Woods Hole Coastal and Marine Science Center

USGS Sediment Studies in Lake Mead

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To accomplish fieldwork in Lake Mead, local houseboats were leased and fitted out for acoustic data acquisition and processing operations. The lowered lake level and the design of the local marinas brought on several challenges. It was difficult to move equipment close to the boat for loading during mobilization. USGS field technicians solved this problem by lifting the boat out of the water and onto the staging area (Figure 1). This process saved considerable time and effort. Click here for a larger view of Figure 1.

Figure 1: Houseboat on staging area
Figure 1

Figure 2: A-frame
Figure 2
Technicians took great care while installing systems in order to minimize permanent damage to the vessels. A wooden A-frame was built on the boat (Figure 2) and a sidescan sonar winch was mounted on the top deck (Figure 3). This heavy equipment was secured to the boat with C clamps, straps, and other non-permanent fastening techniques. Click here for a larger view of Figure 2 and Figure3.
Figure 3: Winch
Figure 3
A purpose-built, gimbaled side mount system was mounted on an adjustable pedestal. It was then installed near the bow and secured with straps, and fore and aft stays (Figure 4). This arrangement was used to deploy transducers for subbottom signals, bathymetry, and towfish positioning. The deck mobilization was completed with antenna installations for a digital global positioning system (DGPS) and radio/phone communications. Click here for a larger view of Figure 4.
Figure 4: Side mount system
Figure 4
Figure 5: Data Aquisition
Figure 5
Inside, the main room and galley area were transformed into a data acquisition and processing laboratory (Figures 5 and 6). Shipping crates and lumber were used to make workbenches for subbottom profiling, bathymetry, and sidescan sonar acquisition electronics with navigation receivers and displays. Click here for a larger view of Figure 5 and Figure 6.

The majority of the lake was surveyed with a Datasonics (now Benthos) SIS-1000 combination chirp subbottom and sidescan system (Figure 7). Data was displayed and logged to a Triton-Elics ISIS system. Click here for a larger view of Figure 7.

A Rockwell PLGR GPS receiver provided positional information, which was logged with the geophysical data to Coastal Oceanographics HYPACK navigation and ISIS. And ODEM dual-channel (24kHz/200kHz) Fathometer provided bathymetry information. Vibracoring, piston, and gravity coring will be used to ground truth the geophysical data in spring 2002. For more information about uses for this equipment, visit the USGS Sea-Floor Mapping website.

Figure 6: Data Processing
Figure 6
Figure 7: Datasonics SIS-1000
Figure 7