized model that assumes along-estuary uniform conditions. Approximate solutions are obtained for arbitrary cross-channel bed profiles by scaling and perturbation analysis. The hydrodynamics include externally driven M2 tidal flow, externally and internally driven M4 tidal flow and residual flow driven by horizontal density gradient, river discharge and nonlinear advection. The sediment concentration includes a mean component, an M2 component driven by bed erosion and an M2 component driven by both bed erosion and inertial terms. Sediment availability is calculated by imposing a morphodynamic equilibrium condition. The model is applied to a transect in the James River estuary where data of flow and suspended sediment concentration are available. Two types of sediment are separately considered, viz., fine silt and coarse silt. Residual advective transport of sediment by the lateral flow induces trapping of sediment over the left shoal (looking landward). Model results also show that the incorporation of M4 tidal flow and spatial settling lag leads to a second sediment trapping region over the right shoal. Model results are qualitatively in good agreement with the observations.

Source: https://erdc-library.erdc.dren.mil/jspui/ Several dredged material disposal alternatives are being investigated by the U.S. Army Engineer District, Norfolk, for the Lower James River. One alternative is to dispose of the material in the deep trough at the entrance of the James River. Evaluation of this alternative is difficult due to the three-dimensional (3-D) nature of currents in the James River entrance. In order for deep trough disposal to be feasible, the disposed material must stay in place and not be redistributed elsewhere in the system. The model RMA-10 was used to simulate the 3-D hydrodynamics of the Lower James River. Currents and tides were compared to physical model data to validate the numerical model. In order to determine if disposed material would stay in place, the shear stress at the bottom was calculated using the model water velocities and sediment grain sizes.