Fig. 7. Multibeam survey form the Mississippi River.

Fig. 6. Structure contour map of the depth to acoustic basement (in meters) that was produced from a detailed shallow seismic survey of the area.

Figure - Fitzgerald-etal-CEJ-030014

Fitzgerald-etal-CEJ-03
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January 13, 2004

Recent Developments in the Geomorphic Investigation

Fig. 7. Multibeam survey form the Mississippi River. Scale was not in oridinal publication (from

Abraham and Pratt, 2002).

Multibeam surveys have been used on the upper Mississippi River to evaluate

the performance of navigation structures (Fig. 7). These surveys were also used to

estimate the bedload transport in the river using the Integrated Surface Difference

Over Time (ISDOT) technique (Abraham and Pratt, 2002). With this technique the

bedload transport is calculated from the change in the elevation of the river bottom

measured from sequential multibeam survey covering the same spatial extent. For

this calculation, three surveys were collected. The surveys have time laps of 2.3 and

then 4.8 hours. The bedload estimate for this area was 0.0041 kg/sec/m (Abraham

and Pratt, 2002).

Morphologic analysis of Egmont Channel in Tampa, Florida, used multibeam

data collected in 1999 and 2001 (Narr et al., 2003). These surveys identified large

subaqueous dunes in the north and west with medium sized dunes superimposed on

top of the larger ones (Fig. 8; Narr et al., 2003). The large dunes migrated 13 m

to the west northwest (Narr et al., 2003). In the deepest part of the channel were

smaller sandwaves.

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