Limnological Studies in Lake Mead

Since 1990, the U.S. Bureau of Reclamation (USBR) has been conducting a series of limnological studies on the Las Vegas and Boulder Basins in Lake Mead, Nevada, to understand the impacts of urban drainage from the Las Vegas Basin on the water quality in the reservoir. These studies have been jointly funded by USBR's Lower Colorado Region and the Technical Service Center in Denver, Colorado.

Figure 1. SonTek ADV within sounding weight

As a part of this study, Tracy Vermeyen, from USBR's Water Resources Research Laboratory, used a SonTek ADV to measure the very small inflows into Lake Mead. The ADV was incorporated into a 23-kg (50-lb) sounding weight (Figure 1) for obtaining high resolution profiles of horizontal current speed and signal strength. Profiles were collected at select locations, with the ADV lowered to the bottom and then raised in 1-m increments with 30-s data bursts of 25 Hz gathered at each level. All operations were conducted in real-time.

The ADV's signal strength data clearly marks the Las Vegas Wash inflow. Furthermore, signal strength data were in close agreement with the specific conductance measurements, which are an independent method used to detect the interflow. Figure 2 shows the signal strength data obtained from six casts taken at different locations throughout Las Vegas Bay. The depth of the interflows is clearly indicated, and moreover, shows how the interflow depth varies with distance traveled into the bay.

Figure 2. ADV signal strength (AMP) collected at several limnological sampling sites in Lake Mead

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