Indian River Inlet Bridge Scour Monitoring System
An estimate of the bathymetry coverage for two sonar units, one installed on each seaward bridge pier
Bathymetry data from 2004 survey performed by the US Army Corps of Engineers. Spatial reference: Delaware State Plane zone 0700; units: feet.
Elevation measured from mean lower low water (MLLW), which falls 1.11' below NGVD 1929; units: feet.
Figure 1 shows a 3D surface of the Inlet bathymetry, as seen in the highly precise Army Corps survey. North is to the right, and you are looking inland.
Figure 1
Figure 2 shows a plan view of the Inlet bathymetry, note that North is to the left in plan view images.
Figure 2
Figure 3 shows the Inlet bathymetry with the centerpoints of the projected sonar scans. The sonar units transmit one beam at a time,
and rotate and tilt in increments of ~1degree, providing coverage over the entire area of interest. Black dots represent beams originating from the southern
pier, while magenta dots represent beams from the northern pier.
Figure 3
Figure 4 shows a plan view of the distribution of sonar centerpoints. Note the area near the northern (left) pier where there is an absence of magenta dots,
this zone will not be visible to the sonar on the northern pier, but the presence of black dots indicates that it will be seen by the sonar on the southern pier -
though at a diminished resolution.
Figure 4
Figure 5 is the simulated surface that our model sonar units would return. This represents a post-processed result of the scans that both units will perform,
with interpolation between data points to produce a smooth surface. For more information on how the model works,
click here.
Figure 5
Figure 6 shows the simulated surface from Figure 5 in plan view. From here it is easy to see that significant
smoothing of some features occured near the northern (left) pier, generally the model seems to agree rather well
with the actual bathymetry.
Figure 6
Figure 7 quantifies the agreement between the simulation and the actual bathymetry by taking the difference
in elevation values between the two surfaces. A positive value indicates the simulation lies above the actual
bathymetry, which is the case for most of the surveyed region. Again note that the worst agreement occurs in the
region shadowed from coverage near the north (left) pier. The contour lines shown for reference, and are the actual bathymetry.
Figure 7
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