ADP Velocity-Indexing Discharge Measurements in Everglades

SonTek/YSI Acoustic Doppler Profilers (ADPs) are being used to continuously measure discharge in three low-velocity tidal tributaries along the southwestern boundary of Everglades National Park (Florida, USA). The tributaries meander through red mangrove forests and swamps, and discharge freshwater into the Gulf of Mexico. The tributaries also experience variable backwater conditions and flow reversals twice per day.

Each ADP is mounted looking up from the streambed in the center of the channel. Figure 1 shows the ADP in its mount, along with the power/communication cable. Water depths at the measurement sites range from about 6 to 12 feet (2 to 4 m), and channel widths range from 250 to 450 feet (75 to 135 m). A communication cable runs along the streambed from the ADP to a datalogger housed in an equipment shelter on the nearby shoreline. A 12-volt battery and solar panel supply power to the ADP.

Figure 1. Bottom-Mounted, Up-Looking ADP*

Discharge at each site is computed by first developing a relation between the mean velocity in the river (collected from discrete discharge measurements) to corresponding velocity measurements by the ADP; this technique is commonly known as "velocity-indexing". Second, a relation between water level and cross-sectional area is developed. The ADP velocity data are then used with water level data to compute continuous discharge at each site.

The results of this application show that using the ADP as a velocity-indexing instrument can help provide accurate and reliable discharge data in rivers and streams that historically have been too difficult to measure because of low-velocity tidal conditions, flow reversals, bi-directional flow, or backwater conditions.

*Photograph courtesy of the USGS.

• ADP